Metal complex electrocatalytic reduction of 1,1-dihalocyclopropanes

Article abstract of DOI:10.1023/A:1024456510964

Catalytic electroreduction of several substituted gem-dihalocyclopropanes was studied in the presence of metal salen-complexes by polarography, cyclic voltammetry, and preparative electrolysis. Monohalocyclopropanes (54-59%) and the corresponding allene (

Full text of DOI:10.1023/A:1024456510964

Russian Chemical Bulletin, International Edition, Vol. 52, No. 4, pp. 923—928, April, 2003
923
Metal complex electrocatalytic reduction of 1,1ꢀdihalocyclopropanes
ꢀ
V. V. Yanilkin, E. I. Strunskaya, N. V. Nastapova, N. I. Маksimyuk, Z. A. Bredikhina,
D. R. Sharafutdinova, and A. A. Bredikhin
A. E. Arbuzov Institute of Organic and Physical Chemistry,
Kazan Research Center of the Russian Academy of Sciences,
8 ul. Akad. Arbuzova, 420088 Kazan, Russian Federation.
Fax: +7 (843 2) 75 2253. Eꢀmail: yan@iopc.knc.ru
Catalytic electroreduction of several substituted gemꢀdihalocyclopropanes was studied in
the presence of metal salenꢀcomplexes by polarography, cyclic voltammetry, and preparative
electrolysis. Monohalocyclopropanes (54—59%) and the corresponding allene (5—9%) were
the main reduction products. The reaction rate constants were determined. The innerꢀsphere
electron transfer was shown to occur under these conditions.
Key words: halocyclopropanes, allene, electrochemistry, catalysis, salenꢀcomplexes, kiꢀ
netics.
Organic electrochemistry is permanently interested in
mediator electrochemical processes. In addition to orꢀ
ganic mediators, which are usually aromatic compounds
with various structures,1,2 metal salts and metal comꢀ
plexes3,4 are widely used with this purpose. Metal salenꢀ
complexes,5,6 which are also known as chiral catalysts for
asymmetric oxidation,7,8 have often been applied recently
as catalysts of redox transformations of organics. Howꢀ
ever, their use as mediators in electrochemical redox proꢀ
cesses is rather restricted and in nonelectrochemical reꢀ
duction processes only single cases are known.9 At the
same time, it seemed promising to use salenꢀcomplexes as
potential inductors of chirality in electrochemical reducꢀ
tion (ER) processes. Available data on the behavior of the
metal salenꢀcomplexes during ER of the С—Hal bonds
indicate that this process occurs ambiguously and often
results in the formation of a variety of unsaturated comꢀ
pounds along with the dehalogenated product5,6 and a
substantial decrease in the yield of the latter. This is
caused, as assumed,10 by both the innerꢀsphere and outerꢀ
sphere electronic transfers in such systems, and the forꢀ
mation of the dehalogenation product is the result of the
outerꢀsphere interaction. However, no special studies, caꢀ
pable of shedding light on specific features of ER proꢀ
cesses involving metal salenꢀcomplexes, were performed
until now.
Results and Discussion
Unsubstituted salenꢀcomplexes of some metals are
used as mediators because they can reversibly be reduced.13
However, it was necessary to reveal metals that form the
salen complexes and conditions for the catalytic ER of
dihalocyclopropanes to stop the process at the step of
formation of monohalocyclopropanes. For this purꢀ
pose, we synthesized N,Nꢀbis(salicylidene)ethylenediꢀ
amine (salen) and (R,R)ꢀN,Nꢀbis(3,5ꢀdiꢀtertꢀbutylsalicylꢀ
idene)cyclohexaneꢀ1,2ꢀdiamine (cgsalen) complexes of
several metals. The electrochemical behavior of the comꢀ
plexes and their catalytic properties in ER processes of
dihaloꢀ and monohalocyclopropanes were characterized
by the data of voltammetry and preparative electrolysis.
The results are presented in Table 1.
This stimulated us to state this work and study the
electrocatalytic properties of salenꢀcomplexes of various
metals during ER of the C—Hal bonds. 1,1ꢀDibromoꢀ
and 1,1ꢀdichlorocyclopropanes were chosen as model subꢀ
strates, although the data on their ER have been pubꢀ
lished,11,12 because they allowed us to determine stereoꢀ
direction of the process under study.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 876—881, April, 2003.
1066ꢀ5285/03/5204ꢀ923 $25.00 © 2003 Plenum Publishing Corporation

924
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Yanilkin et al.
Table 1. Electrochemical characteristics of the reduction waves
of the metal complexes, 1,1ꢀdihalocyclopropanes, and monoꢀ
halocyclopropanes in DMF/0.1 М Et4NClO4
CV curves of Fe(salen)Cl exhibit two reversible oneꢀelecꢀ
tron reduction peaks corresponding to the transitions
Fe(salen)+ + e
Fe(salen) + e
Fe(salen),
c
Comꢀ
pound
–Е1/2/Вa
nb
ian/icat 2.3RT/(αnF)
Fe(salen)–,
/mVd
whereas the CV curve of Mn(salen)Cl contains one reꢀ
versible peak of reduction of Mn(salen)+ to Mn(salen).
Electroreduction of other metal complexes was studied
by classical and commutator polarography and cyclic
voltammetry. The first reduction wave for Zn(salen) is
irreversible, while that for Cu(salen) is quasiꢀreversible,
indicating lability of anionic intermediates formed upon
the oneꢀelectron reduction of these complexes. For all
cobalt and nickel salenꢀcomplexes, the first reduction step
affording anions of these complexes is oneꢀelectron and
reversible. The cobalt complexes are reduced more easily
than the corresponding nickel complexes. Diꢀtertꢀbutylꢀ
substituted salenꢀcomplexes are reduced less easily than
the unsubstituted complexes because of the electronꢀdoꢀ
nating effect of the tertꢀbutyl substituents. As we have
shown previously,2 under polarographic conditions, diꢀ
halocyclopropanes undergo irreversible twoꢀelectron reꢀ
duction to the corresponding monohalogen derivatives.
It follows from the data in Table 1 that the zinc salenꢀ
complexes cannot serve as mediators because their reꢀ
duced forms are unstable. The nickel complexes are reꢀ
duced more easily than dichlorocyclopropanes but less
easily than dibromocyclopropanes and, therefore, can be
used as catalysts only for dichlorides. No basic restricꢀ
tions are known for the study of the catalytic properties of
salenꢀcomplexes of other metals under study in the ER of
monoꢀ and dihalocyclopropanes. These complexes are
reduced reversibly or quasiꢀreversibly and, hence, satisfy
requirements imposed on mediators (electron carriers).
The apparent rate constants of catalytic reduction of
diꢀ and monohalocyclopropanes by electrochemically
generated anions of the metal salenꢀcomplexes are preꢀ
sented in Table 2. These constants were calculated using
the polarographic and CV data from the catalytic increase
in the limiting current of the wave and, correspondingly,
the ER peak of the metal complex in the presence of
halocyclopropane. The data in Table 2 show that the
nickel(II), cobalt(II), and iron(II) salenꢀcomplexes are efꢀ
ficient mediators of ER of dichlorocyclopropanes, and
the cobalt(II) complexes are also efficient in the ER of
dibromocyclopropanes. The complexes of other metals
are inactive under voltammetry conditions in the ER of
both 1,1ꢀdichloroꢀ and 1,1ꢀdibromocyclopropanes. Unꢀ
like monobromocyclopropanes, whose ER occurs with a
high rate under voltammetry conditions, monochloroꢀ
cyclopropanes are not reduced with a detectable rate by
anions of the nickel and cobalt salenꢀcomplexes. In the
case of Сo(salen), the rate of this process is only eightfold
lower than the ER rate of dibromocyclopropane. On the
Zn(salen)
Ni(cgsalen)
Ni(salen)
Co(cgsalen)
Co(salen)
2.50
2.26
2.07
1.94
1.70
1.61
0.75
2.18
0.60
2.0
1.0
1.0
1.0
1.0
1.5
1.0
1.0
1.0
0.0
70
73
62
63
62
62
63
65
65
0.50
0.56
0.73
0.50
0.16
—
Cu(salen)
Fe(salen)+Cl– e
Mn(cgsalen)+Cl– e
—
1.81
2.68
2.0
2.0
0.0
0.0
160
140
1.81
2.70
2.0
2.0
0.0
0.0
73
110
1.96
2.88
2.0
1.9
0.0
0.0
130
130
2.70
2.81
2.0
2.0
0.0
0.0
130
120
2.88
3.13
2.0
2.0
0.0
0.0
140
100
а Against Ag/AgNO3 (0.01 mol L–1) in MeCN.
b Number of electrons determined by comparison with the oneꢀ
electron wave of reduction of pꢀnitrobenzaldehyde.
c Ratio of the anodic commutated current to the limiting caꢀ
thodic current, the switchꢀover frequency being 10 Hz.
d The angular coefficient of the wave was calculated by the
formula 2.3RT/αnF = (Е3/4 – Е1/4)/0.954, where R is the uniꢀ
versal gas constant, Т is the absolute temperature, α is the transꢀ
fer coefficient, n is the number of transferred electrons, and F is
the Faraday number.
e The data were obtained by the CV method on the glassꢀcarbon
electrode.
All complexes are reduced in the accessible potential
region. The Fe(salen)Cl and Mn(salen)Cl complexes reꢀ
act with mercury, and they were studied only by cyclic
voltammetry (CV) on an inert glassꢀcarbon electrode. The

Metal complex electrocatalytic reduction
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 4, April, 2003
925
Table 2. Apparent rate constants kapp/L mol–1 s–1 of the homogeneous reduction of halocyclopropanes by the electrochemically
generated anions of salenꢀcomplexes of some transition metals* in DMF/0.1 М Et4NClO4
Metal
complex
[–1.81]
—
[–1.81]
—
[–1.96]
—
[–2.70]
16000
[–2.81]
4500
[–2.88]
490
[–3.13]
—
Ni(cgsalen)
[–2.26]
Fe(salen)
[–2.18]
—
—
—
—
—
—
—
3600
3500
3260
970
—
—
—
Ni(salen)
[–2.07]
12000
3500
580
560
260
510
Co(cgsalen)
[–1.94]
—
—
—
670
—
Co(salen)
[–1.70]
22900
1550
4180
* The E1/2/V are presented in brackets (see Table 1).
whole, dihalocyclopropanes exhibit a certain tendency
for increasing the rate of their ER with an increase in the
ER potentials of the complex and a decrease in the ER
potentials of the substrate. This is natural for processes
limited by the electron transfer rate. All metal salenꢀcomꢀ
plexes obey the general regularity. In other words, acꢀ
cording to the voltammetric data, diꢀtertꢀbutylꢀsubstituted
complexes during ER of dihalocyclopropanes behave simiꢀ
larly to the unsubstituted analogs, i.e., undergo no steric
hindrance. The situation with ER of monobromonorꢀ
carane by the Ni(cgsalen) complex is somewhat different.
In this case, the apparent rate constant of reduction is
lower, which implies, most likely, a substantial steric efꢀ
fect of the chiral ligand on the kinetics.
cyclopropanes are reduced via the outerꢀsphere electron
transfer and dibromocyclopropanes are not reduced at all
with the rate detectable by the polarographic method
(k ≤ 10 s–1). The reduction rate of dichlorocyclopropanes
increases substantially when the second mediator, viz.,
transition metal complexes or ions, which act as innerꢀ
sphere electron carriers, is introduced in the solution.
As for the reduction of dichlorocyclopropanes by the
salenꢀcomplexes, the rate of this process is by two—three
orders of magnitude higher than the rate of reduction of
these substrates by organic electron carriers at the same or
even greater difference of mediator—substrate potentials.
For example, the apparent rate constant of reduction of
2,2ꢀdiphenylꢀ1,1ꢀdichlorocyclopropane by the 9,10ꢀdiꢀ
phenylanthracene radical anions (Е1/2 = –1.99 V) is
40 L mol–1 s–1, while the rate of reduction by the
Co(cgsalen)– anions is 3260 L mol–1 s–1. These results
indicate an energy gain at the electron transfer step for the
metal complex reduction of dichloroꢀ and dibromoꢀ
cyclopropanes compared to the reduction by organic carꢀ
riers. The latter can be achieved only via the innerꢀsphere
mechanism of transfer of electrons from the metal comꢀ
plex to the substrate.
X = Cl, Br; M = Ni, Co, Fe; L = salen, cgsalen
It is noteworthy that the apparent rate constants of
reduction of dibromocyclopropanes, on the one hand,
and monobromoꢀ and dichlorocyclopropanes, on the
other hand, by the Co(salen)– anions differ slightly. The
difference in ER potentials for these groups of compounds
is ∼1.0 V, which is equivalent, according to the electroꢀ
chemical kinetics laws, to the difference in rate constants
of their heterogeneous ER (at α = 0.5) by approximately
eight orders of magnitude. At the same time, the rate
constants of homogeneous reduction differ less than by
two orders of magnitude (see Table 2).
The R—M—Hal σꢀcomplex is the result of the priꢀ
mary electron transfer. In some cases, in particular,
Ar—Ni—Br or Alk—Co—Hal, the σꢀcomplex is reduced
less easily than the metal complex, resulting in the apꢀ
pearance of a new reduction wave at more negative poꢀ
tentials.14—16 In other cases (when the molecule contains
an organohalogen substrate of acceptor substituents), the
σꢀcomplex is reduced at the same as the metal complex
and even more positive potentials.16
We have previously2 studied the ER of geminal diꢀ
chloroꢀ and dibromocyclopropanes using organic elecꢀ
tron carriers as mediators, whose Е1/2 are less negative by
0.2—0.8 V than those of substrates. In this case, dichloroꢀ
No additional waves appear upon the metal complex
ER of dihalocyclopropanes, and only an increase in the
reduction wave of the metal complex is experimentally

926
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 4, April, 2003
Yanilkin et al.
detected. This means that the σꢀcomplexes are reduced at
the same or less negative potentials.
Based on the obtained results, we performed the preꢀ
parative ER of 1,1ꢀdichloroꢀ2,2ꢀdiphenylcyclpropane and
1,1ꢀdibromoꢀ2,2ꢀdiphenylcyclopropane in DMF using
the nickel and cobalt catalysts on the carbonꢀtissue elecꢀ
trode. The process was catalytic during the whole elecꢀ
trolysis and the loss of metal complexes was insignificant,
which follows from the data on permanent polarographic
monitoring of the reaction mixture composition. The reꢀ
sults of electrolysis are presented in Table 3. In all cases,
monohalocyclopropanes (54—59% yield) and allene
(5—9%) are the main ER products. Similar results were
obtained for the reduction on the mercury electrode and
the use of an alcohol or phenol as a proton donor. The
formation of the reaction products can be described by
Scheme 1.
The obtained data also show that under homogeneous
conditions for both the outerꢀ and innerꢀsphere mechaꢀ
nisms of electron transfer, unlike dichloroꢀ and monoꢀ
bromocyclopropanes, dibromocyclopropanes are reduced
with much lower rate than it could be expected based on
the potentials of heterogeneous reduction of these subꢀ
strates. Three reduction waves are observed in the voltꢀ
ammograms of 1,1ꢀdibromoꢀ2,2ꢀdiphenylcyclopropane
detected on the Hg/Pt ultramicroelectrode at high subꢀ
strate concentrations (0.1 mol L–1). The first and last
waves coincide with the polarographic reduction waves
(Fig. 1). When the concentration of a depolarizer twofold
increases, the height of the first wave remains unchanged
and the subsequent two waves increase proportionally.
Since the Е1/2 value on the mercury calomel electrode is
much lower than on other electrodes, we can assume that
the first wave on the Hg/Pt ultramicroelectrode is cataꢀ
lytic and corresponds to the reduction of dibromoꢀ
cyclopropane molecules adsorbed on the electrode. Then
two subsequent waves can be considered, in the first apꢀ
proximation, as the successive twoꢀstep reduction of the
initial compound from the nonadsorbed state. The differꢀ
ence between the Е1/2 values of the first and second waves
(∆Е1/21,2 = 0.62 V) shows that the energy of adsorption of
the cyclopropyl radical is ∼64 kJ mol–1. The ability of
dibromocyclopropane to be reduced in chemical reacꢀ
tions in the solution bulk is represented by the reduction
potentials of the nonadsorbed compound. This potential
is by ∼0.62 V more negative than the potentials of the first
polarographic wave and is much closer to the reduction
potentials of dichlorocyclopropanes. Therefore, the simiꢀ
larity of the rate constants of metal complex reduction of
dibromoꢀ and dichlorocyclopropanes is quite expected.
Scheme 1
In addition, the fragments Ph2C=CHCH3 (m/z 194),
Ph2C=CPh2 (m/z 332), diphenyl (m/z 154), and
Ph2C=CH2 (m/z 180) were detected in minor amounts by
mass spectrometry for 1,1ꢀdichloroꢀ2,2ꢀdiphenylcycloꢀ
propane. The reduction of 1,1ꢀdibromoꢀ2,2ꢀdiphenylꢀ
cyclopropane does not afford these compounds producꢀ
ing only two byꢀproducts with molecular weights 116
and 234. In the case of the chiral Co(cgsalen) metal comꢀ
i
Table 3. Results of the preparative electroreduction of 1,1ꢀdiꢀ
0.12 µA
haloꢀ2,2ꢀdiphenylcyclopropanes and 1ꢀchloroꢀ2,2ꢀdiphenylꢀ
2
cyclopropane
X
Y
MIIL
I/mA
Yield (%)
1
0.4 µA
Cl Cl Co(salen)
Ni(salen)
Co(cgsalen)
Ni(cgsalen) 25
Br Br Co(salen)
25
25
8
54
54
59
57
54
32
6
6
9
8
5
0
1.5
2
2.5
–E/V
Fig. 1. Polarograms of the reduction of 1,1ꢀdibromoꢀ2,2ꢀ
diphenylcyclopropane on a mercury calomel electrode (С =
1•10–3 mol L–1) (1) and on a Pt/Hg ultramicroelectrode (radius
of the ultramicroelectrode r = 5 µm, С = 0.1 mol L–1) (2).
25
8
H
Cl Ni(cgsalen)

Metal complex electrocatalytic reduction
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 4, April, 2003
927
constants of mediatory reduction of halocyclopropanes were
determined by polarography using the Bendersky—Mairanovsky
approximating formula17 and by CV using the Nicholson correꢀ
lation.18 Procedures of purification of solvents and supporting
salts and methods of polarographic measurements have been
described previously.19 Metal salenꢀcomplexes were synthesized
by known methods.20—26 Halocyclopropanes were synthesized
from the corresponding olefins and haloform using the Makosza
method.27—29
NMR spectra were recorded in CDCl3 on Varian Tꢀ60
(1H, 60 MHz) and Bruker MSLꢀ400 (13C, 100.62 MHz)
spectrometers using CDCl3 and Me4Si as internal standards.
IR spectra were obtained on an URꢀ20 spectrometer in Nujol.
Optical rotation was determined on a Perkin—Elmer 341 polaꢀ
rimeter with a sodium lamp (λ = 589 nm).
Electrochemical reduction of 1,1ꢀdihaloꢀ2,2ꢀdiphenylꢀ
cyclopropanes was carried out using a B5ꢀ70 power pack in a
diaphragm (cellulose) electrolyzer using a Hg pool as a cathode
and a Pt wire as an anode in the galvanostatic regime (I = 25 mA).
A working solution (20 mL) was prepared by dissolution of
Et4NCl (0.1 mol L–1), 1,1ꢀdihalocyclopropane (1.9 mmol),
metal salenꢀcomplex (0.19 mmol), EtOH (0.5 mL), and phenol
(1.9 mmol) in DMF. The reaction course was monitored by
GLCꢀMS on a МАТꢀ212 instrument using an SIꢀ54 column
(50 m × 0.3 mm). During the reaction, chromatograms of the
reaction mixture were recorded by the total ion current and
mass spectra were detected at the chromatographic peaks, Mass
spectra (EI) were recorded in an interval of 40—500 m/z with a
recording rate of decade s–1. The regime of mass spectra recordꢀ
ing: ionizing voltage 70 V, emission current 0.5 A, resoluꢀ
tion 1000, and temperature of the source 120 °С. Chromatoꢀ
graphic regime: temperature of the injector 240 °С, programmed
temperature change (6 deg min–1) from 100 (6 min) to 240 °С
(30 min), and helium as the carrier gas. Petroleum ether in the
concentration ∼1% was used as a solvent of reaction mixture
samples. Recording of chromatograms and mass spectra was
started 5 min after sample injection to cut off the peak of the
solvent.
plex, chirality of monochlorocyclopropane is not virtuꢀ
ally induced. According to measurements of the specific
rotation, the enantiomeric excess ее does not exceed 2%.
It is not clear from the obtained date which species is
protonated ([R—M—L]– or R–) and whether chirality is
lost at the protonation step. To solve this problem on
asymmetric induction by chiral metal complexes in prinꢀ
ciple, a possible influence of the protonation step should
be excluded at the initial stage. We believed that it could
be done in the case of a racemic mixture of nonsymꢀ
metrical dichloroꢀ or monochlorocyclopropanes if the reꢀ
action is performed by 50% and the process is monitored
by the remained amount of dichloroꢀ or monochloroꢀ
cyclopropane. This reduction was carried out for 1ꢀchloroꢀ
2,2ꢀdiphenylcyclopropane using the chiral Ni(cgsalen)
complex as a catalyst (see Table 3). In this case, chirality
is not induced. This suggests, most likely, that the chirality
of the substrate is not induced in the step of electron
transfer from the metal complex to halocyclopropanes
under the conditions used.
It should be mentioned in conclusion that the results
of kinetic studies suggest the efficient innerꢀsphere mechaꢀ
nism of reduction of 1,1ꢀdihalocyclopropanes by the elecꢀ
trochemically generated salenꢀcomplexes of metals in the
low oxidation state. We did not find any indications of the
possibility of the outerꢀsphere mechanism of the reaction.
In this case, the allene to monohalocyclopropane ratio in
the ER products is determined by the ratio of rates of
competitive reactions of elimination of the second halide
ion and protonation of anionic intermediates rather than
by the different mechanism of electron transfer from the
catalyst to substrate, as it was assumed when the chroꢀ
mium ions were used.10
Experimental
After the end of electrolysis, water (20 mL) was added to the
reaction mixture, and the resulting mixture was extracted with
hexane (3×20 mL). The combined organic layers were washed
with water and dried with Na2SO4. After the solvent was disꢀ
tilled off, the residue was separated by column chromatography
on silica gel using hexane as the eluent. The yields of the obꢀ
tained compounds are presented in Table 3. The characteristics
of 1ꢀchloroꢀ2,2ꢀdiphenylcyclopropane coincide with the pubꢀ
lished data.30
1,1ꢀDiphenylallene. 1H NMR, δ: 5.22 (s, 2 H, =СH2);
6.90—7.60 (10 H, 2 Ph). 13С NMR, δ: 78.06 (=CH2); 127.37
(pꢀСН); 128.63 (oꢀCH); 128.56 (mꢀCH); 136.56 (Ph2C=);
142.30 (Cipso); 210.14 (=C=). IR, ν/cm–1: 853 (=CH2); 1934
(С=С=С); 1598 (Ph); 1492 (C=O).
Electrochemical reduction of 1ꢀchloroꢀ2,2ꢀdiphenylcycloꢀ
propanes and further treatment of the reaction mixture were
carried out using a procedure similar to that described above in
the galvanostatic regime at a current of 8 mA. The amount of the
passed electricity was 2.1 F mol–1. The starting 1ꢀchloroꢀ2,2ꢀ
diphenylcyclopropane was separated from the reaction products
by column chromatography on silica gel (hexane as an eluent)
and analyzed polarimetrically.
Electrochemical reduction of 1,1ꢀdihalocyclopropanes was
studied by classical and commutator polarography, cyclic
voltammetry, and electrolysis in DMF against Et4NCl
(0.1 mol L–1). Polarograms were recorded on a PUꢀ1 polaroꢀ
graph. The characteristics of the capillary were the following:
m = 0.71 mg s–1, t1 = 0.5 s. An LP 7e polarograph with a switchꢀ
over frequency of 10 Hz was used as an auxiliary instrument for
recording commutated curves. Polarization curves on the Pt
ultramicroelectrode (r = 5 µm), on which mercury was electroꢀ
chemically deposited (Pt/Hg ultramicroelectrode) were recorded
using a GWP 673 polarograph. Cyclic voltammograms were
detected using a PIꢀ50ꢀ1 potentiostat on a glassꢀcarbon disk
electrode (2 mm in diameter) molded in Teflon. The potential
sweep was 100 mV s–1. A silver Ag/AgNO3 electrode in МеСN
(0.01 mol L–1) served as a reference electrode (Е0(Fc/Fc+) =
+0.16 V), and a Pt wire was used as an auxiliary electrode. The
solution was deaerated by nitrogen. The concentration of the
substrate in polarographic measurements was 1•10–3 mol L–1
and that for recording cyclic voltammograms was
3•10–3 mol L–1, the temperature being 298 K. Apparent rate
,

928
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Yanilkin et al.
ber 24—27, 1997, Kurashiki, Japan), Abstracts, Kurashiki,
1997, 15.
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