Transition Metal Catalysis & Mechanism

Transition metals serve as active sites for a wide range of catalysis. About 1/3 of proteins are metalloproteins, and numerous organic syntheses nowadays require organometallic catalysts. In these reactions, the transition metal centers often determine the activity and selectivity of catalysis. Thus, characterizing the geometric and electronic structure of the metal center is a key to understanding catalytic mechanism and developing optimized catalysts. To define the mechanisms of transition-metal-based catalyses, we utilize various spectroscopic techniques and computation. While conventional techniques such as NMR and IR are useful to analyze organic substrate and product, we employ techniques that allow a direct probe on the transition metal centers. This way we determine catalyst-based reaction kinetics and characterize catalytic intermediates. Magnetic circular dichroism (MCD) spectroscopy collects differential absorption of left- and right-circularly polarized light in the presence of a strong magnetic field (up to 7 T). This condition allows metal-based electronic transitions, which are often forbidden or low resolution in the conventional electronic absorption spectroscopy, and magnetic properties such as exchange coupling and zero-field splitting parameters can be measured. Using this information, we can determine the coordination structure of the metal center in solution and also monitor its variation over the course of a catalytic reaction. We understand reactivity based on frontier molecular orbitals. Based on catalyst-based kinetics, key intermediates are time-isolated and their electronic and geometric structures are determined. Reaction coordinate that involves these intermediates is constructed using quantum computations. Frontier molecular orbital intera