Studies of homolytic organometallic reactions

Abstract

The author's work in the field of homolytic reactions of Main Group organometallic compounds is reviewed. The autoxidation of organometallic compounds, RM, gives the peroxides, ROOM, as the principal products. The mechanism involves a radical chain reaction similar to that of the autoxidation of a hydrocarbon. R · + O 2 → ROO · ROO · + MR → ROOM + R · The key step, in which a radical brings about a bimolecular homolytic substitution ( S H2) at a metal centre, occurs with a wide variety of radicals (e.g. RO ·, RS ·, R 2CO T) and metals (e.g. Mg, Zn, Cd, B, Al, P, Sb, Bi). X · + MR → XM + R · The displaced radicals can be monitored by NMR spectroscopy, and the rate constants for many of these processes have been measured. The influence of steric and electronic factors can be observed which are often not apparent in the more familiar S H2 processes at hydrogen centres. Cyclopentadienyl derivatives of some metals (particularly Li, Hg, Sn, and Pb) undergo unimolecular photolysis by ultraviolet light. ▪ This enables the electronic effect of substituents, including organometallic substituents, on the π-electronic system of the cyclopentadienyl ring to be determined, and it also makes it possible to observe how the properties of the metal-centred radicals depend on the nature of the ligands about the metal.