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.