ISOMERIZATION OF METHYL FORMATE TO ACETIC-ACID CATALYZED BY THE RU(II)-SN(II) HETERONUCLEAR CLUSTER COMPLEX [RU(SNCL3)5(PPH3)]3-

The Ru(II)-Sn(II) 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 Ru(II) and Cl- from Sn(II)) to form the catalyst-reactant complex, where the relatively soft Ru(II) and the hard Sn(II) 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.