Evaluation of the Extent of Conjugation in Symmetrical and Asymmetrical Aryl-Substituted Acetophenone Azines Using Electrochemical Methods

Abstract

The electrochemical behavior of a series of symmetrical and unsymmetrical aryl-substituted acetophenone azines (1-X/Y, where X and Y are 4-NO2, 4-CN, H, 3-OCH3, 4-OCH3, 4-CH3, and 4-N(CH3)2) was studied in acetonitrile and N,N-dimethylformamide (DMF) solution using cyclic voltammetry (CV). Compounds 1-X/Y, where neither X or Y are nitro substituents, undergo successive reduction to their radical anion (1-X/Y.-) and then dianion (1-X/Y2-), respectively. In all cases, the formation of the radical anion is completely reversible and the standard reduction potentials, Eo1-X/Y/1-X/Y.- could be determined. The reversibility of the second electron transfer is substituent dependent with certain dianions sufficiently basic to be protonated under our conditions. Standard reduction potentials (Eo1-X/Y/1-X/Y.-) for the formation of radical anions exhibit a large substituent effect with values differing by more than 0.66 V throughout the series going from 1-4-CN/4-CN to 1-4-OCH3/4-OCH3; similar substituent effects were determined for the formation of the dianion. The nitro-containing azines deviate from the above-mentioned behavior. With the exception of 1-4-NO2/4-NO2, they exhibit single electron waves that have values of Eo1-X/Y/1-X/Y.- within 40 mV of each other and thus the reduction is not subject to the same substituent effect as the other azines. 1-4-NO2/4-NO2 exhibits an Eo at a similar potential, but is a two-electron reversible wave with features indicative of a reduction system containing two localized, nonconjugated redox centers. The reduction potentials of all the aryl azines were correlated with Hammett sigma parameters to look at variations in Eo1-X/Y/1-X/Y.- vs SCE as a function of substituent. The small rho values in combination with the other electrochemical data provide support for single bond character of the N-N bond and evidence for a lack of strong electronic communication between the two aryl centers through the azomethine bonds, especially for those systems with electron-withdrawing groups.

The electrochemical reduction of 1,4-dichloroazoethanes: Reductive elimination of chloride to form aryl azines

“…Table 1 Reduction potentials of the 1,4-dichloroazoethanes in 0.1 M TEAP/DMF solution at a glassy carbon electrode. Product studies and comparison with authentic samples confirmed that waves B and C correspond to the formation of the acetophenone azines (2-X/Y) [21]. Quantitative formation of 2-X/Y was observed by constant potential electrolysis experiments, where solutions of 1-X/Y were electrolyzed at a potential slightly negative to the E p of wave A until no trace of 1-X/Y remained (see Fig.…”

“…The syntheses of the 1-X/Y compounds were performed by chlorination of the corresponding acetophenone azines [19][20][21]. The details and spectral characterization appear in Section 2.…”

“…All 1-X/Y were synthesized in a fumehood by chlorination of the corresponding acetophenone azines (2-X/Y) and purified by recrystallization [19][20][21]. Excess chlorine gas was condensed into a round-bottom flask containing neat 2-X/Y or a suspension of 2-X/Y in CH 2 Cl 2 .…”

Electrochromics by Intramolecular Redox Switching of Single Bonds

“…More than one set of signals have also been observed with some other diarylketazines. [8,9] Figure 2 provides information about the electrochemical behavior of RED-8 and the structures of the possible oxidation products. The CV of RED-8 remained unchanged on multiscanning, indicating an overall reversible chemical reaction.…”

Synthesis, structures, and spectroscopic properties of copper(I) complexes bearing 7-acetamido-4-methyl-1,8-naphthyridin-2-carbaldehyde azine and 1,2-bis(diphenylphosphino)ethane ligands

“…However, the studies on 1,8-Naphthyridyl derivatives with flexible spacers and their metal complexes are rare. The spacers enable the ligand to rotate freely, thereby resulting in various coordination modes and interesting spectroscopic properties [14][15][16][17][18]. Herein, we report on the synthesis, structures and spectroscopic properties of a new ligand napaa with a N-N single bond as a linker (napaa = 7-acetamido-4-methyl-1,8-naphthyridin-2-carbaldehyde azine) and its two dinuclear copper(I) complexes, Cu 2 (napaa) (dppe) 2 (ClO 4 ) 2 (1) and Cu 2 (napaa)(PPh 3 ) 4 (BF 4 ) 2 (2) (dppe = 1,2-bis(diphenylphosphino)ethane and PPh 3 = triphenylphosphine).…”