A computational mechanistic study of the cleavage of sulfur-sulfur bond by Frustrated Lewis Pairs

DFT calculations were performed to gain insight into the detailed mechanism of S[sbnd]S bond cleavage in disulfides (i.e., iPrSSiPr) by a frustrated Lewis pair (FLP) (tBu)₃P/B(C₆F₅)₃. The calculations revealed that the reaction initiates from the generation of weak complex B(C₆F₅)₃/iPrSSiPr (IM1) between iPrSSiPr and Lewis acid B(C₆F₅)₃. Subsequently, the Lewis base (tBu)₃P can activates the S[sbnd]S bond leading to the final cleavage of S[sbnd]S bond to give the product [(tBu)₃P(SiPr)][(iPrS)B(C₆F₅)₃] (PR). The computed kinetics and thermodynamics suggest that the reaction can take place reversibly under ambient conditions, which accounts well for the experimental observations. Furthermore, the mechanism is compared with that of the H[sbnd]H bond cleavages by same FLP. Contrast to the H[sbnd]H bond cleavage, a weak donor–acceptor complex IM1 between iPrSSiPr and B(C₆F₅)₃ could be located before S[sbnd]S bond cleavage. Nonetheless, the complete S[sbnd]S bond cleavage essentially is still due to the synergistic catalytic Lewis acid/base effects of FLP (tBu)₃P/B(C₆F₅)₃.