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

The low temperature reaction of cis-[ReCl(NCC6H4Cl-4)(dppe)(2)] (dppe = Ph2PCH2CH2PPh2) with CO afforded cis-[ReCl(CO)(dppe)(2)] whose P-31-{H-1} 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(pi) 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 ill the anodically induced isomerisation (which is favoured by the pi-electron acceptance ability of the CO ligand) is shown.