Sumio Shinoda

One-step formation of methyl acetate with methanol used as the sole source and catalysis by RuII–SnII cluster complexes

RuII–SnII cluster complexes [Ru(SnCl3)5L]3–(L = MeCN, PPh3) have been found to be effective for the catalytic conversion of methanol to methyl acetate in a single step.

Isomerization of methyl formate to acetic acid catalysed by the Ru(II)-Sn(II) heteronuclear cluster complex [Ru(SnCl3)5(PPh3)]3−

Abstract The RuII-SnII heteronuclear cluster complex [Ru(SnCl3)5(PPh3)]3− has been found to be catalytically active for the isomerization of methyl formate to acetic acid. The initial reaction rate showed a first order dependence on the catalyst concentration, and showed a saturation curve for the reactant concentration in its high-concentration region. Extra addition of PPh3 and Cl− ion considerably retarded the reaction with almost linear relationships between the reciprocal of initial rates and the concentration of additives. A rate equation derived from these kinetic data indicates the presence of a pre-equilibrium of dual ligand dissociation from the catalyst (PPh3 from RuII and Cl− from SnII) to form the catalyst-reactant complex, where the relatively soft RuII and the hard SnII interact simultaneously with the soft CO group and hard OCH3 group of methyl formate, respectively. It is postulated that such a multi-center interaction in this cluster system facilitates the overall rearrangement of CH3 group (from O atom to C atom) to realize the isomerization of methyl formate to acetic acid without CO atmosphere or iodide promoter, but with an activation energy comparable to that for Rh or Ni catalyst which requires both of them.

Photocatalytic dehydrogenation of 2-propanol with carbonyl(halogeno)phosphine-rhodium complexes

Abstract Photocatalytic dehydrogenation of 2-propanol, yielding acetone and dihydrogen, proceeded at high turnover frequencies with carbonyl(halogeno) phosphine-rhodium complexes RhX(CO)(PR 3 ) 2 (X = halogen and PR 3 = t-phosphine) under excitation conditions for the metal-to-ligand charge transfer. The three-coordinate species RhX(PR 3 ) 2 generated by photodissociation of the CO ligand was responsible for the catalytic cycle, irrespective of the kinds of ligands. The importance of both electronic and steric factors was demonstrated for the phosphine ligand.

Transition metal homogeneous catalysis for liquidphase dehydrogenation of methanol

Abstract Transition metal homogeneous catalysts active for liquid-phase dehydrogenation of methanol to yield formaldehyde and dihydrogen under refluxing conditions have been found, in addition to those active only under photoirradiation. From the mixture of [Ru 2 (OAc) 4 Cl] and PR 3 dissolved in methanol, the reactive complex of [Ru(OAc)Cl(PPh 3 ) 3 ] or [Ru(OAc)Cl(PEtPh 2 ) 3 ] was isolated and characterized. The addition of acetic acid enhanced the initial rate, suggesting the proton-hydride reaction scheme. The catalyst complex, [Ru(OAc)Cl(PEtPh 2 ) 3 ], was deactivated gradually, with the bidendate OAc ligand being displaced with H and CO. The mechanism of the C—H cleavage of a methoxy ligand to give HCHO and an intermediate hydride complex, occurring on these cis -disposed sites, and the physico-chemical properties of metal complexes appropriate to methanol dehydrogenation are discussed.

Dehydrogenation of methanol in the liquid phase with a homogeneous ruthenium complex catalyst

Catalytic dehydrogenation of methanol occurs in solution by use of a homogeneous ruthenium complex,[Ru2(OAc)4Cl]–t-phosphine, or mononuclear ruthenium(II) complexes, which can be isolated from the reaction solution as catalysts.

Photoenhanced catalytic dehydrogenation of propan-2-ol with homogeneous rhodium–tin complexes

The effect of photoirradiation was investigated for the catalytic dehydrogenation of propan-2-ol with homogeneous rhodium–tin complexes. A large reduction of activation energy from 117 to 11 kJ mol–1 was observed. The wavelength dependence of quantum efficiency showed that it exceeded unity in the u.v. region with an appropriate catalyst composition. A mechanism is proposed, in which the generation of co-ordinatively unsaturated catalytically active species by the photocleavage of the Rh–Sn co-ordination bond is assumed. Photocatalysis in endothermic reactions is discussed from the viewpoint of solar energy storage.

Tin-119 Fourier-transform nuclear magnetic resonance study of rhodium–tin complexes formed in aqueous hydrochloric acid solutions of RhCl3 and SnCl2

Rhodium–tin complexes, formed in aqueous hydrochloric acid solutions of RhCl3 and SnCl2, have been investigated by 119Sn Fourier-transform n.m.r. spectroscopy. Satellite peaks due to the 117Sn isotope revealed fast intramolecular scrambling of the ligands. The redox process between rhodium(III) and tin(II) species to form a rhodium(I) complex with five tin(II) ligands was demonstrated at a molar ratio of [Sn] : [Rh]= 6 : 1. Nuclear magnetic resonance properties of the rhodium(I) complex and of a series of [Rh(SnCl3)nCl6–n]3–(n= 1–5) complexes are determined and discussed.

Mechanism of 2-propanol dehydrogenation catalyzed by tin(II)-coordinated iridium(III) complexes

Abstract Catalytic dehydrogenation of 2-propanol was carried out with trans-[IrClH(SnCl3)4]3− as well as with trans-[IrCl2(SnCl3)4]3− under refluxing conditions. It was revealed kinetically that one of the SnCl3− ligands was required to predissociate. Deuterium isotope effects indicate that the process of elimination of the methine hydrogen of 2-propanol is rate-determining.

Photo-enhanced production of hydrogen by liquid-phase catalytic dehydrogenation of propan-2-ol with rhodium–tin chloride complexes

Photo-irradiation of a homogeneous solution in propan-2-ol of a rhodium–tin chloride catalyst markedly enhanced the endothermic reaction rate to produce acetone and hydrogen, an energy conversion efficiency as large as 23% being attained.

Catalytic reaction of methanol with a series of ruthenium(II) complexes and the mechanism of the formation of acetic acid from methanol alone

The catalytic abilities of a series of ruthenium(II) complexes containing zero, one and two SnCl3– ligands, [RuCl2{P(OMe)3}4]1, [RuCl(SnCl3){P(OMe)3}4]2 and [Ru(SnCl3)2{P(OMe)3}3]3, have been compared in the reaction of methanol to form acetic acid (and/or methyl acetate due to esterification), as well as their reactions with the possible intermediates (formaldehyde, methyl formate) in the overall reaction. It was found that the formation of acetic acid from methanol occurred only with 3, which also converted paraformaldehyde or methyl formate into acetic acid. Complex 1 showed only a catalytic activity for the Tischenko-type dimerization (2HCHO → HCO2Me), and 2 exhibited an intermediate character, being able to catalyse the two reactions (2HCHO → HCO2Me, HCO2Me → MeCO2H) but unable to react with methanol. Based on kinetic results for the reaction of methanol with 3, a possible reaction pathway is proposed where methyl formate and acetic acid are formed from formaldehyde competitively sharing a common reaction path. For the isomerization of methyl formate as a substrate a separate reaction path is suggested, where the RuII–SnII bimetallic centre of 2 and 3 converts the co-ordinated HCO2Me into a five-membered acetate bridge.