WO2011003029A2

WO2011003029A2 - Catalytic disproportionation and catalytic reduction of carbon-carbon and carbon-oxygen bonds of lignin and other organic substrates

Info

Publication number: WO2011003029A2
Application number: PCT/US2010/040832
Authority: WO
Inventors: Robert Bergman; Jonathan Ellman; Jason Nichols; Lee Bishop; Jerome Volkman; Dean Toste; Sunghee Son; John Hartwig; Alexey Sergeev
Original assignee: University of California Berkeley; University of California San Diego UCSD
Current assignee: University of California Berkeley; University of California San Diego UCSD
Priority date: 2009-07-01
Filing date: 2010-07-01
Publication date: 2011-01-06
Anticipated expiration: 2012-01-01
Also published as: WO2011003029A3

Abstract

The present invention provides methods and catalyst compositions for the catalytic reduction of carbon-oxygen bonds of organic substrates and the catalytic disproportionation of carbon-oxygen or carbon-carbon bonds of organic substrates. These methods and catalyst compositions may be used to depolymerize lignin. The disproportionation of carbon-oxygen or carbon-carbon bonds of organic substrates or lignin is carried out by cleaving a carbon-oxygen bond or a carbon-carbon bond in a catalytic disproportionation reaction. The catalysts may be formed from a metal precursor such as ruthenium or vanadium and a bidentate ligand The catalytic reduction of carbon-oxygen bonds of organic substrates such as lignin is carried out by cleaving a carbon-oxygen bond in the presence of a hydrogen atom source. Lignin fragments produced following depolymerization by such methods may be further processed into fuels.

Description

CATALYTIC DISPROPORTIONATION AND CATALYTIC REDUCTION OF CARBON-CARBON AND CARBON-OXYGEN BONDS OF LIGNIN AND OTHER

ORGANIC SUBSTRATES

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 61/222,349 filed on July 1, 2009, and U.S. Provisional Patent Application Serial No. 61/287,631 filed on December 17, 2009, both of which are incorporated herein by reference in their entireties for all purposes.

BACKGROUND

1. Field

[0002] The present disclosure relates generally to the catalytic cleavage of carbon-carbon and carbon-oxygen bonds of lignin and other organic substrates. More specifically, it relates to compositions and methods for the catalytic reduction of carbon-oxygen bonds and the catalytic disproportionation of carbon-oxygen or carbon-carbon bonds of lignin and organic substrates.

2. Related Art

[0003] Alternate energy sources that mitigate the release of carbon dioxide (CO₂) are being developed as part of an effort to address the issues of climate change and the depletion of oil reserves. Lignocellulosic, or plant-derived, biomass is a renewable energy source that is highly abundant and has the potential to reduce CO₂ emissions as CO₂ is consumed during plant photosynthesis. Current technology for biomass conversion into a liquid fuel, or biofuel, is inefficient and cannot compete with the highly efficient process of refining oil. (Huber, et al, Chem. Rev. (2006) 106:4044-4098; Huber et al, Angew. Chem. Intl. Ed. (2007) 46:7184-7201). [0004] One reason for the disparity in processing efficiency between oil and biomass is the relatively high oxygen content of lignocellulosic biomass compared to that of hydrocarbons found in oil. The available energy in a fuel for combustion is stored in C-C and C-H bonds; C-O bonds represent 'oxidized' carbon and do not contribute energy during combustion. Biomass generally has a lower energy density than hydrocarbons as a result of its oxygenation. Beyond energy content, oxygenation has a negative impact on the physical properties of lignocellulosic biomass. Lignocellulose is a conjugate biopolymer made up of three, smaller biopolymers:

cellulose, hemi-cellulose, and lignin. Lignin constitutes up to 30% of lignocellulosic biomass by weight making lignin the second most abundant natural product on Earth. The carbon-oxygen and carbon-carbon bonds in lignin that constitute the polymer linkages are extremely resistant to cleavage using current technologies. This intractability reduces the world's second most abundant natural product to a waste product in current biofuel conversion strategies. Some approaches address this problem by using high temperatures to fractionate biomass into bio-oil, gas, and a carbonaceous solid called coke. However, the oxygen content of the bio-oil fraction results in undesirable physical properties. Typically, bio-oils are highly viscous, corrosive, unstable liquids with appreciable solubility in water, which severely complicates their use as fuels. If biomass-derived fuel is to become a viable, competitive alternative to fuel generated from oil, then the oxygen content of lignocellulosic biomass must be reduced and lignin must become an input for biofuel production. Each of these goals requires technologies for reductively cleaving carbon-oxygen bonds, particularly the C-O bonds of lignin structures.

[0005] Selective depolymerization of lignin into smaller molecular weight components is an attractive first step for making lignin useful for biofuel production. The biosynthesis of lignin is a

416272008740 random polymerization of phenylpropanoids. Phenylpropanoid compounds may include, for example, coumaryl alcohol, guaiacyl alcohol, and syringyl alcohol:

coumaryl guaiacyl syringyl alcohol alcohol alcohol

[0006] The result of the polymerization of phenylpropanoids is a complex polymer with many types of linkages and an indiscriminate degree of polymerization and cross -linking. An exemplary fragment of a lignin polymer chain is shown in Scheme 1, but persons skilled in the art will understand that this scheme shows only representative linkages between and among the phenylpropanoid monomers that can comprise lignin:

[0007] Scheme 1

416272008740 [0008] Lignin dimer and trimer compounds are shown in Scheme 2 as models of the different types of polymeric linkages found in lignin, and include a representative β-glycerolaryl ether. Lignin itself is a complex mixture of these and other linkages of phenylpropanoid monomers. Where a compound described herein comprises a phenylpropanoid or comprises two or more groups that can represent a link to a lignin or a phenylpropanoid, the components of the phenylpropanoid (or two links from a compound as illustrated herein that can connect to a phenylpropanoid or a lignin) can cyclize together to form a ring (See, e.g., the lignin structure in Scheme 1 and the phenylpropanoid examples in Scheme T). Such rings typically contain at least one and optionally two oxygen atoms as ring members, and are typically 5-8 membered rings. Moreover, in some cases two such rings can be fused together, as in the fused 5,5-bicyclic system of pinoresinol (Scheme T).

[0009] Scheme 2

β-glycerolaryl ether

dibenzodioxicin

[0010] Lignin conversion to a transportation fuel has been carried out by

hydrodeoxygenation using sulfided NiMo and CoMo catalysts supported on alumina, chromium,

416272008740 and zeolites at temperatures of ~ 400⁰C. Ratcliff, et al., Appl. Biochem. Biotechnol. 1988, 17, 151-160. Catalytic cracking of lignin has been carried out with zeolite ZSM-5 catalysts at 500- 65O⁰C. Thring, et al, Fuel Process. Technol. (2000) 62:17. Lignin has also been converted into a high-octane oxygenated gasoline additive by base-catalyzed depolymerization of lignin with NaOH at 32O⁰C and 120 atm followed by hydroprocessing with standard sulfided hydrotreating catalysts. Montague, L. NREL National Renewable Energy Laboratory, Subcontractor Report, Report 42002/02: Review of Design (2003). These processes require harsh reaction conditions and may produce large amounts of coke as a reaction byproduct. Therefore, what is needed is a mild, and selective, catalytic method to depolymerize lignin into fragments, which may then be further processed into a fuel.

SUMMARY

[0011] The present invention provides methods and catalyst compositions for the catalytic reduction of carbon-oxygen bonds of organic substrates and the catalytic disproportionation of carbon-oxygen or carbon-carbon bonds of organic substrates. These methods and catalyst compositions may also be used to depolymerize lignin. The methods include reactions that clip lignin into smaller pieces, i.e., reactions that reduce the average molecular weight of a sample of lignin by at least about 10% or at least about 20%, or that convert a significant proportion (e.g., at least about 10% or at least about 20%) of a lignin sample into fragments having a molecular weight of less than about 1500, preferably less than about 1000. Both the disproportionation reactions and the reduction methods described herein can be used to depolymerize lignin to a useful extent.

[0012] The disproportionation of carbon-oxygen or carbon-carbon bonds of organic substrates or lignin is carried out by cleaving a carbon-oxygen bond or a carbon-carbon bond in a

416272008740 catalytic disproportionation reaction. The catalytic reduction of carbon-oxygen bonds of organic substrates or lignin is carried out by cleaving a carbon-oxygen bond in a catalytic reduction reaction, by contacting lignin with a catalyst and a hydrogen atom source. The catalysts may be formed from a metal precursor such as ruthenium and a bidentate phosphine ligand. The catalysts may also be formed from a metal precursor such as ruthenium or nickel and a phosphine or carbene ligand. The catalysts may also be formed from a metal precursor such as vanadium and a ligand containing oxygen and/or nitrogen donor atoms such as imines, diimines, amines, diamines, phenols, bis-phenols, phenol-imines, or bis-phenol-imines. The lignin fragments produced following depolymerization may be further processed into fuels.

[0013] The invention further provides a method to produce a liquid or gaseous fuel, comprising any of the reactions disclosed herein to cleave bonds of lignin or of a

phenylpropanoid.

[0014] The invention further provides a composition comprising a lignin depolymerization product produced by any of the methods disclosed herein. The lignin depolymerization product may be a partially depolymerized lignin, or a phenylpropanoid (including dimers and trimers of phenylpropanoids), or a deoxygenated product formed by the reactions disclosed herein from a lignin or a phenylpropanoid. The invention further provides a fuel produced at least in part by any of the methods disclosed herein.

[0015] In one embodiment, the present invention provides a method of reducing an α-keto ether compound comprising: cleaving a carbon-oxygen bond between C² and O² of the α-keto ether compound of Formula 1 :

416272008740

wherein R¹, R², and R³ are each independently selected from the group consisting of hydrogen, alkyl, optionally substituted alkyl, aryl, optionally substituted aryl, and optionally substituted heteroaryl;

wherein R² is not hydrogen. As further discussed herein, the optionally substituted alkyl, aryl and heteroaryl groups can comprise a bond linking the group to a lignin or to a phenylpropanoid. In some embodiments, at least one of R¹, R² and R³ comprises a bond to a lignin or a phenylpropanoid. In certain embodiments, R is optionally substituted alkyl, or it is H. In some embodiments, R³ is H, OL, Me, CH₂OH, CH₂L, or CH₂OL, where L represents a bond to lignin or to a phenylpropanoid. In some preferred embodiments, R² is optionally substituted aryl, or it is a bond to a lignin or a phenylpropanoid.

[0016] Note that in formulas 1, 2, 4, etc., some of the C and/or O atoms are depicted with a superscript number to facilitate identification of these atoms in the discussion. While some of the atoms, particularly C, throughout the specification may appear to lack an implicit H atom because of the way they are shown, it is to be understood that these formulas represent stable, neutral compounds having no open valences. Express depictions of certain H atoms are included to emphasize changing or retained features of the compounds, but unless otherwise indicated, the chemical structures depicted herein are intended to be stable, neutral species with fully occupied valences. A carbon atom such as C² in formula 1 thus has an implicit H atom, even if it is not expressly shown.

416₂7₂008740 [0017] In the above reaction, the cleaving forms at least one product selected from the group consisting of: '

2 3

wherein C*-X is C^X=O or C¹H-OH. R¹, R², and R³ in these formulas are as described for Formula 1 above.

[0018] In some embodiments, the cleaving forms the product of Formula 2:

2

[0019] In other embodiments, the cleaving forms a product of Formula 3:

H

R²

Optionally, compounds of Formula 2 and Formula 3 may both be formed in such reactions.

[0020] The present invention also provides a method of disproportionating an β-hydroxy ether compound comprising:

cleaving a carbon-oxygen bond between C² and O² of the β-hydroxy ether compound of Formula 4:

416272008740

wherein each R¹, R², and R³ is independently selected from the group consisting of hydrogen, alkyl, optionally substituted alkyl, aryl, optionally substituted aryl, and optionally substituted heteroaryl;

wherein R is not hydrogen.

[0021] In some embodiments of these compounds, at least one of R¹, R² and R³ comprises a bond to a lignin or a phenylpropanoid. In certain embodiments, R³ is optionally substituted alkyl, or it is H. In some embodiments, R³ is H, OL, Me, CH₂OH, CH₂L, or CH₂OL, where L represents a bond to lignin or to a phenylpropanoid. In some preferred embodiments, R² is optionally substituted aryl, or it is a bond to a lignin or a phenylpropanoid

[0022] In the above reaction, the cleaving forms at least one product selected from the group consisting of:

* H

-"N_y/" '

R¹ -^'CO R³ ,o '

H ^R2

5 6 . wherein C^l-X is C^X=O or C¹H-OH. Optionally, compounds of both Formula 5 and Formula 6 may be produced.

[0023] In some embodiments, the cleaving forms the product of Formula 5:

416₂7₂008740

[0024] In other embodiments, the cleaving forms the product of Formula 6:

R^:

[0025] In some embodiments, the cleaving occurs by tandem dehydrogenation and carbon- oxygen bond cleavage reactions. In certain embodiments, R¹ and R² are optionally substituted aryl and R³ is hydrogen. In some embodiments, at least one of R¹, R² and R³ comprises a bond to a lignin or a phenylpropanoid. In certain embodiments, R³ is optionally substituted alkyl, or it is H. In some embodiments, R³ is H, OL, Me, CH₂OH, CH₂L, or CH₂OL, where L represents a bond to lignin or to a phenylpropanoid. In some preferred embodiments, R² is optionally substituted aryl, or it is a bond to a lignin or a phenylpropanoid.

[0026] The present invention also provides a method of disproportionating a 1,3-diol compound comprising:

cleaving a carbon-carbon bond between C¹ and C² and/or C² and C³ of the 1,3 diol compound of Formula 7:

7

416₂7₂008740 \Q wherein R⁴, R⁵, and R⁶ are each independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted alkoxy, optionally substituted aryloxy.

[0027] In some embodiments, the cleaving forms at least one product selected from the group consisting of:

8 9

X

¹r Cl and p 1

R⁵

10 11 wherein C¹ X is C=O or C¹H-OH and C³-X is C=O or C³H-OH.

[0028] In some embodiments, the cleaving forms the product of Formula 8:

_R4-<V

R⁵

8

[0029] In some embodiments, the cleaving forms the product of Formula 9:

Optionally, compounds of Formula 8 and Formula 9 may both be formed.

[0030] In some embodiments, the cleaving forms the product of Formula 10:

416272008740 \ \

10

[0031] In some embodiments, the cleaving forms the product of Formula 11 :

X

R^4'CiH

11

Optionally, compounds of both Formula 10 and Formula 11 may be formed.

[0032] In certain embodiments, additional products are formed by reactions other than the cleaving reaction, the additional products selected from the group consisting of:

12 13 14

R⁴, R⁵ R⁶ and X in these formulas are as defined for Formulas 7-11.

[0033] In certain embodiments, R⁴ is optionally substituted aryl and R⁵ and R⁶ are hydrogen. In other embodiments, the cleaving occurs via tandem dehydrogenation and retro-aldol reactions.

[0034] The present invention also provides a method of disproportionating a glycerol β- arylether compound of Formula 15, comprising:

cleaving a carbon-oxygen bond between C² and O² of the glycerol β-arylether compound of Formula 15:

416272008740 }2 OH OR

Ar¹ R'

,0²

Ar²

15 wherein Ar¹ and Ar² are optionally substituted aryl and each R and R' is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted aryl, and optionally substituted heteroaryl. In some embodiments, at least one of Ar¹, Ar², R and R' comprises a bond to a lignin or a phenylpropanoid. In certain embodiments, R' is optionally substituted alkyl, or it is H. In some embodiments, R' is H, OL, Me, CH₂OH, CH₂L, or CH₂OL, where L represents a bond to lignin or to a phenylpropanoid. In some preferred embodiments, Ar is optionally substituted phenyl.

[0035] In some embodiments, the cleaving forms at least one product selected from the group consisting of:

16 17 wherein C¹ X is C=O or C¹HO-H.

[0036] In other embodiments, the cleaving forms the product of Formula 16:

16

[0037] In other embodiments, the cleaving forms the product of Formula 17:

416₂7₂008740 }3 Ar²OH

17

Optionally, compounds of Formula 16 and Formula 17 are both formed.

[0038] The present invention also provides a method of disproportionating a glycerol β- arylether compound of Formula 15, comprising:

cleaving a carbon-carbon bond between C¹ and C² and/or C² and C³ of the glycerol β-arylether compound of Formula 15:

OH OR

15 wherein Ar¹ and Ar² are optionally substituted aryl groups and each R and R' is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted aryl, and optionally substituted heteroaryl. In some embodiments, at least one of Ar¹, Ar² , R and R' comprises a bond to a lignin or a phenylpropanoid. In certain embodiments, R' is optionally substituted alkyl, or it is H. In some embodiments, R' is H, OL, Me, CH₂OH, CH₂L, or CH₂OL, where L represents a bond to lignin or to a phenylpropanoid. In some preferred embodiments, Ar² is optionally substituted phenyl.

[0039] In some embodiments, the cleaving forms at least one product selected from the group consisting of:

416₂7₂008740 \\

18 19

X X

^Hγ^c> R⁴

and

20 21 wherein C¹ X is C=O or C¹HOH and C³-X is C=O or CHOR.

[0040] The present invention also provides a method of disproportionating a glycerol β- arylether compound comprising:

cleaving a carbon-carbon bond between C¹ and C² and/or C² and C³ of the glycerol β-arylether compound of Formula 15; and

OH OR

15 wherein Ar¹ and Ar² are optionally substituted aryl groups and each R and R' is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted aryl, and optionally substituted heteroaryl. In some embodiments, at least one of Ar¹, Ar², R and R' comprises a bond to a lignin or a phenylpropanoid. In certain embodiments, R' is optionally substituted alkyl, or it is H. In some embodiments, R' is H, OL,

416272008740 \$ Me, CH₂OH, CH₂L, or CH₂OL, where L represents a bond to lignin or to a phenylpropanoid. In some preferred embodiments, Ar² is optionally substituted phenyl.

[0041] In some embodiments, the cleaving forms at least one product selected from the group consisting of:

16 17 18 19

20 21 22 23 wherein C¹ X is C=O or C¹H-OH and C³-X is C=O or CH-OR. In some embodiments, at least one of Ar¹, Ar², R and R' comprises a bond to a lignin or a phenylpropanoid. In certain embodiments, R' is optionally substituted alkyl, or it is H. In some embodiments, R' is H, OL, Me, CH₂OH, CH₂L, or CH₂OL, where L represents a bond to lignin or to a phenylpropanoid. In some preferred embodiments, Ar is optionally substituted phenyl. In some embodiments of these reactions, R' is H. In some embodiments, R is H.

[0042] In other embodiments, the cleaving forms the product of Formula 17:

Ar²OH

17

[0043] In certain embodiments, additional products are formed by reactions other than the cleaving reaction, the additional products selected from the group consisting of:

416₂7₂008740 \β

17 24 25

[0044] In some embodiments, the cleaving occurs via tandem dehydrogenation and retro- aldol reactions and/or tandem dehydrogenation and carbon-oxygen bond cleavage reactions.

[0045] In some embodiments of the foregoing reactions, at least one, and preferably at least two, of Ar¹, Ar², R and R' in Formula 15 represent a bond to lignin or to a phenylpropanoid. The product of these reactions can be a partially depolymerized lignin.

[0046] The present invention also provides a method of depolymerizing lignin comprising:

cleaving a carbon-oxygen bond or a carbon-carbon bond of a phenylpropanoid unit of lignin in a catalytic disproportionation reaction.

[0047] The present invention also provides a method of disproportionating a glycerol β- arylether unit of lignin comprising:

cleaving a carbon-oxygen bond between C² and O² of the glycerol β-arylether unit of lignin of Formula 26:

OH OR

Ar³ ψ _R.

Ar⁴

26 wherein Ar³ and Ar⁴ are optionally substituted aryl groups of lignin and each R and R' is independently selected from the group consisting of hydrogen or a bond to a phenylpropanoid unit of lignin. In some embodiments, at least one of Ar³, Ar⁴ , R and R' comprises a bond to a lignin or a phenylpropanoid. In certain embodiments, R' is optionally

416272008740 \η substituted alkyl, or it is H. In some embodiments, R' is H, OL, Me, CH₂OH, CH₂L, or CH₂OL, where L represents a bond to lignin or to a phenylpropanoid. In some preferred embodiments, Ar⁴ is optionally substituted phenyl.

[0048] In some embodiments, the cleaving forms at least a product of Formula 27:

Ar⁴OH

27

[0049] The present invention also provides a method of disproportionating a glycerol β- arylether unit of lignin comprising:

cleaving a carbon-carbon bond between C¹ and C² and/or C² and C³ of the glycerol β-arylether unit of lignin of Formula 26:

OH OR

Ar³ ψ _R.

Ar⁴

26 wherein Ar³ and Ar⁴ are optionally substituted aryl groups of lignin and each R and R' is independently selected from the group consisting of hydrogen or a bond to a phenylpropanoid unit of lignin. In some embodiments, at least one of Ar³, Ar⁴ , R and R' comprises a bond to a lignin or a phenylpropanoid. In certain embodiments, R' is optionally substituted alkyl, or it is H. In some embodiments, R' is H, OL, Me, CH₂OH, CH₂L, or CH₂OL, where L represents a bond to lignin or to a phenylpropanoid. In some preferred embodiments, Ar⁴ is optionally substituted phenyl.

[0050] The present invention also provides a method of disproportionating a glycerol β- arylether unit of lignin comprising:

416₂7₂008740 } g cleaving a carbon-carbon bond between C¹ and C² and/or C² and C³ of the glycerol β-arylether unit of lignin of Formula 26;

OH OR

Ar³ Y R'

Ar 4⁴'°²

26 wherein Ar³ and Ar⁴ are optionally substituted aryl groups of lignin and each R and R' is independently selected from the group consisting of hydrogen or a bond to a phenylpropanoid unit of lignin.

[0051] In some embodiments, the cleaving forms at least a product of Formula 27:

Ar⁴OH

27

[0052] In other embodiments, the cleaving occurs via tandem dehydrogenation and retro- aldol reactions and/or tandem dehydrogenation and carbon-oxygen bond cleavage reactions.

[0053] The disproportionation reactions of the present reaction may be catalyzed by a metal- based catalyst. In some embodiments, the metal is selected from the group consisting of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, lanthanum, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, and mercury. In some embodiments, the metal is selected from the group consisting of iron, palladium, ruthenium, nickel, rhodium, and iridium. In certain embodiments, the metal is

416272008740 \g selected from the group consisting of ruthenium, nickel, and rhodium. In particular embodiments, the metal is ruthenium.

[0054] The disproportionation reactions of the present reaction may also be catalyzed by an organometallic catalyst. In some embodiments, the catalyst comprises at least one hydride and at least one carbonyl ligand on a metal center of the catalyst. In certain embodiments, the reactions are catalyzed by a catalyst formed under the reaction conditions from a metal precursor and optionally a ligand.

[0055] In some embodiments, the metal precursor is selected from the group consisting of [Ru₃(CO)I₂], [{Ru(cymene)Cl₂}₂], [(PPh₃)₄RuCl₂], [Ru(PPh₃MCO)(OTf)₂(MeOH)],

[RuH₂CO(PPh₃)₃], [Ru(TFA)₂(CO)(PPh₃),], [Ru(TFA)(PPh₃)₂(CO)H], [RuH(TFA)(CO)(PPh₃)₃], [Ni(COd)₂], and [RhCl(coe)₂]₂.

[0056] In some embodiments, the ligand is a phosphine ligand, which may be a

monophosphine such as triphenylphosphine or other triarylphosphines, including ones having substituted phenyl or aryl groups, or a diphosphine such as diphos or xantphos, e.g.,

diarylphosphino-linker-diarylphosphino compounds that have two diarylphosphino groups positioned to form bidentate complexes with metals such as Ru or Ni. The linker group in these compounds can be C2-C4 optionally substituted alkylene or heteroalkylene, or it can be a C5- C16 ring system that positions the diarylphosphines properly to provide a bidentate complex with Ru or Ni. In certain embodiments, the metal precursor is selected from the group consisting of [RuH₂CO(PPh₃)₃], [Ru(TFA)₂(CO)(PPh₃)₂], [Ru(TFA)(PPh₃)₂(CO)H], and

[RuH(TFA)(CO)(PPh₃)₃ and the ligand is (9,9-dimethylxanthene-4,5- diyl)Ws'(diphenylphosphine) .

416₂7₂008740 20 [0057] In some embodiments, the disproportionation reactions are carried out at a reaction temperature of 80-250⁰C. In some embodiments, the reactions are carried out in the presence of hydrogen or silane. In other embodiments, no external oxygen or silane is included. In some embodiments, the glycerol β-arylether unit is oxidized prior to the cleaving step. In many embodiments, catalyst compositions are formed under the reaction conditions.

[0058] Following the cleaving step, the methods of the present invention may further comprise hydrodeoxygenating the reaction products. In other embodiments, the methods of the present invention may also further comprise cracking and/or hydrogenating the reaction products. In some embodiments, a fuel is produced following the hydrodeoxygenating, cracking, and/or hydrogenating steps.

[0059] In one embodiment, the present invention provides a method of reducing an α-keto ether compound comprising:

cleaving a carbon-oxygen bond between C and O of the α-keto ether compound of Formula 1:

wherein R² is not hydrogen. As further discussed herein, the optionally substituted alkyl, aryl and heteroaryl groups can comprise a bond linking the group to a lignin or to a phenylpropanoid. In some embodiments, at least one of R¹, R² and R³ comprises a bond to a

416272008740 21 lignin or a phenylpropanoid. In certain embodiments, R is optionally substituted alkyl, or it is H. In some embodiments, R³ is H, OL, Me, CH₂OH, CH₂L, or CH₂OL, where L represents a bond to lignin or to a phenylpropanoid. In some preferred embodiments, R² is optionally substituted aryl, or it is a bond to a lignin or a phenylpropanoid.

[0060] Note that in formulas 1, 2, 4, etc., some of the C and/or O atoms are depicted with a superscript number to facilitate identification of these atoms in the discussion. While some of the atoms, particularly C, may appear to lack an implicit H atom because of the way they are shown, it is to be understood that these formulas represent stable, neutral compounds having no open valences. A carbon atom such as C in formula 1 thus has an implicit H atom, even if it is not expressly shown.

[0061] In the above reaction, the cleaving forms at least one product selected from the group consisting of:

R^{i 'C}γ^R3 and R²OH

H

2 3 wherein C*-X is C^X=O or C¹H-OH. R¹, R², and R³ in these formulas are as described for Formula 1 above.

[0062] In some embodiments, the cleaving forms the product of Formula 2:

2

[0063] In other embodiments, the cleaving forms the product of Formula 3:

416₂7₂008740 22 R²OH

3 .

[0064] The present invention also provides a method of disproportionating a β-hydroxy ether compound comprising:

cleaving a carbon-oxygen bond between C and O of the β-hydroxy ether compound of Formula 4:

4

wherein R² is not hydrogen.

[0065] In some embodiments of these compounds, at least one of R¹, R² and R³ comprises a bond to a lignin or a phenylpropanoid. In certain embodiments, R³ is optionally substituted alkyl, or it is H. In some embodiments, R³ is H, OL, Me, CH₂OH, CH₂L, or CH₂OL, where L represents a bond to lignin or to a phenylpropanoid. In some preferred embodiments, R² is optionally substituted aryl, or it is a bond to a lignin or a phenylpropanoid

[0066] In the above reaction, the cleaving forms at least one product selected from the group consisting of:

416₂7₂008740 23

5 6 • wherein C^l-X is C^X=O or C¹H-OH. Optionally, compounds of both Formula 5 and Formula 6 may be produced.

[0067] In some embodiments, the cleaving forms the product of Formula 5:

5

[0068] In other embodiments, the cleaving forms the product of Formula 6:

R²OH

6

[0069] In some embodiments, the cleaving occurs by tandem dehydrogenation and carbon- oxygen bond cleavage reactions. In certain embodiments, R¹ and R² are optionally substituted aryl and R³ is hydrogen. In some embodiments, at least one of R¹, R² and R³ comprises a bond to a lignin or a phenylpropanoid. In certain embodiments, R³ is optionally substituted alkyl, or it is H. In some embodiments, R³ is H, OL, Me, CH₂OH, CH₂L, or CH₂OL, where L represents a bond to lignin or to a phenylpropanoid. In some preferred embodiments, R² is optionally substituted aryl, or it is a bond to a lignin or a phenylpropanoid.

[0070] In some embodiments, the cleaving forms at least one product selected from the group consisting of:

416₂7₂008740 24 X R'

_Rrcyλ R4 and R²OH

H

wherein C¹ X is C¹O or C¹HOH;

and wherein each R⁴ is independently selected from the group consisting of hydrogen, alkyl, optionally substituted alkyl, aryl, optionally substituted aryl, and optionally substituted heteroaryl. Optionally, compounds of both Formula 7 and Formula 8 may be produced.

[0071] In some embodiments, the cleaving forms the product of Formula 7:

R

[0072] In other embodiments, the cleaving forms the product of Formula 8:

R²OH

8

[0073] In other embodiments, an additional product is formed by a reaction other than the cleaving reaction, and wherein the additional product is of Formula 9:

416272008740 25 R¹, R², and R⁴ are as defined for Formulas 4 and 7-8.

[0074] The present invention also provides a method of disproportionating a 1,3-diol compound comprising:

cleaving a carbon-carbon bond between C¹ and C² and/or C² and C³ of the 1,3 diol compound of Formula 10:

10 wherein R⁵, R⁶, and R⁷ are each independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted alkoxy, and optionally substituted aryloxy.

[0075] In some embodiments, the cleaving forms at least one product selected from the group consisting of:

1 1 12

u _r3 and _r i

^ R⁷ R⁵ H

R⁶

13 14 wherein C¹ X is C=O or C¹H-OH and C³-X is C=O or C³H-OH.

[0076] In some embodiments, the cleaving forms the product of Formula 11 :

416272008740 26

1 1

[0077] In some embodiments, the cleaving forms the product of Formula 12: r³

H^R⁷

12

Optionally, compounds of Formula 11 and Formula 12 may both be formed.

[0078] In some embodiments, the cleaving forms the product of Formula 13:

X

HγCt_R7

R⁶

13

[0079] In some embodiments, the cleaving forms the product of Formula 14:

14

Optionally, compounds of both Formula 13 and Formula 14 may be formed.

[0080] In certain embodiments, additional products are formed by reactions other than the cleaving reaction, the additional products selected from the group consisting of:

15 16 17

416272008740 27 R⁵, R⁶, R⁷, and X in these formulas are as defined for Formulas 10-14. In certain embodiments, R⁵ is optionally substituted aryl and R⁶ and R⁷ are hydrogen. In other embodiments, the cleaving occurs via tandem dehydrogenation and retro-aldol reactions.

[0081] The present invention also provides a method of disproportionating a glycerol β- arylether compound of Formula 18, comprising:

cleaving a carbon-oxygen bond between C and O of the glycerol β-arylether compound of Formula 18:

OH OR⁸

r¹ r³

,O²

Ar²

18 wherein Ar¹ and Ar² are optionally substituted aryl and each R⁸ and R⁹ is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted aryl, and optionally substituted heteroaryl. In some embodiments, at least one of Ar¹, Ar², R⁸ and R⁹ comprises a bond to a lignin or a phenylpropanoid. In certain embodiments, R⁹ is optionally substituted alkyl, or it is H. In some embodiments, R⁹ is H, OL, Me, CH₂OH, CH₂L, or CH₂OL, where L represents a bond to lignin or to a phenylpropanoid. In some preferred embodiments, Ar² is optionally substituted phenyl.

[0082] In some embodiments, the cleaving forms at least one product selected from the group consisting of:

19 20 .

416₂7₂008740 28 wherein C^l-X is C=O or C¹HO-H. Optionally, compounds of Formula 19 and Formula 20 are both formed.

[0083] In other embodiments, the cleaving forms the product of Formula 19:

19

[0084] In other embodiments, the cleaving forms the product of Formula 20:

Ar²OH

20

[0085] In other embodiments, the cleaving forms at least one product selected from the group consisting of:

21 22 wherein C¹ X is C¹O or C¹HOH.

[0086] In some embodiments, the cleaving forms the product of Formula 21:

21

[0087] In some embodiments, the cleaving forms the product of Formula 22:

416272008740 29 Ar²OH

22

[0088] In other embodiments, an additional product is formed by a reaction other than the cleaving reaction, and wherein the additional product is of Formula 23:

23

[0089] The present invention also provides a method of disproportionating a glycerol β- arylether compound of Formula 18, comprising:

cleaving a carbon-carbon bond between C¹ and C² and/or C² and C³ of the glycerol β- arylether compound of Formula 18:

18 ;

wherein Ar¹ and Ar² are optionally substituted aryl groups and each R⁸ and R⁹ is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted aryl, and optionally substituted heteroaryl. In some embodiments, at least one of Ar¹, Ar² , R⁸ and R⁹ comprises a bond to a lignin or a phenylpropanoid. In certain embodiments, R⁹ is optionally substituted alkyl, or it is H. In some embodiments, R⁹ is H, OL,

416272008740 3Q Me, CH₂OH, CH₂L, or CH₂OL, where L represents a bond to lignin or to a phenylpropanoid. In some preferred embodiments, Ar² is optionally substituted phenyl.

[0090] In some embodiments, the cleaving forms at least one product selected from the group consisting of:

24 25

26 27 wherein C¹ X is C=O or C¹HOH and C³-X is C=O or CHOR⁸.

[0091] The present invention also provides a method of disproportionating a glycerol β- arylether compound comprising:

cleaving a carbon-carbon bond between C¹ and C² and/or C² and C³ of the glycerol β- arylether compound of Formula 18; and

18 ;

416₂7₂008740 1, 1 wherein Ar¹ and Ar² are optionally substituted aryl groups and each R⁸ and R⁹ is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted aryl, and optionally substituted heteroaryl. In some embodiments, at least one of Ar¹, Ar², R⁸ and R⁹ comprises a bond to a lignin or a phenylpropanoid. In certain embodiments, R⁹ is optionally substituted alkyl, or it is H. In some embodiments, R⁹ is H, OL, Me, CH₂OH, CH₂L, or CH₂OL, where L represents a bond to lignin or to a phenylpropanoid. In some preferred embodiments, Ar is optionally substituted phenyl.

[0092] In some embodiments, the cleaving forms at least one product selected from the group consisting of:

19 20 24 25

26 27 28 29 wherein C¹ X is C=O or C¹H-OH and C³-X is C=O or CH-OR⁸. In some embodiments, at least one of Ar¹, Ar², R⁸ and R⁹ comprises a bond to a lignin or a

phenylpropanoid. In certain embodiments, R⁹ is optionally substituted alkyl, or it is H. In some embodiments, R⁹ is H, OL, Me, CH₂OH, CH₂L, or CH₂OL, where L represents a bond to lignin or to a phenylpropanoid. In some preferred embodiments, Ar² is optionally substituted phenyl. In some embodiments, R⁸ is H. In some embodiments, R⁹ is H.

[0093] In other embodiments, the cleaving forms the product of Formula 20:

416₂7₂008740 32 Ar²OH

20

[0094] In certain embodiments, additional products are formed by reactions other than the cleaving reaction, the additional products selected from the group consisting of:

20 30 31

[0095] In some embodiments, the cleaving occurs via tandem dehydrogenation and retro- aldol reactions and/or tandem dehydrogenation and carbon-oxygen bond cleavage reactions.

[0096] In some embodiments of the foregoing reactions, at least one, and preferably at least two, of Ar¹, Ar², R⁸ and R⁹ in Formula 18 represent a bond to lignin or to a phenylpropanoid. The product of these reactions can be a partially depolymerized lignin.

[0097] The present invention also provides a method of depolymerizing lignin comprising:

cleaving a carbon-oxygen bond or a carbon-carbon bond of a phenylpropanoid unit or a diphenyl ether linkage of lignin in a catalytic disproportionation reaction, using any of the reactions disclosed herein.

[0098] The present invention also provides a method of disproportionating a glycerol β- arylether unit of lignin comprising:

cleaving a carbon-oxygen bond between C and O of the glycerol β-arylether unit of lignin of Formula 32:

416272008740 33 OH OR^{1 0}

_/Cl_x ^C³

Ar³ C² V

Ar 4⁴'°²

32 wherein Ar³ and Ar⁴ are optionally substituted aryl groups of lignin and each R¹⁰ and R¹¹ is independently selected from the group consisting of hydrogen or a bond to a

phenylpropanoid unit of lignin. In some embodiments, at least one of Ar³, Ar⁴ , R¹⁰ and R¹¹ comprises a bond to a lignin or a phenylpropanoid. In certain embodiments, R¹¹ is optionally substituted alkyl, or it is H. In some embodiments, R¹¹ is H, OL, Me, CH₂OH, CH₂L, or CH₂OL, where L represents a bond to lignin or to a phenylpropanoid. In some preferred embodiments, Ar⁴ is optionally substituted phenyl.

[0099] In some embodiments, the cleaving forms at least a product of Formula 33:

Ar⁴OH

33

[00100] The present invention also provides a method of disproportionating a glycerol β- arylether unit of lignin comprising: cleaving a carbon-carbon bond between C¹ and C² and/or C² and C³ of the glycerol β- arylether unit of lignin of Formula 32:

OH OR^{1 0}

_/Cl_x ^C³

Ar³ C² V¹

Ar 4⁴'°²

32

416₂7₂008740 34 wherein Ar³ and Ar⁴ are optionally substituted aryl groups of lignin and each R¹⁰ and R¹¹ is independently selected from the group consisting of hydrogen or a bond to a

[00101] The present invention also provides a method of disproportionating a glycerol β- arylether unit of lignin comprising:

cleaving a carbon-carbon bond between C¹ and C² and/or C² and C³ of the glycerol β- arylether unit of lignin of Formula 32;

phenylpropanoid unit of lignin.

[00102] In some embodiments, the cleaving forms at least a product of Formula 33:

416₂7₂008740 35 Ar⁴OH

33

[00103] In other embodiments, the cleaving occurs via tandem dehydrogenation and retro- aldol reactions and/or tandem dehydrogenation and carbon-oxygen bond cleavage reactions.

[00104] The disproportionation reactions of the present reaction may be catalyzed by a metal- based catalyst. In some embodiments, the metal is selected from the group consisting of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, lanthanum, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, and mercury. In some embodiments, the metal is selected from the group consisting of iron, palladium, ruthenium, nickel, rhodium, and iridium. In certain embodiments, the metal is selected from the group consisting of ruthenium, nickel, and rhodium. In particular

embodiments, the metal is ruthenium. In other particular embodiments, the metal is vanadium.

[00105] The disproportionation reactions of the present reaction may also be catalyzed by an organometallic catalyst. In some embodiments, the catalyst comprises at least one hydride and at least one carbonyl ligand on a metal center of the catalyst. In certain embodiments, the reactions are catalyzed by a catalyst formed under the reaction conditions from a metal precursor and optionally a ligand.

[00106] In some embodiments, the metal precursor is selected from the group consisting of [Ru₃(CO)I₂], [{Ru(cymene)Cl₂}₂], [(PPh₃)₄RuCl₂], [Ru(PPh₃MCO)(OTf)₂(MeOH)],

[RuH₂CO(PPh₃),], [Ru(TFA)₂(CO)(PPh₃),], [Ru(TFA)(PPh₃)₂(CO)H], [RuH(TFA)(CO)(PPh₃)₃], [Ni(COd)₂], and [RhCl(coe)₂]₂.

416₂7₂008740 35 [00107] In some embodiments, the ligand is a phosphine ligand, which may be a monophosphine such as triphenylphosphine, or a diphosphine such as diphos or xantphos. In certain embodiments, the metal precursor is selected from the group consisting of

[RuH₂CO(PPh₃)₃], [Ru(TFA)₂(CO)(PPh₃)₂], [Ru(TFA)(PPh₃)₂(CO)H], and

[RuH(TFA)(CO)(PPh₃)₃] and the ligand is (9,9-dimethylxanthene-4,5- diyl)Ws'(diphenylphosphine).

[00108] In some embodiments, the cleaving occurs via a disproportionation-elimination reaction. In certain embodiments, the metal-based catalyst that cleaves via disproportionation- elimination is vanadium. In some embodiments, the catalyst is formed from a vanadium metal precursor and optionally a ligand under the reaction conditions. The vanadium metal precursors used may include, for example but not limited to [VOSO₄-XH₂O], [VO(acac)₂], and [VO(Oz- Pr)₃]. The ligand may be a phenol-imine or bis-phenol-imine ligand. Other vanadium catalysts that may be used for the cleaving reaction include pre-formed phenol-imine or bis-phenol-imine vanadium catalysts selected from the group consisting of:

416₂7₂008740 37 [00109] In some embodiments, the disproportionation reactions are carried out at a reaction temperature of 80-250⁰C. In some embodiments, the reactions are carried out in the presence of hydrogen, oxygen, or a silane or mixtures of two or more of these components. In other embodiments, no external hydrogen, oxygen, or silane is included. In some embodiments, the glycerol β-arylether unit is oxidized prior to the cleaving step. In many embodiments, catalyst compositions are formed under the reaction conditions.

[00110] Following the cleaving step, the methods of the present invention may further comprise hydrodeoxygenating the reaction products. In other embodiments, the methods of the present invention may also further comprise cracking and/or hydrogenating the reaction products. In some embodiments, a fuel is produced following the hydrodeoxygenating, cracking, and/or hydrogenating steps.

[00111] The present invention also provides a method of degrading lignin comprising:

cleaving a carbon-oxygen bond between C and O of a glycerol β-arylether unit of lignin of Formula 32:

OH OR^{1 0}

Ar³ C² V¹

Ar 4⁴'°²

phenylpropanoid unit of lignin;

and wherein the cleaving is mediated by a catalyst comprising ruthenium. In some embodiments, the catalyst further comprises at least one phosphine ligand.

416272008740 3g [00112] The present invention also provides a method of degrading lignin comprising:

cleaving a carbon-oxygen bond between C² and O² of a glycerol β-arylether unit of lignin of Formula 32:

OH OR^{1 0}

Ar^{3 c} R¹¹

Ar⁴

phenylpropanoid unit of lignin;

and wherein the cleaving is mediated by a catalyst comprising vanadium. In some embodiments, the catalyst further comprises at least one phenol-imine ligand.

[00113] The present invention also provides a method of depolymerizing lignin comprising: cleaving a carbon-oxygen bond or a carbon-carbon bond of a phenylpropanoid of lignin in a catalytic disproportionation reaction. In some embodiments, the carbon-oxygen bond is between C² and O² of a glycerol β-arylether unit of lignin:

OH OR

ci

Ar³

,O²

Ar⁴ wherein Ar³ and Ar⁴ are optionally substituted aryl groups of lignin and each R and R' is independently selected from the group consisting of hydrogen or a bond to a

416272008740 39 phenylpropanoid unit of lignin. In some embodiments, the cleaving forms one or more products, the one or more products comprising Ar⁴OH.

[00114] In some embodiments, the carbon-carbon bond is between C¹ and C² and/or C² and C³ of a glycerol β-arylether unit of lignin:

_?H _?R

ci

Ar³

,O²

Ar⁴ wherein Ar³ and Ar⁴ are optionally substituted aryl groups of lignin and each R and R' is independently selected from the group consisting of hydrogen or a bond to a phenylpropanoid unit of lignin.

[00115] In some embodiments, the carbon-carbon bond between C¹ and C² and/or C² and C³ of the glycerol β-arylether unit of lignin and the carbon-oxygen bond between C² and O² of the glycerol β-arylether unit of lignin are cleaved:

wherein Ar³ and Ar⁴ are optionally substituted aryl groups of lignin and each R and R' is independently selected from the group consisting of hydrogen or a bond to a phenylpropanoid unit of lignin. In some embodiments, the cleaving forms one or more products, the one or more products comprising Ar⁴OH.

[00116] In some embodiments, the cleaving occurs via tandem dehydrogenation and retro- aldol reactions and/or tandem dehydrogenation and carbon-oxygen bond cleavage reactions. In

416272008740 40 other embodiments, the cleaving is catalyzed by a metal-based catalyst. In some embodiments, the metal-based catalyst comprises a metal selected from the group consisting of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, lanthanum, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, and mercury. In some embodiments, the metal-based catalyst comprises a metal selected from the group consisting of iron, palladium, ruthenium, nickel, rhodium, and iridium. In certain embodiments, the metal- based catalyst comprises a metal selected from the group consisting of ruthenium, nickel, and rhodium. In particular embodiments, the metal is ruthenium.

[00117] In some embodiments, the cleaving is catalyzed by an organometallic catalyst. In other embodiments, the cleaving is catalyzed by a catalyst comprising a hydride and carbonyl ligand. In some embodiments, the cleaving is catalyzed by a catalyst formed from a metal precursor and optionally a ligand under the reaction conditions. In some embodiments, the metal precursor is selected from the group consisting of [Ru₃(CO)_I2], [{Ru(cymene)Cl₂}₂],

[(PPhS)₄RuCl₂], [Ru(PPhS)₂(CO)(OTf)₂(MeOH)], [RuH₂CO(PPh₃)₃], [Ru(TFA)₂(CO)(PPh₃)₂], [Ru(TFA)(PPh₃)₂(CO)H], [RuH(TFA)(CO)(PPh₃)₃], [Ni(cod)₂], and [RhCl(coe)₂]₂. In some embodiments, the ligand is a phosphine ligand. In certain embodiments, the metal precursor is selected from the group consisting of [RuH₂CO(PPh₃)₃], [Ru(TF A)₂(CO)(PPh₃)₂],

[Ru(TFA)(PPh₃MCO)H], and [RuH(TFA)(CO)(PPh₃)₃ and the ligand is (9,9-dimethylxanthene- 4,5-diyl)Z?/i'(diphenylphosphine).

[00118] In some embodiments, the cleaving is carried out at a reaction temperature of 80- 25O⁰C. In certain embodiments, the cleaving is carried out in the presence of hydrogen. In certain embodiments, the cleaving is carried out in the presence of a silane. In some

416₂7₂008740 \\ embodiments, the cleaving is carried out in the presence of an acid. In certain embodiments, the acid is selected from the group consisting of AlX₃ where X = tertiary alkoxide, phenoxide, and halogen; TiX₄ where X = tertiary alkoxide, phenoxide, and halogen; BX₃ where X = F, Br;

organic acids X-CO₂H where X = CF₃, CH₃, aryl; and sulfonic acids X-SO₃H where X = Me, aryl.

[00119] Following the cleaving step, the methods of the present invention may further comprise hydrodeoxygenating the reaction products. In other embodiments, the methods of the present invention may also further comprise cracking and/or hydrogenating the reaction products. In some embodiments, a fuel is produced following the hydrodeoxygenating, cracking, and/or hydrogenating steps. In some embodiments, the glycerol β-arylether unit is oxidized prior to the cleaving step.

[00120] The present invention also provides a method of depolymerizing lignin comprising:

cleaving a carbon-oxygen bond or a carbon-carbon bond of a phenylpropanoid unit of lignin in a catalytic disproportionation reaction

wherein the cleaving is catalyzed by a metal-based catalyst comprising vanadium.

[00121] In some embodiments the carbon-oxygen bond is between C² and O² of a glycerol β- arylether unit of lignin:

OH OR

Ar³ ψ _R.

416272008740 42 phenylpropanoid unit of lignin. In certain embodiments, the cleaving occurs via a disproportionation-elimination reaction.

[00122] In some embodiments, the metal-based catalyst comprising vanadium is formed from a vanadium precursor and optionally a ligand under the reaction conditions. In certain embodiments, the vanadium precursor is selected from the group consisting of [VOSO₄-XH₂O], [VO(acac)₂], [VO(OZ-Pr)₃], and mixtures thereof. In certain embodiments, the ligand is a phenol-imine or bis-phenol-imine ligand. In some embodiments, the cleaving is catalyzed by a pre-formed phenol-imine or bis-phenol-imine vanadium catalyst. In some embodiments, the preformed phenol-imine or bis-phenol-imine vanadium catalyst is selected from the group consisting of:

and mixtures thereof.

[00123] The methods of the present invention also provide a method of depolymerizing lignin comprising:

416272008740 43 cleaving a carbon-oxygen bond of lignin in a catalytic reduction reaction, by contacting lignin with a catalyst and a hydrogen atom source.

[00124] In some embodiments, the carbon-oxygen bond comprises a diaryl, alkyl aryl, or benzyl alkyl, or benzyl aryl ether linkage.

[00125] In some embodiments, the cleaving is catalyzed by a metal-based catalyst comprising nickel. In some embodiments, the metal-based catalyst comprising nickel is formed from a nickel precursor and optionally a ligand under the reaction conditions. In certain embodiments, the nickel precursor is selected from the group consisting of Ni(COD)₂, Ni(acac)₂, NiCl₂, NiBr₂, Ni(OAc)₂, Ni(OH)₂, NiCO₃* 2 Ni(OH)₂ (nickel carbonate basic), and mixtures thereof. In some preferred embodiments, the nickel precursor is Ni(COD)₂ or Ni(acac)₂. In some embodiments, the ligand:nickel precursor ratio is approximately 2:1. In certain embodiments, the ligand is a carbene ligand (e.g., N-heterocyclic carbene) or a phosphine ligand. In some embodiments, the phosphine ligand is a trialkylphosphine ligand such as, for example, tricyclohexylphosphine (P(Cy₃)₃). In certain embodiments, the ligand is an N-heterocyclic carbene ligand. The N- heterocyclic carbene ligands may be used as a salt, which may be deprotonated with a base in situ. The salts may have, for example, a halide, tetrafluoroborate, or a triflate counteranion. In some embodiments, the N-heterocyclic carbene ligand is selected from the group consisting of:

416₂7₂008740 44

SIPr HX, X=CI-, BF₄ ^" IPr HCI diMelPr HCI diMeSIPr HCI

MonotBulPr HCI ItBu HCI IMes HCI SIMes HBF₄

6-DIPP HBr 7-DIPP HBr XyI-DIPP HBr

SCAAC HCI

SImAd HBF₄ SImPr HBF₄ SImBu HBF₄ Bu Im HBF₄

[00126] and mixtures thereof. In some preferred embodiments, the N-heterocyclic carbene ligand is a five-membered N-aryl-N-heterocyclic carbene. In some preferred embodiments, the five-membered N-aryl-N-heterocyclic carbene is selected from the group consisting of:

416272008740 45

SIPr HX₁ X=CI-, BF₄ ^" IPr HCI diMelPr HCI diMeSIPr HCI

MonotBulPr HCI ItBu HCI IMes HCI SIMes HBF,

[00127] and mixtures thereof. In other preferred embodiments, the N-heterocyclic carbene ligand is selected from the group consisting of:

SPr HCI IPr_Me HCI ; and mixtures thereof.

[00128] In some embodiments, the cleaving is catalyzed by a pre-formed N-heterocyclic carbene nickel catalyst. In some embodiments, the cleaving is carried out at a reaction temperature of 80-250⁰C.

[00129] The cleaving step in the catalytic reduction reaction is generally carried out in the presence of a hydrogen atom source, the hydrogen atom source selected from the group consisting of hydrogen, a silane, diisobutylaluminum hydride (DIBAL), lithium tή-tert- butoxyalumnium hydride (LiAl(CyBu)₃H), or mixtures thereof. In certain embodiments, the silane is triethylsilane (Et₃SiH) or te/t-butyldimethyl silane (^BuMe₂SiH). In certain preferred embodiments, the hydrogen atom source is dihydrogen.

416272008740 46 [00130] The cleaving step in the catalytic reduction reaction is generally carried out in the presence of an optional base. In some embodiments, the base is selected from the group consisting of sodium te/t-butoxide (YBuONa), sodium te/t-pentoxide (YPentONa), sodium iso- propoxide (/PrONa), lithium te/t-butoxide (YBuOLi), sodium methoxide (MeONa), potassium te/t-butoxide (^BuOK), cesium fluoride (CsF), and cesium carbonate (CS₂CO₃), and mixtures thereof. In certain embodiments, the base is selected from the group consisting of sodium tert- butoxide (^BuONa), sodium te/t-pentoxide (^PentONa), sodium /so-propoxide (/PrONa), and mixtures thereof. In some embodiments, an excess of base may be used in the catalytic reduction reactions. In some embodiments, where the reductive C-O bond cleavage is catalyzed by

Ni(COD)₂ without adding any other ancillary ligands, it is preferable to use a base.

[00131] In some embodiments, the cleaving has a higher selectivity for aryl-carbon-oxygen bonds over alkyl-carbon oxygen bonds in lignin.

[00132] In some embodiments, the cleaving is catalyzed by a metal-based catalyst comprising nickel and an N-heterocyclic carbene ligand in the presence of a hydrogen atom source and a base.

[00133] Following the cleaving step of the catalytic reduction reaction, the methods of the present invention may further comprise hydrodeoxygenating the reaction products. In other embodiments, the methods of the present invention may further comprise cracking and/or hydrogenating the reaction products. In some embodiments, a fuel is produced following the hydrodeoxygenating, cracking, and/or hydrogenating steps.

[00134] The methods of the present invention also provide a method to cleave a diaryl ether linkage comprising contacting a diaryl ether with a nickel catalyst and a hydrogen donor in the presence of a base. In some embodiments, the diaryl ether is an optionally substituted diphenyl

416272008740 47 ether. In some embodiments, the nickel catalyst is formed from a nickel precursor and optionally a ligand under the reaction conditions. In certain embodiments, the nickel precursor is selected from the group consisting of Ni(COD)₂, Ni(acac)₂, NiCl₂, NiBr₂, Ni(OAc)₂, Ni(OH)₂, NiCO₃* 2 Ni(OH)₂ (nickel carbonate basic), and mixtures thereof. In some preferred embodiments, the nickel precursor is Ni(COD)₂ or Ni(acac)₂. In some embodiments, the ligand:nickel precursor ratio is approximately 2:1. In certain embodiments, the ligand is a carbene ligand (e.g., N- heterocyclic carbene) or a phosphine ligand. In some embodiments, the phosphine ligand is a trialkylphosphine ligand such as, for example, tricyclohexylphosphine (P(Cy₃)₃). In certain embodiments, the ligand is an N-heterocyclic carbene ligand. The N-heterocyclic carbene ligands may be used as a salt, which may be deprotonated with a base in situ. The salts may have, for example, a halide, tetrafluoroborate, or a triflate counteranion. In some embodiments, the N-heterocyclic carbene ligand is selected from the group consisting of:

416₂7₂008740 4g

SIPr HX, X=CI-, BF₄ ^" IPr HCI diMelPr HCI diMeSIPr HCI

MonotBulPr HCI ItBu HCI IMes HCI SIMes HBF₄

6-DIPP HBr 7-DIPP HBr XyI-DIPP HBr

SCAAC HCI

SImAd HBF₄ SImPr HBF₄ SImBu HBF₄ Bu Im HBF₄

[00135] and mixtures thereof. In some preferred embodiments, the N-heterocyclic carbene ligand is a five-membered N-aryl-N-heterocyclic carbene. In some preferred embodiments, the five-membered N-aryl-N-heterocyclic carbene is selected from the group consisting of:

416272008740 49

SIPr HX₁ X=CI-, BF₄ ^" IPr HCI diMelPr HCI diMeSIPr HCI

MonotBulPr HCI ItBu HCI IMes HCI SIMes HBF,

[00136] and mixtures thereof. In other preferred embodiments, the N-heterocyclic carbene ligand is selected from the group consisting of:

SPr HCI IPr_MΘ HCI ; and mixtures thereof.

[00137] In some embodiments, the cleaving reaction is catalyzed by a pre-formed N- heterocyclic carbene nickel catalyst. In some embodiments, the cleaving reaction is carried out at a reaction temperature of 80-250⁰C.

[00138] The present invention also provides compositions comprising lignin and a metal- based catalyst. In some embodiments, the metal-based catalyst is formed from a metal precursor and optionally a ligand under the reaction conditions. In some embodiments, the metal precursor comprises a metal selected from the group consisting of ruthenium, rhodium, vanadium, nickel, and mixtures thereof. In some embodiments, the metal precursor is selected from the group consisting Of [Ru₃(CO)₁₂], [{Ru(cymene)Cl₂}₂], [(PPh₃)₄RuCl₂],

416272008740 50 [Ru(PPh₃)I(CO)(OTf)₂(MeOH)] , [RuH₂CO(PPh₃)₃] , [Ru(TFA)₂(CO)(PPh₃)₂] ,

[Ru(TFA)(PPh₃)₂(CO)H], [RuH(TFA)(CO)(PPh₃)₃], [Ni(cod)₂], [RhCl(coe)₂]₂, [VOSO₄ XH₂O], [VO(acac)₂], [VO(OZ-Pr)₃], Ni(acac)₂, NiCl₂, NiBr₂, Ni(OAc)₂, Ni(OH)₂, NiCO₃* 2 Ni(OH)₂ (nickel carbonate basic), and mixtures thereof. In certain embodiments, the metal precursor comprises ruthenium and the ligand is a phosphine ligand. In certain embodiments, the phosphine ligand is (9,9-dimethylxanthene-4,5-diyl)Ws(diphenylphosphine). In certain embodiments, the metal precursor comprises vanadium and the ligand is a phenol-imine or bis- phenol-imine ligand. In certain embodiments, the metal precursor comprises nickel and the ligand is a phosphine or carbene ligand. In certain embodiments, the carbene ligand is an N- heterocyclic carbene ligand. In certain embodiments, the metal-based catalyst is a pre-formed catalyst. In certain embodiments, the pre-formed catalyst comprises ruthenium and a phosphine ligand. In certain embodiments, the pre-formed catalyst comprises vanadium and a phenol-imine or bis-phenol-imine ligand. In certain embodiments, the pre-formed catalyst comprises nickel and a phosphine or carbene ligand.

DETAILED DESCRIPTION

[00139] The following description sets forth exemplary methods, parameters and the like. It should be recognized, however, that such description is not intended as a limitation on the scope of the present invention but is instead provided as a description of exemplary embodiments. From these, a person of ordinary skill would be able to practice the invention without undue experimentation .

1. Definitions

[00140] As used herein, the term "lignin" refers to lignin in lignocellulosic biomass, purified lignin, or lignin fragments that are produced, for example from the pyrolysis of lignin. The

416₂7₂008740 5 } foregoing reactions may be used to depolymerize or partially depolymerize lignin. Lignin comprises polymerized and/or cross-linked phenylpropanoids; for purposes of the invention, a lignin typically comprises at least four phenylpropanoid units linked together.

[00141] As used herein, the term "phenylpropanoid" refers to organic compounds produced biosynthetically by plants from phenylalanine, which comprise a phenyl group having an optionally substituted propyl group or propenyl group as one substituent on the phenyl. The phenyl group may be further substituted, typically with 1-3 groups. In some embodiments, these substituents on phenyl are independently selected from -OH, -OMe, or Me, and in some embodiments one of the substituents is a link to another phenylpropanoid, which link may be a covalent bond, or -O- . Phenylpropanoid compounds may include, for example, coumaryl alcohol, guaiacyl alcohol, and syringyl alcohol, as well as dimeric and trimeric versions of any one or a combination of these. Polymers having over 4 phenylpropanoids covalently linked together are referred to herein as lignins.

[00142] As used herein, the term "fuel" refers to a composition comprising a compound, containing at least one carbon-hydrogen bond, which produces heat and power when burned.

Fuel may be produced using plant-derived biomass as a feedstock, for example from the lignin biopolymer of lignocellulose. Fuel may also contain more than one type of compound and includes mixtures of compounds.

[00143] As used herein, the term "transportation fuel" refers to a fuel that is suitable for use as a power source for transportation vehicles.

[00144] As used herein, the terms "alkyl," "alkenyl" and "alkynyl" include straight-chain, branched-chain and cyclic monovalent hydrocarbyl radicals, and combinations of these, which contain only C and H when they are unsubstituted. Examples include methyl, ethyl, isobutyl,

416272008740 52 cyclohexyl, cyclopentylethyl, 2-propenyl, 3-butynyl, and the like. The total number of carbon atoms in each such group is sometimes described herein, e.g., when the group can contain up to ten carbon atoms it can be represented as 1-lOC or as Cl-ClO or Cl-10. When heteroatoms (N, O and S typically) are allowed to replace carbon atoms as in heteroalkyl groups, for example, the numbers describing the group, though still written as e.g. C1-C6, represent the sum of the number of carbon atoms in the group plus the number of such heteroatoms that are included as replacements for carbon atoms in the ring or chain being described.

[00145] Typically, the alkyl, alkenyl and alkynyl substituents of the invention contain 1-lOC (alkyl) or 2- 1OC (alkenyl or alkynyl). Preferably they contain 1-8C (alkyl) or 2-8C (alkenyl or alkynyl). Sometimes they contain 1-4C (alkyl) or 2-4C (alkenyl or alkynyl). A single group can include more than one type of multiple bond, or more than one multiple bond; such groups are included within the definition of the term "alkenyl" when they contain at least one carbon-carbon double bond, and are included within the term "alkynyl" when they contain at least one carbon- carbon triple bond.

[00146] Alkyl, alkenyl and alkynyl groups are often substituted to the extent that such substitution makes sense chemically. Typical substituents include, but are not limited to, halo, =0, =N-CN, =N-0R, =NR, OR, NR₂, SR, SO₂R, SO₂NR₂, NRSO₂R, NRCONR₂, NRCOOR, NRCOR, CN, COOR, CONR₂, 0OCR, COR, and NO₂, wherein each R is independently H, Cl- C8 alkyl, C2-C8 heteroalkyl, C3-C8 heterocyclyl, C4-C10 heterocyclyclalkyl, C1-C8 acyl, C2- C8 heteroacyl, C2-C8 alkenyl, C2-C8 heteroalkenyl, C2-C8 alkynyl, C2-C8 heteroalkynyl, C6- ClO aryl, or C5-C10 heteroaryl, and each R is optionally substituted with halo, =0, =N-CN, =N- OR', =NR', OR', NR'₂, SR', SO₂R', SO₂NR'₂, NR⁵SO₂R', NR'C0NR'₂, NR'COOR',

NR'COR', CN, COOR', C0NR'₂, 0OCR', COR', and NO₂, wherein each R' is independently

416₂7₂008740 53 H, C1-C8 alkyl, C2-C8 heteroalkyl, C3-C8 heterocyclyl, C4-C10 heterocyclyclalkyl, C1-C8 acyl, C2-C8 heteroacyl, C6-C10 aryl or C5-C10 heteroaryl. Alkyl, alkenyl and alkynyl groups can also be substituted by C1-C8 acyl, C2-C8 heteroacyl, C6-C10 aryl or C5-C10 heteroaryl, each of which can be substituted by the substituents that are appropriate for the particular group. Where a substituent group contains two R or R' groups on the same or adjacent atoms (e.g., - NR₂, or -NR-C(O)R), the two R or R' groups can optionally be taken together with the atoms in the substituent group to which the are attached to form a ring having 5-8 ring members, which can be substituted as allowed for the R or R' itself, and can contain an additional heteroatom (N, O or S) as a ring member.

[00147] "Heteroalkyl," "heteroalkenyl," and "hetero alkynyl" and the like are defined similarly to the corresponding hydrocarbyl (alkyl, alkenyl and alkynyl) groups, but the 'hetero' terms refer to groups that contain 1-3 O, S or N heteroatoms or combinations thereof within the backbone residue; thus at least one carbon atom of a corresponding alkyl, alkenyl, or alkynyl group is replaced by one of the specified heteroatoms to form a heteroalkyl, heteroalkenyl, or

heteroalkynyl group. The typical and preferred sizes for heteroforms of alkyl, alkenyl and alkynyl groups are generally the same as for the corresponding hydrocarbyl groups, and the substituents that may be present on the heteroforms are the same as those described above for the hydrocarbyl groups. For reasons of chemical stability, it is also understood that, unless otherwise specified, such groups do not include more than two contiguous heteroatoms except where an oxo group is present on N or S as in a nitro or sulfonyl group.

[00148] While "alkyl" as used herein includes cycloalkyl and cycloalkylalkyl groups, the term "cycloalkyl" may be used herein to describe a carbocyclic non-aromatic group that is connected via a ring carbon atom, and "cycloalkylalkyl" may be used to describe a carbocyclic non-

416272008740 54 aromatic group that is connected to the molecule through an alkyl linker. Similarly, "heterocyclyl" may be used to describe a non-aromatic cyclic group that contains at least one heteroatom as a ring member and that is connected to the molecule via a ring atom, which may be C or N; and "heterocyclylalkyl" may be used to describe such a group that is connected to another molecule through a linker. The sizes and substituents that are suitable for the cycloalkyl, cycloalkylalkyl, heterocyclyl, and heterocyclylalkyl groups are the same as those described above for alkyl groups As used herein, these terms also include rings that contain a double bond or two, as long as the ring is not aromatic.

[00149] As used herein, "acyl" encompasses groups comprising an alkyl, alkenyl, alkynyl, aryl or arylalkyl radical attached at one of the two available valence positions of a carbonyl carbon atom, and heteroacyl refers to the corresponding groups wherein at least one carbon other than the carbonyl carbon has been replaced by a heteroatom chosen from N, O and S. Thus heteroacyl includes, for example, -C(=O)OR and -Q=C))NR₂ as well as -C(=O)-heteroaryl.

[00150] Acyl and heteroacyl groups are bonded to any group or molecule to which they are attached through the open valence of the carbonyl carbon atom. Typically, they are C1-C8 acyl groups, which include formyl, acetyl, pivaloyl, and benzoyl, and C2-C8 heteroacyl groups, which include methoxyacetyl, ethoxycarbonyl, and 4-pyridinoyl. The hydrocarbyl groups, aryl groups, and heteroforms of such groups that comprise an acyl or heteroacyl group can be substituted with the substituents described herein as generally suitable substituents for each of the corresponding component of the acyl or heteroacyl group.

[00151] "Aromatic" moiety or "aryl" moiety refers to a monocyclic or fused bicyclic moiety having the well-known characteristics of aromaticity; examples include phenyl and naphthyl. Phenyl (optionally substituted) is sometimes selected for the aryl groups of Formulas 1-27

416272008740 55 herein. Phenyl is sometimes substituted with an optionally substituted propyl or propenyl group, to provide a phenylpropanoid. Typically a phenylpropanoid has its phenyl group further substituted with 1-3 hydroxy and/or methoxy groups, and either the propyl / propenyl or a hydroxy group on the phenyl can be linked to another phenylpropanoid.

[00152] Similarly, "heteroaromatic" and "heteroaryl" refer to such monocyclic or fused bicyclic ring systems that contain as ring members one or more heteroatoms selected from O, S and N. The inclusion of a heteroatom permits aromaticity in 5-membered rings as well as 6-membered rings. Typical heteroaromatic systems include monocyclic C5-C6 aromatic groups such as pyridyl, pyrimidyl, pyrazinyl, thienyl, furanyl, pyrrolyl, pyrazolyl, thiazolyl, oxazolyl, and imidazolyl and the fused bicyclic moieties formed by fusing one of these monocyclic groups with a phenyl ring or with any of the heteroaromatic monocyclic groups to form a C8-C10 bicyclic group such as indolyl, benzimidazolyl, indazolyl, benzotriazolyl, isoquinolyl, quinolyl, benzothiazolyl, benzofuranyl, pyrazolopyridyl, quinazolinyl, quinoxalinyl, cinnolinyl, and the like. Any monocyclic or fused ring bicyclic system that has the characteristics of aromaticity in terms of electron distribution throughout the ring system is included in this definition. It also includes bicyclic groups where at least the ring which is directly attached to the remainder of the molecule has the characteristics of aromaticity. Typically, the ring systems contain 5-12 ring member atoms. Preferably the monocyclic heteroaryls contain 5-6 ring members, and the bicyclic heteroaryls contain 8-10 ring members.

[00153] Aryl and heteroaryl moieties may be substituted with a variety of substituents including C1-C8 alkyl, C2-C8 alkenyl, C2-C8 alkynyl, C3-C8 cycloalkyl, C5-C12 aryl, C1-C8 acyl, and heteroforms of these, each of which can itself be further substituted; other substituents for aryl and heteroaryl moieties include halo, OR, NR₂, SR, SO₂R, SO₂NR₂, NRSO₂R,

416₂7₂008740 55 NRCONR₂, NRCOOR, NRCOR, CN, COOR, CONR₂, OOCR, COR, and NO₂, wherein each R is independently H, C1-C8 alkyl, C2-C8 heteroalkyl, C2-C8 alkenyl, C2-C8 heteroalkenyl, C2- C8 alkynyl, C2-C8 heteroalkynyl, C3-C8 heterocyclyl, C4-C10 heterocyclyclalkyl, C6-C10 aryl, C5-C10 heteroaryl, C7-C12 arylalkyl, or C6-C12 heteroarylalkyl, and each R is optionally substituted as described above for alkyl groups. Where a substituent group contains two R or R' groups on the same or adjacent atoms (e.g., -NR2, or -NR-C(O)R), the two R or R' groups can optionally be taken together with the atoms in the substituent group to which the are attached to form a ring having 5-8 ring members, which can be substituted as allowed for the R or R' itself, and can contain an additional heteroatom (N, O or S) as a ring member. The substituent groups on an aryl or heteroaryl group may of course be further substituted with the groups described herein as suitable for each type of such substituents or for each component of the substituent. Thus, for example, an arylalkyl substituent may be substituted on the aryl portion with substituents described herein as typical for aryl groups, and it may be further substituted on the alkyl portion with substituents described herein as typical or suitable for alkyl groups.

[00154] Similarly, "arylalkyl" and "heteroarylalkyl" refer to aromatic and heteroaromatic ring systems that are bonded to their attachment point through a linking group such as an alkylene, including substituted or unsubstituted, saturated or unsaturated, cyclic or acyclic linkers.

Typically the linker is C1-C8 alkyl or a hetero form thereof. These linkers may also include a carbonyl group, thus making them able to provide substituents as an acyl or heteroacyl moiety. An aryl or heteroaryl ring in an arylalkyl or heteroarylalkyl group may be substituted with the same substituents described above for aryl groups. Preferably, an arylalkyl group includes a phenyl ring optionally substituted with the groups defined above for aryl groups and a C1-C4 alkylene that is unsubstituted or is substituted with one or two C1-C4 alkyl groups or heteroalkyl

416₂7₂008740 57 groups, where the alkyl or heteroalkyl groups can optionally cyclize to form a ring such as cyclopropane, dioxolane, or oxacyclopentane. Similarly, a heteroarylalkyl group preferably includes a C5-C6 monocyclic heteroaryl group that is optionally substituted with the groups described above as substituents typical on aryl groups and a C1-C4 alkylene that is unsubstituted or is substituted with one or two C1-C4 alkyl groups or heteroalkyl groups, or it includes an optionally substituted phenyl ring or C5-C6 monocyclic heteroaryl and a C1-C4 heteroalkylene that is unsubstituted or is substituted with one or two C1-C4 alkyl or heteroalkyl groups, where the alkyl or heteroalkyl groups can optionally cyclize to form a ring such as cyclopropane, dioxolane, or oxacyclopentane.

[00155] Where an arylalkyl or heteroarylalkyl group is described as optionally substituted, the substituents may be on either the alkyl or heteroalkyl portion or on the aryl or heteroaryl portion of the group. The substituents optionally present on the alkyl or heteroalkyl portion are the same as those described above for alkyl groups generally; the substituents optionally present on the aryl or heteroaryl portion are the same as those described above for aryl groups generally.

[00156] "Arylalkyl" groups as used herein are hydrocarbyl groups if they are unsubstituted, and are described by the total number of carbon atoms in the ring and alkylene or similar linker. Thus a benzyl group is a C7-arylalkyl group, and phenylethyl is a C8-arylalkyl.

[00157] "Heteroarylalkyl" as described above refers to a moiety comprising an aryl group that is attached through a linking group, and differs from "arylalkyl" in that at least one ring atom of the aryl moiety or one atom in the linking group is a heteroatom selected from N, O and S. The heteroarylalkyl groups are described herein according to the total number of atoms in the ring and linker combined, and they include aryl groups linked through a heteroalkyl linker; heteroaryl groups linked through a hydrocarbyl linker such as an alkylene; and heteroaryl groups linked

416272008740 5g through a heteroalkyl linker. Thus, for example, C7-heteroarylalkyl would include pyridylmethyl, phenoxy, and N-pyrrolylmethoxy.

[00158] "Alkylene" as used herein refers to a divalent hydrocarbyl group; because it is divalent, it can link two other groups together. Typically it refers to -(CH₂)_n- where n is 1-8 and preferably n is 1-4, though where specified, an alkylene can also be substituted by other groups, and can be of other lengths, and the open valences need not be at opposite ends of a chain. Thus -CH(Me)- and -C(Me)₂- may also be referred to as alkylenes, as can a cyclic group such as cyclopropan-l,l-diyl. Where an alkylene group is substituted, the substituents include those typically present on alkyl groups as described herein.

[00159] In general, any alkyl, alkenyl, alkynyl, acyl, or aryl or arylalkyl group or any heteroform of one of these groups that is contained in a substituent may itself optionally be substituted by additional substituents. The nature of these substituents is similar to those recited with regard to the primary substituents themselves if the substituents are not otherwise described. Thus, where an embodiment of, for example, R⁷ is alkyl, this alkyl may optionally be substituted by the remaining substituents listed as embodiments for R⁷ where this makes chemical sense, and where this does not undermine the size limit provided for the alkyl per se; e.g., alkyl substituted by alkyl or by alkenyl would simply extend the upper limit of carbon atoms for these

embodiments, and is not included. However, alkyl substituted by aryl, amino, alkoxy, =0, and the like would be included within the scope of the invention, and the atoms of these substituent groups are not counted in the number used to describe the alkyl, alkenyl, etc. group that is being described. Where no number of substituents is specified, each such alkyl, alkenyl, alkynyl, acyl, or aryl group may be substituted with a number of substituents according to its available

416272008740 59 valences; in particular, any of these groups may be substituted with fluorine atoms at any or all of its available valences, for example.

[00160] "Heteroform" as used herein refers to a derivative of a group such as an alkyl, aryl, or acyl, wherein at least one carbon atom of the designated carbocyclic group has been replaced by a heteroatom selected from N, O and S. Thus the heteroforms of alkyl, alkenyl, alkynyl, acyl, aryl, and arylalkyl are heteroalkyl, heteroalkenyl, heteroalkynyl, heteroacyl, heteroaryl, and heteroarylalkyl, respectively. It is understood that no more than two N, O or S atoms are ordinarily connected sequentially, except where an oxo group is attached to N or S to form a nitro or sulfonyl group.

[00161] "Optionally substituted" as used herein indicates that the particular group or groups being described may have no non-hydrogen substituents, or the group or groups may have one or more non-hydrogen substituents. If not otherwise specified, the total number of such

substituents that may be present is equal to the number of H atoms present on the unsubstituted form of the group being described. Where an optional substituent is attached via a double bond, such as a carbonyl oxygen (=0), the group takes up two available valences, so the total number of substituents that may be included is reduced according to the number of available valences.

[00162] For purposes of the invention, substituents for the alkyl and aryl groups in the compounds can also include a bond to a lignin or to a phenylpropanoid. In some embodiments, the preferred substituents for such alkyl and aryl groups include -OH, -OMe, -CH=CH-CH₂OH, -CH(OH)-CH(OH)-CH₂OH, and derivatives of these wherein a C or O is linked to another phenylpropanoid, whether alone or as part of a lignin.

[00163] In lignin structures, the types and degrees of substitution of aryl or alkyl groups are determined by the natural substrate, and may not be known or readily determined.

416272008740 60 [00164] "Halo," as used herein includes fluoro, chloro, bromo, and iodo. Fluoro and chloro are often preferred.

[00165] "Amino" as used herein refers to NH₂, but where an amino is described as

"substituted" or "optionally substituted," the term includes NR'R" wherein each R' and R" is independently H, or is an alkyl, alkenyl, alkynyl, acyl, aryl, or arylalkyl group or a heteroform of one of these groups, and each of the alkyl, alkenyl, alkynyl, acyl, aryl, or arylalkyl groups or heteroforms of one of these groups is optionally substituted with the substituents described herein as suitable for the corresponding group. The term also includes forms wherein R' and R" are linked together to form a 3-8 membered ring which may be saturated, unsaturated or aromatic and which contains 1-3 heteroatoms independently selected from N, O and S as ring members, and which is optionally substituted with the substituents described as suitable for alkyl groups or, if NR'R" is an aromatic group, it is optionally substituted with the substituents described as typical for heteroaryl groups.

[00166] As used herein, the term "depolymerization" refers to the breaking of at least one bond in a polymer or at least one bond of a dimer. It thus includes reactions that cleave 'whole' or natural lignin, as well as lignins that have been partially processed by other methods but retain at least some polymeric phenylpropanoid structures characteristic of lignins. It includes reactions that break at least some C-C and/or C-O bonds of lignin, without necessarily reducing the molecular weight of the lignin, and reactions that produce modified lignin having increased solubility. It especially includes reactions that clip lignin into smaller pieces, i.e., reactions that reduce the average molecular weight of a sample of lignin by at least about 10% or at least about 20%, or that convert a significant proportion (e.g., at least about 10% or at least about 20%) of a lignin sample into fragments having a molecular weight of less than about 1500, preferably less

416272008740 β\ than about 1000. Both the disproportionation reactions and the reduction methods described herein can be used to depolymerize lignin to a useful extent.

[00167] As used herein, the term "disproportionation" refers to a chemical reaction that rearranges molecular structures without introducing new materials. In the present methods, it may be viewed as a transformation wherein one portion of the molecule is oxidized, providing 'hydrogen' for another portion of the molecule to be reduced. Such reactions can be particularly efficient for degradation of lignins, where they minimize the need for adding a reductant or an oxidant. Such reactions can also be efficient for the cleavage of carbon-oxygen and carbon- carbon bonds of organic substrates such as α-keto ethers and β-hydroxy ethers.

[00168] As used herein the term "pre-formed catalyst" refers to a catalyst that has been prepared by reacting a metal precursor with a ligand and isolated prior to use in the

disproportionation or reduction reactions described herein. This is in contrast to a catalyst that has been prepared in situ, by reacting a metal precursor with a ligand under the reaction conditions.

[00169] As used herein, the abbreviation "PPh₃" refers to "triphenylphosphine"; "PCy₃" refers to "tricyclohexylphosphine"; "OTf refers to "triflate"; "TFA" refers to "trifluoroacetate" or "trifluoroacetato"; "cod" or "COD" refers to "cyclooctadiene"; and "coe" or "COE" refers to "cyclooctene."

2. Description of the Invention

[00170] The present invention provides methods and catalyst compositions for the catalytic reduction of carbon-oxygen bonds of organic substrates and the catalytic disproportionation of carbon-oxygen or carbon-carbon bonds of organic substrates. These methods and catalyst compositions may also be used to depolymerize lignin. The methods include reactions that clip

416272008740 52 lignin into smaller pieces, i.e., reactions that reduce the average molecular weight of a sample of lignin by at least about 10% or at least about 20%, or that convert a significant proportion (e.g., at least about 10% or at least about 20%) of a lignin sample into fragments having a molecular weight of less than about 1500, preferably less than about 1000. Both the disproportionation reactions and the reduction methods described herein can be used to depolymerize lignin to a useful extent. Although lignin does not have a regular structure, the β-glycerolaryl ether unit accounts for 45-50% of the polymeric linkages in lignin. The β-glycerolaryl ether moiety is depicted among the model dimer compounds of lignin in Scheme 2.

[00171] The disproportionation methods of the present invention have advantages over previously used oxidative and reductive depolymerization methods. Oxidative depolymerization decreases the energy content of the degradation products. Reductive depolymerization using molecular hydrogen (H₂) as the reductant generates water (H₂O) as the pendant hydroxyl (OH) groups of lignin are reduced, and requires hydrogen as an input that must be generated at significant energetic cost. Unless the reduction is highly selective for the carbon-oxygen bonds in the polymer linkages, unproductive formation of water can act as an energy sink if reduction does not precede depolymerization. The disproportionation approach utilizes the hydroxyl (OH) groups of lignin as hydrogen sources which may be dehydrogenated to form carbonyls. The carbonyls may protect against unproductive water generation and the liberated hydrogen may be used for the reduction of the aryl ether linkage resulting in depolymerization:

416272008740 53 Ar³ and Ar⁴ are optionally substituted aryl groups of lignin or an organic substrate and each R and R' is independently hydrogen, a bond to a phenylpropanoid unit of lignin, or a substituent in an organic substrate. Therefore, the disproportionation reactions may occur without added oxidant or reductant or acid or base. However, in some embodiments, these additives may be added to the reaction, for example, in order to control selectivity of the bond cleavage reactions.

[00172] The disproportionation reaction may include the step of cleaving a carbon-oxygen double bond between C and O of an α-keto ether compound of Formula 1 :

1

wherein R¹, R², and R³ are each independently selected from the group consisting of hydrogen, alkyl, optionally substituted alkyl, aryl, optionally substituted aryl, optionally substituted heteroaryl; and

wherein R² is not hydrogen.

[00173] In some embodiments, R³ is not aryl or heteroaryl and R¹ is not H. In other embodiments, the structure of Formula 1 represents a lignin component or a phenylpropanoid moiety. In other embodiments, R¹ and R² are optionally substituted aryl. In other embodiments, R¹ and R² are optionally substituted aryl and R³ is H.

[00174] In some embodiments, the reaction may produce at least one product selected from the group consisting of:

416272008740 54

wherein C¹ X is C¹O or C¹HOH.

[00175] In some embodiments, the reaction may produce at least one product selected from the group consisting of:

2 2' 3

In other embodiments, mixtures of compounds in varying ratios may also form depending on the reaction conditions.

[00176] The disproportionation reaction, as defined above, rearranges molecular structures without introducing new materials. The carbon-oxygen bond cleavage of the α-keto ether compound may be preceded by an oxidative dehydrogenation step which may provide the hydrogen to reduce the carbon-oxygen bond:

[00177] Catalysts which catalyze the reduction of α-keto ether compounds may also catalyze the disproportionation of the β-hydroxy ether compound of Formula 4 by cleavage of the bond between C² and O²:

416272008740 55

wherein R² is not hydrogen.

[00178] In some embodiments, R³ is not aryl or heteroaryl and R¹ is not H. In other embodiments, the compound of Formula 5 represents a lignin component or a phenylpropanoid moiety. In other embodiments, R¹ and R² are optionally substituted aryl. In other embodiments, R¹ and R² are optionally substituted aryl and R³ is H. In other embodiments, R¹ and R² are optionally substituted aryl groups of lignin and R³ is a bond to another phenylpropanoid group of lignin.

[00179] In some embodiments, the reaction may produce at least one product selected from the group consisting of:

5 6 .

wherein C¹ X is C^O or C¹HOH.

[00180] In some embodiments, the reaction may produce at least one product selected from the group consisting of:

416272008740 55

5 5'

[00181] In some embodiments, mixtures of compounds in varying ratios may also form depending on the reaction conditions. In some embodiments, the reactions occur via tandem dehydrogenation and carbon-oxygen bond cleavage reactions.

[00182] In some embodiments, the compounds of Formulas 1 and 4 include at least a dimer of a phenylpropanoid moiety. In other embodiments, the compounds of Formulas 1 and 4 are lignins.

[00183] In some embodiments, when R³ is an appropriate substituent, such as hydroxyl- substituted alkyl group, the disproportionation reaction may be a disproportionation-elimination reaction. In these particular embodiments, the cleaving of a compound of Formula 4 forms at least one product selected from the group consisting of:

X R⁴

_Rrcyλ R4 and R²OH

H

wherein C¹ X is C¹O or C¹HOH;

and wherein each R⁴ is independently selected from the group consisting of hydrogen, alkyl, optionally substituted alkyl, aryl, optionally substituted aryl, and optionally substituted heteroaryl.

[00184] In other embodiments, an additional product is formed by a reaction other than the cleaving reaction, and wherein the additional product is of Formula 9:

416272008740 57

[00185] R¹, R², and R⁴ are as defined for Formulas 4 and 7-8.

[00186] Another disproportionation method of the present invention involves cleaving a carbon-carbon bond between C¹ and C² and/or C² and C³ of a 1,3 diol compound of Formula 10:

10

[00187] wherein each R⁵, R⁶, and R⁷ is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted alkoxy, and optionally substituted aryloxy.

[00188] In some embodiments, cleaving a carbon-carbon bond between C¹ and C² and/or C² and C³ of a 1,3 diol compound of Formula 10 may produce at least one product selected from the group consisting of:

1 1 12

u _r3 and _r i

^ R⁷ R⁵ H

R⁶

13 14 wherein C¹ X is C=O or C¹HOH and C³-X is C=O or C³HOH.

416272008740 gg [00189] In some embodiments, the cleaving forms the product of Formula 11 :

1 1

[00190] In some embodiments, the cleaving forms the product of Formula 12:

X

-C^₇

H R

12

[00191] In some embodiments, the cleaving forms the product of Formula 13:

13

[00192] In some embodiments, the cleaving forms the product of Formula 14:

X

R⁵ H

14

[00193] In some embodiments, mixtures of compounds of Formulas 11-14 may also form in varying ratios depending on the reaction conditions. In other embodiments, the reactions occur via tandem dehydrogenation and retro-aldol reactions.

[00194] In some embodiments, other products may form by β-hydroxyl

elimination/hydrogenation of the α-keto ether compound as shown in the following example:

416272008740 gO,

[00195] Therefore, in addition to compounds 11-14, any of the compounds of formulas 15-17 may also form in the product mixture:

15 16 17

[00196] In some embodiments, mixtures of any combination of compounds 11-17 in varying ratios may form depending on the reaction conditions.

[00197] Another disproportionation method of the present invention involves cleaving a carbon-oxygen bond between C² and O² of the glycerol β-arylether compound of Formula 18:

18 ;

[00198] wherein Ar¹ and Ar² are optionally substituted aryl and each R⁸ and R⁹ is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted aryl, and optionally substituted heteroaryl.

416272008740 70 [00199] In some embodiments, the cleaving forms at least one product selected from the group consisting of:

19 20 .

wherein C¹ X is C=O or C¹HOH.

[00200] In some embodiments, the cleaving forms the product of Formula 19:

¹ Q

[00201] In some embodiments, the cleaving forms the product of Formula 20:

Ar²OH

20

[00202] In some embodiments, when R is hydrogen, the disproportionation reaction may be a disproportionation-elimination reaction. In these particular embodiments, the cleaving of a compound of Formula 18 forms at least one product selected from the group consisting of:

21 22 wherein C¹ X is C¹O or C¹HOH.

Optionally, compounds of Formula 21 and 22 may both be formed.

[00203] In some embodiments, the cleaving forms the product of Formula 21:

416272008740 η \

21 [00204] In some embodiments, the cleaving forms the product of Formula 22:

Ar²OH

22

[00205] In other embodiments, an additional product is formed by a reaction other than the cleaving reaction, and wherein the additional product is of Formula 23:

23

[00206] Another disproportionation method of the present invention involves cleaving a carbon-carbon bond between C¹ and C² and/or C² and C³ of a glycerol β-arylether compound of Formula 18:

18 ;

wherein Ar¹ and Ar² are optionally substituted aryl groups and each R⁸ and R⁹ is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted aryl, and optionally substituted heteroaryl.

416272008740 79 [00207] In some embodiments, the cleaving forms at least one product selected from the group consisting of:

24 25

26 27 wherein C¹ X is C=O or CHOH and C³-X is C=O or CHOR⁸.

[00208] Another disproportionation method of the present invention involves cleaving a carbon-carbon bond between C¹ and C² and/or C² and C³of a glycerol β-arylether compound of Formula 18 and cleaving a carbon-oxygen bond between C² and O² of the glycerol β-arylether compound of Formula 18:

18 ;

[00209] In some embodiments, either carbon-oxygen or carbon-carbon bond cleaving may produce at least one product selected from the group consisting of:

416272008740 73 x

_Ari- ^H H'^' R₉

19 20 24 25

26 27 28 29 wherein C¹ X is C=O or C¹HOH and C³-X is C=O or CHOR⁸.

[00210] In some embodiments, the cleaving forms the product of Formula 20:

Ar²OH

20

[00211] In some embodiments, the cleaving occurs via tandem dehydrogenation and retro- aldol reactions and/or tandem dehydrogenation and carbon-oxygen bond cleavage reactions.

[00212] In some embodiments, other products, such as the compounds of Formula 20, and 30- 31, may form by β-hydroxyl elimination/hydrogenation of the α-keto ether compound:

20 30 31

[00213] In some embodiments, mixtures of any combination of compounds 20-31 in varying ratios may form depending on the reaction conditions.

[00214] Another disproportionation method of the present invention involves depolymerizing lignin by cleaving a carbon-oxygen bond or a carbon-carbon bond of a phenylpropanoid unit of lignin in a catalytic disproportionation reaction.

416272008740 74 [00215] In some embodiments, lignin is depolymerized by disproportionating a glycerol β- arylether unit of lignin. The disproportionation includes the step of cleaving a carbon-oxygen bond between C² and O² of the glycerol β-arylether unit of lignin of Formula 32:

phenylpropanoid unit of lignin.

[00216] In some embodiments, the cleaving forms the product of Formula 33:

Ar⁴OH

33

[00217] Another disproportionation method of the present invention involves cleaving a carbon-carbon bond between C¹ and C² and/or C² and C³ of a glycerol β-arylether unit of lignin of Formula 32:

OH OR 10

Ar³ Y R

,O²

Ar⁴

32

416272008740 75 wherein Ar³ and Ar⁴ are optionally substituted aryl groups of lignin and each R¹⁰ and R¹¹ is independently selected from the group consisting of hydrogen or a bond to a

phenylpropanoid unit of lignin.

[00218] Another disproportionation method of the present invention involves cleaving a carbon-carbon bond between C¹ and C² and/or C² and C³ of the glycerol β-arylether unit of lignin of Formula 32 and cleaving a carbon-oxygen bond between C² and O² of the glycerol β- arylether unit of lignin of Formula 32:

phenylpropanoid unit of lignin.

[00219] In some embodiments, the cleaving forms at least a product of Formula 33:

Ar⁴OH

33

[00220] The reactions of the present invention depicted above are typically catalyzed by a catalyst other than a base, acid, enzyme, or zeolite catalyst. The reactions may occur without added oxidant or reductant or acid or base. The catalysts are typically metal-based catalysts formed from a soluble metal precursor and an optional ligand under the reaction conditions with lignin. Alternatively, the catalysts may be preformed metal precursor-ligand complexes. Metals

416272008740 75 which may catalyze the disproportionation reaction include scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, lanthanum, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, and mercury. In some

embodiments, the disproportionation reactions are catalyzed by iron, palladium, ruthenium, nickel, rhodium, or iridium. In certain embodiments, the disproportionation reactions are catalyzed by ruthenium, nickel, and rhodium. In certain embodiments, the disproportionation reactions are catalyzed by ruthenium. In other certain embodiments, the disproportionation reactions are catalyzed by vanadium.

[00221] Disproportionation reactions may be catalyzed by organometallic catalysts optionally containing hydride and carbonyl ligands. In some embodiments, the catalysts are formed by combining a metal precursor complex with lignin under the reaction conditions. In other embodiments, the catalysts are formed by combining a metal precursor complex with a ligand prior to reaction with lignin, or the metal precursor-ligand complex may be isolated prior to reaction with lignin. Alternatively, the metal precursor-ligand complex may be formed in situ under the reaction conditions with lignin. Some examples of metal precursors include, but are not limited to, [Ru₃(CO)₁₂], [{Ru(cymene)Cl₂}₂], [(PPh₃)₄RuCl₂],

[Ru(PPh₃MCOXOTf)₂(MeOH)] , [RuH₂CO(PPh₃)₃] , [Ru(TFA)₂(CO)(PPh₃)₂] ,

[Ru(TFA)(PPh₃)₂(CO)H], [Ni(cod)₂], and [RhCl(coe)₂]₂. Some examples of ligands include, but are not limited to, phosphine ligands having three alkyl and/or aryl groups on the phosphorus, such as, for example, trimethylphosphine, triethylphosphine, triphenylphosphine,

tricyclohexylphosphine. The three groups on P of such phosphines may be the same or different, and are optionally substituted. The phosphine ligands may include chelating, bidentate

416₂7₂008740 77 phosphine ligands such as (9,9-dimethylxanthene-4,5-diyl)Ws(diphenylphosphine); 1,2- bis(dimethylphosphino)ethane; 1 ,2-bis(diphenylphosphino)methane; 1 ,2- bis(diphenylphosphino)ethane; l,2-bis(diphenylphosphino)propane; and 1,2- bis(diphenylphosphino)benzene. Other ligands such as amine and pyridine ligands, both chelating and monodentate, are contemplated.

[00222] In some embodiments, the cleaving occurs via a disproportionation-elimination reaction. In certain embodiments, the metal-based catalyst that cleaves via disproportionation- elimination is vanadium. In some embodiments, the vanadium catalysts produce C-O bond cleavage products (e.g. compounds 35 and 36) via a non-oxidative disproportionation- elimination pathway in addition to benzylic alcohol oxidation products (e.g. compound 37) as shown in the following non-limiting reaction scheme:

37

[00223] In some embodiments, the catalyst is formed from a vanadium metal precursor and optionally a ligand under the reaction conditions. In some embodiments, the vanadium metal precursor is selected from the group consisting of [VOSO₄-XH₂O], [VO(acac)₂], and [VO(Oz- Pr)₃]. The ligand may be a phenol-imine or bis-phenol-imine ligand. Other vanadium catalysts which may be used for the cleaving reaction include pre-formed phenol-imine or bis-phenol- imine vanadium catalysts selected from the group consisting of:

416272008740 78

[00224] In some embodiments, tridentate Schiff base ligands favor C-O bond cleavage over benzylic oxidation. In other embodiments, higher selectivity for C-O bond cleavage was observed when ligands with larger bite angles were employed.

[00225] The vanadium catalysts react with purified lignin to produce various organic compounds as observed by NMR and LCMS (see Example 21). When lignin is reacted under the same conditions without the vanadium catalyst, only trace organic compounds are detected by NMR.

[00226] In some embodiments, the vanadium catalysts are reacted in the presence of air. The role of oxygen in the formally non-oxidative process was studied by carrying out the vanadium catalyzed reactions under anaerobic conditions. The same products as under aerobic conditions were obtained albeit with lower conversions suggesting that oxygen is not essential for catalyst turnover although it increases the reaction rate.

[00227] The methods of the present invention also provide a method of depolymerizing lignin including:

416272008740 79 cleaving a carbon-oxygen bond of lignin in a catalytic reduction reaction. More generally, the invention provides general methods for the reductive cleavage of various types of ether linkages, including diaryl (e.g., diphenyl) ethers having various substitution patterns.

[00228] In some embodiments, the method is used to cleave ether linkages in lignin by breaking a carbon-oxygen bond. In some embodiments, the carbon-oxygen bond includes a diaryl, alkyl aryl, or benzyl alkyl, or benzyl aryl ether linkage. In some embodiments, the linkage being cleaved is a diaryl ether linkage, wherein each aryl group can be substituted or unsubstituted.

[00229] In some embodiments, the cleaving is catalyzed by a metal-based catalyst including nickel. In some embodiments, the metal-based catalyst including nickel is formed from a nickel precursor and optionally a ligand under the reaction conditions. In certain embodiments, the nickel precursor is selected from the group consisting of Ni(COD)₂, Ni(acac)₂, NiCl₂, NiBr₂, Ni(OAc)₂, Ni(OH)₂, NiCO₃* 2 Ni(OH)₂ (nickel carbonate basic), and mixtures thereof. In some preferred embodiments, the nickel precursor is Ni(COD)₂ or Ni(acac)₂. In some embodiments, the ligand:nickel precursor ratio is approximately 2:1. In certain embodiments, the ligand is a carbene ligand (e.g., N-heterocyclic carbene) or a phosphine ligand. In some embodiments, the phosphine ligand is a trialkylphosphine ligand such as, for example, tricyclohexylphosphine P(Cy₃)₃. In certain embodiments, the ligand is an N-heterocyclic carbene ligand. The N- heterocyclic carbene ligands may be used as a salt, which may be deprotonated with a base in situ under the reaction conditions. The salts may have, for example, a halide, tetrafluoroborate, or a triflate counteranion. In some embodiments, the N-heterocyclic carbene ligand is selected from the group consisting of:

416₂7₂008740 gQ

SIPr HX, X=CI-, BF₄ ^" IPr HCI diMelPr HCI diMeSIPr HCI

MonotBulPr HCI ItBu HCI IMes HCI SIMes HBF₄

6-DIPP HBr 7-DIPP HBr XyI-DIPP HBr

SCAAC HCI

SImAd HBF₄ SImPr HBF₄ SImBu HBF₄ Bu Im HBF₄

[00230] and mixtures thereof. In some preferred embodiments, the N-heterocyclic carbene ligand is a five-membered, N-aryl-N-heterocyclic carbene. In some preferred embodiments, the five-membered, N-aryl-N-heterocyclic carbene is selected from the group consisting of:

416272008740 81

SIPr HX₁ X=CI-, BF₄ ^" IPr HCI diMelPr HCI diMeSIPr HCI

MonotBulPr HCI ItBu HCI IMes HCI SIMes HBF,

[00231] and mixtures thereof. In other preferred embodiments, the N-heterocyclic carbene ligand is selected from the group consisting of:

SPr HCI IPr_Me HCI ; and mixtures thereof.

[00232] In some embodiments, the cleaving is catalyzed by a pre-formed N-heterocyclic carbene nickel catalyst. In some embodiments, the cleaving is carried out at a reaction temperature of 80-250⁰C.

[00233] The cleaving step in the catalytic reduction reaction is generally carried out in the presence of a hydrogen atom source, the hydrogen atom source selected from the group consisting of hydrogen, a silane, diisobutylaluminum hydride (DIBAL), lithium tή-tert- butoxyalumnium hydride (LiAl(CyBu)₃H), or mixtures thereof. In certain embodiments, the silane is triethylsilane (Et₃SiH) or te/t-butyldimethyl silane (^BuMe₂SiH). In certain preferred embodiments, the hydrogen atom source is dihydrogen.

416272008740 82 [00234] The cleaving step in the catalytic reduction reaction is generally carried out in the presence of a base. In some embodiments, the base is selected from the group consisting of sodium te/t-butoxide (YBuONa), sodium te/t-pentoxide (YPentONa), sodium /so-propoxide

(/PrONa), lithium te/t-butoxide (YBuOLi), sodium methoxide (MeONa), potassium te/t-butoxide

(^BuOK), cesium fluoride (CsF), and cesium carbonate (CS₂CO₃), and mixtures thereof. In certain embodiments, the base is selected from the group consisting of sodium te/t-butoxide

(^BuONa), sodium te/t-pentoxide (^PentONa), sodium /so-propoxide (/PrONa), and mixtures thereof.

[00235] In some embodiments, the cleaving has a higher selectivity for aryl-carbon-oxygen bonds over alkyl-carbon oxygen bonds in lignin.

[00236] In some embodiments, the cleaving is catalyzed by a metal-based catalyst including nickel and an N-heterocyclic carbene ligand in the presence of a hydrogen atom source and a base.

[00237] Following the cleaving step of the catalytic reduction reaction, the methods of the present invention may further include hydrodeoxygenating the reaction products. In other embodiments, the methods of the present invention may further include cracking and/or hydrogenating the reaction products. In some embodiments, a fuel is produced following the hydrodeoxygenating, cracking, and/or hydrogenating steps.

[00238] In some embodiments, the disproportionation or reduction reactions may be carried out in organic solvents, supercritical CO₂, or ionic liquids at temperatures ranging from 80 -

25O⁰C. The lignin source used in the disproportionation or reduction reactions may be lignin in lignocellulosic biomass, purified lignin, or lignin fragments that are produced, for example, from the pyrolysis of lignin. Lignin sources may include, but are not limited to, hardwoods,

416272008740 g3 softwoods, and Miscanthus. Alcell lignin, lignin which has been processed by an ethanol organosolv pulping method, may also be used as a lignin source. Lignin may optionally be extracted or treated to remove impurities such as nitrogen- or sulfur-containing compounds and/or ash prior to the catalytic reaction using conventional methods known in the art. Lignin may also be chemically derivatized to enhance solubility prior to the disproportionation or reduction reactions of the present invention.

[00239] In some embodiments, the disproportionation reactions may be carried out in the presence of hydrogen. In some embodiments, the rate of any of the individual steps in the disproportionation reaction, for example, the C-O bond cleavage step may be accelerated or decelerated in the presence of hydrogen. In other embodiments, the reduction and/or disproportionation reactions may be carried out in the presence of hydrogen. In some embodiments, the cleaving is carried out in the presence of an acid. In certain embodiments, the acid is selected from the group consisting of AlX₃ where X = tertiary alkoxide, phenoxide, and halogen; TiX₄ where X = tertiary alkoxide, phenoxide, and halogen; BX₃ where X = F, Br; organic acids X-CO₂H where X = CF₃, CH₃, aryl; and sulfonic acids X-SO₃H where X = Me, aryl.

[00240] Following depolymerization by disproportionation or reduction, the products may be further hydrodeoxygenated, hydrocracked, and/or hydrogenated using catalysts that are known in the art to produce fuel from lignin. The overall process of hydrodeoxygenation, hydrocracking, and hydrogenating may be referred to as "hydrotreating." Catalysts which may carry out one or more of the hydrodeoxygenation, hydrocracking, or hydrogenation reactions include, for example, sulfided NiMo, NiW, and CoMo catalysts supported on alumina, chromium, and/or

416272008740 g4 zeolites; PtZSiO_x-Al₂O₃ and PtAVO_xZZrO₂ catalysts; vanadium nitride catalysts; ruthenium catalysts, and zeolite catalysts.

[00241] The methods of the present invention also provide a method to cleave a diaryl ether linkage including contacting a diaryl ether with a nickel catalyst and a hydrogen donor in the presence of a base. In some embodiments, the diaryl ether is an optionally substituted diphenyl ether. In some embodiments, the nickel catalyst is formed from a nickel precursor and optionally a ligand under the reaction conditions. In certain embodiments, the nickel precursor is selected from the group consisting of Ni(COD)₂, Ni(acac)₂, NiCl₂, NiBr₂, Ni(OAc)₂, Ni(OH)₂, NiCO₃* 2 Ni(OH)₂ (nickel carbonate basic), and mixtures thereof. In some preferred embodiments, the nickel precursor is Ni(COD)₂ or Ni(acac)₂. In some embodiments, the ligand:nickel precursor ratio is approximately 2:1. In certain embodiments, the ligand is a carbene ligand (e.g., N- heterocyclic carbene) or a phosphine ligand. In some embodiments, the phosphine ligand is a trialkylphosphine ligand such as, for example, tricyclohexylphosphine (P(Cy₃)₃). In certain embodiments, the ligand is an N-heterocyclic carbene ligand. The N-heterocyclic carbene ligands may be used as a salt, which may be deprotonated with a base in situ. The salts may have, for example, a halide, tetrafluoroborate, or a triflate counteranion. In some embodiments, the N-heterocyclic carbene ligand is selected from the group consisting of:

416₂7₂008740 g5

SIPr HX, X=CI-, BF₄ ^" IPr HCI diMelPr HCI diMeSIPr HCI

MonotBulPr HCI ItBu HCI IMes HCI SIMes HBF₄

6-DIPP HBr 7-DIPP HBr XyI-DIPP HBr

SCAAC HCI

SImAd HBF₄ SImPr HBF₄ SImBu HBF₄ Bu Im HBF₄

[00242] and mixtures thereof. In some preferred embodiments, the N-heterocyclic carbene ligand is a five-membered N-aryl-N-heterocyclic carbene. In some preferred embodiments, the five-membered N-aryl-N-heterocyclic carbene is selected from the group consisting of:

416272008740 86

SIPr HX₁ X=CI-, BF₄ ^" IPr HCI diMelPr HCI diMeSIPr HCI

MonotBulPr HCI ItBu HCI IMes HCI SIMes HBF,

[00243] and mixtures thereof. In other preferred embodiments, the N-heterocyclic carbene ligand is selected from the group consisting of:

SPr HCI IPr_Me HCI ; and mixtures thereof.

[00244] In some embodiments, the cleaving reaction is catalyzed by a pre-formed N- heterocyclic carbene nickel catalyst. In some embodiments, the cleaving reaction is carried out at a reaction temperature of 80-250⁰C.

[00245] The present invention also provides compositions including lignin and a metal-based catalyst. In some embodiments, the metal-based catalyst is formed from a metal precursor and optionally a ligand under the reaction conditions. In some embodiments, the metal precursor includes a metal selected from the group consisting of ruthenium, rhodium, vanadium, nickel, and mixtures thereof. In some embodiments, the metal precursor is selected from the group consisting Of [Ru₃(CO)₁₂], [{Ru(cymene)Cl₂}₂], [(PPh₃)₄RuCl₂],

416272008740 87 [Ru(PPh₃)I(CO)(OTf)₂(MeOH)] , [RuH₂CO(PPh₃)₃] , [Ru(TFA)₂(CO)(PPh₃)₂] ,

[Ru(TFA)(PPh₃)₂(CO)H], [RuH(TFA)(CO)(PPh₃)₃], [Ni(cod)₂], [RhCl(coe)₂]₂, [VOSO₄ XH₂O], [VO(acac)₂], [VO(OZ-Pr)₃], Ni(acac)₂, NiCl₂, NiBr₂, Ni(OAc)₂, Ni(OH)₂, NiCO₃* 2 Ni(OH)₂ (nickel carbonate basic), and mixtures thereof. In certain embodiments, the metal precursor includes ruthenium and the ligand is a phosphine ligand. In certain embodiments, the phosphine ligand is (9,9-dimethylxanthene-4,5-diyl)Z?/i'(diphenylphosphine). In certain embodiments, the metal precursor includes vanadium and the ligand is a phenol-imine or bis-phenol-imine ligand. In certain embodiments, the metal precursor includes nickel and the ligand is a phosphine or carbene ligand. In certain embodiments, the carbene ligand is an N-heterocyclic carbene ligand. In certain embodiments, the metal-based catalyst is a pre-formed catalyst. In certain

embodiments, the pre-formed catalyst includes ruthenium and a phosphine ligand. In certain embodiments, the pre-formed catalyst includes vanadium and a phenol-imine or bis-phenol- imine ligand. In certain embodiments, the pre-formed catalyst includes nickel and a phosphine or carbene ligand.

[00246] The following examples are offered to illustrate but not to limit the invention. The examples include ones using certain model compounds that represent structural features characteristic of lignins; such model systems are conveniently used to illustrate the usefulness of lignin degradation reactions. These models are recognized in the art as suitable for

demonstrating lignin degradation chemistry, and are used in order to facilitate product analysis: it is quite difficult to characterize lignin or its transformations.

EXAMPLES

[00247] All reagents were purchased commercially and used as received unless otherwise specified. All reactions were prepared in a Vacuum Atmospheres inert atmosphere glovebox. ¹H

416₂7₂008740 gg NMR spectra were obtained on a Varian 500 MHz. GC-MS data was obtained using electron- impact ionization on an Agilent 6890N gas chromatograph equipped with an Agilent 5973 mass spectrograph. Size exclusion chromatography (SEC) was carried out using a PL-GPC 50 instrument with a differential refractive index detector and a 100 μL loop with a mobile phase flow rate of 1.0 niL/min (THF). Toluene was dried and stored over activated molecular sieves (3 A) in the glovebox. 2-phenoxyacetophenone was prepared by etherification of 2- bromoacetophenone with phenol. 2-phenoxy-l-phenethanol was prepared by reduction of 2- phenoxyacetophenone with sodium borohydride. l-phenylpropan-l,3-diol was prepared by reduction of benzoylethylacetate with sodium borohydride. 3-hydroxy-l-phenylpropan-l-one was prepared by oxidation of l-phenylpropan-l,3-diol with manganese dioxide.

Example 1

Hydrosilation of 2-phenoxyacetophenone + PhO-Si(J-Pr)₃

[00248] In a vacuum-sealed tube (0.1-0.2 torr) and a final reaction volume of 0.50 ml in toluene, 2-phenoxyacetophenone (0.25 mmol) was heated to 135 ⁰C with tri-isopropylsilane (0.38 mmol), carbonyldihydrido-£ra(triphenylphosphino)rathenium(II) (0.013 mmol) and (9,9- dimethylxanthene-4,5-diyl)Ms(diphenylphosphine) (0.013 mmol). After 0.5 h, full consumption of the starting material yielded acetophenone (0.22 mmol, 86%) as determined by ¹H NMR integration relative to an external capillary standard. Product identification was further confirmed by GC-MS for acetophenone (120 m/z) and tri-isopropylsilylphenyl ether (250 m/z).

416272008740 gO, Example 2

Disproportionation of 2-phenoxy-l-phenethanol

80 %

[00249] In a vacuum- sealed tube (0.1-0.2 torr) and a final reaction volume of 0.50 ml in toluene, 2-phenoxy-l-phenethanol (0.25 mmol) was heated to 135 ⁰C with carbonyldihydrido- £ra(triphenylphosphino)ruthenium(II) (0.013 mmol) and (9,9-dimethylxanthene-4,5- diyl)Ws'(diphenylphosphine) (0.013 mmol). After 2.5 h, full consumption of the starting material yielded acetophenone (0.20 mmol, 80%) as determined by ¹H NMR integration relative to an external capillary standard. Product identification was further confirmed by GC-MS for acetophenone (120 m/z) and phenol (96 m/z).

Example 3

Retro-aldol cleavage of 3-hydroxy-l-phenylpropan-l-one

5% Ru(TFA)₂(CO)(PPh₃)_{2 Q}

W V^H 5% Xantphos W Jt

PIi ^ toluene (0.5 M) Pli ^ ^Pn

2-2.5 h , 175 ^SC

54% 18%

[00250] In a vacuum-sealed tube and a final reaction volume of 0.50 ml in toluene, 3- hydroxy-1-phenylpropan-l-one (0.225 mmol) was heated to 175 ⁰C with carbonyl- b/i'(trifluoroacetato)b/5'(triphenylphosphino)ruthenium(II) (0.0112 mmol) and (9,9- dimethylxanthene-4,5-diyl)Ms(diphenylphosphine) 0.0112 mmol). After 2.5 h, full consumption of the starting material yielded propiophenone (0.115 mmol, 51%) and acetophenone (0.0450 mmol, 20%) as determined by ¹H NMR integration relative to an external capillary standard.

416272008740 O-Q Product identification was further confirmed by GC-MS for propiophenone (134 m/z) and acetophenone (120 m/z).

Example 4

Retro-aldol cleavage of l-phenylpropan-l,3-diol

5% Ru(TFA)₂(CO)(PPh₃)_{2 Q}H Q

9^H 9^H 5% Xantphos H Y Jf

PfT *^ toluene (0.5 M) " Pfi ^ PfT """" Ph"^

1 7 h, 1 75 ^SC

63% 9% 23%

[00251] In a vacuum-sealed tube and a final reaction volume of 0.50 ml in toluene, 1- phenylpropan-l,3-diol (0.225 mmol), was heated to 175 ⁰C with carbonyl- Ws(trifluoroacetato)Ms(triphenylphosphino)rathenium(II) (0.0112 mmol) and (9,9- dimethylxanthene-4,5-diyl)Ms(diphenylphosphine) (0.0112 mmol). After 17 h, full consumption of the starting material yielded propiophenone (0.142 mmol, 63%), 1-phenylpropan-l-ol (0.0203 mmol, 9%), and acetophenone (0.0518 mmol, 23%) as determined by ¹H NMR integration relative to an external capillary standard. Product identification was further confirmed by GC- MS for propiophenone (134 m/z), 1-phenylpropan-l-ol (136 m/z), and acetophenone (120 m/z).

416272008740 O, } Example 5

Disproportionation of 2-phenoxy-l-phenylpropan-l,3-diol

5% 1 0% 20%

[00252] In a vacuum- sealed tube (0.1-0.2 torr) and a final reaction volume of 0.50 ml in toluene, 2-phenoxy-l-phenylpropan-l,3-diol (0.225 mmol), was heated to 175 ⁰C with carbonylhydridotrifluoroacetato-b/i'(triphenylphosphino)ruthenium(II) (0.0112 mmol) and (9,9- dimethylxanthene-4,5-diyl)Ms(diphenylphosphine) (0.0112 mmol). After 6 h, 90% consumption of the starting material yielded propiophenone (0.0450 mmol, 20%), acetophenone (0.0112 mmol, 5%), 2-phenoxyacetophenone (0.0112 mmol, 5%), benzaldehyde (0.0112 mmol, 5%), benzyl alcohol (0.0224 mmol, 10%), and 2-phenoxy-l-phenethanol (0.0450 mmol, 20%) as determined by ¹H NMR integration relative to an external capillary standard.

416272008740 92 Example 6

C-O vs C-C Bond Cleavage Selectivity + PhOH

R = H, 99% at 1 .75 h

R = CH₃, 0% at 6 h

40% 89%

[00253] Without being bound by any theory, an α,β-unsaturated intermediate most likely leads to C-O bond cleavage to yield propiophenone. 2-phenoxyphenylpropanol does not react under the reaction conditions to yield C-O bond cleavage products. However, the α,β-unsaturated ketone reacts faster than phenoxyacetophenone to yield propiophenone at lower temperatures. Thus, when starting with the β-[O]-4'-glycerolaryl ethers, selectivity for producing the α,β- unsaturated ketone may result in higher yields of propiophenone.

416272008740 93 Example 7

Controlling C-O vs C-C Bond Cleavage Selectivity

Total %Yield = (A + B + C + D + E + F) / G

% Cleavage = (A + B + D + E) /G

Elimination vs. Retro-aldol Selectivity (RA/E)

RA/E = (B + C + D + E + F) / A

α-β Cleavage vs. β-γ Cleavage (αβ/βγ)

αβ/βγ = (D + E) / (B + C + F)

Hydrogen Budget (C-O/C=O reduction)

C-O/C=O = (A + C) / (A + E + F)*

*add MeOH if observable

[00254] Measures of selectivity were defined based on relative quantities of the C-terminus products from the decomposition of β-[O]-4'-glycerolaryl ethers. The distinction between C- terminus and O-terminus is only useful for model systems. In the actual lignin biopolymer, the O-terminus would exist on the same molecule as the C-terminus and no distinction would be necessary. In the subsequent data, all parameters are calculated from the product distribution (A-F). The selectivity parameter of interest for C-O bond cleavage processes is the retro-aldol vs. elimination selectivity (RA:E).

416272008740 94

total %

Temp (C) % conv. % cleav. RA/E αβ/βγ C-O/C=O yield

135 94 74 33 15:1 1:1.9 1:4.6 150 80 81 38 15:1 1:1.8 1:4.6 180 96 80 34 22:1 1:1.5 1:4.5

[00255] A baseline reactivity profile for 2-(2-methoxyphenoxy)-l-phenylpropane-l,3-diol, abbreviated as {P,G}-dimer (The {X,Y} nomenclature is defined: X = C-terminus aryl substituent, Y = O-terminus aryl substituent on the 2-arylether-l,3-propanediol backbone. P = phenyl, C = coumaryl, G = guaiacyl, S = syringyl), using conditions derived for the

phenoxyphenethanols is shown above. Without additives, the disproportionation of the {P-G}- dimer favors retro-aldol processes (RA/E = 15:1). The retro-aldol favors cleaving the hydroxymethyl group (αβ/βγ = 1:1.9), and the hydrogen in the system goes primarily to reduce carbonyls (C-O/C=O = 1:4.6). These selectivities are relatively constant over a broad temperature range (135 - 180). Without being bound by any theory, based on these selectivities we can make some qualitative assessment of reaction limiters. For example, the reaction shown above is selective for retroaldol processes that a) reduce the amount of elimination to form the requisite α,β-unsaturated ketone, and b) yields aldehydes that are better hydrogen acceptors. Thus, C-O bond cleavage is suppressed.

416272008740 95 Example 8

Controlling C-O Bond Cleavage Selectivity Using Acidic Additives and Ligand Structural

Modifications

[00256] RA/E selectivity is controllable using acidic additives. Acidic additives would catalyze elimination to form the α,β-unsaturated ketone, and favor C-O bond cleavage if the system remains consistent with our theoretical models.

[00257] For example, an added titanium co-catalyst in which the RA/E selectivity is reduced from 15:1 to 1.3:1, and the cleavage efficiency is dramatically enhanced up to 91%.

total %

% conv. % cleav. RA/E at C-O/C=O

yield

90 90 91 1.3:1 1:3.3 1.7:1

[00258] A second example is a ruthenium salt that liberates a strong acid upon reaction with the substrate. When using carbonylbis(trifluoroacetato)bis-(triphenylphosphine)ruthenium(II) as the ruthenium source, the RA/E selectivity is reduced from 15:1 to 1.7:1 concomitant with an enhancement in cleavage efficiency up to 57% using xantphos.

[00259] Choice of ligand may also be used to control RA/E selectivity. When compared to Ph-xantphos (xantphos), the Et-xantphos increases the amount of favorable retro-aldol cleavage (αβ/βγ = 2.2:1), thus improving cleavage efficiency through C-C bond cleavage.

416272008740 96

total %

Ligand % conv. % cleav. RA/E αL C-0/C=0 yield

Ph-xantphos 85 72 57 1.7:1 1.4:1 1.5:1 Et-xantphos 94 >95 85 2.2:1 2.2:1 1:2.2

Example 9

Acylated Glycerolarylether Linkages in Lignin of Miscanthus Giganteus

[00260] The structure of lignin in Miscanthus giganteus has been analyzed, and the native lignin is composed of 93% β- [O] -4' -glycerolarylether linkages. However, 43% of those linkages are acylated at the hydroxymethyl (γ) position with acetate, or p-coumaric acid. Based on the RA/E selectivity trends, the γ-acylated glycerolarylethers may favor elimination, and therefore C-O bond cleavage.

[00261] A non-natural acylated lignin model, 3-hydroxy-2-(2-methoxyphenoxy)-3- phenylpropyl 2,2-dimethylpropanoate (γ-OPiv-{P,G}-dimer) was reacted with the ruthenium catalyst. Decomposition of the γ-OPiv-{P,G}-dimer produces mostly propiophenone. The RA/E selectivity decreases from 12:1 in favor of retroaldol for X = OH to 1:2.1 in favor of elimination. Changing X to OAc yields a natural model of a lignin linkage (γ-OAc-{P,G}-dimer).

Decomposition of γ-OAc-{P,G}-dimer produces propiophenone and acetophenone as the major products, resulting in a higher overall cleavage when compared to the γ-OPiv-{P,G}-dimer. An increase in retroaldol activity (RA/E = 1:1.5) that was selective for the cleavage of γ-

416272008740 97 hydroxymethyl units (αβ:βγ = 1:1.5) and selectively used liberated H₂ for C-O (C-O/C=O = 1.2:1).

total %

X % conv. % cleav. RA/E αL C-0/C=0 yield

OH* 91 78 33 12:1 1:2.4 1:6.5 OPiv > 99 56 51 1:2.1 1.6:1 1:1.2 OAc > 99 84 78 1:1.5 1:1.5 1.2:1

^* at 24 hr reaction time

Example 10

C-C Bond Cleavage in Glycerolaryl Ethers

[00262] Ruthenium complexes may catalyze both retroaldol chemistry and Cl oxidation chemistry (Eqs. 1 and 2). Ci oxidation may provide hydrogen to the system, but may also inhibit the C-O cleavage reaction (Eq. 3), presumably through carbon-monoxide poisoning. Thus, the αβ-retroaldol is the most desired process and retroaldol selectivity (αβ/βγ) should be controlled in favor of the αβ-retroaldol for cleavage of β-[O]-4'-glycerolaryl ethers.

416272008740 98 )

n_μ n_μ Ru(TFA)₂(CO)(PPh₃)₃ (5 mol%)

V^π ₁₃V^π xantphos (5 mol%)

p_h^^CH₂ ^ _ph ,A. j₂OH_{3 + ph}X 13 CO₉ (2)

PhMe-d₈

175 ⁰C, 17 h

> 99% conv. 63% 23%

(3)

[00263] The decomposition of {P,G}-dimer (Example 7, X = OH) proceeds in high conversion (91%) and reasonable yield of C-terminus products (78%). However, the cleavage efficiency is low (33%). The reaction was selective for the retroaldol manifold over elimination (RA/E = 12:1). However, the retroaldol selectivity was in favor of the βγ-retroaldol (αβ/βγ = 1:2.4) that does not lead directly to dimmer cleavage and inhibits the C-O bond cleavage process. Thus, phenoxyacetophenone derivatives build-up contributing to the C-terminus product yield, but cannot be converted forward resulting in poor cleavage efficiency.

Example 11

Depolymerization of Lignin by Disproportionation Reactions

[00264] Lignin was extracted from Miscanthus angiosperm. A stock solution of lignin (40 mg/mL) was prepared in anhydrous and degassed dioxane. A stock solution of ruthenium catalyst RuH₂CO(PPh₃)₃ (11.4 mg/mL) and a stock solution of ruthenium catalyst

[RuCO(PPh₃)₂(CF₃COO)₂ ^• xCH₃0H] (11.0 mg/mL) were prepared in anhydrous and degassed

416₂7₂008740 99 dioxane. The two ruthenium sources were screened against seven phosphine ligands. Each ligand was loaded in a reaction vessel under N₂ followed by addition of 0.5 rnL of the ruthenium stock solution such that the ligand:metal ratio was 1:1. The reaction vessel was sealed under N₂ and transferred to a pre -heated oil bath at 16O⁰C and was stirred at temperature for 24 hr. The reaction mixture was cooled to -3O⁰C and was freeze-dried. A brown solid was obtained.

Analysis of Depolymerization Products

[00265] The brown solid material was analyzed by size exclusion chromatography (SEC). The solid was dissolved in THF (4.0 mL) and the solution was analyzed as is. All ligands used with either ruthenium source formed depolymerization catalysts. A decrease in the number- average molecular mass (Mn) and weight- average molecular mass (Mw) was observed when compared to the starting material (Table 1). No hydrogen was added to the reactions. The xantphos ligand resulted in the greatest reduction in Mn and Mw, independent of the ruthenium source. Generally, a greater degree of depolymerization was observed with RuH₂CO(PPh₃)₃.

416272008740 jQO [00266] Table 1

Ligand Metal Precursor Mn Mw

Lignin only Lignin only 845 2069 l,2-bis(diphenylphosphino)ethane RuH₂CO(PPh₃)₃ 565 1519 l,3-bis(diphenylphosphino)propane RuH₂CO(PPh₃)₃ 663 1595 l,4-bis(diphenylphosphino)butane RuH₂CO(PPh₃)₃ 485 1522

1 , 1 '-bis(diphenylphosphino)ferrocene RuH₂CO(PPh₃)₃ 511 1471

(R)-(+)-2,2'-bis(diphenylphosphino)-l , 1 '-binaphthyl RuH₂CO(PPh₃)₃ 505 1601 o-bis(diphenylphosphino)benzene RuH₂CO(PPh₃)₃ 562 1518

9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene RuH₂CO(PPh₃)₃ 425 1180

(xantphos) l,2-bis(diphenylphosphino)ethane [RuCO(PPh₃)₂(CF₃COO)₂• XCH₃OH] 529 1729 l,3-bis(diphenylphosphino)propane [RuCO(PPh₃)₂(CF₃COO)₂• XCH₃OH] 559 1738 l,4-bis(diphenylphosphino)butane [RuCO(PPh₃)₂(CF₃COO)₂• XCH₃OH] 450 1598

1 , 1 '-bis(diphenylphosphino)ferrocene [RuCO(PPh₃)₂(CF₃COO)₂• XCH₃OH] 662 1768

(R)-(+)-2,2'-bis(diphenylphosphino)-l , 1 '-binaphthyl [RuCO(PPh₃)₂(CF₃COO)₂• XCH₃OH] 646 1846 o-bis(diphenylphosphino)benzene [RuCO(PPh₃)₂(CF₃COO)₂• XCH₃OH] 653 1967

9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene [RuCO(PPh₃)₂(CF₃COO)₂• XCH₃OH] 535 1543

(xantphos)

Example 12

Depolymerization of lignin related polymer

0.15 mmol in 99% isolated

monomeric equivalents

[00267] Poly(4' -hydroxy- 1-phenethanol) (20 mg, 0.15 mmol), RuH₂(CO)(PPh₃)₃ (6.9 mg, 7.5 μmol), and 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (4.3 mg, 0.01 μmol) were diluted in anhydrous 1,4-dioxane (0.50 mL). The reaction mixture was sealed in a 10 mL reaction vessel under an atmosphere of dry nitrogen. The sealed tube was heated to 175 ⁰C for 3 h. The

416272008740 101 reaction was then cooled to room temperature and purified by silica gel chromatography

(gradient elution, 7-60% EtOAc in hexanes) to yield 4'-hydroxyacetophenone as a white solid (20 mg, 99%).

Example 13

Catalyst Screen of Model C-O Cleavage Reaction

[00268] In a vacuum-sealed tube (0.1-0.2 torr) and a final reaction volume of 0.50 ml in toluene, 2-methoxyacetophenone (0.25 mmol) was heated to 100 ⁰C with a catalyst listed in Table 2 (0.025 mmol). After 18 h, for selected catalysts, acetophenone was formed as determined by ¹H NMR integration relative to an external capillary standard. Product identification was further confirmed by GC-MS for acetophenone (120 m/z). Results for the different catalysts are listed in Table 2.

[00269] Table 2

Catalyst % Yield (isolated)³

Pd(PPh₃)₄ 0

[RuH₂CO(PPh₃)₃] 45(43)

FeH₂(dmpe)₂ 0

[Ni(COd)₂] / 3 equiv. PCy₃ 12(9)

[RhCl(coe)₂]₂/ 3 equiv. PCy₃ 15(16)

Yields determined by GC, isolated yields are in parentheses

416₂7₂008740 102 Example 14

C-O Cleavage of l-(4-ethoxy-3-methoxyphenyl)- 2-(2-methoxy-phenoxy)propan-l,3-diol

[00270] A 4 niL vial charged with l-(4-ethoxy-3-methoxyphenyl)- 2-(2-methoxy- phenoxy)propan-l,3-diol (17 mg, 0.05 mmol), vanadium catalyst (10 mol%), a stir bar, and CD₃CN (0.5 rnL) was closed with a screw cap and heated in an oil bath at 80 ⁰C for 24 h. The reaction mixture was cooled to room temperature, and internal standard (2-trimethylsilylethanol, 7.2 μL, 0.05 mmol) was added before ¹H NMR analysis. Yields of compounds 35, 36, and 37 are reported for different vanadium catalysts are listed in Table 3.

416272008740 }03 [00271] Table 3

Conversion

Entry [V] 35 ^a 36 ^a 2,1 ^a

(%r

1 None O - - -

2 VOSO₄ x H₂O 34 2 2 6

3 VO(acac)₂ 79 13 22 31

4 VO(Oi-Pr)₃ 82 5 11 45

5 38 86 6 6 59

6 39 66 13 14 41

7 40 55 3 - 37

8 41 >95 61 45 27

9 42 86 70 62 8

10 43 95 65 50 18

11 44 >95 82 57 7

All data are the average of two runs. ^a H NMR versus an internal standard.

416272008740 104 Example 15

C-O Cleavage of l-(4-ethoxy-3-methoxyphenyl)- 2-(2-methoxy-phenoxy)propan-l,3-diol in

EtOAc

[00272] A 4 niL vial charged with l-(4-ethoxy-3-methoxyphenyl)- 2-(2-methoxy- phenoxy)propan-l,3-diol (17 mg, 0.05 mmol) 34, vanadium catalyst 44 (10 mol%), a stir bar, and EtOAc (0.5 rnL) was closed with a screw cap and heated in an oil bath at 80 ⁰C for 24 h. The reaction mixture was cooled to room temperature, and internal standard (2- trimethylsilylethanol, 7.2 μL, 0.05 mmol) was added before ¹H NMR analysis. Compounds 35, 36, and 37 were formed in 93%, 70%, and 3%, respectively. The IH NMR of the crude reaction mixture indicated ca. 90% yield of 36 (in parentheses), but the isolated yield was significantly lower (70%) due to its high volatility.

34

Example 16

C-O Cleavage of Trimeric Lignin Model Compound 45

[00273] A 4 mL vial charged with 45 (17 mg, 0.05 mmol), vanadium catalyst 44 (10 mol%), a stir bar, and EtOAc (0.5 mL) was closed with a screw cap and heated in an oil bath at 80 ⁰C for 24 h. The reaction mixture was cooled to room temperature, and internal standard (2- trimethylsilylethanol, 7.2 μL, 0.05 mmol) was added before ¹H NMR analysis. Compounds 35 and 36 were formed in 78% and 61%, respectively.

416272008740 105

45 35 36

78% 61%

Examples 17-20

Mechanistic Studies

[00274] Various derivatives of compound 34 were reacted with vanadium catalyst 44 to gain further insight on the mechanism of the cleaving reaction. To explore the possibility of oxidation of 34 to ketone 37 followed by reductive cleavage, 37 was subjected to the reaction conditions with or without benzylic alcohol (eq 17). In both cases, 37 was recovered in high yield without any evidence for degradation to 35 or 36, and the corresponding ketone was obtained when the benyzlic alcohol was added to reproduce the catalytic species after oxidation of 34 to 37. When the benzylic hydroxyl group was replaced by a methoxy group, the reaction proceeded to only 12% conversion to provide a conjugated aldehyde, indicating the importance of the benzylic hydroxyl group for ligand exchange (eq. 18). In contrast, the methyl ether of the primary hydroxyl group was converted to 35 and 36 with only slightly diminished yield and selectivity compared to 34 (eq. 19). When the aryloxy group was absent, only the corresponding ketone was observed (eq. 20).

416272008740 106

34b

Example 21

Lignin Degradation by Vanadium Catalyst 44

[00275] Lignin was purified by three different methods: (1) dilute acid treatment; (2) dilute base treatment; and (3) extraction with organic solvent. The lignin was reacted with and without vanadium catalyst 44 in CD₃CN at 8O⁰C for 24 hours. The reaction products were isolated from

416272008740 107 the catalyst residues by filtration and characterized using LC-MS and NMR. Without the vanadium catalyst 44, only trace organic compounds were detected by NMR. In the presence of the vanadium catalyst 44, various organic compounds were observed by NMR and LCMS showed small molecules M+H 233, 388, 455, 589, and 744. These results suggest that the vanadium complexes catalyze lignin degradation.

Example 22

Reduction of anisole with triethylsilane

_{+ Et3}g_iH

(25 eq )

77% IPr_Me HCI

[00276] A 4 ml vial was charged with Ni(COD)₂ (8 mg, 0.0298 mmol), IPr_MeΗCl (27.2 mg, 0.060 mmol), 'BuONa (46 mg, 0.479 mmol), and a magnetic stir bar. A solution of anisole (0.165 mmol) in toluene (0.3 ml) and dodecane (internal standard for GC) were added, the mixture was stirred for 3 min followed by addition of triethylsilane (600 μl, 3.75 mmol). The reaction vial was sealed with Teflon-lined screw cap and the heated at 120 ⁰C for 96h. Yield of benzene: 77% (determined by GC using internal standard). The product was identified by GC using authentic compound.

Example 23

Reduction of anisole with diisobutylaluminum hydride (DIBAL)

87% SIPr-HBF₄

416272008740 108 [00277] A 4 ml vial was charged with Ni(COD)₂ (8.4 mg, 0.0305 mmol), SIPr-HBF₄ (30.1 mg, 0.0629 mmol), 'BuONa (43.4 mg, 0.452 mmol), and a magnetic stir bar. A solution of anisole (0.152 mmol) in toluene (0.3 ml) and dodecane (internal standard for GC) were added, the mixture was stirred for 3 min followed by addition of DIBAL (IM solution in hexanes, 240 μl, 0.24 mmol). The reaction vial was sealed with Teflon-lined screw cap and the heated at 120 ⁰C for 4Oh. Yield of benzene: 87% (determined by GC using internal standard). The product was identified by GC using authentic compound.

Example 24

Hydrogenolysis of 4-tør/-butylanisole

27% SIPr-HBF₄

[00278] In a glovebox, a 10 ml glass bomb equipped with Teflon stopcock was charged with Ni(COD)₂ (8.2 mg, 0.0298 mmol), SIPr-HBF₄ (28.5 mg, 0.0595 mmol), 'BuONa (42.2 mg, 0.439 mmol), and a magnetic stir bar. A solution of anisole (0.159 mmol) in m-xylene (0.6 ml) and dodecane (internal standard for GC) were added, the mixture was stirred for 3 min, then the glass bomb was secured and removed from the box. The reaction mixture was degassed via freeze- pump-thaw sequence performed one time and the reactor was pressurized at room temperature with 1 bar of hydrogen. The reaction mixture was stirred at 100⁰C for 16h. Yield of tert- butylbenzene is 27% at 29% conversion. Prolonged heating does not lead to an increase in conversion. The product was identified by GC using authentic compound.

416272008740 }09 Example 25

Hydrogenolysis of 4-ter/-butylanisole

27% SIPr-HBF₄

[00279] In a glovebox, a 10 ml glass bomb equipped with Teflon stopcock was charged with Ni(COD)₂ (8.2 mg, 0.0298 mmol), SIPr-HBF₄ (28.5 mg, 0.0595 mmol), 'BuONa (42.2 mg, 0.439 mmol), and a magnetic stir bar. A solution of anisole (0.159 mmol) in m-xylene (0.6 ml) and dodecane (internal standard for GC) were added, the mixture was stirred for 3 min, then the glass bomb was secured and removed from the box. The reaction mixture was degassed via freeze- pump-thaw sequence performed one time and the reactor was pressurized at room temperature with 1 bar of hydrogen. The reaction mixture was stirred at 100⁰C for 16h. Yield of tert- butylbenzene is 27% at 29% conversion. Prolonged heating does not lead to an increase in conversion. The product was identified by GC using authentic compound.

Example 26

Hydrogenolysis of di-or^o-methoxyphenyl ether (model compound for 5-O-5 lignin linkage).

85% 88%

[00280]

416272008740 110 [00281] In a glovebox, a 4 ml screw cap vial was charged with Ni(COD)₂ (2.1 mg, 0.00763 mmol), 'BuONa (36.8 mg, 0.389 mmol), and a magnetic stir bar. A solution of di-ortho- methoxyphenyl ether (0.153 mmol) in m-xylene (0.6 ml) and dodecane (internal standard for GC) were added, the mixture was stirred for 3 min. The reaction vial was closed with a screw cap equipped with septum and inlet needle, removed from the glovebox and placed in an alloy plate, which was transferred to a 300 mL autoclave from Parr Instruments (Model 4561) under an argon atmosphere. The autoclave was flushed with hydrogen and then pressurized to 1 bar at room temperature and heated at 100° C for 16 h. The reactor was then cooled to room temperature, the reaction vial was taken out and the reaction mixture was diluted with 0.4 ml of toluene and treated with ImI of 1.6M aqueous HCl. The organic layer was subjected to GC analysis. Yields of anisole and guaiacol are 85% and 88% respectively (conversion: 95%). Anisole and guaiacol were identified by GC using authentic compounds and by GC/MS

(guaiacol, 124 m/z).

Example 27

Hydrogenolysis of di-tør/-butylphenyl ether

45% 48% SIPrHBF₄

[00282] The reaction was performed in a similar way to that described in Example 4 using di- tert-butylphenyl ether (0.151 mmol), Ni(COD)₂ (8.5 mg, 0.0309 mmol), SIPr-HBF₄ (26.6 mg, 0.0556 mmol), 'BuONa (36.8 mg, 0.383 mmol) in 0.6 ml of m-xylene to give tert-butylbenzene and para-te/t-butylphenol in 45% and 48% yield respectively (measured by GC using dodecane

416272008740 \ \ \ as internal standard) at 50 % conversion. 7>/t-butylbenzene andpαra-te/t-butylphenol were identified by GC using authentic compounds.

Example 28

Hydrogenolysis of guaiacyl veratryl ether

[00283] The reaction was performed in a similar way to that described in Example 4 using di- tert-butylphenyl ether (0.151 mmol), Ni(COD)₂ (8.3 mg, 0.0302 mmol), 'BuONa (38.7 mg, 0.403 mmol) in 0.6 ml of m-xylene to give 3,4-dimethoxytoluene and guaiacol in quantitative yields (measured by GC using dodecane as internal standard). Product identification was done by GC using authentic compounds and by GC/MS for 3,4-Dimethoxytoluene (152 m/z) and guaiacol (124 m/z). The reaction carried out at a lower catalyst loading (5 mol % vs. 20 mol %) gave 3,4- dimethyoxytoluene and guaiacol in 95% and 95% yield, respectively.

416272008740 \ \2 Examples 29-45

Nickel-catalyzed cleavage of alkyl aryl ethers with hydride donors^a

"H" = Et₃SiH, DIBAL, LiAI(O^fBu)₃H

Λ_Λ 1 ♦^• K ^Yield

Exp JN° ArOAIk "H" MoI. ratⁱo Ni, mol% NHC Time, h^b

ArOAlk/Η" (Conversion),

29 Et₃SiH 2.5 20 SIPr 16 96(100)

30 Et₃SiH 2.5 20 SIPr 16 86(88)

31 Et₃SiH 25 20 SIPr 16 95(100) 32

DIBAL 2.5 20 SIPr 16 99(100) 33 LiAl(0'Bu)₃H 2.5 20 SIPr 16 91(100)

38 Et₃SiH 25 20 SIPr 16 48(64)

39 Et₃SiH 25 20 IPrMe 106 60(66)

40 Et₃SiH 25 20 SIPr 48 28(43)

41

Et₃SiH 25 20 IPr_Me 32 51(48)

42 Et₃SiH 25 20 SIPr 96 53(nd)

^₅ JDMe

43 ( Et₃SiH 25 20 IPr_Me 96 77(84)

44 DIBAL 2.5 20 SIPr 40 87(94)

45 Et₃SiH 25 IPn Me 106 46(51)

416272008740 113 (a) Reaction conditions: 0.15 mmol of alkyl aryl ether, dodecane (internal standard for GC), 0.375-3.75 mmol of Et₃SiH or 0.375 mmol of DIBAL or LiAl(O¹Bu)₃H, 0.375 mmol of 'BuONa, 03 ml of toluene, 120 ⁰C (b) Reactions were carried out until the starting materials stopped to be consumed. Reaction times were not minimized, (c) Determined by GC using internal standard.

[00284] Reactions of 2-methoxynaphfhalene with various hydride donors in the presence of nickel(O) catalysts were carried out in toluene at 120 °C. The nickel catalyst was formed in situ from Ni(C0D)₂, and a carbene ligand SIPr (See Example 29) generated by deprotonation of its hydrochloride salt with sodium tert-butoxide. Reactions conducted with triethylsilane, DIBAL

(diirøέ>utylalummum hydride), and LiAl(0^fBu)3H form 86-99% yields of naphthalene from

reductive cleavage of the C-O bond (see Examples 30-33). No 2-naphthol was detected in the

reaction mixture from aliphatic C-O bond cleavage. This product distribution illustrates

selectivity for reduction of C_A1O bonds over C_AUSO bonds.

[00285] The N-heterocyclic carbene ligand, SIPr, and an excess of base (2.5 equiv) led to an active catalyst for this process. Yields of naphthalene in the model reaction of 2- methoxynaphthalene with 2.5 equiv. of triethylsilane and 'BuONa at 120 °C in toluene using a

1:1, 1:2 and 1:4 ratio of Ni(COD)₂/SIPr-HCl were 44%, 80 and 87%, respectively.

[00286] Other N-heterocyclic carbene ligands were tested under the following conditions: 2- methoxynaphthalene (1 equiv.), nBu₃SiH (2.5 equiv.), 5 mol % Of Ni(COD)₂, 10 mol % of the

corresponding carbene salt, tBuONa (0.2 equiv.), toluene (0.5 M solution of 2-MeONaph), 120

0C, 16 h. The following yields of naphthalene (conversion of 2-methoxynaphthalene) were

obtained: SIPr-HBF₄: 32% (32%), IPr-HCl: 20% (21%), IMes-HCl: 12% (23%), ImIPr-HBF₄ :

0% (2%), ImIBu-HBF₄: 2% (4%), SImIBu-HBF₄: 6% (8%), and SIMes-HBF4: 8% (11%).

Phosphine ligands were tested under the same conditions, but without the base (tBuONa). The following yields of naphthalene (conversion of 2-methoxynaphthalene) were obtained: DPPB:

416272008740 J 14 0% (0%), DPPE: 0% (2%), X-Phos: 0% (2%), 2-BiphenylPCy₂: 0% (1%), PCy₃: 3% (5%), Bippyphos: 0% (0%).

[00287] Other carbene ligands (as the corresponding salts) were tested further, under optimized conditions: 2-methoxynaphthalene (1 equiv.), Et₃SiH (2.5 equiv.), 20 mol % of Ni(COD)₂, 40 mol % of the corresponding carbene salt, tBuONa (2.5 equiv.), toluene (0.5 M solution of 2-MeONaph), 120 ⁰C, 16 h. The following yields of naphthalene (conversion of 2- methoxynaphthalene) were obtained: SIPr HBF₄: 86% (88%), monotBuIPr-HCl: 81% (100%),

6-SIPr HBr: 0% (8%), 6-SIPr-HBF₄: 19% (24%), 7-SIPr-HBr: 0% (6%), 7-SIPr-HBF₄: 5% (5%), XyI-DIPP-HBr: 0% (0%), XyI-DIPP-HBF₄: 0% (1%), SCAAC-HCl: 0% (0%), CAAC- HOTf: 0% (0%).

[00288] Other reducing agents were tested in model cleaving reactions under the following conditions: reduction of 2-methoxynaphthalene with a hydride source (2.5 equiv.) using 5 mol % of Ni(COD)₂ (instead of 20 mol % as in one of the preferred embodiments), 10 mol % of SIPr ^■ HBF₄ (instead of 40 mol% as in one of the preferred embodiments), and tBuONa (0.2 equiv. instead of 2.5 equiv as in one of the preferred embodiments) in toluene (0.5 M solution of 2- MeONaph) at 120 ⁰C, 16 h. Yields of naphthalene (conversions of 2-methoxynaphthalene) under these conditions were: HCO₂Na: 9% (9%), HCO₂Cs: 0% (2%), NaBH₄: 4% (5%), NBu₄BH₄ 0% (79%); NaOiPr 0% (3%); Al(OiPr)3: 0% (2%); (EtO)₃SiH: 0% (2%), Ph₂MeSiH: 16% (26%), Ph₃SiH: 5% (7%), (PhCH₂)(Me)₂SiH: 8 % (23%), 1Bu₃SiH: 13% (15%), 1Pr₃SiH: 3% (10%), nHex₃SiH: 21% (22%), nBu₃SiH: 32 % (32%), and nPr₃SiH: 3% (10 mol%). Of these, nBu₃SiH was selected to screen bases under the following conditions: 2-MeONaph, nBu₃SiH (2.5 equiv.), base (2.5 equiv), 5 mol % of Ni(COD)₂, 10 mol % of SIPr^■ HBF₄, in toluene (0.5 M solution of 2-MeONaph) at 120 ⁰C, 16 h. Yields of naphthalene (conversions of

₄16₂7₂0087₄0 } }5 2-methoxynaphthalene) under these conditions were: tBuOK: 22% (75%), tBuOLi: 28% (30%), iPrONa: 31% (33%), MeONa: 18% (20%), NaH : 21% (24%), CsF: 6% (9%), K₃PO₄: 3% (19%).

[00289] Increasing the catalyst loading to 20 mol % of Ni(COD)₂ and 40 mol% of SIPr-HBF₄ and using 2.5 equiv. of nBu₃SiH and 2.5 equiv. of base in toluene (0.5 M solution of 2- MeONaph) at 120 ⁰C for 16 hr, gave the following yields of naphthalene (conversions of 2- methoxynaphthalene): iPrONa: 84% (88%), tBuONa: 86 (89%), tBuOLi: 46 (49%), Cs₂CO₃: 0% (3%).

[00290] Et₃SiH and nBu₃SiH gave similar yields of naphthalene (conversions of 2- methoxynaphthalene) using 2.5 equiv of tBuONa, 2.5 equiv of a silane, 20 mol % of Ni(COD)₂, 40 mol% of SIPr-HBF₄ in toluene (0.5 M solution of 2-MeONaph) at 120 ⁰C for 16 hr:

nBu₃SiH: 86% (first run) and 75% (second run), Et₃SiH: 81% (first run) and 86% (second run). Other hydride sources under these conditions gave the following yields of naphthalene

(conversions of 2-methoxynaphthalene): LiAlH₄: 4% (4%), (TMSO)₃SiH: 19% (32%).

[00291] Conditions for the reductive cleavage of various aryl alkyl ethers are shown in Examples 34-45, and conditions for the reductive cleavage of diaryl ethers are shown in

Examples 51-59. Benzyl alkyl ethers are typically more reactive toward reductive cleavage by heterogeneous precious metal catalysts based on palladium, rhodium and iridium (see Examples 46-50). However, the soluble nickel complexes selectively catalyze reductive cleavage of biaryl ethers over aryl alkyl and benzyl alkyl ethers.

[00292] A summary of the reactions of alkyl aryl ethers is provided in results for Examples 29-45. Triethylsilane was found to be a general hydrogen atom source leading to arenes in 60- 96% yields in the presence of 20 mol % of Ni(COD)₂ and SIPr. In some cases, conversions and

₄16₂7₂0087₄0 \ \β yields were higher for reactions conducted with more than 2.5 equivalents of the silane or by using of more active hydride donor such as DIBAL or LiAl(O^Bu)₃. Thus reduction of 2- methoxynaphthalene using 2.5 equiv of triethylsilane gives naphthalene with 86% and 88% conversion, whereas the reaction with 25 equiv. of the silane proceeded to complete conversion with 95% yield (see Examples 30-31). The conversion and yield of 4-methoxybiphenyl was improved from 74% (for both) with 2.5 equiv. of triethylsilane to 100% and 99% with DIBAL respectively (see Examples 33-34). Activated aryl ethers, such as 1-and 2-napththyl methyl ethers and 4-methoxybiphenyl reacted with conversions from 96-99% (see Examples 29-33). In these cases reactions were complete in 16 h using the commercially available carbene salt SIPr«HCl as a ligand precursor. Unactivated and o/t/zo-substituted alkyl aryl ethers, such as anisoles and 2-methoxybiphenyl were less reactive, but reactions conducted with 20 mol % Ni(COD)₂ and IPr_Me and a 20 fold excess of triethylsilane, or reactions conducted with SIPr as ligand and DIBAL as hydrogen atom source occurred to yield the corresponding arenes (see Examples 34-45).

416272008740 \ \η Examples 46-50

Nickel-catalyzed cleavage of benzyl ethers with hydride donors^a

"H" = Et₃SiH, DIBAL

Yield

Exp JVo Benzyl alkyl ether Η Solvent T, ⁰C

(Conversion), %'

46 Et₃SiH Toluene 120 61(67) 47 Et₃SiH Toluene 140 60(100) 48 DIBAL Toluene 80 98(100)

49 DIBAL THF 80 82(83)

50 DIBAL THF 80 41(46)

(a) Reaction conditions: 0.15 mmol of benzyl alkyl ether, dodecane (internal standard for GC), 0.375 mmol of DIBAL and Et₃SiH, 0.375 mmol of 'BuONa, 0.3 ml of the corresponding solvent, 80-140 ⁰C. Reactions were carried out until the starting materials stopped to be consumed. Reaction times were not minimized, (c) Determined by GC using internal standard.

[00293] Reductive cleavage of benzyl ethers occurs with many more catalysts than reductive cleavage of aryl ethers and, therefore, benzyl groups are often used to protect alcohols for synthetic organic applications. In contrast to this typical reactivity, comparable reactivity of benzyl alkyl ethers and aryl alkyl ethers occurs in the presence of the Ni(0)/carbene catalyst. For example, the reaction of 2-(methoxymethyl)naphthalene with triethylsilane (2.5 eq) in the presence of 20 mol % of Ni(COD)₂ and 40 mol % of SIPr HCl in toluene at 120 ⁰C forms the product of C-O bond cleavage (61% yield of 2-methylnaphthalene at 67% conversion, see

416272008740 118 Example 46) in lower yield than the reaction of 2-methoxynaphthalene (86% of naphthalene at 88% conversion) under the same conditions (see Example 30). Reactions of the benzyl ethers with triethylsilane or DIBAL occur in the presence of Ni(COD)₂ and SIPr as catalyst to form the methylarene (see Examples 46-50). Benzylic ethers substituted at the α-position, such as 1- methoxy-1-phenylpropane, were less reactive (41% at 46% conversion) than benzylic ethers lacking a substituent in the α-position (see Examples 48-50). The reaction in Example 50 was repeated at a higher temperature (12O⁰C vs. 8O⁰C) to give 94% yield at 100% conversion.

416272008740 \ \() Examples 51-59

Nickel-catalyzed cleavage of biaryl ethers with hydride donors^a

"H" = Et₃SiH, DIBAL

Yield of ArH

Exp JVs Biaryl ether "H" MoI. ratio Ni, mol% Solvent T, ⁰C

ArOAlk/'Η" (Conversion), %^b

51 DIBAL 2.5 20 Toluene 80 93(100)

52 DIBAL 2.5 20 Toluene 60 89(98) 53

Et₃SiH 2.5 20 Toluene 100 60(100) 54 Et₃SiH 10 5 Toluene 100 60 (100)

55 DIBAL 2.5 20 THF 80 97(100) 56 DIBAL 2.5 10 Toluene 80 (94)100^c

57 DIBAL 2.5 10 Toluene 80 82(93) c d

58 DIBAL 2.5 10 Toluene 80 25(29) ^c 59 Et₃SiH 2.5 20 Toluene 120 100(100)

(a) Reaction conditions¹ 0 15 mmol of biaryl ether, dodecane (internal standard for GC), 0 375 mmol of DIBAL and Et₃SiH, 0.375 mmol of 'BuONa, 0.3 ml of the corresponding solvent, 80-120 ⁰C Reactions were carried out until the starting materials stopped to be consumed. Reaction times were not minimized (b) Determined by GC using internal standard, (c) Other biaryl ethers such as mesityl phenyl and p-anisyl phenyl ethers were much less reactive under the same conditions (conversion less than 15%) (d) A mixture of benzene (38%) and anisole (44%) was obtained, (e) A mixture of benzene (4%) and anisole (24%) was obtained.

[00294] Various unactivated and heterocyclic diaryl ethers were cleaved to form the arene and phenolate at 80-120°C in toluene or THF using 2.5 eq. of DIBAL or triethylsilane as hydrogen

416272008740 120 atom sources and 5-20 mol% of Ni(COD)₂/SIPr. Reduction of diphenyl ethers with DIBAL and 20 mol% of the catalyst gave 93% yield of benzene, and the reaction with triethylsilane gave 60% yield at full conversion (see Examples 51-54). The lower yields of arenes from reactions with triethylsilane resulted from formation of aryltriethylsilanes as side products, not from lower amounts of C-O bond cleavage. Reactions with triethylsilane occurred with lower catalyst loadings when large excess of triethylsilane was used. The catalytic reductive cleavage of aromatic ethers also occurred with cyclic diaryl ethers. For example, the reduction of dibenzofuran to 2-hydroxybiphenyl proceeded in 100% yield (see Example 59).

[00295] The nickel(0)/SIPr catalyst was selective for reductive cleavage of C_AΓ-OAΓ bonds over C_Ar-OMe bonds. Di-o/t/zo-methoxyphenyl ether reacted with DIBAL in the presence of the nickel(0)/SIPr catalyst to give anisole and benzene in yields of 94% and 3% respectively (see Example 56). The small amount of benzene forms from cleavage of both the biaryl ether and alkyl aryl ether bonds. The nickel catalyst was as active for cleavage of more and less electron rich aryl-oxygen bonds. For example, cleavage of the unsymmetrical o/t/zo-methoxyphenyl phenyl ether yielded anisole and benzene in 44% and 38% yields respectively (see Example 57).

416272008740 }21 Examples 60

Di-ør/βø-anisyl ether can be reduced in the absence of the added ligand 10% NifCODV,

+ DIBAL

N NaaυO'^fbBuu,, t toolluueennee,,

(2.5 equiv) 100 ⁰C, 16h

conversion¹ 100% 92% 87%

Examples 61-62

Selectivity of nickel-catalyzed cleavage of alkyl aryl, diaryl and benzyl ethers with hydride

donors

Biaryl ethers can be reduced faster than aryl and benzyl alkyl ones

Conversion. 88% 3% Yield: 72% 0%

1 equiv 1 equiv 1.2 equiv

Conversion¹ 80% 10% Yield: 62% 7%

[00296] Selective reduction of C_AΓ-OAΓ bond in the presence of C_Ar-OAIk and Cβ_enzyi-OAlk bonds is illustrated by Examples 61-62. Reduction of biphenyl ether (1 equiv.) and para-tert- butylanisole (1 equiv.) together with DIBAL (1.2 equiv.) in the presence of 20 mol % of nickel(0)/SIPr in toluene at 80 ⁰C led to exclusive formation of benzene (72%) at 88% conversion from cleavage of the biaryl ether, whereas little or no conversion of para-tert- butylanisole (3%) and no product from reduction of C_Ar-OAIk bonds was detected by gas chromatography. Surprisingly, under the same conditions, biphenyl ether was also reduced

416272008740 122 faster than α-ethylbenzyl methyl ether. After 36 h, 80% of biaryl ether versus 10% of the benzylic ether was consumed to give 62% of benzene versus 7% of propylbenzene (See Example 62).

416272008740 }23 Examples 63-74

Nickel catalyzed hydrogenolysis of alkyl aryl, diaryl and benzyl ethers using H₂ ^a

"Ni", Conversion, Yield of Yield of

Exp JVo Aryl ether "Ni" ' Ligand

mol% ^b %^c ArH,% ROH,%

63 Ni(COD)₂ 20 SIPr HBF₄ 38 37

64 Ni(COD)₂ 20 SIPr HBF₄ 31 28 65 Ni(COD)₂ 20 SIPr HBF₄ 100 75

66 Ni(COD)₂ 20 SIPr HBF₄ 34 33 32

67 Ni(COD)₂ 10 SIPr HBF₄ 91 83 85

71 Raney 15 - 0 0 0

72 20 SIPr HBF₄ 2 0

73 20 SIPr HBF₄ 100 87 100 74 20 100 100 100

(a) Reaction conditions: 0 15 mmol of aryl or benzyl ether, dodecane (internal standard for GC), 0.375 mmol of 'BuONa, 5-20 mol% of Ni, 10-40 mol% of ligand, 0.6 ml of the corresponding solvent, 100 ⁰C, 1 bar of hydrogen (pressure at room temperature), 16h. (b) Yield was not determined

416272008740 124 [00297] The same catalytic system that was efficient for the reduction with hydride sources, 20 mol% of Ni(COD)₂ and 40 mol% of SIPr-HBF₄, led to the reductive cleavage of the aromatic C-O bond in 1-methoxynaphthalene with 1 bar of hydrogen and 'BuONa in m-xylene at 100 ⁰C for 16 h. This hydrogenolysis selectively led to naphthalene in 37% yield with 38% conversion (see Example 63). Unactivatedpαra-te/t-butylanisole reacted with a lower yield of 28%, but with excellent selectivity for aromatic C-O bond cleavage (conversion of 31%, see Example 64). In contrast to reductions with DIBAL, hydrogenolysis of diaryl and alkyl aryl ethers proceeded in similar yields (see Examples 65-74). Thus, the reaction of di-pαra-te/t-butylphenyl ether with hydrogen gave the corresponding arene and phenol in 33% and 32%, respectively, at 34% conversion (see Example 66) versus the reaction of pαra-te/t-butylanisole that led to cleavage of the aromatic C-O bond in 31% yield (see Example 64). The hydrogenolysis of biphenyl ether proceeded with full conversion to give phenol in 75% yield (see Example 65). Under the same conditions, α-ethylbenzyl methyl ether was inactive (see Example 72). No detectable amount of products from hydrogenation of the arene ring was observed in any of the above described examples. These results contrast with hydrogenation of aryl ethers over heterogeneous nickel and platinum metal catalysts, in which a mixture of hydrogenated products are usually formed containing no more than 30% of arene.

[00298] To probe the heterogeneous or homogeneous nature of catalyst, hydrogenolysis of di- pαra-te/t-butylphenyl ether was conducted in the presence of 300 fold excess of mercury, with respect to the catalyst. No decrease in conversion and product yields was observed.

[00299] Di-o/t/zo-anisyl ether, one of the stable ether linkages in lignin, was smoothly and selectively cleaved with 1 bar of hydrogen and 10 mol% Of Ni(COD)₂ and 20 mol% of

SIPr-HBF₄ as catalyst at 100⁰C in m-xylene to yield anisole and guaiacol in 83% and 85%

416272008740 }25 yields respectively (see Example 67). Very similar results were obtained using 5 mol% of Ni(COD)₂ and 10 mol% of PCy₃ (see Example 68). Ni(acac)₂ was also found to be viable catalyst for hydrogenolysis (see Example 69).

Examples 75-77

Hydrogenolysis of lignin models using ligandless nickel

75. Hydrogenolysis of the diaryl ether lignin linkage

yields conversion

Model compound for 5-0-5

lignin linkage with base 85% 88% 92% without base 0% 0% 0% with Hg (30 equiv.) 38% 39% 42% without Hg 85% 88% 92%

[00300] Temperature was not minimized in this reaction. "Ligandless" Ni(COD)₂ (5 mol%) with 'BuONa as additive catalyzes reductive cleavage of di-o/t/zo-anisyl ether with 85% yield of anisole and 88% yield of guaiacol. Yields in this reaction decreased in the presence of 30 fold excess of mercury, suggesting that this ligandless system may generate a heterogeneous catalyst. This heterogeneous catalyst is distinct from Raney nickel; Raney nickel 2800 (15 mol %) was completely inactive under the same conditions (see Example 70).

416₂7₂008740 126 76. Hydrogenolysis of the aryl benzyl lignin linkage

Model compound for

OC-O-4 lignin linkage

[00301] Temperature and catalyst loading were not minimized in this reaction. A model compound for the α-O-4 linkage in lignin, veratryl guaiacyl ether, was also selectively hydrogenated at 100 ⁰C using 20 mol% of "ligandless" Ni(COD)₂ in the presence 'BuONa to give guaiacol and 3,4-dimethoxytoluene in 97% and 95%, respectively.

77. Cleavage of the aryl alkyl lignin linkage

Model compound for

β-O-4 lignin linkage

[Ni] GC yield (conversion)

Ni(COD)₂ 21 % (100%)

Ni(COD)₂ZSIPr^■ HCI 24% (100%)

No catalyst 20% (100%)

[00302] Full conversion of the model compound for β-O-4 lignin linkage was observed after

16 h and 20-24% guaicol was detected by GC. Other products were not observed in the GC or

GC/MS.

[00303] Although the methods and compositions described herein have been described in connection with some variations, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the methods and apparatus described herein is limited only by the

416272008740 127 claims. Additionally, although a feature may appear to be described in connection with particular variations, one skilled in the art would recognize that various features of the described variations may be combined in accordance with the methods and compositions described herein.

[00304] Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single apparatus or method. Additionally, although individual features may be included in different claims, these may be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather the feature may be equally applicable to other claim categories, as appropriate.

[00305] Terms and phrases used in this document, and variations thereof, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. As examples of the foregoing: the term "including" should be read to mean "including, without limitation" or the like; the terms "example" or "some variations" are used to provide exemplary instances of the item in discussion, not an exhaustive or limiting list thereof; and adjectives such as

"conventional," "traditional," "normal," "standard," "known" and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. Likewise, a group of items linked with the conjunction "and" should not be read as requiring that each and every one of those items be present in the grouping, but rather should be read as "and/or" unless expressly stated otherwise. Similarly, a group of items linked with the conjunction "or" should not be read as requiring mutual exclusivity among that group, but rather

416272008740 }28 should also be read as "and/or" unless expressly stated otherwise. Furthermore, although items, elements or components of methods and compositions described herein may be described or claimed in the singular, the plural is contemplated to be within the scope thereof unless limitation to the singular is explicitly stated. The presence of broadening words and phrases such as "one or more," "at least," "but not limited to," "in some variations" or other like phrases in some instances shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent.

[00306] In addition, while compositions and processes described herein may be open to inclusion of additional unrecited features, and thus may be described or claimed as 'comprising' the specified features, a composition or process consisting only of the recited features, or consisting essentially of the recited features is expressly within the scope of the invention as well.

416272008740 }29

Claims

CLAIMS We claim:

1. A method of depolymerizing lignin comprising:

cleaving a carbon-oxygen bond or a carbon-carbon bond of a phenylpropanoid of lignin in a catalytic disproportionation reaction.

2. The method of claim 1, wherein the carbon-oxygen bond is between C² and O² of a glycerol β-arylether unit of lignin:

wherein Ar³ and Ar⁴ are optionally substituted aryl groups of lignin and each R and R' is independently selected from the group consisting of hydrogen or a bond to a phenylpropanoid unit of lignin.

3. The method of claim 2, wherein the cleaving forms one or more products, the one or more products comprising Ar⁴OH.

4. The method of claim 1, wherein the carbon-carbon bond is between C¹ and C² and/or C² and C³ of a glycerol β-arylether unit of lignin:

OH OR Ar³ Y R'

,O²

Ar^4'

416272008740 }30 wherein Ar³ and Ar⁴ are optionally substituted aryl groups of lignin and each R and R' is independently selected from the group consisting of hydrogen or a bond to a phenylpropanoid unit of lignin.

5. The method of claim 1, wherein the carbon-carbon bond between C¹ and C² and/or C² and C³ of the glycerol β-arylether unit of lignin and the carbon-oxygen bond between C² and O² of the glycerol β-arylether unit of lignin are cleaved:

and wherein Ar³ and Ar⁴ are optionally substituted aryl groups of lignin and each R and R' is independently selected from the group consisting of hydrogen or a bond to a phenylpropanoid unit of lignin.

6. The method of claim 5, wherein the cleaving forms one or more products, the one or more products comprising Ar⁴OH.

7. The method of claim 1, wherein the cleaving occurs via tandem dehydrogenation and retro-aldol reactions and/or tandem dehydrogenation and carbon-oxygen bond cleavage reactions.

8. The method of claim 1, wherein the cleaving is catalyzed by a metal-based catalyst.

9. The method of claim 1, wherein the cleaving is catalyzed by a metal-based catalyst comprising a metal selected from the group consisting of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, lanthanum, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, and mercury.

416272008740 \2 \

10. The method of claim 1, wherein the cleaving is catalyzed by a metal-based catalyst comprising a metal selected from the group consisting of iron, palladium, ruthenium, nickel, rhodium, and iridium.

11. The method of claim 1 , wherein the cleaving is catalyzed by a metal-based catalyst comprising a metal selected from the group consisting of ruthenium, nickel, and rhodium.

12. The method of claim 1, wherein the cleaving is catalyzed by a metal-based catalyst comprising ruthenium.

13. The method of claim 1, wherein the cleaving is catalyzed by an organometallic catalyst.

14. The method of claim 1, wherein the cleaving is catalyzed by a catalyst comprising a hydride and carbonyl ligand.

15. The method of claim 1, wherein the cleaving is catalyzed by a catalyst formed from a metal precursor and optionally a ligand under the reaction conditions.

16. The method of claim 15, wherein the metal precursor is selected from the group consisting Of [Ru₃(CO)₁₂], [{Ru(cymene)Cl₂}₂], [(PPh₃ )₄RuCl₂],

[Ru(PPh₃MCO)(OTf)₂(MeOH)] , [RuH₂CO(PPh₃)₃] , [Ru(TFA)₂(CO)(PPh₃)₂] ,

[Ru(TFA)(PPh₃MCO)H], [RuH(TFA)(CO)(PPh₃)₃], [Ni(cod)₂], and [RhCl(coe)₂]₂.

17. The method of claim 15, wherein the ligand is a phosphine ligand.

18. The method of claim 15, wherein the metal precursor is selected from the group consisting of [RuH₂CO(PPh₃)₃], [Ru(TFA)₂(CO)(PPh₃)₂], [Ru(TFA)(PPh₃)₂(CO)H], and

416₂7₂008740 }32

19. The method of claim 1, wherein the cleaving is carried out at a reaction temperature of 80-250⁰C.

20. The method of claim 1, further comprising hydrodeoxygenating the reaction products.

21. The method of claim 1, further comprising cracking the reaction products.

22. The method of claim 1, further comprising hydrogenating the reaction products.

23. The method of claim 1, wherein the cleaving is carried out in the presence of hydrogen.

24. The method of claim 1, wherein the cleaving is carried out in the presence of a silane.

25. The method of claim 1, wherein the glycerol β-arylether unit is oxidized prior to the cleaving step.

26. A fuel produced by the method of claim 20.

27. A product formed by the method of claim 1.

28. The method of claim 1, wherein the cleaving is carried out in the presence of an acid.

29. The method of claim 28, wherein the acid is selected from the group consisting of AlX₃ where X = tertiary alkoxide, phenoxide, and halogen; TiX₄ where X = tertiary alkoxide, phenoxide, and halogen; BX₃ where X = F, Br; organic acids X-CO₂H where X = CF₃, CH₃, aryl; and sulfonic acids X-SO₃H where X = Me, aryl.

30. A method of depolymerizing lignin comprising:

416272008740 }33

31. The method of claim 30, wherein the carbon-oxygen bond is between C² and O² of a glycerol β-arylether unit of lignin:

32. The method of claim 30, wherein the cleaving occurs via a disproportionation- elimination reaction.

33. The method of claim 30, wherein the metal-based catalyst comprising vanadium is formed from a vanadium precursor and optionally a ligand under the reaction conditions.

34. The method of claim 33, wherein the vanadium precursor is selected from the group consisting of [VOSO₄-XH₂O], [VO(acac)₂], [VO(OZ-Pr)₃], and mixtures thereof.

35. The method of claim 33, wherein the ligand is a phenol-imine or bis-phenol-imine ligand.

36. The method of claim 33, wherein the cleaving is catalyzed by a pre-formed phenol- imine or bis-phenol-imine vanadium catalyst.

37. The method of claim 36, wherein the preformed phenol-imine or bis-phenol-imine vanadium catalyst is selected from the group consisting of:

416272008740 }34

and mixtures thereof.

38. A method of depolymerizing lignin comprising:

cleaving a carbon-oxygen bond of lignin in a catalytic reduction reaction, by contacting lignin with a catalyst and a hydrogen atom source.

39. The method of claim 38, wherein the carbon-oxygen bond comprises a diaryl, alkyl aryl, or benzyl alkyl, or benzyl aryl ether linkage.

40. The method of claim 38, wherein the cleaving is catalyzed by a metal-based catalyst comprising nickel.

41. The method of claim 40, wherein the metal-based catalyst comprising nickel is formed from a nickel precursor and optionally a ligand under the reaction conditions.

42. The method of claim 41, wherein the nickel precursor is selected from the group consisting Of Ni(COD)₂, Ni(acac)₂, NiCl₂, NiBr₂, Ni(OAc)₂, Ni(OH)₂, NiCO₃* 2 Ni(OH)₂ (nickel carbonate basic), and mixtures thereof.

416₂7₂008740 135

43. The method of claim 42, wherein the nickel precursor is selected from the group consisting of Ni(COD)₂, Ni(acac)₂, and mixtures thereof.

44. The method of claim 41, wherein the ligand:nickel precursor ratio is approximately 2:1.

45. The method of claim 40, wherein the ligand is an N-heterocyclic carbene ligand or a phosphine ligand.

46. The method of claim 45, wherein the ligand is an N-heterocyclic carbene ligand.

47. The method of claim 46, wherein the N-heterocyclic carbene ligand is selected from the group consisting of:

416272008740 }36

SIPr HX, X=CI-, BF₄ ^" IPr HCI diMelPr HCI diMeSIPr HCI

MonotBulPr HCI ItBu HCI IMes HCI SIMes HBF₄

6-DIPP HBr 7-DIPP HBr XyI-DIPP HBr

SCAAC HCI

SImAd HBF₄ SImPr HBF₄ SImBu HBF₄ Bu Im HBF₄ and mixtures thereof.

48. The method of claim 47, wherein the N-heterocyclic carbene ligand is selected from the group consisting of:

416272008740 137

SIPr HX₁ X=CI-, BF₄ ^" IPr HCI diMelPr HCI diMeSIPr HCI

MonotBulPr HCI ItBu HCI IMes HCI SIMeS H BF₄

49. The method of claim 48, wherein the N-heterocyclic carbene ligand is selected from the group consisting of:

SPr HCI I Pr_MΘ HCI ; and mixtures thereof.

50. The method of claim 40, wherein the cleaving is catalyzed by a pre-formed N- heterocyclic carbene nickel catalyst.

51. The method of claim 38, wherein the cleaving is carried out at a reaction temperature of 80-250⁰C.

52. The method of claim 38, further comprising hydrodeoxygenating the reaction products.

53. The method of claim 38, further comprising cracking the reaction products.

54. The method of claim 38, further comprising hydrogenating the reaction products.

416272008740 138

55. The method of claim 38, wherein the cleaving is carried out in the presence of a hydrogen atom source, the hydrogen atom source selected from the group consisting of hydrogen, a silane, diisobutylaluminum hydride (DIBAL), lithium tri-te/t-butoxyalumnium hydride (LiAl(O^Bu)₃H), or mixtures thereof.

56. The method of claim 55, wherein the silane is triethylsilane (Et₃SiH) or tert- butyldimethylsilane (^BuMe₂SiH).

57. The method of claim 55, wherein the hydrogen atom source is dihydrogen.

58. The method of claim 38, wherein the cleaving is carried out in the presence of a base, the base is selected from the group consisting of sodium te/t-butoxide (^BuONa), sodium te/t-pentoxide (^PentONa), sodium /so-propoxide (/PrONa), lithium te/t-butoxide (tBuOLϊ), sodium methoxide (MeONa), potassium te/t-butoxide (^BuOK), cesium fluoride (CsF), and cesium carbonate (Cs₂CO₃), and mixtures thereof.

59. The method of claim 58, wherein the base is selected from the group consisting of sodium te/t-butoxide (^BuONa), sodium te/t-pentoxide (^PentONa), sodium /so-propoxide (/PrONa), and mixtures thereof.

60. The method of claim 38, wherein the cleaving has higher selectivity for aryl-carbon- oxygen bonds over alkyl-carbon oxygen bonds in lignin.

61. The method of claim 38, wherein the cleaving is catalyzed by a metal-based catalyst comprising nickel and an N-heterocyclic carbene ligand in the presence of a hydrogen atom source and a base.

62. A fuel produced by the method of claim 52.

63. A product formed by the method of claim 38.

416272008740 }39

64. A method to cleave a diaryl ether linkage comprising contacting a diaryl ether with a nickel catalyst and a hydrogen donor in the presence of a base.

65. The method of claim 64, wherein the diaryl ether is an optionally substituted diphenyl ether.

63. The method of claim 64, wherein the metal-based catalyst comprising nickel is

formed from a nickel precursor and optionally a ligand under the reaction conditions.

64. The method of claim 64, wherein the nickel precursor is selected from the group consisting Of Ni(COD)₂, Ni(acac)₂, NiCl₂, NiBr₂, Ni(OAc)₂, Ni(OH)₂, NiCO₃* 2 Ni(OH)₂ (nickel carbonate basic), and mixtures thereof.

65. The method of claim 64, the nickel precursor is Ni(COD)₂ or Ni(acac)₂.

66. The method of claim 64, wherein the ligand:nickel precursor ratio is approximately 2:1.

67. The method of claim 64, wherein the ligand is an N-heterocyclic carbene ligand or a phosphine ligand.

68. The method of claim 67, wherein the ligand is an N-heterocyclic carbene ligand.

69. The method of claim 68, wherein the N-heterocyclic carbene ligand is selected from the group consisting of:

416₂7₂008740 }40

SIPr HX₁ X=CI-, BF₄ ^" IPr HCI diMelPr HCI diMeSIPr HCI

MonotBulPr HCI ItBu HCI IMes HCI SIMeS H BF₄ and mixtures thereof.

70. The method of claim 69, wherein the N-heterocyclic carbene ligand is selected from the group consisting of:

SPr HCI IPr_Me HCI and mixtures thereof.

71. The method of claim 64, wherein the cleaving reaction is catalyzed by a pre-formed N-heterocyclic carbene nickel catalyst.

72. The method of claim 64, wherein the cleaving reaction is carried out at a reaction temperature of 80-250⁰C.

73. A composition comprising lignin and a metal-based catalyst.

74. The composition of claim 73, wherein the metal-based catalyst is formed from a metal precursor and optionally a ligand under the reaction conditions.

416272008740 141

75. The composition of claim 74, wherein the metal precursor comprises a metal selected from the group consisting of ruthenium, rhodium, vanadium, nickel, and mixtures thereof.

76. The composition of claim 74, wherein the metal precursor is selected from the group consisting Of [Ru₃(CO)₁₂], [{Ru(cymene)Cl₂}₂], [(PPh₃ )₄RuCl₂],

[Ru(PPh_S)₂(CO)(OTf)₂(MeOH)] , [RuH₂CO(PPh₃)₃] , [Ru(TFA)₂(CO)(PPh₃),] ,

[Ru(TFA)(PPh₃MCO)H], [RuH(TFA)(CO)(PPh₃)₃], [Ni(cod)₂], [RhCl(coe)₂]₂,

[VOSO₄-XH₂O], [V0(acac)₂], [VO(OZ-Pr)₃], Ni(acac)₂, NiCl₂, NiBr₂, Ni(OAc)₂, Ni(OH)₂, NiCO₃* 2 Ni(OH)₂ (nickel carbonate basic), and mixtures thereof.

77. The composition of claim 74, wherein the metal precursor comprises ruthenium and the ligand is a phosphine ligand.

78. The composition of claim 77, wherein the phosphine ligand is (9,9-dimethylxanthene- 4,5-diyl)Ms(diphenylphosphine).

79. The composition of claim 74, wherein the metal precursor comprises vanadium and the ligand is a phenol-imine or bis-phenol-imine ligand.

80. The composition of claim 74, wherein the metal precursor comprises nickel and the ligand is a phosphine or carbene ligand.

81. The composition of claim 80, wherein the carbene ligand is an N-heterocyclic

carbene ligand.

82. The composition of claim 73, wherein the metal-based catalyst is a pre-formed

catalyst.

83. The composition of claim 82, wherein the pre-formed catalyst comprises ruthenium and a phosphine ligand. 740 }42

84. The composition of claim 82, wherein the pre-formed catalyst comprises vanadium and a phenol-imine or bis-phenol-imine ligand.

85. The composition of claim 82, wherein the pre-formed catalyst comprises nickel and a phosphine or carbene ligand.

740 }43