Synthesis and characterization of ruthenium(II)-nitrile complexes with bisamide-tpa ligands (tpa = tris(2-pyridylmethyl)amine)

Ruthenium(II)-acetonitrile complexes having pentadentate tris(2-pyridylmethyl)amine (tpa) derivatives with coordinated amide CO groups were prepared and characterized by various spectroscopic methods, electrochemical measurements, and DFT calculations. The acetonitrile ligand was indicated to tightly bind to the ruthenium(II) center in an η¹-N fashion. The Mulliken charge distribution, obtained by a calculation, indicated that the ruthenium(II)-nitrile bond is more covalent than other coordination bonds of the tpa moiety. The redox potentials of Ru centers and the chemical shifts of methyl groups of the acetonitrile ligands exhibited a linear relationship, indicating that electron density of the Ru center controls that of the acetonitrile ligand. Those complexes showed fluxional behavior in CD ₃CN solutions to exhibit one mode of thermal motion; it also altered the symmetry of the complexes.