A computational experiment to study hydrogenations of various unsaturated compounds catalyzed by a rationally designed metal-free catalyst

Abstract

Metal-free hydrogenation has been proposed to be a green alternative to the conventional hydrogenation mediated by precious transition metal complexes. Thanks to the discovery of FLP (frustrated Lewis pair) chemistry, the field has recently witnessed significant progress. Inspired by the FLP idea of synergically utilizing the catalytic effects of Lewis acid and base, we previously proposed a strategy to construct metal-free active sites for H₂ activation and designed a metal-free molecule (1) that shows high reactivity toward H₂. Encouraged by the recent experimental successes in applying the strategy, we have computationally explored if 1 can go further to serve as a catalyst to promote the hydrogenations of various unsaturated compounds examined by ethylene (CH₂CH₂ (4)), silyl enol ether (CH₂C(Me)OSiMe₃ (5)), imines (Me₂CNMe (6) and Ph(Me)CNMe (7)), and ketone (Ph(Me)CO (9)). The energetic results predicted at the M05-2X(IEFPCM, solvent = THF)/6-311++G** level indicate that these reactions have feasible kinetics and thermodynamics for experimental realization. The hydride transfer step follows the concerted mechanism, although the transfer process has asynchronous character for silyl enol ether (5) and imines (6 and 7). In addition, we have investigated the binding of CO₂ to 1 and the 1-mediated hydrogenation of CO₂.