Electron-transfer chain catalysis for the cis-to-trans isomeric conversion of cis-[ReCl(CO)(Ph2PCH2CH2PPh2)2]

Abstract

The low temperature reaction of cis-[ReCl(NCC₆H₄Cl-4)(dppe)₂] (dppe = Ph₂PCH₂CH₂PPh₂) with CO afforded cis-[ReCl(CO)(dppe)₂] whose ³¹P-{¹H} NMR spectrum has been analysed as an ABCD spin system. The latter complex in CH₂Cl₂ slowly converts into the corresponding trans isomer (which is oxidised at a higher oxidation potential and whose single crystal X-ray diffraction analysis is also reported) and this isomerisation is promoted by oxidation following an electron-transfer chain (ETC) catalytic process, with low net current flow. This behaviour has been investigated by digital simulation of the cyclic voltammograms at different temperatures and scan rates, which allowed an estimate of the rate constant and the activation parameters for the isomerisation. The relative values of the oxidation potential of the cis and trans isomers are interpreted on the basis of a metal d_π orbital splitting model, the ratio of the isomerisation equilibrium constants (for the pairs of oxidised and parent species) is estimated and the relevance of kinetic factors in the anodically induced isomerisation (which is favoured by the π-electron acceptance ability of the CO ligand) is shown.