Publication
Frustrated Lewis pair (FLP) chemistry has gained significant attention in the past decade as the main group hydrogenation catalysts. The majority of the reported FLP catalysts utilize either boron-containing Lewis acids (LAs) or alternatively isolobal and iso(valence)electronic tetrylium analogues for hydrogenation. Recently, a new family of intramolecular FLPs R3E-CH2-PR'(2) (E = Si, Ge, Sn) featuring neutral sp(3) tetrel atoms as LA centers were reported for activation of a range of small molecules under ambient conditions. They have been shown to perform heterolytic cleavage of the hydrogen molecule, a key step in hydrogenation catalysis. In this work, we computationally examine their ability to perform catalytic hydrogenation using CO2, carbonyls, and imines as substrates. Our mechanistic analyses reveal that the transfer of the activated hydrogens from FLP to the unsaturated bond follows a concerted yet asynchronous pathway. The sequence of proton/hydride transfer is largely influenced by the donor/acceptor centers of the FLP as well as the corresponding unsaturated functional group. We find that by varying the donor centers in these FLPs, the dihydrogen release barrier can be tuned, and nitrogen-bearing FLPs have a lower dihydrogen release barrier than those with phosphorus. The reactivity trends are rationalized within the framework of the activation strain model. Finally, two major side reactions pertinent to the performance of the hydrogenation cycle, such as dimer formation of the catalyst and decomposition through reductive elimination, are also investigated in detail.