Electrochemistry of metal-metal bonded diruthenium complexes

Abstract

This review summarizes the known electrochemistry of metal-metal bonded diruthenium complexes containing an air-stable Ru24+, Ru25+ or Ru26+ core or an in-situ generated Ru22+, Ru23+, Ru27+ or Ru28+ core with O,O' -, N,O - or N,N'- donor bridging ligands. The majority of published studies have been carried out in nonaqueous media and involved compounds with a Ru25+ oxidation state and four anionic “ap” or “DPhF”-type bridging ligands where ap and DPhF are the 2-anilinopyridinate and N,N’-diphenylformamidinate anions, respectively. The potentials and mechanisms of electron transfer depend in part upon the properties of the electrochemical solvent and in part upon properties of the compound, the most important of which are the initial oxidation state of the air-stable dimetal unit, the number and type of axial ligands and the type of anionic bridging ligands. The vast majority of redox processes described to date for these compounds involve electron addition or abstraction at the diruthenium core, but redox reactions involving the bridging ligands or other electroactive groups on the molecule have also been observed. In most cases, the redox reactions were reversible on the cyclic voltammetry and spectroelectrochemical timescale, thus enabling the in-situ generation of new compounds in both very low and high oxidation states with dimetal units ranging from Ru22+ to Ru28+.