A Dibenzotetrathiafulvalene-Bridged Bis(alkenylruthenium) Complex and Its One- and Two-Electron-Oxidized Forms

We report on the synthesis of the new bis(alkenylruthenium) complex DBTTF-(ViRu) with a longitudinally extended, π-conjugated dibenzotetrathiafulvalene (DBTTF) bridge, characterized by multinuclear NMR, IR, and UV/vis spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. Cyclic and square-wave voltammetry revealed that DBTTF-(ViRu) undergoes four consecutive oxidations. IR, UV/vis/near-IR, and electron paramagnetic resonance spectroscopy indicate that the first oxidation involves the redox-noninnocent DBTTF bridge, while the second oxidation is biased toward one of the peripheral styrylruthenium entities, thereby generating an electronically coupled mixed-valent state ({Ru}-CH═CH)^•+-DBTTF^•+-(CH═CH-{Ru}) [{Ru} = Ru(CO)Cl(PPr₃)₂]. The latter is apparently in resonance with the ({Ru}-CH═CH)^•+-DBTTF-(CH═CH-{Ru})^•+ and ({Ru}-CH═CH)-DBTTF²⁺-(CH═CH-{Ru}) forms, which are calculated to lie within 19 kJ/mol. Higher oxidized forms proved too unstable for further characterization. The reaction of DBTTF-(ViRu) with the strong organic acceptors 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, tetracyano-p-benzoquinodimethane (TCNQ), and F₄TCNQ resulted in formation of the DBTTF-(ViRu) radical cation, as shown by various spectroscopic techniques. Solid samples of these compounds were found to be highly amorphous and electrically insulating.