Further Investigation on Preparation, Structure and Electrochemical Properties of N-Alkyl- and N-Aryl-2-aza-[3]-ferrocenophanes

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Abstract
The reactions of 1,1′-bis(hydroxymethyl)ferrocene with primary amines such as 6-aminohexanol, cyclohexylamine, 4-phenylbutylamine, 2-isopropylaniline, 4-(trifluoromethyl)benzylamine, and 1-aminomethylferrocene in the presence of [RuCl2(PPh3)3] catalyst led to intermolecular condensation of the CH2OH and NH2 groups to afford N-alkyl- or N-aryl substituted 2-aza-[3]-(1,1′)-ferrocenophanes. Cyclic voltammograms of the obtained N-alkyl-2-aza-[3]-(1,1′)-ferrocenophanes exhibit reversible redox of the Fe center at E1/2 = −0.01 – +0.04 V (vs Ag+/Ag) and subsequent irreversible oxidation of the amino group of the ligand at Eox = 0.41–0.44 V. N-(4-Hydroxyphenyl)-2-aza-[3]-(1,1′)-ferrocenophane shows two pairs of reversible electrochemical oxidation and reduction at E1/2 = 0.04 and 0.44 V. The latter potential is significantly lower than the corresponding electrochemical oxidation of N-aryl-2-aza-[3]-(1,1′)-ferrocenophanes (0.68–0.75 V). The N-alkyl-2-aza-[3]-(1,1′)-ferrocenophanes react with MeI to cause methylation of the amino group to produce cationic 2-aza-[3]-(1,1′)-ferrocenophanes containing a quaternary nitrogen center. The iodo counter anion is easily replaced with BF4− or PF6−. Cyclic voltammograms of the cationic ferrocenophanes show the redox between ferrocene and ferrocenium at E1/2 = 0.37–0.42 V.

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