Piperazine- and DABCO-bridged dinuclear N-heterocyclic carbene palladium complexes: synthesis, structure and application to Hiyama coupling reaction

Article abstract of DOI:10.1002/aoc.3543

Four dinuclear N-heterocyclic carbene (NHC) palladium complexes were prepared by reaction of imidazolinium salts, PdCl₂ and bridging ligands (piperazine and DABCO) in one pot or by direct cleavage of the chloro-bridged dimeric compounds [Pd(μ-Cl)(Cl)(NHC)]₂ with bridging ligands. All of the complexes were fully characterized using ¹H NMR, ¹³C NMR, high-resolution mass and infrared spectroscopies, elemental analysis and single-crystal X-ray diffraction. The catalytic activities of the obtained palladium catalysts towards Hiyama coupling of aryl chlorides with phenyltrimethoxysilane were investigated and the results showed that the dinuclear palladium complexes were considerably active for the coupling reaction. Copyright

Full text of DOI:10.1002/aoc.3543

Full paper
Received: 4 April 2016
Revised: 17 May 2016
Accepted: 28 May 2016
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.3543
Piperazine- and DABCO-bridged dinuclear
N-heterocyclic carbene palladium complexes:
synthesis, structure and application to Hiyama
coupling reaction
Haozhen Wang and Jin Yang*
Four dinuclear N-heterocyclic carbene (NHC) palladium complexes were prepared by reaction of imidazolinium salts, PdCl2 and
bridging ligands (piperazine and DABCO) in one pot or by direct cleavage of the chloro-bridged dimeric compounds [Pd(μ-Cl)
1
(Cl)(NHC)]2 with bridging ligands. All of the complexes were fully characterized using H NMR, 13C NMR, high-resolution mass
and infrared spectroscopies, elemental analysis and single-crystal X-ray diffraction. The catalytic activities of the obtained palla-
dium catalysts towards Hiyama coupling of aryl chlorides with phenyltrimethoxysilane were investigated and the results
showed that the dinuclear palladium complexes were considerably active for the coupling reaction. Copyright © 2016 John
Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web-site.
Keywords: N-heterocyclic carbene; palladium; dinuclear complexes; Hiyama coupling
Based on this, other types of N-donors have received attention
Introduction
and been introduced into the coordination with NHC–Pd complexes,
including triethylamine,[7] diethylamine,[8] 1-methylimidazole,[9]
Since the first successful isolation of a stable carbene by Arguengo
et al. in 1991, N-heterocyclic carbenes (NHCs) and their palladium
complexes have attracted considerable attention due to their high
2-phenyl-4,5-dihydrooxazole,[10] morpholine,[11] 2-phenylimidazole,[12]
acetonitrile,[13] benzoxazole (benzothiazole),[14] (iso)quinoline,[15] 1-
methylpyrazole (1-methylindazole),[16] etc. All of them have shown
catalytic activity in organic transformations including C–C and C–N
coupling reactions.[1,2] One of the most efficient NHC–Pd catalysts is
promising catalytic activity in organic transformations.
(NHC)PdCl2(3-chloropyridine) (Pd-PEPPSI-(NHC), PEPPSI = pyridine,
enhanced, precatalyst, preparation, stabilization and initiation),
which was first reported by Organ’s group in 2006.[3] In a typical
NHC–Pd-catalyzed C–C coupling reaction, the role of NHC has been
recognized as a strong electron donor assisting initial reduction and
oxidative addition, and the steric bulkiness increasing the rate of
reductive elimination. However, the bulky NHC ligand may also
hinder the coordination of the substrate to the metal center,
thus decreasing the catalytic activity.[4] In order to improve the
activity of NHC–Pd complexes, an external hemilabile donor is
incorporated to the Pd center. In Pd-PEPPSI-(NHC) catalyst,
3-chloropyridine allows for efficient stabilization of the NHC–Pd,
while in the catalytic process the Pd center could lose the addi-
tional donor, opening up free coordination site for incoming
substrate. Following the success of Pd-PEPPSI-(NHC) in Pd-
catalyzed coupling reactions, a series of modified NHC–Pd com-
plexes have been developed and applied in organic reactions.[5]
Although the catalytic activity of NHC–Pd is mainly dependent
on the electronic property and steric hindrance of NHC, the an-
cillary ligands also play an important role in the catalytic process.
For example, Organ and co-workers reported that (NHC)PdCl2
(pyridine) were more active than their 3-chloropyridine ana-
logues, due to either a higher dissociation rate of pyridine or a
higher tendency to re-coordinate to [(NHC)Pd(0)] species.[6]
Despite the excellent progress made so far in mononuclear
NHC–Pd complexes, the properties of bridging ligand-
stabilized dinuclear complexes are less studied. A suitable
bridging ligand could effectively conjoin two NHC–Pd units
to form a dinuclear complex and provide a model to test the
catalytic activity of multi-metallic catalytic sites.[17] We have
recently reported pyrazine- and DABCO-bridged dinuclear
NHC–Pd complexes based on unsaturated imidazol-2-ylidene
ligands as well as their application in the Hiyama coupling
reaction.[17] Encouraged by the results mentioned above and
also in continuation of our efforts in the development of
NHC–Pd complexes, herein we present facile synthesis and
characterization of dinuclear NHC–Pd complexes based on
saturated imidazolidin-2-ylidene ligands through reaction of
imidazolinium salt, PdCl2 and bridging ligands (piperazine
and DABCO) in one pot with a simple tandem procedure.
Furthermore, the dinuclear NHC–Pd complexes could also be
*
Correspondence to: Jin Yang, Department of Chemistry, Huaibei Normal
University, Huaibei, Anhui 235000, PR China. E-mail: yangjinlz@163.com
Department of Chemistry, Huaibei Normal University, Huaibei, Anhui, 235000, PR
China
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.

H. Wang and J. Yang
obtained by direct cleavage of [Pd(μ-Cl)(Cl)(NHC)]2 with
piperazine or DABCO (Scheme 1). The application of the
resulting dinuclear complexes in Hiyama coupling reactions of
aryl chlorides with phenyltrimethoxysilane was investigated.
Results and Discussion
Synthesis and Characterization of NHC–Pd Complexes
According to the method reported in the literature,[17] the synthesis
of the dinuclear NHC–Pd complexes is easily done in one pot from
imidazolinium salts, PdCl2 and bridging ligands (piperazine and
DABCO) in tetrahydrofuran (THF) at reflux. The expected dinuclear
complexes 3a–3d are isolated in good yields (74–82%) after purifi-
cation. In addition, the imidazolinium salts can be converted to
chloro-bridged dimeric compounds [Pd(μ-Cl)(Cl)(NHC)]2 under mild
conditions, and [Pd(μ-Cl)(Cl)(NHC)]2 are then readily cleaved with
piperazine or DABCO to provide the dinuclear complexes 3a–3d
in excellent yields (90–95%). All complexes are isolated as yellow,
air-stable solids and fully characterized using 1H NMR and 13C
NMR spectroscopy, high-resolution mass spectrometry (HR-MS), el-
emental analysis, Fourier transform infrared (FT-IR) spectroscopy
and X-ray crystallography. The formation of the dinuclear com-
plexes is evident from the distinctive stoichiometric proton signal
resonances of the NHCs with bridging ligands. In addition, the
chemical shifts of the diagnostic Pd–Ccarbene peaks which appear
in the range 184.6–187.9 ppm in 13C NMR spectra are compared
with the 13C NMR signals of Ccarbene in NHC–Pd analogues. More-
over, their formation is confirmed by HR-MS analysis where
exclusive signals are observed for their respective [M + H]+
fragments.
Figure 1. (a) ORTEP diagram of 3a with thermal displacement parameters
drawn at 30% probability. Hydrogen atoms and solvent molecules (CH2Cl2)
have been omitted for clarity. Symmetry codes: A, 1 À x, 1 À y, 2 À z. (b)
Perspective view of 3a showing the distance between the Pd atoms and
the plane defined by the carbon atoms of piperazine.
Crystal Structures
The X-ray analysis of single crystals reveals the structure of the
obtained complexes. The five-membered ring topology of the
saturated NHCs varies prominently for different complexes with
the absolute values of the N–C–C–N dihedral angles being in the
range 13.02–22.64°. The crystal analysis of 3a–3d shows dinuclear
structures with N-donors bridging across two NHC–Pd units. As
shown in Figs 1 and 2, complexes 3a and 3b have similar composi-
tions and structures, each Pd center being surrounded by an
imidazolidene, a nitrogen atom from piperazine, and two chloro
ligands in a slightly distorted square planar geometry. The two
PdCNCl2 coordination planes, which adopt coplanar arrangements,
are oriented approximately perpendicularly to the carbene ring
planes with dihedral angles of 71.81° and 69.01°, respectively. The
piperazine with chair conformation combines two NHC–Pd units
and the Pd centers out of the plane defined by the carbon atoms
of piperazine with distances of 0.745 and 0.573 Å, respectively. As
usual in NHC-bearing complexes, Pd–Ccarbene distances fall in the
range of a single bond (1.965(2) Å for 3a and 1.964(6) Å for 3b),
which are slightly shorter than in the typical Pd-PEPPSI-(NHC)
(1.990(3) Å for SIPr-PdCl2(3-chloropyridine)].[7] The Pd–N bonds
amounting to 2.125(2)–2.126(7) Å are in the range similar to that
found for other N-donor-stabilized NHC–Pd analogues. The crystal
structures of 3c and 3d (Figs 3 and 4) confirm dinuclear structures
which are bridged by DABCO. All of the Pd centers possess square
planar geometries and the NHC ligands occupy the trans position to
DABCO. The dihedral angles between the PdCNCl2 coordination
planes and carbene rings range from 71.07° to 75.21°, being slightly
larger than those in 3a and 3b. The Pd–Ccarbene bonds (about 1.97
Å) are slightly longer than those in 3a and 3b, but are slightly
shorter than in SIPr-PdCl2-(3-chloropyridine). The Pd–N bond
lengths around the Pd centers are similar and compare well to
those of related NHC–Pd complexes with N-donors.
Hiyama Coupling of Phenyltrimethoxysilane with Aryl
Chlorides
As one of the most convenient methods to create C–C bonds,
Hiyama coupling has been widely applied in organic synthesis.
Scheme 1. Overview the preparation of the dinuclear NHC–Pd complexes
3a–3d.
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Appl. Organometal. Chem. (2016)

Dinuclear N-heterocyclic carbene palladium complexes
Figure 4. ORTEP diagram of 3d with thermal displacement parameters
drawn at 30% probability. Hydrogen atoms have been omitted for clarity.
Symmetry codes: A, 1 À x, 1 À y, Àz.
coupling-based NHC–Pd catalysts have been reported.[19] To test
the catalytic properties of 3a–3d, the coupling of 4-chloroanisole
with phenyltrimethoxysilane was chosen as a model reaction
(Table 1, entries 1–4). It is found that in the presence of 0.25
mol% of the complexes with n-Bu4NF as the base in toluene at
110°C, the corresponding biaryl product is isolated in high yield
after 8 h. However, a reduction in the catalyst loading from 0.25
to 0.125 mol% leads to decreased yields (entries 5–6). Complexes
3b and 3d show higher catalytic activities than 3a and 3c. The
different yields among 3a–3d are possible due to the different
steric hindrance of the NHC ligands. The sterically bulky ligand
(N,N′-bis(2,6-di(isopropyl)phenyl)imidazolidin-2-ylidene) displays
a higher conversion to product.
Figure 2. (a) ORTEP diagram of 3b with thermal displacement parameters
drawn at 30% probability. Hydrogen atoms and solvent molecules (CH2Cl2)
have been omitted for clarity. Symmetry codes: A, 2 À x, Ày, 2 À z. (b)
Perspective view of 3b showing the distance between the Pd atoms and
the plane defined by the carbon atoms of piperazine.
Then some other aryl chlorides were subjected to the
reaction according to the conditions described above. Gener-
ally, most of the coupling reactions proceed efficiently to
provide the biaryl products in good yields. Substrates with
electron-withdrawing group such as nitro group (entries 7–10)
and acetyl group (entries 11–14) are easily coupled with
phenyltrimethoxysilane. In addition, 3-chloroanisole and
2-chloroanisole are also tolerated under these conditions and
moderate to good yields are achieved. For other aryl chlorides,
chlorobenzene and 4-chlorotoluene were tolerated in this
condition and moderate yields were obtained.
Finally, a comparison of the catalytic activities between
the complexes 3c and 3d and some well-defined NHC–Pd
complexes was investigated. Under the same conditions,
the coupling of phenyltrimethoxysilane with 4-chloroanisole
was carried out. As evident from Table 2, the catalytic activ-
ities of the dinuclear complexes 3c and 3d are similar to
those of the unsaturated analogues [(IMes)PdCl2]2(μ-DABCO)
and [(IPr)PdCl2]2(μ-DABCO) and slightly better than that of
the dimer [Pd(μ-Cl)(Cl)(SIPr)]2. But compared with the
mononuclear PEPPSI catalysts (IPr)PdCl2(3-chloropyridine)
and (SIPr)PdCl2(3-chloropyridine), the dinuclear complexes
do not display outstanding superiority in catalyst amount
and reaction activity under the same amount of metal
loading. The reason may be that the distance between the
two palladium centers is so large that the dinuclear
complexes cannot form effective cooperative interactions.
Other factors such as the stability of complexes also have
an influence on the catalytic activity.
Figure 3. ORTEP diagram of 3c with thermal displacement parameters
drawn at 30% probability. Hydrogen atoms and solvent molecules (CH2Cl2)
have been omitted for clarity.
Generally, aryl iodides and bromides have been extensively used
in the reaction; the application of aryl chlorides has recently
attracted much attention because of their low cost and wide
availability.[18] Moreover, only a handful of examples of Hiyama
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.
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H. Wang and J. Yang
Table
1. Hiyama
coupling
of
aryl
chlorides
with
Conclusions
phenyltrimethoxysilane catalyzed by 3a–3da
In summary, four new dinuclear NHC–Pd complexes bridged by pi-
perazine or DABCO have been conveniently synthesized and fully
characterized. These complexes have been utilized as catalysts for
Hiyama coupling of aryl chlorides with phenyltrimethoxysilane to
produce biaryl products. The results demonstrate that these com-
plexes show good catalytic activity and tolerance to various chem-
ical functions. Further modification of the NHC–Pd complexes and
their application are in progress in our laboratory.
Entry
Catalyst
Aryl chloride
Yield (%)b
1
2
3
4
5c
6c
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
3a
3b
3c
3d
3b
3d
3a
3b
3c
3d
3a
3b
3c
3d
3a
3b
3c
3d
3a
3b
3c
3d
3a
3b
3c
3d
3a
3b
3c
3d
R = 4-OMe
R = 4-OMe
R = 4-OMe
R = 4-OMe
R = 4-OMe
R = 4-OMe
R = 4-NO2
R = 4-NO2
R = 4-NO2
R = 4-NO2
R = 4-COCH3
R = 4-COCH3
R = 4-COCH3
R = 4-COCH3
R = 3-OMe
R = 3-OMe
R = 3-OMe
R = 3-OMe
R = 2-OMe
R = 2-OMe
R = 2-OMe
R = 2-OMe
R = H
78
85
80
85
45
36
82
88
80
87
83
85
85
87
75
80
78
83
70
75
68
77
62
70
65
72
63
72
68
68
Experimental
General Remarks
The chemicals were purchased from commercial suppliers and
were used without purification prior to use unless otherwise
indicated. NMR spectra were recorded at 400 MHz (for 1H
NMR) and 100 MHz (for 13C NMR) with a Bruker Avance 400
NMR spectrometer. 1H NMR and 13C NMR spectroscopy was
performed with samples in CDCl3 with tetramethylsilane as an
internal standard. HR-MS was conducted with an Agilent 6550
iFunnel Q-TOF MS system. FT-IR spectra were recorded with a
Bruker IFS 120HR spectrometer using KBr discs. The C, H and
N analyses were performed with a Vario EL III Elementar. Flash
column chromatography was carried out using 300–400 mesh
silica gel. The chloro-bridged dimeric compounds [Pd(μ-Cl)(Cl)
(NHC)]2 were prepared according to the literature.[20]
R = H
R = H
R = H
R = 4-CH3
R = 4-CH3
R = 4-CH3
R = 4-CH3
General Procedure for Synthesis of Complexes 3a–3d
Procedure 1
A mixture of imidazolinium chloride (0.24 mmol), PdCl2 (0.2 mmol),
K2CO3 (0.3 mmol) and piperazine or DABCO (0.12 mmol) was stirred
in anhydrous THF (10.0 mL) under reflux for 12 h. The solvent was
removed under reduced pressure, and the residue was purified by
flash chromatography on silica gel (hexane–CH2Cl2) to afford the
corresponding dinuclear NHC–Pd complexes 3a–3d as yellow solids.
aReaction conditions: aryl chloride (0.50 mmol), phenyltrimethoxysilane
(0.60 mmol), Pd complex (0.00125 mmol), n-Bu4NF (1.0 mmol) in toluene
(2.0 ml) at 110°C for 8 h.
bIsolated yield.
c0.125 mol% of [Pd] catalyst was used.
Procedure 2
A mixture of dimeric compound [Pd(μ-Cl)(Cl)(NHC)]2 (0.10 mmol)
and the bridging ligand (piperazine or DABCO) (0.10 mmol) was
dissolved in CH2Cl2 (10.0 ml) and stirred at room temperature for
12 h. The reaction mixture was then filtered over Celite and the sol-
vent was reduced under reduced pressure. The resulting residue
was washed with ether to give the corresponding dinuclear NHC–
Pd complexes 3a–3d. A single crystal for X-ray diffraction was
obtained by recrystallization from CH2Cl2 and n-hexane.
Table
2. Hiyama
coupling
of
4-chloroanisole
with
phenyltrimethoxysilane catalyzed by NHC–Pd catalystsa
Entry
Catalyst
Pd complex (%)
Yield (%)b
Complex 3a
1
2
3
4
5
6
7
3c
0.25
0.25
0.25
0.25
0.5
80
85
78
84
86
88
68
Yield 78 mg, 74% (Procedure 1); 97 mg, 92% (Procedure 2).
Decomposition temperature > 247°C. 1H NMR (400 MHz,
CDCl3, δ, ppm): 6.95 (s, 8H, m-ArH), 4.12 (q, J = 7.2 Hz, 2H,
piperazine-NH), 3.92 (s, 8H, NCH2CH2N, imidazolidine), 2.52–
2.47 (m, 4H, HNCH2CH2NH, piperazine), 2.44 (s, 24H, o-CH3),
2.31 (s, 12H, p-CH3), 2.28–2.25 (m, 4H, HNCH2CH2NH, pipera-
zine). 13C NMR (100 MHz, CDCl3, δ, ppm): 185.9 (Ccarbene),
138.2 (o-CAr), 137.0 (N-CAr), 134.8 (p-CAr), 129.3 (m-CAr), 50.9
(NCH2CH2N, imidazolidine), 46.8 (HNCH2CH2NH, piperazine),
21.0 (p-CH3), 19.0 (o-CH3). FT-IR (KBr, cmÀ1): 3179, 2916,
1606, 1493, 1453, 1380, 1308, 1270, 1085, 913, 885, 855. HR-
3d
[(IMes)PdCl2]2(μ-DABCO)
[(IPr)PdCl2]2(μ-DABCO)
(IPr)PdCl2(3-chloropyridine)
(SIPr)PdCl2(3-chloropyridine)
[Pd(μ-Cl)(Cl)(SIPr)]2
0.5
0.25
aReaction conditions: aryl chloride (0.50 mmol), phenyltrimethoxysilane
(0.60 mmol), Pd complex (0.25–0.5 mol%), n-Bu4NF (1.0 mmol) in
toluene (2.0 ml) at 110°C for 8 h.
bIsolated yield.
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Appl. Organometal. Chem. (2016)

Dinuclear N-heterocyclic carbene palladium complexes
MS (ESI): calcd for C46H63Cl4N6Pd2 [M + H]+ 1055.1913; found
1055.1948. Anal. Calcd for [PdCl2Mes]2(μ-piperazine)
(C46H62Cl4N6Pd2) (%): C, 52.43; H, 5.93; N, 7.98. Found (%): C,
52.62; H, 5.60; N, 8.12.
room temperature, the filtrate was concentrated with a rotary evap-
orator, and the residue was then subjected to purification via flash
column chromatography with petroleum ether–EtOAc as an eluent
to affoed the corresponding pure products.
Complex 3b
Acknowledgements
Yield 95 mg, 78% (Procedure 1); 116 mg, 95% (Procedure 2).
Decomposition temperature > 282°C. 1H NMR (400 MHz, CDCl3,
δ, ppm): 7.38 (t, J = 7.6 Hz, 4H, p-ArH), 7.24 (d, J = 7.6 Hz, 8H, m-
ArH), 3.97 (s, 8H, NCH2CH2N, imidazolidine), 3.39 (sept, J = 6.8
Hz, 8H, CH(CH3)2), 2.57–2.51 (m, 4H, HNCH2CH2NH, piperazine),
2.29–2.14 (m, 4H, HNCH2CH2NH, piperazine), 2.14 (br, 2H,
piperazine-NH), 1.44 (d, J = 6.4 Hz, 24H, CH(CH3)2), 1.20 (d, J =
6.8 Hz, 24H, CH(CH3)2). 13C NMR (100 MHz, CDCl3, δ, ppm):
187.9 (Ccarbene), 147.5 (o-CAr), 135.2 (N-CAr), 129.3 (p-CAr), 124.2
(m-CAr), 53.6 (NCH2CH2N, imidazolidine), 46.9 (HNCH2CH2NH, pi-
perazine), 28.6 (CH(CH3)2), 26.8 (CH(CH3)2), 24.0 (CH(CH3)2). FT-
IR (KBr, cmÀ1): 3179, 2956, 1589, 1455, 1383, 1363, 1327,
1271, 1056, 1010, 933, 885, 802. HR-MS (ESI): calcd for
Financial support from the National Natural Science Foundation of
China (no. 21301061) and the Natural Science Foundation of Anhui
Province (no. 1408085QB36) is gratefully acknowledged.
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Complex 3c
Yield 86 mg, 80% (Procedure 1); 92 mg, 90% (Procedure 2). De-
composition temperature > 256°C. H NMR (400 MHz, CDCl3, δ,
1
ppm): 6.94 (s, 8H, m-ArH), 3.92 (s, 8H, NCH2CH2N,
imidazolidine), 2.62 (s, 12H, NCH2CH2N, DABCO), 2.46 (s, 24H,
o-CH3), 2.30 (s, 12H, p-CH3). 13C NMR (100 MHz, CDCl3, δ,
ppm): 182.6 (Ccarbene), 138.1 (o-CAr), 137.0 (N-CAr), 134.8(p-CAr),
129.2(m-CAr), 50.9 (NCH2CH2N, imidazolidine), 48.5 (NCH2CH2N,
DABCO), 21.0 (p-CH3), 19.3 (o-CH3). FT-IR (KBr, cmÀ1): 3179,
2916, 1606, 1491, 1451, 1378, 1308, 1269, 1183, 1017, 929,
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1081.2069; found 1081.2075. Anal. Calcd for [PdCl2IMes]2(μ-
DABCO) (C48H64Cl4N6Pd2) (%): C, 53.40; H, 5.97; N, 7.78. Found
(%): C, 53.61; H, 6.26; N, 7.88.
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Complex 3d
Yield 102 mg, 82% (Procedure 1); 112 mg, 90% (Procedure 2).
Decomposition temperature > 282°C. 1H NMR (400 MHz, CDCl3,
δ, ppm): 7.38 (t, J = 7.6 Hz, 4H, p-ArH), 7.24 (d, J = 7.6 Hz, 8H, m-
ArH), 3.99 (s, 8H, NCH2CH2N, imidazolidine), 3.44 (sept, J = 6.8
Hz, 8H, CH(CH3)2), 2.64 (s, 8H, NCH2CH2N, DABCO), 1.44 (d, J =
6.4 Hz, 24H, CH(CH3)2), 1.19 (d, J = 6.8 Hz, 24H, CH(CH3)2). 13C
NMR (100 MHz, CDCl3, δ, ppm): 184.7 (Ccarbene), 147.6 (o-CAr),
135.2 (N-CAr), 129.3 (p-CAr), 124.1 (m-CAr), 53.6 (NCH2CH2N,
imidazolidine), 48.8 (NCH2CH2N, DABCO), 28.6 (CH(CH3)2), 26.7
(CH(CH3)2), 24.0 (CH(CH3)2). FT-IR (KBr, cmÀ1): 3158, 3064,
2964, 2868, 1588, 1479, 1382, 1359, 1323, 1298, 1268, 1178,
1103, 1053, 1013, 931, 806. HR-MS (ESI): calcd for
C
60H89Cl4N6Pd2 [M + H]+ 1249.3947; found 1249.3980. Anal.
Calcd for [PdCl2SIPr]2(μ-DABCO) (C60H88Cl4N6Pd2) (%): C, 57.74;
H, 7.11; N, 6.73. Found (%): C, 57.51; H, 7.42; N, 7.08.
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General Procedure for Hiyama Coupling Reaction
A sealable reaction tube equipped with a magnetic stir bar was
charged with aryl chloride (0.50 mmol), phenyltrialkyoxysilane
(0.60 mmol), n-Bu4NF (1.0 mmol), NHC–Pd complex (0.00125 mmol,
0.25 mmol%) and anhydrous toluene (2.0 ml). The mixture was
stirred at 110°C for 8 h. After the reaction mixture was cooled to
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H. Wang and J. Yang
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Supporting information
Additional supporting information may be found in the online
version of this article at the publisher’s web-site.
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