The methylene bridge: a challenge to synthetic, mechanistic and structural organometallic chemistry

Abstract

Within the past few years transition metal complexes containing bridging alkylidene functions (Fig. 1) have stimulated wide-spread interest in organometallic chemistry, due at least in part to the apparent significance of methylene intermediates in the metal-surface catalyzed reduction of carbon monoxide. Following the preparation of the first unsubstituted µ-methylene complex in 1974, we have continued our investigations into the synthesis, structures, and reactivity of dimetallacyclopropane-type compounds. An overview of these results will be presented. The most versatile synthetic method for the construction of µ-alkylidene systems is carbene transfer from easily accessible, highly reactive diazoalkane precursors to either mononuclear, coordinatively unsaturated substrates, or complexes with metal-metal multiple bonds. The structural features and the reactivity pattern of the resulting dimetallacyclopropanes are governed by both steric and electronic effects arising from the nature of the metals, the methylene bridges as well as the peripheral ligands. Emphasis will also be placed on the spectroscopic characteristics and the bonding situation of simple methylene bridges. © 1982 IUPAC