trans-[Ru(NO)(NH3)P(O−)(OEt)2]2+: A new and robust NO/HNO-donor in aqueous media

This study describes the synthesis and reactivity in aqueous media of a new potential NO/HNO-donor: trans-[Ru(NO)(NH3)4P(O−)(OEt)2](PF6)2. This compound exhibits a remarkable robustness over a wide range of pH relative to other similar ruthenium phosphorus nitrosyl complexes. At pH 3.0 and 25 °C, trans-[Ru(NO)(NH3)4P(O−)(OEt)2](PF6)2 decays, yielding free diethyl phosphite with a half-life of 9 days (k = 8.9 × 10−7 s−1). At pH 7.5 and 25 °C, this complex is competitively consumed by diethyl phosphite dissociation (k = 5.15 × 10−5 s−1) and nucleophilic attack at the nitrosyl group (k = 7.25 × 10−5 s−1). Nevertheless, the trans-[Ru(NO)(NH3)4P(O−)(OEt)2](PF6)2 exhibits a half-life of 1.5 h (pH 7.5 and 25 °C) for delivering NO/HNO by electrochemical activation at potentials of −0.50 and −0.80 V versus SCE. The NO liberation from trans-[Ru(NO)(NH3)4P(O−)(OEt)2]+ ion occurs with k–NO = 0.24 ± 0.01 s−1, and electrochemical data indicate that k–HNO ≫ k–NO.