Small molecules (CO₂, iPrNCO, and iPrNCNiPr) activation by the metallomimetics (-Hydrido) diborane anion: A DFT investigation on mechanism and chemoselectivity controlling

Main-group metallomimetics provide a new way to replace transition metal complexes to activate inert small molecules under mild conditions. In this work, the activation mechanisms of CO2, iPrNCO, and iPrNCNiPr by (mu-Hydrido) diborane anion ([1H]-) have been investigated by density functional theory (DFT) calculations. Two different activation sites, B-B versus B-H bond of [1H]-, are investigated and compared. The results show that these inert molecules can be activated by [1H]- through cycloadditions under mild conditions. The reactions with iPrNCO and iPrNCNiPr are dynamic and thermodynamic controlling, the obtained products are related not only to the energy barrier but also to the stability of the products. Moreover, the competition for B-B/B-H bond site activation is directly related to the steric effect of small molecules. CO2, which is without steric hindrance, can only be activated by the B-B bond, whereas iPrNCNiPr can only be activated by the B-H bond due to the large steric effect. The medium iPrNCO can be activated not only by the B-B bond but also by the B-H bond. Our study provides theoretical explanations for the reaction activity and chemoselectivity controlling of the title reaction, and displays the potential applications for compounds containing boron-boron bonds and inert small molecule activation.