Aminomethyl-Substituted Ferrocenes and Derivatives: Straightforward Synthetic Routes, Structural Characterization, and Electrochemical Analysis

A variety of aminomethyl-substituted ferrocenes and the parent compounds (iminomethyl)ferrocenes, azaferrocenophanes, and diferrocenylamines can be selectively synthesized from reductive amination of 1,1′-diformylferrocene or formylferrocene. The optimized one- or two-step reactions have delivered 13 new compounds, isolated in 65–97% yields, which include tertiary (ferrocenylmethyl)amines and azaferrocenophanes by using NaBH(OAc)3 as a mild reducing agent and (iminomethyl)ferrocenes and secondary (ferrocenylmethyl)amines by using LiAlH4. X-ray structures of representative members of these ferrocene derivative families have evidenced the preferred conformation adopted by ferrocene backbones, in which surprisingly the steric hindrance is apparently not systematically minimized. 15N NMR measurements on aminomethyl-substituted ferrocenes and derivatives are provided for the first time, establishing benchmark values ranging from −330 to −305 ppm (nitromethane δ 0 ppm). The cyclic voltammetry of these species evidences two clearly distinct oxidation potentials related to the iron(II) center and the amino function. These aminomethyl-substituted ferrocenes are potentially valuable for further ortho-directed functionalization of ferrocene.