The indigo isomer epindolidione as a redox‐active bridging ligand for diruthenium complexes

Abstract

Epindolidione (H2L), a heteroatom‐modified analogue of tetracene and a structural isomer of indigo, forms dinuclear complexes with [RuX2]2+, X=bpy (2,2′‐bipyridine, [1]2+) or pap (2‐phenylazopyridine, [2]2+), in its doubly deprotonated bridging form μ‐L2-. The dications in compounds meso‐[1](ClO4)2 and meso‐[2](ClO4)2, [X2Ru(μ‐L)RuX2](ClO4)2, contain five‐membered chelate rings N‐C-C‐O‐RuII with π bridged metals at an intramolecular distance of 7.19 Å. Stepwise reversible oxidation and reduction is mainly ligand centered (oxidation: L2-; reduction: X), as deduced from EPR of one‐electron oxidized and reduced intermediates and from UV/Vis/NIR spectroelectrochemistry, supported by TD‐DFT calculation results. The results for [1](ClO4)2 and [2](ClO4)2 are qualitatively similar to the ones observed with the deprotonated indigo‐bridged isomers with their six‐membered chelate ring structures, confirming the suitability of both π systems for molecular electronics applications, low‐energy absorptions, and multiple electron transfers.