The coordinative flexibility of rigid phenanthroline-analogous di(NHC)-ligands

In 2010 we have introduced a new N-N connected 1,4-dicarbene ligand named 'vegi' based on an imidazo-anellated pyridazine (Kunz et al., 2010) [1]. Although the tricyclic ligand resembles 1,10-phenanthroline, the dicarbene ligand turned out to be much more flexible. It can serve as a chelating as well as a bridging ligand. In addition, the electronic properties (strongly electron-donating) are distinct from 1,10-phenanthroline or 2,2′-bipyridine. This review comprises the synthesis, electronic properties, the coordination chemistry as well as the reactivity of this remarkable ligand and its complexes.