This project in the Inorganic, Bioinorganic and Organometallic Chemistry Program is concerned with the way in which imposing steric constraint on some of the groups bound to a metal changes the properties of the metal in its interactions with other groups. The goal of the work is to use steric constraints to fine-tune the chemical and spectroscopic properties of the metal, and, for example, thereby to provide better control and selectivity in metal-based catalysis. Metal alkoxides and amides will be synthesized utilizing ligand frameworks which constrain the positions of the donor atoms as they bind to the metal. For example, the ligand may have the shape of a tripod, with the donor atoms at the ends of the legs, or it may be quadridentate with the donor atoms positioned as though they were at the ends of the four legs of a table. High local symmetry will exist around the metal atom in these complexes, resulting in a reduction of ligand-to-metal pi bonding compared to complexes of acyclic ligands. The resultant reduction in negative charge on the metal is expected to increase the metal-ligand bonding of ligands other than the donor atoms of the constrained ligand, and also to augment M-M multiple bonding in the dinuclear LMML species, where L is the constrained multidentate ligand. The magnitude of these effects will be studied spectroscopically (heteronuclear NMR and IR), structurally (via X-ray crystallography) and chemically (by studying the tendencies of complexes to undergo coordination sphere expansion, small molecule insertions, alkane metatheses and cluster-forming reactions).
