Ni pincer complex catalytic hydroboration of CO2: a DFT study on the influence of borane reductants on selective reduction

It has been reported that either the boryl formate (HCOOBR2), bis(boryl)acetal (R2BOCH2OBR2), or methoxy borane (R2BOCH3) product of CO2 reduction is selectively afforded adopting the nickel (Ni) pincer catalyst by changing the properties of borane reductants. To obtain an insight into the influence of borane reductants on the selectivity of hydroboration of CO2 catalyzed by ((PCP)-P-tBu)NiH, a density functional theory (DFT) computational study is performed with three different boranes (HBcat (catecholborane), 9-BBN (9-borabicyclo [3.3.1] nonane), and HBpin (pinacolborane)). The detailed formation and conversion of four-electron product R2BOCH2OBR2 were considered for the first time, combining with the three sequential catalytic cycle mechanism, and the calculated results demonstrate that the distinctions of the electronic process in some key intermediates and transition states lead to the selectivity on products for different borane reductants.