A phosphine-free, atom-efficient cross-coupling of aryl iodides with triarylindiums or trialkynylindiums catalyzed by immobilization of palladium(0) in MCM-41

Article abstract of DOI:10.1016/j.jorganchem.2017.10.013

The first phosphine-free heterogeneous atom-efficient cross-coupling reaction of aryl iodides with triarylindiums or trialkynylindiums was achieved in THF at 68 °C by using 1 mol% of MCM-41-immobilized palladium(0)-Schiff base complex [MCM-41-N,N-Pd(0)] as catalyst, yielding a variety of unsymmetrical biaryls and arylalkynes in good to excellent yields. The heterogeneous palladium(0) catalyst could easily be prepared via a simple procedure from commercially readily available reagents, and recovered by filtration of the reaction solution and recycled at least 10 times without significant loss of activity.

Full text of DOI:10.1016/j.jorganchem.2017.10.013

Journal of Organometallic Chemistry 852 (2017) 54e63
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
A phosphine-free, atom-efficient cross-coupling of aryl iodides with
triarylindiums or trialkynylindiums catalyzed by immobilization of
palladium(0) in MCM-41
Zhiwei Lei, Haiyi Liu, Mingzhong Cai*
Key Laboratory of Functional Small Organic Molecule, Ministry of Education and College of Chemistry & Chemical Engineering, Jiangxi Normal University,
Nanchang 330022, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The first phosphine-free heterogeneous atom-efficient cross-coupling reaction of aryl iodides with tri-
arylindiums or trialkynylindiums was achieved in THF at 68 ꢀC by using 1 mol% of MCM-41-immobilized
palladium(0)-Schiff base complex [MCM-41-N,N-Pd(0)] as catalyst, yielding a variety of unsymmetrical
biaryls and arylalkynes in good to excellent yields. The heterogeneous palladium(0) catalyst could easily
be prepared via a simple procedure from commercially readily available reagents, and recovered by
filtration of the reaction solution and recycled at least 10 times without significant loss of activity.
© 2017 Published by Elsevier B.V.
Received 4 August 2017
Received in revised form
14 September 2017
Accepted 13 October 2017
Available online 14 October 2017
Keywords:
Cross-coupling
Supported palladium catalyst
Triorganoindium
Biaryl
Arylalkyne
1. Introduction
Organoindium compounds are potentially useful candidates for
environmentally benign reagents since both indium metal and its
Biaryl compounds are widely used as chiral phosphine ligands
[1], monomers of functional polymers [2e4], and as important
building blocks for a large number of natural products, agro-
chemicals, and pharmaceutics [5e9]. Among many methods for
construction of biaryl structures [10], the palladium-catalyzed
cross-coupling reaction of organometallic reagents with aryl ha-
lides or triflates such as the Suzuki-Miyaura [11e13], Stille [14e16],
and Hiyama [17e19] coupling reactions is one of the most impor-
tant synthetic tools for the construction of unsymmetrical biaryls.
Although various organometallic compounds such as organoboron,
-tin, -silicon, -magnesium, and -zinc reagents have been success-
fully used for these cross-coupling reactions, the development of
novel transition-metal-catalyzed cross-coupling reactions with
high degrees of conversion of the organometallic species and high
chemoselectivity is still of great interest. In addition, the minimi-
zation of byproduct formation [20] and the choice of processes with
little or no risk associated to humans or the environment are major
contemporary concerns in the chemistry community [21,22].
derivatives are known to be less toxic or even nontoxic [23,24].
Besides, the byproduct generated after the reaction of organo-
indium compounds, normally indium(III) halides, are also nontoxic.
Triorganoindiums (R3In) can be easily prepared as solutions in THF
by reaction of InCl3 with readily available organolithium or
Grignard reagents [25,26]. Importantly, triorganoindium com-
pounds, unlike organoboron, organotin, and other organometallic
compounds, can react with three equivalents of an electrophilic
reagent [27,28]. Recently, palladium-catalyzed cross-coupling re-
action [29e33] and carbonylative cross-coupling reaction [34,35] of
triorganoindium compounds with a variety of organic electrophiles
for CeC bond formation have been reported. Among the limited
successful examples for the construction of CeC bonds, homoge-
neous palladium complexes such as Pd(PPh3)4, PdCl2(PPh3)2, and
Pd(dppf)Cl2 are usually used as catalysts for these cross-coupling
reactions. However, the problem with homogeneous catalysis is
the difficulty to separate the expensive palladium catalyst from the
reaction mixture and the impossibility to reuse it in consecutive
reactions. In addition, homogeneous catalysis might result in un-
acceptable heavy metal contamination of the desired isolated
product due to the leaching of the metal. These problems may have
* Corresponding author.
E-mail address: caimzhong@163.com (M. Cai).
https://doi.org/10.1016/j.jorganchem.2017.10.013
0022-328X/© 2017 Published by Elsevier B.V.

Z. Lei et al. / Journal of Organometallic Chemistry 852 (2017) 54e63
55
a very serious negative impact on their possible industrial appli-
cations, especially the pharmaceutical industry. In contrast, het-
erogeneous catalysts can be easily separated from the reaction
mixture by a simple filtration of the reaction solution and reused in
successive reactions provided that the active sites have not become
deactivated. Heterogeneous catalysis also helps to reduce wastes
derived from reaction workup, contributing to the development of
green and sustainable chemical processes [36,37]. Therefore, from
the viewpoints of economical and environmental concern, the
development of recyclable immobilized palladium catalysts
showing a high catalytic activity without leaching is highly desir-
able. So far, supported palladium catalysts have successfully been
used for the Heck coupling, the Suzuki-Miyaura coupling, the
Sonogashira coupling, the Hiyama coupling, and the Stille coupling,
etc [38e41]. In spite of the significant advances in this area, to the
best of our knowledge, no example of a heterogeneous palladium-
catalyzed cross-coupling reaction of triorganoindiums with organic
electrophiles has been described until now. The discovery of mes-
oporous MCM-41 materials has provided a new possible candidate
for an ideal solid support to immobilize homogeneous catalysts and
given an enormous stimulus to research in heterogeneous metal
catalysis [42e44]. The hexagonally ordered MCM-41 material
possesses large and uniform pore size, ultrahigh surface area, big
pore volume and rich silanol groups in the inner walls [45]. To date,
some functionalized MCM-41-supported palladium [46e49],
rhodium [50], molybdenum [51,52], gold [53e55] and copper
[56,57] complexes have been successfully used as potentially green
and sustainable catalysts in organic reactions. In continuation of
our efforts to develop greener synthetic pathways for organic
transformations [48,49,55e57], we herein report the synthesis of
an MCM-41-supported palladium(0)-Schiff base complex [MCM-
41-N,N-Pd(0)] and its successful application to the atom-efficient
cross-coupling of aryl iodides with triarylindiums or trialkynylin-
diums leading to unsymmetrical biaryls and arylalkynes in good to
excellent yields (Scheme 1). This new phosphine-free heteroge-
neous palladium(0) catalyst exhibits high catalytic activity in the
reaction and can easily be separated from the reaction mixture by a
simple filtration of the reaction solution, and its catalytic efficiency
remains unaltered even after recycling ten times.
Microanalyses were measured using a Yanaco MT-3 CHN micro-
elemental analyzer. Melting points are uncorrected. Palladium
content was determined with inductively coupled plasma atom
emission Atomscan16 (ICP-AES, TJA Corporation). X-ray powder
diffraction was obtained on DamaxegA (Rigaku). The BET surface
area and pore analysis were performed on ASAP2010 (micro-
meritics) by N2 physical adsorption-desorption at 77.4 K. X-ray
photoelectron spectra was recorded on XSAM 800 (Kratos).
2.2. Preparation of MCM-41-N,N-Pd(0) complex
A solution of 2.2 g of 3-aminopropyltriethoxysilane in 15 mL of
dry chloroform was added to a suspension of 2.8 g of the MCM-41 in
180 mL of dry toluene. The mixture was stirred for 24 h at 100 ꢀC.
Then the solid was filtered and washed by CHCl3 (2 ꢁ 20 mL), and
dried in vacuum at 160 ꢀC for 5 h. The product was then soaked in a
solution of 4.5 g of Me3SiCl in 80 mL of dry toluene at room tem-
perature under stirring for 24 h. Then the solid was filtered, washed
with acetone (3 ꢁ 20 mL) and diethyl ether (3 ꢁ 20 mL), and dried
in vacuum at 120 ꢀC for 5 h. The dried white solid (3.3 g) was then
reacted with pyridine-2-carboxaldehyde (0.502 g, 4.7 mmol) in
20 mL of dry ethanol at 80 ꢀC for 12 h. The solid product was
filtered, washed with ethanol (3 ꢁ 20 mL) and diethyl ether
(20 mL), and dried in vacuum at 120 ꢀC for 5 h to obtain 3.45 g of
hybrid material MCM-41-N,N. The nitrogen content was found to
be 2.42 mmol/g by elemental analysis.
In a small Schlenk tube, 2.50 g of the above-functionalized
MCM-41 material (MCM-41-N,N) was mixed with 0.216
g
(1.22 mmol) of PdCl2 in 50 mL of dry acetone. The mixture was
refluxed for 72 h under an argon atmosphere. The solid product was
filtered by suction, washed with acetone, distilled water and
acetone successively and dried under vacuum at 80 ꢀC for 5 h to
give 2.63 g of a light yellow palladium(II) complex [MCM-41-N,N-
PdCl2]. The mixture of MCM-41-N,N-PdCl2 (2.2 g) and hydrazine
hydrate (1.5 g) in EtOH (30 mL) was then stirred at 30 ꢀC for 3 h
under Ar. The resulting product was filtered, washed with EtOH
(3 ꢁ 20 mL) and Et2O (2 ꢁ 20 mL) and dried under vacuum at 60 ꢀC
for 3 h to afford 2.15 g of the MCM-41-N,N-Pd(0) complex as a gray
powder. The nitrogen and palladium content was found to be
2.27 mmol/g and 0.42 mmol/g, respectively.
2. Experimental
2.1. General remarks
2.3. General procedure for preparation of triarylindium and
trialkynylindium reagents
All chemicals were reagent grade and used as purchased. The
mesoporous material MCM-41 [45] and triorganoindium com-
pounds [26] were prepared according to literature methods. The
products were purified by flash chromatography on silica gel. Light
petroleum ether (30e60 ꢀC) or a mixture of light petroleum ether
and ethyl acetate was generally used as eluent. All products were
characterized by comparison of their spectra and physical data with
authentic samples. 1H NMR spectra were recorded on a Bruker
Avance 400 (400 MHz) spectrometer with TMS as an internal
standard in CDCl3 as solvent. 13C NMR spectra were recorded on a
Bruker Avance 400 (100 MHz) spectrometer in CDCl3 as solvent.
A 25 mL round-bottomed flask containing a stirrer bar was
charged with InCl3 (0.37 mmol) and dried under vacuum with a
heat gun. The flask was cooled, a positive argon pressure was
established and anhydrous THF (2 mL) was added. The resulting
solution was cooled to ꢂ78 ꢀC and a solution of ArMgBr or
RC≡CMgBr (1.1 mmol, 1.5 M in THF) was slowly added (15e30 min).
The reaction mixture was stirred for 30 min, the cooling bath was
removed, and the mixture was warmed to room temperature over
30 min.
Scheme 1. Heterogeneous phosphine-free palladium(0)-catalyzed cross-coupling of aryl iodides with triarylindiums or trialkynylindiums.

56
Z. Lei et al. / Journal of Organometallic Chemistry 852 (2017) 54e63
2.4. General procedure for the heterogeneous palladium(0)-
catalyzed cross-coupling of aryl iodides with triarylindiums or
trialkynylindiums
NMR (100 MHz, CDCl3):
128.3, 127.3, 127.2, 26.7.
d
¼ 197.8, 145.8, 139.9, 135.9, 129.0, 128.9,
2.4.9. 4-Nitrobiphenyl, 3i [59]
A solution of Ar3In or (RC≡C)3In (0.37 mmol, ca. 0.18 M in dry
THF) was added to a mixture of MCM-41-N,N-Pd(0) (25 mg,1 mol%)
and aryl iodide (1 mmol) in dry THF (2 mL) under Ar. The resulting
mixture was refluxed under Ar until the starting material had been
consumed (TLC). After being cooled to room temperature, the
mixture was diluted with Et2O (30 mL) and filtered. The palladium
catalyst was washed with DMF (2 ꢁ 5 mL), Et2O (2 ꢁ 5 mL) and
reused in the next run. The filtrate was washed with sat. aq NaHCO3
(5 mL), water (3 ꢁ 10 mL) and dried over MgSO4, filtered, and
concentrated under vacuum. The residue was purified by flash
chromatography on silica gel to give the desired cross-coupling
product.
Yellow solid, m.p.: 112e113 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 8.29 (d, J ¼ 8.4 Hz, 2H), 7.73 (d, J ¼ 8.4 Hz, 2H), 7.63 (d, J ¼ 8.0 Hz,
2H), 7.53e7.44 (m, 3H); 13C NMR (100 MHz, CDCl3):
138.8, 129.2, 129.0, 127.8, 127.4, 124.1.
d
¼ 147.7, 147.1,
2.4.10. 4-Bromobiphenyl, 3j [59]
White solid, m.p.: 88e89 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 7.59
(d, J ¼ 7.2 Hz, 2H), 7.54 (d, J ¼ 7.2 Hz, 2H), 7.46e7.32 (m, 5H); 13C
NMR (100 MHz, CDCl3):
127.0, 121.6.
d
¼ 140.2, 140.0, 131.9, 129.0, 128.8, 127.7,
2.4.11. 2-Methylbiphenyl, 3k [58]
Colorless oil. 1H NMR (400 MHz, CDCl3):
d
¼ 7.39 (t, J ¼ 7.6 Hz,
2.4.1. Biphenyl, 3a [58]
2H), 7.35e7.29 (m, 3H), 7.28e7.20 (m, 4H), 2.26 (s, 3H); 13C NMR
White solid, m.p.: 69e70 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 7.59
(100 MHz, CDCl3):
126.9, 126.8, 125.8, 20.6.
d
¼ 142.0, 135.4, 130.4, 129.9, 129.3, 128.1, 127.3,
(d, J ¼ 7.6 Hz, 4H), 7.44 (t, J ¼ 7.8 Hz, 4H), 7.35 (t, J ¼ 7.4 Hz, 2H); 13
C
NMR (100 MHz, CDCl3):
d
¼ 141.3, 128.8, 127.3, 127.2.
2.4.12. 1-Phenylnaphthalene, 3l [59]
2.4.2. 4-Methylbiphenyl, 3b [58]
Colorless oil. 1H NMR (400 MHz, CDCl3):
d
¼ 7.91e7.80 (m, 3H),
White solid, m.p.: 47 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 7.57 (t,
7.55e7.36 (m, 9H); 13C NMR (100 MHz, CDCl3):
d
¼ 140.9, 140.4,
J ¼ 8.0 Hz, 2H), 7.48 (d, J ¼ 8.0 Hz, 2H), 7.42 (d, J ¼ 8.0 Hz, 2H), 7.31 (t,
133.9, 131.7, 130.2, 128.8, 128.4, 127.8, 127.4, 127.3, 127.1, 126.1, 125.9,
125.5.
J ¼ 8.0 Hz, 1H), 7.23 (d, J ¼ 8.0 Hz, 2H), 2.38 (s, 3H); 13C NMR
(100 MHz, CDCl3):
126.9, 21.1.
d
¼ 141.2, 138.4, 137.1, 129.5, 128.8, 127.1, 127.0,
2.4.13. 2-Phenylthiophene, 3m [60]
White solid, m.p.: 36e37 ꢀC. 1H NMR (400 MHz, CDCl3):
2.4.3. 3-Methylbiphenyl, 3c [58]
d
¼ 7.59e7.55 (m, 2H), 7.35e7.18 (m, 5H), 7.04e7.01 (m, 1H); 13C
Colorless oil. 1H NMR (400 MHz, CDCl3):
d
¼ 7.58 (d, J ¼ 7.2 Hz,
NMR (100 MHz, CDCl3):
124.9, 123.2.
d
¼ 144.6, 134.5, 129.0, 128.2, 127.6, 126.1,
2H), 7.46e7.29 (m, 6H), 7.16 (d, J ¼ 7.2 Hz, 1H), 2.42 (s, 3H); 13C NMR
(100 MHz, CDCl3):
127.2, 124.3, 21.6.
d
¼ 141.4, 141.3, 138.3, 128.8, 128.7, 128.6, 128.0,
2.4.14. 2-Phenylpyridine, 3n [60]
Colorless oil. 1H NMR (400 MHz, CDCl3):
d
¼ 8.67 (t, J ¼ 1.2 Hz,
2.4.4. 4-Methoxybiphenyl, 3d [58]
1H), 8.01e7.96 (m, 2H), 7.71e7.66 (m, 2H), 7.48e7.36 (m, 3H),
White solid, m.p.: 89e90 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 7.55
7.20e7.15 (m, 1H); 13C NMR (100 MHz, CDCl3):
d
¼ 157.5, 149.7,
(d, J ¼ 7.6 Hz, 2H), 7.53 (d, J ¼ 8.8 Hz, 2H), 7.42 (t, J ¼ 7.6 Hz, 2H), 7.30
139.4, 136.8, 129.0, 128.8, 126.9, 122.1, 120.6.
(t, J ¼ 7.2 Hz, 1H), 6.98 (d, J ¼ 8.8 Hz, 2H), 3.85 (s, 3H). 13C NMR
(100 MHz, CDCl3):
114.2, 55.4.
d
¼ 159.1, 140.8, 133.8, 128.7, 128.2, 126.8, 126.7,
2.4.15. 4-Acetyl-40-methylbiphenyl, 3o [58]
White solid, m.p.: 102e103 ꢀC. 1H NMR (400 MHz, CDCl3):
¼ 8.00 (d, J ¼ 8.0 Hz, 2H), 7.65 (d, J ¼ 8.0 Hz, 2H), 7.52 (d, J ¼ 7.6 Hz,
d
2.4.5. 4-Methoxycarbonylbiphenyl, 3e [59]
2H), 7.27 (d, J ¼ 7.6 Hz, 2H), 2.62 (s, 3H), 2.40 (s, 3H); 13C NMR
White solid, m.p.: 115e116 ꢀC. 1H NMR (400 MHz, CDCl3):
(100 MHz, CDCl3):
127.1, 126.9, 26.6, 21.2.
d
¼ 197.7, 145.7, 138.2, 136.9, 135.6, 129.7, 128.9,
d
¼ 8.11 (d, J ¼ 8.0 Hz, 2H), 7.66 (d, J ¼ 8.0 Hz, 2H), 7.62 (d, J ¼ 8.0 Hz,
2H), 7.47 (t, J ¼ 7.6 Hz, 2H), 7.39 (t, J ¼ 7.6 Hz, 1H), 3.94 (s, 3H); 13
C
NMR (100 MHz, CDCl3):
128.2, 127.3, 127.1, 52.2.
d
¼ 167.0, 145.7, 140.0, 130.1, 129.0, 128.9,
2.4.16. 4-Cyano-40-methylbiphenyl, 3p [58]
White solid, 106e108 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 7.68 (d,
J ¼ 8.4 Hz, 2H), 7.64 (d, J ¼ 8.4 Hz, 2H), 7.49 (d, J ¼ 8.0 Hz, 2H), 7.29
2.4.6. 4-Chlorobiphenyl, 3f [58]
(d, J ¼ 8.0 Hz, 2H), 2.41 (s, 3H); 13C NMR (100 MHz, CDCl3):
White solid, m.p.: 76e77 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 7.55
d
¼ 145.6, 138.8, 136.3, 132.6, 129.8, 127.5, 127.1, 119.1, 110.5, 21.2.
(d, J ¼ 7.6 Hz, 2H), 7.52 (d, J ¼ 8.4 Hz, 2H), 7.46e7.34 (m, 5H); 13C
NMR (100 MHz, CDCl3):
127.6, 127.0.
d
¼ 140.0, 139.7, 133.4, 128.9, 128.8, 128.4,
2.4.17. 4-Methyl-40-nitrobiphenyl, 3q [60]
Yellow solid, m.p.: 142e144 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 8.27 (d, J ¼ 8.4 Hz, 2H), 7.71 (d, J ¼ 8.4 Hz, 2H), 7.52 (d, J ¼ 8.4 Hz,
2.4.7. 4-Cyanobiphenyl, 3g [58]
2H), 7.30 (d, J ¼ 8.4 Hz, 2H), 2.42 (s, 3H); 13C NMR (100 MHz, CDCl3):
White solid, m.p.: 86e87 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 7.70
d
¼ 147.6, 146.9, 139.1, 135.9, 129.9, 127.5, 127.2, 124.1, 21.3.
(d, J ¼ 8.4 Hz, 2H), 7.66 (d, J ¼ 8.4 Hz, 2H), 7.58 (d, J ¼ 8.0 Hz, 2H),
7.48 (t, J ¼ 7.6 Hz, 2H), 7.41 (t, J ¼ 7.6 Hz, 1H); 13C NMR (100 MHz,
2.4.18. 4-Methyl-20-methylbiphenyl, 3r [60]
CDCl3):
d
¼ 145.6, 139.1, 132.6, 129.1, 128.7, 127.7, 127.2, 119.0, 110.9.
Colorless oil. 1H NMR (400 MHz, CDCl3):
d
¼ 7.26e7.13 (m, 8H),
2.39 (s, 3H), 2.27 (s, 3H); 13C NMR (100 MHz, CDCl3):
d
¼ 142.0,
2.4.8. 4-Acetylbiphenyl, 3h [59]
139.1, 136.4, 135.5, 130.4, 129.9, 129.2, 128.9, 127.1, 125.8, 21.2, 20.6.
White solid, m.p.: 118e119 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 8.03 (d, J ¼ 8.0 Hz, 2H), 7.68 (d, J ¼ 8.0 Hz, 2H), 7.62 (d, J ¼ 7.6 Hz,
2.4.19. 2-(4-Methylphenyl)thiophene, 3s [60]
2H), 7.47 (t, J ¼ 7.6 Hz, 2H), 7.40 (t, J ¼ 7.6 Hz, 1H), 2.64 (s, 3H); 13
C
White solid, m.p.: 63e64 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 7.50

Z. Lei et al. / Journal of Organometallic Chemistry 852 (2017) 54e63
57
(d, J ¼ 8.0 Hz, 2H), 7.27e7.21 (m, 2H), 7.18 (d, J ¼ 8.0 Hz, 2H), 7.06 (t,
d
¼ 7.53e7.51 (m, 2H), 7.42 (d, J ¼ 8.0 Hz, 2H), 7.36e7.27 (m, 3H),
J ¼ 4.4 Hz, 1H), 2.36 (s, 3H); 13C NMR (100 MHz, CDCl3):
d
¼ 144.6,
7.14 (d, J ¼ 8.0 Hz, 2H), 2.36 (s, 3H); 13C NMR (100 MHz, CDCl3):
137.3, 131.7, 129.6, 127.9, 125.9, 124.3, 122.6, 21.2.
d
¼ 138.4, 131.6, 131.5, 129.1, 128.3, 128.1, 123.5, 120.2, 89.6, 88.7,
21.5.
2.4.20. 2-(4-Methylphenyl)pyridine, 3t [60]
Colorless oil. 1H NMR (400 MHz, CDCl3):
d
¼ 8.66e8.64 (m, 1H),
2.4.31. 1-(4-Methoxyphenyl)-2-phenylethyne, 4d [61]
White solid, m.p.: 58e59 ꢀC. 1H NMR (400 MHz, CDCl3):
7.88 (d, J ¼ 7.2 Hz, 2H), 7.65 (t, J ¼ 2.8 Hz, 2H), 7.26e7.22 (m, 2H),
7.16e7.11 (m,1H), 2.37 (s, 3H); 13C NMR (100 MHz, CDCl3):
d
¼ 157.5,
d
¼ 7.52e7.43 (m, 4H), 7.32e7.29 (m, 3H), 6.86e6.83 (m, 2H), 3.76
(s, 3H); 13C NMR (100 MHz, CDCl3):
d
¼ 159.5, 133.0, 131.4, 128.3,
149.7, 149.6, 138.9, 136.7, 129.5, 126.8, 121.8, 120.2, 21.3.
127.9, 123.4, 115.5, 113.9, 89.4, 88.1, 55.2.
2.4.21. 4-Chloro-40-cyanobiphenyl, 3u [58]
White solid, m.p.: 130e131 ꢀC. 1H NMR (400 MHz, CDCl3):
¼ 7.73 (d, J ¼ 8.0 Hz, 2H), 7.65 (d, J ¼ 7.6 Hz, 2H), 7.52 (d, J ¼ 8.0 Hz,
2.4.32. 1-(4-Chlorophenyl)-2-phenylethyne, 4e [62]
White solid, m.p.: 82e83 ꢀC. 1H NMR (400 MHz, CDCl3):
d
2H), 7.45 (d, J ¼ 7.6 Hz, 2H); 13C NMR (100 MHz, CDCl3):
d
¼ 144.4,
d
¼ 7.54e7.51 (m, 2H), 7.46 (d, J ¼ 8.4 Hz, 2H), 7.36e7.31 (m, 5H); 13
C
137.6, 135.0, 132.7, 129.3, 128.5, 127.6, 118.8, 111.3.
NMR (100 MHz, CDCl3):
122.9, 121.8, 90.3, 88.2.
d
¼ 134.3, 132.8, 131.6, 128.7, 128.5, 128.4,
2.4.22. 4-Acetyl-40-chlorobiphenyl, 3v [59]
White solid, m.p.: 101e102 ꢀC. 1H NMR (400 MHz, CDCl3):
¼ 8.03 (d, J ¼ 8.4 Hz, 2H), 7.64 (d, J ¼ 8.4 Hz, 2H), 7.55 (d, J ¼ 8.0 Hz,
2.4.33. 1-(4-Acetylphenyl)-2-phenylethyne, 4f [61]
White solid, m.p.: 98e99 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 7.95
d
2H), 7.43 (d, J ¼ 8.0 Hz, 2H), 2.64 (s, 3H); 13C NMR (100 MHz, CDCl3):
(d, J ¼ 8.0 Hz, 2H), 7.61 (d, J ¼ 8.0 Hz, 2H), 7.55 (d, J ¼ 8.4 Hz, 2H),
7.38e7.36 (m, 3H), 2.62 (s, 3H); 13C NMR (100 MHz, CDCl3):
d
¼ 197.6, 144.4, 138.3, 136.0, 134.4, 129.1, 129.0, 128.5, 127.0, 26.7.
d
¼ 197.3, 136.2, 131.8, 131.7, 128.8, 128.5, 128.3, 128.2, 122.7, 92.7,
2.4.23. 4,40-Dichlorobiphenyl, 3w [60]
88.6, 26.6.
White solid, m.p.: 148e149 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 7.46 (d, J ¼ 8.0 Hz, 4H), 7.39 (d, J ¼ 8.0 Hz, 4H); 13C NMR
2.4.34. Methyl 4-(phenylethynyl)benzoate, 4g [61]
(100 MHz, CDCl3):
d
¼ 138.4, 133.8, 129.1, 128.2.
White solid, m.p.: 119e120 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 8.04e8.02 (m, 2H), 7.61e7.58 (m, 2H), 7.56e7.54 (m, 2H),
2.4.24. 4-Chloro-40-methylbiphenyl, 3x [60]
7.38e7.36 (m, 3H), 3.93 (s, 3H); 13C NMR (100 MHz, CDCl3):
White solid, 121e123 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 7.49 (d,
d
¼ 166.6, 131.8, 131.5, 129.5, 129.4, 128.8, 128.5, 128.0, 122.7, 92.4,
J ¼ 8.4 Hz, 2H), 7.45 (d, J ¼ 8.0 Hz, 2H), 7.38 (d, J ¼ 8.0 Hz, 2H), 7.24
88.6, 52.3.
(d, J ¼ 7.6 Hz, 2H), 2.39 (s, 3H); 13C NMR (100 MHz, CDCl3):
d
¼ 139.6, 137.4, 137.1, 133.0, 129.6, 128.8, 128.2, 126.8, 21.1.
2.4.35. 1-(3-Cyanophenyl)-2-phenylethyne, 4h [62]
White solid, m.p.: 71e72 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 7.77
2.4.25. 4-Chloro-20-methylbiphenyl, 3y [58]
(t, J ¼ 1.2 Hz, 1H), 7.72e7.69 (m, 1H), 7.58e7.51 (m, 3H), 7.43 (t,
Colorless oil. 1H NMR (400 MHz, CDCl3):
d
¼ 7.37 (dd, J ¼ 8.4,
J ¼ 7.6 Hz, 1H), 7.39e7.33 (m, 3H); 13C NMR (100 MHz, CDCl3):
1.6 Hz, 2H), 7.27e7.15 (m, 6H), 2.25 (s, 3H); 13C NMR (100 MHz,
d
¼ 135.7, 134.9, 131.8, 131.4, 129.3, 129.0, 128.5, 124.9, 122.3, 118.2,
CDCl3):
125.9, 20.4.
d
¼ 140.7, 140.4, 135.3,132.8, 130.5,130.4, 129.7, 128.3, 127.6,
112.9, 91.9, 87.0.
2.4.36. 1-(4-Bromophenyl)-2-phenylethyne, 4i
2.4.26. 2-(4-Chlorophenyl)thiophene, 3z [60]
White solid, m.p.: 87e88 ꢀC. 1H NMR (400 MHz, CDCl3):
White solid, m.p.: 82e83 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 7.55e7.51 (m, 2H), 7.37e7.23 (m, 4H), 7.10e7.05 (m, 1H); 13C
d
¼ 7.54e7.50 (m, 2H), 7.48 (d, J ¼ 8.4 Hz, 2H), 7.38 (d, J ¼ 8.4 Hz,
2H), 7.36e7.32 (m, 3H); 13C NMR (100 MHz, CDCl3):
¼ 133.1, 131.7,
131.6, 128.5, 128.4, 122.9, 122.5, 122.3, 90.5, 88.3. Anal. Calcd. for
14H9Br: C, 65.40; H, 3.53. Found: C, 65.13; H, 3.28.
d
NMR (100 MHz, CDCl3):
d
¼ 143.1, 133.2, 133.0, 129.0, 128.2, 127.1,
125.2, 123.4.
C
2.4.27. 2-(4-Chlorophenyl)pyridine, 3a' [60]
Colorless oil. 1H NMR (400 MHz, CDCl3):
d
¼ 8.69e8.66 (m, 1H),
2.4.37. 1-Phenyl-2-(2-trifluoromethylphenyl)ethyne, 4j [62]
Colorless oil. 1H NMR (400 MHz, CDCl3):
¼ 7.70e7.66 (m, 2H),
7.59e7.51 (m, 3H), 7.44e7.35 (m, 4H); 13C NMR (100 MHz, CDCl3):
d
7.93 (dd, J ¼ 8.6, 2.2 Hz, 2H), 7.78e7.65 (m, 2H), 7.43 (dd, J ¼ 8.4,
2.4 Hz, 2H), 7.26e7.21 (m, 1H); 13C NMR (100 MHz, CDCl3):
d
¼ 133.7, 131.7, 131.4, 128.8, 128.4, 127.9, 125.9, 125.0, 122.8, 122.2,
d
¼ 156.2, 149.5, 137.8, 136.9, 135.1, 128.9, 128.2, 122.4, 120.3.
121.6, 94.9, 85.4.
2.4.28. 1,2-Diphenylethyne, 4a [61]
White solid, m.p.: 60e61 ꢀC. 1H NMR (400 MHz, CDCl3):
2.4.38. 1-Phenyl-1-hexyne, 4k [61]
Colorless oil. 1H NMR (400 MHz, CDCl3):
d
¼ 7.40e7.38 (m, 2H),
d
¼ 7.55e7.52 (m, 4H), 7.38e7.31 (m, 6H); 13C NMR (100 MHz,
7.29e7.26 (m, 3H), 2.41 (t, J ¼ 7.2 Hz, 2H), 1.62e1.56 (m, 2H),
CDCl3):
d
¼ 131.6, 128.4, 128.3, 123.3, 89.4.
1.53e1.46 (m, 2H), 0.95 (t, J ¼ 7.2 Hz, 3H); 13C NMR (100 MHz,
CDCl3):
d
¼ 131.6, 128.2, 127.5, 124.2, 90.4, 80.6, 30.9, 22.0, 19.1, 13.7.
2.4.29. 1-(3-Methylphenyl)-2-phenylethyne, 4b
Colorless oil. 1H NMR (400 MHz, CDCl3):
¼ 7.46e7.43 (m, 2H),
7.29e7.22 (m, 5H), 7.15 (t, J ¼ 7.6 Hz,1H), 7.06 (d, J ¼ 7.6 Hz,1H), 2.27
(s, 3H); 13C NMR (100 MHz, CDCl3):
128.7, 128.4, 128.3, 128.2, 123.5, 123.1, 89.6, 89.1, 21.3. Anal. Calcd.
for C15H12: C, 93.71; H, 6.29. Found: C, 93.48; H, 6.36.
d
2.4.39. 1-(3-Methylphenyl)-1-hexyne, 4l
d
¼ 138.0, 132.2, 131.6, 129.2,
Colorless oil. 1H NMR (400 MHz, CDCl3):
d
¼ 7.22e7.13 (m, 3H),
7.06 (d, J ¼ 7.6 Hz, 1H), 2.40 (t, J ¼ 7.2 Hz, 2H), 2.30 (s, 3H), 1.60e1.54
(m, 2H), 1.51e1.39 (m, 2H), 0.94 (t, J ¼ 7.2 Hz, 3H); 13C NMR
(100 MHz, CDCl3):
80.7, 30.9, 22.1, 21.2, 19.1, 13.7. Anal. Calcd. for C13H16: C, 90.64; H,
9.36. Found: C, 90.37; H, 9.19.
d
¼ 137.8, 132.2, 128.6, 128.4, 128.1, 123.9, 90.0,
2.4.30. 1-(4-Methylphenyl)-2-phenylethyne, 4c [61]
White solid, m.p.: 73e74 ꢀC. 1H NMR (400 MHz, CDCl3):

58
Z. Lei et al. / Journal of Organometallic Chemistry 852 (2017) 54e63
2.4.40. 1-(3-Cyanophenyl)-1-hexyne, 4m [62]
2H), 7.26 (d, J ¼ 8.4 Hz, 2H), 0.24 (s, 9H); 13C NMR (100 MHz, CDCl3):
Colorless oil. 1H NMR (400 MHz, CDCl3):
d
¼ 7.66 (s, 1H),
d
¼ 134.6, 133.2, 128.6, 121.7, 103.9, 95.4, ꢂ0.1.
7.60e7.53 (m, 2H), 7.39 (t, J ¼ 7.6 Hz, 1H), 2.42 (t, J ¼ 7.2 Hz, 2H),
1.61e1.56 (m, 2H), 1.50e1.45 (m, 2H), 0.96 (t, J ¼ 7.2 Hz, 3H); 13C
2.4.47. 1-(4-Bromophenyl)-2-trimethylsilylethyne, 4t
Colorless oil. 1H NMR (400 MHz, CDCl3):
d
¼ 7.45 (d, J ¼ 8.4 Hz,
NMR (100 MHz, CDCl3):
112.6, 93.4, 78.5, 30.5, 22.0, 19.1, 13.7.
d
¼ 135.7, 135.0, 130.7, 129.1, 125.7, 118.3,
2H), 7.34 (d, J ¼ 8.4 Hz, 2H), 0.28 (s, 9H); 13C NMR (100 MHz, CDCl3):
d
¼ 133.5, 131.6, 122.9, 122.2, 104.0, 95.7, 0.0. Anal. Calcd. for
2.4.41. 1-(4-Nitrophenyl)-1-hexyne, 4n [61]
C
11H13BrSi: C, 52.18; H, 5.17. Found: C, 51.92; H, 5.28.
Yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼ 8.15 (d, J ¼ 8.8 Hz, 2H),
7.52 (d, J ¼ 8.8 Hz, 2H), 2.46 (t, J ¼ 7.2 Hz, 2H), 1.63e1.57 (m, 2H),
3. Results and discussion
1.51e1.46 (m, 2H), 0.96 (t, J ¼ 7.2 Hz, 3H); 13C NMR (100 MHz,
CDCl3):
d
¼ 146.5, 132.3, 131.2, 123.5, 96.8, 79.3, 30.5, 22.1, 19.3, 13.6.
3.1. Synthesis and characterization of MCM-41-N,N-Pd(0) complex
2.4.42. 1-(2-Trifluoromethylphenyl)-1-hexyne, 4o [62]
Colorless oil. 1H NMR (400 MHz, CDCl3):
Although phosphine ligands stabilize palladium and influence
its catalytic activity, undoubtedly, the simplest and cheapest
palladium catalysts are still the phosphine-free systems. Further-
more, the procedure for the synthesis of immobilized phosphine
palladium complexes is rather complicated since the preparation of
the heterogeneous phosphine ligands requires multi-step se-
quences. Therefore, the development of phosphine-free supported
palladium complex catalysts having a high activity and good sta-
bility is a topic of enormous importance. The MCM-41-immobilized
palladium(0)-Schiff base complex [MCM-41-N,N-Pd(0)] could
easily be prepared starting from mesoporous material MCM-41 and
commercially available 3-aminopropyltriethoxysilane, pyridine-
2-carboxaldehyde, PdCl2, and hydrazine hydrate as shown in
Scheme 2. Firstly, the MCM-41 was condensed with 3-
aminopropyltriethoxysilane in toluene at 100 ꢀC for 24 h, fol-
lowed by the silylation with Me3SiCl in toluene at room tempera-
ture for 24 h to give 3-aminopropyl-functionalized MCM-41
material (MCM-41-NH2). The latter was subsequently treated
with pyridine-2-carboxaldehyde in dry EtOH at 80 ꢀC for 12 h to
afford the Schiff base-functionalized MCM-41 (MCM-41-N,N),
which was then reacted with PdCl2 in acetone under reflux for 72 h
to generate the MCM-41-immobilized palladium(II)-Schiff base
complex [MCM-41-N,N-PdCl2] as a light yellow powder. Finally, the
treatment of MCM-41-N,N-PdCl2 with hydrazine hydrate in EtOH at
30 ꢀC for 3 h afforded the MCM-41-immobilized palladium(0)-
Schiff base complex [MCM-41-N,N-Pd(0)] as a gray powder.
d
¼ 7.61 (d, J ¼ 7.6 Hz,
1H), 7.52 (d, J ¼ 7.6 Hz, 1H), 7.44 (t, J ¼ 7.6 Hz, 1H), 7.34 (t, J ¼ 7.6 Hz,
1H), 2.45 (t, J ¼ 7.2 Hz, 2H), 1.62e1.57 (m, 2H), 1.52e1.46 (m, 2H),
0.95 (t, J ¼ 7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3):
¼ 133.9, 131.6,
d
131.3, 127.2, 125.7, 125.0, 122.4, 96.7, 77.5, 30.5, 21.9, 19.3, 13.6.
2.4.43. 1-Phenyl-2-trimethylsilylethyne, 4p [62]
Colorless oil. 1H NMR (400 MHz, CDCl3):
d
¼ 7.48e7.45 (m, 2H),
7.31e7.29 (m, 3H), 0.25 (s, 9H); 13C NMR (100 MHz, CDCl3):
¼ 132.0, 128.5, 128.2, 123.1, 105.1, 94.1, 0.0.
d
2.4.44. 1-(3-Methylphenyl)-2-trimethylsilylethyne, 4q
Colorless oil. 1H NMR (400 MHz, CDCl3):
¼ 7.34e7.27 (m, 2H),
7.21 (t, J ¼ 7.4 Hz, 1H), 7.15 (d, J ¼ 7.6 Hz, 1H), 2.34 (s, 3H), 0.27 (s,
9H); 13C NMR (100 MHz, CDCl3):
d
d
¼ 137.9, 132.6, 129.4, 129.0, 128.1,
122.9, 105.3, 93.7, 21.2, 0.0. Anal. Calcd. for C12H16Si: C, 76.53; H,
8.56. Found: C, 76.24; H, 8.38.
2.4.45. 1-(4-Methoxyphenyl)-2-trimethylsilylethyne, 4r [62]
Colorless oil. 1H NMR (400 MHz, CDCl3):
d
¼ 7.41 (d, J ¼ 8.8 Hz,
2H), 6.81 (d, J ¼ 8.8 Hz, 2H), 3.81 (s, 3H), 0.24 (s, 9H); 13C NMR
(100 MHz, CDCl3):
d
¼ 159.7, 133.5, 115.3, 113.8, 105.2, 92.5, 55.3, 0.1.
2.4.46. 1-(4-Chlorophenyl)-2-trimethylsilylethyne, 4s [62]
Colorless oil. 1H NMR (400 MHz, CDCl3):
¼ 7.38 (d, J ¼ 8.4 Hz,
d
Scheme 2. Synthesis of MCM-41-N,N-Pd(0) complex.

Z. Lei et al. / Journal of Organometallic Chemistry 852 (2017) 54e63
59
Table 2
The small angle X-ray powder diffraction (XRD) patterns of the
XPS data for MCM-41-N,N-Pd(0), MCM-41-N,N-PdCl2, MCM-41-N,N and PdCl2.a
parent MCM-41 and the MCM-41-N,N-Pd(0) complex are illus-
trated in Fig. 1. Small angle X-ray diffraction of the parent MCM-41
gave three peaks corresponding to hexagonally ordered meso-
porous phases [45]. For the MCM-41-N,N-Pd(0), the (100) reflection
of the parent MCM-41 with decreased intensity was remained after
functionalization, while the (110) and (200) reflections became
weak and diffuse, which may be mainly due to contrast matching
between the silicate framework and organic moieties which are
located inside the channels of MCM-41. These results indicate that
the structure of the mesoporous MCM-41 remains unchanged
through the grafting procedure and the formation of the catalyst
has taken place preferentially inside the pore system of MCM-41.
The nitrogen adsorption studies demonstrated that a significant
decrease in pore size by virtue of silylation of the MCM-41 channels
was observed. Additionally, upon modification the surface area and
pore volume decreased obviously. These results are in good
agreement with the fact that the surface modification indeed
occurred inside the primary mesopores of the parent MCM-41. The
results in detail are summarized in Table 1. Elemental analyses and
X-ray photoelectron spectroscopy (XPS) were also used to charac-
terize the MCM-41-immobilized palladium(0)-Schiff base complex.
The N: Pd mole ratio of the MCM-41-N,N-Pd(0) was determined to
be 5.4. The XPS data for MCM-41-N,N-Pd(0), MCM-41-N,N-PdCl2,
MCM-41-N,N, and PdCl2 are listed in Table 2. It can be seen that the
binding energies of Si2p and O1s of MCM-41-N,N-PdCl2 are similar
to those of MCM-41-N,N, and the binding energy of Cl2p of MCM-
41-N,N-PdCl2 is similar to that of PdCl2. However the difference of
N1s binding energies between MCM-41-N,N-PdCl2 and MCM-41-
N,N is 1.0 eV. The difference of Pd3d5/2 binding energies between
MCM-41-N,N-PdCl2 and PdCl2 is 0.9 eV. These results suggest that a
coordination bond between N and Pd is formed in MCM-41-N,N-
Sample
Pd3d5/2
N1s
Si2p
O1s
Cl2p
MCM-41-N,N-Pd(0)
MCM-41-N,N-PdCl2
MCM-41-N,N
PdCl2
336.3
337.4
400.9
400.8
399.8
103.4
103.3
103.4
533.1
533.1
533.2
199.3
199.2
338.3
a
The binding energies are referenced to C1s (284.6 eV) and the energy differences
were determined with an accuracy of 0.2 eV.
PdCl2. The binding energy (336.3 eV) of Pd3d5/2 of MCM-41-N,N-
Pd(0) was lower than the binding energy (337.4 eV) of Pd3d5/2 of
MCM-41-N,N-PdCl2. The Pd3d5/2 binding energy depends strongly
on the nature of the ligands. Consequently, it is impossible to
identify the reduced complex as a zerovalent one on the basis of its
Pd3d5/2 binding energy only. However, the binding energy of Cl2p in
MCM-41-N,N-Pd(0) cannot be detected, the shift (lower) of Pd3d5/2
binding energy together with the change in color from light yellow
to gray suggests that the reduction of the starting palladium(II)
complex to the lower valent state has taken place.
3.2. Heterogeneous phosphine-free palladium(0)-catalyzed cross-
couplings of aryl iodides with triarylindiums or trialkynylindiums
The MCM-41-supported palladium(0)-Schiff base complex
[MCM-41-N,N-Pd(0)] was then used as catalyst for the cross-
coupling reaction of aryl iodides with triarylindiums. Initial ex-
periments with triphenylindium (1a) and iodobenzene (2a) were
performed to optimize the reaction conditions, and the results
are summarized in Table 3. First, the effect of various supported
palladium complexes on the model reaction was examined in THF
Table 3
Reaction condition screening for the coupling reaction of Ph3In (0.37 equiv) with
iodobenzene.a
Entry
Palladium catalyst
Temp. (ꢀC)
Time (h)
Isolated yield (%)
1
2
3
4
5
6
MCM-41-N,N-PdCl2
MCM-41-N,N-Pd(0)
MCM-41-S-Pd(0)
e
68
68
68
68
68
25
50
68
68
3
2
3
12
2
12
10
4
79
91
75
0
92
trace
73
78
92
PdCl2(PPh3)2
MCM-41-N,N-Pd(0)
MCM-41-N,N-Pd(0)
MCM-41-N,N-Pd(0)
MCM-41-N,N-Pd(0)
7
8b
9c
1
a
All reactions were performed using 1.0 mmol of iodobenzene, 0.37 mmol of
Ph3In, 1 mol% of palladium catalyst in 4.0 mL of THF under Ar.
b
0.5 mol% of MCM-41-N,N-Pd(0) was used.
2 mol% of MCM-41-N,N-Pd(0) was used.
c
Fig. 1. XRD patterns of the parent MCM-41 (1) and MCM-41-N,N-Pd(0) (2).
Table 1
Textural parameters of the catalytic materials.
a
b
Materials
Surface area/(m2gꢂ1
)
Pore volume/(cm3gꢂ1
)
Diameter/(nm)c
MCM-41
MCM-41-N,N
MCM-41-N,N-Pd(0)
903.4
641.8
578.2
0.83
0.52
0.46
2.7
2.1
2.0
a
BET surface area.
Single point total pore volume.
Pore diameter according to the maximum of the BJH pore size distribution.
b
c

60
Z. Lei et al. / Journal of Organometallic Chemistry 852 (2017) 54e63
at 68 ꢀC (Table 3, entries 1e3). When the MCM-41-immobilized
palladium(II)-Schiff base complex [MCM-41-N,N-PdCl2] was used
as catalyst, diphenyl 3a was isolated in 79% yield (entry 1). We were
pleased to observe that the yield of 3a could be increased to 91% by
replacing MCM-41-N,N-PdCl2 complex with the MCM-41-
immobilized palladium(0)-Schiff base complex [MCM-41-N,N-
Pd(0)] (entry 2). We also tested the catalytic activity of an MCM-41-
supported thioether palladium(0) complex [MCM-41-S-Pd(0)] [63],
which is an efficient and phosphine-free heterogeneous palladium
catalyst for Suzuki coupling reported by our group, but the desired
3a was obtained in only 75% yield (entry 3), so the MCM-41-N,N-
Pd(0) complex was finally selected as the catalyst for the reaction.
Control experiments showed that palladium catalyst is essential for
this diphenyl formation reaction (entry 4). When PdCl2(PPh3)2 was
used as the catalyst [29], the desired product 3a was isolated in 92%
yield (entry 5), which indicating that catalytic activity of the
phosphine-free heterogeneous palladium(0) complex [MCM-41-
N,N-Pd(0)] was comparable to that of PdCl2(PPh3)2. The heteroge-
neous cross-coupling reaction proceeded very slowly at 25 ꢀC and
only a trace of 3a was detected (entry 6). Decreasing the reaction
temperature to 50 ꢀC resulted in a decreased yield (entry 7). Finally,
the amount of the palladium catalyst was screened, and 1 mol%
loading of palladium was found to be optimal, a lower yield was
obtained and a longer reaction time was required when the amount
of the catalyst was reduced to 0.5 mol% (entry 8). Increasing the
amount of the palladium catalyst could shorten the reaction time,
but did not improve the yield of 3a obviously (entry 9). Therefore,
the optimized reaction conditions for this transformation are the
MCM-41-N,N-Pd(0) (1 mol%) in THF at 68 ꢀC under Ar for 2 h
(Table 3, entry 2). Furthermore, the atom efficiency of Ph3In, for
which all three phenyl groups efficiently coupled with 3 equiv. of an
electrophilic coupling partner, was thoroughly established.
With the optimized conditions in hand, we then investigated
the scope and limitation of this heterogeneous palladium(0)-
catalyzed cross-coupling reaction using a variety of aryl iodides
and different triarylindiums as the substrates and the results are
summarized in Table 4. As shown in Table 4, the cross-coupling
reaction of Ph3In (1a) with a variety of aryl iodides proceeded
smoothly under the optimized conditions to give the correspond-
ing biaryls 3a-3k in good to excellent yields. Various electron-
donating and electron-withdrawing groups such as methyl,
methoxy, chloro, bromo, nitro, cyano, ketone and ester on the
benzene ring were well tolerated. The reactivity of electron-
deficient aryl iodides was higher than that of electron-rich ones.
For example, the reactions of methyl 4-iodobenzoate, 4-
chloroiodobenzene, 4-cyanoiodobenzene, 40-iodoacetophenone,
and 4-nitroiodobenzene afforded the desired coupled products 3e-
3i in 91e95% yields within 2 h, while the reaction of 4-iodoanisole
having a strong electron-donating group gave 3d in only 72% yield
after 6 h. 4-Bromoiodobenzene was subjected to a coupling reac-
tion to produce selectively 4-bromobiaryl 3j in 87% yield. The ste-
rically hindered 2-iodotoluene also showed lower reactivity and
Table 4
Synthesis of a variety of biaryls by heterogeneous Pd(0)-catalyzed cross-coupling of triarylindiums with aryl iodides.a,b
a All reactions were performed using 1.0 mmol of Ar1-I, 0.37 mmol of Ar3In, 1 mol% of MCM-41-
N,N-Pd(0) in 4.0 mL of THF at 68 ºC under Ar for 2 h. b Isolated yield. c PdCl2(PPh3)2 (1 mol%)
was used as catalyst for 1 h [29].d For 6 h.

Z. Lei et al. / Journal of Organometallic Chemistry 852 (2017) 54e63
61
afforded 3k in 75% yield after 6 h. However, the reaction of bulky 1-
iodonaphthalene with Ph3In provided 90% yield of the expected
product 3l. Heteroatoms turned out to be compatible with the
employed reaction conditions. The reactions of 2-iodothiophene
and 2-iodopyridine with Ph3In could give the corresponding
coupled products 3m and 3n in good yields. The optimized reaction
conditions were also applied to the cross-coupling reactions of
substituted triphenylindiums such as tri(4-methylphenyl)indium
(1b) and tri(4-chlorophenyl)indium (1c) with a variety of aryl and
heteroaryl iodides, the results are also listed in Table 4. The reaction
of tri(4-methylphenyl)indium (1b) with various electron-deficient
aryl iodides afforded the desired biaryls 3o-3q in excellent yields.
The sterically hindered 2-iodotoluene and heteroaryl iodides
proved to be also suitable coupling partners and produced the
corresponding coupled products 3r-3t in good yields. Similarly, the
reaction of tri(4-chlorophenyl)indium (1c) with aryl iodides
bearing various substituents, regardless of their electronic proper-
ties and substitution positions, provided the desired biaryls 3u-3y
in good to excellent yields. In addition, the reaction also worked
equally well with heteroaryl iodides, furnishing the expected
products 3z and 3a' in good yields. The method provides a quite
general, atom-efficient and practical route for the synthesis of un-
symmetrical biaryls having various functionalities.
functionality into organic compounds [64]. Encouraged by the
above results, we next investigated the phosphine-free heteroge-
neous palladium(0)-catalyzed cross-coupling reaction of tri-
alkynylindiums with various aryl iodides in THF at 68 ꢀC and the
results are listed in Table 5. The reactions of tri(phenylethynyl)in-
dium (1d) with a variety of electron-neutral, electron-rich, and
electron-deficient aryl iodides proceeded smoothly to give the
corresponding 1-aryl-2-phenylethynes 4a-4j in good to excellent
yields. The reactivity of aryl iodides having electron-withdrawing
groups was higher than that of aryl iodides having electron-
donating groups. For example, the reaction of 4-iodoanisole affor-
ded the desired 1-(4-methoxyphenyl)-2-phenylethyne 4d in only
70% yield after 6 h. It is noteworthy that 1-(4-bromophenyl)-2-
phenylethyne 4i could be selectively produced in 84% yield by the
coupling of 4-bromoiodobenzene with 1d. The reaction of sterically
congested 2-(trifluoromethyl)iodobenzene could give the desired
product 4j in 82% yield. Besides aromatic tri(phenylethynyl)indium
(1d), an aliphatic tri(hexyn-1-yl)indium (1e) proved to be also good
coupling partner and could be effectively coupled with various aryl
iodides to furnish the corresponding 1-aryl-2-butylethynes 4k-4o
in 79e92% yields. Interestingly, the reaction worked equally well
with a Me3Si-functionalized tri(trimethylsilylethynyl)indium (1f).
The reactions of a variety of aryl iodides bearing either electron-
donating or electron-withdrawing groups with 1f proceeded
smoothly under the optimized conditions to afford the desired
1-aryl-2-(trimethylsilyl)ethynes 4p-4t in 73e89% yields. 4-
Bromoiodobenzene was also subjected to the coupling reaction to
generate selectively 1-(4-bromophenyl)-2-(trimethylsilyl)ethyne
4t in 86% yield. A wide range of functional groups such as methyl,
Arylalkynes are also important intermediates in the synthe-
sis of a broad array of naturally occurring products, biologi-
cally active molecules, and nonlinear optical materials. Among
numerous methods accessing to arylalkynes, the palladium-
catalyzed Sonogashira coupling has proven to be one of the most
popular and efficient methods for the incorporation of alkynyl
Table 5
Synthesis of a variety of arylalkynes by heterogeneous Pd(0)-catalyzed cross-coupling of trialkynylindiums with aryl iodides.a,b

62
Z. Lei et al. / Journal of Organometallic Chemistry 852 (2017) 54e63
methoxy, chloro, bromo, trifluoromethyl, nitro, cyano, trime-
thylsilyl, ketone and ester were tolerated well. The present method
provides a novel, atom-efficient and practical procedure for the
preparation of a variety of arylalkynes.
To ensure that the high activity of MCM-41-N,N-Pd(0) complex
arises from the palladium sites on the channel walls and not from
the leached palladium species in solution, the heterogenity of
MCM-41-N,N-Pd(0) complex was tested by hot filtration [65]. For
this, the coupling reaction of iodobenzene with Ph3In (0.37 equiv)
was carried out until a conversion of 30%. Then the catalyst was
removed by filtration from the solution at the reaction temperature
(68 ꢀC) and the filtrate was allowed to react further under identical
reaction conditions. We found that, after this hot filtration, no in-
crease in conversion of PhI was observed. We also determined the
palladium content in the filtrate by ICP analysis, and no palladium
was detected in the clear solution. These results rule out any
contribution to the observed catalysis from the leached palladium
species indicating that the catalyst was stable during the reaction
and the observed catalysis was intrinsically heterogeneous.
A plausible mechanism for this heterogeneous palladium(0)-
catalyzed cross-coupling reaction of triarylindiums or tri-
alkynylindiums with aryl iodides is illustrated in Scheme 3. First,
oxidative addition of Ar-I (2) to the MCM-41-N,N-Pd(0) complex
generates an MCM-41-bound arylpalladium(II) complex (A), which
should be the rate-limiting step [29]. Subsequent transmetalation
between intermediate A and triorganoindium reagent (1) produces
intermediate B and R2InI, which can re-enter in a new catalytic
cycle and effectively transfer its organic groups. Finally, reductive
elimination of intermediate B affords the desired coupling product
(3 or 4) and regenerates the MCM-41-N,N-Pd(0) complex to com-
plete the catalytic cycle.
Fig. 2. Recycle of the MCM-41-N,N-Pd(0) catalyst.
the reaction, the catalyst was recovered by simple filtration and
washed with DMF and diethyl ether. After being air-dried, it can be
reused directly without further purification. The recovered
palladium catalyst was used in the next run, and almost the same
yield of 3h was observed for ten consecutive cycles (95%, 94%, 95%,
94%, 94%, 93%, 94%, 93%, 92%, and 93%, respectively) as shown in
Fig. 2. In addition, palladium leaching in the heterogeneous catalyst
was also determined by ICP-AES analysis on the recovered catalyst
after ten consecutive runs, which revealing almost the same
palladium content as the fresh one.
3.3. Recycling of the catalyst
4. Conclusion
For the practical application of a heterogeneous precious metal
catalyst system, its stability and reusability are important factors.
The MCM-41-N,N-Pd(0) catalyst can be easily separated and
recovered by a simple filtration of the reaction solution. We next
examined the recycling of the catalyst by using the coupling reac-
tion of Ph3In (1a) with 40-iodoacetophenone. After completion of
In summary, we have successfully developed a novel, atom-
efficient, practical and environmentally friendly method for the
synthesis of biaryls and arylalkynes through the cross-coupling of
triarylindiums or trialkynylindiums with aryl iodides by using an
MCM-41-immobilized palladium(0)-Schiff base complex [MCM-
41-N,N-Pd(0)] as catalyst. This phosphine-free heterogeneous
palladium(0) complex could be easily prepared by a simple pro-
cedure from commercially readily available reagents and exhibited
the same catalytic activity as PdCl2(PPh3)2. The reactions generated
a variety of valuable unsymmetrical biaryls and arylalkynes in good
to excellent yields and were applicable to various triarylindiums or
trialkynylindiums and a wide range of aryl iodides with high
functional group tolerance. In addition, this methodology offers the
competitiveness of recyclability of the palladium(0) catalyst
without significant decrease in activity, and the palladium(0)
catalyst can be easily recovered by a simple filtration of the reaction
solution and recycled at least 10 times, thus making this procedure
economically and environmentally more acceptable.
Acknowledgements
We thank the National Natural Science Foundation of China (No.
21462021), the Natural Science Foundation of Jiangxi Province of
China (No. 20161BAB203086) and Key Laboratory of Functional
Small Organic Molecule, Ministry of Education (No. KLFS-KF-
201409) for financial support.
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