Charge delocalization in a heterobimetallic ferrocene-(vinyl)Ru(CO)Cl(PiPr3)2 system
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Organometallics 28 (14): 4196--4209 (2009)

Ruthenium s-vinylferrocene electronically conjugated redox-active complex was prepd.; mixed-valence cationic states were explored by spectroelectrochem., IR, NIR, ESR spectra, and DFT calcns. Addn. of ruthenium hydride RuH(CO)Cl(iPr3)2 to ethynylferrocene gave s-vinylruthenium complex Cl(CO)(PiPr3)2RuCH:CHFc (1, Fc = ferrocenyl), which was characterized by NMR, IR, ESI-MS, and Moessbauer spectroscopy and by x-ray crystallog. Complex 1 features conjoined ferrocene and (vinyl)ruthenium redox sites and undergoes two consecutive reversible oxidns. Pure samples of cryst., monooxidized 1·+PF6 were prepd. by chem. oxidn. of 1 with the ferrocenium hexafluorophosphate. Structural comparison with 1 reveals an increase of Fe-C and Fe-Cp bond lengths and ring tilting of the Cp decks, as is typical of ferrocenium ions, but also a discernible lengthening of the Ru-C(CO) and Ru-P bonds and a shortening of the Ru-C(vinyl) bond upon oxidn. This supports the general idea of charge delocalization over both redox sites in 1·+. Band shifts of the charge-sensitive IR labels (n(CO) for Ru, n(C-H, Cp) for Fc), the rather small g-anisotropy in the ESR spectrum of 1·+, and the results of quantum chem. calcns. indicate that in soln. the pos. charge partly resides on the vinyl ruthenium moiety. Comparison of IR shifts in the solid state and in soln. and the quadrupole splitting in the Moessbauer spectrum of powd. 1·+ point to a larger extent of charge localization on the ferrocenyl site in solid samples. This is probably due to CH···F hydrogen bonding interactions between the cyclopentadienyl hydrogen atoms of the radical cations and the PF6- counterions. Monooxidized 1·+ displays low-energy electronic absorption bands at 1370 and 2150 nm. According to quantum chem. calcns., the underlying transitions are largely localized on the ferrocene part of the mol. with only little charge transfer into the vinyl ruthenium subunit. The second oxidn. is more biased toward the (vinyl)ruthenium site. on SciFinder(R)
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