Volume 203, 2017

Electron-transfer reactions of halogenated electrophiles: a different look into the nature of halogen bonding

Abstract

The rates of oxidation of ferrocene derivatives by brominated molecules R-Br (CBr3CN, CBr4, CBr3NO2, CBr3COCBr3, CBr3CONH2, CBr3F, and CBr3H) were consistent with the predictions of the outer-sphere dissociative electron-transfer theory. The similar redox-reactions of the R-Br electrophiles with the typical halogen-bond acceptors tetramethyl-p-phenylenediamine (TMPD) or iodide were much faster than calculated using the same model. The fast redox-processes in these systems were related to the involvement of the transient halogen-bonded [R-Br, TMPD] or [R-Br, I] complexes in which barriers for electron transfer were lowered by the strong electronic coupling of reactants. The Mulliken–Hush treatment of the spectral and structural characteristics of the [R-Br, TMPD] or [R-Br, I] complexes corroborated the values of coupling elements, Hab, of 0.2–0.5 eV implied by the kinetic data. The Natural Bond Orbital analysis of these complexes indicated a noticeable donor/acceptor charge transfer, Δq, of 0.03–0.09 ē. The Hab and Δq values in the [R-Br, TMPD] and [R-Br, I] complexes (which are similar to those in the traditional charge-transfer associates) indicate significant contribution of charge-transfer (weakly-covalent) interaction to halogen bonding. The decrease of the barrier for electron transfer between the halogen-bonded reactants demonstrated in the current work points out that halogen bonding should be taken into account in the mechanistic analysis of the reactions of halogenated species.

Associated articles

Supplementary files

Article information

Article type
Paper
Submitted
20 2 2017
Accepted
15 3 2017
First published
15 3 2017

Faraday Discuss., 2017,203, 315-332

Electron-transfer reactions of halogenated electrophiles: a different look into the nature of halogen bonding

Sergiy V. Rosokha, Faraday Discuss., 2017, 203, 315 DOI: 10.1039/C7FD00074J

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