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)(2) with a longitudinally extended, pi-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)(2) 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 & boxH;CH)(center dot+)-DBTTF center dot+-(CH & boxH;CH-{Ru}) [{Ru} = Ru(CO)Cl((PPr3)-Pr-i)(2)]. The latter is apparently in resonance with the ({Ru}-CH & boxH;CH)(center dot+)-DBTTF-(CH & boxH;CH-{Ru})(center dot+) and ({Ru}-CH & boxH;CH)-DBTTF2+-(CH & boxH;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)(2) with the strong organic acceptors 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, tetracyano-p-benzoquinodimethane (TCNQ), and F(4)TCNQ resulted in formation of the DBTTF-(ViRu)(2)(center dot+) radical cation, as shown by various spectroscopic techniques. Solid samples of these compounds were found to be highly amorphous and electrically insulating.

Automated summary

We report on the synthesis and characterization of a new bis(alkenylruthenium) complex with a longitudinally extended, pi-conjugated dibenzotetrathiafulvalene bridge. The complex undergoes four consecutive oxidations and forms an electronically coupled mixed-valent state. It also reacts with strong organic acceptors to form a radical cation.