Synergy in electrocatalysis: electrocatalytic reduction of bromothiophenes vs bromobenzenes on gold and silver electrodes
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Data di Pubblicazione:
2013
Citazione:
Synergy in electrocatalysis: electrocatalytic reduction of bromothiophenes vs bromobenzenes on gold and silver electrodes / S. Arnaboldi, A. Bonetti, C. D'Aloi, M. Magni, P.R. Mussini, F. Sannicolò, T. Benincori, S. Rizzo, E. Giussani, A.A. Isse, A. Gennaro. ((Intervento presentato al 46. convegno Heyrovský Discussion tenutosi a Třešť (Czech Republic) nel 2013.
Abstract:
The reductive cleavage of C-Br bonds on Ag electrodes can be regarded as an
ideal model of dissociative electron transfer (DET) in electrocatalytic conditions,
modulated by many factors, among which the molecular structure is of particular
relevance. A detailed mechanistic study based on a large set of compounds with
different molecular structures allowed us a full rationalization of the process for the
case of aryl bromides in acetonitrile.
Now we are extending this research to heteroaromatic halides, in which the
heteroatom not only makes the aromatic ring asymmetric from the perspective of the
electron density but also can have its own specific interations with the electrode
surface, in addition to those of the halide ions. As a first approach, we have selected
the mono-, di-, tri- and tetra-bromothiophene series, plus a series of substituted
bromothiophenes togeteher with the corresponding bromobenzenes as benchmarks,
investigating (by CV supported by EIS in selected cases), the electrochemical
reduction of the whole family: (a) on glassy carbon GC, assumed as a non-catalytic
reference accounting for intrinsic reactivity; (b) on the highly catalytic silver electrode;
(c) on gold electrode, showing in former halide cases lower catalytic effects than
silver (on account of its much more positive pzc with respect to the working
potentials, hampering halide-surface specific interactions), but having the highest
affinity for the sulphur atom in the thiophene ring.
While the results on GC and on Ag are fully consistent with the formerly studied
aryl bromide case on the same two electrodes (with some enhancement of the
catalytic effects on Ag), the catalytic effects of Au appear to be neatly modulated by
the relative position of the Br leaving group with respect to the sulphur atom. In
particular, the catalytic effects for the reduction of C-Br bonds at a positions are
significantly higher than those at b, and they even approach the high catalytic effects
of Ag. This feature is quite evident and reproducible in the whole series (including
polysubstituted cases), and points to the S atom acting as an asymmetrically
anchoring group for the molecule on the Au surface, particularly fostering specific
interaction of the surface with adjacent halide leaving groups, and thus partially
overcoming the electrostatic repulsion connected with the very positive pzc.
Tipologia IRIS:
14 - Intervento a convegno non pubblicato
Elenco autori:
S. Arnaboldi, A. Bonetti, C. D'Aloi, M. Magni, P.R. Mussini, F. Sannicolò, T. Benincori, S. Rizzo, E. Giussani, A.A. Isse, A. Gennaro
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