Synthesis and isomerization behavior of cyano-vinyl ferrocenes

• Synthesis and coordination behavior of cyano-vinyl ferrocenes.
• The solid state structures of eight compounds are reported.
• Electrochemical studies on cyano-vinyl ferrocenes platinum complexes.

The reaction of Z-FcC(Cl)CHC(O)H (Fc = Fe(η5-C5H5)(η5-C5H4)) with KI/ZnO/NH2OH·HCl gave Z-FcC(Cl)CHCN, which on further treatment with ROH/KOH (R = Me, Et, iPr, OCH2CH2OH) or H2NCH2Ph produced Z-FcC(OR)CHCN, E-FcC(NHCH2Ph)CHCN and FcC(OCH2)2CH2CN. However, the use of the sterically demanding OtBu group resulted in the elimination of HCl giving 3-ferrocenylpropynenitrile. Complex [PtCl2(NCCHC(Cl)Fc)2], as a mixture of E/Z and cis/trans isomers, was accessible by the addition of [PtCl2] to Z-FcC(Cl)CHC(O)H. When Z-FcC(OR)CHCN (R = Me; Et; iPr) was reacted with [PtCl2] in the molar ratio of 2:1, solely trans-[PtCl2(E-NCCHC(OR)Fc)2] was formed with isomerization of the C,C double bond from Z to E. These are the first examples for the entirely conversion of Z to E isomers of coordinated acrylonitriles. The stereochemistry of Z-FcC(OR)CHCN is maintained, when the Pt source is excluded, while a combination of heat and light treatment resulted in the partial isomerization. The electrochemical properties of the chloro- and the methoxy-functionalized vinyl ferrocene were studied. In the corresponding Pt complexes an anodic shift of the ferrocenyl units is observed due to an electron density transfer towards the Pt atom. Spectroelectrochemical studies of the Pt complexes allowed no definite verification that an electronic interaction between the redox-active ferrocenyl/ferrocenium termini occurs even when high ΔEp values in the cyclic indicate that two individual oxidation processes might take place in a close potential range.

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