Accelerated Photorelease of NO from {Ru-NO}6 Nitrosyls Containing Carboxamido-N and Carboxylato-O Donors: Syntheses, Structures, and Photochemistry

Three ruthenium nitrosyls, namely, [(Me(2)bpb)Ru(NO)(OAc)], [(Me(2)bpb)Ru(NO)(OBz)] (1), and [(Me(2)Qb)Ru(NO)(qca))(BF4) (2), have been synthesized from designed ligands with carboxamido-N donors. In all three complexes, a carboxylato-O donor is trans to the bound NO. The structures of 1 and 2 have been determined by X-ray crystallography. The nearly linear Ru-N-O bond angles [175.18(18)degrees and 175.0(3)degrees, respectively] and diamagnetism of the two nitrosyls are indicative of the {Ru-NO}(6) configuration. All three complexes exhibit nu(NO) in the range 1830-1890 cm(-1). When solutions of 1 and 2 are exposed to low-intensity (milliwatts) UV light, rapid release of NO is observed. The results of photochemical measurements indicate that the placement of the carboxylato-O donor trans to NO promotes the photorelease of NO in these nitrosyls much like Cl- and py. The presence of the carboxamido-N donor is, however, essential for the observed NO photolability because the structurally similar nitrosyl [(pyca)(2)Ru(NO)(Cl)] (3) (with carboxylato-O trans to NO) does not release NO upon exposure to UV light. Extension of conjugation in the ligand frame (quinoline rings in place of pyridine rings) increases both the rate of NO photorelease and the quantum yield of 2 compared to 1. The results of this investigation confirm that the combination of carboxamido-N donor(s) in the ligand frame and carboxylato-O trans to NO is a new structural motif in photoactive {Ru-NO}(6) nitrosyls.