WO2011003029A2 - Dismutation catalytique et réduction catalytique des liaisons carbone-carbone et carbone-oxygène de la lignine et autres substrats organiques - Google Patents

Dismutation catalytique et réduction catalytique des liaisons carbone-carbone et carbone-oxygène de la lignine et autres substrats organiques Download PDF

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WO2011003029A2
WO2011003029A2 PCT/US2010/040832 US2010040832W WO2011003029A2 WO 2011003029 A2 WO2011003029 A2 WO 2011003029A2 US 2010040832 W US2010040832 W US 2010040832W WO 2011003029 A2 WO2011003029 A2 WO 2011003029A2
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lignin
cleaving
ligand
carbon
group
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WO2011003029A3 (fr
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Robert Bergman
Jonathan Ellman
Jason Nichols
Lee Bishop
Jerome Volkman
Dean Toste
Sunghee Son
John Hartwig
Alexey Sergeev
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University of California Berkeley
University of California San Diego UCSD
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University of California San Diego UCSD
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    • C07C41/00—Preparation of ethers; Preparation of compounds having groups, groups or groups
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    • B01J2231/64—Reductions in general of organic substrates, e.g. hydride reductions or hydrogenations
    • B01J2231/641—Hydrogenation of organic substrates, i.e. H2 or H-transfer hydrogenations, e.g. Fischer-Tropsch processes
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    • B01J2531/00—Additional information regarding catalytic systems classified in B01J31/00
    • B01J2531/02—Compositional aspects of complexes used, e.g. polynuclearity
    • B01J2531/0238—Complexes comprising multidentate ligands, i.e. more than 2 ionic or coordinative bonds from the central metal to the ligand, the latter having at least two donor atoms, e.g. N, O, S, P
    • B01J2531/0241—Rigid ligands, e.g. extended sp2-carbon frameworks or geminal di- or trisubstitution
    • B01J2531/0252—Salen ligands or analogues, e.g. derived from ethylenediamine and salicylaldehyde
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    • B01J2531/00—Additional information regarding catalytic systems classified in B01J31/00
    • B01J2531/50—Complexes comprising metals of Group V (VA or VB) as the central metal
    • B01J2531/56—Vanadium
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B01J2531/00—Additional information regarding catalytic systems classified in B01J31/00
    • B01J2531/80—Complexes comprising metals of Group VIII as the central metal
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    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts

Definitions

  • 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.
  • Lignocellulose is a conjugate biopolymer made up of three, smaller biopolymers:
  • 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.
  • the oxygen content of the bio-oil fraction results in undesirable physical properties.
  • 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.
  • Phenylpropanoid compounds may include, for example, coumaryl alcohol, guaiacyl alcohol, and syringyl alcohol:
  • 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 ⁇ -glycerolaryl ether. Lignin itself is a complex mixture of these and other linkages of phenylpropanoid monomers.
  • 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 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.
  • two such rings can be fused together, as in the fused 5,5-bicyclic system of pinoresinol (Scheme T).
  • 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.
  • 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
  • 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.
  • a metal precursor such as vanadium
  • 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.
  • 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
  • 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.
  • the present invention provides a method of reducing an ⁇ -keto ether compound comprising: cleaving a carbon-oxygen bond between C 2 and O 2 of the ⁇ -keto ether compound of Formula 1 :
  • R 1 , R 2 , and R 3 are each independently selected from the group consisting of hydrogen, alkyl, optionally substituted alkyl, aryl, optionally substituted aryl, and optionally substituted heteroaryl;
  • R 2 is not hydrogen.
  • the optionally substituted alkyl, aryl and heteroaryl groups can comprise a bond linking the group to a lignin or to a phenylpropanoid.
  • at least one of R 1 , R 2 and R 3 comprises a bond to a lignin or a phenylpropanoid.
  • R is optionally substituted alkyl, or it is H.
  • R 3 is H, OL, Me, CH 2 OH, CH 2 L, or CH 2 OL, where L represents a bond to lignin or to a phenylpropanoid.
  • R 2 is optionally substituted aryl, or it is a bond to a lignin or a phenylpropanoid.
  • the cleaving forms at least one product selected from the group consisting of: '
  • R 1 , R 2 , and R 3 in these formulas are as described for Formula 1 above.
  • the cleaving forms the product of Formula 2:
  • the cleaving forms a product of Formula 3:
  • compounds of Formula 2 and Formula 3 may both be formed in such reactions.
  • the present invention also provides a method of disproportionating an ⁇ -hydroxy ether compound comprising:
  • each R 1 , R 2 , and R 3 is independently selected from the group consisting of hydrogen, alkyl, optionally substituted alkyl, aryl, optionally substituted aryl, and optionally substituted heteroaryl;
  • R is not hydrogen
  • R 1 , R 2 and R 3 comprises a bond to a lignin or a phenylpropanoid.
  • R 3 is optionally substituted alkyl, or it is H.
  • R 3 is H, OL, Me, CH 2 OH, CH 2 L, or CH 2 OL, where L represents a bond to lignin or to a phenylpropanoid.
  • R 2 is optionally substituted aryl, or it is a bond to a lignin or a phenylpropanoid
  • the cleaving forms at least one product selected from the group consisting of:
  • the cleaving forms the product of Formula 5:
  • the cleaving forms the product of Formula 6:
  • the cleaving occurs by tandem dehydrogenation and carbon- oxygen bond cleavage reactions.
  • R 1 and R 2 are optionally substituted aryl and R 3 is hydrogen.
  • at least one of R 1 , R 2 and R 3 comprises a bond to a lignin or a phenylpropanoid.
  • R 3 is optionally substituted alkyl, or it is H.
  • R 3 is H, OL, Me, CH 2 OH, CH 2 L, or CH 2 OL, where L represents a bond to lignin or to a phenylpropanoid.
  • R 2 is optionally substituted aryl, or it is a bond to a lignin or a phenylpropanoid.
  • the present invention also provides a method of disproportionating a 1,3-diol compound comprising:
  • R 4 , R 5 , and R 6 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.
  • the cleaving forms at least one product selected from the group consisting of:
  • the cleaving forms the product of Formula 8:
  • the cleaving forms the product of Formula 9:
  • compounds of Formula 8 and Formula 9 may both be formed.
  • the cleaving forms the product of Formula 10:
  • the cleaving forms the product of Formula 11 :
  • additional products are formed by reactions other than the cleaving reaction, the additional products selected from the group consisting of:
  • R 4 , R 5 R 6 and X in these formulas are as defined for Formulas 7-11.
  • R 4 is optionally substituted aryl and R 5 and R 6 are hydrogen.
  • the cleaving occurs via tandem dehydrogenation and retro-aldol reactions.
  • the present invention also provides a method of disproportionating a glycerol ⁇ - arylether compound of Formula 15, comprising:
  • Ar 1 and Ar 2 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.
  • at least one of Ar 1 , Ar 2 , R and R' comprises a bond to a lignin or a phenylpropanoid.
  • R' is optionally substituted alkyl, or it is H.
  • R' is H, OL, Me, CH 2 OH, CH 2 L, or CH 2 OL, where L represents a bond to lignin or to a phenylpropanoid.
  • Ar is optionally substituted phenyl.
  • the cleaving forms at least one product selected from the group consisting of:
  • the cleaving forms the product of Formula 16:
  • the cleaving forms the product of Formula 17:
  • the present invention also provides a method of disproportionating a glycerol ⁇ - arylether compound of Formula 15, comprising:
  • Ar 1 and Ar 2 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.
  • at least one of Ar 1 , Ar 2 , R and R' comprises a bond to a lignin or a phenylpropanoid.
  • R' is optionally substituted alkyl, or it is H.
  • R' is H, OL, Me, CH 2 OH, CH 2 L, or CH 2 OL, where L represents a bond to lignin or to a phenylpropanoid.
  • Ar 2 is optionally substituted phenyl.
  • the cleaving forms at least one product selected from the group consisting of:
  • the present invention also provides a method of disproportionating a glycerol ⁇ - arylether compound comprising:
  • Ar 1 and Ar 2 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.
  • at least one of Ar 1 , Ar 2 , R and R' comprises a bond to a lignin or a phenylpropanoid.
  • R' is optionally substituted alkyl, or it is H.
  • R' is H, OL,
  • Ar 2 is optionally substituted phenyl.
  • the cleaving forms at least one product selected from the group consisting of:
  • at least one of Ar 1 , Ar 2 , R and R' comprises a bond to a lignin or a phenylpropanoid.
  • R' is optionally substituted alkyl, or it is H.
  • R' is H, OL, Me, CH 2 OH, CH 2 L, or CH 2 OL, where L represents a bond to lignin or to a phenylpropanoid.
  • Ar is optionally substituted phenyl. In some embodiments of these reactions, R' is H. In some embodiments, R is H.
  • the cleaving forms the product of Formula 17:
  • additional products are formed by reactions other than the cleaving reaction, the additional products selected from the group consisting of:
  • the cleaving occurs via tandem dehydrogenation and retro- aldol reactions and/or tandem dehydrogenation and carbon-oxygen bond cleavage reactions.
  • At least one, and preferably at least two, of Ar 1 , Ar 2 , 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.
  • the present invention also provides a method of depolymerizing lignin comprising:
  • the present invention also provides a method of disproportionating a glycerol ⁇ - arylether unit of lignin comprising:
  • Ar 3 and Ar 4 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.
  • at least one of Ar 3 , Ar 4 , R and R' comprises a bond to a lignin or a phenylpropanoid.
  • R' is optionally
  • R' is H, OL, Me, CH 2 OH, CH 2 L, or CH 2 OL, where L represents a bond to lignin or to a phenylpropanoid.
  • Ar 4 is optionally substituted phenyl.
  • the cleaving forms at least a product of Formula 27:
  • the present invention also provides a method of disproportionating a glycerol ⁇ - arylether unit of lignin comprising:
  • Ar 3 and Ar 4 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.
  • at least one of Ar 3 , Ar 4 , R and R' comprises a bond to a lignin or a phenylpropanoid.
  • R' is optionally substituted alkyl, or it is H.
  • R' is H, OL, Me, CH 2 OH, CH 2 L, or CH 2 OL, where L represents a bond to lignin or to a phenylpropanoid.
  • Ar 4 is optionally substituted phenyl.
  • the present invention also provides a method of disproportionating a glycerol ⁇ - arylether unit of lignin comprising:
  • Ar 3 and Ar 4 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.
  • the cleaving forms at least a product of Formula 27:
  • the cleaving occurs via tandem dehydrogenation and retro- aldol reactions and/or tandem dehydrogenation and carbon-oxygen bond cleavage reactions.
  • the disproportionation reactions of the present reaction may be catalyzed by a metal- based catalyst.
  • 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.
  • 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.
  • the metal is ruthenium.
  • the disproportionation reactions of the present reaction may also be catalyzed by an organometallic catalyst.
  • the catalyst comprises at least one hydride and at least one carbonyl ligand on a metal center of the catalyst.
  • the reactions are catalyzed by a catalyst formed under the reaction conditions from a metal precursor and optionally a ligand.
  • the metal precursor is selected from the group consisting of [Ru 3 (CO)I 2 ], [ ⁇ Ru(cymene)Cl 2 ⁇ 2 ], [(PPh 3 ) 4 RuCl 2 ], [Ru(PPh 3 MCO)(OTf) 2 (MeOH)],
  • 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.
  • the metal precursor is selected from the group consisting of [RuH 2 CO(PPh 3 ) 3 ], [Ru(TFA) 2 (CO)(PPh 3 ) 2 ], [Ru(TFA)(PPh 3 ) 2 (CO)H], and
  • the disproportionation reactions are carried out at a reaction temperature of 80-250 0 C. 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 ⁇ -arylether unit is oxidized prior to the cleaving step. In many embodiments, catalyst compositions are formed under the reaction conditions.
  • the methods of the present invention may further comprise hydrodeoxygenating the reaction products.
  • the methods of the present invention may also further comprise cracking and/or hydrogenating the reaction products.
  • a fuel is produced following the hydrodeoxygenating, cracking, and/or hydrogenating steps.
  • the present invention provides a method of reducing an ⁇ -keto ether compound comprising:
  • R 1 , R 2 , and R 3 are each independently selected from the group consisting of hydrogen, alkyl, optionally substituted alkyl, aryl, optionally substituted aryl, and optionally substituted heteroaryl;
  • R 2 is not hydrogen.
  • the optionally substituted alkyl, aryl and heteroaryl groups can comprise a bond linking the group to a lignin or to a phenylpropanoid.
  • at least one of R 1 , R 2 and R 3 comprises a bond to a
  • R is optionally substituted alkyl, or it is H.
  • R 3 is H, OL, Me, CH 2 OH, CH 2 L, or CH 2 OL, where L represents a bond to lignin or to a phenylpropanoid.
  • R 2 is optionally substituted aryl, or it is a bond to a lignin or a phenylpropanoid.
  • the cleaving forms at least one product selected from the group consisting of:
  • the cleaving forms the product of Formula 2:
  • the cleaving forms the product of Formula 3:
  • compounds of Formula 2 and Formula 3 may both be formed in such reactions.
  • the present invention also provides a method of disproportionating a ⁇ -hydroxy ether compound comprising:
  • each R 1 , R 2 , and R 3 is independently selected from the group consisting of hydrogen, alkyl, optionally substituted alkyl, aryl, optionally substituted aryl, and optionally substituted heteroaryl;
  • R 2 is not hydrogen
  • R 1 , R 2 and R 3 comprises a bond to a lignin or a phenylpropanoid.
  • R 3 is optionally substituted alkyl, or it is H.
  • R 3 is H, OL, Me, CH 2 OH, CH 2 L, or CH 2 OL, where L represents a bond to lignin or to a phenylpropanoid.
  • R 2 is optionally substituted aryl, or it is a bond to a lignin or a phenylpropanoid
  • the cleaving forms at least one product selected from the group consisting of:
  • the cleaving forms the product of Formula 5:
  • the cleaving forms the product of Formula 6:
  • the cleaving occurs by tandem dehydrogenation and carbon- oxygen bond cleavage reactions.
  • R 1 and R 2 are optionally substituted aryl and R 3 is hydrogen.
  • at least one of R 1 , R 2 and R 3 comprises a bond to a lignin or a phenylpropanoid.
  • R 3 is optionally substituted alkyl, or it is H.
  • R 3 is H, OL, Me, CH 2 OH, CH 2 L, or CH 2 OL, where L represents a bond to lignin or to a phenylpropanoid.
  • R 2 is optionally substituted aryl, or it is a bond to a lignin or a phenylpropanoid.
  • the cleaving forms at least one product selected from the group consisting of:
  • C 1 X is C 1 O or C 1 HOH
  • each R 4 is independently selected from the group consisting of hydrogen, alkyl, optionally substituted alkyl, aryl, optionally substituted aryl, and optionally substituted heteroaryl.
  • R 4 is independently selected from the group consisting of hydrogen, alkyl, optionally substituted alkyl, aryl, optionally substituted aryl, and optionally substituted heteroaryl.
  • compounds of both Formula 7 and Formula 8 may be produced.
  • the cleaving forms the product of Formula 7:
  • the cleaving forms the product of Formula 8:
  • an additional product is formed by a reaction other than the cleaving reaction, and wherein the additional product is of Formula 9:
  • R 1 , R 2 , and R 4 are as defined for Formulas 4 and 7-8.
  • the present invention also provides a method of disproportionating a 1,3-diol compound comprising:
  • R 5 , R 6 , and R 7 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.
  • the cleaving forms at least one product selected from the group consisting of:
  • the cleaving forms the product of Formula 11 :
  • the cleaving forms the product of Formula 12: r 3
  • compounds of Formula 11 and Formula 12 may both be formed.
  • the cleaving forms the product of Formula 13:
  • the cleaving forms the product of Formula 14:
  • additional products are formed by reactions other than the cleaving reaction, the additional products selected from the group consisting of:
  • R 5 , R 6 , R 7 , and X in these formulas are as defined for Formulas 10-14.
  • R 5 is optionally substituted aryl and R 6 and R 7 are hydrogen.
  • the cleaving occurs via tandem dehydrogenation and retro-aldol reactions.
  • the present invention also provides a method of disproportionating a glycerol ⁇ - arylether compound of Formula 18, comprising:
  • Ar 1 and Ar 2 are optionally substituted aryl and each R 8 and R 9 is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted aryl, and optionally substituted heteroaryl.
  • at least one of Ar 1 , Ar 2 , R 8 and R 9 comprises a bond to a lignin or a phenylpropanoid.
  • R 9 is optionally substituted alkyl, or it is H.
  • R 9 is H, OL, Me, CH 2 OH, CH 2 L, or CH 2 OL, where L represents a bond to lignin or to a phenylpropanoid.
  • Ar 2 is optionally substituted phenyl.
  • the cleaving forms at least one product selected from the group consisting of:
  • the cleaving forms the product of Formula 19:
  • the cleaving forms the product of Formula 20:
  • the cleaving forms at least one product selected from the group consisting of:
  • C 1 X is C 1 O or C 1 HOH.
  • the cleaving forms the product of Formula 21:
  • the cleaving forms the product of Formula 22:
  • an additional product is formed by a reaction other than the cleaving reaction, and wherein the additional product is of Formula 23:
  • the present invention also provides a method of disproportionating a glycerol ⁇ - arylether compound of Formula 18, comprising:
  • Ar 1 and Ar 2 are optionally substituted aryl groups and each R 8 and R 9 is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted aryl, and optionally substituted heteroaryl.
  • at least one of Ar 1 , Ar 2 , R 8 and R 9 comprises a bond to a lignin or a phenylpropanoid.
  • R 9 is optionally substituted alkyl, or it is H.
  • R 9 is H, OL,
  • the cleaving forms at least one product selected from the group consisting of:
  • the present invention also provides a method of disproportionating a glycerol ⁇ - arylether compound comprising:
  • Ar 1 and Ar 2 are optionally substituted aryl groups and each R 8 and R 9 is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted aryl, and optionally substituted heteroaryl.
  • at least one of Ar 1 , Ar 2 , R 8 and R 9 comprises a bond to a lignin or a phenylpropanoid.
  • R 9 is optionally substituted alkyl, or it is H.
  • R 9 is H, OL, Me, CH 2 OH, CH 2 L, or CH 2 OL, where L represents a bond to lignin or to a phenylpropanoid.
  • Ar is optionally substituted phenyl.
  • the cleaving forms at least one product selected from the group consisting of:
  • at least one of Ar 1 , Ar 2 , R 8 and R 9 comprises a bond to a lignin or a
  • R 9 is optionally substituted alkyl, or it is H.
  • R 9 is H, OL, Me, CH 2 OH, CH 2 L, or CH 2 OL, where L represents a bond to lignin or to a phenylpropanoid.
  • Ar 2 is optionally substituted phenyl.
  • R 8 is H.
  • R 9 is H.
  • the cleaving forms the product of Formula 20:
  • additional products are formed by reactions other than the cleaving reaction, the additional products selected from the group consisting of:
  • the cleaving occurs via tandem dehydrogenation and retro- aldol reactions and/or tandem dehydrogenation and carbon-oxygen bond cleavage reactions.
  • At least one, and preferably at least two, of Ar 1 , Ar 2 , R 8 and R 9 in Formula 18 represent a bond to lignin or to a phenylpropanoid.
  • the product of these reactions can be a partially depolymerized lignin.
  • the present invention also provides a method of depolymerizing lignin comprising:
  • the present invention also provides a method of disproportionating a glycerol ⁇ - arylether unit of lignin comprising:
  • Ar 3 and Ar 4 are optionally substituted aryl groups of lignin and each R 10 and R 11 is independently selected from the group consisting of hydrogen or a bond to a
  • At least one of Ar 3 , Ar 4 , R 10 and R 11 comprises a bond to a lignin or a phenylpropanoid.
  • R 11 is optionally substituted alkyl, or it is H.
  • R 11 is H, OL, Me, CH 2 OH, CH 2 L, or CH 2 OL, where L represents a bond to lignin or to a phenylpropanoid.
  • Ar 4 is optionally substituted phenyl.
  • the cleaving forms at least a product of Formula 33:
  • the present invention also provides a method of disproportionating a glycerol ⁇ - arylether unit of lignin comprising: cleaving a carbon-carbon bond between C 1 and C 2 and/or C 2 and C 3 of the glycerol ⁇ - arylether unit of lignin of Formula 32:
  • Ar 3 and Ar 4 are optionally substituted aryl groups of lignin and each R 10 and R 11 is independently selected from the group consisting of hydrogen or a bond to a
  • At least one of Ar 3 , Ar 4 , R 10 and R 11 comprises a bond to a lignin or a phenylpropanoid.
  • R 11 is optionally substituted alkyl, or it is H.
  • R 11 is H, OL, Me, CH 2 OH, CH 2 L, or CH 2 OL, where L represents a bond to lignin or to a phenylpropanoid.
  • Ar 4 is optionally substituted phenyl.
  • the present invention also provides a method of disproportionating a glycerol ⁇ - arylether unit of lignin comprising:
  • Ar 3 and Ar 4 are optionally substituted aryl groups of lignin and each R 10 and R 11 is independently selected from the group consisting of hydrogen or a bond to a
  • the cleaving forms at least a product of Formula 33:
  • the cleaving occurs via tandem dehydrogenation and retro- aldol reactions and/or tandem dehydrogenation and carbon-oxygen bond cleavage reactions.
  • the disproportionation reactions of the present reaction may be catalyzed by a metal- based catalyst.
  • 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.
  • 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,
  • the metal is ruthenium. In other particular embodiments, the metal is vanadium.
  • the disproportionation reactions of the present reaction may also be catalyzed by an organometallic catalyst.
  • the catalyst comprises at least one hydride and at least one carbonyl ligand on a metal center of the catalyst.
  • the reactions are catalyzed by a catalyst formed under the reaction conditions from a metal precursor and optionally a ligand.
  • the metal precursor is selected from the group consisting of [Ru 3 (CO)I 2 ], [ ⁇ Ru(cymene)Cl 2 ⁇ 2 ], [(PPh 3 ) 4 RuCl 2 ], [Ru(PPh 3 MCO)(OTf) 2 (MeOH)],
  • the ligand is a phosphine ligand, which may be a monophosphine such as triphenylphosphine, or a diphosphine such as diphos or xantphos.
  • the metal precursor is selected from the group consisting of
  • the cleaving occurs via a disproportionation-elimination reaction.
  • the metal-based catalyst that cleaves via disproportionation- elimination is vanadium.
  • 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 [VOSO 4 -XH 2 O], [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:
  • the disproportionation reactions are carried out at a reaction temperature of 80-250 0 C. 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 ⁇ -arylether unit is oxidized prior to the cleaving step. In many embodiments, catalyst compositions are formed under the reaction conditions.
  • the methods of the present invention may further comprise hydrodeoxygenating the reaction products.
  • the methods of the present invention may also further comprise cracking and/or hydrogenating the reaction products.
  • a fuel is produced following the hydrodeoxygenating, cracking, and/or hydrogenating steps.
  • the present invention also provides a method of degrading lignin comprising:
  • Ar 3 and Ar 4 are optionally substituted aryl groups of lignin and each R 10 and R 11 is independently selected from the group consisting of hydrogen or a bond to a
  • the cleaving is mediated by a catalyst comprising ruthenium.
  • the catalyst further comprises at least one phosphine ligand.
  • the present invention also provides a method of degrading lignin comprising:
  • Ar 3 and Ar 4 are optionally substituted aryl groups of lignin and each R 10 and R 11 is independently selected from the group consisting of hydrogen or a bond to a
  • the cleaving is mediated by a catalyst comprising vanadium.
  • the catalyst further comprises at least one phenol-imine ligand.
  • 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.
  • the carbon-oxygen bond is between C 2 and O 2 of a glycerol ⁇ -arylether unit of lignin:
  • Ar 4 wherein Ar 3 and Ar 4 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
  • the cleaving forms one or more products, the one or more products comprising Ar 4 OH.
  • the carbon-carbon bond is between C 1 and C 2 and/or C 2 and C 3 of a glycerol ⁇ -arylether unit of lignin:
  • Ar 3 and Ar 4 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.
  • the carbon-carbon bond between C 1 and C 2 and/or C 2 and C 3 of the glycerol ⁇ -arylether unit of lignin and the carbon-oxygen bond between C 2 and O 2 of the glycerol ⁇ -arylether unit of lignin are cleaved:
  • Ar 3 and Ar 4 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.
  • the cleaving forms one or more products, the one or more products comprising Ar 4 OH.
  • the cleaving occurs via tandem dehydrogenation and retro- aldol reactions and/or tandem dehydrogenation and carbon-oxygen bond cleavage reactions.
  • the cleaving is catalyzed by a metal-based catalyst.
  • 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.
  • 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.
  • 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 [Ru 3 (CO) I2 ], [ ⁇ Ru(cymene)Cl 2 ⁇ 2 ],
  • the ligand is a phosphine ligand.
  • the metal precursor is selected from the group consisting of [RuH 2 CO(PPh 3 ) 3 ], [Ru(TF A) 2 (CO)(PPh 3 ) 2 ],
  • the cleaving is carried out at a reaction temperature of 80- 25O 0 C. 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 embodiments,
  • the cleaving is carried out in the presence of an acid.
  • the methods of the present invention may further comprise hydrodeoxygenating the reaction products.
  • the methods of the present invention may also further comprise cracking and/or hydrogenating the reaction products.
  • a fuel is produced following the hydrodeoxygenating, cracking, and/or hydrogenating steps.
  • the glycerol ⁇ -arylether unit is oxidized prior to the cleaving step.
  • the present invention also provides a method of depolymerizing lignin comprising:
  • cleaving is catalyzed by a metal-based catalyst comprising vanadium.
  • the carbon-oxygen bond is between C 2 and O 2 of a glycerol ⁇ - arylether unit of lignin:
  • Ar 4 wherein Ar 3 and Ar 4 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
  • the cleaving occurs via a disproportionation-elimination reaction.
  • the metal-based catalyst comprising vanadium is formed from a vanadium precursor and optionally a ligand under the reaction conditions.
  • the vanadium precursor is selected from the group consisting of [VOSO 4 -XH 2 O], [VO(acac) 2 ], [VO(OZ-Pr) 3 ], and mixtures thereof.
  • the ligand is a phenol-imine or bis-phenol-imine ligand.
  • the cleaving is catalyzed by a pre-formed phenol-imine or bis-phenol-imine vanadium catalyst.
  • the preformed phenol-imine or bis-phenol-imine vanadium catalyst is selected from the group consisting of:
  • 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.
  • the carbon-oxygen bond comprises a diaryl, alkyl aryl, or benzyl alkyl, or benzyl aryl ether linkage.
  • the cleaving is catalyzed by a metal-based catalyst comprising nickel.
  • the metal-based catalyst comprising nickel is formed from a nickel precursor and optionally a ligand under the reaction conditions.
  • the nickel precursor is selected from the group consisting of Ni(COD) 2 , Ni(acac) 2 , NiCl 2 , NiBr 2 , Ni(OAc) 2 , Ni(OH) 2 , NiCO 3 * 2 Ni(OH) 2 (nickel carbonate basic), and mixtures thereof.
  • the nickel precursor is Ni(COD) 2 or Ni(acac) 2 .
  • the ligand:nickel precursor ratio is approximately 2:1.
  • the ligand is a carbene ligand (e.g., N-heterocyclic carbene) or a phosphine ligand.
  • the phosphine ligand is a trialkylphosphine ligand such as, for example, tricyclohexylphosphine (P(Cy 3 ) 3 ).
  • 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.
  • the N-heterocyclic carbene ligand is selected from the group consisting of:
  • the N-heterocyclic carbene ligand is a five-membered N-aryl-N-heterocyclic carbene.
  • the five-membered N-aryl-N-heterocyclic carbene is selected from the group consisting of:
  • N-heterocyclic carbene ligand is selected from the group consisting of:
  • 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 80-250 0 C.
  • 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 t ⁇ -tert- butoxyalumnium hydride (LiAl(CyBu) 3 H), or mixtures thereof.
  • the silane is triethylsilane (Et 3 SiH) or te/t-butyldimethyl silane ( ⁇ BuMe 2 SiH).
  • the hydrogen atom source is dihydrogen.
  • the cleaving step in the catalytic reduction reaction is generally carried out in the presence of an optional base.
  • 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 (CS 2 CO 3 ), and mixtures thereof.
  • 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.
  • ⁇ BuONa sodium tert- butoxide
  • ⁇ PentONa sodium te/t-pentoxide
  • /PrONa sodium /so-propoxide
  • an excess of base may be used in the catalytic reduction reactions.
  • 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.
  • the cleaving has a higher selectivity for aryl-carbon-oxygen bonds over alkyl-carbon oxygen bonds in lignin.
  • 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.
  • the methods of the present invention may further comprise hydrodeoxygenating the reaction products.
  • the methods of the present invention may further comprise cracking and/or hydrogenating the reaction products.
  • a fuel is produced following the hydrodeoxygenating, cracking, and/or hydrogenating steps.
  • 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.
  • the diaryl ether is an optionally substituted diphenyl
  • the nickel catalyst is formed from a nickel precursor and optionally a ligand under the reaction conditions.
  • the nickel precursor is selected from the group consisting of Ni(COD) 2 , Ni(acac) 2 , NiCl 2 , NiBr 2 , Ni(OAc) 2 , Ni(OH) 2 , NiCO 3 * 2 Ni(OH) 2 (nickel carbonate basic), and mixtures thereof.
  • the nickel precursor is Ni(COD) 2 or Ni(acac) 2 .
  • the ligand:nickel precursor ratio is approximately 2:1.
  • the ligand is a carbene ligand (e.g., N- heterocyclic carbene) or a phosphine ligand.
  • the phosphine ligand is a trialkylphosphine ligand such as, for example, tricyclohexylphosphine (P(Cy 3 ) 3 ).
  • 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.
  • the N-heterocyclic carbene ligand is selected from the group consisting of:
  • the N-heterocyclic carbene ligand is a five-membered N-aryl-N-heterocyclic carbene.
  • the five-membered N-aryl-N-heterocyclic carbene is selected from the group consisting of:
  • N-heterocyclic carbene ligand is selected from the group consisting of:
  • 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 80-250 0 C.
  • the present invention also provides compositions comprising lignin and a metal- based catalyst.
  • the metal-based catalyst is formed from a metal precursor and optionally a ligand under the reaction conditions.
  • the metal precursor comprises a metal selected from the group consisting of ruthenium, rhodium, vanadium, nickel, and mixtures thereof.
  • the metal precursor is selected from the group consisting Of [Ru 3 (CO) 12 ], [ ⁇ Ru(cymene)Cl 2 ⁇ 2 ], [(PPh 3 ) 4 RuCl 2 ],
  • the metal precursor comprises ruthenium and the ligand is a phosphine ligand.
  • the phosphine ligand is (9,9-dimethylxanthene-4,5-diyl)Ws(diphenylphosphine).
  • the metal precursor comprises vanadium and the ligand is a phenol-imine or bis- phenol-imine ligand.
  • the metal precursor comprises nickel and the ligand is a phosphine or carbene ligand.
  • the carbene ligand is an N- heterocyclic carbene ligand.
  • the metal-based catalyst is a pre-formed catalyst.
  • the pre-formed catalyst comprises ruthenium and a phosphine ligand.
  • the pre-formed catalyst comprises vanadium and a phenol-imine or bis-phenol-imine ligand.
  • the pre-formed catalyst comprises nickel and a phosphine or carbene ligand.
  • lignin refers to lignin in lignocellulosic biomass, purified lignin, or lignin fragments that are produced, for example from the pyrolysis of 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.
  • 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.
  • 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.
  • 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.
  • transportation fuel refers to a fuel that is suitable for use as a power source for transportation vehicles.
  • alkyl 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,
  • 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.
  • Alkyl, alkenyl and alkynyl groups are often substituted to the extent that such substitution makes sense chemically.
  • a substituent group contains two R or R' groups on the same or adjacent atoms (e.g., - NR 2 , 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.
  • N, O or S additional heteroatom
  • 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.
  • alkyl as used herein includes cycloalkyl and cycloalkylalkyl groups
  • cycloalkyl may be used herein to describe a carbocyclic non-aromatic group that is connected via a ring carbon atom
  • cycloalkylalkyl may be used to describe a carbocyclic non-
  • 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.
  • 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.
  • 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
  • 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.
  • 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.
  • 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
  • Phenyl is sometimes substituted with an optionally substituted propyl or propenyl group, to provide a phenylpropanoid.
  • 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.
  • heteroaryl refers 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.
  • monocyclic C5-C6 aromatic groups such as pyridyl, pyrimidy
  • 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.
  • the ring systems contain 5-12 ring member atoms.
  • the monocyclic heteroaryls contain 5-6 ring members, and the bicyclic heteroaryls contain 8-10 ring members.
  • 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, NR 2 , SR, SO 2 R, SO 2 NR 2 , NRSO 2 R,
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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
  • 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
  • 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.
  • 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.
  • a benzyl group is a C7-arylalkyl group
  • phenylethyl is a C8-arylalkyl.
  • Heteroarylalkyl 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
  • C7-heteroarylalkyl would include pyridylmethyl, phenoxy, and N-pyrrolylmethoxy.
  • Alkylene refers to a divalent hydrocarbyl group; because it is divalent, it can link two other groups together. Typically it refers to -(CH 2 ) 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.
  • 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.
  • R 7 is alkyl
  • this alkyl may optionally be substituted by the remaining substituents listed as embodiments for R 7 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
  • any of these groups may be substituted with fluorine atoms at any or all of its available valences, for example.
  • Heteroform 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.
  • 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.
  • substituents for the alkyl and aryl groups in the compounds can also include a bond to a lignin or to a phenylpropanoid.
  • 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.
  • Halo as used herein includes fluoro, chloro, bromo, and iodo. Fluoro and chloro are often preferred.
  • amino refers to NH 2 , 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.
  • 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.
  • 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.
  • 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 ⁇ -keto ethers and ⁇ -hydroxy ethers.
  • 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
  • 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.
  • the ⁇ -glycerolaryl ether unit accounts for 45-50% of the polymeric linkages in lignin.
  • the ⁇ -glycerolaryl ether moiety is depicted among the model dimer compounds of lignin in Scheme 2.
  • 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 (H 2 ) as the reductant generates water (H 2 O) as the pendant hydroxyl (OH) groups of lignin are reduced, and requires hydrogen as an input that must be generated at significant energetic cost.
  • H 2 O molecular hydrogen
  • OH pendant hydroxyl
  • 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:
  • Ar 3 and Ar 4 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.
  • the disproportionation reaction may include the step of cleaving a carbon-oxygen double bond between C and O of an ⁇ -keto ether compound of Formula 1 :
  • R 1 , R 2 , and R 3 are each independently selected from the group consisting of hydrogen, alkyl, optionally substituted alkyl, aryl, optionally substituted aryl, optionally substituted heteroaryl; and
  • R 2 is not hydrogen
  • R 3 is not aryl or heteroaryl and R 1 is not H.
  • the structure of Formula 1 represents a lignin component or a phenylpropanoid moiety.
  • R 1 and R 2 are optionally substituted aryl.
  • R 1 and R 2 are optionally substituted aryl and R 3 is H.
  • the reaction may produce at least one product selected from the group consisting of:
  • C 1 X is C 1 O or C 1 HOH.
  • the reaction may produce at least one product selected from the group consisting of:
  • mixtures of compounds in varying ratios may also form depending on the reaction conditions.
  • the disproportionation reaction rearranges molecular structures without introducing new materials.
  • the carbon-oxygen bond cleavage of the ⁇ -keto ether compound may be preceded by an oxidative dehydrogenation step which may provide the hydrogen to reduce the carbon-oxygen bond:
  • Catalysts which catalyze the reduction of ⁇ -keto ether compounds may also catalyze the disproportionation of the ⁇ -hydroxy ether compound of Formula 4 by cleavage of the bond between C 2 and O 2 :
  • each R 1 , R 2 , and R 3 is independently selected from the group consisting of hydrogen, alkyl, optionally substituted alkyl, aryl, optionally substituted aryl, and optionally substituted heteroaryl;
  • R 2 is not hydrogen
  • R 3 is not aryl or heteroaryl and R 1 is not H.
  • the compound of Formula 5 represents a lignin component or a phenylpropanoid moiety.
  • R 1 and R 2 are optionally substituted aryl.
  • R 1 and R 2 are optionally substituted aryl and R 3 is H.
  • R 1 and R 2 are optionally substituted aryl groups of lignin and R 3 is a bond to another phenylpropanoid group of lignin.
  • the reaction may produce at least one product selected from the group consisting of:
  • C 1 X is C ⁇ O or C 1 HOH.
  • the reaction may produce at least one product selected from the group consisting of:
  • mixtures of compounds in varying ratios may also form depending on the reaction conditions.
  • the reactions occur via tandem dehydrogenation and carbon-oxygen bond cleavage reactions.
  • 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.
  • the disproportionation reaction may be a disproportionation-elimination reaction.
  • the cleaving of a compound of Formula 4 forms at least one product selected from the group consisting of:
  • C 1 X is C 1 O or C 1 HOH
  • each R 4 is independently selected from the group consisting of hydrogen, alkyl, optionally substituted alkyl, aryl, optionally substituted aryl, and optionally substituted heteroaryl.
  • an additional product is formed by a reaction other than the cleaving reaction, and wherein the additional product is of Formula 9:
  • R 1 , R 2 , and R 4 are as defined for Formulas 4 and 7-8.
  • Another disproportionation method of the present invention involves cleaving a carbon-carbon bond between C 1 and C 2 and/or C 2 and C 3 of a 1,3 diol compound of Formula 10:
  • each R 5 , R 6 , and R 7 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.
  • cleaving a carbon-carbon bond between C 1 and C 2 and/or C 2 and C 3 of a 1,3 diol compound of Formula 10 may produce at least one product selected from the group consisting of:
  • the cleaving forms the product of Formula 11 :
  • the cleaving forms the product of Formula 12:
  • the cleaving forms the product of Formula 13:
  • the cleaving forms the product of Formula 14:
  • mixtures of compounds of Formulas 11-14 may also form in varying ratios depending on the reaction conditions.
  • the reactions occur via tandem dehydrogenation and retro-aldol reactions.
  • any of the compounds of formulas 15-17 may also form in the product mixture:
  • mixtures of any combination of compounds 11-17 in varying ratios may form depending on the reaction conditions.
  • Another disproportionation method of the present invention involves cleaving a carbon-oxygen bond between C 2 and O 2 of the glycerol ⁇ -arylether compound of Formula 18:
  • Ar 1 and Ar 2 are optionally substituted aryl and each R 8 and R 9 is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted aryl, and optionally substituted heteroaryl.
  • the cleaving forms at least one product selected from the group consisting of:
  • the cleaving forms the product of Formula 19:
  • the cleaving forms the product of Formula 20:
  • the disproportionation reaction when R is hydrogen, the disproportionation reaction may be a disproportionation-elimination reaction.
  • the cleaving of a compound of Formula 18 forms at least one product selected from the group consisting of:
  • C 1 X is C 1 O or C 1 HOH.
  • compounds of Formula 21 and 22 may both be formed.
  • the cleaving forms the product of Formula 21:
  • the cleaving forms the product of Formula 22:
  • an additional product is formed by a reaction other than the cleaving reaction, and wherein the additional product is of Formula 23:
  • Another disproportionation method of the present invention involves cleaving a carbon-carbon bond between C 1 and C 2 and/or C 2 and C 3 of a glycerol ⁇ -arylether compound of Formula 18:
  • Ar 1 and Ar 2 are optionally substituted aryl groups and each R 8 and R 9 is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted aryl, and optionally substituted heteroaryl.
  • the cleaving forms at least one product selected from the group consisting of:
  • Another disproportionation method of the present invention involves cleaving a carbon-carbon bond between C 1 and C 2 and/or C 2 and C 3 of a glycerol ⁇ -arylether compound of Formula 18 and cleaving a carbon-oxygen bond between C 2 and O 2 of the glycerol ⁇ -arylether compound of Formula 18:
  • Ar 1 and Ar 2 are optionally substituted aryl groups and each R 8 and R 9 is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted aryl, and optionally substituted heteroaryl.
  • either carbon-oxygen or carbon-carbon bond cleaving may produce at least one product selected from the group consisting of:
  • the cleaving forms the product of Formula 20:
  • the cleaving occurs via tandem dehydrogenation and retro- aldol reactions and/or tandem dehydrogenation and carbon-oxygen bond cleavage reactions.
  • other products such as the compounds of Formula 20, and 30- 31, may form by ⁇ -hydroxyl elimination/hydrogenation of the ⁇ -keto ether compound:
  • mixtures of any combination of compounds 20-31 in varying ratios may form depending on the reaction conditions.
  • 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.
  • lignin is depolymerized by disproportionating a glycerol ⁇ - arylether unit of lignin.
  • the disproportionation includes the step of cleaving a carbon-oxygen bond between C 2 and O 2 of the glycerol ⁇ -arylether unit of lignin of Formula 32:
  • Ar 3 and Ar 4 are optionally substituted aryl groups of lignin and each R 10 and R 11 is independently selected from the group consisting of hydrogen or a bond to a
  • the cleaving forms the product of Formula 33:
  • Another disproportionation method of the present invention involves cleaving a carbon-carbon bond between C 1 and C 2 and/or C 2 and C 3 of a glycerol ⁇ -arylether unit of lignin of Formula 32:
  • Ar 3 and Ar 4 are optionally substituted aryl groups of lignin and each R 10 and R 11 is independently selected from the group consisting of hydrogen or a bond to a
  • Another disproportionation method of the present invention involves cleaving a carbon-carbon bond between C 1 and C 2 and/or C 2 and C 3 of the glycerol ⁇ -arylether unit of lignin of Formula 32 and cleaving a carbon-oxygen bond between C 2 and O 2 of the glycerol ⁇ - arylether unit of lignin of Formula 32:
  • Ar 3 and Ar 4 are optionally substituted aryl groups of lignin and each R 10 and R 11 is independently selected from the group consisting of hydrogen or a bond to a
  • the cleaving forms at least a product of Formula 33:
  • 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.
  • 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.
  • 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.
  • Disproportionation reactions may be catalyzed by organometallic catalysts optionally containing hydride and carbonyl ligands.
  • the catalysts are formed by combining a metal precursor complex with lignin under the reaction conditions.
  • 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.
  • the metal precursor-ligand complex may be formed in situ under the reaction conditions with lignin.
  • metal precursors include, but are not limited to, [Ru 3 (CO) 12 ], [ ⁇ Ru(cymene)Cl 2 ⁇ 2 ], [(PPh 3 ) 4 RuCl 2 ],
  • 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 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
  • 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.
  • the cleaving occurs via a disproportionation-elimination reaction.
  • the metal-based catalyst that cleaves via disproportionation- elimination is vanadium.
  • 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:
  • the catalyst is formed from a vanadium metal precursor and optionally a ligand under the reaction conditions.
  • the vanadium metal precursor is selected from the group consisting of [VOSO 4 -XH 2 O], [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:
  • 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.
  • 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.
  • 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.
  • the methods of the present invention also provide a method of depolymerizing lignin including:
  • 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.
  • the method is used to cleave ether linkages in lignin by breaking a carbon-oxygen bond.
  • the carbon-oxygen bond includes a diaryl, alkyl aryl, or benzyl alkyl, or benzyl aryl ether linkage.
  • the linkage being cleaved is a diaryl ether linkage, wherein each aryl group can be substituted or unsubstituted.
  • the cleaving is catalyzed by a metal-based catalyst including nickel.
  • the metal-based catalyst including nickel is formed from a nickel precursor and optionally a ligand under the reaction conditions.
  • the nickel precursor is selected from the group consisting of Ni(COD) 2 , Ni(acac) 2 , NiCl 2 , NiBr 2 , Ni(OAc) 2 , Ni(OH) 2 , NiCO 3 * 2 Ni(OH) 2 (nickel carbonate basic), and mixtures thereof.
  • the nickel precursor is Ni(COD) 2 or Ni(acac) 2 .
  • the ligand:nickel precursor ratio is approximately 2:1.
  • the ligand is a carbene ligand (e.g., N-heterocyclic carbene) or a phosphine ligand.
  • the phosphine ligand is a trialkylphosphine ligand such as, for example, tricyclohexylphosphine P(Cy 3 ) 3 .
  • 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.
  • the N-heterocyclic carbene ligand is selected from the group consisting of:
  • the N-heterocyclic carbene ligand is a five-membered, N-aryl-N-heterocyclic carbene.
  • the five-membered, N-aryl-N-heterocyclic carbene is selected from the group consisting of:
  • N-heterocyclic carbene ligand is selected from the group consisting of:
  • 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 80-250 0 C.
  • 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 t ⁇ -tert- butoxyalumnium hydride (LiAl(CyBu) 3 H), or mixtures thereof.
  • the silane is triethylsilane (Et 3 SiH) or te/t-butyldimethyl silane ( ⁇ BuMe 2 SiH).
  • the hydrogen atom source is dihydrogen.
  • the cleaving step in the catalytic reduction reaction is generally carried out in the presence of a base.
  • the base is selected from the group consisting of sodium te/t-butoxide (YBuONa), sodium te/t-pentoxide (YPentONa), sodium /so-propoxide
  • the base is selected from the group consisting of sodium te/t-butoxide
  • the cleaving has a higher selectivity for aryl-carbon-oxygen bonds over alkyl-carbon oxygen bonds in lignin.
  • 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.
  • the methods of the present invention may further include hydrodeoxygenating the reaction products.
  • the methods of the present invention may further include cracking and/or hydrogenating the reaction products.
  • a fuel is produced following the hydrodeoxygenating, cracking, and/or hydrogenating steps.
  • the disproportionation or reduction reactions may be carried out in organic solvents, supercritical CO 2 , or ionic liquids at temperatures ranging from 80 -
  • 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,
  • 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.
  • the disproportionation reactions may be carried out in the presence of hydrogen.
  • 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.
  • the reduction and/or disproportionation reactions may be carried out in the presence of hydrogen.
  • the cleaving is carried out in the presence of an acid.
  • 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
  • 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.
  • the diaryl ether is an optionally substituted diphenyl ether.
  • the nickel catalyst is formed from a nickel precursor and optionally a ligand under the reaction conditions.
  • the nickel precursor is selected from the group consisting of Ni(COD) 2 , Ni(acac) 2 , NiCl 2 , NiBr 2 , Ni(OAc) 2 , Ni(OH) 2 , NiCO 3 * 2 Ni(OH) 2 (nickel carbonate basic), and mixtures thereof.
  • the nickel precursor is Ni(COD) 2 or Ni(acac) 2 .
  • the ligand:nickel precursor ratio is approximately 2:1.
  • the ligand is a carbene ligand (e.g., N- heterocyclic carbene) or a phosphine ligand.
  • the phosphine ligand is a trialkylphosphine ligand such as, for example, tricyclohexylphosphine (P(Cy 3 ) 3 ).
  • 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.
  • the N-heterocyclic carbene ligand is selected from the group consisting of:
  • the N-heterocyclic carbene ligand is a five-membered N-aryl-N-heterocyclic carbene.
  • the five-membered N-aryl-N-heterocyclic carbene is selected from the group consisting of:
  • N-heterocyclic carbene ligand is selected from the group consisting of:
  • 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 80-250 0 C.
  • the present invention also provides compositions including lignin and a metal-based catalyst.
  • the metal-based catalyst is formed from a metal precursor and optionally a ligand under the reaction conditions.
  • the metal precursor includes a metal selected from the group consisting of ruthenium, rhodium, vanadium, nickel, and mixtures thereof.
  • the metal precursor is selected from the group consisting Of [Ru 3 (CO) 12 ], [ ⁇ Ru(cymene)Cl 2 ⁇ 2 ], [(PPh 3 ) 4 RuCl 2 ],
  • the metal precursor includes ruthenium and the ligand is a phosphine ligand.
  • the phosphine ligand is (9,9-dimethylxanthene-4,5-diyl)Z?/i'(diphenylphosphine).
  • the metal precursor includes vanadium and the ligand is a phenol-imine or bis-phenol-imine ligand.
  • the metal precursor includes nickel and the ligand is a phosphine or carbene ligand.
  • the carbene ligand is an N-heterocyclic carbene ligand.
  • the metal-based catalyst is a pre-formed catalyst.
  • 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.
  • 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.
  • acetophenone (0.22 mmol, 86%) as determined by 1 H 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).
  • 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 1 H NMR integration relative to an external capillary standard.
  • an ⁇ , ⁇ -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.
  • the ⁇ , ⁇ -unsaturated ketone reacts faster than phenoxyacetophenone to yield propiophenone at lower temperatures.
  • selectivity for producing the ⁇ , ⁇ - unsaturated ketone may result in higher yields of propiophenone.
  • a baseline reactivity profile for 2-(2-methoxyphenoxy)-l-phenylpropane-l,3-diol abbreviated as ⁇ P,G ⁇ -dimer
  • reaction shown above is selective for retroaldol processes that a) reduce the amount of elimination to form the requisite ⁇ , ⁇ -unsaturated ketone, and b) yields aldehydes that are better hydrogen acceptors. Thus, C-O bond cleavage is suppressed.
  • RA/E selectivity is controllable using acidic additives. Acidic additives would catalyze elimination to form the ⁇ , ⁇ -unsaturated ketone, and favor C-O bond cleavage if the system remains consistent with our theoretical models.
  • a second example is a ruthenium salt that liberates a strong acid upon reaction with the substrate.
  • 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.
  • Choice of ligand may also be used to control RA/E selectivity.
  • 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.
  • the ⁇ -retroaldol is the most desired process and retroaldol selectivity ( ⁇ / ⁇ ) should be controlled in favor of the ⁇ -retroaldol for cleavage of ⁇ -[O]-4'-glycerolaryl ethers.
  • 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 RuH 2 CO(PPh 3 ) 3 (11.4 mg/mL) and a stock solution of ruthenium catalyst
  • the two ruthenium sources were screened against seven phosphine ligands. Each ligand was loaded in a reaction vessel under N 2 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 N 2 and transferred to a pre -heated oil bath at 16O 0 C and was stirred at temperature for 24 hr. The reaction mixture was cooled to -3O 0 C and was freeze-dried. A brown solid was obtained.
  • 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 RuH 2 CO(PPh 3 ) 3 .
  • 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 CD 3 CN at 8O 0 C for 24 hours.
  • the reaction products were isolated from
  • DIBAL diisobutylaluminum hydride
  • 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
  • Ni(COD) 2 /SIPr-HCl were 44%, 80 and 87%, respectively.
  • N-heterocyclic carbene ligands were tested under the following conditions: 2- methoxynaphthalene (1 equiv.), nBu 3 SiH (2.5 equiv.), 5 mol % Of Ni(COD) 2 , 10 mol % of the
  • 6-SIPr HBr 0% (8%), 6-SIPr-HBF 4 : 19% (24%), 7-SIPr-HBr: 0% (6%), 7-SIPr-HBF 4 : 5% (5%), XyI-DIPP-HBr: 0% (0%), XyI-DIPP-HBF 4 : 0% (1%), SCAAC-HCl: 0% (0%), CAAC- HOTf: 0% (0%).
  • nBu 3 SiH was selected to screen bases under the following conditions: 2-MeONaph, nBu 3 SiH (2.5 equiv.), base (2.5 equiv), 5 mol % of Ni(COD) 2 , 10 mol % of SIPr ⁇ HBF 4 , in toluene (0.5 M solution of 2-MeONaph) at 120 0 C, 16 h. Yields of naphthalene (conversions of
  • Et 3 SiH and nBu 3 SiH 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-HBF 4 in toluene (0.5 M solution of 2-MeONaph) at 120 0 C for 16 hr:
  • 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.
  • 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
  • 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.
  • 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 ⁇ -position such as 1- methoxy-1-phenylpropane, were less reactive (41% at 46% conversion) than benzylic ethers lacking a substituent in the ⁇ -position (see Examples 48-50).
  • the reaction in Example 50 was repeated at a higher temperature (12O 0 C vs. 8O 0 C) to give 94% yield at 100% conversion.
  • the nickel(0)/SIPr catalyst was selective for reductive cleavage of C A ⁇ -OA ⁇ 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).
  • Di- ⁇ r/ ⁇ -anisyl ether can be reduced in the absence of the added ligand 10% NifCODV,
  • Biaryl ethers can be reduced faster than aryl and benzyl alkyl ones

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Abstract

Cette invention concerne des procédés et des compositions de catalyseurs pour la réduction catalytique des liaisons carbone-oxygène des substrats organiques et la dismutation catalytique des liaisons carbone-oxygène ou carbone-carbone des substrats organiques. Ces procédés et compositions de catalyseurs peuvent être utilisés pour dépolymériser la lignine. La dismutation des liaisons carbone-oxygène ou carbone-carbone des substrats organiques ou de la lignine est mise en œuvre par clivage d'une liaison carbone-oxygène ou d'une liaison carbone-carbone dans une réaction de dismutation catalytique. Les catalyseurs peuvent être formés à partir d'un précurseur métallique tel que le ruthénium ou le vanadium et d'un ligand bidenté. La réduction catalytique des liaisons carbone-oxygène des substrats organiques tels que la lignine est mise en œuvre par clivage d'une liaison carbone-oxygène en présence d'une source d'atomes d'hydrogène. Les fragments de lignine obtenus après la dépolymérisation par ces procédés peuvent, en outre, être convertis en carburants.
PCT/US2010/040832 2009-07-01 2010-07-01 Dismutation catalytique et réduction catalytique des liaisons carbone-carbone et carbone-oxygène de la lignine et autres substrats organiques Ceased WO2011003029A2 (fr)

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WO2014039002A1 (fr) * 2012-09-07 2014-03-13 Kat2Bizab Clivage d'une liaison β-o-4 dans des éthers
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