Ruthenium Nitrosyl Complexes with Bidentate Heterocycles and Chloride Ligands: Synthesis and Photorelease of NO

A set of new coordination compounds of the formula [RuNO(L)Cl3], with L representing the bidentate ligands bipyrimidine (bpym), bipyridine (bpy), or phenanthroline (phen), was prepared and fully characterized. For the isomeric species fac-[RuNO(bpym)Cl3] (1), fac-[RuNO(phen)Cl3] (2), mer-[RuNO(phen)Cl3] (3), fac-[RuNO(bpy)Cl3] (4), and mer-[RuNO(bpy)Cl3] (5), an evaluation of the photoresponse in DMSO was performed under excitation with 450 nm using a continuous-flow arrangement that enabled the simultaneous acquisition of IR and UV-Vis spectral data. Quantum yields for photoinduced release of NO were determined as follows: 5.4 ± 0.5% for fac-[RuNO(bpym)Cl3] (1); 0.8 ± 0.1% for fac-[RuNO(phen)Cl3] (2); 0.6 ± 0.1% for mer-[RuNO(phen)Cl3] (3); 3.7 ± 0.1% for fac-[RuNO(bpy)Cl3] (4); 2.1 ± 0.1% for mer-[RuNO(bpy)Cl3] (5). The product of the photolysis of compound 5 in acetonitrile solution was isolated and structurally characterized as mer-[Ru(CH3CN)(bpy)Cl3] (6). Taking into account the presence of typical DNA intercalating ligands, the complexes can be potentially exploited as photoNORMs.