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

Abstract

International audienceThe 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

Electronic Structures of Divinylchalcogenophene‐Bridged Biruthenium Complexes: Exploring Trends from O to Te

“…Within the broad range of bridging ligands examined within [L n M(µ‐bridge)ML n ] + complexes, thiophene derivatives have attracted attention,, with the lower aromaticity of the heterocyclic ring in comparison with benzene thought likely to lead to increased contributions from a cumulene‐like ground state and more extensively delocalised electronic structures , . For example, Lapinte and Lo Sterzo and their respective co‐workers have reported that 2,5‐diethynylthiophene‐linked Fe(dppe)Cp* and Fe(dppe)Cp [Cp = cyclopentadienyl, Cp* = pentamethylpentadienyl, dppe = 1,2‐bis(diphenylphosphino)ethane] termini are more strongly coupled than the 1,4‐diethynylbenzene‐bridged analogues , .…”

“…[48,69] Many other bimetallic complexes and metallopolymers with 2,5-diethynylthiophene-based bridging ligands are also known to offer highly delocalised electronic structures with significant contributions from the bridging ligand to the frontier molecular orbitals. [36,49,65,[75][76][77][78][79][80][81][82][83] Against this backdrop of long-standing interest in the properties of bimetallic complexes featuring (oligo)thiophene-based bridges, there has been increasing interest in genuine mixedvalence compounds featuring oligofuran-based bridging ligands. [84][85][86][87] Gidron and Bendikov reported that oligofurans can offer stronger electronic coupling between ferrocenyl redox units than oligothiophenes.…”

Electronic Properties of Poly‐Yne Carbon Chains and Derivatives with Transition Metal End‐Groups

“…The atomic contributions computed for the HOMO of the neutral model compound [ 8' ], suggest that in the corresponding mono‐oxidized species the spin density should be equally distributed between the metallic centers, the ethynyl fragments and the aromatic ring. On the other hand, derivative complexes with longer spacers such as [µ‐C≡C–(2,5‐SC 4 H 2 )–(C≡C) X –(2,5‐SC 4 H 2 )–C≡C] ( x = 1, 2) belong to the localized Class‐II MV compounds …”

“…Similarly, the use of a thiophene group in the organic bridge leads to the cationic system [8] + showing the electronic properties of a strongly coupled mixed-valence Class-III complex. [111,112] [114] Recently, the monocationic complexes [M(dppe)Cp*] 2 [μ-C≡C-(2,5-SC 4 H 2 )-C≡C + ] (M = Fe, Ru) were investigated both experimentally and theoretically. [115] As expected, calculations have shown that the spin density is evenly distributed over the metal-bridge-metal backbone.…”

Chelated Fischer carbene complexes of annulated thiophenes: synthesis, structure and electrochemistry

“…Thiophene oligomers (and polymers) are widely studied because of their electroconductive and photonic properties. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] Application of α-connected, conjugated thiophene units in chain stuctures 1,[5][6][7] and α,β-fused thiophene rings in band structures 1,2,4,[8][9][10][11][12] are finding wide application as organic conductors/superconductors 4,7,8 and non-linear optical materials. 1,5,6,9 In addition, oligothiophenes are appealing units to act as spacer-ligands between metal fragments for potential long distance metal-metal communication.…”