Synthesis, characterization and reactivity of trans-[RuCl(NO)(bpydip)]2+ {bpydip = N,N′-bis(7-methyl-2-pyridylmethylene)-1,3-diiminopropane}: a novel nitrosyl ruthenium complex displaying high electronic delocalization

Abstract

A novel trans-[RuCl(NO)(bpydip)]²⁺ species has been obtained by the reaction of nitrite ions with trans-[RuCl₂(bpydip)] {bpydip = N,N′-bis(7-methyl-2-pyridylmethylene)-1,3-diiminopropane}, and extensively characterized by means of elemental analysis, cyclic voltammetry, UV/Visible, FTIR, ¹H NMR and EPR spectroscopy. The electrochemistry in acetonitrile solution, consists of two sets of reversible redox processes ascribed to the Ru^III/II (E_1/2 = +1.92 V versus NHE) and NO^+/˙ (E_1/2 = +0.34 V) redox couples. A relatively high ν(NO) stretching frequency (1920 cm⁻¹) has been observed in the FTIR spectra, indicating a NO⁺ character, while the absence of EPR signals is also consistent with the Ru^II–NO⁺ formulation. The reduction of the complex was monitored spectroelectrochemically, exhibiting a shift of ν(NO) to 1890 cm⁻¹; and giving rise to characteristic EPR signals which evidence the NO˙ character in the product. The nitrosyl (NO⁺) species reacts with H₂O according to the equation [RuCl(NO)(bpydip)]²⁺ + H₂O → [RuCl(NO₂)(bpydip)] + 2H⁺, leading to a pseudo-first order rate constant of 1.40 (± 0.02) × 10⁻² s⁻¹, ΔH^≠ = 47 (± 1) kJ mol⁻¹ and ΔS^≠ = 122 (± 4) J K⁻¹ mol⁻¹.