Role of Dynamics and Spin-State Crossover in Metal-Hydride Hydrogen Atom Transfer (MHAT) and Electron Transfer in Transmetalation during Co–Ni Multimetallic Catalyzed Alkene Hydroarylation

Abstract Metal-hydride hydrogen atom transfer (MHAT) reactions involve hydrogen transfer from a transition-metal hydride to an alkene to generate a metal radical and carbon-centered radical pair. These radicals can then either collapse to a metal–alkyl intermediate or separate into solvent-separated radicals. Little is currently known about the factors that control the lifetime of MHAT-generated radical pairs and subsequent reaction pathway selectivity. Therefore, we used density functional theory calculations and ab initio molecular dynamics trajectories with explicit solvent to evaluate the Co-hydride (Co–H) MHAT reaction in the Co/Ni dual-catalyzed alkene hydroarylation transformation. The trajectories showed that ultrafast dynamic effects combined with singlet-to-triplet spin-state crossover determine whether there is a fast collapse to the Co-alkyl intermediate or a longer-lived solvent-caged radical pair intermediate. Calculations also demonstrated that the Co-alkyl intermediate generated from the MHAT reaction can interface with the Ni catalytic cycle through a combined electron-transfer/alkyl-group-transfer mechanism. Overall, these time-resolved mechanistic details provide insight into the Co–H MHAT reaction process and how Co catalysis is integrated with Ni catalysis.