Electrochemical Formation and Dimerization of α<i>-</i>Substituted Benzyl Radicals. Steric Effects on Dimerization

Fry, Albert J.; Porter, John M.; Fry, P. F.

doi:10.1021/jo951577f

Cited by 33 publications

(19 citation statements)

References 37 publications

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“…29 More interestingly, both 1-methyl-2-(phenylmethyl)benzene and 1-methyl-4-(phenylmethyl)benzene were also found in the products from catalytic reductions, strongly suggesting a radical pathway for the reaction mechanism. 30 Analogous CPE data were obtained as well for the direct and catalytic reduction of 1-bromomethylnaphthalene in the total product yields of around 90%.…”

Section: Resultssupporting

confidence: 52%

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: Resultssupporting

confidence: 52%

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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“…One proposal involves the formation of a radical anion through a single electron transfer (SET) process that give a [PhX] À· radical anion that then dissociates, forming a Ph · radical and ultimately the biaryl product. [4,17] To understand the mechanism in our system, we must first clarify what closes the cata- lytic cycle and what role do the Pd clusters play in this reaction.…”

Section: Mechanistic Studiesmentioning

confidence: 99%

Electroreductive Palladium‐Catalysed Ullmann Reactions in Ionic Liquids: Scope and Mechanism

2006

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A room-temperature catalytic alternative to the Ullmann reaction is presented, based on electroreductive homocoupling of haloarenes catalysed by palladium nanoparticles. The particles are generated in situ in an electrochemical cell, and electrons are used to close the catalytic cycle and provide the motivating force for the reaction. This system gives good yields using iodo-and bromoarenes, and requires only electric current and water as reagents. Using an ionic liquid solvent combines the advantages of excellent conductivity and cluster stabilising. The solvent is reusable at least five times. Kinetic experiments at different electrode potentials show that the two-electron oxidation of water closes the catalytic cycle by regenerating the Pd(0). A mechanism involving radical anion formation is proposed. The advantages and limitations of this new system for carbon-carbon homocoupling and cross-coupling are discussed.

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“…As the rate constants of the abstraction of an H atom from the solvent by the C 6 H 5 and (C 6 H 5 ) 2 radicals are relatively not great [63], the latter can be studied in a broad series of organic solvents. However, for more active radicals, it is frequently possible to use only acetonitrile, as a result of the fact that it possesses a very strong C-H bond, whose BDE value (389-398 kJ mol -1 ) is not much lower than that of ethane (410 kJ mol -1 ) (see for example [64]). …”

Section: Resultsmentioning

confidence: 99%

Thermodynamic and kinetic characteristics of intermediates of electrode reactions: A comparative investigation of a number of alkylaryl and alkyl halide radicals by the laser photoemission methods

2005

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A comparative investigation of thermodynamic and kinetic properties of a number of alkylaryl intermediates (benzyl and benzhydryl radicals) and alkyl halide intermediates (chloromethyl, dichloromethyl, and trifluoromethyl radicals) is performed by methods of laser photoemission. Techniques, aimed at the determination of thermodynamic and kinetic properties of intermediates (standard potentials E 0 of redox pairs / R -, standard adsorption free energies -∆ , values of rate constants W 0 at an equilibrium potential, as well as lifetimes (times of death in the bulk) τ R of radicals and τ X of products of their reduction R -) from a comparison of Tafel plots for quasi-reversible reduction of intermediates with calculated ones and standard potentials E 0 -from Tafel plots for irreversible electroreduction of intermediates, are presented. The transition from irreversible to quasi-reversible reduction in aprotic solvents at E ~ E 0 is observed only in the case of benzyl, benzhydryl, and trifluoromethyl radicals, for which this particular collection of thermodynamic and kinetic properties is obtained, and is not observed for the chloromethyl and dichloromethyl radicals. In this case redox characteristics of intermediates ( E 0 , W 0 ) are estimated from absolute values of rates of their electroreduction. Possible reasons for the differences in the probability of a reversible electron transfer are discussed for the systems studied.

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Electrochemical Formation and Dimerization of α-Substituted Benzyl Radicals. Steric Effects on Dimerization

Cited by 33 publications

References 37 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

Electroreductive Palladium‐Catalysed Ullmann Reactions in Ionic Liquids: Scope and Mechanism

Thermodynamic and kinetic characteristics of intermediates of electrode reactions: A comparative investigation of a number of alkylaryl and alkyl halide radicals by the laser photoemission methods

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