Neutral η1-carbon ligands: Beyond carbon monoxide

Abstract

The Green formalism proposes a natural typology of the metal-carbon ligands. Among the neutral η1 representatives satisfying the octet rule for the carbon atom in the free state, three types are distinguished depending on the hybridization state (or connectivity) of the coordinating carbon atom. Each type corresponds to a well identified class of ligands exhibiting remarkable stability as compared to "anionic" versions: the ylide-type ligands and associated carbodiphosphoranes (sp 3), the N-heterocyclic carbenes (NHCs) and other stabilized carbenes (sp 2), and the cumulenylidenes with an even number of consecutive digonal carbon atoms stabilized by either heteroatomic or simple π-conjugated substituents (sp). © 2010 Springer-Verlag Berlin Heidelberg.