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 2 )-S bonds with CO 2 was studied for the first time by density functional theory calculations. We first proposed another possible reaction pathway in which CO 2 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 2 insertion is the favored pathway for this reaction. Additionally, our calculations disclose that additive Zn 0 acts in multifaceted roles. (1) Zn 0 acts as a reductant to reduce the Ni I and Ni II intermediates. (2) The simultaneously formed Zn II Br 2 can undergo transmetalation with Ni I or Ni II intermediates to produce an aryl reservoir by forming arylzinc species. (3) Zn II Br 2 can also coordinate to the CO 2 to lower the energy barrier of the CO 2 insertion step. Moreover, the calculation results suggest that CO 2 insertion is the rate-determining step of the reaction, and CO 2 is easier to insert into the Ni I -Ph bond rather than into the Ni II -Ph bond. These calculation results can improve our understanding of the mechanism of the carboxylation process and the multifaceted roles of metal additive Zn 0 and provide theoretical guidance for improving the carboxylation reaction.