The role of [2 + 2] cycloaddition-type reactions in catalysis. Activation of H—H, C—H and CC bonds by metal complexes

Abstract

It is argued that direct [2 + 2] cycloadditions and cycloreversions involving MtC and CC species and quasi-metallacyclobutanes are the key steps in olefin metathesis. This theoretical concept is then extended in a novel fashion to describe the mechanisms of many other important reactions in homogeneous and heterogeneous catalysis, and especially the activation of CC, H—H and C—H bonds by metal–alkyl complexes where the metal ion is electron deficient and the alkyl ligand assumes ‘carbenoid’ character.