Electrochemical synthesis of PdII polynuclear complexes based on biquinolyl-containing polymers and their catalytic activity in the Suzuki reaction

Article abstract of DOI:10.1007/s11172-009-0190-4

Electrochemical dissolution of sacrificial Pd anode was used to synthesize novel polynuclear PdII complexes with ligands based on polyamic acids containing in the main chain biquinolyl groups capable of coordination to the metal ions. The synthesized polymeric complexes exhibit high catalytic activity in the Suzuki reaction. The reaction can be run under mild conditions, at 40 °C and with a sufficiently high product yield at a catalyst concentration of 0.05 mol.% (with respect to the starting aryl halide). The polymeric ligand allows immobilization of the catalyst on the graphite fabric with high specific surface area that enhances the catalyst turnover number and promotes its recycling.

Full text of DOI:10.1007/s11172-009-0190-4

Russian Chemical Bulletin, International Edition, Vol. 58, No. 7, pp. 1423—1430, July, 2009
1423
Electrochemical synthesis of PdII polynuclear complexes based
on biquinolylꢀcontaining polymers and their catalytic activity in the Suzuki reaction
T. V. Magdesieva,a O. M. Nikitin,a R. M. Abdullin,a O. V. Polyakova,a
A. V. Yakimanskiy,b M. Ya. Goikhman,b and I. V. Podeshvob
aDepartment of Chemistry, M. V. Lomonosov Moscow State University,
1/3 Leninskie gory, 119992 Moscow, Russian Federation
Eꢀmail: tvm@org.chem.msu.ru
bInstitute of Macromolecular Compounds, Russian Academy of Sciences,
31 Bolshoi prosp., 199004 St.ꢀPetersburg, Russian Federation
Electrochemical dissolution of sacrificial Pd anode was used to synthesize novel polynucleꢀ
ar PdII complexes with ligands based on polyamic acids containing in the main chain biquinolyl
groups capable of coordination to the metal ions. The synthesized polymeric complexes exhibit
high catalytic activity in the Suzuki reaction. The reaction can be run under mild conditions, at
40 °С and with a sufficiently high product yield at a catalyst concentration of 0.05 mol.% (with
respect to the starting aryl halide). The polymeric ligand allows immobilization of the catalyst
on the graphite fabric with high specific surface area that enhances the catalyst turnover numꢀ
ber and promotes its recycling.
Key words: electrosynthesis, sacrificial anode, Pd complexes, polymeric ligands.
PdꢀCatalyzed crossꢀcoupling reactions are attractive
method for a new C—C bond formation for a wide range
of substrates. Crossꢀcoupling can be catalyzed by PdII salts
(see Ref. 1—5 and the publications cited in Ref. 1—3), Pd
nanoparticles (see Ref. 6, 7), PdII complexes with differꢀ
ent Pꢀ, Nꢀ, Sꢀcontaining ligands (see Ref. 1—3 and literaꢀ
ture cited therein), as well as by polymer PdII complexes
(see Ref. 8—10). The challenge currently faced by practiꢀ
tioners of Pdꢀcatalyzed coupling reactions is to minimize
the costs associated with the expensive catalyst by develꢀ
oping high TON (turnover number) catalysts or facilitatꢀ
ing catalyst recovery. In selecting the catalytic system it is
important to optimize it to prevent inactive palladium
black formation and to allow catalyst separation from the
reaction products. One of the ways to comply with these
tasks is the immobilization of catalysts on different supꢀ
ports. They can be supported on inorganic oxides and zeoꢀ
lites,11 silica,12 molecular sieves,13 graphite,14 and also on
a block copolymer matrix.7,15 The presence of a polymeric
ligand often facilitates catalyst immobilization. Thereꢀ
with it offers the advantages of eliminated solubility
problem, easier catalyst recovery, and the enhanced local
concentration of catalytic sites at minimum catalyst
consumption.
Suzuki reaction. The study was performed with three types
of polymers. The first one (PAI) has the biQ groups in
each monomeric unit. The second (PAII) is a copolymer,
in which the biQ groups are engaged only in one type of
monomers. To estimate the effect of conformational riꢀ
gidity of the polymer chain on the catalytic efficiency
of the Pdꢀpolymer complex, the PAII polymer was modiꢀ
fied by a partial replacement of flexible diphenylmethane
units in the main chain with rigid пꢀphenylenediamine
units (PAIII).
Recently we have developed the synthetic approach to
aforesaid PA, the detailed description is given in Ref. 16.
Thermal stability and high tensile strength of such polyꢀ
mers, as well as their solubility in organic solvents is enꢀ
sured by the composition and structure of the polyꢀ
mer chain.
Earlier we have developed an electrochemical method
to synthesize CuI complexes with polymeric ligands
of aboveꢀpointed type (utilizing sacrificial dissolution
of copper anode17) and examined18,19 the product activiꢀ
ty in oxidation reactions of various organic substrates
with molecular О2. This work continues studying the
PAꢀbased metalꢀcontaining polymers. It is the first apꢀ
plication of palladium anodic dissolution for synthesꢀ
izing complexes with polymeric ligands of this type.
The new catalysts synthesized were tested in the crossꢀ
coupling reaction of aryl halides with sodium tetrapheꢀ
nylborate.
This work is aimed to synthesize Pdꢀcontaining polyꢀ
mers based on polyamic acids (PA) with the main chain
carrying biquinolyl (biQ) groups capable of coordinating
to PdII ions, and to examine their catalytic activity in
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1382—1389, July, 2009.
1066ꢀ5285/09/5807ꢀ1423 © 2009 Springer Science+Business Media, Inc.

1424
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 7, July, 2009
Magdesieva et al.
Results and Discussion
is preferred, as affording easy instrumental control over
formation rate of PdII ions with avoidance of unwanted
interference from nucleophilic ions (Cl–, OAc–) in the
Synthesis of Pdꢀcontaining polymers
To synthesize Pdꢀcontaining polymers, two methods
were exploited, i.e., complexation of biQ fragments present
in the polymer chain with PdII salts and electrosynthesis
with a sacrificial Pd anode (Scheme 1).
I/mA
0.01
4
Formation of PdII complexes with the polymers was
determined using cyclic voltammetry (CV) technique. The
PdCl2 and Pd(OAc)2 salts are reduced at a potential rangꢀ
ing from –1.1 to –1.2 V (see Ref. 20, 21). On addition of
the polymeric ligands to the solution containing PdCl2 or
Pd(OAc)2, the PdII/Pd0 redox potential is strongly shifted
to the anodic region (Ep –0.45 V vs. Ag/AgCl/KCl), indiꢀ
cating complex formation (Fig. 1). The observed peak poꢀ
tential value was virtually the same for all polymers tested
and close to the known22 potential for Pd(biQ)Cl2 comꢀ
plex (–0.5 V in MeCN vs. Ag/AgCl/KCl).
0
3
–0.01
2
–0.02
1
–1400
–1000
–600
–200
E/mV
Fig. 1. CV curves for PdCl2 (1), Pd(PAI)Cl2 (2), Pd(PAI)(BF4)2
(3), Pd(PAII)(BF4)2 (4) (NMP, Pt, 0.05 М Bu4NBF4, 200 mV s–1
vs. Ag/AgCl/KCl).
The alternative approach to the polynuclear PdII comꢀ
plexes is anodic dissolution of palladium. Electrosynthesis
,

Polynuclear PdII complexes
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 7, July, 2009
1425
Scheme 1
— polymer chain
–
X = BF4–, Cl , OAc–; L = MeCN, NMP (NMP — Nꢀmethylpyrrolidone)
solution. The latter are inevitably present if the PdII salts
are used, that may be disastrous for catalysis since these
ions are capable of occupying free sites in the metal coorꢀ
dination sphere. Electrolysis was performed in galvanoꢀ
static mode (I = 1 mA), with the Pd wire used as the
working electrode and a Pt sheet as the auxiliary electrode.
In the CV curve for the solution formed upon anodic disꢀ
solution of Pd in the presence of foregoing polymers, the
quasiꢀreversible PdII/Pd0 couple appears at –0.45 V. For
the polymers differing in the main chain structure (PAI,
PAII, PAIII), PdII/Pd0 redox potentials are almost equal
(see Fig. 1, curves 3 and 4) and close to the values found
for the analogous polymers obtained by complexation, as
well as to the known values for Pd(biQ)Cl2 complex. From
these data it can be concluded that it is certainly biQ
groups of the polymer, with which Pd coordinates.
The PdII ion is known23,24 to have a tendency to form
square planar complexes. For two biquinolyl ligands this
is, however, impossible because of steric repulsion of
H atoms in 8 and 8´ positions of two different biQ
ligands.25,26 To prove the suspected structure of PdII coorꢀ
dination patterns in the polymers and for the purpose of
estimating the number of biQ groups in the PdII coordinaꢀ
tion environment, we synthesized the model complexes
with the lowꢀmolecular analogs of the polymeric ligand,
4,4´ꢀbiquinolyldicarboxylic acid (biQ(COOH)2), and its
hexyl ester biQ(COOHex)2 (Hex is hexyl). These comꢀ
plexes were prepared by adding biQ(COOH)2 either
biQ(COOHex)2 to the solution of PdCl2 in acetonitrile. It
should be noted that PdII complexes with biQ(COOH)2
and biQ(COOHex)2 are formed slowly, in contrast to rathꢀ
er rapidly formed complexes with the polymer ligand.
The electroreduction potentials for the complexes preꢀ
pared by both complexation with PdII salts (see Fig. 1,
curve 2) and electrochemical synthesis (see Fig. 1, curve 3)
are equal, that is indicative of the same coordination unit
I/mA
0.010
structure. Correspondingly, Cl–, OAc–, and BF4 ions
–
0.005
occupy the outer coordination sphere of PdII ions, whereꢀ
as free binding sites are occupied by the solvent molecules.
Varying electrosynthesis conditions and the polymer
concentration, it is possible to adjust the molar ratio
Pd : biQ in the solutions formed. All CV curves recorded
for the solutions with Pd : biQ ratio varied from 1 : 2 to
2 : 1 showed only one peak corresponding to PdII/Pd0
redox couple — at a potential of –0.45 V. The peak current
increases with increasing polymer concentration in the
solution and reaches maximum at Pd : biQ = 1 : 1 (Fig. 2).
Such behavior is observed for all polymers tested. The
conclusion that follows is that the PdII coordination sphere
contains only one biQ group of the polymer ligand, while
the other coordination sites are occupied by the solvent.
0
–0.005
–0.010
1
–0.015
2
–0.020
–0.025
3
–600
–400
–200
0 E/mV
Fig. 2. Sequential addition of PAI to 10–3 М Pd(BF4)2. PAI :
PdII = 1 : 2 (1); 1 : 1 (2); 2 : 1 (3) (Pt, 0.05 М Bu4NBF4, NMP,
100 mV s–1).

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Russ.Chem.Bull., Int.Ed., Vol. 58, No. 7, July, 2009
Magdesieva et al.
Massꢀspectrometric (MALDIꢀTOF) examination showed
intense peaks of molecular ions, corresponding to the comꢀ
position of the complexes with one biQ group per one PdII
ion, (biQ(COOH)2)2Pd2X2 (X = Cl, OAc). This formula
most likely designates a binuclear complex with bridgꢀ
ing anions.
complexes (formed upon crystallization), whereas in the
solution, regardless of the synthetic method, [biQPdLn]2+
(where L is the solvent molecule, Nꢀmethylpyrrolidone
(NMP)) coordination units are always formed, in which
the counterions Cl–, OAc–, BF4– occupy the outer coorꢀ
dination sphere. The number of ligands, n, most probably
equals 2, since Pd was demonstrated23 to be not prone of
forming fiveꢀcoordinated complexes.
Catalytic activity of PdIIꢀcontaining polymeric systems
The PdII complexes are known to be good catalysts of
crossꢀcoupling reactions. In this work, the catalytic propꢀ
erties of electrochemically synthesized polymeric and lowꢀ
molecular complexes were tested in the Suzuki crossꢀcouꢀ
pling of different aryl halides with NaBPh4 (Scheme 2).27
In the presence of a base, the catalytic crossꢀcoupling
involves four consecutive cycles, thus the reactants were
taken in a 4 : 1 (ArHal : NaBPh4) ratio. Without a base,
the process includes only one (the first) cycle.27
X = Cl, OAc; R = H, Hex
Thus, electrochemical and MALDI data indicate that
the synthesized polymers have only one biquinolyl group
in the PdII coordination environment. Syntheses of comꢀ
plexes using PdCl2, and Pd(OAc)2 salts lead to the bridged
The catalytic studies were performed with a range of
aryl halides and also with the diphenyliodonium salt. The
Scheme 2

Polynuclear PdII complexes
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 7, July, 2009
1427
Table 2. Yields of Ph2 at homogeneous catalysis with
reaction was conducted in NMP in the presence of a base
(Na2CO3). The model reactants to examine the effect of
polymeric ligand structure on the catalytic activity were
PhI and NaBPh4. Electrochemically synthesized (see
above) Pd complexes with polymers varying in the number
of biQ fragments in the main chain, as well as in conforꢀ
mational rigidity (PAI, PAII, PAIII) were evaluated as catꢀ
alysts. The total number of biQ fragments in the solution
was equal in all samples, this achieved by loading a preset
amount of the polymer when synthesizing palladium
complexes.
[Pd(PAI)L2](BF4)2]
Catalyst content
Yield of Ph2 (%)
(mol.% relative to PhI)
5
1
>99
98
0.5
0.05
96
95
Note: NMP, 130 °C, 4 h, NaBPh4 (0.5•10–4 mol), PhI
(2•10–4 mol), Na2CO3 (10–3 mol).
As can be seen from Table 1, the most effective catalyst
is the polymer containing biQ fragments in all monomeric
units (PAI). So, PAI was the polymer of choice. It is also
worth mentioning that with none of the polymer ligands
tested Pd black precipitation was observed. The resulting
order of catalytic activity found for the polymers is oppoꢀ
site to that observed while studying the counterpart Cu(I)
complexes in redox processes involving molecular O2 (see
Ref. 18, 19). In the latter case, the enhancement of the
polymer chain rigidity and decrease in total number of biQ
groups led to the increased specific content of catalytically
active coordination units with CuI atom linked to only
one biQ ligand and the remaining coordination sites occuꢀ
pied by the solvent. In contrast to CuI, PdII was not found
to form [Pd(biQ)2]2+ type complexes with any of the conꢀ
sidered polymers. Thus, an additional gain in the polymer
chain rigidity cannot influence the competitive formation
of the two types of coordination units. However, presence
of the second coꢀmonomer in PAII and PAIII structure
impedes the formation of [Pd(biQ)L2]2+ catalytic sites
(L is the solvent molecule), for example, through steric
interactions. This possibility explains the observed rank
order of catalytic activity of the polymers tested.
The [Pd(PAI)L2](BF4)2] catalyst concentration was
optimized in the same model reaction, namely, NaBPh4
coupling with PhI in the presence of Na2CO3. The results
are given in Table 2. As seen, biphenyl yield decreases only
slightly with a 100ꢀfold decrease in the catalyst concenꢀ
tration, thus, in further studies 0.05 mol.% of the catalyst
was used (respectively to the starting halide). The number
of catalytic cycles determined as the product : catalyst
molar ratio is in this case as much as 1900. It should be
noted that all the four phenyl groups in NaBPh4 are inꢀ
volved in the reaction.
We have also tested the chosen catalytic system,
[Pd(PAI)L2](BF4)2, in the crossꢀcoupling of other phenyl
halides (Table 3). As it was expected, Ph2 yield decreases
when passing from PhI to PhCl, because iodides are more
readily involved in the oxidative addition, which is typiꢀ
cally rate determining step in a catalytic cycle.1,2 The efꢀ
fect of the substituent in the aromatic ring on the crossꢀ
coupling product yield was abundantly investigated (see
Ref. 1—3 and the literature cited therein). The oxidative
addition is shown to proceed more easily and with better
yields of crossꢀcoupling products for the substrates bearꢀ
ing electronꢀwithdrawing groups in a benzene ring.1 The
data in Table 4 are not an exception.
The Suzuki reaction is normally conducted at high
temperatures which restricts its application for volatile
and thermolabile substrates. It is therefore important to
design a catalytic system, which would allow running the
reaction at nearꢀroom temperatures. We varied the temꢀ
perature conditions in the model reaction between PhBr
and NaBPh4 in NMP in the presence of Na2CO3 as a base.
The reaction turned out to afford sufficiently high yield
even at room temperature (Table 5), when Pdꢀpolymer
complex [Pd(PAI)L2](BF4)2 was used.
To explore the efficiency of reaction optimization through
adjusting polymeric ligand, the catalytic activity of PdII
complexes with lowꢀmolecular analogs of polymer ligands,
biQ(COOH)2 and biQ(COOHex)2 (Table 6) was studied.
Table 3. Yields of Ph2 in NaBPh4 crossꢀcoupling
Table 1. Yields of Ph2 in the crossꢀcoupling of
PhI (2•10–4 mol) with NaBPh4 (0.5•10–4 mol)
with different benzyl halides
Starting halide
Yield of Ph2 (%)
Catalyst
Yield of Ph2 (%)
Ph2IBF4
PhI
PhBr
PhCl
99
95
92
43
Pd(BF4)2
82
95
58
18
[Pd(PAI)L2](BF4)2
[Pd(PAII)L2](BF4)2
[Pd(PAIII)L2](BF4)2
Note: NMP, 130 °C, 4 h, NaBPh4 (2•10–4 mol),
PhHal (0.5•10–4 mol), Na2CO3 (10–3 mol),
0.05 mol.% [Pd(PAI)L2](BF4)2.
Note: NMP, 130 °C, 4 h, Na2CO3 (10–3 mol),
catalyst content 0.05 mol.% relative to PhI.

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Russ.Chem.Bull., Int.Ed., Vol. 58, No. 7, July, 2009
Magdesieva et al.
Table 4. Product yields in crossꢀcoupling of difꢀ
Table 6. Catalytic activity of Pd complexes with lowꢀmolecuꢀ
ferent aryl bromides with NaBPh4
lar and polymeric ligands
Starting halide
Yield of ArPh (%)
Reaction conditions
Solvent
Crossꢀcoupling
product yield
(%)
Catalyst
T
/°C
pꢀPhC6H4Br
pꢀMeOC6H4Br
PhBr
pꢀAcOC6H4Br
pꢀNO2C6H4Br
68
—
92
>99
95
PdCl2
PdCl2
MeCN
H2O
82
100
82
100
80
57
4
79
15
84
PdbiQ(COOHex)2Cl2 MeCN
Note: NMP, 130 °C, 4 h, NaBPh4 (0.5•10–4 mol),
ArBr (2•10–4 mol), Na2CO3 (10–3 mol),
0.05 mol.% [Pd(PAI)L2](BF4)2.
PdbiQ(COOH)2Cl2
[Pd(PAI)L2](BF4)2
H2O
NMP
Note: 4 h, NaBPh4 (0.5•10–4 mol), PhI (2•10–4 mol), Na2CO3
(10–3 mol), 0.05 mol.% of Pdꢀcontaining catalyst.
Catalytic efficiency of PdII complexes with polymer
and lowꢀmolecular ligands, PAI and biQ(COOR)2, reꢀ
spectively (see Table 6) is practically equal. The polymer,
however, has a considerable advantage, namely, it can
be immobilized on a graphite surface (see below) that
makes it more easily recyclable. Taking into account the
solubility of PdbiQ(COOH)2Cl2 complex in aqueous
Na2CO3, we attempted to carry out the reaction in water;
yet Ph2 yield turned out to be rather low, which could
be due to immiscibility of iodobenzene with water. Still
there are successful examples28 of performing the Suzuki
reaction with the starting materials insoluble under reacꢀ
tion conditions.
as the cathode. After passing a preset charge (2 F per 1 mol
of biQ fragments), graphite cloth was taken out, washed
with methylene chloride and examined by CV technique.
The CV curve (Fig. 3) shows the peak at a potential of
the formed [Pd(PAI)L2](BF4)2 complex electroreduction
(–0.55 V) which corresponds well with electroreduction
potential of [Pd(PAI)L2](BF4)2 on the graphite electrode
in the solution (E = –0.58 V).
Catalytic activity of the immobilized polymer complex
in Suzuki reaction was tested in PhI coupling with NaBPh4
in CH2Cl2 in the presence of Na2CO3, at the solvent
boiling point. The data characterizing the efficiency
of the palladiumꢀpolymer complex under conditions of
homogeneous and heterogeneous catalysis are listed in
Table 7.
Immobilization of [Pd(PAI)L2](BF4)2
on graphite cloth surface
With using the immobilized catalyst, the reaction afꢀ
fords sufficiently high yield under mild conditions (see
Table 7). Besides that, immobilization makes markedly
easier catalyst separation from the reaction products (catꢀ
alyst is just removed from reaction mixture with the carꢀ
rier). Immobilized catalyst is consumed in much lesser
To improve catalytic efficiency of Pdꢀpolymer comꢀ
plexes in Suzuki reaction, the catalyst, [Pd(PAI)L2](BF4)2,
was immobilized on the graphite cloth with rather high
specific surface area (12 m2 g–1). Immobilization proceꢀ
dure was as follows. The required amount of PAI solution
in NMP was deposited on the graphite cloth and then
dried at 220 °C for 2 h to remove the solvent. The next step
was galvanostatic electrolysis with the Pd anode and the
conductive cloth impregnated with PAI polymer serving
I/mA
0.02
–0.02
–0.06
–0.10
Table 5. Effect of temperature on Ph2 yield in
Suzuki reaction
Reaction conditions
Yield of Ph2
(%)
T/°C
τ/h
20
40
120
160
24
5
4
72
69
92
96
4
–800
–600
–400
–200
0 E/mV
Note: NMP, NaBPh4 (0.5•10–4 mol), PhBr
(2•10–4 mol), Na2CO3 (10–3 mol), 0.05 mol.%
[Pd(PAI)L2](BF4)2.
Fig. 3. CV curve for [Pd(PAI)L2](BF4)2, complex immobilized
on graphite electrode (CH2Cl2, 0.05 M Bu4NBF4, 100 mV s–1
vs. Ag/AgCl/KCl).
,

Polynuclear PdII complexes
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 7, July, 2009
1429
Table 7. Efficiency of [Pd(PAI)L2](BF4)2 catalyst in Suzuki
reaction with homogeneous (NMP) and heterogeneous
(CH2Cl2) catalysis
Experimental
NMP (Aldrich) was dried over CaH2 and distilled, collectꢀ
ing a fraction with b.p. 80 °C (7 Torr).
Catalyst: [Pd(PAI)L2](BF4)2
In solution (5•10–2 mol.%)
Yield of Ph2 (%)
69
Acetonitrile (pure grade) was stirred for 12 h over CaH2, and
distilled; then it was refluxed over P2O5 for 2 h and distilled
again, collecting a fraction with b.p. 81—82 °C (760 Torr).
Methylene chloride (chemically pure grade) was stored over
CaH2 in darkness. Prior to each distillation it was stirred during
1 h, and then distilled, collecting a fraction with b.p. 41—42 °C
(760 Torr).
Electroreduction and electrooxidation potentials were meaꢀ
sured with a computerized IPCꢀWin digital potentiostat using
stationary Pt electrode. CV curves were recorded at varied poꢀ
tential sweep rate, at 20 °C in 10ꢀmL electrochemical cell with
0.05—0.15 M Bun4NBF4 in NMP and CH2Cl2 as a supporting
electrolyte. Oxygen was removed from the cell by blowing off
with dry argon. Electrolysis was performed using an Pꢀ5827 М
potentiostat in an undivided 10ꢀmL cell. A palladium wire
(d 2 mm) was used as the working electrode. The auxiliary elecꢀ
trode was either platinum or a cellulose hydrateꢀbased special
type graphite bearing the immobilized tested polymer, and
the reference electrode was KCl saturated Ag/AgCl electrode
(the potential vs. Fc/Fc+ = –0.48 V in NMP). Peak potentials
were recalculated taking into account ohmic losses.
The reaction mixture was analyzed using a GC/MS Finigan
MAT SSQ 7000 instrument (ionization energy 70 eV, DVꢀ5
quartz capillary column (30 m), temperature: 70 °C (2 min) →
→ heating at 20 deg min–1 → 280 °C (10 min)).
Mass spectra (MALDIꢀTOF) were recorded on a Bruker
Daltonics Autoflex II spectrometer with 337 nm laser radiation
using a cryogenic 9ꢀnitroanthracene matrix.
Preparation of biQ(COOR)2)2Pd2X2 complexes (X = Cl, OAc).
PdX2 (10–5 mol) was dissolved in MeCN (10 mL) in the presꢀ
ence of biQ(COOR)2 ligand (10–5 mol) and heated at 80 °C
Immobilized on graphite
cloth (10–3 mol.%)
88
Note: NaBPh4 (0.5•10–4 mol), PhI (2•10–4 mol), Na2CO3
(10–3 mol), 40 °C, 4 h.
amounts; its content in graphite cloth is 50 times lower
than that used in homogeneous catalysis. Catalyst TON in
the case of heterogeneous catalysis is 8.8•104.
We have tested recyclability of [Pd(PAI)L2](BF4)2
polymers anchored on the graphite cloth. After the reacꢀ
tion completion, graphite cloth with the coated polymeric
catalyst was washed with boiling CH2Cl2, then without
any other treatment used again in a new batch of the same
reaction with the new portion of reactants. The model
reaction was PhI crossꢀcoupling with NaBPh4 in the presꢀ
ence of Na2CO3.
As it is seen from the data obtained (Table 8), the
immobilized polymer is recyclable. The catalyst can be
reused after washing with only a minor decrease in bipheꢀ
nyl yield and catalytic activity (resulting in inconsiderable
reaction time growth), its TON, however, is therewith
enhanced almost threefold.
In summary the Pd complexes with PAꢀbased polyꢀ
meric ligands were synthesized electrochemically employꢀ
ing sacrificial anode. The complexes show high catalytic
activity in the Suzuki reaction. The reaction can be run at
low temperatures (40—80 °C), under conditions of homoꢀ
geneous catalysis as well as with the catalyst immobilized
on the graphite cloth with high specific surface; the resultꢀ
ant crossꢀcoupling products are formed in a sufficiently
high yield. When immobilized on graphite fabric, the catꢀ
alyst benefits enhanced activity, high TON (up to 105)
and easy separation from the reaction products allowing
its recycling.
for
2
h. MS MALDIꢀTOF, m/z (X
=
Cl): 1309
[biQ(COOHex)2)2Pd2Cl2], 513 [(biQ(COOHex)2]; m/z (X = OAc):
1357 [(biQ(COOHex)2)2Pd2(OAc)2], 513 [(biQ(COOHex)2].
Immobilization of PA polymer on graphite electrode. Preꢀ
weighed 1.5×1ꢀcm graphite cloth with a specific surface area of
12 m2 g–1 was placed on a watch crystal and then 10–5 M soluꢀ
tion of PAI in NMP (5•10–9 mol) was deposited (slowly in small
portions, so to allow complete take up by graphite). Thus polyꢀ
merꢀimpregnated electrode was dried at 220 °C.
Electrosynthesis of [PdIIPAI][BF4]2 complex in solution. Pd
wire was dissolved in galvanostatic mode (I = 1•10–3 A) in 10 mL
of 10–3 M PAI solution in NMP in the presence of 0.05 M
Bu4NBF4. The process was stopped after passing 2.1 F per 1 mol
of biQ fragments.
Table 8. Yields of Ph2 in NaBPh4 crossꢀcoupling with
Electrosynthesis of Pdꢀcontaining polymer complex immobiꢀ
lized on graphite electrode. Pd wire was dissolved in galvanostatic
mode (I = 1•10–3 A) in 10 mL of CH2Cl2 in the presence of
0.15 M Bu4NBF4. Graphite electrode modified with the polyꢀ
mer served as auxiliary electrode. The required charge was deꢀ
termined from the known mass of the polymer introduced and
the number of biquinolyl groups, assuming PdII coordination to
one biquinolyl ligand. The process was stopped after passing
1.1 charge equivalent (2.2 F per 1 mol of biQ). After electrolysis
completion the solution was intensively stirred for 2 h, then
graphite cloth was recovered, washed with CH2Cl2 and used in
catalytic process.
PhI with catalyst recycle
Cycle
τ/h
Yield of Ph2 (%)
1
2
3
4
6
7
88
72
67
Note: CH2Cl2, NaBPh4 (0.5•10–4 mol), PhI
(2•10–4 mol), Na2CO3 (10–3 mol), 40 °C,
4•10–3 mol.% [Pd(PAI)L2](BF4)2 immobilized on
graphite cloth.

1430
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 7, July, 2009
Magdesieva et al.
Suzuki reaction (general procedure). Aryl halide (2 10–4 mol)
was dissolved in 5 mL of NMP, then NaBPh4 (0.5 10–4 mol) and
Na2CO3 (10–3 mol) (fiveꢀfold excess with respect to starting
halide) were added. After passing the flow of dry argon through
13. C. P. Mehnert, D. W. Weaver, and J. Y. Ying, J. Am. Chem.
Soc., 1998, 120, 12289.
14. B. M. Bahanage, S.ꢀI. Fujita, and M. Arai, J. Organomet.
Chem., 2003, 687, 211.
15. J. GilꢀMolto, S. Karlstrom, and C. Najera, Tetrahedron,
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Z. Pientka, L. Brozova, and M. Bleha, Polymer, 2005,
46, 3730.
17. T. V. Magdesieva, A. V. Dolganov, A. V. Yakimansky, M. Ya.
Goikhman, I. V. Podeshvo, and V. V. Kudryavtsev,
Elektrokhimiya, 2007, 43, 1194 [Russ. J. Electrocthem.
(Engl. Transl.), 2007, 43].
reaction mixture for 15 min to remove oxygen, 0.1 mL of 10–3
М
solution of Pdꢀcontaining catalyst in NMP (0.05 mol.% with
respect to starting halide) was added. The reaction mixture was
heated under argon at fixed temperature for the fixed time. Then
was added water (15 mL) and reaction products were extracted
with diethyl ether. Yield of biphenyls was determined by GC/MS
using anthracene as internal standard.
The authors are grateful to N. A. Bumagin for his valuꢀ
able advice.
This study was financially supported by the Russian
Foundation for Basic Research (Project No. 08ꢀ03ꢀ00142).
18.
T. V. Magdesieva, A. V. Dolganov, A. V. Yakimansky, M. Ya.
Goikhman, I. V. Podeshvo, and V. V. Kudryavtsev, Electroꢀ
chim. Acta, 2008, 53, 3960.
19. T. V. Magdesieva, A. V. Dolganov, A. V. Yakimansky, M. Ya.
Goikhman, and I .V. Podeshvo, Electrochim. Acta, 2009.
20. K. Winkler, A. De BettencourtꢀDias, and A. L. Balch, Chem.
Mater., 2000, 12, 1386.
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Received July 25, 2008;
in revised form January 14, 2009