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–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, multinuclear 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) wer...