Platinum Metals Rev., 1967, 11, (3), 93
Oxidation and Reduction by Transition Metal Complexes
A symposium entitled “Oxidation and Reduction”, organised jointly by the Chemical Society and the Royal Institute of Chemistry, was recently held in London as a part of the latter body’s Annual Conference. In the course of this symposium, Dr Bernard Shaw of Leeds University reviewed the application of transition metal complexes in oxidation and reduction reactions.
Dr Shaw explained that the ability of such complexes to act catalytically arises from the fact that the metal atom can assume various valencies and co-ordination numbers. There are large differences between the strength with which, for example, olefins are co-ordinated to metal atoms; this binding strength increases from NiII to PdII to PtII, but the reason for this is not well understood. By decreasing the metal’s valency, more electrons are made available for back-donation to the olefin, and a stronger bond results.
Optimum catalytic reactivity results when an olefin is neither too strongly nor too weakly bound to the metal atom: hence PdII complexes are most suitable for oxidation processes. Since PdII complexes are easily reduced, Rh complexes are more suitable for reductions, and the ready ability of RhI to be oxidised to RhIII is of great importance in these reactions.