Computational Investigation of the Mechanism of FLP Catalyzed H 2 Activation and Lewis Base Assisted Proton Transfer

Density functional calculations have been performed to elucidate the mechanism of formation of N ‐phenylbenzylamine ( Am ) from alkylation of aniline ( An ) with benzaldehyde ( Bz ), with the intermediacy of the imine, N ‐benzylideneaniline ( Im ), catalyzed by the triaryl borane ( BAr 3 ), B(2,6‐Cl 2 C 6 H 3 )( p ‐HC 6 F 4 ) 2 , and utilizing H 2 as the reductant. Our computational investigation reveals that H 2 activation by BAr 3 / LB ( LB =Lewis Base; An , Im , THF or Bz ) frustrated Lewis pairs (FLPs) proceeds through a stepwise mechanism consisting of initial H 2 capture followed by heterolytic H−H cleavage, via a 3c–2e H 2 coordinated borane species. H 2 activation subsequently leads to a H 2 dissociated ion pair, overcoming energy barriers (31 kcal/mol at M06‐2X/6‐311++G(d,p)) accessible at the experimental temperature (100 °C). Consequently, the iminium hydridoborate ion pair, [ BAr 3 ‐H] − [ Im ‐H] + , undergoes hydride transfer from boron (−BH) to the imine carbon (−C=N−) and develops the targeted amine. Furthermore, we also identify the crucial role of an unbound aniline and imine which actively participates in proton shuttle mechanism from a coordinated aniline to −C=O of benzaldehyde to generate the desired imine, along with the release of water.