σ-Bond Metathesis: A 30-Year Retrospective

A review of σ-bond metathesis is presented using Watson's 1983 observation of degenerative methyl ligand exchange at metallocene compounds as a starting point. This review has two major parts. The first presents identifying features and reactivity characteristics of this pivotal mechanistic step for high oxidation state metals, which are given with some historical context, though not in historical order for clarity of discussion. The second part presents several selected examples of the exploits of this transformation with a particular focus on catalytic bond forming reactions.