COMMUNICATIONS
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thiazolium ring. Therefore, the oxidative electron transfer
processes of the active aldehyde can be described as shown in
Scheme 1. The highly negative oxidation potentials of active
R1
N
R1
N
R1
N
R2
R3
R2
R3
R2
R3
O–
R
O
R
O
R
– e–
– e–
S
2–
S
S
2+
2•
Scheme 1. Oxidation of active aldehydes 2 by two electron transfer steps.
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aldehydes and the spin distribution of the intermediate
radicals determined for the first time in this study provide
the energetic basis for the ThDP-dependent electron trans-
port systems as well as valuable mechanistic insight into the
enzymatic reactions.
[12] The more positive oxidation potentials of O-methylated analogues of
active aldehydes have been reported. The formation of a radical
cation intermediate upon electrochemical oxidation is suggested
based on the chemical demonstration of the formation of a dimer at
the C2a atom: G. Barletta, A. C. Chung, C. B. Rios, F. Jordan, J. M.
Schlegel, J. Am. Chem. Soc. 1990, 112, 8144 ± 8149.
[13] The generation of active aldehydes derived from o-tolualdehyde
(lmax 380 nm) was confirmed by UV/Vis spectroscopy.[5e]
[14] S. Fukuzumi, Y. Tokuda, T. Kitano, T. Okamoto, J. Otera, J. Am.
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McGraw-Hill, New York, 1972.
Experimental Section
Thiazoles, benzyl bromide, acetaldehyde, and benzaldehyde were pur-
chased from Tokyo Chemical Industry and used as received. MeCN was
purified and dried with CaH2 by the standard procedure.[15] TBAP was
recrystallized from ethanol and dried in vacuum at 408C prior to use. 3-
Benzylthiazolium bromide was prepared by the reaction of the corre-
sponding thiazole with benzyl bromide at 808C, and purified by recrystal-
lization from acetone. Cyclic voltammetry measurements were performed
on a BAS 100B electrochemical analyzer with solutions in deaerated
MeCN containing 0.10m TBAP as supporting electrolyte. The Pt working
electrode (BAS) was polished with a BAS polishing alumina suspension
and rinsed with acetone before use. The counter electrode was a platinum
wire. The measured potentials were recorded with respect to the Ag/
AgNO3 (0.01m) reference electrode and converted into values versus SCE
by adding 0.29 V.[16] All electrochemical measurements were carried out
under an atmospheric pressure of argon. EPR spectra were recorded on a
JEOL JES-RE1XE instrument under nonsaturating microwave power
conditions. The magnitude of the modulation was chosen to optimize the
resolution and the signal-to-noise (S/N) ratio of the observed spectra. The g
values and hyperfine splitting (hfs) constants were calibrated with a Mn2
marker. Computer simulations of the EPR spectra were carried out with
the program Calleo ESR Version 1.2 (Calleo Scientific) on a Macintosh
personal computer.
[15] D. D. Perrin, W. L. F. Armarego, D. R. Perrin, Purification of Labo-
ratory Chemicals, Pergamon, Elmsford, 1966.
[16] C. K. Mann, K. K. Barnes, Electrochemical Reactions in Non-aqueous
Systems, Marcel Deker, New York, 1990.
Generation of ªNakedº Fluoride Ions in
Unprecedentedly High Concentrations
from a Fluoropalladium Complex**
Vladimir V. Grushin*
Received: September 18, 1997 [Z10944IE]
German version: Angew. Chem. 1998, 110, 1040 ± 1042
Since the discovery of the first reliable sources of weakly
solvated (ªnakedº) fluoride ions,[1, 2] a number of intriguing
reactivity patterns and applications of the F ion in synthesis
have been reported which clearly indicate its extraordinarily
strong basicity and nucleophilicity in media of low polarity.[1±8]
However, the number of sources for ªgenuinely nakedº F
Keywords: coenzymes ´ cyclic voltammetry ´ EPR spectro-
scopy ´ radicals ´ thiamin
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[*] Prof. Dr. V. V. Grushin[]
Department of Chemistry
Wilfrid Laurier University
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Waterloo, Ontario N2L 3C5 (Canada)
[ ] Current address:
DuPont CR&D, E328/306
Experimental Station
Wilmington, DE 19880-0328 (USA)
Fax: (1)302-695-8281
[**] This work was supported by DuPont and Wilfrid Laurier University.
Dr. V. A. Petrov (DuPont) is thankfully acknowledged for many
fruitful discussions.
[6] D. Hilvert, R. Breslow, Bioorg. Chem. 1984, 12, 206 ± 220.
994
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