Synthesis and spectro-electrochemical aspects of [Ru^II(trpy)(pdt)(X)]ⁿ⁺ (trpy = 2,2':6',2"-terpyridine, pdt = 5,6-Diphenyl-3-pyridyl-as-triazine, X = Cl^-, CH₃CN, NO₂^-, NO⁺, NO^.) - electrophilicity of {Ru^II-NO⁺} and photolability of {Ru^II-NO^.}

Abstract

Nitrosylruthenium derivatives having NO⁺ and NO^. states have been synthesized in a stepwise manner starting from [Ru^II(trpy)(pdt)(Cl)](ClO⁴) {[1](ClO⁴)} → [Ru^II(trpy)(pdt)(CH₃CN)](ClO₄)₂ {[2](ClO₄₎₂} → [Ru^II(trpy)(pdt)(NO₂)](ClO₄) {[3](ClO₄)} → [Ru^II(trpy)(pdt)(NO⁺)](ClO₄)₃ {[4](ClO₄)₃} → [Ru^II(trpy)(pdt)(NO^.)](ClO₄)2 {[4](ClO₄)₂} [trpy = 2,2':6',2"-terpyridine, pdt = 5,6-diphenyl-3-pyridyl-as-triazine]. The molecular identity of [1](ClO₄) and [2](ClO₄)₂ and the subsequent stereoretentive transformation of [1](ClO₄) → [2](ClO₄)₂ have been authenticated by single-crystal X-ray structures. Electrochemical and spectral features are investigated as a function of the monodentate ligands (Cl^-, CH₃CN, NO₂^-, NO⁺, NO^.). The kinetic and thermodynamic aspects of the reaction of the moderately strong electrophilic {Ru^II-NO⁺} center [ν(NO): 1944 cm^-1] in [4]³⁺ with a nucleophile such as OH^- have been studied. The nitrosyl species [Ru^II(trpy)(pdt)(NO⁺)]³⁺ ([4]³⁺) can be selectively reduced to [Ru^II(trpy)(pdt)(NO^.)]²⁺([4]²⁺) electrochemically as well as chemically by hydrazine hydrate. On exposure to light an acetonitrile solution of [Ru^II(trpy)(pdt)(NO^.)]²⁺ ([4]²⁺) undergoes slow photocleavage of the Ru^II-NO bond over a period of 4 h, resulting in the corresponding solvated species [Ru^II(trpy)(pdt)(CH₃CN)]²⁺ ([2]²⁺). The rate of photolability of the Ru^II-NO bond in [4]²⁺has been monitored spectrophotometrically.