Catalytic activities of NHC-PdCl2 species based on functionalized tetradentate imidazolium salt in three types of C-C coupling reactions

Article abstract of DOI:10.1002/aoc.4429

A functionalized tetradentate imidazolium salt 9,10-bis{di[2′-(N-ethylimidazolium-1-yl)ethyl]aminomethyl}anthracene tetrakis(hexafluorophosphate) (1) has been synthesized and characterized. The catalytic activity of the NHC-PdCl₂ species formed by compound 1 and PdCl₂ was tested in Suzuki-Miyaura, Heck-Mizoroki and Sonogashira reactions. The results showed that this catalytic system was effective for above three types of C-C coupling reactions.

Full text of DOI:10.1002/aoc.4429

Received: 26 February 2018
DOI: 10.1002/aoc.4429
Revised: 24 April 2018
Accepted: 27 April 2018
F U L L P A P E R
Catalytic activities of NHC‐PdCl2 species based on
functionalized tetradentate imidazolium salt in three types
of C‐C coupling reactions
Qing‐Xiang Liu1,2
| Dong‐Xue Zhao1,2 | Hao Wu1,2 | Zhi‐Xiang Zhao1,2 | Shi‐Zhen Lv1,2
1 Key Laboratory of Inorganic‐Organic
Hybrid Functional Materials Chemistry
(Tianjin Normal University), Ministry of
Education, College of Chemistry, Tianjin
Normal University, Tianjin 300387, China
2 Tianjin Key Laboratory of Structure and
Performance for Functional Molecules,
College of Chemistry, Tianjin Normal
University, Tianjin 300387, China
A
functionalized
tetradentate
imidazolium
salt
9,10‐bis{di[2′‐(N‐
ethylimidazolium‐1‐yl)ethyl]aminomethyl}anthracene tetrakis(hexafluorophos-
phate) (1) has been synthesized and characterized. The catalytic activity of the
NHC‐PdCl2 species formed by compound 1 and PdCl2 was tested in Suzuki‐
Miyaura, Heck‐Mizoroki and Sonogashira reactions. The results showed that this
catalytic system was effective for above three types of C‐C coupling reactions.
KEYWORDS
Correspondence
N‐heterocyclic carbene, palladium, catalytic activity, C‐C coupling reaction
Qing‐Xiang Liu, Key Laboratory of
Inorganic–Organic Hybrid Functional
Materials Chemistry (Tianjin Normal
University), Ministry of Education,
College of Chemistry, Tianjin Normal
University, Tianjin 300387, China; Tianjin
Key Laboratory of Structure and
Performance for Functional Molecules,
College of Chemistry, Tianjin Normal
University, Tianjin 300387, China.
Email: tjnulqx@163.com
Funding information
National Natural Science Foundation of
China, Grant/Award Number: 21572159;
Tianjin Natural Science Foundation,
Grant/Award Number: 11JCZDJC22000
1 | INTRODUCTION
complexes have been applied to many catalytic reactions
including Suzuki‐Miyaura, Heck‐Mizoroki and so on,
N‐Heterocyclic carbenes (NHCs) based on imidazolium
salts have received great attention since the isolation of
first stable free carbene in 1991 by Arduengo et al.[1]
The NHC metal complexes have some distinguished
properties compared with widely used metal complexes
of phosphine ligands. These NHC metal complexes have
high stability toward heat, moisture and air due to the
strong σ‐donating ability of NHCs.[2–9] The N‐heterocy-
clic carbenes have now been regarded as prospective
replacers for phosphines in catalytic reactions. Over the
past two decades, a variety of NHC transition metal
and these catalysts displayed good catalytic activity in
some organic reactions.[10–15] For example, many cases
of Suzuki‐Miyaura reaction were carried out under high
reaction temperature or air‐free conditions.[16–18] Also
the majority of Heck‐Mizoroki reactions were conducted
under an inert atmosphere, and only the minority of
examples were carried out under air.[19–21] Therefore,
developing new catalysts of NHC‐metal complexes under
mild conditions in air is still highly desirable work.
To develop new NHC metal complexes with highly
catalytic activity, the design and synthesis of
Appl Organometal Chem. 2018;e4429.
wileyonlinelibrary.com/journal/aoc
Copyright © 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4429

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LIU ET AL.
monodentate or polydentate ligands have been stud-
ied.[22–26] Some catalytic systems based on NHC Pd(II)
complexes with monodentate ligands have been
reported.[27,28] But among NHC ligands, polydentate
ligands are believed to be more useful for the stabilization
of the catalysts and enhancement of the catalytic activ-
ity.[29–31] During the course of searching for the catalysts
of NHC metal complexes, we focused our efforts on the
synthesis of new polydentate imidazolium salt precursors.
In this paper, we report the synthesis of a tetradentate
imidazolium salt 9,10‐bis{di[2′‐(N‐ethylimidazolium‐1‐yl)
ethyl]aminomethyl}anthracene
aminomethyl]anthracene with N‐ethylimidazole to afford
tetra‐imidzolium salt 9,10‐bis{di[2′‐(N‐ethylimidazolium‐
1‐yl)ethyl]aminomethyl}anthracene tetrachloride, and
the preparation of 9,10‐bis{di[2′‐(N‐ethylimidazolium‐1‐
yl)ethyl]aminomethyl}anthracene
tetrakis(hexafluorophosphate) (1) was accomplished via
anion exchange using ammonium hexafluorophosphate
in methanol. Compound 1 is stable to air, heat and mois-
ture. It is soluble in high polar organic solvents, such as
DMSO, CH3CN and CH2Cl2, but insoluble in benzene,
diethyl ether and petroleum ether. Compound 1 was con-
firmed by 1H NMR and 13C NMR spectroscopy. In the 1H
NMR spectrum of 1, the imidazolium proton signal
(NCHN) appears at δ = 8.87 ppm. In the 13C NMR spec-
trum, the resonance of imidazolium carbon (NCN)
appears at 135.3 ppm. These values are consistent with
those of reported imidazolium salts.[33–39] The NHC‐
PdCl2 species was prepared via the reaction of compound
1 with PdCl2 in the presence of base, and it was used in
situ and not separated.
tetrakis(hexafluorophosphate) (1). Particularly, the cata-
lytic activity of the NHC‐PdCl2 species formed in situ by
compound 1 and PdCl2 is investigated in Suzuki‐Miyaura,
Heck‐Mizoroki and Sonogashira reactions.
2 | RESULTS AND DISCUSSION
2.1 | Synthesis and characterization of
tetra‐imidazolium salt 1
2.2 | Catalytic activity of NHC‐PdCl2
species in the Suzuki‐Miyaura reaction
As shown in Scheme 1, the anthracene as a starting mate-
rial reacted with paraformaldehyde to afford 9,10‐
bis(chloromethyl)anthracene according to the literature
method.[32] Then 9,10‐bis(chloromethyl)anthracene was
treated by diethanolamine to form 9,10‐bis[di(2′‐
The catalytic activity of NHC‐PdCl2 complex in the cross‐
coupling of 4‐bromotoluene and phenylboronic acid
under different conditions was investigate (Table S1).
Use of toluene as solvent and K2CO3 as base gave 67%
coupling yield at 60 °C in 24 hr (entry 1). Under the same
condition, 0.1 ml PEG400 was added to give 92% coupling
yield in 24 hr (entry 2), and 93% coupling yield in 36 hr
(entry 3). Use of toluene as solvent and K3PO4·3H2O as
base gave 64% coupling yield (entry 4). Under the same
condition, 0.1 ml PEG400 was added to give 88% coupling
yield (entry 5). This result showed that the reaction could
be dramatically improved in the presence of PEG400. It
has been known that the addition of PEG400 as a cocata-
lyst can enhance the activity of many catalytic systems.
Use of H2O as solvent and K2CO3 as base gave poor yield
of 5% at 60 °C in 24 hr (entry 6). Under the same condi-
tion, the addition of 10 mol% TBAB led to 65% coupling
yield (entry 7), and the addition of 0.1 ml PEG400 gave
68% coupling yield (entry 8). Use of H2O as solvent and
K3PO4·3H2O as base gave 16% coupling yield at 60 °C in
24 hr in the presence of TBAB (entry 9). Other solvents,
such as 1,4‐dioxane or 1,4‐dioxane/H2O (1:1), were
proved to be poor for this reaction (entries 10–12). Based
on the extensive screen, toluene and K2CO3 proved to be
the efficient solvent and base in the presence of 0.1 ml
PEG400 with a catalyst loading of 0.2 mol% of compound
1 and 0.4 mol% of PdCl2 at 60 °C in air, thus giving the
optimal coupling result. In order to further study the
influence of compound 1 on catalysis, the control
hydroxylethyl)aminomethyl]anthracene.
Subsequent
chlorination of hydroxyl groups with thionyl chloride to
generate 9,10‐bis[di(2′‐chloroethyl)aminomethyl]anthra-
cene. The reaction of 9,10‐bis[di(2′‐chloroethyl)
SCHEME 1 Preparation of compound 1 and NHC‐PdCl2 species

LIU ET AL.
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experiment was performed, in which PdCl2 and PEG400
were added in the absence of compound 1 with the opti-
mized conditions. Only 8% coupling product was
obtained (entry 13), and this value was lower than 92%
yield in the case of NHC‐PdCl2 species as catalyst. This
result shows that the compound 1 has the preponderant
function in the catalytic reaction. The above reactions
were monitored by GC analysis after the appropriate
intervals using tridecane as internal standard.
We attempted the cross‐coupling reaction of various
aryl halides with phenylboronic acid under the optimal
reaction conditions (Table 1). In general, the NHC‐PdCl2
species could catalyze the cross‐coupling of various aryl
bromides with phenylboronic acid to give different
yields. The activated aryl bromides with an electronic
withdrawing substituent in para‐position (such as 4‐
bromoacetophenone and 4‐nitrobromobenzene) could be
transformed to the biaryl products with the yields of
91% and 99% (2a and 2b(2)). The deactivated aryl
bromides with an electronic donating substituent (such
as 4‐bromoanisole and 3‐bromoanisole) could also be
coupled with phenylboronic acid to afford yields of
86% and 78% (2c and 2d). The coupling of 1‐
bromonaphthalene with phenylboronic acid gave high
yield of 90% (2e). The coupling of 4‐bromoaniline
with phenylboronic acid gave poor yield of 20% (2f).
The couplings of aryl dibromide (such as 9,10‐
dibromoanthracene, 1,4‐dibromonaphthalene and 4,4′‐
disbromobiphenyl) with phenylboronic acid afforded
excellent yields of 92%–94% (2 g‐2i). The catalyst was
also effective toward the coupling of aryl chlorides
with phenylboronic acid. The coupling of 4‐
nitrochlorobenzene with phenylboronic acid gave moder-
ate yield of 75% (2b(1)), while chlorobenzene gave poor
yields of 13% in 24 h and 42% in 48 h (2j(1) and 2j(2)).
The coupling of iodobenzene with phenylboronic acid
gave quantitative yield (2j(3)).
Above results showed that this catalytic system had
high stability to air and water, and good tolerance
toward various functional groups. These advantages
make it a valuable precatalyst for thermally sensitive
substrates. Therefore, this provides an effective phos-
phine‐free catalyst system for facile coupling of aryl
halides in toluene under mild conditions in air. The
favorable reaction condition of this catalytic system for
Suzuki‐Miyaura reaction is important to the reduction
of cost in the field of fine chemical and pharmaceutical
industries.
TABLE 1 Suzuki‐Miyaura reaction of aryl halides with phenylboronic acid catalyzed by NHC‐PdCl2 speciesa
2c
2a
2b
X = Br, 24 h, 86%
X = Br, 24 h, 91%
(1) X = Cl, 24 h, 75%
(2) X = Br, 24 h, 99%
2e
2f
2d
X = Br, 48 h, 20%
X = Br, 24 h, 90%
X = Br, 24 h, 78%
2i
X = Br, 24 h, 92%
2 h
X = Br, 24 h, 92%
2 g
X = Br, 24 h, 94%
2j
(1) X = Cl, 24 h, 13%
(2) X = Cl, 48 h, 42%
(3) X = I, 24 h, 99%
aReaction conditions: aryl halide (0.5 mmol), phenylboronic acid (0.6 mmol), K2CO3 (1.0 mmol), compound 1 (0.2 mol%) and PdCl2 (0.4 mol%), toluene (5 ml),
PEG400 (0.1 ml), 60 °C in air.

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LIU ET AL.
2, only decreasing catalyst loading (0.1% mmol of com-
pound 1 and 0.2 mol% of PdCl2) gave 64% coupling yields
(entry 5). Use of DMF or DME as solvent and K2CO3 as
base gave 72% or 79% coupling yields at 110 °C in 24 hr
in the presence of TBAB (entries 6 and 7). Other common
and less expensive inorganic bases have also been tested.
Use of K3PO4·3H2O or Na2CO3 as base and 1,4‐dioxane
as solvent in the presence of TBAB gave coupling yields
of 76% or 56%, respectively (entries 8 and 9), while KOH
as base gave trace yield (entry 10). Based on the extensive
screen, 1,4‐dioxane and K2CO3 were found to be the most
efficient solvent and base in the presence of 10 mol% of
TBAB as cocatalyst with a catalyst loading of 0.2 mol% of
compound 1 and 0.4 mol% of PdCl2 at 110 °C in air, thus
giving the optimal coupling result. Additionally, the con-
trol experiment was also conducted, in which PdCl2 and
TBAB were added in the absence of compound 1 with
the optimized conditions, and only 38% coupling product
was observed (entry 11), and this value was lower than
83% yield in the case of NHC‐PdCl2 species as catalyst.
This result highlighted the preponderant catalytic role of
compound 1 in these coupling reactions.
2.3 | Catalytic activity of NHC‐PdCl2
species in the Heck‐Mizoroki reaction
The Heck‐Mizoroki reaction has evolved significantly
from its original mode as the arylation of olefins with aryl
iodides, and the reaction has been further developed to
allow the coupling of less reactive bromides, chlorides
and pseudo‐halides such as triflates, tosylates, mesylates,
and aryl diazonium salts.[40–43] We used bromobenzene
and styrene as the coupling partners to test the solvent
and base effects in air (Table S2). Use of 1,4‐dioxane as sol-
vent and K2CO3 as base gave trace coupling product at
110 °C in 12 hr (entry 1). Under the same conditions, the
addition of 10 mol% TBAB gave 83% coupling yield in
12 hr (entry 2), and 84% coupling yield in 24 hr (entry 3).
This result shows that the reaction could be effectively
improved in the presence of TBAB. It has been known that
the addition of TBAB as a cocatalyst can enhance the activ-
ity of many catalytic systems. And TBAB is able to activate
and stabilize the palladium(0) species in situ generated,
which is believed to be the real catalytically active spe-
cies.[44–46] The coupling yield was 80% in the N2 atmo-
sphere (entry 4) and other conditions were the same with
entry 2, which showed that the atmosphere did not have
effect on the yield. Under the same conditions with entry
Based on above results, we attempted the cross‐
coupling reactions of various aryl halides with styrene
under the optimized conditions (Table 2). The couplings
TABLE 2 Heck‐Mizoroki reaction of aryl halides with styrene catalyzed by NHC‐PdCl2 speciesa
3b
3c
3a
X = Br, 5 h, 95%
X = Br, 3 h, 81%
X = Br, 6 h, 81%
3d
3e
(1) X = Cl, 24 h, 66%
(2) X = Br, 12 h, 83%
3f
(1) X = Cl, 24 h, trace
(2) X = Br, 8 h, 92%
X = Br, 24 h, 57%
3 h
3i
3 g
(1) X = Cl, 24 h, trace
(2) X = I, 5 h, 96%
X = Br, 6 h, 99%
X = Br, 4 h, 94%
3 l
3j
X = Cl, 24 h, trace
X = Br, 6 h, 94%
3 k
X = Br, 6 h, 95%
aReaction conditions: aryl halide (0.5 mmol), styrene (0.75 mmol), K2CO3 (1.0 mmol), compound 1 (0.2 mol%), PdCl2 (0.4 mol%), TBAB (10 mol%), dioxane
(5 ml), 110 °C in air.

LIU ET AL.
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of aryl bromides with a substituent in para‐position with
styrene afforded good to excellent yields of 81%–95% (3a‐
3c, 3d(2) and 3e(2)). While 3‐bromoanisole gave the mod-
erate coupling yield of 57% (3f). The couplings of 1‐
bromonaphthalene or iodobenzene with styrene afforded
yields of 94% and 96%, respectively (3 g and 3 h(2)).
The couplings of aryl dibromide (such as 1,4‐
dibromonaphthalene, 4,4‐disbromobiphenyl and 9,10‐
dibromoanthracene) with styrene afforded excellent
yields of 94%–99% (3i‐3 k). This catalytic system had poor
catalytic activities to the couplings of aryl chloride with
styrene, and only 4‐nitrochlorobenzene gave moderate
yield of 66% (3d(1)). While 4‐chloroaniline, 1‐chloroben-
zene and 2‐nitriochlorobenzene gave trace coupling prod-
ucts (3e(1), 3 h(1) and 3 l). There was a high selectivity for
the trans product in this reaction system, and any corre-
sponding cis product could be hardly detected after the
reaction, which could be attributed to trans conformation
being a dominant conformation.
reaction, and this value was lower than 93% yield in the
case of NHC‐PdCl2 species as catalyst. This result
highlighted the preponderant catalytic role of compound
1 in these coupling reactions.
We attempted the cross‐coupling reactions of
various aryl halides with phenylacetylene under the opti-
mized conditions (Table 3). The couplings of activated
aryl bromide (such as 4‐bromoacetophenone and 4‐
bromonitrobenzene) with phenylacetylene afforded high
yields of 89% and 98%, respectively (4a and 4b(2)).
The couplings of aryl dibromide (such as 1,4‐
dibromonaphthalene, 4,4‐disbromobiphenyl and 9,10‐
dibromoanthracene) with phenylacetylene afforded
excellent yields of 93–96% (4c‐4e). And the couplings of
3‐bromoanisole
and
1‐bromonaphthalene
with
phenylacetylene gave moderate yields of 49% and 55%,
respectively (4f and 4 g), while 4‐bromobenzenamine
afforded trace coupling product (4 h). This catalytic
system had poor catalytic activities to the coupling
reactions of aryl chloride with phenylacetylene. 4‐
Nitrochlorobenzene gave yield of 23% in 20 hr (4b(1)),
while 2‐nitrochlorobenzene and 2‐chlorobenzaldehyde
gave trace coupling products (4i and 4j).
2.4 | Catalytic activity of NHC‐PdCl2
species in the Sonogashira reaction
We chose the cross‐coupling reaction of 4‐bromoanisole
with phenylacetylene as a model reaction to test the sol-
vent and base effects under N2 (Table S3). Use of 1,4‐diox-
ane or DMF as solvent and K2CO3 or Cs2CO3 as base gave
trace coupling products at 80 °C under N2 (entries 1 and
2). Through inspection of the literatures, we found that
Sonogashira reaction needs to add ancillary catalysts
(such as PPh3 and CuI).[47,48] Under the conditions of
DMF as solvent, Cs2CO3 as the base, 10 mol% of PPh3
and 10 mol% of CuI as ancillary catalysts, high yields of
93% in 8 hr and 94% in 12 h were obtained (entries 3
and 4). But this coupling reaction could not be carried
out in air (entry 5). When the amount of catalyst was
decreased to 0.5 fold compared with entry 3, the coupling
yield dropped to 50% (entry 6). Under the same condi-
tions with entry 3, using DMSO or 1,4‐dioxane as solvent
gave the yield of 58% or 10% (entries 7 and 8). Other
bases, such as K2CO3, K3PO4·3H2O and Et3N, have been
tested to afford relatively poor yields of 18–43% (entries
9–11). Based on the extensive screen, DMF and Cs2CO3
were found to be the most efficient solvent and base in
the presence of 10 mol% of PPh3 and 10 mol% of CuI as
ancillary catalysts with a catalyst loading of 0.5 mol% of
compound 1 and 1.0 mol% of PdCl2 at 80 °C in nitrogen,
thus giving the optimal coupling result. Additionally, the
control experiment was also conducted, in which PdCl2,
PPh3 and CuI were added in the absence of compound
1 with the optimized conditions, and only 40% coupling
product was observed (entry 12). This result showed that
compound 1 had the important function in the catalytic
2.5 | Kinetic studies of Suzuki‐Miyaura,
Heck‐Mizoroki and Sonogashira coupling
reactions
To investigate the mechanisms of reactions, the kinetic
experiments of three types of C‐C coupling reactions were
performed under their optimized conditions (entry 2 in
Table S1, entry 2 in Table S2 and entry 3 in Table S3).
As shown in Figure 1, there are induction periods of
6 hr for Suzuki‐Miyaura reactions, 2 hr for Heck‐
Mizoroki reactions and 1 hr for Sonogashira reactions.
These reactions conducted rapidly from the beginning,
and gave the yield of 80% in 16 hr for Suzuki‐Miyaura
reaction, the yield of 74% in 8 hr for Heck‐Mizoroki reac-
tion and the yield of 80% in 6 hr for Sonogashira reaction.
Then the reactions slowed down, and gave the yields of
92% in 24 hr, 83% in 12 hr and 93% in 8 hr at the end
of the reactions, respectively. The experimental results
indicated that NHC‐Pd(II) complex are precatalysts and
Pd(0) may be the active catalytic species.[49,50]
In Hg drop experiments of three types of C‐C coupling
reactions, when a drop of mercury was added to the reac-
tion mixture before starting the model reactions, the sup-
pressions of three types of coupling reactions have been
observed, which indicated that these reactions are hetero-
geneous and further proved that Pd(0) is the active cata-
lytic species. Therefore, the way in these cross‐coupling
reactions should be that imidazolium salt as molecular
ligand formed Pd‐NHC bond.[11,51]

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LIU ET AL.
TABLE 3 Sonogashira reaction of aryl halides with phenylacetylene catalyzed by NHC‐PdCl2 speciesa
4a
4b
X = Br, 3 h, 89%
(1) X = Cl, 20 h, 23%
(2) X = Br, 3 h, 98%
4c
X = Br, 5 h, 93%
4f
4d
X = Br, 20 h, 49%
X = Br, 5 h, 96%
4e
X = Br, 5 h, 95%
4 h
4i
X = Br, 20 h, trace
4 g
X = Cl, 20 h, trace
X = Br, 20 h, 55%
4j
X = Cl, 20 h, trace
aReaction conditions: aryl halide (0.5 mmol), phenylacetylene (0.75 mmol), Cs2CO3 (1.0 mmol), compound 1 (0.5 mol%), PdCl2 (1 mol%), PPh3 (10 mol%), CuI
(10 mol%), DMF (5 ml), 80 °C in N2.
of analytical grade and used without further purification.
Melting points were determined with a Boetius Block
1
apparatus. H and 13C NMR spectra were recorded on a
Varian Mercury Vx 400 spectrometer at 400 MHz and
100 MHz, respectively. Chemical shifts, δ, are reported
in ppm relative to the internal standard TMS for both
1H and 13C NMR. J values are given in Hz. Elemental
analyses were measured using a Perkin‐Elmer 2400C Ele-
mental Analyzer. GC analysis was carried out using a
Focus DSQI GC–MS equipped with an integrator (C‐
R8A) with a capillary column (CBP‐1 or CBP‐5,
0.25 mm i.d. × 40 m).
3.2 | Preparation of 9,10‐bis[di(2′‐
chloroethyl)aminomethyl]anthracene
FIGURE
1
Kinetic experiments of Suzuki‐Miyaura, Heck‐
A
suspension of 9,10‐bis(chloromethyl)anthracene
Mizoroki and Sonogashira reactions
(4.950 g, 18.0 mmol), diethanolamine (11.355 g,
108.0 mmol), K2CO3 (24.840 g, 180.0 mmol), KI
(0.896 g, 5.4 mmol) in CH3CN (100 ml) were stirred
under refluxing for 36 hr. After filtration, the solvent
was removed in vacuo to give a yellow oil, and the oil
was washed with water to give 9,10‐bis[di(2′‐
hydoxylethyl)aminomethyl]anthracene as a yellow pow-
der. Yield: 5.241 g (71%). M.p.: 154–156 °C. 1H NMR
3 | EXPERIMENTAL
3.1 | General procedures
N‐Ethylimidazole[52] and 9,10‐bis(chloromethyl)anthra-
cene[32] were prepared according to the literature
methods. All the reagents for synthesis and analyses were

LIU ET AL.
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(400 MHz, CDCl3): δ 1.95 (s, 4H, OH), 2.78 (t, J = 5.4 Hz,
8H, CH2), 3.44 (t, J = 5.4 Hz, 8H, CH2), 4.74 (s, 4H, CH2),
7.56 (q, J = 3.4 Hz, 4H, ArH), 8.52 (q, J = 3.4 Hz, 4H,
ArH). 13C NMR (100 MHz, CDCl3): δ 130.8 (ArC), 130.6
(ArC), 125.7 (ArC), 125.1 (ArC), 59.7 (CH2), 56.1 (CH2),
51.6 (CH2).
8.87 (s, 4H, 2‐imiH). 13C NMR (100 MHz, DMSO‐d6): δ
135.3 (2‐imiC), 130.1 (ArC), 125.3 (ArC), 125.0 (ArC),
122.1 (ArC), 121.5 (ArC), 51.4 (CH2), 45.9 (CH2), 44.0
(CH2), 14.9 (CH3) (imi = imidazolium).
3.4 | General method for Suzuki‐Miyaura
reaction
A
solution
of
9,10‐bis[di(2′‐hydoxylethyl)
aminomethyl]anthracene (3.999 g, 9.7 mmol) in CHCl3
(30 ml) was added dropwise into the solution of thionyl
chloride (9.278 g, 78.0 mmol) in CHCl3 (50 ml). The mix-
ture was stirred for 72 h at 60 °C. After filtration, a yellow
In a typical reaction, compound 1 (0.2 mol%), PdCl2
(0.4 mol%), base (1.0 mmol) and solvent (5 ml) were added
to a 20 ml flask, and stirred for 2 h at room temperature
under N2. Then aryl halide (0.5 mmol), phenylboronic acid
(0.6 mmol) and PEG‐400 (0.1 ml) or TBAB (10 mol%) were
added to above solution, and stirred at 60 °C for the desired
time until complete consumption of aryl halide as judged
by TLC or GC analysis. After removal of the solvent, water
(5 ml) was added to the reaction mixture. The solution was
extracted with diethyl ether (8 ml × 3), and dried over
anhydrous MgSO4. Then the solution was filtered and con-
centrated to 2 ml. The solution was analyzed by GC or sep-
arated by a column in silica (400 mesh) to get the products.
powder
of
9,10‐bis[di(2′‐chloroethyl)aminomethyl]
anthracene hydrochloride was obtained. The powder was
added to NaOH aqueous solution (200 ml, 60%) and stirred
for 15 min to wipe off hydrochloric acid, and then CHCl3
(30 ml) was added to the solution. The organic layer was
separated and washed with water (20 ml × 3), and dried
over anhydrous MgSO4. The solvent was evaporated in
vacuo to afford 9,10‐bis[di(2′‐chloroethyl)aminomethyl]
anthracene as a yellow powder. Yield: 3.100 g (77%). M.
1
p.: 132–134 °C. H NMR (400 MHz, DMSO‐d6): δ 2.96 (t,
1
J = 6.8 Hz, 8H, CH2), 3.57 (q, J = 6.0 Hz, 8H, CH2), 4.73
(s, 4H, CH2), 7.58 (q, J = 3.3 Hz, 4H, ArH), 8.62 (q,
J = 3.3 Hz, 4H, ArH). 13C NMR (100 MHz, DMSO‐d6): δ
130.9 (ArC), 130.8 (ArC), 126.0 (ArC), 125.8 (ArC), 55.4
(CH2), 50.3 (CH2), 42.6 (CH2).
All compounds were subjected to H NMR or GC–MS
analysis.
3.5 | General method for Heck‐Mizoroki
reaction
In a typical reaction, compound 1 (0.2 mol%), PdCl2
(0.4 mol%), base (1.0 mmol) and solvent (5 ml) were
added to a 20 ml flask, and stirred for 2 h at room temper-
ature under N2. Then aryl halide (0.5 mmol), styrene
(0.75 mmol) and TBAB (10 mol%) were added and stirred
at 110 °C for the desired time until complete consump-
tion of aryl halide as judged by TLC. After removal of
the solvent, water (5 ml) was added to the mixture. The
solution was extracted with diethyl ether (8 ml × 3),
and dried over anhydrous MgSO4. The solvent was
removed and the residue was chromatographed in silica
(400 mesh) to afford the pure products. All compounds
3.3 | Preparation of 9,10‐bis{di[2′‐(N‐
ethylimidazolium‐1‐yl)ethyl]aminomethyl}
anthracene tetrakis(hexafluorophosphate)
(1)
A suspension of 9,10‐bis[di(2′‐chloroethyl)aminomethyl]
anthracene (2.000 g, 4.2 mmol) and N‐ethylimidazole
(2.364 g, 24.6 mmol) in THF (100 ml) was stirred for
7 days under refluxing, and a yellow oil of 9,10‐bis{di[2′‐
(N‐ethylimidazolium‐1‐yl)ethyl]aminomethyl}anthracene
tetrachloride was formed. Then NH4PF6 (4.010 g,
24.6 mmol) was added to a solution of 9,10‐bis{di[2′‐(N‐
ethylimidazolium‐1‐yl)ethyl]aminomethyl}anthracene
tetrachloride (5.193 g, 4.2 mmol) in methanol (100 ml)
with stirring for 3 days and a white precipitate was
formed. The precipitate was collected by filtration and
washed with a small portion of methanol to give 9,10‐
bis{di[2′‐(N‐ethylimidazolium‐1‐yl)ethyl]aminomethyl}
anthracene tetrakis(hexafluorophosphate) (1) as a pale
yellow powder. Yield: 4.838 g (88%). M.p.: 122–124 °C.
Anal. Calcd for C44H60N10P4F24: C, 40.37; H, 4.62; N,
1
were subjected to H NMR analysis.
3.6 | General method for Sonogashira
reaction
In a typical reaction, compound 1 (0.5 mol%), PdCl2
(1.0 mol%), base (1.0 mmol) and solvent (5 ml) were
added to a 20 ml flask, and stirred for 2 h at room temper-
ature under N2. Then aryl halide (0.5 mmol),
phenylacetylene (0.75 mmol), PPh3 (10 mol%) and CuI
(10 mol%) were added and stirred at 80 °C under N2 for
the desired time until complete consumption of aryl
halide as judged by TLC. After removal of the solvent,
water (5 ml) was added to the mixture. The solution
1
10.70%. Found: C, 40.58; H, 4.33; N, 10.52%. H NMR
(400 MHz, DMSO‐d6): δ 1.33 (t, J = 7.2 Hz, 12H, CH3),
3.06 (s, 8H, CH2), 4.03 (q, J = 7.2 Hz, 8H, CH2), 4.34 (t,
J = 5.4 Hz, 8H, CH2), 4.64 (s, 4H, CH2), 7.32 (s, 4H,
ArH), 7.51 (m, 8H, ArH), 8.24 (q, J = 3.1 Hz, 4H, ArH),

8 of 9
LIU ET AL.
was extracted with diethyl ether (8 ml × 3) and dried over
anhydrous MgSO4. The solvent was removed and the res-
idue was chromatographed in silica (400 mesh) to afford
ORCID
Qing‐Xiang Liu http://orcid.org/0000-0002-8815-2652
1
the pure products. All compounds were subjected to H
NMR analysis.
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How to cite this article: Liu Q‐X, Zhao D‐X, Wu
H, Zhao Z‐X, Lv S‐Z. Catalytic activities of NHC‐
PdCl2 species based on functionalized tetradentate
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