Nitrosyl induces phosphorous-acid dissociation in ruthenium (II)

The trans-[Ru(NO)(NH3)4(P(OH)3)]Cl3 complex was synthesized by reacting [Ru(H2O)(NH3)5]2+ with H3PO3 and characterized by spectroscopic (31P-NMR, δ = 68 ppm) and spectrophotometric techniques (λ = 525 nm, ε = 20 L mol-1 cm-1; λ = 319 nm, ε = 773 L mol-1 cm-1; λ = 241 nm, ε = 1385 L mol-1 cm-1; νNO+ = 1879 cm-1). A pKa of 0.74 was determined from infrared measurements as a function of pH for the reaction: trans-[Ru(NO)(NH3)4(P(OH)3)]3+ + H2O ⇌ trans-[Ru(NO)(NH3)4(P(O-)(OH)2)]2+ + H3O+. According to 31P-NMR, IR, UV-vis, cyclic voltammetry and ab initio calculation data, upon deprotonation, trans-[Ru(NO)(NH3)4(P(OH)3)]3+ yields the O-bonded linkage isomer trans- [Ru(NO)(NH3)4(OP(OH)2)]2+, then the trans-[Ru(NO)(NH3)4(OP(H)(OH)2)]3+ decays to give the final products H3PO3 and trans-[Ru(NO)(NH3)4(H2O)]3+. The dissociation of phosphorous acid from the [Ru(NO)(NH3)4]3+ moiety is pH dependent (kobs = 2.1 × 10-4 s-1 at pH 3.0, 25 °C).FAPESP (05/53266-4, 08/02014-0)CNPqCAPE