Electrochemical transformations and evaluation of antioxidant activity of some Schiff bases containing ferrocenyl and (thio‐)phenol, catechol fragments

Abstract

Electrochemical transformations and antioxidant activity of some Schiff bases 1–5 containing ferrocenyl group and (thio‐)phenol, catechol fragments were investigated. Compounds under investigation are: 2‐(ferrocenylmethylene)amino)phenol (1), 2‐((ferrocenylmethylene)amino)‐4,6‐di‐tert‐butylphenol (2), 2‐((ferrocenylmethylene)amino)‐thiophenol (3), 3‐((ferrocenylmethylene)hydrazonomethyl)‐4,6‐di‐tert‐butylcatechol (4) and 2‐((3,5‐di‐tert‐butyl‐4‐hydroxybenzylidene)amino)thiophenol (5). In a case of compounds 1–3 it has shown that the sequence of electrochemical transformations leads to the products of intramolecular cyclization – 2‐ferrocenylbenzoxazole (benzothiazole). o‐Quinone formation occurs during the electrochemical oxidation of catechol‐ferrocene 4 at the first anode stage. Electrochemical oxidation of the redox‐active fragments in Schiff bases 1–4 can be achieved indirectly at a lower potential corresponding to the oxidation of ferrocenyl moiety, consequently these substances can reveal more pronounced antioxidant properties. The antioxidant activities of the compounds were evaluated using 2,2′‐diphenyl‐1‐picrylhydrazyl radical (DPPH) assay, the reaction of 2,2′‐azobis(2‐amidinopropane hydrochloride) (AAPH) induced glutathione depletion (GSH), the oxidative damage of the DNA, the process of lipid peroxidation of rat (Wistar) brain homogenates in vitro. The compounds 1–4 in the antioxidant assays show effectiveness comparable with standard antioxidants (vitamin E, Trolox) and in some parameters superior to them. In the reaction of AAPH with the glutathione compounds 2–5 have a more pronounced protective activity than Trolox. Compounds 1–5 inhibit AAPH induced oxidation damage of the DNA. The more effective inhibitors of the lipid peroxidation process in vitro are molecules containing the bulky tert‐butyl groups: 2 and 4 and Schiff base 3.

Polyfunctional Sterically Hindered Catechols with Additional Phenolic Group and Their Triphenylantimony(V) Catecholates: Synthesis, Structure, and Redox Properties

“…In contrast to the previously studied triphenylantimony(V) catecholato complexes with additional redox centers (ferrocenyl, morpholine, piperazine groups [18,24,30]), whose electrochemical activation is observed at potentials shifted to the cathode region as compared to the "catechol/o-semiquinone" transition, compounds 1 and 2 are characterized by electrooxidation of the phenolic fragment at potentials that are close to the second redox transition "o-semiquinone/obenzoquinone". This fact indicates the convergence of the boundary redox orbitals of the phenolic and o-semiquinone fragments in the electro-generated monocationic complexes.…”

“…Organic and organometallic compounds containing several redox centers are of particular interest in view of a number of their specific features: the possibility of indirect activation through certain functional groups, intramolecular electron transfer, proton-conjugated electron transfer, etc. From the example of ferrocene derivatives (ferrocifenes) as well as quinoid compounds, it was shown that various types of biological activities (cytotoxicity, antibacterial, antiparasitic, antioxidant) depend directly on the presence of a redox-active group and its transformations [21][22][23][24]. Redox-asymmetric systems can be built not only on the basis of a ferrocenyl fragment but also on a combination of phenolic, amide, and amino groups, which are also of interest because of the possibility of proton-conjugated charge transfer reactions [25][26][27].…”

Heteroligand α-Diimine-Zn(II) Complexes with O,N,O′- and O,N,S-Donor Redox-Active Schiff Bases: Synthesis, Structure and Electrochemical Properties

“…Stabilization of this type of intermediate can be achieved due to the presence of a neocuproine ligand in 7 , since complex 6 with the Bipy ligand does not exhibit such behaviour. For Schiff bases acting as ligands, electrically induced cyclization is a typical reaction [ 44 , 45 ]. The ratio of currents for the second stage is less than 1, which implies the occurrence of the subsequent chemical stage, i.e., deprotonation of the tertiary carbon atom with the formation of benzothiazole.…”

Ferrocene‐appended donor–π–acceptor Schiff base: Structural, nonlinear optical, aggregation‐induced emission and density functional theory studies

“…Research on ferrocene‐containing compounds has drawn immense attention due to their wide‐ranging applications in the fields of catalysis, sensors, luminescent systems, nonlinear optics[4a] and molecular electronic devices due to their well‐established redox switching abilities . Since ferrocene displays a good electrochemical response because of its strong π‐donating ability and good reversibility in one‐electron oxidation at a desirable range, ferrocene‐based receptors for anion/cation recognition are of considerable interest.…”