Controllable Reactivity Tuned by the Cooperativity in B/P and B/N Intermolecular Frustrated Lewis Pairs

Frustrated Lewis pairs (FLPs) are able to heterolytically split hydrogen through the centers of Lewis acid (LA) and Lewis base (LB). In this study, seven typical B/N or B/P intermolecular FLPs composed of LA/LB with different acidity/basicity were selected and designed, where FLPs composed of soft strong LA and hard moderate LB appear to offer best activity and reversibility in hydrogenation. It has been demonstrated that the cooperativity between LA and LB determines the catalytic performance in hydrogen activation. There are two different mechanisms in hydrogenation of FLPs including direct synergetic pathway and single-electron transfer pathway. For the synergetic mechanism, there are four-step pathways in hydrogenation dominated by the acidity of the FLPs, while the reversible dehydrogenation is triggered by the isomerization of LB of the FLPs. But for FLPs composed of very weak LA or LB, accelerating single-electron transfer is an effective method to enhance the reactivity. These results are helpful in designing and synthesizing FLPs with better catalysis efficiency in the field of hydrogen storage or asymmetric hydrogenation.