Frustrated Lewis pairs in ionic liquids – the first operando experiment!

Main group catalysis, largely centred around Lewis acidic boranes, is rapidly gaining attention in the area of frustrated Lewis pairs (FLPs). FLPs are a combination of a Lewis acid and a Lewis base (e.g. borane/phosphine), prevented from forming an adduct by steric hindrance. In a solvent, the acid and the base remain partly associated in a weakly bound encounter complex, in which the HOMO orbital of the base and the LUMO orbital of an acid remain free. This allows for transition metal-like reactivity of FLPs, including metal-free activation of H2 (Fig. 1) CO2, N2, and other small molecules. Our previous work (RB1710311) provided the first experimental evidence that these encounter complexes exist at a significant concentration that could be observed by neutron scattering: from all FLP components, 0.7% were found to be present as direct-contact pairs, and 5% as solvent-separated pairs. Subsequently, FLPs in ionic liquids (ILs) were studied (RB1710311, RB1810465). Advantages of ILs include non-volatility (a much more practical system when working with gases) and increased concentration of encounter complexes. Building on this, we plan to measure FLP/IL systems immobilised in pores, in preparation for operando hydrogenation studies (December 2024, RB2420443). Here, we apply for beamtime for a follow-up experiment, where hydrogen gas is passed through the sample, to observe - for the first time - in operando hydrogen splitting by FLPs in ionic liquids.