Activation of Small Molecules by Readily Accessible Alkylborane-Based Frustrated Lewis Pairs

Abstract

Herein, we report that sterically encumbered (thio)imidazolones react with simple aliphatic boranes, such as 9-borabicyclo[3.3.1]nonane (H-B-9-BBN) or dicyclohexylborane (HBCy₂), at room temperature to form (thio)imidazolonate boranes,which function as intramolecular frustrated lewis pairs (FLPs). Although direct observation of hydrogen activation by these FLPs is not possible, alkene hydroboration occurs when they are reacted with styrene under hydrogen pressure, suggesting that hydrogen activation is kinetically feasible. In addition, these FLPs rapidly activate NH bonds, as demonstrated by the activation of ammonia and amines under mild conditions. They also cleave the CH bond of terminal alkynes. Density functional theory (DFT) calculations are used to investigate the thermodynamics and kinetics of hydrogen and ammonia activation by these FLPs.