Photocleavage of Coordinated NO under Visible Light from Two Different Classes of Organometallic Ruthenium Nitrosyl Complexes: Reversible Binding of Phenolato Function

The structurally similar Ru(III) complexes [Ru(LSB1)(PPh3)2Cl] (1), where LSB1H2 = 2-(4-chlorobenzylidineamino)phenol and H = dissociable protons, and [Ru(LAZ1)(PPh3)2Cl] (2), where LAZ1H2 = 4-methyl-2-(p-tolyldiazenyl)phenol and H = dissociable protons, were reacted with in situ generated NO derived from acidified nitrite solution. These reactivity studies on 1 and 2 afforded the complexes [Ru(LSB2H)(PPh3)2(NO)Cl](ClO4) (1a) and [Ru(LAZ2H)(PPh3)2(NO)Cl](ClO4) (2a), respectively, where LSB2H = 2-(4-chlorobenzylidineamino)-4-nitrophenol, LAZ2H = 4-methyl-2-nitro-6-(p-tolyldiazenyl)phenol, and H = dissociable proton. Complexes 1a and 2a were found to be diamagnetic and were characterized by 1H and 31P NMR spectral studies. Both 1a and 2a exhibited νNO bands near 1800 cm−1 in their IR spectra. The molecular structures of 1a·CH2Cl2·3H2O and 2a·2H2O were determined by X-ray crystallography, and NO coordination as well as ligand nitration were authenticated from the crystal structure. In both of the nitrosyl complexes coordinated NO was found to be photolabile under visible light and photocleaved NO was transferred to reduced myoglobin. The photolability of NO in 1a and 2a afforded the complexes [Ru(LSB2)(PPh3)2Cl] (1b) and [Ru(LAZ2)(PPh3)2Cl] (2b), respectively, and the molecular structure of 1b·2CH2Cl2 was confirmed by an X-ray crystal structure solution. A novel type of reversible binding of the phenolato function to the metal center was revealed during NO coordination and photocleavage.