Influence of the Lewis Acid/Base Pairs on the Reactivity of Geminal E-CH2 -E' Frustrated Lewis Pairs.

The influence of the nature of the acid/base pairs on the reactivity of geminal frustrated Lewis pairs (FLPs) (Me2 E-CH2 -E'Ph2 ) has been computationally explored within the density functional theory framework. To this end, the dihydrogen-activation reaction, one of the most representative processes in the chemistry of FLPs, has been selected. It is found that the activation barrier of this transformation as well as the geometry of the corresponding transition states strongly depend on the nature of the E/E' atoms (E=Group 15 element, E'=Group 13 element) in the sense that lower barriers are associated with earlier transition states. Our calculations identify the geminal N/Al FLP as the most active system for the activation of dihydrogen. Moreover, the barrier height can be further reduced by replacing the phenyl group attached to the acidic atom by C6 F5 or 3,5-(CF3 )2 C6 H3 (Fxyl) groups. The physical factors controlling the computed reactivity trends are quantitatively described in detail by means of the activation strain model of reactivity combined with the energy decomposition analysis method.