Theoretical Insights into the Regiodivergence in Ni-Catalyzed [2+2+2] Cycloaddition of Unsymmetric Diynes and CO2

To achieve the peak of carbon dioxide emission and carbon neutrality, utilizing it as a renewable carbon unit in organic synthesis presents an effective chemical solution for sustainable development. In this study, we report a theoretical investigation into the reaction mechanism and the regiodivergence of the Ni-catalyzed [2+2+2] cycloaddition of unsymmetric diynes and CO2 by using DFT calculations. The reaction mechanisms can be classified into two types: one is related to the oxidative coupling of the C equivalent to C moiety with CO2, and the other is related to the oxidative coupling of the two C equivalent to C moieties of diyne. In each type, two possible paths were proposed depending upon the positions of the substituents (H and silyl). Our calculation results indicate that the oxidative coupling of the C equivalent to C moiety and CO2 favors the positions of H-substituent, while the oxidative coupling of the two C equivalent to C moieties is beneficial for inserting CO2 at the positions of silyl-substituent. The regiodivergence is controlled by substrate chain-length and ligand in the different reaction mechanisms.