The chemistry of functionalised N-heterocyclic carbenes.

This tutorial review presents the synthesis, chemistry and applications of functionalised N-heterocyclic carbenes NHC and their transition metal complexes. Functionalised NHC comprise those carrying a phosphino-, amino-, imino- or oxygen-containing functionality on the imidazole sidechain. Main applications have been the modification of catalysts and their immobilisation by fixation on a polymeric support using the functional group. Whereas the functionalisation of the NHC has not improved their performance in catalysis, new developments have occurred in the use of imidazole-containing biomolecules such as L-histidine or caffeine as precursors for NHC.