Unraveling the Role of Silyl and Silane in Si-Ni Catalysts for Hydrogenation

Transition-metal complexes with Si-M bonds are important catalysts for hydrosilylation and hydrogenation reactions. However, the function of the ligated silicon atom in the organosilicon metal catalysts remains unknown. Herein, we unravel the intriguing role of silyl and silane types of active modes in the Si-Ni complex-catalyzed selective hydrogenation of alkyne. Comprehensive density functional theory calculations were performed to investigate the nickel hydride insertion, silicon hydride migration, H-2 metathesis, and H-2 oxidative addition mechanisms. The results suggest that the silyl and silane types of active species display distinct catalytic properties in the hydrogenation reaction. During the hydrogenation of alkyne, Ni-H insertion heavily relies on the highly active nickel hydride in the silyl-nickel intermediate. Conversely, in the hydrogenation of stilbene, the driving force is the oxidation of the Ni(0) center in the silane-nickel intermediate. The revealed roles of silicon as silyl and silane during the catalysis well explained the E/Z stereoselectivity and chemoselectivity between the olefin product and the alkane product for the Si-Ni-catalyzed hydrogenation of alkyne. Furthermore, we explored the structure-activity relationship of bifunctional sites that incorporate group IVA elements (C, Si, Ge, and Sn). Hydrogenation of both alkynes and olefins can be accomplished via analogous silyl- and silane-metal transformations. Our theoretical study provides valuable insights into the mechanism and role of silicon in Si-Ni-catalyzed hydrogenation and would be helpful for future catalyst design with ligands containing group IVA elements.