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

Nitrosyl complexes with {Ru-NO}<SUP>6</SUP> and {Ru-NO}<SUP>7</SUP> configurations have been isolated in the framework of [Ru(trpy)(L)(NO)]<SUP>n+</SUP> [trpy = 2,2':6',2''-terpyridine, L = 2-phenylimidazo[4,5-f]1,10-phenanthroline] as the perchlorate salts [4](ClO<SUB>4</SUB>)<SUB>3</SUB> and [4](ClO<SUB>4</SUB>)<SUB>2</SUB>, respectively. Single crystals of protonated material [4-H<SUP>+</SUP>](ClO<SUB>4</SUB>)<SUB>4</SUB>.2H<SUB>2</SUB>O reveal a Ru-N-O bond angle of 176.1(7)° and triply bonded N-O with a 1.127(9) Å bond length. Structures were also determined for precursor compounds of [4]<SUP>3+</SUP> in the form of [Ru(trpy)(L)(Cl)](ClO<SUB>4</SUB>).4.5H<SUB>2</SUB>O and [Ru(trpy)(L-H)(CH<SUB>3</SUB>CN)](ClO<SUB>4</SUB>)<SUB>3</SUB>.H<SUB>2</SUB>O. In agreement with largely NO centered reduction, a sizable shift in ν(NO) frequency was observed on moving from [4]3+ (1953 cm<SUP>-1</SUP>) to [4]<SUP>2+</SUP> (1654 cm<SUP>-1</SUP>). The Ru<SUP>II</SUP>-NO°in isolated or electrogenerated [4]<SUP>2+</SUP> exhibits an EPR spectrum with g<SUB>1</SUB> = 2.020, g<SUB>2</SUB> = 1.995, and g<SUB>3</SUB> = 1.884 in CH<SUB>3</SUB>CN at 110 κ, reflecting partial metal contribution to the singly occupied molecular orbital (SOMO); <SUP>14</SUP>N (NO) hyperfine splitting (A<SUB>2</SUB> = 30 G) was also observed. The plot of ν(NO) versus E°({RuNO}<SUB>6</SUB> → {RuNO}<SUB>7</SUB>) for 12 analogous complexes [Ru(trpy)(L')(NO)]<SUP>n+</SUP> exhibits a linear trend. The electrophilic Ru-NO<SUP>+</SUP> species [4]<SUP>3+</SUP> is transformed to the corresponding Ru-NO<SUB>2</SUB><SUP>-</SUP> system in the presence of OH<SUP>-</SUP> with k = 2.02 × 10<SUP>-4</SUP> s<SUP>-1 </SUP>at 303 κ. In the presence of a steady flow of dioxygen gas, the Ru<SUP>II</SUP>-NO<SUP>·</SUP>state in [4]<SUP>2+</SUP> oxidizes to [4]<SUP>3+</SUP> through an associatively activated pathway (ΔS ≠-190.4 J K<SUP>-1 </SUP>M<SUP>-1</SUP>) with a rate constant (k [s<SUP>-1</SUP>]) of 5.33 × 10<SUP>-3</SUP>. On irradiation with light (Xe lamp), the acetonitrile solution of paramagnetic [Ru(trpy)(L)(NO)]<SUP>2+</SUP> ([4]<SUP>2+</SUP>) undergoes facile photorelease of NO (k<SUB>NO</SUB> = 2.0 × 10<SUP>-1</SUP> min<SUP>-1</SUP> and t<SUB>½ </SUB> ≈ 3.5 min) with the concomitant formation of the solvate [Ru<SUP>II</SUP>(trpy)(L)(CH<SUB>3</SUB>CN)]<SUP>2+</SUP> [2']<SUP>2+</SUP>. The photoreleased NO can be trapped as an Mb-NO adduct