Stabilization of {RuNO}~6 and {RuNO}~7 States in [Ru~(II)(trpy)(bik)(N_)I~(n+) {trpy = 2,2:6,2-terpyridine,bik = 2,2-bis(1-methylimidazolyl) ketone} _ Formation, Reactivity, and Photorelease of Metal-Bound Nitrosyl

摘要

Ruthenium nitrosyl complexes have been isolated in the {RuNO}~6 and {RuNO)~7 configurations, employing the following reaction pathway for [Ru(trpy)(bik)(X)]~(n+): X = Cl-, [1](ClO_4) → X = CH_3CN, [2](ClO_4)_2 → X = NO_2~- , [3](ClO_4) → X = NO~+, [4](Cl0_4)_3 → X = NO~-, [4](ClO_4)_2. The single-crystal X-ray structures of [1](ClO_4)_(C_6H_6)_H_2O, [2](ClO_4)_2_H_2O, and [3]ClO_4)_H_20 have been determined. The successive NO~+/NO~- (reversible) and NO~-/NO~- (irreversible) reduction processes of [4]~(3+) appear at +0.36 and -0.40 V vs. SCE, respectively. While the v(C=O) frequency of the bik ligand at about 1630 cm~(-1) is largely invariant on complexation and reduction, the v(NO) frequency for the {RuNO}~6 state in [4]~(3+) at 1950 cm~(-1) shifts to about 1640 cm~(-1) on one-electron reduction to the {RuNO)~7 form in [4]~(2+), reflecting the predominant NO~+ → NO~- character of this electron transfer. However, a sizeable contribution from ruthenium with its high spin-orbit coupling constant to the singly occupied molecular or bital (SOMO) is apparent from the enhanced g anisotropy in the EPR spectrum [4]~(2+) (g_1 =2.015, g_2 = 1.995, g_3 = 1.881; g_(ay) = 1.965; Δg = 0.134). The {RuNO}~6 unit in [4]~(3+) reacts with OH~- via an associatively activated process (ΔS~# = -126.5 ± 2 J K~(-1) mol~(-1)) with a second-order rate constant of k = 3.3 × 10~(-2) M~(-1) s~(- 1), leading to the corresponding-nitro complex [3]~+. On exposure to light both {RuNO}~6 and {RuNO}~7 in [4]~(3+) and [4]~(2+) undergo Ru-NO photocleavage in CH_3CN via the formation of [Ru(trpy)(bik)(CH_3CN)]~(2+), [2]~(2+). The rate of photocleavage of the Ru~(II)-NO~+ bond in [4]~(3+) (k_(NO), 8.57 × 10~(-1) s~(-1), t_(1/2) = 0.80 s) is found to be much faster than that of the Ru~(II)-NO~- bond in [4]~(2+), [k_(NO), 5.45 × 10~(-4) s~(-1), t_(1/2) = 21.2 min (= 1272 s)]. The photoreleased nitrosyl can be trapped as an Mb-NO adduct.