Deeper Insight into the Factors Controlling H2 Activation by Geminal Aminoborane-Based Frustrated Lewis Pairs

H-2 activation mediated by geminal aminoboranebased frustrated Lewis pairs (FLPs; R2N-CH2-BR'(2)) has been computationally explored within the density functional theory framework. It is found that the activation barrier of this process as well as the geometry of the corresponding transition states strongly depend on the nature of the substituents directly attached either to the acidic or the basic centers of the FLPs. The physical factors controlling the whole activation path are quantitatively described in detail by means of the activation strain model of reactivity combined with the energy decomposition analysis method. This methodology suggests a highly orbital-controlled mechanism where the degree of charge transfer cooperativity between the most important donor-acceptor orbital interactions, namely LP(N)->sigma*(H-2) and sigma(H-2)-> p(pi)(B), along the reaction coordinate constitutes a suitable indicator of the reaction barrier.