Reaction of electrogenerated square-planar nickel(I) complexes with alkyl halides

Gosden, C.; Healy, K. P.; Pletcher, Derek

doi:10.1039/dt9780000972

Cited by 119 publications

(72 citation statements)

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“…These electrochemical behaviors are similar to those shown in previous studies for the nickel(I) salen-catalyzed reduction of alkyl halides. 4,6,9,[19][20][21] Some small anodic peaks also appear at −0.15 to −0.30 V for Curves B−D, possibly caused by oxidation of the products.…”

Section: Resultsmentioning

confidence: 99%

Reaction Mechanism for the Formation of Dialkylated Nickel(II) Salen Involved in the Catalytic Reduction of (Bromomethyl)cyclopropane

Lambert

Enters

Rastogi

et al. 2016

J. Electrochem. Soc.

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Cyclic voltammetry (CV) and controlled-potential electrolysis (CPE) were employed to examine the reaction between electrogenerated ligand-reduced nickel(II) salen and (bromomethyl)cyclopropane. Cyclic voltammograms for nickel(II) salen in the presence of (bromomethyl)cyclopropane exhibit characteristic features for the catalytic reduction of the substrate. Bulk electrolyses of (bromomethyl)cyclopropane at carbon cathodes in dimethylformamide catalyzed by nickel(II) salen were carried out to investigate the mechanism for the formation of dialkylated nickel(II) salen, which was analyzed and identified by high-performance liquid chromatography (HPLC). The corresponding dialkylated nickel(II) salen was further purified and collected by preparative-scale HPLC. Its complete structure was revealed by electrospray-ionization mass spectrometry (ESI-MS), 1 H NMR, COSY, and HECTOR NMR spectrometry. The clear-cut reaction mechanism for its formation was proposed on the basis of current and previous studies.

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Section: Resultsmentioning

confidence: 99%

Reaction Mechanism for the Formation of Dialkylated Nickel(II) Salen Involved in the Catalytic Reduction of (Bromomethyl)cyclopropane

Lambert

Enters

Rastogi

et al. 2016

J. Electrochem. Soc.

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“…On the basis of established mechanistic pathways [17][18][19][20]22 and our current findings, a possible mechanism for the nickel(I) salen-catalyzed reduction of the two aryl halides is proposed in Scheme 2. The electrogenerated metal-reduced nickel(I) (2) or the ligand-reduced radical−anion (3) can transfer one electron to the substrate, which undergoes reductive cleavage of the carbon−bromine bond to form the corresponding radical and regenerates nickel(II) salen (1) (reaction 1). The aryl radicals can couple with each other to give the dimers (reaction 2) or abstract hydrogen atom from solvent (reaction 3).…”

Section: Comparison Of Cyclic Voltammograms For the Nickel(ii) Salen mentioning

confidence: 99%

“…1−16 In recent years, the corresponding catalytic reaction has been carefully examined to establish detailed mechanistic steps. 17−20 Generally, nickel(II) salen (1) would undergo a one-electron reversible reduction to generate either the metal-reduced nickel(I) salen (2) or the ligand-reduced radical−anion (3, Scheme 1), which can subsequently transfer an electron to the organic halide substrate to produce a radical and a halide ion. Afterward, the substrate radicals can undergo different follow up reactions such as coupling, 7,8 disproportionation, 7 intramolecular cyclization, 5,10 abstraction of hydrogen atom from solvent, etc to afford a series of compounds.…”

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confidence: 99%

Reaction of Electrogenerated Ligand-Reduced Nickel Salen with Benzyl Bromide, 1-Bromomethylnaphthalene, and α-Bromodiphenylmethane: A Study of Steric Effects

Nguyen

Tomasso

Easter

et al. 2015

J. Electrochem. Soc.

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Cyclic voltammetry (CV) and controlled-potential electrolysis (CPE) were employed to examine the reactions of electrogenerated ligand-reduced nickel(II) salen with benzyl bromide, 1-bromomethylnaphthalene, and α-bromodiphenylmethane. Cyclic voltammograms for nickel(II) salen in the presence of benzyl bromide or 1-bromomethylnaphthalene exhibit characteristic features for the catalytic reduction of substrates involving radical intermediates. Bulk electrolyses of benzyl bromide and 1-bromomethylnaphthalene at carbon cathodes catalyzed by nickel(II) salen were also carried out at selected potentials to afford various products. These results were compared with similar reaction involving 1-bromooctane as the substrate. Further comparison of the CVs for nickel(II) salen before and after reactions with the four different organic halides reveals that the steric effect could play an important role in the corresponding nucleophilic attack of the substrates by ligand-reduced catalyst (a radical−anion), which follows the sequence of 1-bromooctane > benzyl bromide > 1-bromomethylnaphthalene > α-bromodiphenylmethane in terms of reaction efficiency. Moreover, theoretical calculations using density functional theory were carried out to establish a proposed mechanism for the electrochemical reactions on the basis of previous and current studies.

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“…atalytic reduction of halogenated organic compounds by electrogenerated nickel(I) complexes first appeared in the literature as a series of publications [1][2][3][4][5] from the laboratory of Derek Pletcher. In this early work, a family of nickel(II) procatalysts (or catalyst precursors) was employed, which included the compound [[2,2′-[1,2-ethanediylbis-(nitrilomethylidyne)]bis [phenolato]]-N,N′,O,O′]nickel(II), hereafter called nickel(II) salen (1).…”

mentioning

confidence: 99%

“…In this early work, a family of nickel(II) procatalysts (or catalyst precursors) was employed, which included the compound [[2,2′-[1,2-ethanediylbis-(nitrilomethylidyne)]bis [phenolato]]-N,N′,O,O′]nickel(II), hereafter called nickel(II) salen (1). At a variety of cathodes (mercury, glassy carbon, platinum, and gold) and in numerous non-aqueous solventelectrolyte media [for example, dimethylformamide containing tetran-butylammonium tetrafluoroborate (DMF-TBABF 4 ) or acetonitrile containing tetramethylammonium perchlorate (CH 3 CN-TMAP)], chocolate-brown nickel(II) salen (1) undergoes a reversible, metalcentered, one-electron reduction to green nickel(I) salen (2).…”

mentioning

confidence: 99%

Catalytic Reduction of Organic Halides by Electrogenerated Nickel(I) Salen

2016

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Catalytic reduction of halogenated organic compounds by electrogenerated nickel(I) complexes first appeared in the literature as a series of publications [1][2][3][4][5] from the laboratory of Derek Pletcher. In this early work, a family of nickel(II) procatalysts (or catalyst precursors) was employed, which included the compound [[2,2′-[1,2-ethanediylbis-(nitrilomethylidyne)]bis [phenolato]]-N,N′,O,O′]nickel(II), hereafter called nickel(II) salen (1). At a variety of cathodes (mercury, glassy carbon, platinum, and gold) and in numerous non-aqueous solventelectrolyte media [for example, dimethylformamide containing tetran-butylammonium tetrafluoroborate (DMF-TBABF 4 ) or acetonitrile containing tetramethylammonium perchlorate (CH 3 CN-TMAP)], chocolate-brown nickel(II) salen (1) undergoes a reversible, metalcentered, one-electron reduction to green nickel(I) salen (2). On the basis of density functional theory, it was established later 6 that reduction of nickel(II) salen can also produce a ligand-reduced form (3) of the parent complex in which a single electron is added to the carbon atom of one imino (C=N) bond of the ligand:Furthermore, the energy of 3 was calculated to be approximately only 2-3 kcal mol -1 higher than that of 2, meaning that both reduced states of 1 are accessible electrochemically-which becomes vitally important in later discussion.Shown in Fig. 1 is a cyclic voltammogram, recorded at 100 mV s -1 on a glassy carbon electrode in dimethylformamide containing tetramethylammonium tetrafluoroborate (TMABF 4 ) as the supporting electrolyte, which reveals the reversible one-electron reduction of nickel(II) salen. For the experimental conditions employed, the cathodic and anodic peak potentials (E pc and E pa ) are -0.95 and -0.84 V, respectively, and the cathodic and anodic peak currrents (I pc and I pa ) are identical. What is not seen in Fig. 1 (and what must be avoided) is that, at more negative potentials, another prominent cathodic peak is observed, due to the fact that the salen ligand itself can undergo further and irreversible degradation-which destroys the desired catalytic ability of 2. Our First Use of Electrogenerated Nickel(I) SalenOur first published effort to employ nickel(I) salen (2), electrogenerated at a reticulated vitreous carbon cathode in dimethylformamide-tetraethylammonium perchlorate (DMF-TEAP), was as a catalyst for the reductive intramolecular cyclizations of two acetylenic halides-namely, 6-bromo-1-phenyl-1-hexyne (4) and 6-iodo-1-phenyl-1-hexyne (5) Our goals were: (a) to overcome problems associated with direct reduction of these two compounds at mercury pool or reticulated vitreous carbon electrodes; and (b) to maximize the yield of the desired product (benzylidenecyclopentane, 6). Earlier, when these two acetylenic halides were reduced directly at a mercury pool cathode, 8 more than seven different products were obtained, and 6 was obtained in a yield below 25%. Then, in a subsequent investigation of the direct reduction of 6-iodo-1-phenyl-1-hexyne at a reticulated...

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Reaction of electrogenerated square-planar nickel(I) complexes with alkyl halides

Cited by 119 publications

References 0 publications

Reaction Mechanism for the Formation of Dialkylated Nickel(II) Salen Involved in the Catalytic Reduction of (Bromomethyl)cyclopropane

Reaction Mechanism for the Formation of Dialkylated Nickel(II) Salen Involved in the Catalytic Reduction of (Bromomethyl)cyclopropane

Reaction of Electrogenerated Ligand-Reduced Nickel Salen with Benzyl Bromide, 1-Bromomethylnaphthalene, and α-Bromodiphenylmethane: A Study of Steric Effects

Catalytic Reduction of Organic Halides by Electrogenerated Nickel(I) Salen

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