Effect of strain and π-acidity on the catalytic efficiency of carbones in carbodiimide hydroboration.

Abstract

Density functional theory (DFT) calculations provide insights into how structural and electronic modifications around zerovalent carbon centers (carbones) affect their catalytic efficiency in the hydroboration of carbodiimides. Carbones selectively activate pinacolborane (HBpin) through Lewis acid-base adduct formation, with the subsequent hydride transfer to the carbodiimide as the turnover-determining step. Cyclic carbodiphosphoranes emerge as superior catalysts over their acyclic variants due to the preorganized structure of the former, which promotes efficient substrate activation and hydride transfer with minimal distortion, as revealed by distortion/interaction-activation strain analysis. Furthermore, kinetic hydricity calculations show that carbodiphosphoranes outperform carbodicarbenes in this context because the stability of the 1,2-addition intermediate formed in the latter renders them less effective as hydride-donors at room temperature. Overall, this study addresses gaps in our understanding of how structural variations affect the ability of carbones to activate substrates and alter the energetically preferred activation mechanism, underscoring the potential of carbones as an emerging class of organocatalysts.