Facile Hydrogenolysis Research Articles

Facile Hydrogenolysis of Sugars to 1,2-Glycols by Ru@PPh3/OPPh3 Confined Large-Pore Mesoporous Silica.

Tandem hydrogenation vis-à-vis hydrogenolysis of xylose to 1,2-glycols remains a major challenge. Although one-pot conversion of xylose to 1,2-glycols requires stringent conditions, a sustainable approach would be quite noteworthy. We have developed a microwave route for the one-pot conversion of pentose (C5) and hexose (C6) sugars into glycol and hexitol, without pressurized hydrogen reactors. A pronounced hydrogenolysis of sugars to glycols is observed by Ru single atom (SA) on triphenylphosphine/phosphine oxide-modified silica (Ru@SiP), in contrast to Ru SA on pristine (Ru@SiC) and 3-aminopropyl-modified silica (Ru@SiN). A promising "ligand effect" was observed through phosphine modification of silica that presents a 70% overall yield of all reduced sugars (xylitol + glycols) from a 99% conversion of xylose with Ru@SiP. A theoretical study by DFT depicts an electronic effect on Ru-SA by triphenylphosphine that promotes the catalytic hydrogenolysis of sugars under mild conditions. Hence, this research represents an important step for glycols from biomass-derived sources.

Catalytic Upgrading of n-Hexane and n-Octane for Light Hydrocarbons Production

Light hydrocarbon compounds are of great importance for direct usage as gaseous fuels or the production of petrochemicals. Therefore, their synthesis via catalytic upgrading of heavier hydrocarbons in the gasoline or diesel feedstock would be economically relevant. The current research developed a Mo2C/ZrO2 catalyst modified with Rh species for n-hexane and n-octane hydroconversion to light hydrocarbons (i.e. C1 to C4) at 450oC and 1 atm in a fixed-bed continuous flow reactor system. Both reactants produced similar conversions in the range of 18 to 20%, with more than 88% selectivity to the desired hydrocarbons. Mechanistically, the reaction was assumed to proceed via facile hydrogenolysis, involving the central and end C-C bonds. Overall, the catalyst could be considered industrial suitable but new parameters for improving catalytic conversion must be designed.

C2‐Symmetric Cinchona Alkaloid Derivatives: Versatile Catalysts for the Enantioselective C−C Bond Forming Conjugate Addition of Nucleophiles to Simple α,β‐Unsaturated Acyl Pyrazoles

AbstractA single C2‐symmetric squaramide catalyst system allows the facile addition of either malononitrile or benzyl nitroacetate to simple pyrazole‐based Michael acceptors with excellent enantiocontrol and at lower catalyst loadings than previously possible. The latter reactions are not diastereoselective, however facile hydrogenolysis leads to decarboxylation and formation of the formal adduct from the addition of nitromethane (a very recalcitrant nucleophile in this chemistry) with excellent yield and enantiocontrol.

Hydrosilane Synthesis by Catalytic Hydrogenolysis of Chlorosilanes and Silyl Triflates

Hydrogenolysis of the chlorosilanes and silyl triflates (triflate = trifluoromethanesulfonate, OTf-) Me3- nSiX1+ n (X = Cl, OTf; n = 0, 1) to hydrosilanes at mild conditions (4 bar of H2, room temperature) is reported using low loadings (1 mol %) of the bifunctional catalyst [Ru(H)2CO( HPNP iPr)] ( HPNP iPr = HN(CH2CH2P( iPr)2)2). Endergonic chlorosilane hydrogenolysis can be driven by chloride removal, e.g., with NaBArF4 [BArF4- = B(C6H3-3,5-(CF3)2)4-]. Alternatively, conversion to silyl triflates enables facile hydrogenolysis with NEt3 as the base, giving Me3SiH, Me2SiH2, and Me2SiHOTf, respectively, in high yields. An outer-sphere mechanism for silyl triflate hydrogenolysis is supported by density functional theory computations. These protocols provide key steps for synthesis of the valuable hydrochlorosilane Me2SiClH, which can also be directly obtained in yields of over 50% by hydrogenolysis of chlorosilane/silyl triflate mixtures.

Dihydrogen Addition in a Dinuclear Rare-Earth Metal Hydride Complex Supported by a Metalated TREN Ligand

The dinuclear lutetium dihydride dication supported by metalated tripodal ligands undergoes facile hydrogenolysis with H(2) to form a trihydride dication. Molecular orbital analysis shows that the LUMO is a bonding Lu···Lu orbital that is poised to activate dihydrogen.

A Palladium‐Catalyzed Multicascade Reaction: Facile Low‐Temperature Hydrogenolysis of Activated Nitriles and Related Functional Groups

AbstractThe facile hydrogenolysis of various nitriles, imines, and amines over Pd/C has been achieved by using straightforward and relatively mild conditions. Substrates that contain an aryl group adjacent to the nitrogen‐containing functionality were hydrogenolyzed most effectively. The stabilization of the proposed η2‐coordinated palladium intermediate by this group was partly responsible for this observation and is borne out by ab initio calculations.

Ammonia formation by metal–ligand cooperative hydrogenolysis of a nitrido ligand

Bioinspired hydrogenation of N(2) to ammonia at ambient conditions by stepwise nitrogen protonation/reduction with metal complexes in solution has experienced remarkable progress. In contrast, the highly desirable direct hydrogenation with H(2) remains difficult. In analogy to the heterogeneously catalysed Haber-Bosch process, such a reaction is conceivable via metal-centred N(2) splitting and unprecedented hydrogenolysis of the nitrido ligands to ammonia. We report the synthesis of a ruthenium(IV) nitrido complex. The high nucleophilicity of the nitrido ligand is demonstrated by unusual N-C coupling with π-acidic CO. Furthermore, the terminal nitrido ligand undergoes facile hydrogenolysis with H(2) at ambient conditions to produce ammonia in high yield. Kinetic and quantum chemical examinations of this reaction suggest cooperative behaviour of a phosphorus-nitrogen-phosphorus pincer ligand in rate-determining heterolytic hydrogen splitting.

Reactions of polycyclic alkylaromatics. 4. Hydrogenolysis mechanisms in 1-alkylpyrene pyrolysis

The pyrolyses of 1-methylpyrene and 1-ethylpyrene were conducted at 400, 425, and 450°C in constant-volume batch reactors for holding times up to 300 min. The major products from methylpyrene pyrolysis were pyrene and dimethylpyrene whereas the major products from ethylpyrene pyrolysis were pyrene and methylpyrene. These results show that the aryl−alkyl C−C bond in methyl- and ethylpyrene is susceptible to facile hydrogenolysis. The relative importance of different hydrogenolysis mechanisms was examined through the development of mechanistic models

ChemInform Abstract: Metallacarboranes in Catalysis. Part 8. Catalytic Hydrogenolysis of Alkenyl Acetates. Catalytic Alkene Isomerization and Hydrogenation Revisited.

AbstractThe facile hydrogenolysis of alkenyl acetates such as isopropenyl‐ and 1‐phenylvinyl‐acetates with rhodacarborane catalyst precursors such as (I) and its 2,1,7‐ and 2,1,12‐RhC2B9H11 analogues, to yield acetic acid and the corresponding alkenes is described by kinetic and deuterium‐labeling investigations.

Metallacarboranes in catalysis. 8. I: Catalytic hydrogenolysis of alkenyl acetates. II: Catalytic alkene isomerization and hydrogenation revisited

Part I of this study describes the facile hydrogenolysis (and deuteriolysis) of alkenyl acetates, such as isopropenyl acetate (D) and 1-phenylvinyl acetate (E), with rhodacarborane catalyst precursors to yield acetic acid and the corresponding alkene. The catalyst precursors employed were (closo-3,3-(PPh{sub 3}){sub 2}-3-H-3,1,2-RhC{sub 2}B{sub 9}H{sub 11}) (I), (closo-2,2-(PPh{sub 3}){sub 2}-2-H-2,1,7-RhC{sub 2}B{sub 9}H{sub 11}) (II), and (closo-2,2-(PPh{sub 3}){sub 2}-2-H-2,1,12-RhC{sub 2}B{sub 9}H{sub 11}) (III). The hydrogenolysis of alkenyl acetates D and E produced propene and styrene, respectively, along with acetic acid in essentially quantitative yields. Deuterium at Rh was demonstrated not to enter the hydrogenolysis reaction. These results suggest a reaction mechanism for hydrogenolysis that is based upon the relatively slow formation and decomposition of a very reactive rhodium(III) monohydride formed through the regioselective oxidative addition of Rh{sup 1} (in the exo-nido tautomer of the rhodacarborane) to terminal B-H bonds. This new information predicated part II of this study, which is devoted to a modification of previously advanced proposals for the mechanisms of alkene isomerization and hydrogenation with rhodacarborane precursors.

Mild hydrogenolysis process by catalytic transfer hydrogenation

A facile hydrogenolysis of allylic acetates was developed with the catalytic transfer hydrogenation using palladium hydroxide on carbon and cyclohexene.

Ready formation of phosphonate complexes of rhodium and iridium from [M(P(OMe 3) 5]Cl compounds (M = Rh, Ir). Differences between reactions of dihydrogen with [Mp(O)(OMe) 2(P(OMe) 3) 4] complexes (M = Co, Rh, Ir), including facile hydrogenolysis of a rhodiumphosphorus bond

The ease of formation of the phosphonate complexes [M(P(O)(OMe) 2(P(OMe) 3) 4] (M = Rh, Ir), from the pentakis-trimethylphosphite complexes [M(P(OMe) 3) 5]Cl is reported. Differences in the interaction of H 2 with the complexes [M′(P(O)(OMe) 2(P(OMe) 3) 4), (M′ = Co, Rh, Ir) are presented and discussed.

Lactams. IV. The Synthesis of Benzo [α] quinolizine Derivatives from Piperidine through 1-Substituted 2-Piperidones

The mercuric acetate-(ethylenedinitrilo) tetraacetic acid oxidation of aminoalcohol III furnished lactamalcohol V in 73% yield and its O-acetyl derivative (VI) as a minor product. Treatment of V with phosphoryl chloride gave tetrahydrobenzo [α] quinolizinium salt X in 87% yield, whereas hydrogenolysis of V in the presence of perchloric acid and ring-closure of the resulting lactam VIII afforded hexahydrobenzo [α] quinolizinium salt IX, which produced benzo [α] quinolizidine Ia on hydrogenation. When treated with perchlo-ric acid, lactamalcohol V yielded oxazolinium salt VIIa in a good yield. The facile hydrogenolysis of VIIa to VIII has suggested the possibility that the perchloric acid-accelerated, direct hydrogenolysis of V may proceed through VIIa. The starting aminoalcohol III was synthesized either by the sodium borohydride reduction of aminoketone II obtained from piperidine and 3, 4-dimethoxyphenacyl bromide or by reduction of quaternary salt IV from pyridine and 3, 4-dimethoxyphenacyl bromide.