Gold catalyzed hydrogenations of small imines and nitrites: enhanced reactivity of Au surface toward H2 via collaboration with a Lewis base

Clean gold surface is inactive toward H-2, however, computations, aided by experiments, reveal that gold surface could serve as a Lewis acid coupling with Lewis bases (e.g. imine and nitrite) to construct effective frustrated Lewis pairs (FLPs) to activate H-2 and subsequently to achieve hydrogenation of small imines and nitrites. The Lewis base-coupled Au FLPs avoid tight adsorption of Lewis bases to gold surface via repulsion between nitrogen tone pair and the filled d-band electrons of the gold surface. This is different from the normal FLPs that use stericalty demanding groups or a molecular scaffold to prevent formation of stable Lewis acid-base complexes. The enhanced reactivity of the gold surface toward H2 is due to the synergetic catalytic effects of Lewis acid (Au surface) and the coupled Lewis base (imine or nitrite), which is supported by projected density of states (PDOS) analyses. Among Cu, Ag and Au surfaces, Au surface exhibits such reactivity most significantly, because Au is much more electronegative than Cu and Ag. The study enriches the FLP chemistry by adding a new type (heterogeneous) of FLPs and reveals a new reaction mode for gold surface.