Electrochemistry of metal-metal bonded diruthenium complexes

• Published in: Coordination chemistry reviews 2021-05, Vol.434, p.213706, Article 213706
• Main Authors: Van Caemelbecke, Eric, Phan, Tuan, Osterloh, W. Ryan, Kadish, Karl M.
• Format: Article
• Language: English
• Subjects: Diruthenium; Electrochemistry; Metal-metal bonds; Paddlewheel; Redox properties
• ISSN: 0010-8545; 1873-3840
• DOI: 10.1016/j.ccr.2020.213706

[Display omitted] •Electrochemistry of Ru2 paddlewheel complexes spanning seven oxidation states.•Effects of bridging and axial ligands on redox potentials from 6+ decades of research.•Redox potentials for 350+ Ru2 complexes from over 120 references are tabulated. 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+.