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Double Insertion of Thiophene Rings in Polyynediyl Chains to Stabilize Nanoscaled Molecular Wires with [Cp*(dppe)Fe] Termini

Abstract : The dinuclear iron complexes [Cp*(dppe)Fe-C C C4H2S-(C C)(x)-C4H2S-C C-Fe(dppe)Cp*] (2, x = 1; 3 x = 2) and [Cp*(dppe)Fe-C C-C4H2S-C C-C C-Fe(dppe) Cp*] (4) were prepared in one -pot procedures from known organometallic precursors. Compound 2 was obtained from Cp,*(dppe)Fe-C C-C4H2S-C C-C4H2S-C CH (6) and Cp*(dppe)FeCl (5) in 74% yield. Its relative 3, isolated in 84%, resulted from the oxidative coupling of Cp*(dppe)Fe-C C-C4H2S-C CH (7) in the presence of Cu(OAc)(2) and 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU). Complex 4 was obtained from the bridging ligand 2,5-bis(trimethylsilylbutadiynyl)thiophene (8) and two equiv of 5. The new complexes were characterized by ESI-mass spectrometry, IR, multi-nuclear NMR, cyclic voltammetry, and Mossbauer spectroscopy. Complex 3 was also analyzed by X-ray diffraction on a single crystal. The data are consistent with a sizable metal metal interaction across the 14- and 16 -carbon atoms of the bridges. The singly and doubly oxidized forms 2(PF6)(n) and 3(PF6)(n) (n = 1, 2) were obtained by oxidation of the corresponding 18 -electron iron(II) precursors with 1 and 2 equivs of ferrocenium salt, while 4 decomposed very quickly upon oxidation. The thermally stable salts 2(PF6)(n) and 3(PF6)(n) (n = 1, 2) were subjected to analyses by ESI-mass spectrometry, IR, Mossbauer, ESR, UV-vis, and NIR spectroscopies. The radical cations 2(PF6) and 3(PF6) belong to Class II of the mixed-valence Robin and Day classification with quite sizable electronic coupling parameters for large metal-metal separation (2(PF6), H-ab = 262 cm(-1), d(FeFe) = 17.7 angstrom; 3(PF6), H-ab = 203 cm(-1), d(FeFe) = 19.7 angstrom). Paramagnetic H-1 NMR spectroscopy was also performed on the dicationic salts to measure the magnetic exchange between the distant spin carriers (2(PF6)(2), Delta G(ST) = -120 cm(-1)). The data were analyzed with the support of quantum chemistry calculations at the DFT level of theory.
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https://hal-univ-rennes1.archives-ouvertes.fr/hal-01357398
Contributor : Laurent Jonchère <>
Submitted on : Monday, August 29, 2016 - 4:40:54 PM
Last modification on : Friday, July 10, 2020 - 4:24:44 PM

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Severine Roue, Hiba Sahnoune, Loic Toupet, Jean-François Halet, Claude Lapinte. Double Insertion of Thiophene Rings in Polyynediyl Chains to Stabilize Nanoscaled Molecular Wires with [Cp*(dppe)Fe] Termini. Organometallics, American Chemical Society, 2016, 35 (12), pp.2057--2070. ⟨10.1021/acs.organomet.6b00209⟩. ⟨hal-01357398⟩

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