Computationally designed metal-free hydrogen activation site: reaching the reactivity of metal-ligand bifunctional hydrogenation catalysts.

In this study, a strategy to design a metal-free hydrogen activation site has been proposed. On the basis of our so-called sp(3) carbon bridged FLPs (Frustrated Lewis Pairs), we first hypothesized that a more reactive activation site should arrange the nitrogen lone pair and the boron vacant orbital to lie in the same plane face-to-face, because such orbital orientations can simultaneously enhance the interaction between the nitrogen lone pair and the H(2) sigma* antibonding orbital and the interaction between the boron vacant orbital and the H(2) sigma bonding electrons. To verify that such an active site is achievable, we then computationally designed molecules and studied their reactions with hydrogen. The energetic results show the designed molecules are indeed more reactive than the sp(3) carbon bridged FLPs. Some of the hydrogen activations reach kinetics and thermodynamics comparable with those of the hydrogen activations mediated by the well-known metal-ligand bifunctional hydrogenation catalysts. The designed molecules could be the targets for experimental synthesis. The pattern of the proposed active site can be based to design similar molecules for metal-free hydrogenations.