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

• Published in: Organometallics 2016-06, Vol.35 (12), p.2057-2070
• Main Authors: Roué, Séverine, Sahnoune, Hiba, Toupet, Loïc, Halet, Jean-François, Lapinte, Claude
• Format: Article
• Language: English
• Subjects: Chemical Sciences
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/acs.organomet.6b00209

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 Mössbauer 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(PF 6 ) n and 3­(PF 6 ) 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(PF 6 ) n and 3­(PF 6 ) n (n = 1, 2) were subjected to analyses by ESI-mass spectrometry, IR, Mössbauer, ESR, UV–vis, and NIR spectroscopies. The radical cations 2­(PF 6 ) and 3­(PF 6 ) belong to Class II of the mixed-valence Robin and Day classification with quite sizable electronic coupling parameters for large metal–metal separation (2­(PF 6 ), H ab = 262 cm–1, d FeFe = 17.7 Å; 3­(PF 6 ), H ab = 203 cm–1, d FeFe = 19.7 Å). Paramagnetic 1H NMR spectroscopy was also performed on the dicationic salts to measure the magnetic exchange between the distant spin carriers (2­(PF 6 ) 2 , ΔG ST = −120 cm–1). The data were analyzed with the support of quantum chemistry calculations at the DFT level of theory.