Metal‐Carbon and Metal‐Metal Multiple Bonds as Ligands in Transition‐Metal Chemistry: The Isolobal Connection

A new domain for synthesis has developed following recognition that the metal‐carbon and metal‐metal multiple bonds present in certain low‐valent transition‐metal complexes are reactive centers for the attachment of metal‐ligand fragments. The products contain metal‐metal bonds which may be homo‐or heteronuclear in nature. If bridging carbon atoms are present, leading to dimetallacyclopropane or ‐cyclopropene structures, the organic groups (alkylidene or alkylidyne) have an extensive chemistry. The isolobal connection, developed by Hoffmann et al., relating the frontier orbitals of organic groups with those of metal‐ligand fragments, has been crucial in guiding the preparative work.