Abstract by James Coombs
Chemistry and Biochemistry
Mechanistic Study for Co–Zr Phosphinoamide Catalyzed Kumada Coupling Reaction
Early–Late Heterodinuclear transition metal complexes with a direct metal–metal bond offer the possibility of increased reactivity compared to analogous mononuclear catalysts. Heterodinuclear Co–Zr complexes with bridging phosphinamido ligands catalyze C–C bond formation between alkyl halides and alkyl Grignard reagents. The Co-only analogues exhibited ineffective catalysis thereby demonstrating the importance of the Zr–Co interaction. Density Functional Theory (DFT) calculations revealed that the Co–Zr pairing facilitated effective catalysis at several key mechanistic steps. First, it enables 2 electron reduction of the pre-catalytic species, facilitating a lower barrier for electron transfer. Second, the Lewis acidic nature of Zr stabilizes the rate limiting reductive elimination transition state. Finally, the two metal centers of the catalyst allow phosphine to dissociate from cobalt in a hemilabile manner. This helps to facilitate optimal electron density on Cobalt and accelerates catalysis.