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‐12 and meso‐22, X2Ru(μ‐L)RuX22, 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 12 and 22 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.