Theoretical study on the possibility of using frustrated lewis pairs as bifunctional metal-free dehydrogenation catalysts of ammonia-borane.

Density functional theory calculations have been carried out to study the possibility of using "frustrated Lewis pairs" (FLPs) as bifunctional metal-free dehydrogenation catalysts of ammonia-borane, NH(3)BH(3) (AB), according to the following points: (1) some FLPs react with H(2) at low temperature and the hydrogenated products release H(2) at high temperature; (2) some FLPs hydrogenate imines by taking the protic (N-bound) and hydridic (B-bound) H atoms of AB. In this work, the N/B pair (N-PMTN-CH(2)C(6)H(4)B(C(6)F(5))(2)) is chosen to explore the possibility that FLPs release H(2) from AB. Two steps are involved in the proposed mechanism: first, AB is dehydrogenated by the N/B pair to form the NH/BH compound and NH(2)BH(2) at low temperature, and then H(2) is released from the NH/BH compound at 110 degrees C and the N/B pair regenerates. Several competitive reaction channels have been considered. The calculational results show that the dehydrogenation of AB by the N/B pair has the lowest free-energy barrier. On the basis of the experimental N/B pair, a new dehydrogenation catalyst of AB has been designed, which can release H(2) from AB under milder conditions than the former. This work may be helpful for the experimental chemists to broaden the application of FLPs and to design new dehydrogenation catalysts of AB.