Platinum Complexes with Carbonyl, Isocyanide, and Carbene Ligands

Abstract

The literature relating to the synthesis, characterization, and properties of both mononuclear and polynuclear platinum complexes with carbonyl, isocyanide, and carbene ligands over the period 1995–2004 is reviewed. Carbonyl complexes of all types are normally synthesized via the direct reaction of carbon monoxide with a platinum precursor. Infrared spectroscopic data are best interpreted in terms of a σ-donation from the carbonyl ligand together with varying degrees of π-backbonding to the carbonyl ligand; X-ray data on bond lengths provide support for this bonding model. The carbonyl ligand is widely used in platinum complexes of all oxidation states, and is commonly found in both homo- and heteronuclear cluster complexes. The isocyanide ligand proves to be a versatile ligand in platinum complexes, and such complexes are normally synthesized via the direct reaction of an isocyanide ligand with a platinum precursor. Isocyanide complexes of platinum in all its common oxidation states have been characterized. Besides behaving as a spectator ligand, isocyanide ligands are often attacked by nucleophiles to give carbene complexes. Increasingly, however, carbene complexes are now being synthesized via the reaction of imidazoles or imidazolium salts with platinum salts in the presence of bases. Heterocycle-stabilized carbene ligands offer advantages over conventional phosphine ligands in that they are stronger σ-donors and weaker π-acceptors.