Formation, reactivity, and photorelease of metal bound nitrosyl in [Ru(trpy)(L)(NO)](n+) (trpy = 2,2':6',2'-terpyridine, L = 2-phenylimidazo[4,5-f]1,10-phenanthroline)

Nitrosyl complexes with {Ru-NO} (6) and {Ru-NO} (7) configurations have been isolated in the framework of Ru(trpy)(L)(NO)] ( n+ ) trpy = 2,2':6',2'-terpyridine, L = 2-phenylimidazo4,5- f]1,10-phenanthroline] as the perchlorate salts 4](ClO 4) 3 and 4](ClO 4) 2, respectively. Single crystals of protonated material 4-H (+)](ClO 4) 4.2H 2O reveal a Ru-N-O bond angle of 176.1(7) degrees and triply bonded N-O with a 1.127(9) A bond length. Structures were also determined for precursor compounds of 4] (3+) in the form of Ru(trpy)(L)(Cl)](ClO 4).4.5H 2O and Ru(trpy)(L-H)(CH 3CN)](ClO 4) 3.H 2O. In agreement with largely NO centered reduction, a sizable shift in nu(NO) frequency was observed on moving from 4] (3+) (1953 cm (-1)) to 4] (2+) (1654 cm (-1)). The Ru (II)-NO* in isolated or electrogenerated 4] (2+) exhibits an EPR spectrum with g 1 = 2.020, g 2 = 1.995, and g 3 = 1.884 in CH 3CN at 110 K, reflecting partial metal contribution to the singly occupied molecular orbital (SOMO); (14)N (NO) hyperfine splitting ( A 2 = 30 G) was also observed. The plot of nu(NO) versus E degrees ({RuNO} (6) --> {RuNO} (7)) for 12 analogous complexes Ru(trpy)(L')(NO)] ( n+ ) exhibits a linear trend. The electrophilic Ru-NO (+) species 4] (3+) is transformed to the corresponding Ru-NO 2 (-) system in the presence of OH (-) with k = 2.02 x 10 (-4) s (-1) at 303 K. In the presence of a steady flow of dioxygen gas, the Ru (II)-NO* state in 4] (2+) oxidizes to 4] (3+) through an associatively activated pathway (Delta S++ = -190.4 J K (-1) M (-1)) with a rate constant ( k s (-1)]) of 5.33 x 10 (-3). On irradiation with light (Xe lamp), the acetonitrile solution of paramagnetic Ru(trpy)(L)(NO)] (2+) ( 4] (2+)) undergoes facile photorelease of NO ( k NO = 2.0 x 10 (-1) min (-1) and t 1/2 approximately 3.5 min) with the concomitant formation of the solvate Ru (II)(trpy)(L)(CH 3CN)] (2+) 2'] (2+). The photoreleased NO can be trapped as an Mb-NO adduct.