Palladium supported on amine-functionalized mesoporous silica: Highly efficient phosphine-free catalyst for alkyne-alkyne cross-coupling reaction

Article abstract of DOI:10.1016/j.catcom.2011.10.027

An amine-functionalized mesoporous silica SBA-15 supported palladium catalyst was prepared and characterized. For the first time, this supported palladium has been used as an efficient phosphine-free and reusable catalyst for the cross-coupling of haloalkynes with terminal alkynes. A variety of haloalkynes and aromatic/aliphatic terminal alkynes were selectively coupled to afford unsymmetrical 1,4-disubstituted 1,3-diynes in good yields.

Full text of DOI:10.1016/j.catcom.2011.10.027

Catalysis Communications 17 (2012) 179–183
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Palladium supported on amine-functionalized mesoporous silica: Highly efficient
phosphine-free catalyst for alkyne–alkyne cross-coupling reaction
a,
Hongling Li a,b, Lailai Wang a, Min Yang a, , Yanxing Qi
⁎
⁎
a
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, Gansu 730000, PR China
State Key Laboratory of Applied Organic Chemistry, Department of Chemistry, Lanzhou University, Lanzhou, Gansu, 730000, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 August 2011
Received in revised form 19 October 2011
Accepted 26 October 2011
Available online 4 November 2011
An amine-functionalized mesoporous silica SBA-15 supported palladium catalyst was prepared and charac-
terized. For the first time, this supported palladium has been used as an efficient phosphine-free and reusable
catalyst for the cross-coupling of haloalkynes with terminal alkynes. A variety of haloalkynes and aromatic/
aliphatic terminal alkynes were selectively coupled to afford unsymmetrical 1,4-disubstituted 1,3-diynes in
good yields.
© 2011 Elsevier B.V. All rights reserved.
Keywords:
Palladium
SBA-15
Alkyne
Unsymmetrical diyne
Cross-coupling
1. Introduction
Because of their advantages such as the easy handling and good
recyclability, heterogeneous catalysts are usually the first choice for
Conjugated diynes are important building blocks in natural prod-
ucts, pharmaceutical intermediates, nonlinear optical materials and
liquid crystals [1–5]. As a result, artificial synthesis of diyne deriva-
tives has attracted much attention [1,3,6–8]. Cu-salt mediated Glaser
coupling and its modifications are the major methods to prepare sym-
metrical diynes [9–12]. Cadiot–Chodkiewicz coupling and related
modified methods, Cu-catalyzed cross-couplings between a haloalk-
yne and a terminal alkyne, are widely used for constructing unsym-
metrical diynes [13–16]. Palladium catalysts have also been
developed for heterocoupling of a haloalkyne and a terminal alkyne
[17–22]. To improve the yield and selectivity, Alami et al. introduced
palladium/phosphine complex PdCl2(PPh3)2 into the C(sp)–C(sp)
cross-coupling reactions for the preparation of unsymmetrical diynes
[18]. However, these reactions often suffer from poor selectivity and
lead to a considerable amount of homo-coupled byproducts. Thus, ex-
cessive amount of alkynes (up to 5 equivalents) is necessary to en-
hance the selectivity of cross-coupled products [1,3,6,17]. Recently,
Lei et al. have successfully developed a highly efficient method by
using a π-acceptor phosphine ligand/Pd as the catalyst to prepare un-
symmetrical 1,3-diynes [23]. However, efficient phosphine-free palla-
dium catalysts for the alkyne–alkyne cross-coupling reactions have
not been explored [17].
constructing a new catalytic system. In recent years, mesoporous sil-
ica materials as catalyst supports for synthetic organic chemistry have
attracted much attention, due to their well-defined micro-structure
that forms the basis of uniform active sites of the catalyst and well-
controlled steric effects [24]. Among them, SBA-15 has been widely
used as support for palladium catalysts [25]. However, a supported
palladium as the catalyst for the synthesis of unsymmetrical diynes
has not been studied yet. Triethylenediamine, an inexpensive com-
mercially available ligand, has been successfully used in the Suzuki
cross-coupling reaction [26]; thus we envisioned that triethylenedia-
mine may work in the alkyne–alkyne cross-coupling reaction. In con-
tinuation of our interest in exploring phosphine-free catalytic
systems for C―C bond formation [27–29], an amine-functionalized
mesoporous silica SBA-15 supported palladium has been successfully
applied for alkyne–alkyne cross-coupling reactions with high
selectivity.
2. Experimental methods
2.1. Catalyst preparation
As shown in Scheme 1, Cl-SBA-15 [30] and Amine-SBA-15 [31]
were prepared according to the reported method. Firstly, SBA-15
(1 g, BET surface area=554.7 m2g−1 and pore size=6.0 nm) was
dispersed in boiling toluene (25 mL) and then (3-chloropropyl) tri-
methoxysilane (1.5 mL) was added dropwise. The mixture was
refluxed for 24 h. After cooling, the suspension was filtered and the
⁎
Corresponding authors. Tel.: +86 931 4968689; Tel./fax: +86 931 4968190.
E-mail addresses: minyang1@gmail.com (M. Yang), qiyanxing@gmail.com (Y. Qi).
1566-7367/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2011.10.027

180
H. Li et al. / Catalysis Communications 17 (2012) 179–183
Scheme 1. Schematic diagram of Pd-(SBA-15) preparation.
Fig. 2. TEM image of Pd-(SBA-15).
solid residue was extracted thoroughly in a Soxhlet extractor with
dichloromethane before being dried in vacuum at 70 °C for 5 h. Sec-
ondly, Cl-SBA-15 (1 g) was refluxed with triethylenediamine
(73 mg) in acetone (60 mL) for 24 h under argon atmosphere. The
resulting solid powder was recovered by filtration and extracted
with dichloromethane in a Soxhlet extractor overnight and then
dried in vacuum at 50 °C for 4 h. The white powder, designated as
Amine-SBA-15, was collected (BET surface area=392.7 m2g−1, pore
size=5.8 nm and elemental analysis of nitrogen=1.04 mmol g−1).
Finally, Amine-SBA-15 (1 g) was refluxed with Pd(OAc)2 (117.6 mg)
in acetone (30 mL) at 50 °C for 5 h. After filtration, the solid powder
was washed three times with ethyl ether (10 mL) and methanol
(10 mL), respectively, and then dried under air. The yellow powder
was collected and designated as Pd-(SBA-15) (BET surface
area=353.8 m2g−1, pore size=5.5 nm and 4.06% Pd based on ICP-
AES).
chromatography on silica gel (ethyl acetate/hexane) to afford the
pure product. After the first reaction cycle, the catalyst was recovered
by centrifugation and filtration. After being washed by deionized
water and ethyl acetate, respectively, the recovered catalyst was
dried under vacuum and then might be directly used for the next
cycle. The identification was conducted by GC analysis and 1H NMR
measurement.
3. Results and discussion
3.1. Catalyst characterization results
XRD analysis of SBA-15 before and after the modification both
showed a strong peak at 0.8° and two weak peaks around 1.45°
and 1.65°, which were assigned to 1 0 0, 1 1 0 and 2 0 0 reflections
of the ordered periodic arrangement of hexagonal channels (Fig. 1),
implying that the mesoporous structure of the carrier was not dete-
riorated after introduction of ligands and Pd [32]. The HRTEM mor-
phology further confirmed that the Pd-(SBA-15) had well-ordered
mesostructure as shown in Fig. 2. Nitrogen adsorption–desorption
isotherms of SBA-15, Amine-SBA-15 and Pd-(SBA-15) (Fig. 3)
exhibited typical IV type isotherm pattern with an H2 hysteresis
loop, implying the characteristic of the mesoporous structure is
remained. Step-wise desorption of N2 can be clearly seen for freshly
prepared Pd-(SBA-15) (Fig. 3), which might be attributed to the
physical adsorption of N2 on Pd nanoparticles [33]. The values of
the surface area and pore volume gradually decrease with intro-
duction of triethylenediamine and Pd, suggesting the ligands and
Pd are successfully anchored to the pore channels. XPS analysis
2.2. Catalyst characterization
The as-synthesized materials were characterized by means of the
elemental analysis, ICP-AES, XRD, HRTEM, BET and XPS techniques.
The detailed procedures were described in Appendix A. The conver-
sion was determined by gas chromatography (GC7890II, Techcomp)
analysis equipped with a SE-54 column and a flame ionization detec-
tor (FID) using biphenyl as an internal standard.
2.3. Catalytic reactions
Typically, a mixture of bromoethynylbenzene (0.5 mmol), 2-
methylbut-3-yn-2-ol (0.6 mmol), Pd-(SBA-15) (2 mol%), CuI
(2.0 mol%), Et3N (2 eq.) and DMF (1 mL) was stirred at room temper-
ature under argon atmosphere for the desired time. The reaction mix-
ture was then centrifuged and washed with ethyl acetate. The
combined organic phase was dried over anhydrous Na2SO4 and con-
centrated under vacuum. The residue was purified by flash
Fig. 3. N2 sorption isotherms: (a) SBA-15; (b) Amine-SBA-15; (c) Pd-(SBA-15).
Fig. 1. Low-angle XRD patterns of SBA-15 and Pd-(SBA-15).

H. Li et al. / Catalysis Communications 17 (2012) 179–183
181
showed that the fresh Pd-(SBA-15) catalyst consists of both Pd(II)
and Pd(0) and the ratio of Pd(II) to Pd(0) was about 3.5:1
(Fig. 4). As shown in Fig. 4, the measured binding energies of the
Pd 3d5/2 and 3d3/2 electrons at 337.8 and 343.2 eV, respectively cor-
responding to Pd(II) [34]. In addition, a weak contribution on the
Pd 3d peak was also distinguishable at 336.0 and 341.6 eV ascribed
to the presence of Pd(0) species. The existence of triethylenedia-
mine group could also be confirmed by the FT-IR spectrum
(Fig. 5). Both Cl-SBA-15 and Amine-SBA-15 materials showed char-
acteristic bands at 1652 cm− 1 the O–H stretching vibration and
bands at 1089, 802 and 462 cm− 1 due to the Si–O stretching vibra-
tion. FT-IR spectrum of Amine-SBA-15 (Fig. 5b) exhibited two
bands at 2975 cm− 1 and 1465 cm− 1, assigned to the C–H stretch-
ing vibration and C–N bending vibration of triethylenediamine
group, respectively [35]. These two peaks are not observed in the
spectrum of the Cl-SBA-15 (Fig. 5a).
Fig. 4. XPS spectra of the Pd 3d5/2 and 3d3/2 electrons' binding energies for Pd-(SBA-15).
3.2. Pd-(SBA-15) catalyzed cross-coupling reaction of terminal alkynes
As shown in Table 1, the reaction of bromoethynylbenzene (1a) and
2-methylbut-3-yn-2-ol (2a) was chosen as the model and effects of dif-
ferent parameters were examined to figure out the optimum condition.
Different catalytic system were firstly tested in the presence of Et3N
(2 Eq), CuI (2 mol%) and DMF (1 mL) at room temperature. Pd(OAc)2
(2 mol%) as the catalyst afforded 3a in a yield of 36% (entry 1). It was
noteworthy that when Pd-(SBA-15) (1 mol%) was utilized as the cata-
lyst, 3a was obtained in 76% yield along with only 5% 1,4-diphenylbuta-
diyne product (entry 2). Further increase the loading of Pd-(SBA-15) to
2 mol%, the yield of 3a was improved to 88% (entry 3). Trace desired
product 3a was obtained when Amine-SBA-15 (2 mol%) as the catalyst
(entry 4). The mixture of Pd(OAc)2 (2 mol%) and the equal amounts of
SBA-15 and/or triethylenediamine as the catalysts were less effective
than that of 2 mol% Pd-(SBA-15) (entries 5–7). Further optimization in-
dicated that CuI was crucial in this reaction as well. When the amount of
CuI decreased to 1 mol%, the yield of 3a decreased to 53%, while without
CuI, only 9% 3a was got and the selectivity dropped to 50% (entries 8 and
9). Moreover, the effects of solvent and base were also studied (entries
Fig. 5. FT-IR spectra: (a) Cl-SBA-15; (b) Amine-SBA-15.
Table 1
Effect of various parameters on the reaction of bromoethynylbenzene (1a) and 2-methylbut-3-yn-2-ol (2a).a
Entry
Catalyst (mol%)
Solvent
Time
(h)
Conv.
(%)b
3a
Yield (%)b
Selectivity (%)
1
2
3
4
5
6
Pd(OAc)2 (2)
DMF
DMF
DMF
DMF
DMF
DMF
5.5
16
16
15
15
16
100
100
100
48
100
100
36
–
Pd-(SBA-15) (1)
Pd-(SBA-15) (2)
Amine-SBA-15 (2)
Pd(OAc)2 (2)/SBA-15
Pd(OAc)2 (2)/
76 (72)
88 (79)
b1
57
67
91
92
–
91
92
triethylenediamine
Pd(OAc)2 (2)/SBA-15/
triethylenediamine
Pd-(SBA-15) (2)
Pd-(SBA-15) (2)
Pd-(SBA-15) (2)
Pd-(SBA-15) (2)
Pd-(SBA-15) (2)
Pd-(SBA-15) (2)
7
DMF
16
100
73 (70)
92
8c
DMF
DMF
CH3CN
THF
DMF
DMF
15
15
12
12
15
15
100
93
100
100
100
100
53
9
52
51
72 (67)
33
93
50
68
68
84
72
9d
10
11
12e
13f
a
Reaction conditions: 1a (0.5 mmol), 2a (0.6 mmol), catalyst, Et3N (2 eq.), CuI (2 mol%), and solvent (1 mL) at room temperature.
Determined by GC using biphenyl as internal standard and numbers in parentheses are the isolated yields.
CuI (1 mol%).
Without CuI.
Triethylenediamine as the base.
Piperidine as the base.
b
c
d
e
f

182
H. Li et al. / Catalysis Communications 17 (2012) 179–183
Table 2
Pd-(SBA-15) catalyzed cross-coupling reactions of haloalkynes with terminal alkynes.a
Entry
Substrate 1
Substrate 2
Time (h)
Yield (%)b
1
2
1a
2a
16
12
3a, 79, 88c
3a, 87c
2b
1b
3
1b
1b
1b
1b
1b
1b
1a
1a
1a
2c
24
8
3b, 73
3c, 88
3d, 81
3e, 90
3f, 61
3g, 85
3h, 78
3i, 75
3j, 74
4
2d
2e
5
7.5
15
24
24
24
16
24
6
2f
7
2g
2h
8
9
2f
10
11
2h
2i
a
Reaction conditions: 1 (0.5 mmol), 2 (0.6 mmol), Pd-(SBA-15) (2 mol%), Et3N (2 eq.), CuI (2 mol%), and DMF (1 mL) at room temperature.
Isolated yield.
Determined by GC using biphenyl as internal standard.
b
c
10–13). The results showed that when DMF was chosen as the solvent
reusable catalyst for the cross-coupling of haloalkynes with terminal al-
kynes to afford the corresponding unsymmetrical diynes. Tolerant of a
variety of functional groups, this new protocol had a broad substrate
scope including haloalkynes and aromatic as well as aliphatic terminal
alkynes. Under mild condition, the reaction could be performed with
high conversion and chemoselectivity without using large excessive
amount of one substrate. These advantages make the present catalytic
procedure an attractive option for the synthesis of unsymmetrical 1,3-
diynes.
and Et3N as the base higher yield and selectivity were obtained.
To evaluate the substrate scope, we examined the protocol employ-
ing various 1-bromoalkynes and terminal alkynes (Table 2). The results
showed Pd-(SBA-15) was tolerant of a variety of functional groups in-
cluding –OH, –F, –Br, –Cl and –CH3. It is interesting to note that the
cross-coupling of 1-ethynyl-4-fluorobenzene (2c) and 4-bromo ethy-
nylbenzene (2d) with 4-bromo-2-methylbut-3-yn-2-ol (1b) selectively
afforded desired unsymmetrical diynes 3b (73% yield) and 3d (88%
yield), respectively (entries 3 and 4). No dehalogenation proceeded in
the case of halogen-substituted ethynylbenzene derivatives (2c and
2d), which gives an opportunity for further functionalization at the in-
tact halide group in the product diynes. A number of aliphatic terminal
alkynes with different functional groups such as hex-5-yn-1-ol (2f), 5-
chloropent-1-yne (2g) and but-3-yn-1-ol (2h) reacted smoothly with
4-bromo-2-methylbut-3-yn-2-ol (1b), providing corresponding prod-
ucts 3e, 3f, 3g in 90, 61 and 85% yields, respectively (entries 6–8). It
also worked well for the cross-coupling reactions of bromoethynylben-
zene (1a) and aliphatic terminal alkynes bearing a hydroxyl group in-
cluding 2f, 2h and but-3-yn-2-ol (2i) (entries 9–11).
Reusability of Pd-(SBA-15) was then investigated through the
cross-coupling reaction of 4-bromo-2-methylbut-3-yn-2-ol (1b) and
phenylacetylene (2b). Pd-(SBA-15) was found to be easily separated
from the reaction mixture by simple filtration. The recovered catalyst
was then reused for the reaction of 1b and 2b under conditions exact-
ly same as those of the first run except the catalyst. Pd-(SBA-15)
showed very good reusability. Under the reaction conditions shown
in Table 2, the yields of the cross-coupling reaction of 1b and 2b
from the 1st run to the 3rd run were 90%, 90% and 65%, respectively.
Acknowledgements
This project was supported by Chinese Academy of Science and
Technology Project in Support of Gansu (XBLZ-2011-013), Technologies
R&D Program of Gansu Province (No. 1104FKCA156) and Joint Scholars
of Western Light Project from the Chinese Academy of Sciences.
Appendix A. Supplementary data
Supplementary data to this article can be found online at doi:10.
1016/j.catcom.2011.10.027.
References
[1] F. Diederich, P.J. Stang, R.R. Tykwinski (Eds.), Acetylene Chemistry: Chemistry, Bi-
ology and Material Science, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim,
Germany, 2005.
[2] M.M. Haley, R.R. Tykwinski (Eds.), Carbon-Rich Compounds: From Molecules to
Materials, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, 2006.
[3] P. Siemsen, R.C. Livingston, F. Diederich, Angewandte Chemie, International Edi-
tion 39 (2000) 2632–2657.
[4] S. Kanokmedhakul, K. Kanokmedhakul, I. Kantikeaw, N. Phonkerd, Journal of Nat-
ural Products 69 (2006) 68–72.
[5] X. Lv, J. Mao, Y. Liu, Y. Huang, Y. Ma, A. Yu, S. Yin, Y. Chen, Macromolecules 41
(2008) 501–503.
[6] A.L.K.S. Shun, R.R. Tykwinski, Angewandte Chemie, International Edition 45
(2006) 1034–1057.
4. Conclusions
An amine-functionalized mesoporous silica SBA-15 supported pal-
ladium has been successfully utilized as an efficient phosphine-free,

H. Li et al. / Catalysis Communications 17 (2012) 179–183
183
[7] C. Zhang, C.F. Chen, Journal of Organic Chemistry 72 (2007) 9339–9341.
[8] J.A. Marsden, J.J. Miller, M.M. Haley, Angewandte Chemie, International Edition 43
(2004) 1694–1697.
[9] K. Kamata, S. Yamaguchi, M. Kotani, K. Yamaguchi, N. Mizuno, Angewandte Che-
mie, International Edition 47 (2008) 2407–2410.
[10] H.F. Jiang, J.Y. Tang, A.Z. Wang, G.H. Deng, S.-R. Yang, Synthesis (2006)
1155–1161.
[11] Y. Nishihara, K. Ikegashira, K. Hirabayashi, J.-i. Ando, A. Mori, T.J. Hiyama, Organic
Chemistry 65 (2000) 1780–1787.
[12] W. Yin, C. He, M. Chen, H. Zhang, A. Lei, Organic Letters 11 (2009) 709–712.
[13] W. Chodkiewicz, P. Cadiot, Comptes Rendus 241 (1955) 1055–1057.
[14] S. Kim, S. Kim, T. Lee, H. Ko, D. Kim, Organic Letters 6 (2004) 3601–3604.
[15] F. Bellina, A. Carpita, L. Mannocci, R. Rossi, European Journal of Organic Chemistry
(2004) 2610–2619.
[22] C. Amatore, E. Blart, J.P. Genet, A. Jutand, S. Lemaire-Audoire, M. Savignac, Journal
of Organic Chemistry 60 (1995) 6829–6839.
[23] W. Shi, Y. Luo, X. Luo, L. Chao, H. Zhang, J. Wang, A. Lei, Journal of the American
Chemical Society 130 (2008) 14713–14720.
[24] T. Maschmeyer, F. Rey, G. Sankar, J.M. Thomas, Nature 378 (1995) 159–162.
[25] A. Molnár, Chemical Reviews 111 (2011) 2251–2320.
[26] J.H. Li, X.C. Hu, Y.X. Xie, Tetrahedron Letters 47 (2006) 9239–9243.
[27] Z.S. Wu, M. Yang, H.L. Li, Y.X. Qi, Synthesis (2008) 1415–1419.
[28] H.L. Li, Z.S. Wu, M. Yang, Y.X. Qi, Catalysis Letters 137 (2010) 69–73.
[29] H.L. Li, M. Yang, Y.X. Qi, J.J. Xue, European Journal of Organic Chemistry (2011)
2662–2667.
[30] K. McEleney, C.M. Crudden, J.H. Horton, Journal of Physical Chemistry C 113
(2009) 1901–1907.
[31] C.M. Crudden, M. Sateesh, R. Lewis, Journal of the American Chemical Society 127
(2005) 10045–10050.
[32] P. Han, H.M. Zhang, X.P. Qiu, X.L. Ji, L.X. Gao, Journal of Molecular Catalysis A:
Chemical 295 (2008) 57–67.
[33] R. Vanharde, A. Vanmontf, Surface Science 4 (1966) 396–430.
[34] A.R. Siamaki, A.E.R.S. Khder, V. Abdelsayed, M.S. El-Shall, B.F. Gupton, Journal of
Catalysis 279 (2011) 1–11.
[16] S. Lopez, F. Fernandez-Trillo, P. Midon, L. Castedo, C. Saa, Journal of Organic Chem-
istry 71 (2006) 2802–2810.
[17] E.-I. Negishi, L. Anastasia, Chemical Reviews 103 (2003) 1979–2017.
[18] M. Alami, F. Ferri, Tetrahedron Letters 37 (1996) 2763–2766.
[19] S. Eisler, A.D. Slepkov, E. Elliott, T. Luu, R. McDonald, F.A. Hegmann, R.R. Tyk-
winski, Journal of the American Chemical Society 127 (2005) 2666–2676.
[20] E.-i. Negishi, M. Qian, F. Zeng, L. Anastasia, D. Babinski, Organic Letters 5 (2003)
1597–1600.
[35] S.C. Blackstock, J.P. Lorand, J.K. Kochi, Journal of Organic Chemistry 52 (1987)
1451–1460.
[21] T. Luu, Y. Morisaki, N. Cunningham, R.R. Tykwinski, Journal of Organic Chemistry
72 (2007) 9622–9629.