Polymerization of acetylene in aqueous PdCl2-CuCl solutions: Novel catalytically active palladium-copper-containing carbon materials

Full text of DOI:10.1134/S0012500810030080

ISSN 0012ꢀ5008, Doklady Chemistry, 2010, Vol. 431, Part 1, pp. 94–98. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © B.A. Trofimov, A.G. Mal’kina, A.N. Sapozhnikov, I.E. Vasil’eva, A.F. Shmidt, A.A. Kurokhtina, T.I. Vakul’skaya, S.S. Khutsishvili, 2010, published in
Doklady Akademii Nauk, 2010, Vol. 431, No. 3, pp. 356–360.
CHEMISTRY
Polymerization of Acetylene in Aqueous PdCl –CuCl Solutions:
2
Novel Catalytically Active
Palladium–CopperꢀContaining Carbon Materials
a
a
b
b
Academician B. A. Trofimov , A. G. Mal’kina , A. N. Sapozhnikov , I. E. Vasil’eva ,
c
c
a
a
A. F. Shmidt , A. A. Kurokhtina , T. I. Vakul’skaya , and S. S. Khutsishvili
Received September 28, 2009
DOI: 10.1134/S0012500810030080
Catalysis by transition metal complexes plays pounds, one can expect their transformation into
an important and increasing role in fine organic carbon materials incorporating polymerization catꢀ
synthesis [1, 2] and chemical technology [3]. alysts in resulting macrochains, globules, and
Homogeneous catalysis by metal complexes is fast nanometer and submicron spheres.
progressing [4]. In recent years, there is an
This approach opens an opportunity for the tailorꢀ
increasing trend to combine the advantages of
made synthesis of nanoꢀ and microreactors as nanoꢀ
homogeneous and heterogeneous catalysis by
clusters of catalytically active metals or their comꢀ
immobilization of transition metal compounds on
pounds encapsulated into a carbon material (polyconꢀ
active surfaces [5]. Carbon supports are of particuꢀ
jugated polymers with electron conductivity). The
lar interest among such surfaces [6]. As a rule, catꢀ
hydrogen content in these composites can be conꢀ
alysts are prepared by impregnation of the supports
trolled owing to the capacity of acetylene compounds
with transition metal compounds showing cataꢀ
for oxidative polycondensation to eliminate hydrogen
lytic activity followed by their modification
and owing to oxidative aromatization. In this paper, we
through thermal or chemical treatment [7] or by
consider the efficacy of this approach using the simꢀ
the grafting of metal complexes to functional polyꢀ
plest example of redox polymerization of acetylene in
mers [8].
aqueous PdCl –CuCl solutions. The use of these tranꢀ
2
In this paper, we briefly discuss a new concept for
the synthesis of catalysts, nanoꢀ and microreactors
that are carbon materials incorporating transition
metal compounds. The concept is that the carbon
material is formed in a solution of transition metal
compounds through the polymerization of lowꢀ
molecularꢀweight precursors (acetylene, vinylacetꢀ
ylene, divinylacetylene, diacetylene, their oligoꢀ
mers and functional derivatives, for example,
sition metal salts is determined by the tremendous
upgrowth of catalysis by palladium compounds [9] and
by the fact that copper compounds are wellꢀknown
catalysts of oligomerization and polymerization of
acetylene and its oxidative polycondensation (vinyꢀ
lacetylene; divinylacetylene; “oneꢀdimensional carꢀ
bon,” Sladkov’s carbyne [10]).
Under these conditions, one can expect the formaꢀ
diacetylene alcohols, acids, amines, and heterocyꢀ tion of both polyvinylene
cles with acetylene substituents). Taking into via the triple bond):
account the high propensity of acetylene and
1 (acetylene polymerization
PdCl /CuCl/O (H O )
2
2
2 2
diacetylene compounds to undergo polymerization,
especially in the presence of transition metal comꢀ
nHC≡CH
[CH=CH]n,
(1)
H O
2
1
and polyethynylene
of acetylene):
2 (the oxidative polycondensation
aFavorsky Irkutsk Institute of Chemistry, Siberian Branch,
Russian Academy of Sciences, ul. Favorskogo 1, Irkutsk,
PdCl /CuCl/O (H O )
2
2
2 2
nHC≡CH
[C≡C]n + H O. (2)
6
64033 Russia
H O
2
2
b
Vinogradov Institute of Geochemistry, Siberian Branch,
Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk,
2
6
64033 Russia
Furthermore, expected reactions are the cyclooliꢀ
gomerization of acetylene to yield, for example
cyclooctatetraene, and trimerization of oligomers
c
Irkutsk State University, ul. K. Marksa 1, Irkutsk, 664033
Russia
94

POLYMERIZATION OF ACETYLENE IN AQUEOUS
95
Table 1. Composition of acetylene polymerization products obtained in aqueous PdCl –CuCl solutions
2
Composition, %
Sample
Yield, %a
Сb
Hb
Clb
Ashb
Pdc
Cuc
1d
2e
3f
4g
5h
81
72
67
81
91
26.3
50.3
54.2
55.2
55.5
1.3
3.6
4.1
3.1
3.8
9.4
4.7
61.3
19.3
17.5
18.5
11.2
6.4 (± 0.5) 56.8 (± 5.8)
34.2 (± 0.7)
29.6 (± 2.3)
24.2 (± 3.7)
1.0 (± 0.1)
1.5 (± 0.2)
3.7 (± 0.4)
13.6
11.7
3.3
13.3 (± 2.9) 13.5 (± 0.6)
a
Note: Reaction conditions: 100 mL of H O, 0.12% of PdCl , and 2.4% of CuCl, 20–25°C, acetylene passage rate is 20–30 mL/min. Per
2
2
b
c
d
e
PdCl incorporated in the composite. Elemental analysis data. Data of atomic emission analysis. Reaction time is 18 h. Ammoꢀ
nium chloride (2.2 g) and 5 mL of 36% HCl were added to the reaction mixture, reaction time was 48 h, the composite was additionally
washed with aqueous ammonia solution. The composite contained 4% of nitrogen in addition to the noted elements. Reaction was
2
f
carried out in 100 mL of 36% aqueous solution of hydrogen peroxide in the presence of 2.2 g NH Cl and 5 mL of 36% HCl, reaction
4
g
time was 12 h. Ammonium chloride (2.2 g) and 5 mL of 36% HCl were added to the reaction mixture, reaction time was 12 h.
h
Ammonium chloride (2.2 g) and 5 mL of 36% HCl were added to the reaction mixture, reaction time was 12 h, the composite was
additionally washed with aqueous ammonia solution. The composite contained 8% of nitrogen in addition to the noted elements.
containing triple bonds to form compounds with cage
or crosslinked structures:
The composites were also studied by Xꢀray diffracꢀ
tion analysis and ESR spectroscopy (Table 2).
Elemental analysis and atomic emission spectromꢀ
etry showed that the composites contained PdCl2,
copper chlorides, Pd(0), and, in some cases, Cu(0)
PdCl /CuCl/O (H O )
2
2
2 2
(3)
(
sample 1) in different ratios depending on polymerꢀ
H O
2
ization conditions. It is important that the main porꢀ
tion of palladium binds to the resulting polymer (the
yield of the composite is 67–91% as calculated for palꢀ
3
The resulting polyconjugated blocks containing ladium) (Table 1), the ratio is one palladium atom per
double ( ) and triple bonds ( ) and benzene rings (
8–10 vinylene (ethynylene) units. The presence of up
show a reduced ionization potential (lowꢀenergy to 11% of Pd(0) (sample ) and up to 18% of Cu(0)
HOMOs) and enhanced electron affinity (lowꢀenergy (sample ) follows from the fact that the equivalent
1
2
3)
3
1
LUMOs) and, hence, should be apt to complexation content of chlorine in the samples is much lower than
with transition metal compounds.
the content of the metals.
The Xꢀray diffraction pattern of sample
1 shows
Thus, the formation of the coordination sphere
composed of a polyconjugated chain of a carbon polyꢀ
mer around the transition metal cation is probable in
the course of polymerization.
narrow lines of paratacamite Cu Cl(OH) [11]. The
2
3
line with the interplanar spacing
d
= 2.115 Å, accordꢀ
ing to [12], refers to skaergaardite (PdCu) whose most
intense line has = 2.122 Å, the weak shoulder with
= 2.093 Å seems to refer to copper metal. The
= 2.2458 Å) is likely to be overꢀ
d
The results of our experiments confirm the above
d
assumptions. The polymerization of acetylene was intense line of Pd(0) (
d
carried out in air in diluted aqueous PdCl –CuCl lapped with the nearby line of paratacamite (d =
2
2
.265 Å), and the Pd(0) lines of lower intensity may
solutions at ambient temperature and atmospheric
not be detected on account of its low concentration.
pressure. In certain experiments, NH Cl and/or HCl
4
were added to the salt solution. Atmospheric oxygen or
hydrogen peroxide was used as the oxidizing agent.
After 5–10 min of acetylene passage, the solution
became rich black, which indicates the formation of a
sol of a polymeric complex composed of polyacetyꢀ
lene, polydiacetylene, and palladium and copper
compounds. The sol was gradually transformed into
highly dispersed suspension (sol–gel transition). The
resulting composites (dark brown light electrifiable
powders) were analyzed. Their composition was deterꢀ
mined by elemental analysis and atomic emission
spectrometry (Table 1).
Table 2. ESR characteristics of the composites
10–19
spin/g
N
×
,
Asymmetry paꢀ
rameter
Sample
g
factor
Δ
H, G
A/B
1
2
4
5
0.28
0.49
5.30
0.87
2.0041
2.0044
2.0010
2.0012
6.3
7.0
4.6
7.1
Not determined
0.79
0.83
Not determined
DOKLADY CHEMISTRY Vol. 431
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2010

9
6
TROFIMOV et al.
The catalytic activity of the composites was tested
by the examples of important crossꢀcoupling reactions
Sonogashira, Heck, and Suzuki reactions) and the
(
oxidative coupling of acetylenes.
Under Sonogashira reaction conditions, sample
catalyses mainly the crossꢀcoupling of phenylacetyꢀ
2
lene with iodobenzene (the yield of diphenylacetylene
200 nm
1
345 nm
(
4) is 31%) :
Sample 2 (6.6 wt %)
Et N, 90–93°C, 3 h
Ph–≡–H + Ph–I
Ph–≡–Ph .
3
4
485 nm
1
0
µ
m
Sample
1 under the same conditions selectively
catalyses the oxidative dimerization of phenylacetyꢀ
lene (the yield of diphenyldiacetylene (5) is 94%) :
1
A micrograph of sample
2
.
Sample 1 (6.7 wt %)
Ph–≡–H + Ph–I
Ph–≡–≡–Ph
Et N, 90–93°C, 3 h
3
The Xꢀray diffraction patterns of samples
three significantly broadened lines (halfꢀwidth is ~6
) which indicates the ultradisperse state of the comꢀ
posites (nanosystems). The interplanar spacing of
lines with maxima at = 6.3, 2.93, and 2.21 Å accordꢀ
2–5 show
5
°
2
θ
The catalytic activity of composite
reaction,1
3
in the Heck
d
ing to the data of [13, 14] refer to compounds
Sample 3 (1.5 wt %)
DMF, 140°C, 3 h
Ph
Ph
+
Ph–Br
Pd(NH ) PdCl and Pd(NH ) Cl2. The profile of
3
4
4
3 2
experimental diffraction reflections is an envelope
covering the lines (from three to seven) of the noted
compounds; therefore it is difficult to assess the
parameters of coherent scattering.
Ph
6
and Suzuki reaction was studied in comparison
with couplings in the presence of PdCl and
2
4
% Pd/C (Table 3).
The relative content of carbon and hydrogen in the
polymers indicates that, along with polyvinylene fragꢀ
ments
polyethynylene blocks
1
, they contain up to 4–5% (samples 1–3) of
B(OH) + Br
OMe
2
2
(hydrogenꢀfree). Thus, this
confirms that the oxidative polycondensation of acetꢀ
ylene (equation (2)) also proceeds along with its polyꢀ
merization at the triple bond (equation (1)).
Sample 3 (1.4–1.6 wt %)
C H OH (or DMF/H O),
OMe
2
5
2
The polyconjugated (polyvinylene–polyethyꢀ
nylene) structure of the polymers is confirmed by their
characteristic paramagnetism (Table 2).
22–140°C, 3 h
7
Sample 3 catalyzes the Heck reaction between broꢀ
The ESR spectra of the composites show singlets mobenzene and styrene with efficacy virtually the
common for polyconjugated polymers. They differ same as 4% Pd/C or PdCl and gives close yields of
2
from narrow symmetrical lines typical for polyacetyꢀ transꢀstilbene
6
(Table 3, runs 1–3).
lenes [15] and show marked asymmetry and a larger
At the same time, sample
active catalyst in the Suzuki reaction than 4% Pd/C:
the yield of the product of crossꢀcoupling with ꢀbroꢀ
moanisole was ~23%, whereas 4% Pd/C even with
more reactive bromobenzene afforded about 5% yield.
At the same time, sample
3
proved to be a more
width between maximal slope points. The spectra also
show wide signals of different intensity related to
Cu(II). The lack of correlation between the copper
concentration and the intensity of Cu(II) signals conꢀ
firms that copper in the composites is present preferaꢀ
bly in nonmagnetic forms (Cu(0) or Cu(I)).
p
3 in the same reaction was
found to be less active than PdCl . However, its activꢀ
2
As for the morphology of the polymers (figure),
they are nanometer and submicron spheres of 200–
ity at 140 C is close to that of PdCl (Table 3, runs 8, 9).
°
2
In the presence of 4% Pd/C, comparable yields were
obtained only for more reactive bromobenzene
1
000 nm in size where metallic components seem to be
distributed over the surface as molecular complexes.
The radius of the polymeric spheres and the extent of
their dimensional homogeneity are dependent on
polymerization conditions.
(
Table 3, run 10).
1
The concentration of samples is given toward the initial
reagents.
DOKLADY CHEMISTRY Vol. 431
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2010

POLYMERIZATION OF ACETYLENE IN AQUEOUS
Table 3. Heck and Suzuki reaction conditions
97
Run
Bromoarene (5 mmol)
Catalyst (wt %)a
Heck reactionb
Solvent (5 mL)
Yield of product, %
1
2
3
PhBr
PhBr
PhBr
Sample
3
(1.5)
DMF
16.0
16.0
16.3
PdCl (0.8)
2
“
“
4% Pd/C (10.4)
Suzuki reaction
4c
5c
6c
7c
п
ꢀBrC H OMe
4
Sample
3
(1.6)
Ethanol
22.9
66.3
–
6
пꢀBrC H OMe
6
PdCl (0.8)
2
“
“
“
4
пꢀBrC H OMe
6
Pd/C (10.7), 4%
Pd/C (11.5), 4%
4
PhBr
5.3
8d
9d
0d
п
ꢀBrC H OMe
6
Sample
3
(1.4)
DMFꢀH O
2
66.7
67.6
70.1
4
пꢀBrC H OMe
6
PdCl (0.7)
2
“
4
1
PhBr
4% Pd/C (9.9)
“
Note: a Toward the initial reagents. Styrene (5 mmol), NaOAc (6.5 mmol), 140°C, 3 h. Phenylboronic acid (5 mmol), NaOH (6 mmol),
b
c
2
2°C, 3 h. d Phenylboronic acid (5 mmol), NaOAc (6.5 mmol), DMF–H O, 4 : 1 (5 mL), 140°C, 3 h.
2
EXPERIMENTAL
Xꢀray diffraction analysis was performed on a D8
and submicron spheres by the polymerization of acetꢀ
ylene in aqueous PdCl –CuCl solutions.
2
The obtained composites catalyze synthetically
important crossꢀcoupling reactions (Sonogashira,
Heck, Suzuki) and the oxidative dimerization of acetꢀ
ylenes. Change in polymerization conditions provides
a possibility to vary within a wide range the morpholꢀ
ogy and filling of carbon matrix with palladium and
copper in different valence states and hence to manage
the catalytic activity of the composites. The results
illustrate the new concept for the synthesis of catalysts
applied on carbon matrix. The concept is based on the
formation of carbon material from lowꢀmolecularꢀ
weight precursors, for example, acetylene or its derivꢀ
atives, in the presence of compounds of catalytically
active metals.
Advance diffractometer with Cu radiation. Atomic
K
α
emission analysis was carried out on a DFSꢀ458 difꢀ
fraction spectrograph with an MAES multichannel
analyzer of emission spectra (VMK–Optoelektronika,
Russia) using the method of complete evaporation of a
sample from a channel of the graphite electrode in the
direct current arc. ESR spectra were recorded on a
Bruker ELEXSYS E 580 spectrometer. The concenꢀ
tration of paramagnetic centers was calculated with
the use of diphenylpicrylhydrazyl standard. The
micrographs of powders were obtained with a Hitachi
TMꢀ1000 scanning electron microscope. The powders
were applied to a carbon support. The survey was carꢀ
ried out under reduced vacuum conditions (1.5 ×
⎯
1
1
0 mm Hg).
ACKNOWLEDGMENTS
Polymerization of acetylene in aqueous solutions
We thank Dr. E.V. Karpova (Novosibirsk Institute
of Organic Chemistry, Siberian Branch, Russian
Academy of Sciences) for providing micrographs of
the composites.
(
typical example). A mixture of 2.35 g (23.6 mmol) of
CuCl, 2.24 g (42.0 mmol) of NH Cl, 0.123 g
4
(
0.7 mmol) of PdCl , and 100 mL of water was placed
2
in a wide glass beaker and 5 mL of 36% HCl was
added. Acetylene was passed through the solution at
This work was supported by the Council for Grants
ambient temperature at a rate of 20–30 mL/min for of the President of the Russian Federation for Support
2 h, a black suspension formed in the solution, the of Leading Scientific Schools (grant no. NSh–
4
suspension was allowed to stand for 12 h and filtered, 263.2008.3) and the Russian Academy of Sciences
the precipitate was washed with water (200 mL), alcoꢀ (the Integration Project of the Presidium of the RAS,
hol (30 mL), and diethyl ether (30 mL). The precipiꢀ Program 15).
tate was dried in vacuum (1 mmHg) for 12 h to give
0
.41 g (81% based upon taken PdCl ) of a darkꢀbrown
2
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DOKLADY CHEMISTRY Vol. 431
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2010