Free Radicals in Organometallic Chemistry

Abstract

Publisher Summary The chapter focuses on the classification of the area of free radicals in organometallic chemistry, discusses in very general terms the experimental methods as well as the relevant literature. The chapter divides organometallic chemistry into the following classification: (i) organometallic paramagnetic compounds, and (ii) organometallic reactions, in which paramagnetic transient species, usually organic free radicals, are implicated in the reaction pathway. Class (i) may be divided into compounds in which the unpaired electron is localized principally on the metal M (I); or remote from the metal (11). The former belong to a wider group, the metal-centered radicals, encompassing not only, for example, the organometallic SiMe3, but also the inorganic SiC13. Corresponding paramagnetic transition metal complexes (I) are rarely named as radicals because they are often stable, and the term “radical” has traditionally had the connotation of a species of low kinetic stability. Class (ii) is conveniently separated into free radical reactions involving (a) substitution at the metal center, SH2, or bimolecular homolytic substitutions at M. Electron spin resonance spectroscopy has made a considerable impact on the study of organometallic free radical chemistry. Evidence for the participation of a free radical in an organometallic reaction, using one or more of the above methods, may still leave two major questions. The first is whether the radical pathway is a principal or a side reaction. The second is whether the mechanism of the reaction is a chain or a nonchain process.