(Phosphinito)aryl benzimidazole PCN pincer palladium(II) complexes: Synthesis, characterization and catalytic activity in C–H arylation of azoles with aryl iodides

Article abstract of DOI:10.1016/j.poly.2017.10.005

The PCN pincer Pd(II) complexes 4a–c with (phosphinito)aryl benzimidazole ligands were conveniently synthesized by one-pot phosphorylation/palladation reaction of a (2-benzimidazolyl)-containing m-phenol derivative 3. The three complexes were well characterized by spectroscopic methods, elemental analysis and their molecular structures were further determined by X-ray single-crystal diffraction. The Pd(II) center in each complex adopts a typical distorted-square-planar geometry. With a catalyst loading of 0.25–0.5 mol%, complex 4a could effectively catalyze C–H arylation of benzothiazole, benzoxazole and thiazole with various aryl iodides in the presence of CuI as a cocatalyst.

Full text of DOI:10.1016/j.poly.2017.10.005

Accepted Manuscript
(Phosphinito)aryl benzimidazole PCN pincer palladium(II) complexes: synthe-
sis, characterization and catalytic activity in C-H arylation of azoles with aryl
iodides
Cong Wang, Yang Li, Beibei Lu, Xin-Qi Hao, Jun-Fang Gong, Mao-Ping Song
PII:
S0277-5387(17)30646-0
https://doi.org/10.1016/j.poly.2017.10.005
POLY 12868
DOI:
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
7 July 2017
6 October 2017
Please cite this article as: C. Wang, Y. Li, B. Lu, X-Q. Hao, J-F. Gong, M-P. Song, (Phosphinito)aryl benzimidazole
PCN pincer palladium(II) complexes: synthesis, characterization and catalytic activity in C-H arylation of azoles
with aryl iodides, Polyhedron (2017), doi: https://doi.org/10.1016/j.poly.2017.10.005
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(Phosphinito)aryl benzimidazole PCN pincer palladium(II)
complexes: synthesis, characterization and catalytic activity in C-H
arylation of azoles with aryl iodides
Cong Wang, Yang Li, Beibei Lu, Xin-Qi Hao, Jun-Fang Gong,* Mao-Ping Song*
College of Chemistry and Molecular Engineering, Henan Key Laboratory of Chemical
Biology and Organic Chemistry, Zhengzhou University, Zhengzhou 450001, People’s
Republic of China
ABSTRACT: The PCN pincer Pd(II) complexes 4a-c with (phosphinito)aryl
benzimidazole ligands were conveniently synthesized by one-pot
phosphorylation/palladation reaction of a (2-benzimidazolyl)-containing m-phenol
derivative 3. The three complexes were well characterized by spectroscopic methods,
elemental analysis and their molecular structures were further determined by X-ray
single-crystal diffraction. The Pd(II) center in each complex adopts a typical
distorted-square-planar geometry. With a catalyst loading of 0.25-0.5 mol%, complex 4a
could effectively catalyze C-H arylation of benzothiazole, benzoxazole and thiazole with
various aryl iodides in the presence of CuI as a cocatalyst.
Keywords: PCN pincer Pd(II) complex; (Phosphinito)aryl benzimidazole ligand; C-H
arylation; Azole; Aryl iodide
1. Introduction
Aryl-based pincer palladium complexes, in which the terdentate ligand coordinates to
the Pd(II) center in a meridional fashion through sigma and dative bonds, have been
proven to be effective catalysts for diverse organic transformations such as allylation of
aldehydes or imines, Michael additions, aldol reactions and particularly for a variety of
cross-coupling reactions including Heck, Suzuki-Miyaura, Sonogashira, Hiyama, Stille,
and Negishi couplings [1]. Most of the reported pincer Pd(II) catalysts are symmetrical
DCD types (D = NR2, PR2, OPR2, SR, SeR, etc.) with two identical donor groups and two
equivalent five-membered palladacycles. By contrast, the unsymmetrical pincer Pd
* Tel.: (+86)-371-6776-3869. E-mail: mpsong@zzu.edu.cn (M.-P. Song) or gongjf@zzu.edu.cn (J.-F. Gong).

catalysts with two different donors have been less developed although the different donors
may provide a better tuning of the catalytic properties of the corresponding Pd pincers [2].
One obvious reason for the result is the relatively complicated synthesis of the
unsymmetrical pincer Pd complexes which requires additional steps to introduce two
different donors one by one. In 2007, we found that the PCN Pd pincer complexes with
phosphinito group as the P-donor could be prepared in a facile and efficient manner via
one-pot phosphorylation/palladation reaction of N-donor-containing m-phenol derivatives
[3]. In this one-pot strategy, the phosphorylation with R2PCl occurred first to give the
PCHN ligands and the subsequent in-situ palladation with PdCl2 furnished the expected
PCN Pd pincers. Further studies indicated that one-pot phosphorylation/palladation
reaction of N-donor-containing m-aniline and m-benzyl alcohol derivatives were also
feasible. Thus, a wide variety of PCN Pd pincer complexes including achiral [3-5] and
chiral [6-9] ones have been successfully generated by using this method (Fig.1).
Fig.1. Achiral and chiral PCN pincer Pd complexes prepared by one-pot
phosphorylation/palladation reaction
On the other hand, transition metal catalyzed C-H functionalization has emerged as a
powerful tool for the formation of C-C and C-X bonds in organic synthesis over the past
decade [10]. In this context, the potential of pincer Pd complexes in functionalization of
C-H bonds has also been evaluated and promising results have been achieved [11-15]. For
example, Szabó demonstrated that aryl-based bis(phosphinite) PCP and bis(amine) NCN
Pd pincer complexes were effective catalysts for C-C coupling of allyl nitriles with tosyl
imines via regioselective allylic C-H bond functionalization [11a] and selective C-H
borylation of alkenes [12], respectively. The two types of reactions both proceeded well

under mild conditions. In addition, pincer Pd complexes exhibited good activity in
intramolecular C-H arylation of amides and sulfonamides [13] as well as intermolecular
arylation of indoles [14] and azoles [15] with aryl iodides. Among them, CuI cocatalyst
was also needed in the C-H arylation of azoles [15]. Despite the impressive progress, the
application of pincer Pd complexes as catalysts for C-H functionalization still remains
scarce. With this in mind and also in continuation of our studies on the pincer metal
complexes [16], herein we would like to report the preparation of the new PCN pincer
Pd(II) complexes with aryl-based phosphinite-benzimidazole ligands (Scheme 1). The
crystal structures of the obtained Pd pincer complexes as well as their potential in the C-H
arylation of azoles with aryl iodides are also presented.
Scheme 1. Synthesis of the PCN pincer Pd(II) complexes 4a-c.
2. Results and discussion
2.1. Synthesis of the PCN pincer Pd(II) complexes (4)
The synthetic route of the PCN pincer Pd(II) complexes (4) is shown in Scheme 1. First,
reaction of 3-acetoxybenzoic acid, which was easily produced by protection of 3-hydroxyl
group in commercially available 3-hydroxybenzoic acid, with thionyl chloride and
subsequently with N1-butylbenzene-1,2-diamine in the presence of Et3N in CH2Cl2 gave
3-acetoxybenzamide (1) as a white solid. Then, the benzamide (1) was stirred in refluxing
HOAc to afford 1-acetoxy-3-(2-benzimidazolyl)benzene (2) as an oil. Next, the acetyl
protecting group in (2) was readily removed by treatment (2) with 15% aqueous NaOH in
MeOH to provide 3-(2-benzimidazolyl)phenol (3) as a white solid. With the

(2-benzimidazolyl)-containing m-phenol derivative 3 in hand, the one-pot
phosphorylation/palladation reaction was carried out as previously reported [3,4,6,9]. Thus,
compound (3) was treated with Ph2PCl, iPr2PCl or Cy2PCl in the presence of Et3N in
refluxing toluene for 6 h, followed by the addition of PdCl2 and refluxing for another 12 h.
After purification by preparative TLC on silica gel plates, the expected PCN pincer Pd(II)
complexes 4a-c were isolated in 69%, 32% and 34% yields, respectively as pale yellow
solids. For complexes 4b and 4c, the yields were much lower than that of complex 4a. In
this one-pot procedure, the phosphorylation and palladation reactions occurred
successively. The former provided the PCHN ligands via construction of the R2PO- group
and the latter gave the Pd pincers via C2-palladation of the PCHN ligands. From our
previous studies on the related PCN Pd pincers which also contained R2PO- group (Fig.1),
it was found that the complexes with Cy2PO- or iPr2PO- group could be obtained in yields
comparable to those with Ph2PO- group [3,4,6]. Furthermore, literature results showed that
the PCHN ligands with either Ph2PO- or iPr2PO- group could be isolated in high yields
[15a-c]. Therefore, it seemed reasonable to assume that in the one-pot procedure the
phosphorylation proceeded with high efficiency while the following palladation was a
yield-determining process for the synthesis of the PCN Pd pincers. As for the lower yields
of complexes 4b and 4c with iPr2PO- or Cy2PO- group, it was possibly due to the
formation of other Pd complexes in the palladation of the corresponding PCHN ligands
such as P,N-coordinated complex, C6-palladated PC complex, C4-palladated NC complex
or even C4,C6-dipalladated NCPC complex [15b].
The three PCN Pd pincer complexes 4a-c are air- and moisture- stable both in the solid
state and in solution. They were fully characterized by elemental analysis, 1H NMR,
13C{1H} NMR and 31P{1H} NMR. The NMR data of the Pd complexes 4a-c are in good
agreement with the assigned structures. The 1H NMR spectrum of each complex showed a
set of four signals in a 1:4:1:1 ratio in the range of 8.68-6.85 ppm. These signals
corresponded to seven aryl protons including the central aryl protons and the
benzimidazole protons, suggesting the formation of the pincer Pd complexes. The 31P{1H}
NMR spectra of the complexes exhibited a singlet at δ 153.9, 202.4 and 196.2 ppm,
respectively, indicating the generation of the corresponding R2PO- donor groups (R = Ph,

iPr and Cy). These 31P chemical shifts were comparable to those reported for the related
PCN pincer Pd complexes with the same R2PO- groups [3,4,6,9,15a-c]. Existence of the
R2PO- groups in the Pd complexes was also confirmed by their 1H NMR and 13C{1H}
NMR spectra. For example, in the 1H NMR spectrum of complex 4a the two multiplets in
a 4:6 ratio appeared at 8.19-8.04 and 7.56-7.43 ppm, respectively which were assigned to
the ten phenyl protons in the Ph2PO- group. In addition, intensive 31P-13C couplings were
observed in the 13C{1H} NMR spectra of all the three complexes.
2.2. Molecular structures of the PCN Pd(II) pincer complexes (4)
The molecular structures of the complexes 4a-c have been determined by X-ray single
crystal analysis. The molecules are illustrated in Fig.2. Selected bond lengths and bond
angles are listed in Table 1. The structural features of the three complexes are almost
identical. The Pd(II) center in each complex adopts a typical distorted-square-planar
configuration with the ligand coordinated to the metal via phosphinite-P, the central aryl-C
and benzimidazole-N in a terdentate manner and the chloride ligand occupying the fourth
coordination site. The metal-ligand distances and bond angles around the Pd(II) center in
the three complexes are similar except for a smaller C-Pd-Cl angle in complex 4a. The
bond angles of N-Pd-P are around 159o and the C-Pd-Cl angles are 176-179o, which are in
accordance with pincers consisting two fused five-membered-ring palladacycles and
reflect a relative steric strain of the system. In comparison with the closely related PCN
pincer palladium complexes with (phosphinito)aryl imine ligands [4], complexes 4a-c
exhibit comparable bond distances and angles for the metal coordination sphere except for
shorter Pd-N distances (around 2.12 Å vs 2.18 Å). The Pd-N distances in these complexes
are also found to be shorter than those observed in the (phosphinito)aryl amine PCN
pincer Pd complexes (around 2.12 Å vs 2.19-2.22 Å) [15a-c]. In addition, complexes 4a-c
have smaller N-Pd-P angles (around 159o vs 161-162o) when compared with the
(phosphinito)aryl amine PCN Pd pincers [15a-c].

Fig. 2. Molecular structures of the PCN pincer Pd (II) complexes 4a, 4b and 4c (from left
to right). Hydrogen atoms are omitted for clarity.
Table 1 Selected bond lengths (Å) and angles (o) for complexes 4a, 4b and 4c
4a
4b
4c
Pd(1)-C(13)
1.975 (4)
2.1904 (11)
2.111 (3)
2.3870 (12)
99.73 (4)
101.20 (11)
158.80(11)
1.973 (3)
2.2005 (9)
2.115 (2)
2.3899 (9)
98.93 (3)
101.38 (8)
159.69 (8)
179.54 (10)
80.64 (10)
79.05 (12)
1.974 (3)
2.2017 (9)
2.123 (3)
2.3871 (8)
99.28 (3)
101.04 (7)
159.67 (7)
179.56 (9)
80.69(9)
78.99 (11)
Pd(1)-P(1)
Pd(1)-N(1)
Pd(1)-Cl(1)
P(1)-Pd(1)-Cl(1)
N(1)-Pd(1)-Cl(1)
N(1)-Pd(1)-P(1)
C(13)-Pd(1)-Cl(1) 175.98 (11)
C(13)-Pd(1)-P(1) 80.02 (11)
C(13)-Pd(1)-N(1) 79.33 (15)
2.3. Catalytic studies
The catalytic activity of the obtained PCN pincer Pd complexes 4a-c in the C-H
arylation of azoles with aryl iodides was examined. Coupling of benzothiazole with
phenyl iodide was chosen as a model to optimize the reaction conditions (Table 2). It was
found that 2-phenylbenzothiazole could be obtained in 99% yield when the reaction was
performed in the presence of 0.5 mol% of Pd complex 4a and 2.5 mol% of CuI with
Cs2CO3 as the base in DMF at 120 oC for 24 h (entry 1). The yield was maintained for a
reaction time of 18 h (99%, entry 2). However, further shortening in the reaction time led
to a decreased yield (92%, entry 3). The arylation could still proceed in the absence of CuI
although the isolated yields of the coupled product were low with 0.5-1.0 mol% of Pd
complex 4a (10% and 17%, respectively, entries 4 and 5). By contrast, in the absence of

Pd complex 4a only trace amounts of the product were obtained with 2.5 mol% of CuI
(entry 6). The yield was not improved much even with a large amount of CuI such as 20
mol% which merely gave a 4% yield (entry 7). The results indicated that both the Pd
complex 4a and CuI were essential for an efficient arylation to occur where the Pd
complex 4a was the catalyst and CuI acted as a cocatalyst. The loadings of 4a and CuI
could be reduced to 0.25 mol% and 1.25 mol%, respectively without loss of activity (99%
yield, entry 8). While the yield decreased dramatically to 42% with 0.125 mol% of Pd
complex 4a and 0.625 mol% of CuI (entry 9). Interestingly, high yields could be achieved
by increasing the loading of CuI to 1.25 or 2.5 mol% (entries 10 and 11). These results
further confirmed the positive effect of the CuI cocatalyst on the reaction. With 0.1 mol%
of Pd complex 4a and 0.5 mol% of CuI, the coupled product could still be obtained in 38%
yield (entry 12). Under the same reaction conditions complex 4b gave a better yield of 47%
(entry 13) and complex 4c only afforded 10% yield (entry 14). Despite the fact that
complex 4b performed better than complex 4a, in the following experiments complex 4a
was still chosen as the catalyst since its synthetic yield was much higher than that of 4b
(69% vs 32%). A quick survey of the reaction temperature revealed that 120 oC was an
appropriate temperature (entries 8 vs 15-17). Changing the solvent from DMF to dioxane
and toluene resulted in low yields (entries 18 and 19). Then the influence of several bases
was tested. Compared with Cs2CO3, the use of K2CO3, K3PO4 or KOAc as the base
provided much inferior results (entries 20-22). In addition, trace amounts of the product
were obtained or no reaction occurred when Na2CO3, tBuOK, KOH, KF or Et3N was
employed as the base (data not shown in Table 2). Thus, the optimized conditions included
using 0.25 mol% of 4a as the catalyst with 1.25 mol% of CuI cocatalyst and Cs2CO3 as the
base in DMF at 120 oC for 18 h (entry 8).
Table 2 Optimization of the reaction conditions for the C-H arylation of benzothiazole
with phenyl iodide catalyzed by the PCN pincer Pd(II) complexes 4a
Entry Pd cat. (mol%) Base
Solvent
Cs2CO3 DMF
Cs2CO3 DMF
Temp. (oC) Time (h) Yieldb (%)
1
2
4a (0.5)
4a (0.5)
120
120
24
18
99
99

3
4a (0.5)
4a (0.5)
4a (1.0)
/
Cs2CO3 DMF
Cs2CO3 DMF
Cs2CO3 DMF
Cs2CO3 DMF
Cs2CO3 DMF
Cs2CO3 DMF
Cs2CO3 DMF
Cs2CO3 DMF
Cs2CO3 DMF
Cs2CO3 DMF
Cs2CO3 DMF
Cs2CO3 DMF
Cs2CO3 DMF
Cs2CO3 DMF
Cs2CO3 DMF
120
120
120
120
120
120
120
120
120
120
120
120
100
80
12
18
18
18
18
18
18
18
18
18
18
18
18
18
18
18
18
18
18
18
92
4
10c
17c
traced
4e
5
6
7
/
8
4a (0.25)
4a (0.125)
4a (0.125)
4a (0.125)
4a (0.1)
4b (0.1)
4c (0.1)
4a (0.25)
4a (0.25)
4a (0.25)
4a (0.25)
4a (0.25)
4a (0.25)
4a (0.25)
4a (0.25)
99
9
42
10
11
12
13
14
15
16
17
18
19
20
21
22
75 f
85g
38
47
10
43
17
rt
N.R.
15
Cs2CO3 1,4-Dioxane 120
Cs2CO3 Toluene
K2CO3 DMF
K3PO4 DMF
120
120
120
120
41
16
43
KOAc
DMF
35
aBenzothiazole (0.5 mmol), PhI (0.75 mmol), catalyst 4 : CuI = 1: 5, base (0.75 mmol), solvent (1.0
mL). bIsolated yield. cWithout CuI. dCuI (2.5 mol%), conversion of benzothiazole was 24%.eCuI (20
mol%), conversion of benzothiazole was 36%. fCuI (1.25 mol%). gCuI (2.5 mol%).
With the optimal conditions established, arylation of benzothiazole with other aryl
iodides was investigated (Table 3). p-Tolyl, m-tolyl, p-methoxyphenyl and p-chlorophenyl
iodides afforded the corresponding 2-arylated benzothiazoles in excellent yields
(96%-99%, entries 2,4-6). Unfortunately, o-tolyl, p-bromophenyl, p-cyanophenyl and
o-fluorophenyl iodides gave rather low yields (10-15%, entries 3, 7-9). In the case of
p-bromophenyl iodide no other compounds could be isolated in pure form and appreciable
amount except for the corresponding coupled product although the conversion of
benzothiazole was as high as 79%. For o-fluorophenyl iodide, conversion of benzothiazole
was 37%. When 4-iodo pyridine was used as the coupling partner a moderate yield was

obtained (45%, entry 10). Pleasingly, the yields could be greatly improved by increasing
the catalyst loadings for o-tolyl iodide and 4-iodo pyridine (entries 3 and 10). The
application of the current system to arylation of benzoxazole and thiazole was also
attempted. In general, the results were inferior to those of benzothiazole (entries 11-17). In
most cases, higher catalyst loadings were necessary to obtain good yields (entries 11,
14-16).
Table 3 Substrate scope for the C-H arylation of azoles with aryl iodides catalyzed by the
PCN pincer Pd(II) complex 4aa
Entry
1
ArI
Product
Yieldb (%)
99
2
3
4
5
6
7
8
96
15(97c)
99
99
99
10
15(41c)

9
11
10
11
12
13
14
15
16
17
45(89d)
36(79d)
72
61
72d
97d
23(68c)
18(29c)
aReaction conditions: azole (0.5 mmol), ArI (0.75 mmol), catalyst 4a (0.25 mol%), CuI (1.25 mol%),
Cs2CO3 (0.75 mmol), DMF (1.0 mL), 120 oC, 18 h. bisolated yield. cwith 4a (0.5 mol%), CuI (5 mol%).
dwith 4a (0.5 mol%), CuI (2.5 mol%).
It should be mentioned that in 2010 a highly efficient Pd/Cu cocatalytic system was
developed by Huang et al for the arylation of azoles where
dichlorobis(chloro-di-tert-butylphosphine)palladium and Cu(Xantphos)I (Xantphos =
9,9-dimethyl-4,5-bis(diphenylphosphine)xanthene) were employed as the catalysts [17].
With low catalyst loadings (0.25 mol% Pd and 1 mol% Cu), arylation of a broad range of
azoles including benzothiazoles, benzoxazole and N-methyl benzimidazole with a variety
of aryl bromides proceeded very efficiently in the presence of Cs2CO3 base under
relatively mild conditions (toluene, 100 oC). Activated aryl chlorides and phenyl triflate

were also good coupling partners. However, phenyl iodide reacted sluggishly with
benzothiazole, giving 2-phenylbenzothiazole only in a moderate yield of 68% under the
optimized reaction conditions. Recently, Cai reported a Pd(OAc)2/Cu(TFA)2 cocatalyst
system for arylation of thiazole derivatives with aryl iodides [18]. The reactions were
carried out under ligand-free conditions in the presence of tBuOLi base in DMF at 130 oC.
In this report, relatively high catalyst loadings with 1 mol% of Pd(OAc)2 and 20 mol% of
Cu(TFA)2 were required to ensure good results. In addition, it was noted that the pincer Pd
catalyst 4a behaved similarly to the (phosphinito)aryl amine PCN pincer Pd catalysts
developed by Punji et al [15a,c] in terms of either catalytic activity or arylation reaction
conditions.
To gain more insights into the mechanism of arylation reaction catalyzed by the
complex 4a, the PCN pincer Pd(II)-benzothiazolyl complex 5a was prepared and applied
in both the catalytic and the stoichiometric processes (Scheme 2). Thus, treatment of the
Pd-Cl complex 4a with benzothiazolyl-lithium in THF at -78 oC gave 5a in 33% yield.
Then 5a instead of 4a was used as the catalyst for the C-H arylation of benzothiazole with
phenyl iodide under standard reaction conditions. With 0.5 mol% of 5a, the expected
coupled product was obtained in 92% yield although the yield was only 31% with 0.25
mol% of 5a. Furthermore, a stoichiometric reaction of 5a with phenyl iodide in DMF at
120 oC for 10 h afforded 2-phenylbenzothiazole in 66% yield and the Pd-I complex 6a in
43% yield as well. The results clearly indicated that complex 5a was a key intermediate in
the catalytic cycle of C-H arylation reactions of benzothiazole with aryl iodides.

Scheme 2. Synthesis of the Pd(II)-benzothiazolyl complex 5a from 4a as well as arylation
with phenyl iodide in the presence of 5a.
On the basis of the experimental results and the literature precedents [15a,c], a plausible
mechanism was proposed in Scheme 3. Initially, the base-assisted concerted deprotonation
metalation of benzothiazole with CuI affords the benzothiazolyl-copper species (A) [17].
Then transmetalation of A with the pincer Pd(II)-X complex (X = Cl or I) generates the
Pd(II)-benzothiazolyl complex 5a. The subsequent oxidative addition of aryl iodide to 5a
leads to the formation of the Pd(IV) intermediate (B). Finally, reductive elimination of B
gives the desired coupled product and regenerates the catalytically active pincer Pd(II)-X
complex. Thus, it is believed that the pincer Pd complex 4a-catalyzed C-H arylation
reactions of benzothiazole with aryl iodides in the presence of CuI cocatalyst proceed via a
Pd(II)-Pd(IV)-Pd(II) pathway [15c] rather than a classical Pd(0)-Pd(II)-Pd(0) cycle
[17,18].

Scheme 3. Proposed mechanism for the C-H arylation of benzothiazole with aryl iodides
catalyzed by the PCN pincer Pd(II) complex 4a.
3. Conclusions
In summary, three new PCN pincer Pd(II) complexes with aryl-based
phosphinite-benzimidazole ligands have been synthesized and well characterized. In the
presence of CuI cocatalyst the pincer Pd complex acted as an effective catalyst for the
intermolecular arylation of azoles with aryl iodides, giving the 2-arylated azoles in
generally good to excellent yields.
4. Experimental
4.1. General
1H, 13C{1H} and 31P{1H} NMR spectra were recorded on a Bruker DPX-400 instrument
in CDCl3 with TMS as an internal standard for 1H, 13C{1H} NMR and 85% H3PO4 as
external standard for 31P{1H} NMR. HRMS were determined on a Waters Q-Tof Micro
MS/MS System ESI spectrometer. Elemental analyses were performed on a Thermo Flash

EA 1112 elemental analyzer. Melting points were measured on a WC-1 microscopic
apparatus and are uncorrected. Solvents were dried with standard methods and freshly
distilled prior to use if needed. 3-Acetoxybenzoic acid [6], N-butyl-2-nitroaniline and
N1-butylbenzene-1,2-diamine [19] were prepared according to the literature methods. All
other chemicals were used as purchased.
4.2. Synthesis of the PCN Pd(II) pincer complexes (4)
4.2.1. Synthesis of 3-acetoxy-N-[2-(n-butylamino)phenyl]benzamide (1)
The reaction of 3-hydroxybenzoic acid with acetic anhydride in aqueous NaOH at room
temperature easily gave the white solids of 3-acetoxybenzoic acid. Then 3-acetoxybenzoic
acid (1.80 g, 10 mmol) reacted with SOCl2 (1.1 mL, 15.1 mmol) at reflux for 5 h. After
that, the excess SOCl2 was removed under reduced pressure to afford 3-acetoxybenzoyl
chloride which was used in the next step without further purification. Next,
3-acetoxybenzoyl chloride was dissolved in CH2Cl2 (25 mL) and added dropwise to a
stirred solution of N1-butylbenzene-1,2-diamine (1.64 g, 10 mmol) and Et3N (1.5 mL) in
dry CH2Cl2 (20 mL) at 0 oC. After stirring at room temperature for 16-24 h, the reaction
mixture was filtered and evaporated. The residue was purified by column chromatography
on silica gel with EtOAc/petroleum ether (1:6, v/v) as eluent to afford the compound 1.
White solid (1.32 g, 40%). M.p. 95-96 oC. 1H NMR (400 MHz, CDCl3): δ 8.20 (s, 1H,
NHCO), 7.65 (d, J = 7.5 Hz, 1H, ArH), 7.59 (s, 1H, ArH), 7.35 (t, J = 7.9 Hz, 1H, ArH),
7.29-7.15 (m, 2H, ArH), 7.15-7.04 (m, 1H, ArH), 6.78-6.62 (m, 2H, ArH), 3.92 (brs, 1H,
NHBun), 3.00 (t, J = 7.2 Hz, 2H, CH2CH2CH2CH3), 2.23 (s, 3H, Ac), 1.59-1.47 (m, 2H,
CH2CH2CH2CH3), 1.43-1.30 (m, 2H, CH2CH2CH2CH3), 0.90 (t, J = 7.3 Hz, 3H,
CH2CH2CH2CH3). 13C{1H} NMR (100 MHz, CDCl3): δ 169.5, 165.3, 150.8, 142.9, 135.9,
129.7, 127.5, 125.7, 125.1, 124.7, 123.8, 121.1, 117.8, 113.1, 44.0, 31.6, 21.0, 20.4, 14.0.
HRMS (positive ESI): [M+H]+ calcd for C19H23N2O3: 327.1709. Found: 327.1703.
4.2.2. Synthesis of 1-acetoxy-3-(1-butyl-1H-benzo[d]imidazol-2-yl)benzene (2)
The compound 1 (1.63 g, 5 mmol) was stirred in CH3CO2H (5.5 mL) at reflux for 16 h.
After cooling, water was added and the mixture was extracted with CH2Cl2. The combined
organic layer was dried, filtered, and concentrated. The residue was purified by column
chromatography on silica gel with EtOAc/petroleum ether (1:3, v/v) as eluent to afford the

compound 2. Colorless oil (832.0 mg, 54%). 1H NMR (400 MHz, CDCl3): δ 7.87-7.77 (m,
1H, ArH), 7.62-7.45 (m, 3H, ArH), 7.44-7.37 (m, 1H, ArH), 7.36-7.16 (m, 3H, ArH), 4.22
(t, J = 7.7 Hz, 2H, CH2CH2CH2CH3), 2.30 (s, 3H, Ac), 1.86-1.70 (m, 2H,
CH2CH2CH2CH3), 1.35-1.20 (m, 2H, CH2CH2CH2CH3), 0.86 (t, J = 7.4 Hz, 3H,
CH2CH2CH2CH3). 13C{1H} NMR (100 MHz, CDCl3): δ 169.2, 152.4, 150.7, 142.7, 135.5,
131.6, 129.8, 126.6, 122.97, 122.95, 122.8, 122.6, 119.9, 110.3, 44.6, 31.8, 21.1, 19.9,
13.5. HRMS (positive ESI): [M+H]+ calcd for C19H21N2O2: 309.1603. Found: 309.1598.
4.2.3. Synthesis of 3-(1-butyl-1H-benzo[d]imidazol-2-yl)phenol (3)
To a stirred solution of the compound 2 (414.1 mg, 1.34 mmol) in MeOH (3 mL) was
added 15% aqueous NaOH (12.6 mmol) at room temperature. Then the reaction mixture
was stirred at room temperature for 6-12 h. After that, the mixture was adjusted to pH = 7
and extracted with CH2Cl2. The combined organic layer was dried over MgSO4, filtered,
and concentrated in vacuo to give a residue, which was purified by column
chromatography on silica gel with CH2Cl2/MeOH (40:1, v/v) as eluent to afford the
compound 3. White solid (315.0 mg, 88%). M.p. 161-162 oC. 1H NMR (400 MHz, CDCl3):
δ 11.58 (s, 1H, OH), 7.90-7.76 (m, 1H, ArH), 7.56 (s, 1H, ArH), 7.45-7.36 (m, 1H, ArH),
7.35-7.21 (m, 3H, ArH), 7.05-6.87 (m, 2H, ArH), 4.20 (t, J = 7.6 Hz, 2H,
CH2CH2CH2CH3), 1.84-1.69 (m, 2H, CH2CH2CH2CH3), 1.34-1.19 (m, 2H,
CH2CH2CH2CH3), 0.85 (t, J = 7.3 Hz, 3H, CH2CH2CH2CH3). 13C{1H} NMR (100 MHz,
CDCl3): δ 158.4, 154.1, 141.7, 134.8, 130.0, 129.7, 123.0, 122.7, 119.4, 119.1, 118.3,
117.7, 110.4, 44.5, 31.8, 20.0, 13.5. HRMS (positive ESI): [M+H]+ calcd for C17H19N2O:
267.1497. Found: 267.1492.
4.2.4. Synthesis of the PCN Pd(II) pincer complexes (4)
To a stirred solution of 3 (133.2 mg, 0.5 mmol) and triethylamine (84 µL, 0.6 mmol) in
toluene (20 mL) was added diphenylchlorophosphine, diisopropylchlorophosphine or
dicyclohexylchlorophosphine (0.6 mmol) under argon atmosphere at room temperature.
Then the mixture was stirred at reflux for 6 h. After that, PdCl2 (89.0 mg, 0.5 mmol) was
added directly to the reaction mixture and refluxed for another 12 h. After cooling,
filtration, and evaporation, the residue was purified by preparative TLC on silica gel plates
eluting with CH2Cl2 to afford the corresponding PCN pincer complexes 4a-c.

2-(N-butyl-benzimidazol-2-yl)-6-(diphenylphosphinoxy)phenylchloropalladium(II)
(4a). Pale yellow solid (205.3 mg, 69%). M.p. >295 oC. 1H NMR (400 MHz, CDCl3): δ
8.68 (d, J = 8.1 Hz, 1H, ArH), 8.19-8.04 (m, 4H, PhH), 7.56-7.43 (m, 6H, PhH), 7.31-7.11
(m, 4H, ArH), 7.05 (td, J = 7.9, 1.0 Hz, 1H, ArH), 6.92 (d, J = 7.9 Hz, 1H, ArH), 4.44 (t, J
= 7.5 Hz, 2H, CH2CH2CH2CH3), 1.88-1.76 (m, 2H, CH2CH2CH2CH3), 1.46-1.34 (m, 2H,
CH2CH2CH2CH3), 0.93 (t, J = 7.3 Hz, 3H, CH2CH2CH2CH3). 13C{1H} NMR (100 MHz,
CDCl3): δ 162.9 (d, JCP = 10.7 Hz), 157.2 (d, JCP = 2.8 Hz), 149.8, 140.7 (d, JCP = 3.3 Hz),
135.9, 134.2 (d, JCP = 4.4 Hz), 133.2 (d, 1JCP = 54.6 Hz, Ph2PO), 132.1 (d, 4JCP = 2.1 Hz,
Ph2PO), 131.8 (d, 2JCP = 14.4 Hz, Ph2PO), 128.9 (d, 3JCP = 11.7 Hz, Ph2PO), 127.1, 124.3,
123.4, 119.2, 118.4, 113.7 (d, 3JCP = 17.3 Hz), 109.4, 44.7, 31.8, 20.2, 13.8. 31P{1H} NMR
(162 MHz, CDCl3): δ 153.9. Anal. Calcd for C29H26ClN2OPPd: C, 58.90; H, 4.43; N, 4.74.
Found: C, 59.15; H, 4.56; N 4.57%.
2-(N-butyl-benzimidazol-2-yl)-6-(diisopropylphosphinoxy)phenylchloropalladium(II)
(4b). Pale yellow solid (83.9 mg, 32%). M.p. >260 oC. 1H NMR (400 MHz, CDCl3): δ
8.66 (d, J = 7.7 Hz, 1H, ArH), 7.42-7.19 (m, 4H, ArH), 7.12 (t, J = 7.9 Hz, 1H, ArH), 6.86
(d, J = 8.0 Hz, 1H, ArH), 4.48 (t, J = 7.5 Hz, 2H, CH2CH2CH2CH3), 2.60-2.44 (m, 2H,
CH(CH3)2), 2.03-1.85 (m, 2H, CH2CH2CH2CH3), 1.57-1.42 (m, 8H, CH2CH2CH2CH3 and
CH(CH3)2), 1.41-1.30 (m, 6H, CH(CH3)2), 1.00 (t, J = 7.3 Hz, 3H, CH2CH2CH2CH3).
13C{1H} NMR (100 MHz, CDCl3): δ 164.5 (d, JCP = 7.2 Hz), 157.4 (d, JCP = 2.6 Hz),
149.0 (d, JCP = 1.4 Hz), 140.8 (d, JCP = 2.6 Hz), 136.2 (d, JCP = 0.9 Hz), 134.5 (d, JCP = 4.3
Hz), 126.7, 124.3, 123.4, 119.5, 117.9, 113.0 (d, 3JCP = 15.3 Hz), 109.2, 44.5, 31.9, 29.1 (d,
1JCP = 25.5 Hz), 20.3, 17.4 (d, 2JCP = 5.7 Hz), 16.8, 13.8. 31P{1H} NMR (162 MHz,
CDCl3): δ 202.4. Anal. Calcd for C23H30ClN2OPPd: C, 52.78; H, 5.78; N, 5.35. Found: C,
52.48; H, 5.98; N 4.96%.
2-(N-butyl-benzimidazol-2-yl)-6-(dicyclohexylphosphinoxy)phenylchloropalladium(II)
(4c). Pale yellow solid (101.6 mg, 34%). M.p. >290 oC. 1H NMR (400 MHz, CDCl3): δ
8.66 (d, J = 7.7 Hz, 1H, ArH), 7.39-7.19 (m, 4H, ArH), 7.12 (t, J = 7.8 Hz, 1H, ArH), 6.85
(d, J = 8.0 Hz, 1H, ArH), 4.47 (t, J = 7.4 Hz, 2H, CH2CH2CH2CH3), 2.39-2.25 (m, 2H,
Cy), 2.24-2.13 (m, 2H, Cy), 2.03-1.63 (m, 13H, CH2CH2CH2CH3 and Cy), 1.56-1.44 (m,
2H, CH2CH2CH2CH3), 1.44-1.27 (m, 7H, Cy), 1.00 (t, J = 7.3 Hz, 3H, CH2CH2CH2CH3).

13C{1H} NMR (100 MHz, CDCl3): δ 164.5 (d, JCP = 7.2 Hz), 157.4 (d, JCP = 2.6 Hz),
149.2 (d, JCP = 1.5 Hz), 140.8 (d, JCP = 2.8 Hz), 136.2, 134.5 (d, JCP = 4.0 Hz), 126.6,
124.3, 123.4, 119.6, 117.8, 112.9 (d, 3JCP = 15.4 Hz), 109.1, 44.5, 37.9 (d, 1JCP = 25.7 Hz),
31.9, 27.0 (d, 2JCP = 4.1 Hz), 26.7 (d, 4JCP = 1.0 Hz), 26.4, 26.3 (d, 2JCP = 3.7 Hz), 26.2,
25.7, 20.3, 13.8. 31P{1H} NMR (162 MHz, CDCl3): δ 196.2. Anal. Calcd for
C29H38ClN2OPPd: C, 57.72; H, 6.35; N, 4.64. Found: C, 57.88; H, 6.41; N 4.42%.
4.3. X-ray crystallographic studies
Crystals of complexes 4a-c were obtained by recrystallization from CH2Cl2/n-hexane at
ambient temperature. The data were collected on an Oxford diffraction Gemini E
diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.7107 Å) at ambient
temperature. The structures were solved by direct methods using the SHELXS-97 program,
and all non-hydrogen atoms were refined anisotropically on F2 by the full-matrix
least-squares technique, which used the SHELXL-97 crystallographic software package
[20]. The hydrogen atoms were included but not refined. Details of the crystal structure
determination are summarized in Table 4.
Table 4 Summary of crystallographlic data for complexes 4a, 4b and 4c
Complex
Formula
Mr
4a
4b
4c
C29H26ClN2OPPd
591.34
C23H30ClN2OPPd
523.31
C29H38ClN2OPPd
603.43
Crystal size (mm) 0.2×0.18×0.16
0.2×0.17×0.08
triclinic
0.2×0.18×0.16
triclinic
Crystal system
a (Å)
b (Å)
monoclinic
18.8585 (6)
8.1898 (3)
33.8275 (11)
90.00
101.123 (3)
90.00
5126.4 (3)
8
7.8547 (4)
10.1821 (6)
15.7444 (9)
95.748 (5)
104.094 (5)
108.380 (5)
1137.37 (11)
2
9.1958 (7)
10.4511 (8)
15.9995 (12)
107.672 (7)
99.326 (6)
103.021 (6)
1382.73 (18)
2
c (Å)
α (o)
β (o)
γ (o)
V (Å3)
Z
space group
ρcalc(g/cm3)
µ (mm-1)
θ range (o)
Number of data
collected
C2
1.532
0.916
5.8-52.74
15945
P-1
1.528
1.020
6.06-52.74
9398
P-1
1.449
0.850
5.86-52.74
11498
Number of unique 5226
4652
5644

data
R1(all data)
wR2 (all data)
R1 (I>2σ(I))
wR2 (I>2σ(I))
R(int)
0.0755
0.1101
0.0398
0.0832
0.0576
2400.0
0.0490
0.0780
0.0362
0.0714
0.0304
536.0
0.0481
0.0823
0.0374
0.0769
0.0252
624.0
F(000)
peak/hole (e·Å-3) 0.66/-0.70
0.50/-0.45
0.71/-0.43
4.4. Catalytic studies
4.4.1. General procedure for the catalytic C-H arylation of azoles with aryl iodides
To a stirred solution of Cs2CO3 (0.75 mmol) and CuI (1.25 mol%) in DMF (1.0 mL)
was added aryl iodide (0.75 mmol), azole (0.5 mmol) and 4a (0.25 mol%) under argon
atmosphere at room temperature. Then the mixture was stirred at 120 oC for 18 h. After
cooling, filtration, and evaporation, the residue was purified by preparative TLC on silica
gel plates eluting with petroleum ether/EtOAc to afford the corresponding products.
4.4.2. Synthesis of the pincer Pd(II)-benzothiazolyl complex 5a
To a stirred solution of benzothiazole (0.043 g, 0.318 mmol) in THF (10 mL) was
added n-BuLi (0.15 mL, 2.5 M in hexane, 0.375 mmol) under argon atmosphere at -78 oC.
After the mixture was stirred at -78 oC for 1 h, a cold solution (-78 oC) of 4a (0.038 g,
0.065 mmol) in THF (10 mL) was added via cannula. The resultant reaction mixture was
further stirred at -78 oC for 2 h. The volatiles were evaporated under reduced pressure and
the residue was purified by column chromatography on neutral alumina with petroleum
ether/EtOAc ( 20:1→5:1→2:1, v/v) to afford the pincer Pd(II)-benzothiazolyl complex 5a.
Pale yellow solid (14.7 mg, 33%). M.p. 177-179 oC. 1H NMR (400 MHz, CDCl3): δ 8.10
(d, J = 7.9 Hz, 1H, ArH), 7.93-7.78 (m, 5H, PhH and ArH), 7.50-7.38 (m, 6H, PhH),
7.37-7.29 (m, 2H, ArH), 7.27-7.19 (m, 2H, ArH), 7.18-7.07 (m, 2H, ArH), 7.03 (d, J = 7.9
Hz, 1H, ArH), 6.93-6.87 (m, 1H, ArH), 6.74 (d, J = 8.2 Hz, 1H, ArH), 4.50 (t, J = 7.5 Hz,
2H, CH2CH2CH2CH3), 1.96-1.87 (m, 2H, CH2CH2CH2CH3), 1.52-1.41 (m, 2H,
CH2CH2CH2CH3), 0.98 (t, J = 7.3 Hz, 3H, CH2CH2CH2CH3). 13C{1H} NMR (100 MHz,
CDCl3): δ 201.2 (d, JCP = 14.0 Hz), 162.4 (d, JCP = 10.2 Hz), 160.5 (d, JCP = 2.5 Hz),
159.2 (d, JCP = 3.1 Hz), 156.6, 140.2 (d, JCP = 2.3 Hz), 138.3, 136.6, 134.4 (d, JCP = 4.2

Hz), 133.5 (d, 1JCP = 55.6 Hz, Ph2PO), 132.2 (d, 2JCP = 14.6 Hz, Ph2PO), 131.8 (d, 4JCP
=
2.1 Hz, Ph2PO), 128.6 (d, 3JCP = 11.7 Hz, Ph2PO), 127.4, 124.2, 123.8, 123.1, 121.6, 120.9,
120.8, 118.4, 118.1, 113.2 (d, 3JCP = 16.7 Hz), 109.3, 44.6, 31.9, 20.2, 13.8. 31P{1H} NMR
(162 MHz, CDCl3): δ 154.2. HRMS (positive ESI): [M+H]+ calcd for C36H31N3OPPdS:
690.0960. Found: 690.0963.
4.4.3. Reaction of complex 5a with phenyl iodide
A mixture of 5a (0.030 g, 0.043 mmol) and phenyl iodide (0.009 g, 0.043 mmol) in
DMF (0.5 mL) was stirred at 120 oC for 10 h under argon atmosphere. Then the volatiles
were evaporated under reduced pressure. The residue was purified by preparative TLC on
silica gel plates to afford 2-phenylbenzothiazole (petroleum ether/EtOAc 8:1, v/v) in 66%
yield and the pincer Pd-I complex 6a (petroleum ether/CH2Cl2 1:1, v/v). Complex 6a:
Yellow solid (10.7 mg, 43%). M.p. >280 oC. 1H NMR (400 MHz, CDCl3): δ 9.00 (d, J =
8.0 Hz, 1H, ArH), 8.14-8.00 (m, 4H, PhH), 7.56-7.44 (m, 6H, PhH), 7.34-7.20 (m, 4H,
ArH), 7.16 (td, J = 7.9, 1.1 Hz, 1H, ArH), 7.02 (d, J = 8.0 Hz, 1H, ArH), 4.49 (t, J = 7.5
Hz, 2H, CH2CH2CH2CH3), 1.94-1.84 (m, 2H, CH2CH2CH2CH3), 1.50-1.41 (m, 2H,
CH2CH2CH2CH3), 0.98 (t, J = 7.4 Hz, 3H, CH2CH2CH2CH3). 13C{1H} NMR (100 MHz,
CDCl3): δ 162.3 (d, JCP = 10.1 Hz), 158.8 (d, JCP = 2.8 Hz), 154.0 (d, JCP = 5.8 Hz), 141.3
(d, JCP = 3.5 Hz), 135.8 (d, JCP = 1.6 Hz), 134.1 (d, JCP = 4.9 Hz), 132.9 (d, 2JCP = 13.6 Hz,
Ph2PO), 132.8 (d, 1JCP = 56.9 Hz, Ph2PO), 132.2 (d, 4JCP = 2.2 Hz, Ph2PO), 128.6 (d, 3JCP
= 11.7 Hz, Ph2PO), 127.2, 124.2, 123.6, 121.3, 118.2, 113.9 (d, 3JCP = 17.7 Hz), 109.3,
44.7, 31.8, 20.2, 13.8. 31P{1H} NMR (162 MHz, CDCl3): δ 159.8. HRMS (positive ESI):
[M-I]+ calcd for C29H26N2OPPd: 555.0818. Found: 555.0819.
4.4.4. Characterization data of the catalysis products
2-Phenylbenzo[d]thiazole. White solid. M.p. 106-108 oC. 1H NMR (400 MHz, CDCl3): δ
8.15-8.04 (m, 3H, ArH), 7.97-7.85 (m, 1H, ArH), 7.55-7.45 (m, 4H, ArH), 7.42-7.34 (m,
1H, ArH).
2-(p-Tolyl)benzo[d]thiazole. White solid. M.p. 78-79 oC. 1H NMR (400 MHz, CDCl3): δ
8.06 (d, J = 8.2 Hz, 1H, ArH), 7.99 (d, J = 8.2 Hz, 2H, ArH), 7.93-7.84 (m, 1H, ArH),
7.53-7.42 (m, 1H, ArH), 7.42-7.33 (m, 1H, ArH), 7.30 (d, J = 7.9 Hz, 2H, ArH), 2.42 (s,
3H, CH3).

2-(o-Tolyl)benzo[d]thiazole. White solid. M.p. 54-58 oC. 1H NMR (400 MHz, CDCl3): δ
8.10 (d, J = 8.1 Hz, 1H, ArH), 7.92 (d, J = 8.0 Hz, 1H, ArH), 7.75 (d, J = 7.6 Hz, 1H, ArH),
7.54-7.46 (m, 1H, ArH), 7.46-7.27 (m, 4H, ArH), 2.66 (s, 3H, CH3).
2-(m-Tolyl)benzo[d]thiazole. White solid. M.p. 71-72 oC. 1H NMR (400 MHz, CDCl3): δ
8.07 (d, J = 8.2 Hz, 1H, ArH), 7.94 (s, 1H, ArH), 7.92-7.83 (m, 2H, ArH), 7.54-7.43 (m,
1H, ArH), 7.43-7.33 (m, 2H, ArH), 7.30 (d, J = 7.6 Hz, 1H, ArH), 2.45 (s, 3H, CH3).
2-(4-Methoxyphenyl)benzo[d]thiazole. White solid. M.p. 120-122 oC. 1H NMR (400
MHz, CDCl3): δ 8.03 (d, J = 8.7 Hz, 3H, ArH), 7.86 (d, J = 7.9 Hz, 1H, ArH), 7.51-7.40
(m, 1H, ArH), 7.34 (t, J = 7.3 Hz, 1H, ArH), 6.99 (d, J = 8.8 Hz, 2H, ArH), 3.86 (s, 3H,
OCH3).
2-(4-Chlorophenyl)benzo[d]thiazole. White solid. M.p. 114-115 oC. 1H NMR (400 MHz,
CDCl3): δ 8.07 (d, J = 8.0 Hz, 1H, ArH), 8.05-7.99 (m, 2H, ArH), 7.90 (d, J = 7.9 Hz, 1H,
ArH), 7.55-7.43 (m, 3H, ArH), 7.42-7.36 (m, 1H, ArH).
2-(4-Bromophenyl)benzo[d]thiazole. White solid. M.p. 124-128 oC. 1H NMR (400 MHz,
CDCl3): δ 8.07 (d, J = 8.1 Hz, 1H, ArH), 8.01-7.93 (m, 2H, ArH), 7.90 (d, J = 7.7 Hz, 1H,
ArH), 7.67-7.58 (m, 2H, ArH), 7.56-7.45 (m, 1H, ArH), 7.45-7.34 (m, 1H, ArH).
2-(4-Cyanophenyl)benzo[d]thiazole. White solid. M.p. 170-174 oC. 1H NMR (400 MHz,
CDCl3): δ 8.20 (d, J = 8.4 Hz, 2H, ArH), 8.11 (d, J = 8.2 Hz, 1H, ArH), 7.94 (d, J = 7.9 Hz,
1H, ArH), 7.78 (d, J = 8.4 Hz, 2H, ArH), 7.62-7.50 (m, 1H, ArH), 7.50-7.37 (m, 1H, ArH).
2-(2-Fluorophenyl)benzo[d]thiazole. White solid. M.p. 70-72 oC. 1H NMR (400 MHz,
CDCl3): δ 8.42 (td, J = 7.7, 1.8 Hz, 1H, ArH), 8.12 (d, J = 8.2 Hz, 1H, ArH), 7.95 (d, J =
8.0 Hz, 1H, ArH), 7.58-7.37 (m, 3H, ArH), 7.36-7.28 (m, 1H, ArH), 7.28-7.19 (m, 1H,
ArH).
2-(Pyridin-4-yl)benzo[d]thiazole. White solid. M.p. 135-136 oC. 1H NMR (400 MHz,
CDCl3): δ 8.77 (dd, J = 4.5, 1.6 Hz, 2H, ArH), 8.13 (d, J = 8.0 Hz, 1H, ArH), 8.01-7.88 (m,
3H, ArH), 7.59-7.51 (m, 1H, ArH), 7.51-7.40 (m, 1H, ArH).
2-Phenylbenzo[d]oxazole. White solid. M.p. 102-105 oC. 1H NMR (400 MHz, CDCl3): δ
8.32-8.22 (m, 2H, ArH), 7.83-7.74 (m, 1H, ArH), 7.62-7.56 (m, 1H, ArH), 7.56-7.49 (m,
3H, ArH), 7.40-7.31 (m, 2H, ArH).
2-(p-Tolyl)benzo[d]oxazole. White solid. M.p. 102-105 oC.1H NMR (400 MHz, CDCl3): δ

8.15 (d, J = 8.2 Hz, 2H, ArH), 7.81-7.71 (m, 1H, ArH), 7.61-7.52 (m, 1H, ArH), 7.39-7.29
(m, 4H, ArH), 2.44 (s, 3H, CH3).
2-(4-Methoxyphenyl)benzo[d]oxazole. White solid. M.p. 95-96 oC. 1H NMR (400 MHz,
CDCl3): δ 8.21 (d, J = 8.9 Hz, 2H, ArH), 7.78-7.69 (m, 1H, ArH), 7.60-7.50 (m, 1H, ArH),
7.38-7.27 (m, 2H, ArH), 7.03 (d, J = 8.9 Hz, 2H, ArH), 3.89 (s, 3H, OCH3).
2-(4-Chlorophenyl)benzo[d]oxazole. White solid. M.p. 152-153 oC. 1H NMR (400 MHz,
CDCl3): δ 8.26-8.13 (m, 2H, ArH), 7.81-7.73 (m, 1H, ArH), 7.62-7.54 (m, 1H, ArH),
7.54-7.46 (m, 2H, ArH), 7.41-7.32 (m, 2H, ArH).
2-(Pyridin-4-yl)benzo[d]oxazole. White solid. M.p. 131-133 oC. 1H NMR (400 MHz,
CDCl3): δ 8.83 (d, J = 5.4 Hz, 2H, ArH), 8.09 (d, J = 5.6 Hz, 2H, ArH), 7.87-7.76 (m, 1H,
ArH), 7.67-7.56 (m, 1H, ArH), 7.49-7.34 (m, 2H, ArH).
2-Phenylthiazole. Colorless oil. 1H NMR (400 MHz, CDCl3): δ 8.00-7.95 (m, 2H, ArH),
7.87 (d, J = 3.2 Hz, 1H, ArH), 7.46-7.41 (m, 3H, ArH), 7.33 (d, J = 3.2 Hz, 1H, ArH).
2-(4-Chlorophenyl)thiazole. Brown solid. M.p. 40 oC. 1H NMR (400 MHz, CDCl3): δ
7.93-7.88 (m, 2H, ArH), 7.87 (d, J = 3.2 Hz, 1H, ArH), 7.45-7.40 (m, 2H, ArH), 7.35 (d, J
= 3.2 Hz, 1H, ArH).
Appendix A. Supplementary data
CCDCs 1558938, 1558939 and 1558940 contain the supplementary crystallographic data
for the three pincer Pd(II) complexes 4a-c. These data can be obtained free of charge via
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.
Acknowledgments
We are grateful to the National Natural Science Foundation of China (21472176,
21672192) and Program for Science & Technology Innovation Talents in Universities of
Henan Province (2012HASTIT003) for financial support of this work.
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Three new PCN pincer Pd(II) complexes with (phosphinito)aryl benzimidazole ligands
have been synthesized and well characterized. The pincer Pd complex acted as effective
catalyst for the intermolecular arylation of azoles with aryl iodides in the presence of CuI
cocatalyst, giving the 2-arylated azoles in generally good to excellent yields.