Ruthenium Complexes Bearing Unsymmetric CNC′ Pincer Ligands: Molecular Structures and Electronic Properties

Homoleptic ruthenium complexes [Ru­(Ln)2]2+ bearing unsymmetric pyridine-based bis N-heterocyclic carbene (NHC) pincer ligands are synthesized and structurally characterized. These complexes feature the coexistence of a five-membered and a six-membered ruthenacycle within the same ligand framework, allowing an ideally octahedral CNHC–Ru–NPy bite angle close to 90°. In the solid state, impressive 3MLCT lifetimes of microsecond regime were detected in all of the complexes, of which [Ru­(L4)2]2+, featuring four benzimidazol-2-ylidene donors, exhibited the longest values. Electronic properties of all of the ruthenium complexes are investigated by cyclic voltammetry and spectroscopic techniques. Density functional theory results were used to support the experimental observations.