Hydrogen activation by frustrated lewis pairs: insights from computational studies

Sterically encumbered Lewis acid-base pairs, the so-called frustrated Lewis pairs, can split dihydrogen heterolytically and act as transition metal free catalysts for the hydrogenation of unsaturated compounds. Here we review the results from our quantum chemical calculations aimed at the understanding of this remarkable class of reactions and we put them into the context of related works from other research groups. The thermodynamics of the H2 splitting reaction is discussed first; the role of acid-base properties, intramolecular cooperativity, and other factors is assessed, employing an energy partitioning scheme and also in the light of the latest experimental findings. The mechanism of hydrogen cleavage is then examined, and an overview about the applicability of our reactivity model involving synergistic electron transfers between H2 and preorganized Lewis acid/base centers is given. Finally, insights about catalytic cycles in FLP-mediated hydrogenations are summarized, pinpointing the diversity of the involved elementary steps and their possible sequences.