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Syntheses, Spectroelectrochemical Studies, and Molecular and Electronic Structures of Ferrocenyl Ene-diynes

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journal contribution
posted on 18.02.2016 by Kevin B. Vincent, Qiang Zeng, Matthias Parthey, Dmitry S. Yufit, Judith A.K. Howard, František Hartl, Martin Kaupp, Paul J. Low
The readily available complex 1,1-dibromo-2-ferrocenylethylene provides a convenient entry point for the preparation of a wide range of cross-conjugated 1,1-bis­(alkynyl)-2-ferrocenylethenes through simple Pd(0)/Cu­(I)-mediated cross-coupling reactions with 1-alkynes. The ferrocene moiety in compounds of the general form FcCHC­(CCR)2 is essentially electronically isolated from the cross-conjugated π system, as evidenced by IR and UV–vis spectroelectrochemical experiments and quantum chemical calculations. In contrast to the other examples which give stable ferrocenium derivatives upon electrochemical oxidation, the aniline derivatives [FcCHC­(CCC6H4NH2-4)2]+ and [FcCHC­(CCC6H4NMe2-4)2]+ proved to be unstable on the time scale of the spectroelectrochemical experiments, leading to passivation of the electrode surface over time. There is no significant thermodynamic stabilization of the radical anion [FcCHC­(CCC6H4NO2-4)2] relative to the neutral and dianionic analogues, although the dianion [FcCHC­(CCC6H4NO2-4)2]2– could be studied as a relatively chemically stable species and is well described in terms of two linked nitrophenyl radicals. The capacity to introduce a relatively isolated point charge at the periphery of the cross-conjugated π system appears to make these complexes useful templates for the construction of electrochemically gated quantum interference transistors.