A ligand substitution reaction of oxo-centred triruthenium complexes assembled as monolayers on gold electrodes

Abstract

A terminal ligand-substitution reaction at triruthenium redox centres within monolayer films is investigated. For this purpose, a new redox-active trinuclear ruthenium complex containing one carbonyl ligand at a terminal site, [Ru₃(O)(CH₃COO)₆(CO)(mpy)(C10PY)] (mpy = 4-methylpyridine, C10PY = {(NC₅H₄)CH₂NHC(O)(CH₂)₁₀S–}₂) 1, has been chemically adsorbed onto a gold electrode surface with a disulfide-alkyl spacer C10PY. Densely packed monolayers of complex 1 on Au electrodes (surface coverage, Γ(Ru₃) = 1.8 × 10⁻¹⁰ mol cm⁻²) display the {Ru^II–CO}Ru^IIIRu^III/{Ru^III–CO}Ru^IIIRu^III couple at E_1/2 = + 0.61 V s. Ag–AgCl in a 0.1 mol dm⁻³ HClO₄ aqueous solution. Upon electrochemical oxidation of the adsorbed complex at + 0.80 V, where the triruthenium carbonyl complex is in the oxidized form {Ru^III–CO}Ru^IIIRu^III, the coordinated CO is replaced by an aqua ligand present in the bulk phase, which is followed by cyclic voltammetry at appropriate electrolysis time intervals. During 8000 s of electrolysis, ca. 67% of the initially assembled carbonyl complexes are converted to the triruthenium aqua complexes, while ca. 25% desorbed from the electrode surface.