The ternary system consisting of [RuCl2(η6-benzene)]2, N-tosylethylenediamine or ethanolamine, and KOH (Ru:amine:KOH = 1:1:2 molar ratio) catalyzes reversible hydrogen transfer between alcohols and carbonyl compounds. The use of chiral amine auxiliaries effects asymmetric transformation. The theoretical calculations using methanol/formaldehyde transformation as the model indicates the operation of a novel metal−ligand bifunctional catalysis, which is contrary to currently accepted putative pathways. The results reveal that:  (1) KOH is necessary for the generation of a formal 16-electron Ru complex, Ru(NHCH2CH2Y)(η6-benzene) (Y = O or NH) (catalyst), from an 18-electron Ru chloride, RuCl(NH2CH2CH2Y)(η6-benzene) (precatalyst), by a Dcb elimination of HCl, and not for increasing alkoxide concentration; (2) Ru alkoxides do not intervene in transfer hydrogenation; (3) the Ru alkoxide, even if formed, serves merely as a reservoir of the 16-electron catalyst; (4) the key 18-electron Ru hydride, RuH(NH2CH2CH2Y)(...

The Metal−Ligand Bifunctional Catalysis: A Theoretical Study on the Ruthenium(II)-Catalyzed Hydrogen Transfer between Alcohols and Carbonyl Compounds

Iridium compounds in catalysis

THE use of carbon dioxide as a starting material for the synthesis of organic compounds has long been a goal for synthetic chemists. The hydogenation of carbon dioxide to formic acid, methanol and other organic substances is particularly attractive, but has remained difficult. This route to formic acid has been described recently, based on the use of organometallic rhodium catalysts in dimethyl sulphoxideII and aqueous2 solvents. We report here the efficient production of formic acid in a supercritical mixture of carbon dioxide and hydrogen containing a catalytic ruthenium() phosphine complex. The use of a supercritical phase, in which hydrogen is highly miscible, leads to a very high initial rate of reaction up to 1,400 moles of formic acid per mole of catalyst per hour. The same reaction under identical conditions but in liquid organic solvents is much slower. Our results suggest that supercritical fluids represent a promising medium for homogeneous catalysis.

Homogeneous catalytic hydrogenation of supercritical carbon dioxide

Intramolecular aromatic substitution in transition metal complexes

A comprehensive overview on homogeneous catalytic hydrogenation of carboxylic acids and its derivatives as well as carbonic acid derivatives with transition metal-based molecular catalysts is described. Despite the tremendous potential in the hydrogenation of these less electrophilic carbonyl compounds using molecular hydrogen in synthetic organic chemistry, their reduction still relies mostly on the stoichiometric use of metal hydride reagents, such as LiAlH4, NaBH4, and their derivatives. For the past decade, a significant and rapid progress in particularly ester hydrogenation has been achieved by utilization of conceptually new bifunctional molecular catalysts originating from the metal–ligand cooperation effects. The bifunctional-catalyst-promoted hydrogenation using molecular hydrogen is now realized to be a practical tool in synthetic organic chemistry in both academia and industry. The industrial outlook for the present hydrogenation is bright because of its operational simplicity, scope, economic ...

Catalytic Reductive Transformations of Carboxylic and Carbonic Acid Derivatives Using Molecular Hydrogen

The complex hydridochlorotris(triphenylphosphine)ruthenium(II) as a benzene solvate, RuClH(PPh3)3,C6H6, has been obtained by the interaction of the dichloride, RuCl2(PPh3)3, with molecular hydrogen at ambient temperature pressure in the presence of a base such as triethylamine; other preparative methods are described. The corresponding bromide, RuBrH(PPh3)3,C6H6, has been prepared. From the chloride by interaction with norbornadiene and 2,2′-bipyridyl, the complexes RuClH(C7H8)(PPh3)2 and [RuClH(bipyr)(PPh3)2]2 respectively have been obtained; the complex RuH2(CO)(PPh3)3 has also been prepared.The complex RuClH(PPh3)3 is the most active catalyst yet discovered for the homogeneous hydrogenation of alk-1-enes in benzene or toluene solution. The interaction is highly specific and rates for other types of alkene are slower by a factor of at least 2 × 103. The inherent difficulties of the system however preclude detailed kinetic study and it is shown that slow poisoning of the catalyst occurs under hydrogenation conditions.N.m.r. studies of the hydrido-complex and its deuteride have allowed hydrogen atom exchange studies to be made. Isomerisation of alkenes is studied. The slow exchange between molecular hydrogen and the α-proton of a phenyl group on the phosphine is demonstrated.

G. Wilkinson

Papers

The preparation and reactions of hydridochlorotris(triphenylphosphine)ruthenium(II) including homogeneous catalytic hydrogenation of alk-1-enes