Electronic Interactions in the Electroactive Iron σ-Ethynyl-2-Phenyltetramethyldisilanes [Cp*(dppe)Fe–C≡C–Si(CH3)22–1,4-C6H4X](PF6)n (n = 0, 1)

International audienceTreatment of the triflate complex [Cp*(dppe)FeOTf] ₅; Cp* = η5-C5(CH3)5, dppe = 1,2-bis(diphenylphosphanyl)ethane, OTf = CF3SO3_ with an excess of HC≡C–[Si(CH3)2]2–1,4-C6H4X (6a–e) in a mixture of THF and triethylamine (NEt3) provides the new complexes ₁a: X = H; 1b: X = CH3; 1c: X = N(CH3)2; 1d: X = CF3; 1e: X = Br_, which were isolated in 64 to 81 % yields as orange powders. The cyclic voltammetry, and multinuclear NMR, IR, and UV/Vis spectroscopic data obtained for 1a–e, as well as the X-ray crystal structures determined for 1a, 1c, and 1e, reveal the importance of the σ–π conjugation (hyperconjugation) between the Si–Si σ-bond and the vicinal C≡C π-orbitals in the description of the electronic structure of the ground state of these complexes. When compounds 1a–e are reacted with [(C5H5)2Fe](PF6) (1 equiv.) at 20 °C, they provide [1a–e](PF6), which partially decompose in solution during the reaction process. They were isolated as mixtures with the mononuclear [Cp*(dppe)Fe=C=CH2](PF6) (7) and binuclear [Cp*(dppe)Fe=C=CH–CH=C=Fe(dppe)Cp*](PF6)2 (8) vinylidenes. Reduction of these mixtures with cobaltocene affords the parent neutral compounds 1a–e in analytically pure forms. The iron(III) complexes were characterized by IR and Mössbauer spectroscopy, which clearly showed that the iron(III) nucleus sensed the electronic effect of the X substituents. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei