Complexes with sterically bulky allyl ligands: Insights into structure and bonding

The allyl anion [C₃H₅]- is often found in combination with other ligands in organometallic complexes. Compounds in which allyl groups are the only or principal type of ligand, however, are often coordinatively unsaturated and prone to decomposition. It is possible to increase the thermal and sometimes oxidative stability of such complexes by adding sterically bulky substituents (e.g., -SiMe₃) to the allyl group. Main group, transition metal, and f-element compounds constructed with bulky allyl ligands display a wide range of monomeric, oligomeric, and polymeric structures. Some of these complexes have no counterparts with unsubstituted allyl groups, and others are active polymerization catalysts. Research in this area has served to expand the range of structural types and bonding that can be incorporated into metal allyl chemistry.