Synthesis, structure, and redox and catalytic properties of a new family of ruthenium complexes containing the tridentate bpea ligand

We have prepared a new family of ruthenium complexes containing the bpea ligand (where bpea stands for N,N-bis(2-pyridyl)ethylamine), with general formula [Ru(bpea)(bpy)(X)]n+ (2, X = Cl-; 3, X = H2O; 4, X = OH-), and the trisaqua complex [Ru(bpea)(H2O)3]2+, 6. The complexes have been characterized through elemental analyses, UV-vis and 1H NMR spectroscopy, and electrochemical studies. For complex 3, the X-ray diffraction structure has also been solved. The compound belongs to the monoclinic P21/m space group, with Z = 2, a = 7.9298(6) Å, b = 18.0226(19) Å, c = 10.6911(8) Å, and β = 107.549(8)°. The Ru metal center has a distorted octahedral geometry, with the O atom of the aquo ligand placed in a trans position with regard to the aliphatic N atom of the bpea ligand so that the molecule possesses a symmetry plane. NMR spectra show that the complex maintains its structure in aqueous solution, and that the corresponding chloro complex also has a similar structural arrangement. The pH dependence of the redox potential for the complex [Ru(bpea)(bpy)(H2O)](PF6)2 is reported, as well as the ability of the corresponding oxo complex to catalyze the oxidation of benzylic alcohol to benzaldehyde in both chemical and electrochemical manners.