Regulation of electron donating ability to metal center: isolation and characterization of ruthenium carbonyl complexes with N,N- and/or N,O-donor polypyridyl ligands

Polypyridyl ruthenium(II) dicarbonyl complexes with an N,O- and/or N,N-donor ligand, [Ru(pic)(CO)2Cl2]− (1), [Ru(bpy)(pic)(CO)2]+ (2), [Ru(pic)2(CO)2] (3), and [Ru(bpy)2(CO)2]2+ (4) (pic=2-pyridylcarboxylato, bpy=2,2′-bipyridine) were prepared for comparison of the electron donor ability of these ligands to the ruthenium center. A carbonyl group of [Ru(L1)(L2)(CO)2]n (L1, L2=bpy, pic) successively reacted with one and two equivalents of OH− to form [Ru(L1)(L2)(CO)(C(O)OH)]n−1 and [Ru(L1)(L2)(CO)(CO2)]n−2. These three complexes exist as equilbrium mixtures in aqueous solutions and the equilibrium constants were determined potentiometrically. Electrochemical reduction of 2 in CO2-saturated CH3CN–H2O at −1.5 V selectively produced CO.