Water as Solvent for Nickel-2,2′-Bipyridine-Catalysed Electrosynthesis of Biaryls from Haloaryls

Article abstract of DOI:10.1002/1615-4169(200201)344:1<45::AID-ADSC45>3.0.CO;2-E

Reductive homocoupling of aryl halides into biaryls was achieved by electrolysis of aqueous emulsions, either in an undivided cell fitted with a sacrificial anode, or in a divided diaphragm cell, and in the presence of nickel-2,2′-bipyridine as catalyst. Reactions were also run in a filter-press cell.

Full text of DOI:10.1002/1615-4169(200201)344:1<45::AID-ADSC45>3.0.CO;2-E

FULL PAPERS
Water as Solvent for Nickel-2,2'-Bipyridine-Catalysed Electrosynthesis of
Biaryls from Haloaryls
a
a
a
b
a,
¬ ¬
¬
¬
Frederic Raynal, Rachid Barhdadi, Jacques Perichon, Andre Savall, Michel Troupel *
a
¡
¬
Laboratoire d×Electrochimie, Catalyse et Synthese Organique (UMR 7582), C.N.R.S. À Universite Paris 12 Val de Marne, 2 rue Henry Dunant,
94320 Thiais, France
Fax: ( ‡ 33)-149-78-11-48, e-mail: Michel.Troupel@glvt-cnrs.fr
b
¬
¬
Laboratoire de Genie Chimique (UMR 5503), C.N.R.S. À Universite Paul Sabatier, 118 route de Narbonne, 31062 Toulouse, France
Received June 22, 2001; Received revised October 31, 2001; Accepted November 9, 2001
Abstract: Reductive homocoupling of aryl halides into
biaryls was achieved by electrolysis of aqueous emulsions,
either in an undivided cell fitted with a sacrificial anode, or
in a divided diaphragm cell, and in the presence of nickel-
2,2'-bipyridine as catalyst. Reactions were also run in a
filter-press cell.
Keywords: biaryl electrosynthesis; nickel-bipyridine cata-
lysis; water as solvent.
Introduction
Association of zinc powder and palladium catalysis is also
efficient to convert aryl iodides into biaryls in water/acetone
mixtures.[11] To our knowledge, similar reactions have not been
attempted in water by use of both electrochemistry and
catalysis by transition metal complexes. The sole related
examples are the work by Rusling et al. who reported that
electrolysis of heterogeneous aqueous solutions containing an
Environmental considerations now constrain chemists to
integrate the control of risks (and costs) into their procedures,
and the recent literature includes various approaches which
have been developed with the aim of achieving a ™green
chemistry∫.[1]
In this context, synthetic electrochemical processes belong
to the environmentally friendly methods since the use of
electricity as a reagent does not involve the formation of any
side-product. However, the range of carbon-carbon bond
forming reactions by direct electroreduction is not very large,
and the reactions are mostly conducted in polar aprotic
solvents (DMF, NMP, etc.).[2,3] Several groups, including our
laboratory, have found interest in combining electrochemistry
and homogeneous catalysis in view of developing new organic
synthetic processes.[4] In this field, a large part of our work
organic halide (RX) and a complex of cobalt leads to the
[12]
coupling product R R. Thus 1,5 hexadiene or bibenzyl[13]
À
were obtained in low yields from the respective allyl chloride or
benzyl halide.
We chose the homocoupling of haloaryls into biaryls as a
model reaction to show that association of electrochemistry
and homogeneous catalysis can offer an efficient and clean
À
method to achieve reductive syntheses of C C bonds from
organic halides in water. Synthesis of biaryls is of interest since
the biaryl moiety is a building block of many pharmaceutical or
agrochemical products.[14]
À
focuses on the formation of C C bonds by electroreductive
coupling of organic halides with electrophiles in the presence
of catalytic systems involving low-valent transition metal
complexes generated electrochemically.[4]
Two electrochemical devices were employed to perform the
reaction. In order to demonstrate the ability of the coupling,
the electrolyses were first conducted in an undivided cell fitted
with a sacrificial metallic anode (M) as previously used with
aprotic or alcoholic solvents,[3,5-7] and the model reagent was
We have shown recently that the low-valent nickel-mediated
electroreductive coupling of aryl halides can be efficiently
achieved in methanol/ethanol mixtures[5] or in pure ethanol[6]
instead of the usual polar aprotic solvents.[7] This infers that the
required electroreduction of the Ni(II) catalyst precursor
arises in the usable cathodic potential range of alcohols, and
also that the intermediate organonickel species are compatible
with the proton activity of an alcoholic medium. Then, a new
challenge was to attempt similar coupling reactions in water,
the safest solvent, which also would allow the use of common
and cheap salts as supporting electrolytes.
At the cathode:
catalyst: Ni-bipy
2 PhBr + 2 e
Ph-Ph + 2 Br−
(1)
(2)
At the anode:
M
M2+ + 2 e
Two groups have already reported the chemical conversion
of aryl halides into biaryls with moderate to good yields, by
using zerovalent palladium complexes as catalysts and formate
ions,[8] or pressurised molecular hydrogen,[9] or zinc powder[10]
as reducing agents in hot organic/water (o/w) emulsions.
bromobenzene. In these experimental conditions the electro-
chemical reactions are as shown in Equations (1) and (2).
The metal M is sufficiently electropositive to be easily
oxidised, e.g., M ˆ Mg, Zn, Fe, Ni, etc. The use of the
consumable anode technique in aprotic solvents offers the
Adv. Synth. Catal. 2002, 344, No. 1
¹ VCH Verlagsgesellschaft mbH, D-69451 Weinheim, 2002 1615-4150/02/34401-045 049 $ 17.50+.50/0
45

¬ ¬
Frederic Raynal et al.
FULL PAPERS
advantage of not requiring a separator between catholyte and
anolyte.[3] Actually, the ion-exchanger membranes commonly
used as separators have low performances (high resistivity, life-
time, etc.) in organic solvents.
Although this electrochemical device is simple and easy to
scale-up,[15] it does not offer an environmentally friendly
method since metallic salts are produced in stoichiometric
amounts. This is the reason why we later used the two-
compartment cell described in the experimental section.
The cathodic reaction is the same as the one in the undivided
cell (Equation 1). However, in the anolyte a ™green process∫ is
however advanced enough to fully explain the positive effect of
the surfactants. In addition to their properties both as stabilis-
ing agent of the o/w emulsion and catalyst of phase transfer,
several other features can be envisaged. An adsorption of the
surfactant at the surface of the cathode may induce the
presence of an hydrophobic layer which allows a limitation of
protonation reactions of organometallic intermediates, so
favouring the transformation of PhBr into Ph-Ph rather than
into PhH. We do not either exclude that some of the surfactant
used can act as ancillary ligand of the intermediary Ni-bipy
species. Also, most of the studied surfactants give micelles in
water, which could possibly act as hydrophobic micro-reactors.
Nevertheless, the presence of micelles does not seem crucial
since the results are not very different with DDAB, which is not
a micellar agent in water.
A catalytic pathway involving nickel species is undoubtedly
involved since, in the absence of nickel salt, the direct
electroreduction of PhBr is not possible; only water is reduced.
With regard to the ligand of nickel, we have electrolysed
solutions of NiBr2 either free of ligand, or supplemented with
pyridine or 2,2'-dipyridylamine. Compared to solutions sup-
plemented with bipy, the rate of conversion of PhBr was very
weak in the absence of ligand and only traces of Ph-Ph were
obtained.
1/2 O2 + 2 H+ + 2 e (3)
H2O
now involved since it consists in electrooxidation of water into
dioxygen, Equation (3).
The use of an anion-exchanger diaphragm between the two
compartments avoids migration of protons toward the cathodic
compartment. The electric neutrality of the anolyte is kept by
the transfer of anions from the catholyte to the anolyte.
Results and Discussion
Electrosynthesis of Biphenyl from Bromobenzene in an
Undivided Cell
However, even with NiBr2 ‡ bipy, the faradaic yield of
conversion of PhBr was low (25 À 30%). This can be due to a
side-reaction involving a direct or a nickel-mediated electro-
reduction of protons. Indeed, when an acid, e.g., acetic acid,
was added to the initial solution, PhBr was scarcely consumed.
We have then investigated if the reaction could be improved by
increasing the pH of the solution. The data presented in Table 2
show the relevant results.
We can see that the addition of NaOH (0.1 mol LÀ1) to the
initial solution increased the yield in biphenyl, but such a high
value of pH induced the formation of an abundant precipitate,
presumably nickel hydroxide arising from Ni2‡ anions released
by the electrooxidation of the nickel rod used as anode. A
better solution was the use of a buffering system involving a
weak base like ammonia or an amine. In these conditions, the
formation of biphenyl became the major reaction and simulta-
neously the electric charge required to consume the bromo-
benzene did not exceed 1.6 À 2 F/mol of PhBr, corresponding
The solutions consisted of a PhBr/H2O emulsion with added
NaCl as supporting electrolyte and stabilised by a surfactant.
The catalyst was an equimolar mixture of divalent nickel
bromide and 2,2'-bipyridine (bipy) as ligand. The electrolyses
were carried out under galvanostatic conditions between two
nickel electrodes.
As shown in Table 1, the yields in biphenyl are strongly
dependent on the nature of the surfactant. In the absence of
surfactant, or when the solution contained an anionic surfac-
tant, PhBr was reduced mainly to benzene. The yields in
biphenyl were only slightly higher in the presence of a
zwitterionic or a cationic surfactant. Actually the best yield
was obtained from solutions supplemented with a neutral
surfactant. Therefore, further experiments were conducted
only by using either Igepal CO-720 or Brij 35. This work is not
Table 1. Influence of a surfactant on the Ni-catalysed electrosynthesis of Ph-Ph from PhBr in an undivided cell.[a]
current density (mA/cm2)
À
Ph Ph Yield (%)
surfactant
formula
name
class
amount (mmol)
none
1.2
1.2
1.2
1.2
1.2
2.5
2.5
1.2
1.2
10
19
27
34
27
34
23
44
45
Me-(CH2)11OSO3À, Na
SDS
BetaÔne
CTAB
DDAB
Igepal CO-720
Igepal CO-720
Igepal CO-720
Brij 35
anionic
zwitterionic
cationic
cationic
neutral
neutral
neutral
neutral
3
3
3
‡
‡
À
À
(Me)3N CH2 CO2
Me-(CH2)15N (Me)3, BrÀ
‡
(Me-(CH2)11)2N (Me)2, BrÀ
0.15[b]
3
‡
Me-(CH2)8-C6H4-(OCH2-CH2)12OH
Me-(CH2)8-C6H4-(OCH2-CH2)12OH
Me-(CH2)8-C6H4-(OCH2-CH2)12OH
Me-(CH2)11-(OCH2-CH2)23OH
0.3
3
0.3
[a]
General conditions : water (50 cm3) ‡ NaCl (0.1 mol LÀ1) ‡ PhBr (10 mmol) ‡ NiBr2 ¥ 5 H2O (1.5 mmol) ‡ bipy (1.5 mmol) ‡ surfactant, q ˆ 408C,
electric charge ˆ 4000 C (4 F/mol of PhBr) allowing a full consumption of PhBr.
DDAB is weakly soluble.
[b]
46
Adv. Synth. Catal. 2002, 344, 45 49

Water as Solvent for Nickel-2,2'-Bipyridine-Catalysed Electrosynthesis of Biaryls from Haloaryls
FULL PAPERS
Table 2. Influence of pH on the Ni-bipy-catalysed electrosynthesis of Ph-Ph from PhBr in an undivided cell.[a]
current density (mA/cm2)
À
Ph Ph Yield (%)
buffering system
measured pH
surfactant
NaOH, 0.1 mol LÀ1
NH3, 0.1 mol LÀ1
NH3, 0.1 mol LÀ1
NH3, 0.1 mol LÀ1
NH3, 0.1 mol LÀ1
NH3, 0.1 mol LÀ1
NH3, 0.1 mol LÀ1
NH3, 0.1 mol LÀ1
Pyridine, 0.1 mol LÀ1
MeNH2, 0.1 mol LÀ1
NH3, 0.1 mol LÀ1
‡NH4Cl, 0.01 mol LÀ1
MeNH2, 0.1 mol LÀ1
‡HCl, 0.05 mol LÀ1
12.4
11
11
11
11
11
11
11
9.4
11.7
Brij 35
Brij 35
Brij 35
Brij 35
8
1.2
2.5
8
13.5
1.2
2.5
8
55
63
68
76
70
67
58
38
20
49
Brij 35
Igepal CO-720
Igepal CO-720
Igepal CO-720
Brij 35
8
8
Brij 35
10.1
10.4
Brij 35
Brij 35
8
8
73
72
[a]
General conditions: water (50 cm3) ‡ NaCl (0.1 mol LÀ1) ‡ PhBr (10 mmol) ‡ surfactant (0.3 mmol for Brij 35 or 3 mmol for Igepal CO-720) ‡ NiBr2 ¥
5 H2O (1.5 mmol) ‡ bipy (1.5 mmol), q ˆ 408C, electric charge ˆ 2000 C (2 F/mol of PhBr) allowing a full consumption of PhBr.
to a 50 À 65% faradaic yield. Undoubtedly, both the proto-
nation reaction leading to benzene and the direct or mediated
side-electroreduction of water decreased when the value of pH
was increased. Besides the effect of the pH, we do not exclude
that ammonia or an amine can also be involved as ligand of Ni2‡
ions or some other nickel intermediates. Actually, during the
progress of electrolyses we could observe a lowering of the pH,
probably due to the complexation between the base and the
Ni2‡ ions released by the electrooxidation of the sacrificial
anode. In this series of experiments we have also noted that the
neutral surfactant Brij 35 gave higher yields than Igepal CO-
720, especially when the current density was increased.
The method has been successfully extended to other liquid
aryl bromides, e.g., 4-FC6H4Br and 4-CF3-C6H4Br. When
starting from a solid compound, e.g., 4-BrC6H4-COCH3, the
o/w emulsion was obtained by the previous dissolution of the
substrate in a minimum amount of toluene or o-xylene. If the
aryl bromide, ArBr, bears an acidic function, e.g., 4-BrC6H4-
CO2H, addition of one equivalent of NaOH induces its
dissolution in the solution buffered with ammonia or methyl-
amine so giving a homogeneous solution. In all these cases,
after addition of the surfactant Brij 35 and NiBr2 ‡ bipy, ArBr
was converted into Ar-Ar with moderate to good yields (50 À
70%), ArH being the sole side-product detected.
and the nickel catalyst. Electrolyses were run by applying a
constant current intensity and the rate of conversion of ArX
during the electrolysis was measured by GC analysis of
samples. Figure 1 presents the results of a typical experiment
with PhBr. The GC analysis of samples was not convenient to
monitor the formation of biphenyl since it precipitates in part,
especially when PhBr is almost fully consumed. The evolution
of the selectivity in Ph-Ph was then obtained from several
experiments involving various electric charges, followed by the
analysis of the mixture.
The rates of conversion of PhBr both in the undivided or in
the divided cell are close to the theoretical value, up to half
consumption of PhBr (cf. Figure 1). During the first part of
À
electrolysis, Ph Ph is obtained with quite similar selectivity
(60 À 70%) in both devices. However, discrepancies appear in
Electrosynthesis of Biaryls from Haloarenes in a Divided
Cell
As mentioned above, the sacrificial anode technique was later
replaced by a ™less polluting∫ one using a cell divided in two
compartments separated by an anion-exchanger membrane.
The cell design is described in the experimental part.
The anodic compartment was filled with aqueous potassium
hydroxide and the anode was a Ti-Pt plate allowing the
oxidation of water into oxygen, and of transferred ClÀ into
ClOÀ. The cathodic compartment was fitted with a nickel foam
cathode and contained the ArX/H2O emulsion, the surfactant
Brij 35, the supporting electrolyte NaCl, a pH buffering system,
Figure 1. Ni-bipy-catalysed electrolytic conversion of PhBr in a
&
*
PhBr/H2O emulsion:
in the undivided cell;
in the two-
compartments cell; ----- theoretical curve for a 100% faradaic
À
~
yield;
selectivity in Ph Ph (%) for electrolyses, in the divided
cell, stopped respectively at 5 ¥ 102, 103 and 2.2 ¥ 103 C. General
conditions: water (50 cm3) ‡ NaCl (0.1 mol LÀ1) ‡ Brij 35
(0.3 mmol) ‡ NH3 (0.1 mol LÀ1) ‡ PhBr (10 mmol) ‡ NiBr2 ¥
5 H2O (1.5 mmol) ‡ bipy (1.5 mmol), q ˆ 40 8C, current
density ˆ 8 mA/cm2.
Adv. Synth. Catal. 2002, 344, 45 49
47

¬ ¬
Frederic Raynal et al.
FULL PAPERS
Table 4. Ni-bipy-catalysed electrosynthesis of biaryls from aryl halides in a
prolonged electrolyses. As shown by Figure 1, the reaction
requires a larger electric charge in the divided cell than in the
undivided one. Also, the selectivity in Ph-Ph becomes lower
during the progress of the electrolyses in the two-compartment
cell and reaches only 40 À 45% for a full consumption of PhBr,
while this selectivity was almost constant (60 À 70%) in the
undivided cell. These differences in behaviour do not seem to
arise from a deactivation of the catalyst since extra addition of
NiBr2 ¥ 5 H2O or NiBr2 ¥ 5 H2O ‡ bipy does not modify appre-
ciably the results.
divided cell.[a]
ArX
rate conversion of ArX (%) Ar-Ar selectivity (% CPG)
PhCl
4-CF3C6H4Cl
3-CF3C6H4Cl
4-CH3C6H4Cl 67
4-FC6H4Cl 92
3-CH3OC6H4Cl 75
PhBr 86
86
60
81
59
29
28
32
40
38
54
72
4-CF3C6H4Br 70
Another difference we have remarked between the two
methods is the evolution of the pH. Contrary to what was
observed in the undivided cell, we have noted, in the
diaphragm cell, an increase of the pH, due to the side reduction
reaction of water which releases hydroxide anions. However,
we cannot confirm at the present time that this explains the
lowering of the faradaic yield and the selectivity.
[a]
General catholyte conditions: water (50 cm3) ‡ NaCl (0.3 mol LÀ1) ‡
MeNH2 (0.5 mol LÀ1) ‡ HCl (0.25 mol LÀ1) ‡ ArX (10 mmol) ‡ Brij 35
(0.1 mmol.) ‡ NiBr2 ¥ 5 H2O (1.5 mmol) ‡ bipy (1.5 mmol), q ˆ 408C,
current density ˆ 30 mA/cm2, electric charge ˆ 1700 C (1.7 F/mol of
ArX).
Exhaustive electrolyses of some aryl bromides have been
performed in the diaphragm cell. In each experiment 20 mmol.
of ArBr were involved and a constant current intensity of 0.1 A
was supplied during 14 hours what corresponds to an electric
charge of 2.5 F/mol of ArBr. Results are presented in Table 3.
In these experiments, ArBr was almost fully consumed and the
yields in biaryl were moderate.
We are currently attempting the transposition of reactions
described in this paper in a filter-press cell. The experimental
conditions are not yet optimised but the preliminary results,
presented in Table 5, are encouraging since three aryl bro-
mides have been converted into the corresponding biaryls with
a moderate to good selectivity.
According to preceding remarks about the progress of the
electrolyses, a better selectivity is expected if the electrolysis is
stopped when only apartof ArBr is converted. Then we carried
out electrolyses involving a lower electric charge in order to
transform only about 60 À 85% of the starting molecule. In this
series of experiments aryl bromides and aryl chlorides were
tested. Results in Table 4 show that the selectivity in biaryl
from ArBr is good in this case. It appears also that the reaction
is moderately effective when starting with aryl chlorides.
Table 5. Ni-bipy-catalysed electrosynthesis of biaryls from aryl bromides
in a filter-press cell.[a]
ArBr
PhBr
4-CF3C6H4Br 40
3-CF3C6H4Br 39
rate conversion of ArBr (%) Ar-Ar selectivity (% CPG)
43
56
69
58
[a]
General catholyte conditions: NaCl (0.5 mol LÀ1) ‡ MeNH2 (0.5 mol
LÀ1) ‡ HCl (0.25 mol LÀ1) ‡ ArBr (0.4 mol LÀ1) ‡ Brij 35 (6 ¥ 10À3
mol LÀ1) ‡ NiBr2 ¥ 5 H2O (6¥ 10À2 mol LÀ1)‡ bipy (6¥ 10À2 mol LÀ1), q ˆ
408C, current density ˆ 40 mA/cm2, electric charge ˆ 1 F/mol of ArBr.
Syntheses with a Filter-Press Cell
All these results concerning partial or exhaustive electrolyses
in the diaphragm cell show that our initial goal has been Conclusion
obtained. However, the laboratory electrochemical device
used until now does not allow a scale-up of the process. The
most common type of design for large-scale electroorganic
preparation is the commercially available filter-press type,
where pumps ensure the flow through the cell of solutions
contained in tanks.
In conclusion, we have shown that the electroreductive
coupling of aryl halides mediated by a catalytic system based
on nickel-2,2'-bipyridine complexes can be achieved in water,
which avoids the use of polar aprotic solvents. Moreover, the
electrolyses can then be conducted in a divided cell equipped
with a usual ion-exchanger which allows us to choose at will a
simple and clean anodic reaction. At present the performance
of this work is devoted, on the one hand to the scale-up of this
homocoupling reaction by using classical electrolytic flow cells,
on the other hand to an extension to cross-coupling reactions of
aryl halides with electrophiles. We have also initiated an
electroanalytical study of the Ni-bipy complexes in water with
a view to determine the behaviour and properties of the
catalytic system in this solvent.
Table 3. Ni-bipy-catalysed electrosynthesis of biaryls from aryl bromides
in a divided cell.[a]
ArBr
rate conversion of ArBr (%) Ar-Ar isolated yield (%)
PhBr
100
90
100
88
38
57
62
16
33
21
4-CF3C6H4Br
3-CF3C6H4Br
4-CH3C6H4Br
4-FC6H4Br
100
3-CH3OC6H4Br 96
[a]
General catholyte conditions: water (50 cm3) ‡ NaCl (0.3 mol LÀ1) ‡
NH3 (0.1 mol LÀ1) ‡ ArBr (20 mmol) ‡ Brij 35 (0.3 mmol) ‡ NiBr2 ¥
5 H2O (1.5 mmol) ‡ bipy (1.5 mmol), q ˆ 408C, current density ˆ
10 mA/cm2, electric charge ˆ 5000 C (2.5 F/mol of ArBr).
48
Adv. Synth. Catal. 2002, 344, 45 49

Water as Solvent for Nickel-2,2'-Bipyridine-Catalysed Electrosynthesis of Biaryls from Haloaryls
FULL PAPERS
Experimental Section
Syntheses with an Undivided Cell
The solution: The solvent (50 cm3) was distilled water without further
purification and all products were used as received. The supporting
electrolyte was NaCl (0.1 mol LÀ1). The solution was buffered by addition
of a base (aqueous NH3 or MeNH2, etc.) and aqueous HCl in a suitable
amount and the pH was then measured (see Table 2). For the catalyst, no
preliminary preparation of an NiBr2-bipy complex was required: NiBr2 ¥ 5
H2O (1.5 mmol) and 2,2'-bipyridine (1.5 mmol) were added to the solution.
The surfactant (for nature and amount see Tables 1 and 2) and the aryl
Figure 2. Diagram of the two-compartment cell used for the
electroconversion of aryl halides into biaryls.
bromide was finally added. The ArBr/H2O emulsion was then obtained by
stirring with a magnet then warmed at 408C.
The electrochemical cell: The electrochemical undivided cell used for the
consumable anode technique has been already described elsewhere.[3,15] This
∫beaker-cell∫ had a volume of 50 cm3 and was fitted with a cylindrical nickel
foam cathode (40 cm2) which surrounded a sacrificial nickel rod (diameter
1 cm) anode. Before each experiment the cell and electrodes were rinsed
with dichloromethane then with water.
Br¸ker 200 MHz instrument, and by mass spectrometry (GCQ Thermofin-
nigan). All the biaryls obtained are known products and gave satisfactory
spectroscopic values.
The electrolysis: Galvanostatic electrolyses were carried out with a power
source (TTI, PL 310, 32V-1A) by applying a current intensity (for values see
Table 2) between the two electrodes. The progress of the aryl bromide
consumption vs. the electric charge was checked by GC analysis of samples.
Assuming a 100% faradaic yield, the theoretical electric charge required to a
Acknowledgements
¬
We thank Electricite de France for the financial support of this work.
À1
À
full conversion of ArBr into Ar Ar is 96500 C mol
.
References
Syntheses with a Two-Compartment Cell
[1] P. T. Anastas, J. C. Warner, Green Chemistry: Theory and Practice,
Oxford University Press, Oxford, 1998; Pure Appl. Chem. (special
issue on green chemistry) 2000, 72, 1207 1403.
[2] M. F. Nielsen, J. H. P. Utley, in Organic Electrochemistry, (Eds.: H.
Lund, O. Hammerich), Chap. 21, Marcel Dekker, New York, 2001,
pp. 795 882.
The used divided cell is presented in Figure 2. Each compartment had a
volume of 50 cm3. The cathode was a circular (10 cm2) nickel foam. The
anode was a circular (10 cm2) Ti-Pt plate. The diaphragm was a circular
peace of an anionic membrane (neosepta AHA-1). The catholyte was
prepared in the same manner as the solution used with the undivided cell
(see above). The anolyte was an aqueous solution (50 cm3) of KOH
(0.5 mol LÀ1). Electrolyses were also carried out under galvanostatic
conditions (0.1 À 0.3 A) and checked by GC analysis of samples.
¬
¬
¬
[3] J. Chaussard, J. C. Folest, J. Y. Nedelec, J. Perichon, S. Sibille, M.
Troupel, Synthesis 1990, 369 381, and references cited therein.
¬
¬
¬
[4] J. Y. Nedelec, J. Perichon, M. Troupel, Top. Curr. Chem. 1997, 185,
141 173, and references cited therein.
¬
[5] V. Courtois, R. Barhdadi, M. Troupel, J. Perichon, Tetrahedron 1997,
Syntheses with a Filter-Press Cell
53, 11569 11576.
[6] V. Courtois, R. Barhdadi, S. Condon, M. Troupel, Tetrahedron Lett.
1999, 40, 5993 5996.
The filter-press device was a commercially available cell (Microflow,
Electrocell AB, Sweden). This design consisted of rectangular plate
electrodes (16 cm2 for each) separated by insulating frames, which formed
compartments for the electrolyte. The anion-exchanger membrane was
maintained between a pair of gaskets. Each solution was passed from a tank
through the cell by a peristaltic pump. The aqueous catholyte (0.1 À 1 L)
contained NaCl (0.5 mol LÀ1), MeNH2 (0.5 mol LÀ1) and aqueous HCl
(0.25 mol LÀ1), NiBr2 ¥ 5 H2O and 2,2'-bipyridine (6 ¥ 10À2 mol LÀ1 for each),
the surfactant Brij 35 (6 ¥ 10À3 mol LÀ1) and ArBr (0.4 mol LÀ1). The anolyte
contained KOH (0.3 mol LÀ1). Electrolyses were also carried out under
galvanostatic conditions (0.3 A À 1.8 A) and checked by GC analysis of
samples.
¬
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When the aryl halide was almost fully consumed, the catholyte (or the global
solution in the case of the undivided cell) was extracted twice with
dichloromethane (2 Â 50 cm3) and the cathodic compartment was rinsed
with dichloromethane (20 cm3). The organic layer was dried over magne-
sium sulphate and evaporated. The crude products were purified by
chromatography on a silica gel column (elution by pentane). The biaryls
were characterised by 1H NMR (d ppm vs. TMS) and 13C NMR (d ppm vs.
CDCl3) plus 19F NMR (d ppm vs. CFCl3) for fluorinated products, with a
Adv. Synth. Catal. 2002, 344, 45 49
49