Ligating properties of anionic Fischer-type carbene complexes, [(CO)₅MC(X)Y]⁻

With the simplest of anionic Fischer-type carbene complexes acting as ligands, Cp₂Zr(Cl){OCMe}M(CO)₅ compounds (M = Cr or W) promote α-olefin oligomerization and polymerization in the presence of MAO. Attaching an N-heterocyclic ring to the carbene carbon atom in similar precursors, allows a variety of hard metal ions and fragments to be captured by external bidentate coordination. The outcome of the attachment of a phosphorus or sulfur functionality to an α-carbon of an O-anionic carbene is formation of a bidentate ligand and then internal four-membered carbene–heteroatom chelate formation. α-Deprotonated carbene complexes are also precursors for remote, one-N, six-membered carbene complexes of various metals whereas α-C-, α-N- or α-O-deprotonated as well as β-deprotonated Fischer-type carbene complexes display unique synthon properties towards Ph₃PAu⁺ and partake in unusual ensuing coordination of liberated group 6 metal carbonyl moieties to form dinuclear products.