Electrochemical arylation of cobalt and nickel chelates with diphenyliodonium salts

Article abstract of DOI:10.1023/A:1015009729780

Electrochemical arylation of cobalt chelates with diphenyliodonium salts occurs at low cathodic potentials (viz., potential of the first reduction wave of the diphenyliodonium salt) and affords the phenyl derivatives of Co ^III chelates containi

Full text of DOI:10.1023/A:1015009729780

Russian Chemical Bulletin, International Edition, Vol. 51, No. 1, pp. 85—89, January, 2002
85
Electrochemical arylation of cobalt and nickel chelates
with diphenyliodonium salts

T. V. Magdesieva, D. N. Kravchuk, and K. P. Butin
Department of Chemistry, M. V. Lomonosov Moscow State University,
Leninskie gory, 119899 Moscow, Russian Federation.
Fax: (095) 939 5546. Eꢀmail: tvm@org.chem.msu.ru
Electrochemical arylation of cobalt chelates with diphenyliodonium salts occurs at low
cathodic potentials (viz., potential of the first reduction wave of the diphenyliodonium salt)
and affords the phenyl derivatives of CoIII chelates containing the σꢀCo—C(sp2) bond. Nickel
complexes should be arylated at higher cathodic potentials because it is necessary to generate
paramagnetic NiI complexes.
Key words: cobalt, nickel, chelates, diaryliodonium salts, arylation, electrochemical acꢀ
tivation.
Transition metal chelates are known as systems modꢀ
eling active sites of several natural metal enzymes and as
catalysts for many organic reactions, viz., alkylation, acyꢀ
lation, homoꢀ and crossꢀcoupling, and others (see,
e.g., Ref. 1 and literature cited therein). The catalytic
process often produces intermediate compounds containꢀ
ing σꢀmetal—carbon bonds, which further serve as the
carriers of alkyl, aryl, alkenyl, acyl, and other groups to
an organic substrate. In this connection, the synthesis and
study of the properties of such organometallic intermediꢀ
ates are of interest.
Three main approaches2 were developed for the synꢀ
thesis of organocobalt compounds containing the covaꢀ
lent Co—C bond: reactions of СоIII complexes with nuꢀ
cleophiles, reactions of СоII complexes with radicals, and
reactions of СоI complexes with electrophiles.
Syntheses of monoꢀ and dialkyl СоIII derivatives using
each of these approaches are widely exemplified in the
literature.3—5 Syntheses of aryl and vinyl organocobalt
compounds are much more rare.6—11
Great attention is given to a combination of organic
electrosynthesis with catalysis by transition metal comꢀ
plexes. Complexes of lowꢀvalence transition metals, for
example, supernucleophilic anions containing CoI or NiI,
are easily generated electrochemically and are capable of
reacting in situ with many organic substrates to form comꢀ
pounds with the σꢀcarbon—metal bonds, which in turn
can be carriers of an organic group to the second organic
or inorganic reactant present in a solution.12—18
Electrochemical alkylation19—28 of the Co complexes
has been studied in rather detail. Meanwhile, data for the
Ni complexes are scarce. In these reactions supernucleoꢀ
philes, such as anionic CoI complexes, are electrochemiꢀ
cally generated and then are introduced in situ into the
reaction with alkyl halides or methylcobaloxime. The aryl
and alkyl СоIII complexes are reduced at much higher
cathodic potentials than those of their precursors,29 CoII
complexes containing no Co—C bond. Therefore, it is
possible to electrochemically generate anions of the CoI
complexes by electrolysis at a controlled potential with no
risk of the subsequent destructive reduction of the reacꢀ
tion product. The situation is more complicated for the
nickel complexes.
There is a basic distinction between the anionic CoI
and NiI chelates: the CoI anions are evenꢀelectron
with the 16ꢀelectron valent metal shell (ignoring axial
ligands, e.g., solvent molecules), whereas the NiI anꢀ
ions are oddꢀelectron with the 17ꢀelectron valent shell.
Therefore, it can be expected that the NiI compounds
react preferentially with alkylating agents, viz., radical
precursors. This reactant is, e.g., methylcobaloxime
MeCoIII(dmgH)2:28
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 83—87, January, 2002.
1066ꢀ5285/02/5101ꢀ85 $27.00 © 2002 Plenum Publishing Corporation

86
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 1, January, 2002
Magdesieva et al.
containing ligands* based on αꢀthiopicolinamides were syntheꢀ
sized according to a previously published method.32 Diphenylꢀ
iodonium was prepared by a known procedure.33 nꢀBu4NBF4
(Aldrich) was used.
In the case of alkyl halides, the probability of the
single electron transfer (SET) mechanism increases:
[(Chel)2NiI]– + RHal
[(Chel)2NiI]– + R•
[(Chel)2NiIIR]– – e
[(Chel)2NiII] + R• + Hal–,
[(Chel)2NiIIR]–,
Acetonitrile (reagent grade) was stirred for 24 h above CaH2
and filtered. KNO3 (5 g) and concentrated H2SO4 (3 mL) were
added, and the resulting mixture was refluxed for 3 h and disꢀ
tilled. After this, MeCN was refluxed for 2 h above P2O5 and
distilled, collecting the fraction with b.p. 81—82 °С. The
concentration of solutions of the studied compounds was
[(Chel)2NiIIIR].
Unlike the CoII complexes, the nickel complexes used
as catalysts are divided into two groups. The first group
contains the NiII complexes that are immediately reduced
electrochemically to the corresponding zeroꢀvalence speꢀ
cies in one reversible twoꢀelectron stage (viz., NiII comꢀ
plexes with bpy, phen, PPh3, or dppe). The second group
represents the complexes that are reduced stepwise through
the intermediate formation of NiI, which transforms into
Ni0 at much more cathodic potentials (e.g., NiII comꢀ
plexes with cyclames, salenes, as well as dmgH, and sulꢀ
furꢀcontaining chelating ligands studied in this work).24
The distinction in behavior of these complexes in the
presence of organic halides is that the complexes of the
first group, being reduced to the Ni0 compounds, loose
one of their ligands and react with RHal or ArHal via the
oxidative addition route, for example,
(3—5)•10–4 mol L–1
.
Preparative electrolysis (general procedure). Electrolysis at a
controlled potential was conducted in a 10ꢀcm3 cell in MeCN
with 0.05 M nꢀBu4NBF4 solution. Weighted samples of the cheꢀ
late (5•10–4 mol) and Ph2I+BF4 (0.08 g, 1•10–3 mol) were
–
dissolved in MeCN (10 mL) and subjected to electrolysis at the
potential of the first wave reduction of Ph2I+BF4–. To remove
dioxygen and to stir the electrolyte solution, argon saturated
with a solvent vapor was passed through the cell. The completeꢀ
ness of electrolysis was concluded from a drop of current passing
through the system. Electrolysis was stopped when the current
became at most 10—15% of the initial value. The obtained soluꢀ
tion was studied by CVA on a platinum electrode.
Results and Discussion
The CoII, CoIII, and NiII complexes with chelating
ligands containing N and S atoms were chosen for invesꢀ
tigation.
[(bpy)2NiII]+ + 2e–
(bpy)Ni0 + bpy,
(bpy)Ni0 + ArHal
ArNiII(bpy)Hal.
Electrochemically activated arylation reactions of the
cobalt and nickel complexes were not studied earlier. The
purpose of this work is to develop methods for the introꢀ
duction of the phenyl group in various CoII, СоIII, and
NiII chelates using electrochemically generated phenyl
radicals. The diaryliodonium salts Ph2IBF4, Ph2IВr, and
(pꢀtꢀBuꢀC6H4)2IBF4 served as the source of aryl radicals.
Experimental
Instruments and electrodes. Electrochemical reduction poꢀ
tentials were measured using a PIꢀ50ꢀ1.1 potentiostat, a PRꢀ8
programmer, and a PDAꢀ1 twoꢀcoordinate recorder on a staꢀ
tionary and rotating platinum electrode with a working surface
area of 5.14 mm2 in a 0.05 M solution of nꢀBu4NBF4 at 20 °С in
a special electrochemical cell in anhydrous MeCN.
Cyclic voltammetry (CVA) curves were recorded on a staꢀ
tionary Pt electrode at a sweep of 200 mV s–1. The electrode was
thoroughly cleaned by polishing after recording each curve.
Preparative electrolysis was carried out using a Pꢀ5827M
potentiostat in an electrolytic cell with separated anodic and
cathodic spaces on an electrode from a graphite tissue (surface
area 2.29 cm2) in the presence of nꢀBu4NBF4 (0.05 mol L–1) as
a supporting electrolyte in anhydrous acetonitrile at 20 °С.
In all the cases, platinum served as an auxiliary electrode,
and a saturated Ag/AgCl electrode was used as a reference.
Starting compounds and reagents. The СоII and CoIII diꢀ
methyl glyoximate complexes were synthesized according to
known procedures.30,31 The Co and Ni complexes with sulfurꢀ
The electrochemical properties of the Co dimethyl
glyoximate complexes are well known,34 whereas the elecꢀ
trochemical behavior of sulfurꢀcontaining complexes
* The Co and Ni complexes with sulfurꢀcontaining ligands were
kindly presented by I. G. Il´ina.

Electrochemical arylation of chelates
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 1, January, 2002
87
based on αꢀthiopicolinamides 1—3 has been studied reꢀ
cently.28 The reduction of these compounds involves orꢀ
bitals localized on the metal:
The diphenyliodonium salts are also reduced
stepwise.35 The first reduction peak is observed at –0.6 V.
Ph2I+X– + e–
Ph• + PhI + X–
CoIII(Chel)2X
NiII(Chel)2
CoII(Chel)2
[CoI(Chel)2]–,
The further transformations of the primarily formed
phenyl radicals are determined mainly by the composiꢀ
tion of the solution. The presence in the reaction mixture
of compounds capable of fast reacting with phenyl radiꢀ
cals decreases substantially the contribution of further
reduction of radicals on the electrode and abstraction of
the hydrogen atom from the solvent. The second peak
corresponding to the reduction of iodobenzene appears at
a potential of –2.02 V (vs. Ag/AgCl/KCl(sat.)).
Thus, if a reaction mixture containing paramagnetic
СоII or NiI chelates, which react readily with radicals,
contains a diphenyliodonium salt, its oneꢀelectron reꢀ
duction can initiate arylation, for example, according to
Schemes 1 and 2.
[NiI(Chel)2]–.
According to the CVA data, the potentials of the
CoII/CoIII and CoII/CoI redox transitions fall within the
intervals from –0.6 to –0.7 V and from –1.08 to –1.28 V,
respectively (vs. Ag/AgCl/KCl(sat.)). For the studied NiII
αꢀthiopicolinamide complex, the NiII/NiI redox transiꢀ
tion is observed at a potential of –1.38 V (Table 1).
Table 1. Potentials of reduction peaks of the initial Со
and Ni chelates and reaction mixtures obtained by preꢀ
parative electrolysis of these complexes in the presence
of Ph2IBF4 or (p—ButꢀC6H4)2IBF4
–E red/V
Scheme 1
Compound or mixture
(dmgH)2CoPy2
Ph2IBF4
(dmgH)2CoPy2a + Ph2IBF4
1.08, 2.10
0.58, 2.02
0.65, 1.10,
1.56c, 2.05
0.60, 2.06
0.60, 1.08,
1.62c, 2.10
1.28, 1.80
0.60, 1.18,
1.66c, 1.83
1.20, 1.96
0.70, 1.20,
1.68c, 2.00
0.68, 1.68c
Ph2I+ + e–
Ph• + PhI,
(Chel)2PhCoIII
b
Ph• + (Chel)2CoII
.
(pꢀButꢀC6H4)2IBF4
(dmgH)2CoPy2a + (pꢀButꢀC6H4)2IBF4
b
Scheme 2
1
Ph2I+ + e–
Ph• + PhI,
[(Chel)2NiI]–,
b
1a + Ph2IBF4
(Chel)2NiII + e–
[(Chel)2NiI]– + Ph•
[(Chel)2NiIIPh]– – e–
2
[(Chel)2NiIIPh]–,
(Chel)2NiIIIPh.
b
2d + Ph2IBF4
2d + Ph2IBF4 after preparative
b
electrolysis at –0.8 V
Organometallic complexes with the NiIII—C bond are
kinetically unstable and easily dissociate through a cleavꢀ
3
1.38, 2.02
1.66c
3d + Ph2IBF4 after preparative
b
age of the metal—carbon bond (NiIII—R
NiII + R•).
electrolysis at –1.4 V
(dmgH)2CoPyCl
Stability of these compounds depends strongly on the
nature of polydentate ligands bound to the metal (see,
e.g., Ref. 34 and literature cited therein). For instance,
the anionic [2,6ꢀ(Me2NCH2)C6H3]– ligand stabilizes the
NiIII organometallic compounds36—38 and strongly deꢀ
creases the redox potential of the NiII/NiIII pair.39
The formation of lowꢀstability compounds with the
NiIII—C bonds as intermediates is postulated by many
authors34,40—45 in metallocomplex catalysis and biology.
The data presented below show that the complex with the
NiIII—Ph bond obtained from compound 3 is rather stable
in the CVA time scale.
The CVA curves for all studied mixtures containing
the СоII complex and Ph2I+X– (twoꢀ to fivefold excess of
the latter) exhibit the appearance of a lowꢀintensity
peak in the potential region from –1.5 to –l.7 V (vs.
Ag/AgCl/KCl(sat.)) already at the first scan. This peak
0.68, 1.10,
1.96
0.72, 1.10,
1.54c, 2.01
0.71, 1.54c
b
(dmgH)2CoPyCla + Ph2IBF4
(dmgH)2CoPyCla + Ph2IBF4 after
preparative electrolysis at –0.8 V
(dmgH)2CoPyCla + (pꢀButꢀC6H4)2IBF4
after preparative electrolysis at –0.8 V
(dmgH)2PhCoPy
b
0.70, 1.64c
1.56
b
Note. Electrolysis was conducted on the Pt electrode
in MeCN in the presence of a 0.05 M solution of
Bu4NBF4. The potential values are presented relatively
to Ag/AgCl/KCl(sat.).
Concentrations of solutions/mol L–1
d 1•10–4
: ;
a 2•10–4; b 1•10–3
.
c The potentials correspond to the reduction of the elecꢀ
trolysis products, viz., aryl СоIII and NiIII complexes
containing the σꢀM—C(sp2) bond.

88
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 1, January, 2002
Magdesieva et al.
(pꢀButC6H4)2IBF4 with the Co dimethyl glyoximate comꢀ
plex affords the corresponding aryl derivatives, whose reꢀ
duction potential is a little shifted to the cathodic region
compared to that of PhCo(dmgH)2Py (see Table 1).
The above arylation reaction can involve not only CoII
but also CoIII complexes, which, as a rule, are more stable
and accessible. However, in this case, both participants of
the reaction need electrochemical activation, i.e., genꢀ
eration of the aryl radicals from the diphenyliodonium
salt and reduction of CoIII to the paramagnetic CoII comꢀ
plex. The value of the controlled electrolysis potential
remains virtually unchanged. This is related to the fact
that the CoIII/CoII redox transition for the most of comꢀ
plexes occurs in a potential range of –0.4—–0.8 V (vs.
Ag/AgCl/KCl(sat.)), i.e., very close to the reduction poꢀ
tential of the iodonium salts. Therefore, at specified poꢀ
tential values, we can simultaneously generate Ph• and
the CoII complex, which then react with each other in situ.
Our studies showed that electrolysis of reaction mixꢀ
tures containing the СоII or CoIII dimethyl glyoximate
complexes gives the same arylation product, namely,
(dmgH)2PhCoPy (Scheme 3, see Table 1).
i
1
2
3
5 µA
0
–1.0
–2.0 E/V
Fig. 1. Cyclic voltammograms for Ph2IBF4 (2•10–4 mol L–1, 1),
(dmgH)2CoPy2 (2•10–4 mol L–1, 2), and resulting mixture obꢀ
tained after preparative electrolysis at –0.8 V (Pt, MeCN, vs.
Ag/AgCl/KCl(sat.), 3).
corresponds to the reduction of the arylated complexes
(see Table 1).
Preparative electrolysis of these mixtures at the potenꢀ
tial of diphenyliodonium reduction (–0.6 V) results in the
appearance of a compound characterized by the cathodic
peak in the same potential region (–1.5 to –1.7 V) (see
Table 1, Fig. 1). The graphite tissue with the high specific
surface area was used as a working electrode in electrolyꢀ
sis because a platinum electrode is rapidly passivated. We
showed that the reduction potentials of the starting comꢀ
pounds slightly change when the platinum material of the
working electrode is replaced by graphite.
Scheme 3
(dmgH)2CoIIIPyCl + e– + MeCN
(dmgH)2CoIIPy(MeCN) + Cl–,
Ph2I+BF4– + e–
(dmgH)2CoIIPy(MeCN) + Ph•
(dmgH)2PhCoIIIPy + MeCN.
Ph• + PhI + BF4
,
–
In order to prove the assignment of the cathodic peaks
(E = –1.5—–1.7 V), we synthesized the (dmgH)2PhCoPy
complex by the reaction of the CoIII complex with the
Grignard reagent:
Preparative electrolysis of the sulfurꢀcontaining coꢀ
balt and nickel chelates in a mixture with Ph2I+BF4– also
produces compounds with reduction peaks at potentials
of –1.66 and –1.68 V, respectively, which indicate
arylation to occur (see Table 1). This is characteristic of
compounds containing the σꢀСо—С and Ni—C bonds.
However, nickel complex 3 is arylated only at the
potential of the first reduction wave (–1.38 V), i.e., the
paramagnetic NiI complex reacts with phenyl radicals.
The initial diamagnetic NiII complex, unlike the paramagꢀ
netic СоII compounds, reacts very slowly. The arylation
product is not formed by preparative electrolysis of a mixꢀ
ture of diphenyliodonium borofluoride and complex 3 at
the potential of the first wave of Ph2IBF4 reduction.
The preparative electrolysis of a mixture of the ligand
from complexes 2 or 3 and diphenyliodonium borofluoride
at the reduction potential of the latter produces a comꢀ
pound, which is reduced at potentials being 120 mV less
cathodic than that of the arylation product, e.g., comꢀ
plex 2. This indicates that the arylation of the chelate
results in the formation of the σꢀcarbon—metal bond
(dmgH)2CoPyCl + PhMgBr
(dmgH)2PhCoPy + MgBrCl.
It turned out that the CVA curves for a solution of the
authentic complex contain the characteristic irreversible
cathodic peak at a potential –1.56 V, which coincides in
position with the potential of the cathodic peak of the
product of electrochemical arylation. The potentials of
peaks of the electrolysis products and a solution of the
(dmgH)2PhCoPy complex in the anodic branch of the
cyclic voltammogram also coincide.
Thus, for the reaction of the CoII complexes with
diphenyliodonium salts, it is enough to activate electroꢀ
chemically only one of these reactants. The active phenyl
radicals generated by the reduction of Ph2I+ react rapidly
with the CoII complex (see Scheme 1).
Diphenyliodonium salts with various substituents in
the benzene ring can also be introduced into the reaction.
For example, preparative electrolysis of a mixture of

Electrochemical arylation of chelates
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 1, January, 2002
89
21. G. B Majya, B. C. Han, and K. M. Kadish, Langmuir,
1989, 5, 645.
22. D. Lexa, J. M. Saveant, and J. P. Soufflet, J. Electroanal.
Chem., 1979, 100, 159.
23. B. Steiger, A. Ruhe, and L. Walder, Anal. Chem., 1990,
62, 759.
rather than ligand arylation. In addition, if complex 2 is
arylated at the S atoms, the reaction product would be the
СоI complex, which is reduced at much more cathodic
potentials (about –2.0 V vs. Ag/AgCl/KCl(sat.)), which
was not in fact found.
The obtained results show a possibility of electrochemiꢀ
cal arylation of the CoII, CoIII, and NiII chelates with
diphenyliodonium salts. In the case of the cobalt comꢀ
plexes, the reaction occurs at low cathodic potentials (poꢀ
tential of the first wave of diphenyliodonium salt reducꢀ
tion) and results in the formation of phenyl derivatives of
the CoIII chelates containing the σꢀCo—C(sp2) bond. The
application of diphenyliodonium salts as arylating agents
has a doubtless advantage over such traditionally used in
SRN1 reactions reagents as halobenzene because the genꢀ
eration of phenyl radicals due to their electroreduction
occurs at much lower cathodic overvoltages.
24. R. D. Rakhimov, E. R. Milaeva, O. V. Polyakova, and K. P.
Butin, Izv. Akad. Nauk, Ser. Khim., 1994, 309 [Russ. Chem.
Bull., 1994, 43, 289 (Engl. Transl.)].
25. K. P. Butin, R. D. Rakhimov, and I. G. Il´ina, Izv. Akad.
Nauk, Ser. Khim., 1999, 71 [Russ. Chem. Bull., 1999, 48, 71
(Engl. Transl.)].
26. R. D. Rakhimov, E. R. Milaeva, and K. P. Butin, Izv. Akad.
Nauk, Ser. Khim., 1998, 289 [Russ. Chem. Bull., 1998, 47,
282 (Engl. Transl.)].
27. R. D. Rakhimov and K. P. Butin, Izv. Akad. Nauk, Ser.
Khim., 1997, 2157 [Russ. Chem. Bull., 1997, 46, 2044 (Engl.
Transl.)].
28. R. D. Rakhimov and K. P. Butin, Izv. Akad. Nauk, Ser.
Khim., 2000, 55 [Russ. Chem. Bull., Int. Ed., 2000, 49, 56].
29. G. Costa, Pure Appl. Chem., 1972, 30, 335.
30. G. N. Schrauzer and L. P. Lee, J. Am. Chem. Soc., 1970,
92, 1551.
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos. 00ꢀ03ꢀ
32888а and 01ꢀ03ꢀ33147а).
31. Inorganic Syntheses, McGrawꢀHill Book Company, New
York, 1974, 11, 62.
32. I. G. Mochalina, Ph. D. (Chem.) Thesis, Moscow State
Univ., Moscow, 1964, 180 pp. (in Russian).
33. Organic Syntheses, Collect. Vol. 3, Ed. A. H. Blatt, Queens
College, Flushing, New York, 1953.
References
1. L. S. Hegedus, Coord. Chem. Rev., 2000, 204, 199.
2. G. N. Shrauzer and G. Kohnle, Chem. Ber., 1964, 97, 3056.
3. D. Dodd and M. D. Johnson, J. Organomet. Chem. Rev.,
1973, 52, 1.
34. P. J. Chmielewski, L. LatosꢀGrazynski, and T. Glowiak,
J. Am. Chem. Soc., 1996, 118, 5690.
4. M. B. Davies, Coord. Chem. Rev., 1998, 169, 237.
5. R. W. Witman and J. A. Weber, Inorg. Chim. Acta, 1977,
23, 263.
6. F. Rogo and J. Sancho, J. Organomet. Chem., 1977, 131, 439.
7. M. F. Corrigan, G. B. Deacan, B. O. West, and D. G. Vince,
J. Organomet. Chem., 1976, 105, 119.
8. J. Kwiatek and J. K. Seyler, J. Organomet. Chem.,
1965, 3, 421.
9. A. Bigotto, G. Costa, G. Mestroni, G. Pellizer, A. Puxeddu,
E. Reisenhofer, L. Stefani, and G. Tauzher, Inorg. Chim.
Acta Rev., 1970, 4, 41.
35. F. M. Beringer and R. A. Falk, J. Chem. Soc., 1964, 4442.
36. D. M. Grove, G. van Koten, R. Zoet, N. W. Murrall, and
A. J. Welch, J. Am. Chem. Soc., 1983, 105, 1379.
37. D. M. Grove, G. van Koten, P. Mul, R. Zoet, J. G. M.
van der Linden, J. Legters, J. E. J. Schmitz, N. W. Murrall,
and A. J. Welch, Inorg. Chem., 1988, 27, 2466.
38. D. M. Grove, G. van Koten, W. P. Mul, A. A. H. van der
Zejden, J. Terheiden, M. C. Zoutberg, and C. H. Stam,
Organometallics, 1986, 5, 322.
39. L. A. van der Kuil, H. Luitjes, D. M. Grove, J. W. Zwikker,
A. A. H. van der Linden, A. M. Roelofsen, L. W. Jenneskens,
W. Drenth, and W. G. van Koten, Organometallics, 1994,
13, 468.
10. K. NguyenꢀVanꢀDuong and A. Gaudemer, J. Organomet.
Chem., 1970, 22, 473.
11. A. W. Jonson and B. S. Meeks, J. Chem. Soc., 1971, 185.
12. H. Lemkuhl, Synthesis, 1973, 377.
13. C. P. Andrieux, J. M. DumasꢀBouchiat, and J. M. Saveant,
J. Electroanal. Chem., 1978, 87, 39.
14. V. G. Mairanovskii, Elektrosintez monomerov [Electrosynthesis
of Monomers], Mir, Moscow, 1983, 300 pp. (in Russian).
15. M. Troupel, Ann. Chim., 1986, 76, 151.
40. P. J. Schebler, B. S. Mandimutsira, C. G. Riordan, L. M.
LiableꢀSands, C. D. Incarvito, and A. L. Rheingold, J. Am.
Chem. Soc., 2001, 123, 331.
41. M. S. Mubarak, M. Pagel, L. M. Marcus, and D. G. Peters,
J. Org. Chem., 1998, 63, 1319.
42. M. Durandetti, J.ꢀY. Nedelec, and J. Perichon, J. Org. Chem.,
1996, 61, 1748.
16. S. Torii, Synthesis, 1986, 873.
43. M. Kumar, Chem. Rev., 1996, 96, 2515.
44. U. Ermler, W. Grabarse, S. Shima, M. Goubeaud, and R. K.
Thauer, Science, 1997, 278, 1457.
45. T. Wondimagegen and A. Ghosh, J. Am. Chem. Soc., 2001,
123, 1543.
17. E. Stecman, Electrochemistry, Springer, Berlin, 1987, 195.
18. O. N. Efimov and V. V. Strelets, Usp. Khim., 1988, 57, 238
[Russ. Chem. Rev., 1988, 57 (Engl. Transl.)].
19. Yu. G. Budnikova, Doct. Sci. (Chem.) Thesis, Kazan State
Univ., Kazan, 1999, 374 pp. (in Russian).
20. T. V. Magdesieva, Doct. Sci. (Chem.) Thesis, Moscow State
Univ., Moscow, 2000, 373 pp. (in Russian).
Received March 5, 2001;
in revised form July 26, 2001