Density Functional Theory Study of the Mechanism of Ni-Catalyzed Carboxylation of Aryl C(sp 2 )-S Bonds with CO 2 : Computational Evidence for the Multifaceted Role of Additive Zn

The mechanism of Ni-catalyzed carboxylation of aryl C(sp )-S bonds with CO was studied for the first time by density functional theory calculations. We first proposed another possible reaction pathway in which CO insertion occurs prior to reduction. Then, we performed calculations on all proposed reaction pathways, and our calculation results show that the pathway in which reduction occurs prior to CO insertion is the favored pathway for this reaction. Additionally, our calculations disclose that additive Zn acts in multifaceted roles. (1) Zn acts as a reductant to reduce the Ni and Ni intermediates. (2) The simultaneously formed Zn Br can undergo transmetalation with Ni or Ni intermediates to produce an aryl reservoir by forming arylzinc species. (3) Zn Br can also coordinate to the CO to lower the energy barrier of the CO insertion step. Moreover, the calculation results suggest that CO insertion is the rate-determining step of the reaction, and CO is easier to insert into the Ni -Ph bond rather than into the Ni -Ph bond. These calculation results can improve our understanding of the mechanism of the carboxylation process and the multifaceted roles of metal additive Zn and provide theoretical guidance for improving the carboxylation reaction.