Di- and Triferrocenyl (Hetero)Aromatics: Synthesis, Characterization, (Spectro-)Electrochemistry, and Calculations

Abstract

A series of di- and triferrocenyl (hetero)aromatics including 2,5-diferrocenylpyridine ( 4 ), 2,6-diferrocenylpyridine ( 5 ), 1,3,5-triferrocenylbenzene ( 9 ), 2,4,6-triferrocenylpyridine ( 10 ), and 2,4,6-triferrocenyl-1,3,5-triazine ( 11 ) have been prepared using the Negishi C,C cross-coupling protocol. Characterization of the molecules was performed by spectroscopic means and single-crystal X-ray diffraction study ( 10 ). The electrochemical properties of these compounds were determined by cyclic voltammetry, square wave voltammetry, and in situ NIR spectroelectrochemistry. The cyclic voltammograms show well-defined, separated, and reversible one-electron processes for each ferrocenyl moiety with Δ E °′ values (= separation between two formal potentials) ranging from 140 to 185 mV. The UV–vis/NIR spectra of the partially oxidized mixed-valent complexes of 4, 5, 9, and 10 show weak intervalence charge transfer absorptions, while only electrostatic interactions exist between the different oxidized iron centers of 11 . Supporting DFT calculations were carried out to establish a basic understanding of the electronic structure.