Tri-Molecular Homolytic Combination Mechanism for Carbon–Halogen Bond Activation in Ni/Co Synergistic Catalysis

Abstract

Elucidating the various mechanisms of carbon–halogen (C–X, where X = Cl, Br, I) bond activation is of great significance, as the functionalization of C–X bonds is widely utilized in synthesizing high-value compounds. In classical single-metal catalytic systems, the σ*(C–X) orbital of the C–X bond plays a crucial role; however, this approach limits the diversity of applicable substrates. To overcome this limitation, a dual-metal cooperative catalysis strategy offers a promising pathway to leverage the σ(C–X) orbital for the activation of C–X bonds. In this study, density functional theory (DFT) calculations were employed to comprehensively compare the activation of C–X bonds in aryl halides, benzyl halides, and alkyl halides using either Ni catalysis or Ni/Co cooperative catalysis. The findings reveal that C–X bonds in aryl halides and benzyl halides can be activated through distinct mechanisms: double-electron oxidative addition and single-electron transfer, respectively, when a single transition metal (Ni) is employed. This activation process involves electron transfer to the antibonding orbital σ*(C–X). Interestingly, the homolytic cleavage of C–X bonds in alkyl halides through Ni/Co bimetallic synergistic catalysis proceeds via a termolecular elementary reaction, described as a trimolecular homolytic combination (C_H3) that utilizes the bonding orbital σ(C–X). This process results in the formation of Co–C and Ni–Br bonds. Moreover, the C_H3 reaction can be further enhanced by adjusting the bond energies of the resulting metal–carbon and metal–halogen bonds, allowing for greater control over the reaction pathway.