New Opportunities in Metal-Organic Framework Catalysis: From Bifunctional to Frustrated Lewis Pairs Catalysis.

This article highlights novel prospects for metal-organic frameworks (MOFs) in heterogeneous catalysis as having frustrated Lewis acid-base pairs (FLPs) or as bifunctional acid-base solid catalysts able to activate molecular hydrogen. Starting from the extensive application MOFs as Lewis acid and Lewis base catalysts, this article uses catalytic hydrogenation to briefly summarize the efforts made to heterogenize boron and amine in MOFs to mimic molecular FLP systems. The core of this concept is based on recent findings which demonstrate the ability of two commonly used MOFs, namely UiO-66 and MIL-101, to catalyze the selective hydrogenation of polar double X=Y bonds at moderate H pressures below 10 bar. The influence of electron-donating, the withdrawal of substituents on the linker, and the aniline poisoning effect highlight the significance of Lewis acid sites, while density-functional theory calculations indicate the heterolytic H-H bond cleavage at the MOF metal oxo clusters. It is expected that this new perspective on MOFs as solid FLP systems will spur further research to explore and define the potential of dual sites in the catalytic activation of small molecules.