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 {RuII–CO}RuIIIRuIII/{RuIII–CO}RuIIIRuIII couple at E1/2 = + 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 {RuIII–CO}RuIIIRuIII, 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.