Proton-Coupled Electron Transfer and Lewis Acid Recognition at Self-Assembled Monolayers of an Oxo-Bridged Diruthenium(III) Complex Functionalized with Two Disulfide Anchors

Abstract

A new μ-oxo-bis­(μ-acetato)­diruthenium­(III) complex bearing two pyridyl disulfide ligands {[Ru₂(μ-O)­(μ-OAc)₂(bpy)₂(L_py‑SS)₂]­(PF₆)₂ (OAc = CH₃CO₂^–, bpy = 2,2′-bipyridine, L_py‑SS = (C₅H₄N)­CH₂NHC­(O)­(CH₂)₄CH­(CH₂)₂SS) (<b>1</b>)} has been synthesized to prepare self-assembled monolayers (SAMs) on the Au(111) electrode surface. The SAMs have been characterized by contact-angle measurements, reflection–absorption surface infrared spectroscopy, cyclic voltammetry, and reductive desorption experiments. The SAMs exhibited proton-coupled electron transfer (PCET) reactions when the electrochemistry was studied in aqueous electrolyte solution (0.1 M NaClO₄ with Britton–Robinson buffer to adjust the solution pH). The potential–pH plot (Pourbaix diagram) in the pH range from 1 to 12 has established that the dinuclear ruthenium moiety was involved in the interfacial PCET processes with four distinct redox states: Ru^IIIRu^III(μ-O), Ru^IIRu^III(μ-OH), Ru^IIRu^II(μ-OH), and Ru^IIRu^II(μ-OH₂). We also demonstrated that the interfacial redox processes were modulated by the addition of Lewis acids such as BF₃ or Al³⁺ to the electrolyte media, in which the externally added Lewis acids interacted with μ-O of the dinuclear moiety within the SAMs