Determination of the Mechanism and True Catalyst in CO₂ Hydroboration Catalyzed by the Low-Valent Magnesium(I) Dimer: A Computational Study

CO2 hydroboration is an important method of CO2 conversion. Developing low-cost and environmentally friendly metal catalysts that can facilitate valuable chemical transformations is of great significance. In the present study, the detailed reaction mechanisms of CO2 hydroboration catalyzed by low-valent Mg(I) dimers ([Mg(I)]2) and monomagnesium hydride [Mg]-H were investigated by DFT calculations. The work determined the detailed catalytic cycle of the bimetallic [Mg(I)]2-catalyzed CO2 hydroboration, confirming that [Mg(I)]2 is merely the precatalyst, and that complex A2, in which one HBpin is inserted into the carbonate [Mg(I)]2 complex, is the true catalyst. Although [Mg]-H can catalyze the CO2 hydroboration, it is not the true catalyst in the title reaction because the formation of [Mg]-H is strongly endothermic. CH3OBpin is the thermodynamic-controlled product and O(Bpin)2 is the kinetic-controlled product. Our results identify the true catalyst, offering a rational explanation for the experimental results of [Mg(I)]2-catalyzed CO2 hydroboration, which shed light on the small-molecule activation and expand the usage of the environment friendly main-group metal compounds.