N-Heterocyclic carbene ligands bearing redox-active and non-innocent moieties in combination with transition metals

Abstract

Many biochemical transformations for small molecules functionalization depend on the temporal delivery of multiple protons and electrons. For this purpose, Nature elegantly combines transition metals with redox-active and non-innocent cofactors. In a biomimetic spirit, we report on the synthesis and coordination chemistry of an N-heterocyclic carbenes ligands flanked with either a quionone or a pyridinone moiety. The carbenes were coordinated to a various transition metals. The complexes with NHC bearing quinone moiety were characterized by cyclic voltammetry, which suggested that redox events occur both on the naphthoquinone and on the metal for the iridium and ruthenium complexes. We have obtained several crystal structures that gave us structural insight on the coordination properties and geometry of the resulting complexes. Thanks to the X-ray analysis, we were able to confirm that the imidazolium salt bearing pyridinol moiety, looses its proton upon coordination and forms complexes with the metal in its pyridinone form. The obtained results allowed us to suggest the most suitable synthesis of imidazolium salts bearing a quionone or a pyridinol moiety. We were also able to identify the best method of coordination of these compounds to the transition metals. In the end we can say that this thesis comprises some guidelines for the synthesis of the transition metal complexes with the new group of NHCs ligands.