The mechanism of electropolymerization of nickel(ii) salen type complexes

Abstract

Ni(II) complexes with (AE)-trans-N,N 0 -bis(salicylidene)-1,2-cyclohexanediamine ([Ni(salcn)]), and its methyl ([Ni(salcn(Me))]) and tert-butyl ([Ni(salcn(Bu))]) derivatives have been synthesized. Anodic electropolymerization has been used to form electrodes modified by polymer films. FTIR and FTIR ATR methods showed that the obtained films consist of polymers of phenyl-phenyl type. The structure of poly[Ni(salcn)] is built with 1,2,4-and 1,2,3,5-substituted chains. A three-step process of the oxidation of the complexes and their films has been ascertained on the basis of cyclic voltammetry measurements.Furthermore we have also detected the oxidized species which probably serve as intermediates for polymer formation. The influence of the substituent in the phenolate moiety on the type of reaction after which the dimerization and polymerization reaction occurs has been evidenced. Furthermore the substituent dependence on the stability of the phenoxyl radical complex and the Ni(II)-phenoxonium cation has been noticed. For the [Ni(salcn(Bu))] complex, an additional electropolymerization step -the adsorption of the reagent on the electrode surface -has been observed. † Electronic supplementary information (ESI) available: Table S1. Comparison of the FTIR ATR bands of poly[Ni(salcn)] films (electrosynthesized in Bu 4 NPF 6 or Bu 4 NClO 4 ) with the FTIR bands of the [Ni(salcn)] complex; Fig. S1. Cyclic voltammograms of complexes in TBAH/CH 2 Cl 2 , 0.1-1.6 V, v = 0.05 V s À1 , 1st scans vs. Ag/AgCl and Fig. S2. Cyclic voltammograms of complexes in TBAH/CH 2 Cl 2 , 0.1-2.1 V, v = 0.05 V s À1 , 1st scans vs. Ag/AgCl. See

Electrocatalytic Properties of Ni(II) Schiff Base Complex Polymer Films

“…Polymers were obtained by anodic electropolymerization using cyclic voltammetry. Curves were recorded in solutions of complexes (10 −3 mole·dm −3 ) in CH 2 Cl 2 /TBAH (0.1 mole·dm −3 ), at scan rates of 0.005–0.5 V·s −1 in positive potential ranges (0–1.6 V), involving two-step oxidation of complexes [ 35 , 37 ]; 1 to 20 electropolymerization cycles were recorded. As a result of the electropolymerization process, yellow electroactive, well adhering to the electrode surface polymer films, were obtained.…”

“…Our research presents electrodes modified with polymers of Ni (II) complexes with (±)- trans -N,N′-bis(salicylidene)-1,2-cyclohexanediamine ( poly [Ni(salcn)]) and its tert -Bu derivative, substituted in ortho positions of phenolate moieties ( poly [Ni(salcn(Bu))]). In previous studies, we have shown that they are conductive polymers [ 35 ]. They oxidize in two steps to the macro phenoxyl radical and macro bisphenoxyl radical [ 36 , 37 ].…”

Aryl‐Aryl Coupling of Salicylic Aldehydes through Oxidative CH‐activation in Nickel Salen Derivatives

“…Oxidation of NiSalens in solution proceeds via three consequent oxidation steps . The potential applied is high enough to ensure the oxidation of the phenolate moiety to the Ni(II)‐phenoxyl radical complex (I oxidation step, E pa (I step) =0.7 – 1.2 V for different Salen‐type complexes) and then the oxidation of the Ni(II)‐phenoxyl radical complex to the Ni(II)‐bis‐phenoxyl radical complex (II oxidation step, E pa (II step) =1.1 – 1.4 V, depending on ligand structure) . Completion of these oxidation steps assures the possibility of the follow‐up reactions (dimerization and polymerization), regardless of the nature of the substituent affecting the reactivity of the radicals, thus making the synthetic protocol most universal.…”

“…Completion of these oxidation steps assures the possibility of the follow‐up reactions (dimerization and polymerization), regardless of the nature of the substituent affecting the reactivity of the radicals, thus making the synthetic protocol most universal. At the same time the applied potential is low enough to prevent the unwanted formation of Ni(II)‐phenoxonium cation form in solution (III oxidation step, E pa (III step) > 1.6 V), which can terminate the oligomerization of the complexes. In the papers cited above, the potentials were measured vs .…”

“…Oxidation of NiSalens in solution proceeds via three consequent oxidation steps . The potential applied is high enough to ensure the oxidation of the phenolate moiety to the Ni(II)‐phenoxyl radical complex (I oxidation step, E pa (I step) =0.7 – 1.2 V for different Salen‐type complexes) and then the oxidation of the Ni(II)‐phenoxyl radical complex to the Ni(II)‐bis‐phenoxyl radical complex (II oxidation step, E pa (II step) =1.1 – 1.4 V, depending on ligand structure) .…”