Kinetics and mechanism of the reaction of benzyl bromide with copper in hexamethylphosphoramide

Abstract

The reaction of copper with benzyl bromides in hexamethylphosphoramide has been studied. The kinetic and thermodynamic parameters of the reaction have been obtained. Hammett plots of log (k/k o ) vs the substituent constant σ gave good correlations (ρ = 0.15, S ρ = 0.02, r = 0.954). The structure of the organic group has little effect on the rate of reaction of benzyl bromide with copper. In the absence of atmospheric oxygen, the oxidative dissolution of copper occurred by the mechanism of single-electron transfer with the formation of 1,2-diphenylethane and copper(I) complexes. The stereochemistry and intermediates compound was also investigated.The reaction mechanism is discussed. C 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: [296][297][298][299][300][301][302][303][304][305] 2005

The effect of ligand on the rate of propagation of Cu(0)‐wire catalyzed SET‐LRP of MA in DMSO at 25 °C

“…Here, with [Me 6 ‐TREN] o = 0, no polymerization occurs, although activation followed by bimolecular termination takes place. Studies into the kinetics of Cu(0) mediated activation of benzyl halides and CCl 4 , indicated that even in the absence of an N‐ligand, carbon halide bond dissociation did occur with the fastest rate being observed in DMSO solvent 35–37. Without ligand, the extent and rate disproportionation of Cu(I)Br is significantly lower than in the presence of Me 6 ‐TREN.…”

“…The increase in rate with increasing ligand concentration is consistent with Langmuir‐Hinshelwood kinetics previously proposed for Cu(0) activation of benzyl halides, if the solvent is replaced with more strongly coordinating N‐ligand (eqs 1– 3). 35–37 …”

The kinetics of reaction of copper with substituted benzyl bromides in dipolar aprotic solvents

“…The rate constant ( k ), enthalpies, and entropies of adsorption of the reactants on the surface of copper obtained here are represented in Table III in comparison with reaction of copper with benzyl bromide in DMF 1, DMAA 2, and HMPA 3.…”

“…The kinetics‐related data of 1–3 indicate that bromine atom abstraction or single electron transfer is the most likely rate‐limiting step for the reaction of substituted benzyl bromides with copper in dipolar aprotic solvents. These data allow the authors to hypothesize a mechanism as described above 1–3.…”

“…Recently we have shown that copper reacts fast with benzyl bromide in some dipolar aprotic solvents (dimethylformamide (DMF), DMAA, hexamethylphosphoramide (HMPA)) 1–3. The limiting step of the reaction of benzyl bromides with copper is the dissociative electron transfer on a metal surface.…”