Why Two Metals Are Better Than One for Heterodinuclear Cobalt–Zirconium-Catalyzed Kumada Coupling

Abstract

Heterodinuclear transition metal complexes with a direct metal–metal interaction offer the potential of unique reactivity compared with mononuclear catalysts. Heterodinuclear Co–Zr complexes with phosphinoamide ligands bridging Co and Zr metal centers are effective precatalysts for Kumada C–C bond coupling reactions between alkyl halides and alkyl Grignards. In contrast, the analogous mononuclear Co tris(phosphinoamine) complex without Zr provides very inefficient catalysis. Here we describe density functional theory calculations that reveal the mechanistic and reactivity impact of the Co–Zr metal–metal interaction and phosphinoamide ligands on alkyl halide–alkyl Grignard Kumada coupling catalysis. The Co–Zr interaction enables two-electron reduction of the precatalyst to form an active catalyst, which then promotes a low-energy electron-transfer alkyl halide oxidative addition mechanism. The Co–Zr interaction and the phosphinoamide ligands bridging the metal centers provide a dialkyl intermediate with a ...