891203-09-1Relevant articles and documents
Synthesis, characterization, electrochemistry, and computational studies of ferrocenyl-substituted siloles
Lehrich, Steve W.,Hildebrandt, Alexander,Rüffer, Tobias,Korb, Marcus,Low, Paul J.,Lang, Heinrich
, p. 4836 - 4845 (2015/04/27)
Ferrocenylsiloles of the type 2,5-Fc2-3,4-Ph2-cC4SiR2 (3a, R = Me; 3b, R = Ph) have been prepared by reductive cyclization from diethynylsilanes, followed by ferrocenylation using the Negishi C,C cross-coupling protocol with the silole ring serving as either the vinyl halogenide species or as the zinc organic component and the complementary functionality introduced on the ferrocenyl moiety. The electrochemical behavior of these silacyclic-bridged bis(ferrocenyl) complexes was investigated by cyclic and square wave voltammetry, and the nature of the redox products was studied by in situ UV-vis-near-IR spectroelectrochemical measurements. 3a,b each undergo two sequential ferrocenyl-based redox processes, the separation of which (δE°′ = δE2°′ - δE1°′ = 300 mV (3a), 280 mV (3b)) is in the range of structural similar systems such as 2,5-diferrocenyl-1-phenyl-1H-phosphole (280 mV) and 2,5-diferrocenylfuran (290 mV). Interestingly, the more electron rich silole 3b, in comparison to 3a, shows a modestly lower redox separation between the individual ferrocenyl oxidation processes, which may be due to the capacity of this group to shield the effect of an adjacent positive charge. An intervalence charge transfer (IVCT) absorption was found in the in situ NIR spectra of [3a]+ and [3b]+, the analysis of which is consistent with a moderate electronic interaction between the iron atoms through the cis-diene-like fragment of the silole bridge, allowing their description as Robin and Day class II mixed-valence systems. These conclusions are supported by results from quantum chemical calculations, which together with NMR studies of 3b, also reveal the likely presence of a range of molecular conformations in solution. (Figure Prsented)
