Novel [Ru(polypyridine)(CO)2Cl2] and [Ru(polypyridine)2(CO)Cl]+-type complexes: Characterizing the effects of introducing azopyridyl ligands by electrochemical, spectroscopic and crystallographic measurements

The reaction of ruthenium carbonyl polymer ([Ru(CO)2Cl2]n) with azopyridyl compounds (2,2′-azobispyridine; apy or 2-phenylazopyridine; pap) generated new complexes, [Ru(azo)(CO)2Cl2] (azo = apy, pap). [Ru(apy)(CO)2Cl2] underwent photodecarbonylation to give a chloro-bridged dimer complex, whereas the corresponding pap complex ([Ru(pap)(CO)2Cl2]) was not converted to a dimer. The reactions of the chloro-bridged dimer containing the bpy ligand (bpy = 2,2′-bipyridine) with either apy or pap resulted in the formation of mixed polypyridyl complexes, [Ru(azo)(bpy)(CO)Cl]+. The novel complexes containing azo ligands were characterized by various spectroscopic measurements including the determination of X-ray crystallographic structures. Both [Ru(azo)(CO)2Cl2] complexes have two CO groups in a cis position to each other and two chlorides in a trans position. The azo groups are situated cis to the CO ligand in [Ru(azo)(bpy)(CO)Cl]+. All complexes have azo N–N bond lengths of 1.26–1.29 Å. The complexes exhibited azo-based two-electron reduction processes in electrochemical measurements. The effects of introducing azopyridyl ligands to the ruthenium carbonyl complexes were examined by ligand-based redox potentials, stretching frequencies and force constants of CO groups and bond parameters around Ru–CO moieties.