Redox Behavior of a Dinuclear Ruthenium(II) Complex Bearing an Uncommon Bridging Ligand: Insights from High-Pressure Electrochemistry

Metal/Metal Redox Isomerism Governed by Configuration

A pair of diastereomeric dinuclear complexes, [Tp′(CO)BrW{μ‐η²‐C,C′‐κ²‐S,P‐C₂(PPh₂)S}Ru(η⁵‐C₅H₅)(PPh₃)], in which W and Ru are bridged by a phosphinyl(thiolato)alkyne in a side‐on carbon P,S‐chelate coordination mode, were synthesized, separated and fully characterized. Even though the isomers are similar in their spectroscopic properties and redox potentials, the like‐isomer is oxidized at W while the unlike‐isomer is oxidized at Ru, which is proven by IR, NIR and EPR‐spectroscopy supported by spectro‐electrochemistry and computational methods. The second oxidation of the complexes was shown to take place at the metal left unaffected in the first redox step. Finally, the tipping point could be realized in the unlike isomer of the electronically tuned thiophenolate congener [Tp′(CO)(PhS)W{μ‐η²‐C,C′‐κ²‐S,P‐C₂(PPh₂)S}Ru(η⁵‐C₅H₅)‐(PPh₃)], in which valence trapped W^III/Ru^II and W^II/Ru^III cationic species are at equilibrium.

Versatile Coordination of Azocarboxamides: Redox-Triggered Change of the Chelating Binding Pocket in Ruthenium Complexes

Azocarboxamides occupy a special place among azo ligands owing to their versatility for metal coordination. Herein ruthenium complexes with two different azocarboxamide ligands that differ in the presence (or not) of a coordinating pyridyl heterocycle are presented. By making full use of the O,N(amide), N(azo), and N(pyridyl) coordinating sites, the first diruthenium complex that is bridged by an azo ligand containing two different binding pockets was obtained. Moreover, it was conclusively proven that, in the mononuclear complexes, oxidation at the ruthenium center leads to a complete change of coordination at the chelating binding pocket. The complexes were characterized by NMR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. Additionally, the mechanism of the aforementioned redox-triggered change in the chelating binding pocket and the electronic structures of all the complexes were investigated by a combination of electrochemistry, UV/Vis/NIR/EPR spectroelectrochemistry, and DFT calculations. This is first instance in which a redox-driven change in the complete chelating binding pocket has been observed in a ruthenium complex as well as with azo-based ligands. These results thus show the potential of these versatile azocarboxamide ligands to act as redox-driven switches with possible relevance to electrocatalysis.

Mixed valency in ligand-bridged diruthenium frameworks: divergences and perspectives

Emerging fundamental issues involving intramolecular electron transfer at the mixed valent diruthenium frameworks and its application prospects have been highlighted.