ChemInform Abstract: Transition-Metal η2-Vinyl Complexes

Abstract

Abstract Transition metal η 2 -vinyl complexes, L n M(η 2 -CRCR 2 ), adopt structures in which both alkenyl carbons are bound to the metal. The M(CRCR 2 ) unit is not planar in these 1-metallocyclopropene complexes. Instead, the CR 2 entity is twisted by ca. 90° away from planarity with the three-membered ring formed by M, C α , and C β . The ring carbons of η 2 -vinyl ligands are bound asymmetrically to the metal with one short metal–carbon bond and one long metal–carbon bond. These geometrical features reflect double bond character between C α and the metal at the expense of the carbon–carbon double bond in the classic organic vinyl moiety. Coordination of both carbons of the four-electron donating η 2 -vinyl ligand increases the electron count at the metal by two electrons relative to an η 1 -bound vinyl ligand. This review summarizes synthetic methods which yield η 2 -vinyl complexes, describes bonding and structural characteristics of η 2 -vinyl ligands, tabulates NMR spectroscopic signatures of η 2 -vinyl ligands, and outlines reactions of this growing class of compounds.