Synthesis, FTIR, NMR, UV–vis and electrochemistry analysis of ferrocenyl Schiff bases

Five derivatives of 3-ferrocenylphenylimine were synthesized through arylation of ferrocene by diazonium salt under phase transfer conditions. Sn/HCl was used to reduce the nitro derivatives to ferrocenylanilines, which was followed by addition of aromatic aldehydes. The thus obtained compounds N-(2,3-dimethoxybenzylidene)-3-ferrocenylimine (L₁), N-(4-nitrobenzylidene)-3-ferrocenylimine (L₄), N-(2-thiophenecarboxbenzylidene)-3-ferrocenylimine (L₅), N-(3-nitrobenzylidene)-3-ferrocenylimine (L₉), and N-(2-furabenzylidene)-3-ferrocenylimine (L₁₀) showed similar UV–vis absorption spectra with the exception of L₄ which is the nitro-substituted benzylideneimine. Cyclic voltammetry of peak potential separation of the compounds under light and dark conditions was studied and the redox couple ferrocene/ferrocenium showed half-wave potentials around 0.05 V vs Ag/AgCl which is markedly higher than ferrocene. The dependence of the peak potentials and currents from the scan rates was studied in detail. While the energy of the highest occupied molecular orbital was obtained from the half-wave potential of the oxidation, the energy of the lowest unoccupied molecular orbital (LUMO) was estimated from the onset of the absorption spectra. The gaps range from 2.87 to 3.05 eV.