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Gouverd C, Biaso F, Cataldo L, Berclaz T, Geoffroy M, Levillain E, Avarvari N, Fourmigue M, Sauvage FX, Wartelle C: Tetrathiafulvalene-phosphine-based iron and ruthenium carbonyl complexes: electrochemical and EPR studies. Phys Chem Chem Phys. 2005 Jan 7;7(1):85-93.
The radical cation of the redox active ligand 3,4-dimethyl-3',4'-bis-(diphenylphosphino)-tetrathiafulvalene (P2) has been chemically and electrochemically generated and studied by EPR spectroscopy. Consistent with DFT calculations, the observed hyperfine structure (septet due to the two methyl groups) indicates a strong delocalization of the unpaired electron on the central S2C=CS2 part of the tetrathiafulvalene (TTF) moiety and zero spin densities on the phosphine groups. In contrast with the ruthenium (0) carbonyl complexes of P2 whose one-electron oxidation directly leads to decomplexation and produces P2*+, one-electron oxidation of [Fe (P2)(CO) 3] gives rise to the metal-centered oxidation species [Fe (I)(P2)(CO) 3], characterized by a coupling with two 31P nuclei and a rather large g-anisotropy. The stability of this complex is however modest and, after some minutes, the species resulting from the scission of a P-Fe bond is detected. Moreover, in presence of free ligand, [Fe (I)(P2)(CO) 3] reacts to give the complex [Fe (I)(P2) 2 (CO)] containing two TTF fragments. The two-electron oxidation of [Fe (P2)(CO) 3] leads to decomplexation and to the P2*+ spectrum. Besides EPR spectroscopy, cyclic voltammetry as well as FTIR spectroelectrochemistry are used in order to explain the behaviour of [Fe (P2)(CO) 3] upon oxidation. This behaviour notably differs from that of the Ru (0) counterpart. This difference is tentatively rationalized on the basis of structural arguments. |
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