Ferrocenyl Maleimides – Synthesis, (Spectro‐)Electrochemistry, and Solvatochromism

Abstract

Ferrocenylmaleimides have been synthesized from 2,5‐dibromo‐N‐methyl‐1H‐pyrrole. Bromine shift and oxidation of the pyrrole core with subsequent ferrocenylation using the Negishi C–C cross‐coupling protocol led to the formation of 3‐ferrocenyl‐N‐methylmaleimide (3), 3‐bromo‐4‐ferrocenyl‐N‐methylmaleimide (4), and 3,4‐diferrocenyl‐N‐methylmaleimide (5). The structural properties of 4 and 5 were investigated by single‐crystal X‐ray diffraction. Cyclic and square‐wave voltammetry, in situ UV/Vis/NIR and IR spectroelectrochemistry (5) highlight the electrochemical properties of these compounds. Compounds 3 and 4 exhibit one reversible ferrocenyl‐based redox event, whereas 5 shows two separate electrochemically reversible one‐electron transfer processes with remarkably high ΔE°′ values and reduction potentials of E1°′ = 50 and E2°′ = 380 mV (ΔE°′ = 330 mV), respectively, with [NBu4][B(C6F5)4] as the supporting electrolyte. The NIR measurements confirm the electronic communication between the iron centers (FeII/FeIII) as intervalence charge transfer absorptions were observed in 5+. Compound 5 was classified as a weakly coupled class II system, according to Robin and Day. UV/Vis investigations of the solvatochromic behavior of 3–5 revealed the complex solvation of these push–pull systems, which reflects that three important solvent properties (hydrogen bond formation ability, polarizability, and solvation of the carbonyl group and the C=C bond) affect $\tilde {\nu}$max.

Ferrocenyl‐Pyrenes, Ferrocenyl‐9,10‐Phenanthrenediones, and Ferrocenyl‐9,10‐Dimethoxyphenanthrenes: Charge‐Transfer Studies and SWCNT Functionalization

“…As imilarb ehavior was observed for ferrocenyl-substituted maleimides. [68] These compounds also show ap ositive solvatochromism, but as maller solvatochromic range (Dṽ max )o f1 820-2460 cm À1 in contrastt o10 with 2880 cm À1 ,w hich indicates a stronger solvatochromic behavior. [68] Electrochemistry and spectroelectrochemistry…”

Electronic Tuneable Dynamic and Electrochemical Behavior of N‐(Diferrocenylmethylene)anilines

“…On the other hand, compounds in which two ferrocenyl termini are connected via a single atomic bridge, including C,16 N,17 O,18 Si,19,20 P,21 Hg,22 Sn,23 display interesting chemical and electrochemical properties. In addition, it has been demonstrated on the example of ferrocenyl functionalized pyrroles that the electronic characteristics of the bridge can be modified in a very controlled manner by electron‐withdrawing and electron‐donating functionalities at the nitrogen atom 24,25…”

Crystal structure of 3-ferrocenyl-1-phenyl-1H-pyrrole, [Fe(η5-C5H4cC4H3NPh)(η5-C5H5)]

“…Comparing the plane intersections between the ferrocenyl and the pyrrolic ring systems, compound (I) exhibits the most coplanar torsion of 8.17 (18) followed by 3,4-diferrocenyl-Ntosyl pyrrole (Korb et al, 2014) with 19.855 (6) or, in the case of maleimides, the 3-bromo-4-ferrocenyl-N-phenyl-derivative with 9.8 (Hildebrandt et al, 2012).…”