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3] M. B. Smith, J. March, in March’s Advanced Organic Chemistry: Reactions,
Mechanisms and Structure, Fourth Edition, Wiley-VCH, Chichester, 2001,
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perimental rate and the activation energy means that a small change in
rate is accompanied by a change in the activation energy that exceeds
the accuracy of the theoretical method. Nevertheless, a correlation of
0.78 is obtained between the relevant magnitudes. Additionally, there
also exists a good correlation (r=0.87, Figure S8) between the two (BP
and M06) theoretical methods, which provides an indication of the ac-
[
4] a) L. J. Gooben, C. Linder, N. Rodrꢃguez, P. P. Lange, A. Fromm, Chem.
McGraw-Hill, New York, 1940, pp. 186–194.
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[25] It is assumed that groups such as OR orientate themselves in such
a way as to minimise their size; thus, the van der Waals radius is only
directly related to the size of the oxygen atom (see ref. [17]).
[26] a) F. D’Anna, F. Ferroni, V. Frenna, S. Guernelli, C. Z. Lanza, G. Macaluso,
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[
[
11] With one exception, in which Pd was shown to exclusively mediate the
[
[
12] L. J. Gooben, N. Rodrꢃguez, C. Linder, P. P. Lange, A. Fromm, ChemCat-
[
[
14] A combined computational study was carried out by Gooben et al. (see
ref. [12]) using an Ag/NMP catalyst system, which yielded a reduced ac-
tivation barrier to decarboxylation with Ag compared to the Cu/1,10-
phenanthroline system.
15] Kozlowski et al. have recently reported a combined experimental and
theoretical study on Pd-catalysed decarboxylation (see ref. [8b]), from
which they concluded that the rate-determining step can be either the
decarboxylation or the protodemetallation, depending on the sub-
strate. The Pd-catalysed protodecarboxylation regularly requires an
exogenous proton/hydride source for catalyst regeneration, whereas
this is not required in the Ag-catalysed system. The aryl-Ag intermedi-
ate is very nucleophilic and readily undergoes protodemetallation, thus
supporting the inference that the decarboxylation is the rate-determin-
[
[30] Gaussian 09, Revision A.02, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.
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[
19] The prominence of the ortho effect is also observed in the correlation
°
°
between the DG ꢀDG difference and the activation energy barrier
ortho
para
°
ortho
DG , with a significant correlation coefficient (r) of 0.86 (Figure S3).
Moreover, a correlation of 0.93 is observed when comparing the ortho
and meta isomers (Figure S4). Accordingly, there is also a positive corre-
lation of 0.77 between the Cipso-CO
and CP3 structures and the activation energies for the ortho isomers
Figure S5). Therefore, compounds that require greater structural
2
bond length differences in the TS
(
change between the CP3 and TS structures tend to be less susceptible
to decarboxylation. This relationship infers that electron-withdrawing
groups weaken the adjacent Cipso-CO bond by removing bonding elec-
2
[33] a) NBO Version 3.1, E. D. Glendening, A. E. Reed, J. E. Carpenter, F. Wein-
hold.
tron density, indicating that the electronic influence is not limited to
a stabilisation of the transition-state structure.
[34] R Core Team (2013). R: A language and environment for statistical com-
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[
20] It is important to note the great difficulty of achieving full agreement
between experimental and theoretical data. This is due, on the one
hand, to the intrinsic limitations of DFT (see R. G. Parr, W. Yang, Density
Functional Theory of Atoms and Molecules, Oxford University Press,
New York, 1989) and the non-inclusion of certain effects, such as explic-
it solvation. Furthermore, the logarithmic relationship between the ex-
Received: April 3, 2014
Published online on && &&, 0000
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Chem. Eur. J. 2014, 20, 1 – 9
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