Frustrated Lewis Pairs (FLPs) integrate Lewis acidic and basic sites (that can either accept or donate a pair of electrons), which then act in partnership to activate small molecules. They are often based on abundant elements and are notable as metal-free catalysts for hydrogen activation, a characteristic that can be extended to other small molecules, such as nitrogen. As hydrogen activation catalysts, they offer an inexpensive alternative to platinum-group metal catalysts, avoiding the risk of heavy metal pollution.
In work published in Chemical Communications, chemists from Queen's University Belfast teamed up with members of the ISIS Disordered Materials Group to study the liquid structure of a FLP solution using the instrument SANDALS. Their findings agree with predictions made via density functional theory structural modelling, enabling the determination of catalytically active sites and offering the first direct observational evidence for the formation of weakly associated Lewis acid-base 'encounter complexes' in solution.
The researchers then carried out the first study of FLPs in ionic liquids, showing that the formation of an encounter complex could be enhanced by use of an ionic liquid solvent. Significantly higher concentrations of long-lived associated FLPs were reported which, it is anticipated, will enhance catalytic activity compared to conventional solvents.
Related publication: “Frustrated Lewis pairs in ionic liquids and molecular solvents – a neutron scattering and NMR study of encounter complexes" Chem. Commun., 2018,54, 8689 DOI: 10.1039/c8cc03794a
Authors: Lucy C. Brown (Queen's University of Belfast), James M. Hogg (Queen's University of Belfast), Mark Gilmore (Queen's University of Belfast), Leila Moura (Queen's University of Belfast), Silvia Imberti (ISIS), Sabrina Gärtner (ISIS), H. Q. Nimal Gunaratne (Queen's University of Belfast), Ruairi J. O'Donnell (Queen's University of Belfast), Nancy Artioli (Queen's University of Belfast), John D. Holbrey (Queen's University of Belfast) and Małgorzata Swadźba-Kwaśny (Queen's University of Belfast).