Pd(0)-arabinogalactan nanocomposites as catalysts for dimerization of acetylenic compounds

Full text of DOI:10.1134/S0012500807110018

ISSN 0012-5008, Doklady Chemistry, 2007, Vol. 417, Part 1, pp. 261–263. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © B.A. Trofimov, B.G. Sukhov, V.V. Nosyreva, A.G. Mal’kina, G.P. Aleksandrova, L.A. Grishchenko, 2007, published in Doklady Akademii Nauk, 2007,
Vol. 417, No. 1, pp. 62–64.
CHEMISTRY
Pd(0)–Arabinogalactan Nanocomposites as Catalysts
for Dimerization of Acetylenic Compounds
Academician B. A. Trofimov, B. G. Sukhov, V. V. Nosyreva, A. G. Mal’kina,
G. P. Aleksandrova, and L. A. Grishchenko
Received March 28, 2007
DOI: 10.1134/S0012500807110018
In recent years, nanoclusters of catalytically active arabinogalactan (AG) possessing promising magnetic,
metals have started to attract attention as highly effi-
cient ligand-free catalysts [1, 2]. The fundamental ideas
and results in this field belong to I.I. Moiseev, who was
the first to synthesize a giant Pd cluster (561 atoms) sta-
bilized by phenanthroline molecules [3].
optical, and catalytic properties and biological activity
[4, 5].
In this paper, we briefly report the results of a study
of the catalytic activities of Pd(0)–AG nanocomposites
in the oxidative and addition dimerization of acetylene
Recently we reported the synthesis of a new group
of metal and metal oxide nanocomposites stabilized by compounds
catalyst
(1)
(2)
Ph
H
Ph
Ph
,
Ph
catalyst
+
Ph
H
Ph
Ph
.
Ph
These reactions (1, 2) form the basis for elegant ies showed that these nanocomposites can efficiently
catalyze both the oxidative and the addition dimeriza-
tion of acetylenic compounds:
atom-economical methods for the synthesis of diynes
and enynes, which are important building blocks
widely used now in fine organic synthesis [2, 6, 7].
The Pd(0)–AG nanocomposites were prepared by
treatment of PdCl2 with an alkaline aqueous solution of
larch arabinogalactan as a nanoparticle stabilizer. The
catalyst systems used were nanocomposites with a total
globule size of 200–600 nm (Fig. 1) consisting of
spherical metallic cores with a size of 2–25 nm (the
average size was 5 nm and the average number of Pd
atoms per particle was 4300) (Fig. 2) and a stabilizing
arabinogalactan shell [5]. These composites can be
regarded as catalytic microreactors that can, in princi-
ple, ensure asymmetric synthesis due to the chiral sur-
rounding by enantiomerically pure structural blocks
(polysaccharides). An important feature of Pd(0)–AG
composites is their water solubility, which makes it
possible to carry out reactions in aqueous media. Stud-
1 µm 30.2 kV 1.00 E4 7295/53
PD 1.9
Favorsky Institute of Chemistry, Siberian Branch,
Russian Academy of Sciences, ul. Favorskogo 1, Irkutsk,
664033 Russia
Fig. 1. SEM image of Pd(0)–AG nanocomposites.
261

262
Ph
TROFIMOV et al.
Pd(0)–AG
cases, the piperidine–phenylacetylene adduct, namely,
H
Ph
Ph
PhBr, CuBr(LiBr)
piperidine
1-(2-phenylethynyl)piperidine 3, is detected in the
reaction mixture. If bromotoluene is taken instead of
bromobenzene, the yields of dimers 1 and 2 decrease to
31 and 6%, respectively, which is in line with the lower
anionic mobility of bromine in bromotoluene caused by
the electron-donating effect of the methyl group. Inter-
estingly, the cross-coupling (the Cassar–Heck–Sono-
gashira reaction) expected under these conditions [8]
does not take place; not even traces of the product of
this reaction, 1-(2-phenylethynyl)benzene, were detected
in the reaction mixture. The oxidative coupling is likely to
mainly follow reactions (4) and (5), proposed previously
1
60–100°C
Ph
+
+
Ph
N
.
(3)
Ph
2
3
In the presence of Pd(0)–AG nanocomposites
(0.14–1.60 wt % Pd), CuBr (0.3 wt %), LiBr (1 wt % or
none), and bromobenzene in piperidine (or aqueous
piperidine) at 60–100°C in a specially purified argon
atmosphere, phenylacetylene is converted into 1,4-
diphenyl-1,3-butadiyne 1 (yield 45–49%) and 1,4-
diphenyl-1-buten-3-yne 2 (yield 15–18%). In some [9]:
Ph
H + Pd(0)
Ph
Pd H
4
PhBr
Ph
PdBr + C6H6
,
(4)
(5)
5
Ph
H/CuBr
piperidine
–Pd(0)
Ph
Br
NH · HBr
.
5
1 +
Cadiot–Chodkiewicz
One more possible channel of the formation of upon partial hydrogenation of diyne 1 with the evolved
diyne 1 is disproportionation of hydride complex 4 with hydrogen
hydrogen evolution:
1 + H2
2.
(7)
When the reaction is carried out in an air flow, prod-
ucts 1 and 2 are formed in lower yields.
2 (4)
1 + 2 Pd(0) + H2.
(6)
This is confirmed by the fact that diyne 1 is formed,
In the case of 2-methyl-3-butyn-2-ol and Pd(0)–AG,
although in a lower yield, when the reaction is carried only oxidative dimerization takes place, resulting in
out without bromobenzene. Enyne 2 may be formed 2,7-dimethyl-3,5-octadiyne-2,7-diol 6 in 47% yield:
Me
OH
Me
OH
Me
Pd(0)–AG
Me
H
Me
Me
.
PhBr, CuBr
piperidine
20–25°C, 15 h
(8)
OH
6
It is noteworthy that, according to our results, the
Cassar–Heck–Sonogashira reaction (Pd(Ph3P)4, LiBr,
CuBr, Ph3P, piperidine–THF, 90°C, 2 h, argon) [8] of
phenylacetylene with bromobenzene also does not
yield even traces of 1-(2-phenylethynyl)benzene;
instead, compounds 1 (yield 45%) and 3 (yield 4%)
were isolated.
EXPERIMENTAL
IR spectra were measured on a Bruker IFS-25 spec-
1
trophotometer in a thin film and in KBr. H NMR
(400.13 MHz) were recorded on a Bruker DPX-400
spectrometer in ëDCl3 using HMDS as the internal ref-
erence; mass spectra were run on a Shimadzu GCMS-
QP5050A mass spectrometer. The Pd nanoparticle size
was calculated from transmission electron microscope
images (Leo 906E microscope, accelerating voltage
80 kV); that of nanobiocomposites was found from
scanning electron microscope images (Philips 525M
microscope).
Thus, even under unoptimized reaction conditions,
the nanosized composite Pd(0)–AG is not inferior in
efficiency and corresponds in chemoselectivity to the
catalyst system Pd(Ph3P)4 widely used in this reaction.
DOKLADY CHEMISTRY Vol. 417 Part 1 2007

Pd(0)–ARABINOGALACTAN NANOCOMPOSITES AS CATALYSTS
263
(2 × 3 mL) and dried with MgSO4. The solvent was
removed in a vacuum to give 0.20 g of residue, which
was chromatographed (Al2O3, hexane) to give 1,4-
diphenyl-1,3-butadiyne (0.09 g, 45%) and 1,4-diphe-
1
nyl-1-buten-3-yne (0.03 g, 15%). ç NMR (δ, ppm):
7.02 d, 6.37 d, J = 16.3 Hz; 6.68 d, 5.90 d, J = 12.7 Hz;
E : Z = 1 : 1. MS, m/z: 202, 204.
(b) The reaction of phenylacetylene (1 g, 10 mmol)
in the presence of Pd(0)–AG nanocomposite (0.1 g,
4.6% Pd) in piperidine (4 mL) carried out in a similar
way with heating (95°C, 9 h, Ar) followed by the
above-described workup afforded 1,4-diphenyl-1,3-
butadiyne (0.12 g, 15%), E-1,4-diphenylbut-1-en-3-
yne (0.34 g, 41%), and 1-(2-phenylethynyl)piperidine
(0.02 g, 1%). 1H NMR (δ, ppm): 6.63 d, 5.33 d, J = 14.6
Hz; 5.71 d, 5.20 d, J = 11.4 Hz; E : Z = 1 : 1. The phe-
nylacetylene conversion was 82%. MS, m/z: 187, 202,
204.
100 nm
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Dimerization of phenylacetylene. (a) Bromoben-
zene (0.13 g, 0.8 mmol) and phenylacetylene (0.2 g,
2 mmol) were added to a mixture of Pd(0)–AG nano-
composite (0.01 g, 4.6% Pd) and CuBr (0.001 g,
0.006 mmol) in piperidine (1 mL). The mixture was
stirred under argon (being passed preliminarily through
a pyrogallol solution and NaOH) for 10 min (22°C) to
obtain a uniform slurry and then heated (60–100°C) for
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refluxed (93°C) for 15 min. The reaction mixture was
diluted with water (3 mL) and extracted with ether
(5 × 4 mL). The ethereal extract was washed with water
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DOKLADY CHEMISTRY Vol. 417 Part 1 2007