Nickel Salen Research Articles

Infrared spectral features of the charge carriers in nickel salen polymeric complexes

A series of the polymeric complexes (PCs) of nickel(II) with N2O2 Schiff base ligands have been studied by in situ Fourier Transform Infrared (FTIR) spectroelectrochemistry. The molecular structure of the metal-salen complexes as starting materials for the polymer synthesis was modulated by various substituents in the phenolate moieties and diimine bridge. Two groups of the infrared-active vibration (IRAV) bands are obtained in the spectra depending on the oxidation level of the polymers. The assignment of the main IRAV bands was carried out and the electrochemically generated charge carriers were determined. Analysis of the spectroscopic features observed in the mid and near IR region provides information on the charge distribution within the polymer film.

A Highly Active Nickel Catalyst for the Selective Hydrogenation of Functionalized Nitroarenes

AbstractThe catalytic hydrogenation of nitroarenes using hydrogen gas as reducing agent to form substituted aniline derivates is an important reaction in industry and academic research. Here, we report on the nitroarene hydrogenation capability of a nanostructured nickel catalyst synthesized from a nickel salen complex and a commercially available porous silica support. Our catalyst allows the selective hydrogenation of nitroarenes under mild conditions while tolerating various functional groups and hydrogenation‐sensitive examples such as iodine, nitrile or olefinic groups. The use of the nickel salen complex as metal precursor is crucial for the high activity and selectivity observed.

Nickel–salen as a model for bifunctional OER/UOR electrocatalysts: pyrolysis temperature–electrochemical activity interconnection

The Nickel-Salen precursor was pyrolyzed to Ni/NiOx nanostructure OER/UOR electrocatalysts, where the process was tracked by TG-MS technology detecting small-molecule fragments.

Exciton Coupling in Redox-Active Salen based Self-Assembled Metallacycles.

The incorporation of a redox-active nickel salen complex into supramolecular structures was explored via coordination-driven self-assembly with homobimetallic ruthenium complexes (bridged by oxalato or 5,8-dihydroxy-1,4-naphthoquinato ligands). The self-assembly resulted in the formation of a discrete rectangle using the oxalato complex and either a rectangle or a catenane employing the larger naphthoquinonato complex. The formation of the interlocked self-assembly was determined to be solvent and concentration dependent. The electronic structure and stability of the oxidized metallacycles was probed using electrochemical experiments, UV-Vis-NIR absorption, EPR spectroscopy and DFT calculations, confirming ligand radical formation. Exciton coupling of the intense near-infrared (NIR) ligand radical intervalence charge transfer (IVCT) bands provided further confirmation of the geometric and electronic structures in solution.

Unsymmetrical salen nickel (II) complex embracing phenol bridge: X-ray structure, redox investigation, computational calculations, antimicrobial and catalytic activities

An exhaustive description of the crystal structure, DFT, TD-DFT and redox properties of a non-symmetrical nickel complex NiLOH, N,N’-2,3-hydroxyphenol -2,3-dyil-bis (salicylideneimine)nickel(II), are reported. The complex crystallizes, in the monoclinic crystal system, with P21/c space group. Oxygen-atom of the phenolic spacer contributes in hydrogen bonding forming a zigzag chain along a axis. Cyclic voltammetric study of the complex revealed a quasi-reversible process Ni(II)/Ni(I) on a glassy carbon electrode at E1/2 = -1371, -1312, -1305 mV/SCE in DMSO, CH3CN and DCM, respectively. From DFT calculations, the electronic properties of NiLOH complex and its reactivity with DNA bases, in polar and non-polar media, shows a good agreement with the experimental results. TD-DFT revealed that the absorption electronic states correspond to a mixture of metal to ligand charge transfer (d→π*) and intra-ligand charge transfer (π→π*) transitions. The NiLOH complex as catalyst proved to be catalytically active in the cyclohexene epoxidation reaction. The ligand and the NiLOH complex were scrutinized for their antibacterial activity in agar medium by the disk diffusion method against some Gram positive and Gram negative strains. Better inhibitory potential towards some examined bacteria was shown.

Mechanistic Insight into the Catalytic Electroreduction of Tetrabromobisphenol-a at Carbon Cathodes

Polyhalogenated phenols are a class of environmental pollutants that serve as precursors to dioxins and behave as endocrine disruptors.1,2 As a result, an efficient route of degradation is needed. Traditional methods of remediation include microbial, thermal, and chemical pathways; however, these typically require large amounts of toxic solvents, excessive amounts of energy, and can be tremendously time-consuming.3 Electrochemistry has become a growing area of research for the remediation of environmentally-harmful compounds, as the electroreductive behavior of carbon–halogen bonds is well understood.Herein, we report the electrochemical reduction of the flame retardant 3,3',5,5'-tetrabromobisphenol-A (TBBPA), at carbon cathodes in the absence and presence of nickel(II) salen. Cyclic voltammograms at varying scan rates, coupled with voltammograms in the presence of a hydrogen-bonding stabilizer, suggest reduction proceeds by cleavage of a carbon–bromine bond, followed by reduction of a short-lived intermediate. Controlled-potential (bulk) electrolysis was performed to determine the extent of reduction that could be achieved; moreover, gas chromatography–mass spectrometry was utilized to separate and identify reduction products. Electrolyses performed in the presence of deuterium oxide and 1,1,1,3,3,3-hexafluoroisopropanol-OD reveal a carbanion intermediate present in the reduction mechanism. References M. Montaño, A. C. Gutleb, and A. J. Murk, Environ. Sci. Technol., 2013, 47, 6071–6081.C. D. Klaassen, Casarett & Doull’s Toxicology the Basic Science of Poisons, McGraw-Hill Education, 2013.E. T. Martin, C. M. McGuire, M. S. Mubarak and D. G. Peters, Chem. Rev., 2016, 116, 15198–15234.

Green synthesis of MCM-41 from rice husk and its functionalization with nickel(II) salen complex for the rapid catalytic oxidation of benzyl alcohol

Abstract N,Nʹ-bis(4-hydroxysalicylidene)ethylenediamine nickel(II) complex was synthesized and functionalized onto MCM-41. The catalyst denoted as MCMSalenNi, was found to retain its hexagonal mesoporous structure as indicated from the TEM images. It however, had a reduced surface area and lower x-ray diffraction intensity than the parent MCM-41. Both FT-IR and solid-state MAS NMR (29Si, 13C) analyses proved that the complex was successfully functionalized onto the MCM-41 support. The catalyst was used in the rapid oxidation of benzyl alcohol and it afforded a high conversion (~98%) with benzaldehyde as the major product within 90 min. Periodic acid was used as a mild oxidant. In addition, the catalyst was reused up to six times with minimal loss of activity.

Nickel(I) salen-catalyzed reduction of 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113): CO2-mediated carbon–fluorine bond cleavage

Cyclic voltammetry, controlled-potential (bulk) electrolysis, gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS), and high-performance liquid chromatography–electrospray ionization–mass spectrometry (HPLC–ESI–MS) have been used to investigate the direct and nickel(I) salen-catalyzed reduction of 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) in both Ar- and CO2-saturated dimethylformamide (DMF) containing 0.10 M tetra-n-butylammonium tetrafluoroborate (TBABF4). Cyclic voltammograms show one irreversible cathodic peak for direct reduction of CFC-113 in CO2-saturated DMF to afford 1-chloro-1,2,2-trifluoroethene (CFC-1113), whereas cyclic voltammograms in Ar-saturated DMF exhibit two irreversible cathodic peaks. Bulk electrolyses of CFC-113 in CO2-saturated DMF at a potential 400 mV more negative than the resolved cathodic peak cause partial reduction of CFC-1113 to yield di-, tri-, and tetrafluoro species. Cyclic voltammograms for reduction of nickel(II) salen in the presence of CFC-113 in CO2-saturated DMF show two cathodic peaks attributable to formation of CFC-1113 and HFC-1123; cyclic voltammograms in Ar-saturated DMF exhibit similar behavior. Bulk electrolyses involving electrogenerated nickel(I) salen in CO2-saturated DMF yield mixtures of HFC-1123, isomers of difluoroethene, and traces of other species. No electrocarboxylation of CFC-113 or its derivatives was seen in the presence of CO2; however, excess CO2 increases the extent of dechlorination of CFC-113 during bulk electrolyses when compared with analogous electrolyses in an Ar-saturated medium. Structural modification of nickel(II) salen during catalytic reduction of CFC-113 in the presence of CO2 was determined with the aid of HPLC–ESI–MS.

Enantioselective Alkynylation of Trifluoromethyl Ketones Catalyzed by Cation‐Binding Salen Nickel Complexes

AbstractCation‐binding salen nickel catalysts were developed for the enantioselective alkynylation of trifluoromethyl ketones in high yield (up to 99 %) and high enantioselectivity (up to 97 % ee). The reaction proceeds with substoichiometric quantities of base (10–20 mol % KOt‐Bu) and open to air. In the case of trifluoromethyl vinyl ketones, excellent chemo‐selectivity was observed, generating 1,2‐addition products exclusively over 1,4‐addition products. UV‐vis analysis revealed the pendant oligo‐ether group of the catalyst strongly binds to the potassium cation (K+) with 1:1 binding stoichiometry (Ka=6.6×105 m−1).

Enantioselective Alkynylation of Trifluoromethyl Ketones Catalyzed by Cation-Binding Salen Nickel Complexes.

Cation-binding salen nickel catalysts were developed for the enantioselective alkynylation of trifluoromethyl ketones in high yield (up to 99 %) and high enantioselectivity (up to 97 % ee). The reaction proceeds with substoichiometric quantities of base (10-20 mol % KOt-Bu) and open to air. In the case of trifluoromethyl vinyl ketones, excellent chemo-selectivity was observed, generating 1,2-addition products exclusively over 1,4-addition products. UV-vis analysis revealed the pendant oligo-ether group of the catalyst strongly binds to the potassium cation (K+ ) with 1:1 binding stoichiometry (Ka =6.6×105 m-1 ).

People, Travel, Seminars, Reading, the Classroom, and Curiosity-Sources of Research Inspiration

This manuscript is the outgrowth of a plenary lecture delivered by the author at the 44th Congreso Mexicano de Química that was held in Puebla, Mexico from 26-30 September of 2009. In formulating the presentation, consideration was given to thinking about the origins of the ideas that were integral to the formulation of the research to be described. The intent was to address the younger members of the audience – advanced undergraduate and graduate students, and those beginning the process of searching for a job. At a similar stage in my scientific career, I realized the need to formulate research plans in order to complete job applications where they were required. Where do these ideas come from? What factors stimulate one’s curiosity? What stimulates one to pursue a particular line of research? Topics discussed within the context of attempting to address these questions include electrohydrocyclization and electroreductive cyclization, and their application to the total synthesis of natural products, the use of nickel salen and triarylamines as mediators and redox catalysts, the regiospecific rearrangement of cation radicals derived from strained hydrocarbons and the application of the chemistry to the synthesis of a sesquiterpene, and finally, a discussion of the role redox chemistry may play in the expression of the bioactivity of the pseudopterosin class of marine natural products.
 
 

Mechanistic Insight into Photoelectrochemical Conversion of Alkyl Monohalides to Aldehydes

Aldehydes are important starting materials for a variety of chemical processes such as the synthesis of food preservatives. For example, certain aldehydes may be used for improving sensory quality and shelf-life of milk.1 Synthesis of aldehydes from alkyl monohalides involves a multi-stage reaction which various reagents are needed for each step of the conversion.2 Previous works from our laboratory showed that simultaneous introduction of UV radiation and oxygen during electrolysis of an alkyl monohalide with electrogenerated nickel(I) salen affords the corresponding aldehyde or ketone with relatively high yield (Figure 1). 3,4 The purpose of the present work is to elucidate the mechanism for the above-mentioned conversion. For this purpose, a solution of 1-bromooctane (5 mM) and nickel(II) salen (5 mM) was electrolyzed at –1.0 V in DMF–water containing TMABF4 (0.10 M). At the end of the electrolysis, modified nickel(II) salen was separated from the electrolysis mixture with application of normal phase flash chromatography. Modified nickel(II) salen was dissolved in DMF–water containing TMABF4 (0.10 M) and exposed to UV radiation (440 nm); the product of the photoreaction was identified as octanal. In respect, we believe the reaction passes through a series of the intermediates are proposed in Figure 2. This reaction features a single-step and efficient method for transforming alkyl monohalides into the desired aldehydes. References Kelly, P. Woonton, B. W. Smithers, G. W. Woodhead. Woodhead Publishing Ltd. 2009. 170.Hendrickson, J. B., Sternbach, D. D. J. Org. Chem. 1975, 40, 3450.Vanalabhpatana, P.; Peters, D. G. Tetrahedron Lett. 2003, 44, 3245.Vanalabhpatana, P.; Peters, D. G. J. Electroanal. Chem. 2006, 593, 34. Figure 1

Electrochemical Reduction of Acetochlor at Carbon and Silver Cathodes in Dimethylformamide

Chloroacetamides are a popular class of herbicides often used against weeds in a variety of major crops, such as corn, cotton, rice, and soybeans.1 One such herbicide is acetochlor or 2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide that, since its registration in 1994, has become commonly used in the United States.2 Although acute and chronic toxicological effects in humans of acetochlor at low environmental exposures are still unknown, animal tests have shown in some species the development of lung tumors, nasal epithelia, and thyroid cancer; for that reason, the U.S. EPA classifies acetochlor as likely to be carcinogenic in humans.3,4 This project’s primary objective is to investigate the electrochemical behavior of acetochlor and to develop a possible degradation method for acetochlor as well as other chloroacetamide-type herbicides. To the best of our knowledge, previous electrochemical studies of acetochlor have been performed only via anodic Fenton treatment;5 electrochemical reduction has not yet been pursued. In the present study, we have conducted cyclic voltammetry to evaluate the electrochemical behavior of acetochlor at carbon and silver cathodes in dimethylformamide (DMF) containing 0.05 M tetramethylammonium tetrafluoroborate (TMABF4). Glassy carbon is a traditional electrode material and silver has been shown to be catalytic for the cleavage of carbon–halogen bonds. Reduction of acetochlor at silver (–0.95 V vs. Cd/Hg) occurs at more positive potentials than at carbon (–1.4 V vs. Cd/Hg) and affords primarily the dechlorinated parent compound, N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide. In addition, reduction of acetochlor in the presence of electrogenerated nickel(I) salen (–0.95 V vs. Cd/Hg) indicates that nickel salen complexes can be an alternative to silver in order to achieve catalytic reduction. Controlled-potential (bulk) electrolysis coupled with traditional analytical methods such as gas chromatography–mass spectrometry (GC–MS) led to the identification and quantitation of reduction products. References Lamberth, C. Chloroacetamide Herbicides. In Bioactive Carboxylic Compound Classes, Pharmaceuticals and Agrochemicals, Lamberth, C., Dinges, J., Eds.; Wiley: Germany, 2016; pp 293–302.Lerro, C. C.; Koutros, S.; Andreotti, G.; Hines, C. J.; Blair, A; Lubin, J.; Ma, X.; Zhang, Y.; Beane Freeman, L. E. Int. J. Cancer. 2015, 137, 1167–1175.U.S. Environmental Protection Agency. Acetochlor (Harness) Pesticide Petition Filing 1/00. Fed Regist. 2000, 65, 3682–3690. Report of the Food Quality Protection Act (FQPA) Tolerance Reassessment Progress and Risk Management Decision (TRED) for Acetochlor. EPA 738-R-00-009; U.S. Environmental Protection Agency (U.S. EPA): 2006, 1–9.Friedman, C. L.; Lemley, A. T.; Hay, A. J. Agric. Food Chem. 2006, 54, 2640–2651.

The effect of phenolic compounds on salicylaldimine nickel-catalyzed ethylene oligomerization

A salen nickel complex has been prepared in good yield with ethylenediamine, salicylaldehyde, and NiCl2·6H2O as raw materials. The structure of the complex was characterized by FTIR, 1H NMR, UV, and ESI-MS. Upon activation with methylaluminoxane (MAO), the precatalyst showed high activity for ethylene oligomerization. To reduce the simultaneous production of insoluble polymers during the nickel-catalyzed ethylene oligomerization, a series of phenolic compounds were introduced as modifiers for the production of linear α-olefins. The researched result showed that the phenolic compounds have a significant impact on the selectivity of oligomers and the concentration of polymers. With the increase of phenolic compounds, the content of polymers decreased and the distribution of oligomers gradually shifted toward lighter olefins. The sterically hindered 4-tert-butyphenol proved to be an especially efficient polymer-retarding modifier among the studied phenolic compounds in this work. Furthermore, the retarding effect of phenolic compounds toward insoluble polymers may be mainly related to their interaction with MAO, giving rise to larger MAO aggregates.

Reduction of α,ω-Dihalohexanes with Electrogenerated Nickel(I) Salen

A recent study has described the electrocatalytic reduction of 1,6-dibromohexane at a silver electrode.1 To mitigate the costs of silver electrodes, glassy carbon electrodes can be used in the presence of a solution-phase catalyst. [[2,2′-[1,2-Ethanediylbis-(nitrilomethylidyne)]bis[phenolato]-N,N′,O,O′]nickel(I), further referred to as nickel(I) salen, has been used as an electrogenerated catalyst in tandem with glassy carbon electrodes due to its ability to reductively cleave carbon—halogen bonds in organic compounds. Previous studies at glassy carbon electrodes with nickel(I) salen or at silver electrodes have primarily focused on reduction of monohalogenated compounds or linear hydrocarbons substituted at both primary positions with mixed halogens. Catalytic reduction of such straight-chain alkyl halides with electrogenerated nickel(I) salen yielded both straight-chain monomeric and dimeric products in high yields.2 In this study, electrogenerated nickel(I) salen was used to reduce 1,6-dibromohexane, 1,6-diiodohexane, and 1-bromo-6-iodohexane catalytically. These substrates were electrolyzed in the presenece of 0.10 M tetramethylammonium tetrafluoroborate (TMABF4) in N,N-dimethylformamide at a glassy carbon electrode. Cyclic voltammetry indicated that direct reduction of 1,6-dibromohexane and 1,6-diiodohexane occurs respectively at –1.64 and –1.56 V vs. a cadmium mercury amalgam reference electrode (Cd(Hg)) with a potential of –0.76 V vs. an aqueous saturated calomel electrode. In contrast, catalytic cathodic peaks are at –0.92 and –0.97 V vs. Cd(Hg) for 1,6-dibromohexane and 1,6-diiodohexane, respectively, indicating that nickel(I) salen does indeed reduce these substrates electrocatalytically. Controlled-potential (bulk) electrolyses of the halogenated substrates led to minor conversion to cyclohexane and halogenated dimers with significant amounts of starting material remaining in solution. This drastic decrease in yield compared to previous studies is hypothesized to be the result of alkylation of the imino bond on the salen ligand.2,3 Though nickel(II) salen can undergo a reversible, one-electron reduction to form nickel(I) salen, reduction of nickel(II) salen can also create a ligand-reduced radical at the imino bond, thus resulting in alkylation of both imino bonds on the salen ligand during electrolysis.3 This dialkylation is responsible for the decreased yield of reaction products and was confirmed with the aid of liquid chromatography—mass spectrometry. A mechanism is proposed with radical intermediates which result in dialkylated nickel(II) salen. Martin, E. T.; Strawsine, L. M.; Mubarak, M. S.; Peters, D. G., Direct Reduction of 1,2- and 1,6-Dibromohexane at Silver Cathodes in Dimethylformamide. Electrochim. Acta 2015, 186, 369–376.Mubarak, M. S.; Peters, D. G., Homogeneous Catalytic Reduction of α,ω-Dihaloalkanes with Electrogenerated Nickel(I) Salen. J. Electroanal. Chem. 1995, 388, 195–198.Martin, E. T.; McGuire, C. M.; Peters, D. G., Catalytic Reduction of Organic Halides by Electrogenerated Nickel(I) Salen. Electrochem. Soc. Interface 2016, 25, 41–45. Figure 1

Catalytic Reduction of α,ω-Dihalohexanes By Electrogenerated Nickel (I) Salen in Dimethylformamide

A previous study has described that [[2,2′-[1,2-ethanediylbis(nitrilomethylidyne)]bis[phenolato]-N,N′,O,O′]nickel(I), also known as nickel(I) salen, can be electrogenerated from nickel(II) salen. Through the use of controlled–potential electrolysis, nickel(I) salen can catalytically reduce α,ω-dihaloalkanes. Early work focused on reduction of α,ω-dihaloalkanes substituted by mixed halogens, and revealed that this reduction could yield both straight-chain monomeric and dimeric products.1 This research project involves the catalytic reduction of 5.0 and 10.0 mM solutions of 1,6-dibromohexane and 10.0 mM 1,6-diiodohexane by nickel(I) salen electrogenerated at a glassy carbon cathode in dimethylformamide containing 0.10 M tetramethylammonium tetrafluoroborate (TMABF4) as a supporting electrolyte. A point of major interest is to separate, identify, and quantitate the products that arise from this catalytic process. Cyclic voltammetry indicates that the reduction peaks for 1,6-dibromohexane are –1.64 V for direct reduction and –0.92 V in the presence of nickel(I) salen; all potentials are reported versus a cadmium mercury amalgam reference electrode with a potential of –0.76 V versus an aqueous saturated calomel electrode. Reduction potentials for 1,6-diiodohexane are –1.56 V and –0.97 V, respectively. Bulk electrolysis of nickel(II) salen in the presence of these substrates has been performed, and the various products were separated and identified with the aid of gas chromatography–mass spectrometry and electrospray ionization–mass spectrometry. The results revealed that there were small amounts of cyclohexane and dihalogenated dimers with a significant amount of starting material left after electrolysis. This low yield is assumed to be from the alkylation of the imino bond on the salen ligand on the basis of previous studies; dihaloalkylated salen species were identified with the aid of liquid chromatography–mass spectrometry.1,2 Reference: Mubarak, M. S.; Peters, D. G., Homogeneous Catalytic Reduction of α,ω-Dihaloalkanes with Electrogenerated Nickel(I) Salen. Electroanal. Chem. 1995, 388, 195–198.Martin, E. T.; McGuire, C. M.; Peters, D. G., Catalytic Reduction of Organic Halides by Electrogenerated Nickel(I) Salen. Soc. Interface 2016, 25, 41–45.

Catalytic reduction of 1-bromodecane and 1-iododecane by electrogenerated, structurally modified nickel(I) salen

Cyclic voltammetry and controlled-potential (bulk) electrolysis have been used to characterize the behavior of a structurally modified nickel(I) salen species, that can be electrogenerated at carbon cathodes in dimethylformamide (DMF) containing 0.10 M tetra‑n‑butylammonium tetrafluoroborate (TBABF4) to catalyze the reductions of 1‑bromodecane (1) and 1‑iododecane (2). This nickel(I) complex possesses a methyl protecting group on each imino (CN) bond, as well as a N‑methyl‑N‑phenylaminomethyl moiety on each aryl group. In its active form, the nickel(I) species can reduce 1 or 2 at a more positive potential than is needed to reduce either substrate directly at a carbon cathode. Bulk electrolysis of the parent nickel(II) complex in the presence of 1 and 2 results in a mixture of n‑eicosane, n‑decane, 1‑decene, and N,N‑dimethylundecanamide, that were identified and quantitated with the aid of gas chromatography–mass spectrometry (GC–MS) and gas chromatography (GC). A mechanistic scheme is proposed to account for the formation of the various products. Robustness of the new nickel(I) catalyst was also investigated and was compared to that encountered with unmodified nickel(I) salen.

Schiff base complexes that form sandwich compounds.

In this article, we explore the capacity of formed Schiff base complexes to trap metal atoms or ions, using their aromatic ends. The intrinsic geometry of each complex defines the process of substitution. Two cases were studied; one involving a trans Schiff base complex and the other considering how a salen ligand, with nickel systems traps chromium. We also assessed the nature of the new bonds and the frontier molecular orbitals. Graphical abstract Two salen nickel compounds are joint by a Cr(0) atom forming an organometallic interaction.

Encapsulation of a nickel Salen complex in nanozeolite LTA as a carbon paste electrode modifier for electrocatalytic oxidation of hydrazine

A nickel salen complex was encapsulated in the supercages of nanozeolite NaA, LTA (linde type A) structure, using the flexible ligand method. The electrochemical behavior and electrocatalytic activity of a carbon paste electrode (CPE) modified with Ni(II)-Salen-A (Ni(II)-SalenA/CPE) for hydrazine oxidation in 0.1 mol/L NaOH solution were investigated by cyclic voltammetry, chronoamperometry, and chronocoulometry. First, organic-template-free synthesis of nanozeolite LTA was performed and the obtained material was characterized by various techniques. The average particle size of the LTA crystals was estimated to be 56.1 and 72 nm by X-ray diffraction and particle size analysis, respectively. The electron transfer coefficient was found to be 0.64 and the catalytic rate constant for oxidation of hydrazine at the redox sites of Ni(II)-SalenA/CPE was found to be 1.03 × 105 cm3/(mol·s). Investigation of the electrocatalytic mechanism suggested that oxidation of hydrazine occurred through reaction with Ni3+(Salen)O(OH) and also direct electrooxidation. The anodic peak currents revealed a linear dependence on the square root of the scan rate, indicating a diffusion-controlled process, and the diffusion coefficient of hydrazine was found to be 1.18 × 10−7 cm2/s. The results indicated that Ni(II)-SalenA/CPE displays good electrocatalytic activity toward hydrazine oxidation owing to the porous structure of nanozeolite LTA and the Ni(II)-Salen complex. Finally, the general reaction mechanism for the electrooxidation of hydrazine on Ni(II)-SalenA/CPE in alkaline solution involves the transfer of four electrons, in which the first electron transfer reaction acts as the rate-limiting step followed by a three-electron process to generate environmentally friendly nitrogen and water as final products.

Cyclohexyl Bromide and Iodide: Direct Reduction at Vitreous Carbon Cathodes together with Nickel(I) Salen‐ and Cobalt(I) Salen‐Catalyzed Reductions in Dimethylformamide

AbstractCyclic voltammetry and controlled‐potential (bulk) electrolysis have been used to study the direct electrochemical reduction of cyclohexyl bromide (1) and cyclohexyl iodide (2) at glassy carbon cathodes in dimethylformamide (DMF) containing 0.10 M tetramethylammonium tetrafluoroborate (TMABF4). Direct reduction of 1 is a one‐step process that affords a carbanion intermediate, whereas 2 undergoes stepwise reduction to a radical and then a carbanion intermediate. Mixtures of cyclohexane, cyclohexene, and bicyclohexyl arise from bulk electrolyses of both 1 and 2. Catalytic reduction of 1 and 2 by nickel(I) salen and cobalt(I) salen electrogenerated at glassy carbon cathodes in DMF‐TMABF4 has been investigated with the aid of both cyclic voltammetry and bulk electrolysis. Products arising from these catalytic reductions are cyclohexane, cyclohexene, and bicyclohexyl, although significant amounts of unreduced 1 are found when cobalt(I) salen is utilized as the catalyst. Mechanistic aspects of the direct and catalyzed reductions of 1 and 2 are discussed.