Hydrophobic vitamin B12· part 19: Electroorganic reaction of DDT mediated by hydrophobic vitamin B12

Article abstract of DOI:10.1039/b315170k

The controlled-potential electrolysis of 1,1-bis(4-chlorophenyl)-2,2,2- trichloroethane (DDT) was carried out at -1.4 V vs. Ag-AgCl in the presence of a hydrophobic vitamin B₁₂, heptamethyl cobyrinate perchlorate. DDT was dechlorinated to form 1,1-bis(4-chlorophenyl)-2,2-dichloroethane (DDD), 1,1-bis(4-chlorophenyl)-2,2-dichloroethylene (DDE), 1-chloro-2,2-bis(4- chlorophenyl)ethylene (DDMU) and 1,1,4,4-tetrakis(4-chlorophenyl)-2,3-dichloro- 2-butene (TTDB) (E/Z), and quantitative recovery of the catalyst after the electrolysis was confirmed by electronic spectroscopy. A photo-sensitive intermediate having a cobalt-carbon bond formed during the electrolysis was characterized by electronic spectroscopy. A mechanism for the formation of various dechlorinated products was investigated by using deuterium solvents and various spectroscopic measurements such as UV-VIS and the EPR spin-trapping technique.

Full text of DOI:10.1039/b315170k

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Hydrophobic vitamin B . Part 19:† Electroorganic reaction of
12
DDT mediated by hydrophobic vitamin B12
Hisashi Shimakoshi, Mami Tokunaga and Yoshio Hisaeda*
Department of Chemistry and Biochemistry, Graduate School of Engineering,
Kyushu University, Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
E-mail: yhisatcm@mbox.nc.kyushu-u.ac.jp; Fax: 81-92-632-4718; Tel: 81-92-642-3592
Received 24th November 2003, Accepted 9th February 2004
First published as an Advance Article on the web 24th February 2004
The controlled-potential electrolysis of 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT) was carried out at
Ϫ1.4 V vs. Ag–AgCl in the presence of a hydrophobic vitamin B , heptamethyl cobyrinate perchlorate. DDT was
12
dechlorinated to form 1,1-bis(4-chlorophenyl)-2,2-dichloroethane (DDD), 1,1-bis(4-chlorophenyl)-2,2-dichloro-
ethylene (DDE), 1-chloro-2,2-bis(4-chlorophenyl)ethylene (DDMU) and 1,1,4,4-tetrakis(4-chlorophenyl)-2,3-
dichloro-2-butene (TTDB) (E/Z), and quantitative recovery of the catalyst after the electrolysis was confirmed by
electronic spectroscopy. A photo-sensitive intermediate having a cobalt–carbon bond formed during the electrolysis
was characterized by electronic spectroscopy. A mechanism for the formation of various dechlorinated products was
investigated by using deuterium solvents and various spectroscopic measurements such as UV-VIS and the EPR
spin-trapping technique.
Introduction
Among the reported methods for dehalogenation of chlorin-
1,14–16
ated organic compounds,
the electrochemical method has
Reductive dehalogenation reactions are presently of great inter-
est, primarily because of their potential use in the treatment of
halogenated solvent wastes as well as in remedial approaches
to removing such chemicals from contaminated soils. Recently,
it has been demonstrated that certain bacteria can use tetra-
chloroethane as electron acceptors by reducing it to cis-
dichoroethane. The enzyme reductive dehalogenase contains
cobalamin as cofactor. A Co() species of cobalamin is a
supernucleophile and reacts with an alkyl halide to form an
alkylated complex with dehalogenation. The ability of cobal-
amin for reductive dehalogenation prompted us to investigate
the catalysis of a cobalamin derivative for degradation of
various halogenated organic compounds.
We have been dealing with a hydrophobic vitamin B , hepta-
methyl cobyrinate perchlorate [Cob(II)7C ester]ClO , which
has ester groups in place of the peripheral amide moieties of the
naturally occurring cobalamin as shown in Chart 1, and per-
formed various enzymic reactions, mainly isomerization reac-
tions leading to the intramolecular exchange of a functional
group and a hydrogen atom, using hydrophobic vitamin B
various advantages, such as cleanness and energy efficiency, and
is proved to be an excellent approach for degradation of various
halogenated organic compounds. The direct reductive dehalo-
genation reactions of chlorinated organic compounds has been
1
17,18
19
reported by several groups.
Peters and co-workers and
20
Rusling and co-workers reported indirect electrolysis of
halogenated organic compounds using a cobalt complex as
mediator. Electron-transfer mediators can cleave the carbon–
halogen bond at a more positive potential than that required for
direct reduction of the carbon–halogen bond. In connection
with such study, Keese and co-workers reported the electro-
2,3
2
,3
4–6
21
lysis of trichlorotoluene catalyzed by [Cob(II)7C ester]ClO .
1
4
Recently, we also reported dehalogenation of benzyl bromide
1
2
and phenethyl bromide catalyzed by hydrophobic vitamin B12
1
4
22,23
derivatives, which are immobilized on electrodes.
It is shown
in these studies that the hydrophobic vitamin B12 is clearly a
promising catalyst for dehalogenation of chlorinated organic
compounds.
7
Among the chlorinated organic compounds, 1,1-bis(4-chloro-
phenyl)-2,2,2-trichloroethane (DDT) is characterized by a
pronounced insecticidal property and has been used worldwide
for the last several decades despite its known hazardous effects
on human health and wildlife. Because of recent environmental
concerns, there is pressing need for efficient methods for
degradation of such chlorinated compounds accumulated in
12
8
–13
derivatives as catalysts.
In the course of these studies, hydro-
phobic vitamin B12 derivatives were found to act as excellent
model compounds for the functional simulation of cobalamin-
dependent enzymes.
14–16
the soil.
Therefore, much attention will be focused on the
reaction between the hydrophobic vitamin B12 and DDT under
electrochemical conditions. In this paper, electrolysis of DDT
catalyzed by hydrophobic vitamin B12 was carried out as shown
in Scheme 1.
Experimental
Materials
All solvents and chemicals used in the syntheses were of reagent
grade, and were used without further purification. For electro-
chemical studies, dmf was stirred for one day in the presence
of BaO under a nitrogen atmosphere, and distilled under
reduced pressure. Deuterium solvents, dmf-d7 (99.5% atom
Chart 1
D) and deuterium oxide (D O) (99.9% atom D), were pur-
2
†
For Part 18 see ref. 22.
chased from ACROS and CEA, respectively, and used without
8
78
D a l t o n T r a n s . , 2 0 0 4 , 8 7 8 – 8 8 2
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

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Scheme 1
further purification. Tetra-n-butylammonium perchlorate
n-Bu NClO ) was purchased from Nakalai Chemicals (special
electrode served as a reference. Non-aqueous dmf solutions
Ϫ3
(
containing a cobalt complex (1.0 × 10 M) and n-Bu NClO4
4
4
4
Ϫ1
grade) and dried at room temperature under vacuum before use.
Heptamethyl cobyrinate perchlorate, [Cob(II)7C ester]ClO ,
(1.0 × 10 M) were deaerated prior to each measurement, and
the inside of the cell was maintained under an argon atmos-
phere throughout each measurement. All measurements were
1
7
4
,24
was synthesized by a previously reported method.
[Co()-
(
Hdmg) ] (Hdmg = monoanion of dimethylglyoxime), was syn-
carried out at room temperature. The E value of ferrocene–
ferrocenium (Fc/Fc ) was 0.56 V vs. Ag–AgCl with this setup.
2
1/2
25
ϩ
thesized by the reported method. 1,1-Bis(4-chlorophenyl)-
,2,2-trichloroethane, DDT, was purchased from Tokyo Kasei
2
Kogyo (TCI) and was recrystallized from 2-propanol–
water before use. α-Phenyl N-(tert-butyl)nitrone (PBN) was
purchased from Aldrich and was used without further purifi-
cation. TLC was performed on Merck Kieselgel 60 F254 pre-
coated plates. Silica gel used for column chromatography was
Silica Gel 60N (spherical: 60–210 µm, neutral) purchased from
Kanto Chemical Co., Inc.
Electrolysis of DDT
The controlled-potential electrolysis of DDT was carried out at
Ϫ1.40 V vs. Ag–AgCl in the presence of [Cob(II)7C ester]ClO4
in a cylindrical three-electrode cell which was divided into
two internal compartments with a single sheet of micro-
porous polypropylene membrane equipped with a platinum
1
2
mesh cathode and a zinc plate anode (1 × 3 cm ) at 308 K under
an argon atmosphere. The applied potential between the work-
ing and reference electrodes during the electrolysis was main-
tained constant with a Hokuto Denko HA-501 potentiostat/
galvanostat, and the reaction was monitored on a Hokuto
Denko HF-201 coulomb/ampere-hour meter. Initial concen-
General analyses and measurements
Elemental analyses were obtained from the Service Center of
Elementary Analysis of Organic Compounds at Kyushu Uni-
1
13
versity. The H, C, COSY, HMQC and HMBC NMR spectra
were recorded on a Bruker Avance 500 spectrometer installed at
the Center of Advanced Instrumental Analysis in Kyushu Uni-
versity, and the chemical shifts (in ppm) were referenced relative
to the residual protic solvent peak. HPLC analyses were per-
formed on a column of Inertsil ODS-3 (GL Scinences Inc.;
length 150 mm; ID 4.6 mm, particle size 5 µm): flow rate, 1 mL
Ϫ4
Ϫ2
trations: cobalt complex, 5.0 × 10 M; DDT, 5.0 × 10 M;
dmf solution containing 0.1 M n-Bu NClO . After the electro-
4
4
lysis, dmf was removed by evaporation under reduced pressure
and 30 mL of CHCl was added to the residue. The chloroform
3
layer was washed with water (3 × 40 mL) to remove dmf com-
pletely, and dried with MgSO . Then the filtrate was concen-
4
Ϫ1
min (CH CN–H O) by employing an apparatus assembled
trated to dryness. The residue was passed through a silica gel
3
2
with a Hitachi L-6200 intelligent pump, L-3000 photodiode
array detector and D-2500 chromato-integrator. The GC-
mass spectra were obtained using a Shimadzu GC-QP5050A
equipped with a column J&W Scientific DB-1 (length 30 m; ID
short column eluting with CHCl to remove n-Bu NClO and
3
4
4
hydrophobic vitamin B , and then the products were analyzed
12
by HPLC, NMR and GC-MS.
0
.25 mm, film 0.25 µm). Gel permeation chromatography was
Isolation and identification of products
carried out on a Japan Analytical Industry Co. Ltd., LC-908
apparatus combined with UV-3702 attachment, using three
connected columns, JAIGEL-1H, 2H and 2.5H, with CHCl3
eluent. The EPR spectra were obtained on a JEOL JES-FE1G
X-band spectrometer equipped with an Advantest TR-5213
microwave counter and an Echo Electronics EFM-200 NMR
field meter. The UV-VIS absorption spectra were measured on
a Hitachi U-3300 spectrophotometer at room temperature.
The products were separated by gel permeation chromatography
and preparative TLC after the above work-up procedure, and
characterized as follows. The products, 1,1-bis(4-chlorophenyl)-
2
,2-dichloroethane (DDD) and 1,1-bis(4-chlorophenyl)-2,2-
dichloroethylene (DDE) were identified by HPLC and GC-MS
comparison with authentic samples which were purchased from
TCI, and 1-chloro-2,2-bis(4-chlorophenyl)ethylene (DDMU) was
1
13
26
identified by H, C NMR and GC-MS analyses. The dimers,
1
,1,4,4-tetrakis(4-chlorophenyl)-2,3-dichloro-2-butene (TTDB
Cyclic voltammetry
1
13
(
E/Z)), were identified by H, C, HMQC and HMBC NMR
27
The cyclic voltammograms (CV) were obtained using a BAS
CV 50W electrochemical analyzer. A three-electrode cell
equipped with a 1.6-mm diameter platinum wire as the working
and counter electrodes were used. An Ag–AgCl (3.0 M NaCl)
and mass spectral comparison to the reported values.
1
DDMU: mp. 65 ЊC, H NMR (CDCl ): δ 6.61 (s, 1H, CH),
3
13
7.15 (d, 2H, Ph), 7.30 (m, 4H, Ph), 7.41 (d, 2H, Ph), C NMR:
δ 116.8, 128.6, 128.8, 128.9, 131.2, 134.2, 134.4, 135.5, 138.2,
D a l t o n T r a n s . , 2 0 0 4 , 8 7 8 – 8 8 2
879

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ϩ
1
41.8. EI MS, m/z: [M] , 282. Found: C, 59.38; H, 3.23. Calc.
reaction of DDT was performed in the presence of a catalytic
for C H Cl : C, 59.30; H, 3.20%.
amount of hydrophobic vitamin B12 as described below.
14
9
3
TTDB (E): R = 0.82 (eluent, n-hexane–CHCl = 10 : 1), mp
f
3
1
2
34 ЊC, H NMR (CDCl ): δ 5.95 (s, 2H, methine), 7.09 (d, 8H,
Controlled-potential electrolysis of DDT
3
3
1
Ph), 7.29 (d, 8H, Ph), C NMR: δ 52.7, 128.8, 130.3, 133.0,
ϩ
The electrolyses were carried out at Ϫ1.4 V vs. Ag–AgCl in a
cylindrical three-electrode cell which was divided into two
internal compartments with a single sheet of microporous
polypropylene membrane equipped with a platinum mesh
cathode and a zinc plate anode. After a charge of 1.4 electron/
molecule based on the substrate was passed, almost no electro-
lysis current was detected. Then, the products were analyzed by
the procedure described in the Experimental section. DDT was
decomposed by over 80% based on its initial concentration, and
the turnover number based on the hydrophobic vitamin B12 as a
catalyst was ca. 80. The dechlorinated products, DDD, DDE,
DDMU and dimers TTDB (E/Z) were detected by HPLC and
GC-MS analysis as shown by entry 1 in Table 1. Reductive
dechlorination of DDT did not proceed under the corre-
sponding conditions without hydrophobic vitamin B12 as a
catalyst as shown by entry 2 in Table 1. In addition, it should be
noted that the catalyst was recovered quantitatively after the
electrolysis based on electronic and mass spectrometric analy-
sis. In contrast, the electrolyzed solution of [Co()(Hdmg)2],
which is a well-known functional model compound of cobal-
amin, was decolorized under the same conditions during the
course of the electrolysis and a small amount of DDT was
dechlorinated as shown by entry 3 in Table 1. Therefore, the
hydrophobic vitamin B12 is a tough and excellent catalyst.
1
33.4, 137.7. EI MS, m/z: [M] , 564. Found: C, 59.46; H, 3.21.
Calc. for C H Cl : C, 59.30; H, 3.20%.
28
18
6
TTDB (Z): R = 0.74 (eluent, n-hexane–CHCl = 10 : 1), mp
f
3
1
1
71 ЊC, H NMR (CDCl ): δ 5.55 (s, 2H, methine), 7.00 (d, 8H,
3
13
Ph), 7.28 (d, 8H, Ph), C NMR: δ 52.8, 128.8, 130.4, 133.7,
ϩ
1
34.3, 137.7. EI MS, m/z: [M] , 564. Found: C, 59.36; H, 3.31.
Calc. for C H Cl : C, 59.30; H, 3.20%.
28
18
6
Results and discussion
Redox behavior of hydrophobic vitamin B12 in the presence of
DDT
A redox potential for the Co()/Co() couple of hydrophobic
vitamin B12 in dmf was observed at Ϫ0.49 V vs. Ag–AgCl
ϩ
(
Ϫ1.05 V vs. Fc/Fc ) as shown in Fig. 1(a). The hydrophobic
vitamin B12 is easily reduced to a supernucleophilic Co()
species. The addition of an excess of DDT dramatically
changed the voltammetric pattern and gave rise to a new
irreversible redox wave at ca. Ϫ1.4 V vs. Ag–AgCl as shown in
Fig. 1(b), which is ascribed to the reduction of an organocobalt
28
complex formed in the electrolysis process. This voltammetric
pattern is in agreement with that for heptamethyl methyl-
8
aquacobyrinate perchlorate in dmf. To the extent that such a
result involved an alkylated-cobalt species formed in situ, it
was expected that the desired dechlorination process for DDT
could take place. Based on this result, a preparative electrolysis
Mechanistic aspects of the catalytic process
The controlled potential electrolysis was followed by elec-
tronic spectroscopy. When the electrolysis was carried out
at Ϫ1.40 V vs. Ag–AgCl, [Cob(II)7C ester]ClO4 was trans-
1
formed into the corresponding photo-sensitive complex with
absorption maxima at 313, 354 and 470 nm (Fig. 2, spectrum
A). Spectrum B in Fig. 2 was obtained by irradiation with
visible light under aerobic conditions. These absorption maxi-
ma and the photochemical behavior are characteristic of
4
those for the complex with a cobalt–carbon bond. This
result indicates that the electrolysis reaction proceeds via form-
ation of an alkylated complex with the cobalt–carbon bond as
an intermediate.
Fig. 2 Electronic spectra observed during electrolysis of a dmf
Ϫ4
solution containing [Cob(II)7C ester]ClO (5.0 × 10 M), DDT (5.0 ×
1
4
Ϫ2
Ϫ1
1
0
M) and n-Bu NClO (1.0 × 10 M): A, at Ϫ1.4 V vs. Ag–AgCl; B,
4 4
after irradiation with visible light under aerobic conditions.
The reaction mechanism was also examined by the spin-
2
9,30
trapping technique with PBN.
observed for the PBN spin adduct formed during the electro-
lysis at Ϫ1.40 V vs. Ag–AgCl: g = 2.007, A = 14.5 G, A =
H
An EPR spectrum was
Fig. 1 Cyclic voltammograms of hydrophobic vitamin B in dmf
1
2
Ϫ1
N
containing 1.0 × 10 M n-Bu NClO at room temperature; sweep rate:
00 mV s : (a) 1.0 × 10 M [Cob(II)7C ester]ClO and (b) 1.0 × 10
1 4
Ϫ2
4
4
4
Ϫ1
Ϫ3
Ϫ3
3.7 G (10 G = 1 Tesla). Upon addition of PBN, the formation
1
M [Cob(II)7C ester]ClO and 1.0 × 10 M DDT.
of the products was somewhat inhibited as shown by entry 4 in
1
4
8
80
D a l t o n T r a n s . , 2 0 0 4 , 8 7 8 – 8 8 2

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a
Table 1 Electrolyses of DDT catalyzed by cobalt complexes
d
Electrolyses conditions
Product yields (%)
b
Ϫ1
c
e
Entry Catalyst
Charge /F mol
Time/h Conversion (%) DDD DDE DDMU (E)-TTDB
(Z)-TTDB
TN
1
2
3
4
5
6
[Cob(II)7C ester]ClO
None
[Co()(Hdmg)2]
1.4
4
1
1
1
3
3
82
4
9
77
91
91
20
–
3
9
17
22
19
3
4
16
11
17
6
–
–
4
9
3
25
–
–
10
18
11
12
–
82
–
7
43
61
56
1
4
0.01
0.08
0.7
1.4
1.6
–
f
[Cob(II)7C ester]ClO
4
1
4
4
4
g
h
[Cob(II)7C ester]ClO
6
3
1
[Cob(II)7C ester]ClO
1
a
Ϫ4
Controlled-potential electrolyses were carried out in dmf at Ϫ1.40 V vs. Ag–AgCl under Ar atmosphere. Initial concentration: [catalyst], 5.0 × 10
Ϫ2
b
c
M; DDT, 5.0 × 10 M; n-Bu NClO , 0.1 M. Electrical charge passed per mol of DDT. Conversion was estimated by the recovery of DDT.
4
4
d
e
f
Products were analyzed by NMR, HPLC and GC-MS. Total turnover number (TN) based on the initial amount of the catalyst. In the presence
Ϫ1
g
h
of PBN, 5.0 × 10 M. Solvent, dmf-d7. In the presence of 5% D O. Yield of DDD is the sum of DDD-d and DDD (see Chart 2)
2
1
Chart 2
Scheme 2
Table 1. These results indicate that a radical species is generated
as the electrolysis intermediate under the present conditions.
In order to determine the source of the hydrogen in the
the cobalt complex acts as a mediator. DDE would be formed
by β-elimination of the substrate radical and not by the dispro-
portionation of the corresponding radical species. If dispropor-
tionation of the substrate radical occurred, a deuterium ion
products, the electrolyses were carried out in dmf-d and in
7
dmf containing 5% D O. The distributions of products were
analyzed by H NMR and GC-MS, and the results are summar-
ized in entries 5 and 6 in Table 1. The incorporation of deuter-
from D O would not be incorporated into DDD. (see Chart 2)
2
2
1
At this electrolysis potential, further one-electron reduction of
the substrate radical produces a carbanion and a subsequent
protonation gives DDD as shown in Scheme 2. This carbanion
may lead to a carbene with the elimination of the chloride
ium did not occur in the reaction in dmf-d . In contrast, 88% of
7
the deuterium ion was incorporated into DDD in the presence
31,32
of D O as shown in Chart 2. Therefore, DDD was mainly pro-
ion,
and the carbene dimerises to TTDB. The minor product
2
duced from an anionic intermediate and not directly from a
radical intermediate.
DDMU may be formed by a rearrangement of the carbene or
by an elimination of HCl from DDD.
The proposed reaction mechanism is shown in Scheme 2. The
Co() complex is electrochemically reduced to the Co() species,
and the corresponding alkylated complex is generated by the
reaction of the supernucleophilic Co() species with DDT. The
alkylated complex is subsequently reduced by electrolysis at this
potential to form the substrate radical and Co() species, and
In conclusion, controlled potential electrolyses of DDT were
carried out in dmf in the presence of a catalytic amount of
hydrophobic vitamin B12 to form various dechlorinated com-
pounds. The environmental pollutant DDT was dechlorinated
via formation of a cobalt–carbon bond under electrochemical
conditions. The hydrophobic vitamin B12 is one of the best
D a l t o n T r a n s . , 2 0 0 4 , 8 7 8 – 8 8 2
881

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catalysts acting as an electrolysis mediator in the present
system.
12 Y. Murakami, Y. Hisaeda, T. Ozaki and Y. Matsuda,
Chem. Commun., 1989, 1094.
1
1
3 Y. Murakami, Y. Hisaeda and T. Ozaki, J. Coord. Chem., 1991, 23,
7
7.
4 M. L. Hitchman, R. A. Spackman, N. C. Ross and C. Agra,
Acknowledgements
Chem. Soc. Rev., 1995, 423.
We wish to thank Mr H. Horiuchi, a glassworker in our
department, for his skill in preparing the special electrode
cells. The present work was supported by a Grant-in-Aid for
Scientific Research on Priority Areas (417) from the Ministry of
Education, Culture, Sports, Science and Technology (MEXT)
of Japan, a Grant-in-Aid for Scientific Research from the Japan
Society for the Promotion of Science (JSPS), and Academia
Showcase program, Japan Chemical Innovation Institute.
15 C. Holliger, S. Gaspard, G. Glod, C. Heijman, W. Schumacher,
R. P. Schwarzenbach and F. Vazquez, FEMS Microbiol. Rev., 1997,
2
0, 517.
1
6 M. M. Häggblom and I. D. Bossert ed., Dehalogenation Microbial
Processes and Environmental Applications, Kluwer Academic
Publishers, Boston, MA, 2003.
17 S. Rondinini, P. R. Mussini, P. Muttini and G. Sello, Electrochim.
Acta, 2001, 46, 3245.
1
1
8 N. Sonoyama, K. Hara and T. Sakata, Chem. Lett., 1997, 131.
9 A. J. Moad, L. J. Klein, D. G. Peters, J. A. Karty and J. P. Reilly,
J. Electroanal. Chem., 2002, 531, 163.
2
0 S. Schweizer, J. F. Rusling and Q. Huang, Chemosphere, 1994, 28,
References
9
61.
1
2
3
4
5
6
F. Alonso, I. P. Beletskaya and M. Yus, Chem. Rev., 2002, 102,
009.
C. Holliger, G. Wohlfarth and G. Diekert, FEMS Microbiol. Rev.,
999, 22, 383.
G. Wohlfarth and G. Diekert, Chemistry and Biochemistry of B ,
ed. R. Banerjee, Wiley-Interscience, New York, 1999, p. 871.
H. Shimakoshi, A. Nakazato, T. Hayashi, Y. Tachi, Y. Naruta and
21 T. Darbre, D. Zheng, R. Fraga and R. Keese, Electrochem. Soc.
Proc., 2000, 2000–15, 53.
22 H. Shimakoshi, A. Nakazato, M. Tokunaga, K. Katagiri, K. Ariga,
J. Kikuchi and Y. Hisaeda, Dalton Trans., 2003, 2308.
23 H. Shimakoshi, M. Tokunaga, K. Kuroiwa, N. Kimizuka and
Y. Hisaeda, Chem. Commun., 2004, 50.
24 L. Werthemann, R. Keese and A. Eschenmoser, unpublished results;
see: L. Werthemann, Dissertation, ETH Zürich (Nr. 4097),
Juris Druck and Verlag, Zürich, 1968.
4
1
1
2
Y. Hisaeda, J. Electroanal. Chem., 2001, 507, 170.
B. Kräutler, Vitamin B12 and B -Proteins, ed. B. Kräutler,
12
D. Arigoni and B. T. Golding, Wiley-VCH, Weinheim, 1998.
R. Scheffold, G. Rytz and L. Walder, Modern Synthetic Methods,
ed. R. Scheffold, John Wiley & Sons, Chichester, 1983, vol. 3,
p. 355.
25 G. N. Schrauzer and R. J. Windgassen, J. Am. Chem. Soc., 1967, 89,
1999.
26 D. Zanette and F. Nome, J. Org. Chem., 1979, 44, 2308.
27 L. L. Miller, R. S. Narang and G. D. Nordblom, J. Org. Chem., 1973,
38, 340.
28 Y. Hisaeda, T. Nishioka, Y. Inoue, K. Asada and Y. Hisaeda, Coord.
Chem. Rev., 2000, 198, 21.
29 A. J. Bard, J. C. Gilbert and R. D. Goodin, J. Am. Chem. Soc., 1974,
96, 620.
30 E. E. Bancroft, H. N. Blount and E. G. Janzen, J. Am. Chem. Soc.,
1979, 101, 3692.
7
8
9
Y. Murakami, Y. Hisaeda and A. Kajihara, Bull. Chem. Soc. Jpn.,
1
983, 56, 3642.
Y. Murakami, Y. Hisaeda, T. Tashiro and Y. Matsuda, Chem. Lett.,
985, 1813.
Y. Murakami, Y. Hisaeda, T. Tashiro and Y. Matsuda, Chem. Lett.,
986, 555.
1
1
1
1
0 Y. Murakami, Y. Hisaeda, T. Ozaki, T. Tashiro, T. Ohno, Y. Tani and
Y. Matsuda, Bull. Chem. Soc. Jpn., 1987, 60, 311.
1 Y. Murakami, Y. Hisaeda, T. Ozaki and Y. Matsuda, Chem. Lett.,
31 K. Brand and M. Matsui, Ber. Dtsch. Chem. Ges., 1913, 46, 2942.
32 J. March, Advanced Organic Chemistry: Reactions, Mechanisms, and
Structures, 4th edn., John Wiley & Sons, New York, 1992.
1
988, 469.
8
82
D a l t o n T r a n s . , 2 0 0 4 , 8 7 8 – 8 8 2