The electrochemistry of square planar macrocyclic nickel complexes and the reaction of Ni(I) with alkyl bromides: Tetradentate Schiff base complexes

Gosden, C.; Kerr, John B.; Pletcher, Derek; Rosas, Raul

doi:10.1016/s0022-0728(81)80453-6

Cited by 98 publications

(61 citation statements)

References 9 publications

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“…1I depicts the CVs for reduction of nickel(II) salen in the presence of four different concentrations of benzyl bromide (as well as for reduction of nickel(II) salen or benzyl bromide by itself) recorded at a scan rate of 100 mV s -1 with a glassy carbon electrode in DMF containing 0.050 M TMABF 4 . Curve A, is a cyclic voltammogram for a 2.0 mM solution of nickel(II) salen, showing a reversible redox couple at E pc of −1.69 V and E pa of −1.61 V. Meanwhile, the irreversible direct reduction of benzyl bromide was found to have a peak potential of −1.77 V (Curve F).…”

Section: Resultsmentioning

confidence: 99%

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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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Section: Resultsmentioning

confidence: 99%

“…and product yields for the reductions of benzyl bromide and 1-bromomethylnaphthalene, respectively, at reticulated vitreous carbon cathodes in DMF containing 0.050 M TMABF 4 . Each tabulated entry is the average of at least three identical experiments.…”

Section: Resultsmentioning

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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“…where the added electron is nickel centred and the reduction is fast and occurs without significant changes in the geometry of the complex [5][6][7]. In both cases the experiments show that addition of unsaturated halide to the Ni(II) complex solution results in the increase of the reduction peak height of the mediator and disappearance of the anodic wave.…”

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confidence: 83%

Catalytic Reduction of Unsaturated Halides by Ni(II) Complexes

Ataíde¹,

Esteves²,

Freitas³

et al. 1999

Port. Electrochim. Acta

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“…In their pioneering papers, Pletcher and co-workers [1][2][3][4][5] In the early 2000s, our laboratory endeavored to employ in situ electrochemical-electron paramagnetic resonance (EC-EPR) studies of the nickel(I) salen-catalyzed reduction of some n-alkyl bromides and iodides to search for the possible intermediacy of organonickel(III) intermediates, such as [RNi(III)X salen] -depicted in the preceding three reactions. Despite the fact that this species should be paramagnetic, no evidence for its existence in these systems was obtained by means of EC-EPR.…”

Section: Are Nickel(iii) Intermediates Involved?mentioning

confidence: 99%

“…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).…”

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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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The electrochemistry of square planar macrocyclic nickel complexes and the reaction of Ni(I) with alkyl bromides: Tetradentate Schiff base complexes

Cited by 98 publications

References 9 publications

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

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

Catalytic Reduction of Unsaturated Halides by Ni(II) Complexes

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

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