Mechanistic Insights into Ni-Catalyzed Difunctionalization of Alkenes Using Organoboronic Acids and Organic Halides: Understanding Remarkable Substrate-Dependent Regioselectivity

Transition metal catalyzed difunctionalization reactions of alkenes using simple chemical feedstocks are powerful strategies for the synthesis of valuable compounds and materials. Density functional theory (DFT) calculations reported in the present paper reveal detailed mechanistic insight and the origin of the substrate-dependent regioselectivity in the titled reactions. Computational results demonstrate that these reactions are generally composed of several steps including oxidative addition, carbonickelation, H-shift/transmetalation, and reductive elimination. Among these steps, the key one responsible for the regioselectivity depends upon the organic halides utilized. Natural bond orbital (NBO) analysis, energy decomposition analysis (EDA), and buried volume calculations indicate that steric effect is a common contributor of the regioselectivity, while other energy terms, such as electrostatic interaction, have significant and even dominant effects on the specific regioselectivity. Furthermore, the key reason for successfully suppressing Heck and/or Suzuki products lies in that the formation of Heck and/or Suzuki products is thermodynamically less favorable. Comparison of the total reaction barriers of the rate-limiting step (combined transmetalation and reductive elimination processes) demonstrates that the electron-induced effect of various organic halides significantly causes the different bonding ability between Ni atom and allyl moiety. As a result, transmetalation and reductive elimination processes made distinct contributions to reducing the total activation free energy of the rate-limiting step of various difunctionalized reactions.