Fluorinated NHC ligands - predisposing metal complexes as better catalysts.

One of the key goals of modern chemistry is to develop greener processes, ie chemical transformations that operate with high efficiency using environmentally benign reagents in as few steps as possible. One such system is catalytic transfer hydrogenation, in which addition of hydrogen to organic substrates is achieved using cheap, readily available, easily handled alternatives to high pressure, flammable hydrogen gas. High efficiency is achieved through the use of catalysts based on metal centres that are supported by ligands with very specific size and electronic properties.
Recent work within our group and others has shown that for one particular type of ligands - N-heterocyclic carbenes (NHCs) the introduction of fluorine (the most electronegative element in the period table) results in catalysts capable of delivering more rapid conversion than is possible for those based on ligands without fluorine. Based on initial work, the pattern of fluorine substitution appears to be strongly correlated with the observed catalytic activity.
The objectives of this project are to understand the extent to which the enhanced performance of the catalysts containing these ligands is linked to electronic factors, the steric demand (size) of the ligands or interactions between the ligand and the metal centre. The approach that will be taken will involve: Synthesis of a series of new fluorine-containing NHC ligand systems with well-defined fluorine substitution patterns; Assessment of the steric and electronic properties of these NHCs; Generation of catalysts, not just for transfer hydrogenation, but for C-C bond forming reactions, and an investigation of the efficacy of each catalyst as a function of the ligand properties, based on spectroscopic probes and structural analysis of the systems generated.
Taken together this should provide predictive understanding that can be used to generate a priori novel ligand/catalyst systems that are predisposed to maximize the catalytic performance of the catalysts and so generate new catalytic systems capable of highly efficient, green transformations.