Polymeric 2,2′-biquinolyl-containing NiII complexes as catalysts for the Suzuki reaction

Article abstract of DOI:10.1007/s11172-012-0162-y

The Suzuki reaction with polymeric Ni catalysts based on the biquinolyl-containing polyamic acids can be carried out under conditions close to the conditions used for the catalytic transformations in the presence of Pd^II complexes with the same polymeric ligands. However, the yields of the cross-coupling products on the Ni catalysts are somewhat lower than those obtained in the presence of palladium complexes. The yield of the cross-coupling product increases with the increase in the conformational mobility of the polymeric ligand. Unlike catalysis by palladium complexes, in catalytic transformations by nickel complexes activation of the catalyst is required. Such an activation can be carried out either by addition of chemical reducing agents or by applying the corresponding cathodic potential (-0.8 V relative to Ag/AgCl/KCl). The electrochemical activation was shown to lead to higher yields of the cross-coupling product than the use of chemical reducing agents.

Full text of DOI:10.1007/s11172-012-0162-y

Russian Chemical Bulletin, International Edition, Vol. 61, No. 6, pp. 1193—1198, June, 2012
1193
Polymeric 2,2´ꢀbiquinolylꢀcontaining NiII complexes
as catalysts for the Suzuki reaction
T. V. Magdesieva,a O. M. Nikitin,a,b O. V. Polyakova,a A. V. Yakimansky,c M. Ya. Goikhman,c and I. V. Podeshvoc
aM. V. Lomonosov Moscow State University, Department of Chemistry,
Build. 3, 1 Leninskie Gory, 119991 Moscow, Russian Federation.
Eꢀmail: tvm@org.chem.msu.ru
bA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation
cInstitute of Polimer Compounds, Russian Academy of Sciences,
31 Bol´shoi prosp., 199004 Saint Petersburg, Russian Federation
The Suzuki reaction with polymeric Ni catalysts based on the biquinolylꢀcontaining polyamic
acids can be carried out under conditions close to the conditions used for the catalytic transꢀ
formations in the presence of PdII complexes with the same polymeric ligands. However, the
yields of the crossꢀcoupling products on the Ni catalysts are somewhat lower than those obꢀ
tained in the presence of palladium complexes. The yield of the crossꢀcoupling product inꢀ
creases with the increase in the conformational mobility of the polymeric ligand. Unlike catalꢀ
ysis by palladium complexes, in catalytic transformations by nickel complexes activation of the
catalyst is required. Such an activation can be carried out either by addition of chemical
reducing agents or by applying the corresponding cathodic potential (–0.8 V relative to
Ag/AgCl/KCl). The electrochemical activation was shown to lead to higher yields of the crossꢀ
coupling product than the use of chemical reducing agents.
Key words: electrocatalysis, biquinolyl, Ni polymeric complexes, crossꢀcoupling reaction.
Nickel complexes with various Oꢀ, Nꢀ, Pꢀ, and Sꢀconꢀ
taining ligands are widely used in catalysis.1—9 In many
cases, they can replace more expensive Pdꢀ and Ptꢀconꢀ
taining catalysts and maintain high activity.1,2,9 However,
to prepare complicated polyfunctional molecules, it is
necessary to develop new catalysts. Requirements, which
modern catalysts should meet, are becoming increasingly
severe. One of the possible approaches allowing one to
combine high catalytic activity and easy isolation of the
catalyst from the reaction mixture is the use of coordinaꢀ
tion complexes with polymeric ligands as the catalysts.
The presence of a macroligand makes the catalytic system
very susceptible to the choice of a solvent, therefore, such
catalysts, as a rule, can be easily separated from the reacꢀ
tion mixture by adding small amounts of the correspondꢀ
ing solvent. Polymeric macroligand serve to stabilize coorꢀ
dinatively unsaturated metal centers, which usually are
the most active sites in catalysis. Variation in the structure
of the polymeric chain gives virtually unlimited possibiliꢀ
ties for the "fine tuning" of the system to the required
parameters and properties.
reaction.1—4,9—13 Application of Ni catalysts, as a rule,
requires introduction of an additional reducing agent (for
example, Zn dust) or electrochemical activation. The reaꢀ
son is that the formation of an active form of the catalyst
(Ni0 complex) needs a stronger reducing agent than, for
example, NaBPh4. Electrocatalytic processes of crossꢀcouꢀ
pling with the use of nickel complexes are known and
studied in sufficient detail.14,15 However, little attention
so far was paid to the application of Ni complexes with
polymeric ligands in catalysis and electrocatalysis. Among
few examples are the catalytic oxidation processes of alkꢀ
enes,16,17 phenol16 with participation of NiII complexes
with Schiff bases or bipyridyl ligands covalently bonded to
the polymeric chain, a number of crossꢀcoupling processꢀ
es,18 hydroesterification of styrene in the presence of biꢀ
metallic palladiumꢀnickel catalyst based on polyvinylpyrꢀ
rolidone,19 and polymerization of ethylene, which is cataꢀ
lyzed by Ni complexes with the diimine ligands bound to
a polymeric support.20,21
Recently, we have developed an approach to the synꢀ
thesis of polymeric nickel complexes based on polyamic
acids (PA).22 It was shown22 that polyamic acids containꢀ
ing biquinolyl (biQ) fragments in the main chain can beꢀ
come coordinated to the NiII ions to form coordination
sites of two types: with one or two biQꢀligands in the
The Suzuki reaction (crossꢀcoupling of aryl halides
with arylboronic acids or tetraarylborates10—12) belongs to
the pool of the most important catalytic reactions. Comꢀ
plexes of Ni and Pd are widely used as catalysts of this
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1181—1186, June, 2012.
1066ꢀ5285/12/6106ꢀ1193 © 2012 Springer Science+Business Media, Inc.

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Russ.Chem.Bull., Int.Ed., Vol. 61, No. 6, June, 2012
Magdesieva et al.
coordination sphere of the NiII ion. A relative amount of
the coordination sites [Ni(biQ)2]2+ in the polymeric chain
increases as the concentration of the biQꢀunits in the soꢀ
lution increases, as well as when conformation mobility of
the polymer increases. The purpose of the present work is
to investigate catalytic activity of new polymeric nickel
complexes in the coupling reaction of various aryl bromides
and sodium tetraphenylborate both under conditions of
electrocatalysis and in the presence of chemical reducing
agent, the Zn dust (Scheme 1).
and –650 mV (for polymer I) and –350 and –640 mV (for polyꢀ
mer II).22
The Suzuki coupling. Chemical activation of the catalyst. Soꢀ
dium tetraphenylborate (0.05 mmol), Na2CO3 (1 mmol) (fiveꢀ
fold excess with respect to the starting halide), and powdered Zn
(1 mg, 0.015 mmol, for the activation of the catalyst) were added
to a solution of aryl halide (0.2 mmol) in NMP (5 L). A flow of
dry argon was passed through the reaction mixture for 15 min to
remove the oxygen, a 1 mM solution of NiIIꢀcontaining catalyst
in NMP (200 L, 0.1 mol.% as calculated to the starting halide)
was added. The reaction mixture was heated at 100 C for 4 h
under argon, followed by addition of water (30 mL) and saturatꢀ
ed aqueous NaCl, and the reaction products were extracted with
diethyl ether. The yields of arylphenyls were determined by
GCꢀMS spectrometry, using anthracene as an internal standard.
Reaction of PhBr with NaBPh4 in the presence of the complex
NiII—polymer I as a catalyst. Sodium tetraphenylborate (17 mg,
0.05 mmol), Na2CO3 (105 mg, 1 mmol), and powdered Zn
(1 mg) were added to a solution of PhBr (31 mg, 0.2 mmol) in
NMP (5 mL). Then the reaction was carried out according to
the general procedure. The yield of biphenyl was 65%. MS, m/z:
154 [M+], 77 [M+ – Ph].
Scheme 1
i. Ni—PA, Zn or electrode, Nꢀmethylpyrrolidone (NMP),
Na2CO3.
Experimental
Reaction of PhBr with NaBPh4 in the presence of the complex
NiII—polymer II as a catalyst. Sodium tetraphenylborate (17 mg,
0.05 mmol), Na2CO3 (105 mg, 1 mmol), and powdered Zn
(1 mg) were added to a solution of PhBr (31 mg, 0.2 mmol) in
NMP (5 mL). Then the reaction was carried out according to
the general procedure. The yield of biphenyl was 21%. MS, m/z:
154 [M+], 77 [M+ – Ph].
NꢀMethylpyrrolidone (Aldrich) was dried over calcium hyꢀ
dride and distilled, the fraction with the b.p. of 80 C (7 Torr)
was collected.
Acetonitrile (pure grade) was stirred for 12 h over CaH2 and
distilled. Then, it was refluxed for 2 h over P2O5, followed by
distillation and collection of the fraction with the b.p. of
81—82 C (760 Torr).
Reaction of pꢀNO2C6H4Br with NaBPh4 in the presence of
the complex NiII—polymer I as a catalyst. Sodium tetraphenylꢀ
borate (17 mg, 0.05 mmol), Na2CO3 (105 mg, 1 mmol), and
powdered Zn (1 mg) were added to pꢀNO2C6H4Br (41 mg,
0.2 mmol). Then the reaction was carried out according to the
general procedure. The yield of pꢀnitrobiphenyl was 82%. MS,
m/z: 199 [M+], 153 [M+ – NO2], 76 [M+ – NO2 – Ph].
Reaction of pꢀNO2C6H4Br with NaBPh4 in the presence of
the complex NiII—polymer II as a catalyst. Sodium tetraphenylꢀ
borate (17 mg, 0.05 mmol), Na2CO3 (105 mg, 1 mmol), and
powdered Zn (1 mg) were added to pꢀNO2C6H4Br (41 mg,
0.2 mmol). Then the reaction was carried out according to the
general procedure at 140 C. The yield of pꢀnitrobiphenyl was
62%. MS, m/z: 199 [M+], 153 [M+ – NO2], 76 (M+ – NO2 – Ph].
Reaction of pꢀMeC6H4Br with NaBPh4 in the presence of the
complex NiII—polymer I as a catalyst. Sodium tetraphenylborate
(17 mg, 0.05 mmol), Na2CO3 (105 mg, 1 mmol), and powdered
Zn (1 mg) were added to pꢀMeC6H4Br (34 mg, 0.2 mmol). Then
the reaction was carried out according to the general procedure.
The yield of pꢀmethylbiphenyl was 34%. MS, m/z: 168 [M+],
153 [M+ – Me], 76 [M+ – Me – Ph].
Electrochemical activation of the catalyst. Aryl halide
(0.2 mmol) was dissolved in NMP (5 mL) in an electrochemical
cell in the presence of Bu4NBF4 (0.25 mmol), followed by addiꢀ
tion of NaBPh4 (0.05 mmol) and Na2CO3 (1 mmol). A flow of
dry argon was passed through the reaction mixture for 15 min to
remove the oxygen, a 1 mM solution of NiIIꢀcontaining catalyst
in NMP (200 L, 0.1 mol.% as calculated to the starting halide)
was added. Then, electric current (0.1 C) was passed through
the reaction mixture (which allowed a complete reduction of
the catalyst used) in the potentiostatic mode (at the potential of
–0.8 V relative to Ag/AgCl/KCl). After this, the electrochemiꢀ
Electrolysis was performed using an Pꢀ5827 M potentiostat
in a 10ꢀmL undivided electrochemical cell. Nickel wire 2 mm in
diameter was used as a reference electrode, platinum was used as
an auxiliary electrode. Saturated silver chloride electrode was
used as a reference electrode (the potential relative to Fc/Fc+
was –0.48 V in NMP).
Reaction mixtures were analyzed on a Finnigan MAT SSQ
7000 GCꢀMS spectrometer (70 eV, a DVꢀ5 quartz capillary
column (30 m), the temperature regime: 70 C (2 min) —
20 C min–1 — 280 C (10 min)).
The equilibrium geometry of the oligomers was calculated
using the AMBER molecular mechanics method in the Gaussꢀ
ian 09 program package. The equilibrium geometry of the comꢀ
plexes of lowꢀmolecularꢀweight ligand (biQ(COOEt)2) with NiII
was calculated by DFT method (PBE, L1)23 in the PRIRODA 9
program.24
Electrochemical synthesis of polymeric NiII complexes (genꢀ
eral procedure). Polymeric NiII complexes were synthesized by
the anodic dissolution of Ni in the presence of the polymer of
choice in NMP containing 0.05 M Bu4NBF4 and H2O (10 L,
5.5•10–4 mol). Nickel wire (99.99%, d = 2 mm, S = 0.38 cm2)
was used as the anode, platinum wire was the cathode (d = 1.5 mm).
Oxygen was removed by passing dry argon through the cell for
10 min just before the electrolysis and during the experiment.
The electrolysis was performed in the galvanostatic mode with
I = 1•10–3 A. An electric current of 2.1 equivalent of electricity
was passed through a cell containing 10 mL of the polymer soluꢀ
tion in NMP (with the concentration of the biQꢀfragments
of 10–3 mM). The formation of the polymeric NiII complexes
was indicated by the appearance in the voltammogram of peaks
corresponding to the reduction Ni2+/0 at the potentials –390

Polymeric Ni catalysts for Suzuki reaction
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 6, June, 2012
1195
cal cell was switched off, and the solution was heated at 100 C
for 4 h under argon, then, the reaction mixture was cooled,
diluted with water (30 mL), saturated with aq. NaCl, and the
reaction products were extracted with diethyl with ether. The
yields of arylphenyls were determined by GCꢀMS spectrometry,
using anthracene as an internal standard.
Reaction of PhBr with NaBPh4 in the presence of the complex
NiII—polymer I as a catalyst, electrochemical activation. Sodium
tetraphenylborate (17 mg, 0.05 mmol) and Na2CO3 (105 mg,
1 mmol) were added to a solution of PhBr (31 mg, 0.2 mmol) in
NMP (5 mL). Then the reaction was carried out according to
the general procedure. The yield of biphenyl was 76%. MS, m/z:
154 [M+], 77 [M+ – Ph].
Reaction of pꢀNO2C6H4Br with NaBPh4 in the presence of
the complex NiII—polymer I as a catalyst, electrochemical activation.
Sodium tetraphenylborate (17 mg, 0.05 mmol) and Na2CO3
(105 mg, 1 mmol) were added to pꢀNO2C6H4Br (41 mg, 0.2 mmol)
in NMP (5 mL). Then the reaction was carried out according to
the general procedure. The yield of pꢀnitrobiphenyl was 92%.
MS, m/z: 199 [M+], 153 [M+ – NO2], 76 [M+ – NO2 – Ph].
for considerable conformational rigidity due to the presꢀ
ence of linear Nꢀphenylenediamine fragments in the polyꢀ
meric chain. These fragments decrease the conformational
mobility of the polymer and can influence its coordinating
ability. As it has been shown in our group earlier,22 an
increase in the conformational rigidity of the polymer faꢀ
cilitated formation of the coordination sites [Ni(biQ)Ln]
(n = 2—4), in which the nickel ion contained only one
biQꢀfragment in its ligand sphere, whereas the rest of the
coordination sites was occupied by readily eliminating
solvent molecules. It could be expected that such metal
centers would be the most active in catalysis, as we
observed earlier in the studies of catalytic activity of CuI
complexes with analogous ligands.25,26
For the sake of comparison and to reveal the role of
polymeric ligands in catalytic processes, we have also
chosen a lowꢀmolecularꢀweight analog of the polymeric
complexes, viz., the nickel complex with dihexyl ester of
2,2´ꢀbiquinolylꢀ4,4´ꢀdicarboxylic acid (biQ(COOHex)2).
The model calculations by the DFT method (PBE, L1)
showed that for the nickel ions, the formation of two octaꢀ
hedral coordination sites Ni[biQ(COOEt)2](NMP)4 and
Ni[(biQ(COOEt)2)]2(NMP)2 with comparable equilibriꢀ
um concentrations in the NMP solution was possible (see
Fig. 1). The formation of tetrahedral structures was less
probable in the case of the model compounds, however, it
could be fairly acceptable in the complexes with polyꢀ
meric ligands.
Earlier, we have synthesized27 the PdII complexes with
such polymeric ligands. It turned out27 that these comꢀ
plexes displayed high catalytic activity in the Suzuki reacꢀ
tion. The reaction could be carried out at moderate temꢀ
peratures (40—80 C) with the use of 0.05 mol.% of the
catalyst both under conditions of the homogeneous catalꢀ
ysis and upon immobilization of the catalyst on a graphite
felt with a high specific surface area. The reaction resulted
in high yields of the crossꢀcoupling products. The imꢀ
mobilization of the catalyst on the graphite felt inꢀ
creased its activity and facilitated separation of the cataꢀ
lyst from the reaction products and its reuse, the catalyst
turnover number reached 105. It was interesting to find
out, whether the NiII complexes with analogous polyꢀ
Results and Discussion
The polymers I and II, with the main chain containing
the biQꢀfragments capable of coordinating to NiII ions,
have been chosen for the study.
Both polymers belong to the polyamic acids, however,
they have a number of essential differences. Polymer I
contains a coordinating biQꢀfragments in each monomeric
unit. The model calculations by the AMBER method for
the oligomer containing four monomeric units showed
that it possesses sufficient conformational mobility (Fig. 1).
Due to such a mobility, the energetically favorable conꢀ
tacts emerge: the stacking interactions in the absence of
nickel ions and the coordination of NiII to one or two
biQꢀfragments of the same or neighboring polymeric
chains in the presence of NiII ions. Polymer II is a blockꢀ
copolymer, in which the biQꢀfragments are present only
in one of the monomeric units. By varying the structure of
the comonomer it is possible to obtain polymers with the
desired thermomechanical properties. The introduction
of ether fragments in this case makes the polymer more
thermally stable, which can be important in its further use
in catalytic processes. In addition, polymer II is notable

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Russ.Chem.Bull., Int.Ed., Vol. 61, No. 6, June, 2012
Magdesieva et al.
a
b
Fig. 1. An equilibrium geometry of the tetramer corresponding to the polymer I (a) (calculation by the AMBER method in the Gaussian
09 program package) and the lowꢀmolecularꢀweight model complexes Ni[(biQ(COOEt)2)]2(NMP)2 and Ni[biQ(COOEt)2](NMP)4 (b)
(calculation by the DFT method).
meric ligands would possess such a high catalytic activity
in the Suzuki reaction.
the concentration of 0.1 mol.% calculated based on the
starting aryl bromide. The reaction was performed under
conditions of the homogeneous catalysis, using NMP as
a solvent, in which polymeric complexes are readily soluble.
The composition of the reaction mixture was analyzed by
GCꢀMS spectrometry in the presence of anthracene as
the internal standard. Bromobenzene, treated with the Ni
complex of polymeric ligand I, reacted with sodium tetraꢀ
phenylborate in the presence of a base at 100 C to form
biphenyl (65%) within 4 h, with 32% of PhBr remained
unreacted. When oneꢀhalf of the amount (0.05 mol.%) of
palladium complex with the same polymeric ligand I was
used under similar conditions, the yield of biphenyl was
92%. This indicated the lower efficiency of the Niꢀconꢀ
Polymeric Ni complexes were obtained by the anodic
dissolution of Ni in the galvanostatic mode in the presꢀ
ence of polymer I or II. The formation of polymeric NiII
complexes was monitored by the appearance in the voltaꢀ
mmogram of peaks corresponding to the Ni2+/0 reduction
at the potentials –390 and –650 mV (for polymer I) or
–350 and –640 mV (for polymer II).22
Aryl bromides with both electronꢀdonating and elecꢀ
tronꢀwithdrawing substituents have been chosen for the
studies. First, we used Zn dust as the chemical reducing
agent to obtain an active form of the catalyst, i.e., Ni0
complex. The catalyst was involved into the reaction in

Polymeric Ni catalysts for Suzuki reaction
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 6, June, 2012
1197
Table 1. Yields (%) of biaryls in the Suzuki reaction for Niꢀ and Pdꢀcontaining catalysts*
ArBr
Polymer I
Polymer II
Ni (0.1 mol.%)
Pd (0.05 mol.%)
Ni (0.1 mol.%)
Pd (0.05 mol.%)
PhBr
4ꢀNO2C6H4Br
65
82
92
99
21
—
12
—
* Conditions: 0.2 mmol of ArBr, 0.05 mmol of NaBPh4, NMP, 100 C, 4 h, 1 mmol of Na2CO3,
0.015 mmol of Zn in the case of nickel.
taining catalyst. The use of the Ni complex with more
conformationally rigid polymeric ligand II gave even lowꢀ
er yield of biphenyl (21%). Polymeric ligand II in the case
of Pdꢀcatalyst showed lower catalytic activity than polyꢀ
mer I, as well.27 Comparative data on the yields of biaryls
for both catalysts are given in Table 1.
and as it is usually observed for this type of the reactions,
electronꢀwithdrawing substituents accelerate the catalytic
process. When these conditions are applied to chlorobenꢀ
zene, no reaction takes place.
The use of the NiII complex with the lowꢀmolecularꢀ
weight ligand biQ(COOHex)2 as the catalyst under such
conditions does not lead to the formation of the crossꢀ
coupling product at all. This is an evidence that the polyꢀ
meric ligand plays a key role.
Electrolysis at a controlled potential can serve as an
alternative to the chemical reducing agents. In the polyꢀ
meric complexes with ligands I and II, the redox transiꢀ
tion Ni2+/0 occurs at the potentials from –350 to –390 mV
and from –640 to –650 mV for the coordination sites
[Ni(biQ)2]2+ and [NibiQLn]2+, respectively.22 Therefore,
in order to activate both forms of the complex, the elecꢀ
trochemical activation of the catalyst was performed at
the potential of –0.8 V, a somewhat higher cathodic poꢀ
tential than the reduction of the coordination site with
one biQꢀfragment.
The lower yields of the crossꢀcoupling product obꢀ
served when the conformationally more rigid ligand II was
used to prepare Pdꢀcontaining catalysts can be easily exꢀ
plained. As we have shown earlier,27 the PdII ion, irreꢀ
spective of the polymeric ligand (I or II), always forms
coordination sites with only one biQꢀfragment in the coꢀ
ordination sphere of the metal ion. Two biQꢀfragments
cannot be accomodated in the square planar PdII complex
because of steric reasons.28 The complexation of PdII ions
with the conformationally more rigid ligand II proceeds
slowly and less efficiently, therefore, the use of the conforꢀ
mationally more flexible ligand I is preferable. In the case
of NiII, which prefers a tetrahedral geometry or at favorꢀ
able steric condition octahedral surrounding), formation
of coordination sites of two types is possible, with two or
one biQꢀfragment in the coordination sphere of the metal
ion.29 It could be expected that such sites are more
active in catalysis, since the presence of the weakly bound
solvent molecules instead of the strong biQꢀligand in
the coordination sphere of the metal provides more possiꢀ
bilities for the coordination of NiII with the substrate
molecule. However, the experimental data given above
contradict this suggestion. It can be assumed that the catꢀ
alytic activity is exhibited by the coordination sites of both
types due to the ability of Ni to increase its coordination
number to 5—6.29 In this case, an increase in the conforꢀ
mational rigidity of the polymeric ligand, which hinders
complexation, should lead to a decrease in the catalytic
activity, and this fact is observed experimentally.
The catalyst was activated in an electrochemical cell
in the potentiostatic mode, passing the amount of elecꢀ
Table 2. Yields of Ph—Ar in the crossꢀcoupling reaction of aryl
halides (2•10–4 mol) and NaBPh4* (0.5•10–5 mol) in the presꢀ
ence of Ni catalysts
Entry
ArHal
Catalyst,
Yield of
conditions
Ph—Ar (%)
1
2
3
4
5
6
7
8
PhBr
PhBr
PhBr
PhBr
PhBr
Ni—I
65
58
62
21
76
—
34
82
—
92
62
Ni—I, NiII : biQ = 2 : 1
Ni—I, NiII : biQ = 1 : 1
Ni—II
Ni—I, –0.8 V**
Ni—biQCOOR
Ni—I
Ni—I
Ni—I
PhBr
The change in the ratio Ni : biQ (1 : 1, 1 : 2, and 2 : 1)
in the synthesis of polymeric Ni catalysts has little effect
on the catalytic activity of the complex (Table 2). Apparꢀ
ently, coordination sites of both types, [NibiQLn]2+ and
[Ni(biQ)2]2+, are catalytically active, which agrees with
the data on the comparative activity of NiII complexes
with polymeric ligands I and II given above.
4ꢀMeC6H4Br
4ꢀNO2C6H4Br
PhCl
4ꢀNO2C6H4Br
4ꢀNO2C6H4Br
9
10
11
Ni—I, –0.8 V**
Ni—II***
* Conditions: 0.1 mol.%, the ratio NiII : biQ = 1 : 2 except if
stated otherwise; NMP, 100 C, 4 h, 10–3 mol of Na2CO3.
** For the preparation of the active form of the catalyst.
*** T = 140 C.
The reaction is applicable to aryl bromides with both
electronꢀdonating and electronꢀwithdrawing substituents,

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Magdesieva et al.
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25. T. V. Magdesieva, A. V. Dolganov, A. V. Yakimansky, M. Ya.
Goikhman, I. V. Podeshvo, V. V. Kudryavtsev, Electrochim.
Acta, 2008, 53, 3960.
In conclusion, the Suzuki reaction with the polymeric
Ni catalysts can be carried out under conditions close to
the reaction conditions used to perform reactions in the
presence of PdII complexes with the same polymeric
ligands. However, the yields of the crossꢀcoupling prodꢀ
ucts are somewhat lower than those obtained with the Pd
complexes. In addition, catalysis by nickel complexes reꢀ
quires activation of the catalyst either by addition of chemꢀ
ical reducing agents or by applying the corresponding caꢀ
thodic potential. The electrochemical activation allows
one to obtain the crossꢀcoupling products with higher
yields than in the case of chemical reducing agents. An
increase in the conformational mobility of the polymeric
ligand also leads to the increase in the yield of the crossꢀ
coupling product.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 11ꢀ03ꢀ00220ꢀa).
26. T. V. Magdesieva, A. V. Dolganov, A. V. Yakimansky, M. Ya.
Goikhman, I. V. Podeshvo, Electrochim. Acta, 2009, 54, 1444.
27. T. V. Magdesieva, O. M. Nikitin, R. M. Abdullin, O. V.
Polyakova, A. V. Yakimanskii, M. Ya. Goikhman, I. V. Poꢀ
deshvo, Russ. Chem. Bull., Int. Ed., 2009, 58, 1423 [Izv. Akad.
Nauk, Ser. Khim., 2009, 1382].
28. E. D. McKenzie, Coord. Chem. Rev., 1971, 6, 187.
29. F. Meyer, H. Kozlowski, in Comprehensive Coordination
Chemistry II, Eds J. A. McCleverty, T. J. Meyer, Elsevier
Ltd., Amsterdam, 2004, Vol. 6, p. 52.
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Received November 11, 2011;
in revised form April 19, 2012