Hydroboration reduction of CO 2 by HBpin catalyzed by ambiphilic boron centers, a doubly reduced 9,10-dimethyl-9,10-dihydro-9,10diboraanthracene [DBA-Me 2 ] 2− (A0) and its metal salts ( M A0) reported by Wagner, M. et al. (Angew. Chem., Int. Ed. 2018, 57, 16491−16495), has been explored by density functional theory (DFT) calculations. Unexpectedly, the cycloadduct (A1 a ) from the barrier-free activation of CO 2 and bridging across the two B atoms of A0 may serve as a highly active catalyst to boost the CO 2 hydroboration reduction through a single active-site mechanism. The catalytic hydroboration of CO 2 by dianion A0 and its metal salts M n -[DBA-Me 2 ] (n = 2 for M = Li + , Na + , K + ; and n = 1 for M = Mg 2+ , Ca 2+ ) follows the double active-site mechanism, where the diboron site acts as the active center. Generally, the CO 2 hydroboration reduction by HBpin may take place through three independent and cascade subcycles, leading to primary HCOOBpin, secondary HCHO, and reduction product CH 3 OBpin, respectively. Counter cations and THF solvent molecules remarkably influence the activation of HBpin and H 2 by A0, but the relative energetics of the overall hydroboration process mediated by A1 a is less changed. The present results show that the doubly reduced arylborane and its CO 2 adduct, as well as their metal salts are quite promising for the hydroboration reduction of CO 2 .