Synthesis, structure and catalysis of a NHC-Pd(II) complex based on a tetradentate mixed ligand

Article abstract of DOI:10.1039/c5ra11089k

Bis-benzimidazolium salt (S)-2,2′-bis[2′′-(N-picolyl-benzimidazoliumyl)ethoxy]-1,1′-binaphthyl hexafluorophosphate [(S)-LH₂]·(PF₆)₂ and its NHC palladium(ii) complex [(S)-LPd](PF₆)₂ (1) have been prepared and characterized. Complex 1 is formed by one tetradentate mixed ligand (S)-L and one Pd(ii) ion, in which one 15-membered ring and two 6-membered rings are present. In this complex, intramolecular π-π interactions between naphthalene rings and benzimidazole rings are observed. Additionally, the catalytic activity of complex 1 in three types of C-C coupling reactions (Suzuki-Miyaura, Heck-Mizoroki and Sonogashira reactions) was investigated. The results show that complex 1 is an effective catalyst in these coupling reactions.

Full text of DOI:10.1039/c5ra11089k

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: Q. liu, K. Cai and
Z. Zhao, RSC Adv., 2015, DOI: 10.1039/C5RA11089K.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Page 1 of 26
RSC Advances
View Article Online
DOI: 10.1039/C5RA11089K
Synthesis, Structure and Catalysis of NHC-Pd(II) Complex Based on
Tetradentate Mixed Ligand
Qing-Xiang Liu*, Kang-Qing Cai, Zhi-Xiang Zhao
Tianjin Key Laboratory of Structure and Performance for Functional Molecules; Key
Laboratory of Inorganic-Organic Hybrid Functional Material Chemistry, Ministry of
Education; College of Chemistry, Tianjin Normal University, Tianjin 300387, China.
* Corresponding author, E-mail: tjnulqx@163.com
Bis-benzimidazolium
salt
(S)-2,2’-bis[2’’-(N-picolyl-benzimidazoliumyl)ethoxy]-1,1’-binaphthyl
hexafluorophosphate [(S)-LH2]·(PF6)2 and its NHC palladium(II) complex
[(S)-LPd](PF6)2 (1) have been prepared and characterized. Complex 1 is formed by
one tetradentate mixed ligand (S)-L and one Pd(II) ion, in which one 15-membered
ring and two 6-membered rings are contained. In this complex, the intramolecular π-π
interactions between naphthalene rings and benzimidazole rings are observed.
Additionally, the catalytic activity of complex 1 in three types of C-C coupling
reactions (Suzuki-Miyaura, Heck-Mizoroki and Sonogashira reactions) was
investigated. The results show that complex 1 is an effective catalyst in these coupling
reactions.
Keywords: N-heterocyclic carbene, palladium(II) complex, structure, catalysis
Introduction
N-Heterocyclic carbenes (NHCs) have become a type of important ligands of
organometallic chemistry and catalysis.1 NHC ligands can form strong carbon-metal
bonds with transition metals due to the strong σ-donating ability of carbene carbon.2
So far, numerous successful methods have been developed to synthesize NHC
complexes with different metal centers. Among these NHC-metal complexes, NHC
palladium(II) complexes play a very important role in the N-heterocyclic carbene
1

RSC Advances
Page 2 of 26
View Article Online
DOI: 10.1039/C5RA11089K
chemistry, 3, 4 and they have turned out to be efficient catalysts for some C-C coupling
reactions, such as Suzuki-Miyaura, Heck-Mizoroki and Sonogashira reactions.5
Compared with palladium(II) complexes based on phosphine ligands, NHC
palladium(II) complexes have better stability to air and moisture and catalytic
activity.6 Some NHC palladium(II) complexes bearing monodentate or polydentate
ligands have been prepared and studied, and they show good catalytic activity in the
construction of C-C, C-N and other C-heteroatom bonds.4, 7-9 In order to improve
further catalytic activity of NHC palladium(II) complexes, some heteroatoms (P,10
N,10a, 11 or O12) were introduced into NHC ligands. The research results show that the
catalytic activity of palladium(II) complexes bearing mixed ligands of NHC and
heteroatoms can be improved remarkably, and the reason may be that strong
coordinating NHC and weak coordinating heteroatoms easily form catalytically active
species with vacant coordination sites. Therefore, these NHC palladium(II) complexes
bearing mixed ligands may have potential applications in organic reactions.13
We are interested in NHC palladium(II) complexes with mixed ligands. Herein, we
report the preparation of bis-benzimidazolium salt (S)-2,2’-bis[2’’-(N-
picolyl-benzimidazoliumyl)ethoxy]-1,1’-binaphthyl
hexafluorophosphate
[(S)-LH2]·(PF6)2, as well as the preparation and structure of N-heterocyclic carbene
palladium(II) complex [(S)-LPd](PF6)2 (1). Additionally, the catalytic activity of
complex 1 in three types of C-C coupling reactions (Suzuki-Miyaura, Heck-Mizoroki
and Sonogashira reactions) was investigated.
Results and discussion
Synthesis and characterizations of precursor [(S)-LH2]·(PF6)2. As shown in
Scheme 1, the (S)-2,2’-dihydroxy-1,1’-binaphthyl as starting material was reacted
with 2-chloroethanol to afford (S)-2,2’-di(2’’-hydroxyethoxy)-1,1’-binaphthyl,
followed by chlorination of hydroxyl groups with thionyl chloride to form
(S)-2,2’-di(2’’-chloroethoxy)-1,1’-binaphthyl,
which
was
reacted
with
N-picolyl-benzimidazole in toluene to afford the bis-benzimidazolium salt
[(S)-LH2]·Cl2, and subsequent anion exchange with ammonium hexafluorophosphate
2

Page 3 of 26
RSC Advances
View Article Online
DOI: 10.1039/C5RA11089K
in
methanol
was
carried
out
to
give
(S)-2,2’-bis[2’’-(N-picolyl-benzimidazoliumyl)ethoxy]-1,1’-binaphthyl
hexafluorophosphate ([(S)-LH2]·(PF6)2). This precursor is stable toward air and
moisture, and soluble in organic solvents, such as CH2Cl2, CH3CN and DMSO,
1
however, the solubility is poor in water, petroleum ether and diethyl ether. In the H
NMR spectra of [(S)-LH2]·(PF6)2, the proton signals (NCHN) of benzimidazolium
appear at δ = 9.43 ppm, which is consistent with the chemical shifts of reported
benzimidazolium salts.14
OH
OH
O
O
OH
OH
Cl
Cl
O
O
SOCl2
Cl OH
N
N
N
N
N
N
N
(1)
(2)
N
N
N
N
O
O
O
O
N
N
-
Pd(OAc)2
K2CO3
2PF6
Pd
NH4PF6
N
N
-
2PF6
[(S)-LH2]·(PF6)2
1
Scheme 1 Preparation of precursor [(S)-LH2]·(PF6)2 and complex 1
Synthesis, characterization and structure of complex 1. As shown in Scheme 1,
complex [(S)-LPd](PF6)2 (1) was prepared via the reaction of [(S)-LH2]·(PF6)2 with
Pd(OAc)2 in the presence of K2CO3 in acetonitrile/ethylene glycol solution. The
single crystals of complex 1 suitable for X-ray diffraction were grown by slow
diffusion of diethyl ether into its solution. Complex 1 is stable to heat, air and
moisture, soluble in CH3CN and DMSO, but scarcely soluble in diethyl ether and
1
hydrocarbon solvents. In the H NMR spectra of 1, the disappearance of the
resonances for the benzimidazolium protons (NCHN) shows the formation of the
expected metal carbene complexes, and the chemical shifts of other hydrogen atoms
are similar to those of corresponding precursor. In 13C NMR spectra, the signals for
the carbene carbon of 1 appear at δ = 179.2 ppm, which are similar to known metal
carbene complexes.15
3

RSC Advances
Page 4 of 26
View Article Online
DOI: 10.1039/C5RA11089K
Complex 1 is formed by one tetradentate mixed ligand (S)-L and one Pd(II) ion, in
which one 15-membered ring and two 6-membered rings are contained (Fig. 1). The
Pd(II) ion is tetra-coordinated with two carbene carbon atoms and two nitrogen atoms
from two pyridine rings to adopt a square-planar geometry. The bond distances of
Pd-C and Pd-N are 1.966(3)-1.976(3) Å and 2.095(3)-2.098(3) Å, respectively. The
bond angles of C(7)-Pd(1)-C(38) and N(1)-Pd(1)-N(6) are 96.0(1)˚ and 94.4(1)˚,
respectively. The bond angles of C-Pd-N are from 84.9(1)˚ to 175.0(1)˚. These values
are similar to those of reported NHC-Pd(II) complexes.16 The axial chirality of
complex 1 is consistent with corresponding precursor because its chiral binaphthyl
unit (S configuration) was not changed during the preparation of metal complex. In
this complex, two naphthalene rings form the dihedral angle of 69.2(3)˚, and the
dihedral angle between two benzimidazole rings is 87.2(2)˚. The dihedral angle
between benzimidazole ring and adjacent pyridine ring is 71.5(3)˚, and the dihedral
angle between two pyridine rings is 50.7(4)˚. The internal ring angles (N-C-N) at the
carbene centers are 107.1(3)˚ and 107.6(3)˚, and these values are similar to those of
known NHC-metal complexes.15 Besides, the intramolecular π-π interactions between
the naphthalene rings and the benzimidazole rings are observed17 with the face-to-face
distance of 3.405(4) Å and the center-to-center distance of 3.858(3) Å.
In the crystal packing of 1, 2D supramolecular layer is formed through three types
of π···π stacking interactions as shown in Fig. S1. In three types of π···π stacking
interactions, one is from intermolecular pyridine rings with the face-to-face distance
of 3.761(7) Å and the center-to-center distance of 3.773(2) Å, and another is from
intermolecular benzimidazole rings with the face-to-face distance of 3.654(5) Å and
the center-to-center distance of 3.659(3) Å, and third is from naphthalene rings and
pyridine rings with the face-to-face distance of 3.534(5) Å and the center-to-center
distance of 3.901(3) Å.
4

Page 5 of 26
RSC Advances
View Article Online
DOI: 10.1039/C5RA11089K
Fig. 1. Perspective view of 1. All hydrogen atoms were omitted for clarity. Selected
bond lengths (Å) and angles (˚): C(38)-Pd(1) 1.966(3), C(7)-Pd(1) 1.976(3),
N(6)-Pd(1) 2.095(3), N(1)-Pd(1) 2.098(3), O(1)-C(15) 1.409(4), O(2)-C(36) 1.432(4);
N(4)-C(38)-N(5) 107.6(3), N(2)-C(7)-N(3) 107.1(3), C(38)-Pd(1)-C(7) 96.0(1),
C(38)-Pd(1)-N(6) 84.9(1), N(1)-Pd(1)-N(6) 94.4(1), C(7)-Pd(1)-N(1) 85.2(1),
C(7)-Pd(1)-N(6) 172.3(1), C(38)-Pd(1)-N(1) 175.0(1).
Catalytic activity of NHC-Pd(II) complex 1 in the Suzuki-Miyaura reaction. The
Suzuki-Miyaura reaction, a cross-coupling process between an organoboron reagent
and an aryl halide, has become a successful and useful tools for forming C-C bonds.18
In order to examine the catalytic activity of NHC-Pd(II) complex 1 in the
Suzuki-Miyaura reaction, we chose the cross-coupling reaction of 4-bromotoluene
with phenylboronic acid as a model reaction in the air to test the effects of solvent and
base (Table S1 in Supplementary Information). Use of K2CO3 as base and water as
solvent gave 97% coupling yield at 40 ˚C over the course of 12 h in the presence of
air (Table S1, Entry 1), whereas use of CH3OH/H2O (1:1) as solvent gave 98% yield
in 6 h (Table S1, Entry 2). Use of K2CO3 as base and other solvents (such as MeOH,
C2H5OH, 1,4-dioxane, THF or C2H5OH/H2O (1:1)) gave yields of 7-80% (Table S1,
Entries 3-7). Additionally, use of water as solvent and other common bases (such as
tBuOK, K3PO4·3H2O and NaOAc) gave yields of 52-74% (Table S1, Entries 8-10).
Under conditions similar to those of entry 1 (but the time being shorten from 12 h to 6
h), 10 mol% of TBAB were added to afford 99% yield (Table S1, Entry 11). The
5

RSC Advances
Page 6 of 26
View Article Online
DOI: 10.1039/C5RA11089K
result indicates that the reaction could be effectively improved in the presence of
TBAB. It has been known that the addition of TBAB as a co-catalyst can enhance the
activity of many catalytic systems. Besides, TBAB is able to activate and stabilize
palladium(0) species generated in situ, which is believed to be the real catalytically
active species.19 Based on this extensive screening, water and K2CO3 were found to
be the efficient solvent and base in the presence of 10 mol% TBAB with a catalyst
loading of 0.1 mol% of complex 1 at 40 ˚C in the air, and these conditions proved
ideal. Reactions were monitored by GC at appropriate time intervals. Althouth the
good yield can be also obtained using CH3OH/H2O (1:1) as solvent, we chose water
as solvent for the purpose of environmental benignancy.
We attempted cross-coupling reactions of various aryl halides with phenylboronic
acids under the optimal reaction conditions. The catalyst is highly efficient toward the
coupling of aryl bromides (or aryl dibromides) with phenylboronic acid to afford
excellent yields of 90-98% (Table 1, 2a, 2b, 2c(1)-2e(1) and 2f-2i, 2n(2)). The
catalyst is also effective toward the coupling of aryl chlorides bearing
electronic-donating or -withdrawing substituents with phenylboronic acid to give
moderate to high yields of 64-89% (Table 1, 2c(2)-2e(2) and 2j-2m). Coupling
reaction of chlorobenzene with phenylboronic acid gave relatively poor yields of 43%
(Table 1, 2n(1)). The coupling of iodobenzene with phenylboronic acid gave
quantitative yield (Table 1, 2n(3)).
In order to further study the influence of the ligand on catalysis, the control
experiment was performed using 4-bromotoluene and phenylboronic acid as
substrates, in which Pd(OAc)2 (or PdCl2) and TBAB were added in the absence of the
ligand with the optimized conditions. Only 39% for Pd(OAc)2 and 32% for PdCl2
desired coupling product were obtained, and these values are smaller than 99% yield
in the case of complex 1 as catalyst. This result highlights the preponderant catalytic
role of the ligand in these aqueous and aerobic coupling reactions.
6

Page 7 of 26
RSC Advances
View Article Online
DOI: 10.1039/C5RA11089K
Table 1 Suzuki-Miyaura Reaction of aryl halides with phenylboronic acid catalyzed
by complex 1[a]
0.1 mol% cat.
K2CO3, TBAB
Ar
(HO)2B
Ar
X
H2O, 40
2a-2n
X = Cl, Br, I
H3CO
H2N
H3CO
2c
2a
2b
X = Br, 10 h, 90%
(1) X = Br, 6 h, 98%
(2) X = Cl, 8 h, 81%
X = Br, 10 h, 92%
O2N
H3COC
2d
2e
(1) X = Br, 6 h, 91%
(2) X = Cl, 6 h, 85%
(1) X = Br, 6 h, 96%
(2) X = Cl, 8 h, 89%
2f
X = Br, 6 h, 95%
2g
2h
2i
X = Br, 8 h, 93%
X = Br, 10 h, 95%
X = Br, 12 h, 92%
O2N
NO2
NO2
CHO
2j
2k
2l
X = Cl, 8 h, 81%
X = Cl, 10 h, 74%
X = Cl, 8 h, 83%
CH3
2n
2m
(1) X = Cl, 8 h, 43%
(2) X = Br, 8 h, 94%
(3) X = I, 8 h, 100%
X = Cl, 6 h, 64%
[a] Reaction conditions: Aryl halide (0.5 mmol), phenylboronic acid (0.6 mmol), K2CO3 (1.2
mmol), complex 1 (0.1 mol %), TBAB (10 mol %), H2O (6 mL) at 40 ˚C in the air.
[b] Reactions were monitored by TLC.
[c] Isolated yield using aryl halide as a standard.
7

RSC Advances
Page 8 of 26
View Article Online
DOI: 10.1039/C5RA11089K
The above results show that complex 1 has high stability to both air and water,
while also demonstrating excellent tolerance of various functional groups.
Additionally, complex 1 can resolve partly in aqueous medium due to the existence of
hydrophilic groups (such as oxygen atom and nitrogen atom). These qualities make 1
a valuable precatalyst for thermally sensitive substrates. This provides an effective
phosphine-free catalyst system for facile coupling of aryl halides with aryl boronic
acids in water under mild and aerobic conditions. These favorable reaction conditions
of Suzuki-Miyaura reaction are important toward ensuring environmental
responsibility while also reducing costs for fine chemical and pharmaceutical
industries.
Catalytic activity of NHC-Pd(II) complex 1 in the Heck-Mizoroki reaction. The
Heck reaction has evolved significantly from its original mode as the arylation of
olefins with aryl iodides, and it is a powerful tool for the coupling of less reactive
bromides, chlorides and pseudo-halides such as triflates, tosylates, mesylates, and aryl
diazonium salts.20 We chose bromobenzene and styrene as the coupling partners to
test the solvent and base effects in the air (Table S2). Using 1,4-dioxane as solvent
and NaOAc as base gave 92% coupling yields at 120 ˚C over the course of 24 h in the
presence of air (Table S2, Entry 1), whereas using other bases (such as K2CO3,
t
K3PO4·3H2O, Et3N, BuOK, KOH, NaHCO3 and Cs2CO3) gave the yields of 15-83%
(Table S2, Entries 2-8). Using NaOAc as base and other solvents (such as H2O, DMF,
CH3CN, THF, DME or DMSO) gave the yields from trace to 61% (Table S2, Entries
9-15). Under conditions similar to those of entry 1 (but temperature being dropped
from 120 ˚C to 100 ˚C), 10 mol% of PEG-400 was added to give coupling yields of
95% (Table S2, Entry 16). This result shows that the reaction could be dramatically
improved in the presence of PEG-400. It has been known that the addition of
PEG-400 as a co-catalyst can enhance the activity of many catalytic systems.21 Based
on this extensive screening, 1,4-dioxane and NaOAc were found to be the efficient
solvent and base in the presence of 10 mol% of PEG-400 as co-catalyst with a catalyst
8

Page 9 of 26
RSC Advances
View Article Online
DOI: 10.1039/C5RA11089K
loading of 0.1 mol% of complex 1 at 100 ˚C in the air, thus giving the optimal
coupling result.
We attempted cross-coupling reactions of various aryl halides with styrene under
the optimal reaction conditions. The cross-coupling of various aryl bromides with
styrene gave good to excellent yields of 80-98% (Table 2，3a, 3b, 3c(1)-3e(1) and
3f-3i). The coupling of 4-chloronitrobenzene or 2-chloronitrobenzene with styrene
gave good yields of 85% or 80%, respectively (Table 2, 3d(2) and 3j). The coupling
of
4-chloroaniline,
4-chloroacetophenone,
2,4-dinitrochlorobenzene,
2-chlorobenzaldehyde or chlorobenzene with styrene gave relatively poor yields of
20-56% (Table 2, 3c(2), 3e(2), 3k, 3l and 3n(1)). And 2-chlorotoluene even gave trace
coupling yield (Table 3: 3m). The catalyst is highly efficient in the coupling of
iodobenzene with styrene to give almost quantitative yield (Table 2, 3n(3)). Notably,
there is high selectivity for the trans product in this reaction system. Hardly any cis
products could be detected after the reaction. The trans isomer appears to be the
dominant conformation assumed during the course of these reactions.
Considering all these facts, complex 1 is an effective catalyst for Heck-Mizoroki
reaction. In order to further study the influence of the ligand on catalysis, the control
experiment was performed using bromobenzene and styrene as substrates, in which
Pd(OAc)2 (or PdCl2) and PEG-400 were added in the absence of the ligand with the
optimized conditions. Only 26% for Pd(OAc)2 and 21% for PdCl2 coupling product
were obtained, and these values are smaller than 95% yield in the case of complex 1
as catalyst. This result highlights the preponderant catalytic role of the ligand in the
coupling reactions.
9

RSC Advances
Page 10 of 26
View Article Online
DOI: 10.1039/C5RA11089K
Table 2 Heck-Mizoroki reaction of aryl halides with styrene catalyzed by complex 1[a]
0.1 mol% cat.
NaOAc, PEG-400
Ar
X
Ar
1,4-dioxane, 100
3a-3n
X = Cl, Br, I
H3CO
H2N
H3CO
3c
3a
3b
(1) X = Br, 24 h, 85%
(2) X = Cl, 24 h, 20%
X = Br, 20 h, 98%
X = Br, 24 h, 91%
O2N
H3COC
3d
3e
3f
(1) X = Br, 24 h, 93%
(2) X = Cl, 24 h, 85%
(1) X = Br, 24 h, 95%
(2) X = Cl, 24 h, 38%
X = Br, 24 h, 82%
3g
3h
3i
X = Br, 24 h, 80%
X = Br, 24 h, 85%
X = Br, 20 h, 86%
NO2
CHO
NO2
O2N
3j
3k
3l
X = Cl, 24 h, 80%
X = Cl, 24 h, 68%
X = Cl, 24 h, 56%
CH3
3m
3n
X = Cl, 24 h, trace
(1) X = Cl, 24 h, 39%
(2) X = Br, 24 h, 95%
(3) X = I, 24 h, 99%
[a] Reaction conditions: aryl halide (0.5 mmol), styrene (0.6 mmol), K2CO3 (1.2 mmol), complex
1 (0.1 mol%), PEG-400 (10 mol%), 1,4-dioxane (6 mL), 100 ˚C in air.
[b] Monitored by TLC.
[c] Isolated yield using aryl halide as a standard.
10

Page 11 of 26
RSC Advances
View Article Online
DOI: 10.1039/C5RA11089K
Catalytic activity of NHC-Pd(II) complex 1 in the Sonogashira reaction. In order
to prove that complex 1 would be a good precatalyst for the Sonogashira reaction, we
chose the cross-coupling reaction of 4-bromoanisole with phenylacetylene as a model
reaction to test the solvent, base and catalyst activity in the air.22 As illustrated in
Table S3, using K3PO4·3H2O as base and 1,4-dioxane/H2O (1:1) as solvent gave 79%
yield at 100 ˚C over the course of 24 h in the presence of air (Table S3, entry 1). In the
same conditions, when 10 mol% of TBAB was added, the yield rose to 93% (Table S3,
entry 2). Using Cs2CO3 as base and other solvents (such as 1,4-dioxane, DMF, DMSO,
CH3CN, H2O, THF, DMF/H2O (1:1) or 1,4-dioxane/H2O (1:1)) gave yields from trace
to 69% (Table S3, Entries 3-10). Using 1,4-dioxane/H2O (1:1) as solvent in the
presence of 10 mol% of PPh3 or TBAB, the different bases (such as K2CO3, KOH,
NaOAc, Et3N or NaHCO3) were investigated to give the yields of 70-91% (Table S3,
Entries 11-17). Based on this extensive screening, 1,4-dioxane/H2O (1:1) and
K3PO4·3H2O were proved to be the efficient solvent and base in the presence of 10
mol% of TBAB with a catalyst loading of 0.1 mol% of complex 1, thus giving the
optimal coupling result.
We attempted the cross-coupling reactions of various aryl halides with
phenylacetylene under the optimized conditions. Various aryl bromides could be
easily coupled to phenylacetylene to give the good to excellent yields of 86-96%
(Table 3, 4a, 4b, 4c(1)-4e(1), 4f-4i and 4n(2)). Coupling reactions of 4-chloroaniline,
4-chloronitrobenzene or 2-chloronitrobenzene with phenylacetylene gave good yields
of 76-83% (Table 3, 4c(2), 4d(2) and 4j). While the couplings of
4-chloroacetophenone,
2,4-dinitrochlorobenzene,
2-chlorobenzaldehyde,
2-chlorotoluene or chlorobenzene with phenylboronic acid gave poor yields of
10-45% (Table 3, 4e(2), 4k-4m and 4n(1)). The catalyst was highly efficient in the
coupling of iodobenzene with phenylacetylene to give almost quantitative yield (Table
3, 4n(3)). The above results show complex 1 is an effective precatalyst for
Sonogashira reaction. Additionally, a control experiment was also performed using
4-bromoanisole with phenylacetylene as substrates, in which Pd(OAc)2 (or PdCl2) and
TBAB were added without the ligand with the optimized conditions. Only 31% for
11

RSC Advances
Page 12 of 26
View Article Online
DOI: 10.1039/C5RA11089K
Pd(OAc)2 and 29% for PdCl2 coupling product were obtained, and these values are
smaller than 93% yield in the case of complex 1 as catalyst. This result highlights the
preponderant catalytic role in the coupling reaction.
Table 3 Sonogashira reaction of aryl halides with phenylacetylene catalyzed by
complex 1[a]
0.1 mol% cat.
K3PO4·3H2O, TBAB
Ar
X = Cl, Br, I
H3CO
X
Ar
1,4-dioxane/H2O (1:1), 100
4a-4n
H2N
H3CO
4c
4a
4b
(1) X = Br, 24 h, 96%
(2) X = Cl, 30 h, 78%
X = Br, 24 h, 93%
X = Br, 24 h, 90%
O2N
H3COC
4d
4e
(1) X = Br, 24 h, 89%
(2) X = Cl, 30 h, 83%
(1) X = Br, 24 h, 95%
(2) X = Cl, 30 h, 34%
4f
X = Br, 24 h, 91%
4i
4g
4h
X = Br, 24 h, 92%
X = Br, 30 h, 86%
X = Br, 24 h, 93%
O2N
NO2
NO2
CHO
4j
4k
4l
X = Cl, 30 h, 76%
X = Cl, 30 h, 45%
X = Cl, 30 h, 10%
CH3
4n
4m
(1) X = Cl, 24 h, 43%
(2) X = Br, 24 h, 87%
(3) X = I, 24 h, 99%
X = Cl, 30 h, 11%
[a] Reaction conditions: aryl halide (0.5 mmol), phenylacetylene (0.6 mmol), base (1.2 mmol),
12

Page 13 of 26
RSC Advances
View Article Online
DOI: 10.1039/C5RA11089K
complex 1 (0.1 mol%), TBAB (10 mol%), 1,4-dioxane/H2O (6 mL), 100 ˚C in air.
[b] Monitored by TLC.
[c] Isolated yield using aryl halide as a standard.
It is noteworthy that the good catalytic activity of NHC-Pd(II) complex 1 can be
ascribed to the strong donating ability of NHC and the weak coordination of nitrogen.
The weak coordinating abilities of nitrogen atoms allow them to readily dissociate
from metal centers thus creating catalytically active species with vacant coordination
sites. The strong Pd-C bond presumably facilitates oxidative addition of aryl halogens
to the metal. The dynamic dissociation and association of nitrogen atoms allows the
approach of substrate to the metal center, and the substituents on the benzimidazole
rings favor stabilization of the active metal species after reductive elimination of the
products.
Additionally, the reaction conditions (catalyst loading, temperature, solvents and
bases) between the present paper and literatures are compared as shown in Table S4.
The catalyst loading of complex 1 is all 0.1% in three types of C-C coupling reactions,
which is same as the most case of reported data in Suzuki-Miyaura22(b), 23 and
Heck-Mizoroki reactions,22(b), 23(k), 23(l), 24 whereas this value is smaller than reported
data (1-4%) in Sonogashira reaction.22, 23m, 25 The reaction temperature for these
reactions in the present paper is in the middle of reported data (in three types of C-C
coupling reactions: 40 ˚C, 100 ˚C and 100 ˚C, respectively, in the present paper;
25-140 ˚C, 80-150 ˚C and 80-120 ˚C, respectively, in literatures). In the present paper,
pure water, organic solvent and water/organic solvent are used, respectively, in three
types of C-C coupling reactions, and the similar cases can be also found in reported
results. In the use of bases, we selected inexpensive K2CO3, NaOAc and K3PO4·3H2O,
respectively, in three types of C-C coupling reactions, and the similar bases are also
used in literatures.
On the whole, the results obtained using tetradentate Pd(II) complex 1 as catalyst in
most Suzuki-Miyaura, Heck-Mizoroki and Sonogashira reactions are similar to or
slightly better than those of related NHC Pd(II) complexes. By the analysis and
comparison of complex 1 with other NHC metallic catalysts published,26-28 we can
13

RSC Advances
Page 14 of 26
View Article Online
DOI: 10.1039/C5RA11089K
know that the catalytic activity of a catalyst is related to a number of factors such as
the steric hindrance and electronic effects of different substituents around Pd, as well
as the stability and solubility of complexes. Besides, the reaction conditions are also
unneglected factors.
Conclusion
In summary, bis-benzimidazolium salt [(S)-LH2]·(PF6)2 and its NHC palladium(II)
complex 1 have been prepared and characterized. In the crystal structure of complex 1,
one 15-membered ring and two 6-membered rings are contained. Additionally, the
catalytic activity of the complex 1 in three types of C-C coupling reactions
(Suzuki-Miyaura, Heck-Mizoroki and Sonogashira reactions) was studied. The results
show that complex 1 can smoothly catalyze most Suzuki-Miyaura reactions of various
aryl halides (iodide, bromide and chloride) with arylboronic acids using water as
solvent and K2CO3 as base in the air at 40 ˚C to afford moderate to high yields.
Likewise, most Heck-Mizoroki or Sonogashira reactions can also be performed
efficiently at 100 ˚C in the air.
Compared with reported NHC Pd(II) complexes, complex 1 shows similar or
slightly better catalytic activity in these coupling reactions. Complex 1 may be a
valuable precatalyst for the preparation of diaryl derivatives, styrene derivatives or
phenylacetylene derivatives. Further studies of new organometallic complexes from
precursor [(S)-LH2]·(PF6)2 as well as analogous ligands are underway.
Experimental section
General procedures. N-Picolyl-benzimidazole was prepared according to the
literature method.29 All the reagents for synthesis and analyses were of analytical
grade and used without further purification. Melting points were determined on an
1
Digital Vision MP Instrument. H and 13C NMR spectra were recorded at 400 MHz
and 100 MHz, respectively. Chemical shifts, δ, are reported in ppm relative to the
1
internal standard TMS for both H and 13C NMR. J values are given in Hz. The
elemental analyses of all compounds were obtained from the powder compounds
14

Page 15 of 26
RSC Advances
View Article Online
DOI: 10.1039/C5RA11089K
recrystallised. GC analyses were carried out with a capillary column (CBPī or CBP-5,
0.25 mm i.d × 40 m).
Preparation of (S)-2,2’-di(2’’-hydroxyethoxy)-1,1’-binaphthyl. A DMF (100 mL)
suspension of (S)-2,2’-dihydroxy-1,1’-binaphthyl (5.000 g, 17.4 mmol) and potassium
carbonate (9.646 g, 69.9 mmol) was stirred for 1 h at 50 ˚C. Then 2-chloroethanol
(5.628 g, 69.9 mmol) was added dropwise, and stirred continually for 24 h under
refluxing. The solvent was removed under vacuum, and 500 mL water was added.
The solution was extracted with CH2Cl2 (3 × 30 mL) and the extracting solution was
dried over anhydrous MgSO4. After removing CH2Cl2, a pale yellow oil was obtained,
and the crude product was recrystallized with MeOH to give
(S)-2,2’-di(2’’-hydroxyethoxy)-1,1’-binaphthyl as a white powder. Yield: 6.008 g
(92%). M.p.: 112-114 ˚C. Anal. Calcd for C24H22O4: C, 76.98; H, 5.92%. Found: C,
1
76.63; H, 5.88%. H NMR (400 MHz, CDCl3): δ 8.02 (d, J = 8.8 Hz, 2H, ArH), 7.93
(d, J = 8.0 Hz, 2H, ArH), 7.48 (d, J = 9.2 Hz, 2H, ArH), 7.41 (t, J = 7.4 Hz, 2H, ArH),
7.30 (t, J = 7.4 Hz, 2H, ArH), 7.17 (d, J = 8.4 Hz, 2H, ArH), 4.28 (m, 2H, CH2), 4.08
13
(m, 2H, CH2), 3.66 (m, 4H, CH2), 2.31 (s, 2H, OH). C NMR (100 MHz, CDCl3): δ
153.5 (PhC), 133.8 (PhC), 129.8 (PhC), 129.6 (PhC), 128.1 (PhC), 126.7 (PhC), 125.2
(PhC), 124.2 (PhC), 120.3 (PhC), 115.9 (PhC), 71.7 (OCH2CH2), 61.2 (OCH2CH2).
Preparation of (S)-2,2’-di(2’’-chloroethoxy)-1,1’-binaphthyl. To a chloroform (100
mL) solution of (S)-2,2’-di(2’’-hydroxyethoxy)-1,1’-binaphthyl (5.000 g, 13.4 mmol)
and pyridine (5.288 g, 66.8 mmol), thionyl chloride (7.947 g, 66.8 mmol) was added
dropwise at room temperature within 1 h. Then the solution was stirred continually for
12 h at 70 ˚C. The mixture was cooled and washed with water (3 × 100 mL). The
organic layer was dried over anhydrous MgSO4. After removing chloroform,
(S)-2,2’-di(2’’-chloroethoxy)-1,1’-binaphthyl was obtained as a pale yellow powder.
Yield: 3.571 g (65%). M.p.: 101-103 ˚C. Anal. Calcd for C24H20O2Cl2: C, 70.08; H,
4.90%. Found: C, 70.37; H, 5.14%. 1H NMR (400 MHz, CDCl3): δ 7.97 (d, J = 8.8 Hz,
2H, ArH), 7.88 (d, J = 8.4 Hz, 2H, ArH), 7.43 (d, J = 8.8 Hz, 2H, ArH), 7.37 (t, J =
15

RSC Advances
Page 16 of 26
View Article Online
DOI: 10.1039/C5RA11089K
7.4 Hz, 2H, ArH), 7.25 (t, J = 7.6 Hz, 2H, ArH), 7.13 (d, J = 8.4 Hz, 2H, ArH),
4.22(m, 4H, CH2), 3.40 (m, 4H, CH2). 13C NMR (100 MHz, CDCl3): δ 153.6 (PhC),
147.9 (PhC), 134.0 (PhC), 129.6 (PhC), 127.9 (PhC), 126.5 (PhC), 125.4 (PhC), 124.1
(PhC), 121.0 (PhC), 116.3 (PhC), 70.1 (OCH2CH2), 41.7 (OCH2CH2).
Preparation of [(S)-LH2]·(PF6)2.
A
toluene (35 mL) solution of
g, 6.1 mmol) and
(S)-2,2’-di(2’’-chloroethoxy)-1,1’-binaphthyl (1.000 g, 2.4 mmol) was stirred for 7
days under refluxing, and brown oil of
N-picolyl-benzimidazole
(1.274
a
(S)-2,2’-bis[2’’-(N-picolyl-benzimidazoliumyl)ethoxy]-1,1’-binaphthyl chloride was
obtained after the solvent was removed via a rotary evaporator. Then NH4PF6 (0.938 g,
5.7 mmol) was added to
a
methanol solution (100 ml) of
chloride
(S)-2,2’-bis[2’’-(N-picolyl-benzimidazoliumyl)ethoxy]-1,1’-binaphthyl
(2.016 g, 2.4 mmol) 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 [(S)-LH2]·(PF6)2. Yield: 1.734 g (68%). M.p.: 148-150 ˚C. Anal. Calcd for
C50H42F12N6O2P2: C, 57.25; H, 4.03; N, 8.01%. Found: C, 57.62; H, 4.41; N,
8.35%.1H NMR (400 MHz, DMSO-d6): δ 9.43 (s, 2H, 2-bimiH), 8.43 (d, J = 4.4 Hz,
2H, ArH), 7.98 (d, J = 8.8 Hz, 2H, ArH), 7.90 (q, J = 2.6 Hz, 4H, ArH), 7.77 (d, J =
8.4 Hz, 2H, ArH), 7.63 (d, J = 8.0 Hz, 2H, ArH), 7.50 (t, J = 7.8 Hz, 2H, ArH), 7.43
(d, J = 9.6 Hz, 2H, ArH), 7.37 (q, J = 4.0 Hz, 2H, ArH), 7.28 (t, J = 8.4 Hz, 4H, ArH),
7.21 (t, J = 7.8 Hz, 2H, ArH), 6.99 (m, J = 5.0 Hz, 2H, ArH), 6.58 (d, J = 8.4 Hz, 2H,
ArH), 5.68 (m, 3H, CH2), 4,63 (t, J = 4.6 Hz, 3H, CH2), 4.38 (t, J = 4.4 Hz, 3H, CH2),
4.15 (q, J = 5.2 Hz, 3H, CH2). 13C NMR (100 MHz, DMSO-d6): δ 153.1 (ArC), 149.9
(ArC), 142.9 (ArC), 138.0 (ArC), 132.9 (bimi-NCN), 131.1 (ArC), 130.9 (ArC),
130.0 (ArC), 129.3 (ArC), 128.4 (ArC), 126.8 (ArC), 126.7 (ArC), 126.6 (ArC), 126.4
(ArC), 125.5 (ArC), 125.0 (ArC), 124.2 (ArC), 123.2 (ArC), 119.6 (ArC), 116.3
(ArC), 114.0 (ArC), 113.0 (ArC), 67.8 (OCH2CH2), 51.2 (OCH2CH2), 49.0 (CH2),
47.2 (CH2) (bimi = benzimidazole).
16

Page 17 of 26
RSC Advances
View Article Online
DOI: 10.1039/C5RA11089K
Prepartion of [(S)-LPd](PF6)2 (1). An acetonitrile/ethylene glycol (20 mL, v:v = 1:1)
suspension of K2CO3 (0.179 g, 1.3 mmol), [(S)-LH2]·(PF6)2 (0.209 g, 0.2 mmol) and
Pd(OAc)2 (0.042 g, 0.2 mmol) was stirred for 24 h under 60 ˚C. The resulting solution
was filtered and concentrated to 10 mL, and Et2O (5 mL) was added to precipitate 1
as a yellow powder. Yield: 0.057 g (25%). M.p.: 280-282 ˚C. Anal. Calcd for
C50H40F12N6O2P2Pd: C, 52.07; H, 3.49; N, 7.29%. Found: C, 52.34; H, 3.63; N,
1
7.52%. H NMR (400 MHz, DMSO-d6): δ 8.24 (m, 7H, PhH), 7.98 (m, 4H, PhH),
7.80 (d, J = 8.4 Hz, 2H, PhH), 7.65 (t, J = 6.6 Hz, 2H, PhH), 7.44 (m, 7H, PhH), 4.90
(m, 2H, CH2), 4.52 (m, 2H, CH2), 4.24 (m, 2H, CH2), 2.89 (s, 3H, CH2 ), 2.73 (s, 3H,
CH2). 13C NMR (100 MHz, DMSO-d6): δ 179.2 (bimi-NCN), 154.5 (PhC), 153.8
(PhC), 153.2 (PhC), 147.5 (PhC), 135.2 (PhC), 133.6 (PhC), 133.0 (PhC), 129.6
(PhC), 129.5 (PhC), 126.6 (PhC), 126.4 (PhC), 125.8 (PhC), 125.2 (PhC), 124.7
(PhC), 124.6 (CH3), 112.4 (PhC), 111.7 (PhC), 68.9 (CH2), 63.3 (CH2), 62.9 (CH2).
General procedure for the Suzuki-Miyaura reaction. In a typical reaction, aryl
halide (0.5 mmol), arylboronic acid (0.6 mmol), base (1.2 mmol), NHC-Pd(II)
complex 1 (0.1 mol%) and TBAB (10 mol%) in solvent (6 mL) were stirred at 40 ˚C
in air. After the desired reaction time, the reaction was stopped, and water (20 mL)
was added to the reaction mixture. The mixture was extracted by n-hexane (10 mL ×
3), and the organic layer was washed with water (10 mL × 3) and dried over
anhydrous MgSO4. For the determination of GC-MS yields, the above solution was
filtered through a thin pad of silica gel (elution with CH2Cl2 (100 mL)) and
concentrated to 5 mL. n-Tridecane (92 mg) was added as internal standard. The
isolated products were purified by column chromatography on silica gel using a
mixture of n-hexane and dichloromethane (from pure n-hexane to
n-hexane/dichloromethane = 10/1) as eluant. The isolated yields were determined
using aryl halides as standards.
General procedure for the Heck-Mizoroki reaction. A mixture of aryl halide (0.5
mmol), styrene (0.6 mmol), base (1.2 mmol), complex 1 (0.1 mol%) and PEG-400 (10
17

RSC Advances
Page 18 of 26
View Article Online
DOI: 10.1039/C5RA11089K
mol%) in solvent (6 mL) was stirred at 100 ˚C or 120 ˚C in air. After the desired
reaction time, the reaction was stopped, and water (20 mL) was added to the reaction
mixture. The mixture was extracted by ethyl ether (10 mL × 3), and the organic layer
was washed with water (10 mL × 3) and dried over anhydrous MgSO4. Then the
solution was filtered and concentrated to about 2 mL. The isolated products were
purified by column chromatography on silica gel using a mixture of n-hexane and
dichloromethane (from pure n-hexane to n-hexane/dichloromethane = 10/1) as eluant.
The isolated yields were determined using aryl halides as standards.
General procedure for the Sonogashira reaction. A mixture of aryl halide (0.5
mmol), phenylacetylene (0.6 mmol), base (1.2 mmol), complex 1 (0.1 mol%) and
TBAB (10 mol%) in solvent (6 mL) was stirred at 100 ˚C in air. After the desired
reaction time, the reaction was stopped, and water (20 mL) was added to the reaction
mixture. The mixture was extracted by diethyl ether (10 mL × 3), and the organic
layer was washed with water (10 mL × 3) and dried over anhydrous MgSO4. Then the
solution was filtered and concentrated to about 2 mL. The isolated products were
purified by column chromatography on silica gel using a mixture of n-hexane and
dichloromethane (from pure n-hexane to n-hexane/dichloromethane = 10/1) as eluant.
The isolated yields were determined using aryl halides as standards
X-ray data collection and structure determinations. X-ray single-crystal
diffraction data for complexs were collected by using a Bruker Apex II CCD
diffractometer at 173(2) K for 1 with Mo-Ka radiation (λ = 0.71073 Å) by ω scan
mode. There was no evidence of crystal decay during data collection in all cases.
Semiempirical absorption corrections were applied by using SADABS and the
program SAINT was used for integration of the diffraction profiles.30 All structures
were solved by direct methods by using the SHELXS program of the SHELXTL
package and refined with SHELXL31 by the full-matrix least-squares methods with
anisotropic thermal parameters for all non-hydrogen atoms on F2. Hydrogen atoms
bonded to C atoms were placed geometrically and presumably solvent H atoms were
18

Page 19 of 26
RSC Advances
View Article Online
DOI: 10.1039/C5RA11089K
first located in difference Fourier maps and then fixed in the calculated sites. Further
details for crystallographic data and structural analysis are listed in Table 4. Figures
were generated by using Crystal-Maker.32
Table 4 Summary of crystallographic data complex 1
1·0.5C2H6O2
Chemical
formula
Formula weight
Cryst syst
Space group
a, Å
C50H40F12N6O2P2Pd
·0.5C2H6O2
1184.25
Triclinic
Pī
F(000)
1198
Cryst size, mm
θmin, θmax, deg
T, K
0.18 × 0.17 × 0.15
1.36, 25.01
173(2)
12.526(1)
14.488(1)
15.330(1)
98.5(1)
No. of data collected
No. of unique data
No. of refined params
Goodness-of-fit on F2 a
Final R indicesb [I > 2σ(I)]
R1
12770
b, Å
8625
c, Å
677
α, deg
1.016
β, deg
95.0(1)
γ, deg
V, Å3
115.0(1)
2456.2(3)
2
0.0397
0.1012
wR2
Z
R indices (all data)
R1
Dcalcd, Mg m-3
Abs coeff, mm-1
1.601
0.0469
0.1077
0.540
wR2
2
aGOF = [Σw(Fo - Fc2)2/(n-p)]1/2, where n is the number of reflection and p is the
b
2
number of parameters refined. R1 = Σ(||Fo| - |Fc||)/Σ|Fo|; wR2 = [Σ[w(Fo - Fc2)2 ]/
2 2 1/2
Σw(Fo ) ] .
Acknowledgements
This work was financially supported by the National Natural Science Foundation of
China (No.21172172), Tianjin Natural Science Foundation (No.11JCZDJC22000) and
The Program for Innovative Research Team in University of Tianjin (TD12-5038).
Supplementary information
1
Tables and figures for complex 1, and H NMR and 13C NMR spectra for precursor,
complex and all coupling products in Suzuki-Miyaura, Heck-Mizoroki and
Sonogashira reactions. CCDC 1023636 contains the supplementary crystallographic
data for complex 1. These data can be obtained free of charge via
19

RSC Advances
Page 20 of 26
View Article Online
DOI: 10.1039/C5RA11089K
http//www.ccdc.cam.ac.uk/conts/retrieving.html,
or
from
the
Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
References
1 (a) M. Melaimi, M. Soleilhavoup and G. Bertrand, Angew. Chem., Int. Ed., 2010, 49,
8810; (b) M. Poyatos, J. A. Mata and E. Peris, Chem. Rev., 2009, 109, 3677; (c) F.
E. Hahn and M. C. Jahnke, Angew. Chem., Int. Ed., 2008, 47, 3122; (d) W. A.
Herrmann, Angew. Chem., Int. Ed., 2002, 41, 1290; (e) L. Mercs and M. Albrecht,
Chem. Soc. Rev., 2010, 39, 1903; (f) S. Budagumpi and S. Endud, Organometallics,
2013, 32, 1537; (g) W. A. Herrmann, Angew. Chem., 2002, 114, 1342; (h) S. P.
Nolan, Acc. Chem. Res., 2011, 44, 91; (i) S. Gaillard, C. S. J. Cazin and S. P. Nolan,
Acc. Chem. Res., 2012, 45, 778; (j) F. Wang, L. J. Liu, W. Wang, S. Li and M. Shi,
Coord. Chem. Rev., 2012, 256, 804.
2 (a) C. Boehme and G. Frenking, J. Am. Chem. Soc., 1996, 118, 2039; (b) M. S.
Viciu, O. Navarro, R. F. Germaneau, R. A. Kelly, W. Sommer, N. Marion, E. D.
Stevens, L. Cavallo and S. P. Nolan, Organometallics, 2004, 23, 1629.
3 (a) W. N. O. Wylie, A. J. Lough and R. H. Morris, Organometallics, 2010, 29, 570;
(b) A. R. Chianese, P. T. Bremer, C. Wong and R. J. Reynes, Organometallics,
2009, 28, 5244; (c) X. Q. Zhang, Y. P. Qiu, B. Rao and M. M. Luo,
Organometallics, 2009, 28, 3093; (d) N. D. Clement, K. J. Cavell and L. L. Ooi,
Organometallics, 2006, 25, 4155.
4 (a) N. Marion and S. P. Nolan, Acc. Chem. Res., 2008, 41, 1440; (b) J. Houghton, G.
Dyson, R. E. Douthwaite, A. C. Whitwood and B. M. Kariuki, Dalton Trans., 2007,
28, 3065; (c) W. A. Herrmann, M. Elison, J. Fischer, C. Koecher and G. R. J. Artus,
Angew. Chem., Int. Ed., 1995, 34, 2371.
5 (a) N. Stylianides, A. A. Danopoulos, D. Pugh, F. Hancock and A. Zanotti-Gerosa,
Organometallics, 2007, 26, 5627; (b) S. Ahrens, A. Zeller, M. Taige and T.
Strassner, Organometallics, 2006, 25, 5409; (c) E. A. B. Kantchev, C. J. O’Brien
and M. G. Organ, Angew. Chem., Int. Ed., 2007, 46, 2768; (d) L. G. Guang, G. Pei,
20

Page 21 of 26
RSC Advances
View Article Online
DOI: 10.1039/C5RA11089K
H. Pan, Q. Cheng, C. S. Cao, Y. Peng, Z. Shi, G. S. Pang and Y. H. Shi, Dalton
Trans., 2012, 41, 5020; (e) A. Rit, T. Pape, A. Hepp and F. E. Hahn,
Organometallics, 2011, 30, 334; (f) A. Suzuki, J. Organomet. Chem., 2002, 653, 83;
(g) A. F. Littke and G. C. Fu, Angew. Chem., 2002, 41, 4176; (h) Q. X. Liu, W.
Zhang, X. J. Zhao, Z. X. Zhao, M. C. Shi and X. G. Wang, Eur. J. Org. Chem.,
2013, 7, 1253; (i) Q. X. Liu, L. X. Zhao, X. J. Zhao, Z. X. Zhao, Z. Q. Wang, A. H.
Chen and X. G. Wang, J. Organomet. Chem., 2013, 731, 35.
6 (a) S. P. Nolan, N-Heterocyclic Carbenes in Synthesis, Wiley-VCH Verlag GmbH
& Co., KGaA, Weinheim, 2006. (b) N. Marion, O. Navarro, J. G. Mei, E. D.
Stevens, N. M. Scott and S. P. Nolan, J. Am. Chem. Soc., 2006, 128, 4101; (c) G.
Altenhoff, R. Goddard, C. W. Lehmann and F. Glorius, J. Am. Chem. Soc., 2004,
126, 15195; (d) V. César, S. Bellemin-Laponnaz and L. H. Gade, Organometallics,
2002, 21, 5204; (e) B. Karimi and D. Enders, Org. Lett., 2006, 8, 1237.
7 F. W. Li, S. Q. Bai and T. S. A. Hor, Organometallics, 2008, 27, 672.
8 H. L. Qiu, S. M. Sarkar, D. H. Lee and M. J. Jin, Green Chem., 2008, 10, 37.
9 (a) F. Glorius (Ed.), N-heterocyclic Carbenes in Transition Metal Catalysis, in:
Topics in Organometallic Chemistry, Springer, Berlin/Heidelberg, Germany, 2007,
vol. 21; (b) S. K. Yen, L. L. Koh, F. E. Hahn, H. V. Huynh and T. S. A. Hor,
Organometallics, 2006, 25, 5105.
10 (a) A. A. Danopoulos, N. Tsoureas, S. A. Macgregor and C. Smith,
Organometallics, 2007, 26, 253; (b) C. C. Lee, W. C. Ke, K. T. Chan, C. L. Lai, C.
H. Hu and H. M. Lee, Chem. Eur. J., 2007, 13, 582; (c) J. Wolf, A. Labande, J. C.
Daran and R. Poli, J. Organomet. Chem., 2006, 691, 433; (d) J. Y. Zeng, M. H.
Hsieh and H. M. Lee, J. Organomet. Chem., 2005, 690, 5662; (e) L. D. Field, B. A.
Messerle, K. Q. Vuong and P. Turner, Organometallics, 2005, 24, 4241; (f) P. L.
Chiu and H. M. Lee, Organometallics, 2005, 24, 1692; (g) H. M. Lee, J. Y. Zeng, C.
H. Hu and M. T. Lee, Inorg. Chem., 2004, 43, 6822; (h) C. L. Yang, H. M. Lee and
S. P. Nolan, Org. Lett., 2001, 3, 1511; (i) N. Tsoureas, A. A. Danopoulos, A. A. D.
Tulloch and M. E. Light, Organometallics, 2003, 22, 4750.
11 (a) M. Y. Chiang, Y. X. Li, D. Krishnan, P. Sumod, K. H. Ng and P. H. Leung, Eur.
21

RSC Advances
Page 22 of 26
View Article Online
DOI: 10.1039/C5RA11089K
J. Inorg. Chem., 2010, 1413; (b) N. Stylianides, A. A. Danopoulos and N. Tsoureas,
J. Organomet. Chem., 2005, 690, 5948; (c) D. S. McGuinness and K. J. Cavell,
Organometallics, 2000, 19, 741.
12 (a) N. A. Jones, S. T. Liddle, C. Wilson and P. L. Arnold, Organometallics, 2007,
26, 755; (b) P. L. Arnold, M. Rodden and C. Wilson, Chem. Commun., 2005, 1743;
(c) P. L. Arnold, M. Rodden, K. M. Davis, A. C. Scarisbrick, A. J. Blake and C.
Wilson, Chem. Commun., 2004, 1612; (d) H. Clavier, L. Coutable, L. Toupet, J. C.
Guillemin and M. Mauduit, J. Organomet. Chem., 2005, 690, 5237; (e) A. W.
Waltman and R. H. Grubbs, Organometallics, 2004, 23, 3105; (f) P. L. Arnold, A.
C. Scarisbrick, A. J. Blake and C. Wilson, Chem. Commun., 2001, 2340.
13 (a) A. T. Normand and K. J. Cavell, Eur. J. Inorg. Chem., 2008, 2781; (b) E. A. B.
Kantchev, C. J. O’Brien and M. G. Organ, Angew. Chem., 2007, 119, 2824.
14 (a) P. L. Arnold and I. J. Casely, Chem. Rev., 2009, 109, 3599; (b) X. L. Liu and W.
Z. Chen, Organometallics, 2013, 31, 6614; (c) Q. Li, X. Li, J. Yang, H. B. Song
and L. F. Tang, Polyhedron, 2013, 59, 29; (d) J. H. Chen, X. Q. Zhang, Q. Feng
and M. M. Luo, J. Organomet. Chem., 2006, 691, 470; (e) J. W. Wang, F. H. Meng
and L. F. Zhang, Organometallics, 2009, 28, 2334; (f) C. Yan, X. M. Zeng, W. F.
Zhang, M. Yan and M. M. Luo, J. Organomet. Chem., 2006, 691, 3391.
15 (a) J. J. Van Veldhuizen, J. E. Campbell, R. E. Giudici and A. H. Hoveyda, J. Am.
Chem. Soc., 2005, 127, 6877; (b) J. C. Y. Lin, R. T. W. Huang, C. S. Lee, A.
Bhattacharyya, W. S. Hwang and I. J. B. Lin, Chem. Rev., 2009, 109, 3561; (c) C.
M. Crudden and D. P. Allen, Coord. Chem. Rev., 2004, 248, 2247; (d) Y. S. Jiang,
W. Z. Chen and W. M. Lu, Tetrahedron, 2013, 69, 3669; (e) C. H. Cheng, D. F.
Chen, H. B. Song and L. F. Tang, J. Organomet. Chem., 2013, 726, 1; (f) X. Wang,
S. Liu, L. H. Weng and G. X. Jin, Organometallics, 2006, 25, 3565; (g) L. H. Gade
and S. Bellemin-Laponnaz, Coord. Chem. Rev., 2007, 251, 718; (h) B. Liu, C. Y.
Chen, Y. J. Zhang, X. L. Liu and W. Z. Chen, Organometallics, 2013, 32, 5451; (i)
D. W. Zhao, Y. F. Xie, H. B. Song and L. F. Tang, J. Organomet. Chem., 2013,
718, 89; (j) J. W. Wang, Q. S. Li, F. B. Xu, H. B. Song and Z. Z. Zhang, Eur. J. Org.
Chem., 2006, 1310.
22

Page 23 of 26
RSC Advances
View Article Online
DOI: 10.1039/C5RA11089K
16 (a) Q. Xu, W. L. Duan, Z. Y. Lei, Z. B. Zhu and M. Shi, Tetrahedron, 2005, 61,
11225; (b) C. S. Cao, Y. Z. Zhuang, J. F. Zhao, Y. Peng, X. L. Li, Z. Shi, G. S.
Pang and Y. H. Shi, Inorg. Chim. Acta, 2010, 363, 3914; (c) C. S. Cao, L. L. Wang,
Z. Y. Cai, L. Q. Zhang, J. Guo, G. S. Pang and Y. H. Shi, Eur. J. Org. Chem., 2011,
1570.
17 (a) W. Wei, M. Y. Wu, Y. G. Huang, Q. Gao, F. L. Jiang and M. C. Hong, Z. Anorg.
Allg. Chem., 2008, 634, 2623; (b) A. L. Pickering, G. Seeber and D. L. Long,
CrystEngComm, 2005, 7, 504.
18 A. Suzuki, J. Organomet. Chem., 1999, 576, 147.
19 (a) K. Selvakumar, A. Zapf and M. Beller, Org. Lett., 2002, 4, 3031; (b) R. B.
Bedford, M. E. Blake, C. P. Butts and D. Holder, Chem. Commun., 2003, 466; (c)
D. Yang, Y. C. Chen and N. Y. Zhu, Org. Lett., 2004, 6, 1557; (d) H. V. Huynh, Y.
Han, J. H. Ho and G. K. Tan, Organometallics, 2006, 25, 3267; (e) S. H. Li, Y. J.
Lin, J. G. Cao and S. B. Zhang, J. Org. Chem., 2007, 72, 4067.
20 (a) H. A. Dieck and R. F. Heck, J. Am. Chem. Soc., 1974, 96, 1133; (b) Y.
Ben-David, M. Portnoy, M. Gozin and D. Milstein, Organometallics, 1992, 11,
1995; (c) A. Jutand and A. Mosleh, Organometallics, 1995, 14, 1810; (d) X. Fu, S.
Zhang, J. Yin, T. L. Mcallister, S. A. Jiang, C. H. Tann, T. K. Thiruvengadam and
F. Zhang, Tetrahedron Lett., 2002, 43, 573; (e) A. L. Hansen and T. Skrydstrup,
Org. Lett., 2005, 7, 5585.
21 (a) J. H. Li, X. C. Hu, Y. Liang and Y. X. Xie, Tetrahedron Lett., 2006, 62, 31; (b)
J. H. Li, W. J. Liu and Y. X. Xie, J. Org. Chem., 2005, 70, 5409.
22 (a) L. G. Yang, Y. F. Li, C. Qian, Y. F. Du and C. S. Cao, Tetrahedron, 2013, 69,
5178; (b) F. T. Luo and H. K. Lo, J. Organomet. Chem., 2011, 696, 1262.
23 (a) N. Debono, A. Labande, E. Manoury, J. C. Daran and R. Poli, Organometallics,
2010, 29, 1879; (b) M. Charbonneau, G. Addoumieh, P. Oguadinma and A. R.
Schmitzer, Organometallics, 2014, 33, 6544; (c) L. Benhamou, C. Besnard and E.
P. Kündig, Organometallics, 2014, 33, 260; (d) L. Wu, A. Salvador, A. Ou, M. W.
Shi, B. W. Skelton and R. Dorta, Synlett., 2013, 24, 1215; (e) S. Meiries, G. L. Duc,
A. Chartoire, A. Collado, K. Speck, K. S. A. Arachchige, A. M. Z. Slawin and S. P.
23

RSC Advances
Page 24 of 26
View Article Online
DOI: 10.1039/C5RA11089K
Nolan, Chem. Eur. J., 2013, 19, 17358; (f) G. Grach, G. Pieters, A. Dinut, V.
Terrasson, R. Medimagh, A. Bridoux, V. Razafimahaleo, A. Gaucher, S. Marque, J.
Marrot, D. Prim, R. Gil, J. G. Planas, C. Viñas, I. Thomas, J. P. Roblin and Y. Troin,
Organometallics, 2011, 30, 4074; (g) G. W. Shigeng, J. K. Tang, D. Zhang, Q. R.
Wang, Z. X. Chen and L. H. Weng, J. Organomet. Chem., 2012, 700, 223; (h) Y. L.
Li, J. K. Tang, J. Gu, Q. R. Wang, P. P. Sun and D. Zhang, Organometallics, 2014,
33, 876; (i) Y. Q. Tang, J. M. Lu and L. X. Shao, J. Organomet. Chem., 2011, 696,
3741; (j) M. M. T. Strassner, Eur. J. Inorg. Chem., 2012, 5872; (k) H. Lebel, M. K.
Janes, A. B. Charette and S. P. Nolan, J. Am. Chem. Soc., 2004, 126, 5046; (l) J. D.
Blakemore, M. J. Chalkley, J. H. Farnaby, L. M. Guard, N. Hazari, C. D. Incarvito,
E. D. Luzik Jr. and H. W. Suh, Organometallics, 2011, 30, 1818; (m) C. E. Ellul, G.
Reed, M. F. Mahon, S. I. Pascu and M. K. Whittlesey, Organometallics, 2010, 29,
4097.
24 (a) Y. F. Li, L. G. Yang, Q. Chen, C. S. Cao, P. Guan, G. S. Pang and Y. H. Shi, Z.
Anorg. Allg. Chem., 2013, 639, 575; (b) K. Q. Ge, C. S. Cao, G. Liu, Y. L. Li, J.
Zhang, G. S. Pang and Y. H. Shi, Z. Anorg. Allg. Chem., 2014, 640, 444; (c) U. I.
Tessin, X. Bantreil, O. Songis and C. S. J. Cazin, Eur. J. Inorg. Chem., 2013, 2007;
(d) C. S. Lee, Y. B. Lai, W. J. Lin, R. R. Zhuang and W. S. Hwang, J. Organomet.
Chem., 2013, 724, 235; (e) H. V. Huynh and R. Jothibasu, J. Organomet. Chem.,
2011, 696, 3369; (f) T. Yagyu, A. Tsubouchi and Y. Nishimura, J. Organomet.
Chem., 2014, 767, 1; (g) H. Türkmen, T. Pape, F. E. Hahn and B. Çetinkaya, Eur. J.
Inorg. Chem., 2009, 285; (h) H. B. Metzner, P. T. Körzdörfer, A. Kelling and H. J.
Holdt, Eur. J. Inorg. Chem., 2014, 2952; (i) A. L. Gottumukkala, J. G. de Vries and
A. J. Minnaard, Chem. Eur. J., 2011, 17, 3091; (j) Q. Teng, D. Upmann, S. A. Z. N.
Wijaya and H. V. Huynh, Organometallics, 2014, 33, 3373; (k) A. Z. Wilczewska
and I. Misztalewska, Organometallics, 2014, 33, 5203.
25 (a) L. G. Yang, Y. F. Li, Q. Chen, Y. F. Du, C. S. Cao, Y. H. Shi and G. S. Pang,
Tetrahedron, 2013, 69, 5178; (b) S. C. Holm, F. Rominger and B. F. Straub, J.
Organomet. Chem., 2012, 719, 54; (c) A. John, S. Modak, M. Madasu, M. Katari
and P. Ghosh, Polyhedron, 2013, 64, 20; (d) L. G. Yang, Y. F. Li, Q. Chen, J. F.
24

Page 25 of 26
RSC Advances
View Article Online
DOI: 10.1039/C5RA11089K
Zhao, C. S. Cao, Y. H. Shi and G. S. Pang, Transition Met. Chem., 2013, 38, 367; (e)
C. Dash, M. M. Shaikh and P. Ghosh, Eur. J. Inorg. Chem., 2009, 1608; (f) C. Chen,
H. Qiu and W. Z. Chen, Inorg. Chem., 2011, 50, 8671; (g) J. C. Bernhammer, N. X.
Chong, R. Jothibasu, B. Zhou and H. V. Huynh, Organometallics, 2014, 33, 3607;
(h) L. Ray, S. Barman, M. M. Shaikh and P. Ghosh, Chem. Eur. J., 2008, 14, 6646.
26 (a) Y. H. Chang, Z. Y. Liu, Y. H. Liu, S. M. Peng, J. T. Chen and S. T. Liu,
Dalton Trans., 2011, 40, 489; (b) T. Zhang, S. J. Liu, M. Shi and M. X. Zhao,
Synthesis, 2008, 17, 2819; (c) M. T. Ma and J. M. Lu, Appl. Organometal. Chem.,
2012, 26, 175.
27 (a) A. Zanardi, J. A. Mata and E. Peris, Organometallics, 2009, 28, 4335; (b) A.
Zanardi, J. A. Mata and E. Peris, Organometallics, 2009, 28, 1480; (c) S. K. Yen,
L. L. Koh, H. V. Huynh and T. S. A. Hor, Chem. Asian J., 2008, 3, 1649.
28 (a) E. Mas-Marzà, J. A. Mata and E. Peris, Angew. Chem., Int. Ed., 2007, 46, 3729;
(b) A. Zanardi, R. Corberan, J. A. Mata and E. Peris, Organometallics, 2008, 27,
3570; (c) M. Viciano, M. Sanaú and E. Peris, Organometallics, 2007, 26, 6050.
29 M. L. Cole and P. C. Junk, CrystEngComm, 2004, 6, 173.
30 Bruker AXS, SAINT Software Reference Manual, Madison, WI, 1998.
31 G. M. Sheldrick, SHELXTL NT (Version 5.1), Program for Solution and
Refinement of Crystal Structures, University of Göttingen, Germany, 1997.
32 D. C. Palmer, CrystalMaker 7.1.5, CrystalMaker Software, Yarnton, UK, 2006.
25

RSC Advances
Page 26 of 26
View Article Online
DOI: 10.1039/C5RA11089K
A table of contents entry:
NHC-Pd(II) complex 1 has been prepared. The catalytic activity of 1 in C-C coupling
reactions was studied.
Software of Graphics:
Scheme 1: Chem Draw 8.0
Fig. 1: Diamand 3.0
26