Preparation and catalytic properties of the triphenylarsine and triphenylstibine-stabilized tri-heteroleptic NHC–Pd?allyl complexes

Article abstract of DOI:10.1016/j.jorganchem.2019.01.011

A series of triphenylarsine and triphenylstibine-stabilized tri-heteroleptic NHC–Pd?allyl complexes were synthesized and characterized. The solid-state structures of the complexes shown mononuclear carbene palladium complexes, in which, each palladium cen

Full text of DOI:10.1016/j.jorganchem.2019.01.011

Accepted Manuscript
Preparation and catalytic properties of the triphenylarsine and triphenylstibine-
stabilized tri-heteroleptic NHC Pd‒allyl complexes
Jin Yang
PII:
S0022-328X(19)30015-4
DOI:
https://doi.org/10.1016/j.jorganchem.2019.01.011
JOM 20689
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 7 December 2018
Revised Date: 9 January 2019
Accepted Date: 16 January 2019
Please cite this article as: J. Yang, Preparation and catalytic properties of the triphenylarsine and
triphenylstibine-stabilized tri-heteroleptic NHC Pd‒allyl complexes, Journal of Organometallic
Chemistry (2019), doi: https://doi.org/10.1016/j.jorganchem.2019.01.011.
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Graphical abstract
The graphical abstract synopsis：
A series of triphenylarsine and triphenylstibine-stabilized tri-heteroleptic
NHC‒Pd‒allyl complexes were synthesized and used in Sonogashira coupling
reaction.
Highlights
• Triphenylarsine and triphenylstibine-stabilized tri-heteroleptic NHC‒Pd‒allyl
complexes were synthesized.
• Molecular structures have been elucidated by X-ray single-crystal diffraction.
• The catalytic activities of the complexes were examined in Sonogashira coupling
reaction.

ACCEPTED MANUSCRIPT
Preparation and catalytic properties of the triphenylarsine and
triphenylstibine-stabilized tri-heteroleptic NHC‒Pd‒allyl complexes
Jin Yang1*
1 Department of Chemistry, Huaibei Normal University, Huaibei, Anhui 235000, P. R.
China;
*Corresponding
yangjinlz@163.com
Abstract
author:
Jin
Yang,
Tel:
(+)86-561-380-2235,
Email:
A series of triphenylarsine and triphenylstibine-stabilized tri-heteroleptic
NHC‒Pd‒allyl complexes were synthesized and characterized. The solid-state
structures of the complexes shown mononuclear carbene palladium complexes, in
which, each palladium centre was coordinated by an N-heterocyclic carbene, the
η3-coordinated allyl moiety and an As or Sb donor. Further investigation of the Pd
complexes as catalysts in Sonogashira coupling reaction was carried out and the
obtained complexes exhibited good reactivities for aryl bromides.
Keywords: N-Heterocyclic carbene, Palladium complexes, Triphenylarsine,
Triphenylstibine, Sonogashira coupling reaction.
1. Introduction
The chemical property of the transition metal complexes is significantly influenced by
the coordination of the ligand in transferring electronic density to the metal centre.[1]
Recently years, the predominant performances of the N-heterocyclic carbene (NHC)
palladium catalysts in cross-coupling reactions have aroused great interest.[2]
A
number of well-defined NHC–Pd(II) complexes have been widely exploited in
organic synthesis. Further study shown that the activity of the NHC–Pd(II) complexes
can be modified by the introduction of the ancillary ligands. For example, Nolan’s
NHC-palladacycles, allyl-based NHC–Pd(II) complexes, acac-based NHC–Pd(II)
complexes and Organ’s Pd-PEPPSI-NHC complexes have exhibited good catalytic

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activities due to the weak coordinating ancillary ligands can disassociate from the
metal centre to form catalytically active species with vacant coordination sites and
then re-coordinate to it after the catalytic cycle.[3] In order to further explore the
catalytic activities of NHC–Pd(II) complexes, some heteroatomic compound have
been introduced into the coordination with the palladium centres and these complexes
bearing mixed ligands may have potential application in organic synthesis. Among the
known dual-ligand systems, the combination of NHC with phosphine is of special
interest, due to the important role of phosphines in catalysis as well as the synergistic
effect of these two ligands.[4] Recently, the phosphino-carbene–Pd(II)–allyl complexes
have been investigated in detail in order to determine the influence of the trans effect
of the complexes.[5] Despite the progress made so far in the use of mixed-ligand
complexes to promote catalysis, very little research has been reported on heteroleptic
NHC‒Pd complexes with group 15 donor ligands. Recently, we have reported the
synthesis and application of triphenylarsine and triphenylstibine-stabilized NHC‒Pd
complexes (NHC)PdCl2(EPh3) (E = As, Sb).[6] With one of our efforts being the
development of well-defined NHC–Pd complexes and their utility in catalysis, herein
we reported the synthesis and characterization of triphenylarsine and
triphenylstibine-stabilized
tri-heteroleptic
NHC‒Pd‒allyl
complexes
[(NHC)Pd(allyl)(EPh3)]ClO4 (E = As, Sb) (3a‒3h) and their further utility in
Sonogashira coupling reaction.
Scheme 1. Synthesis of the well-defined tri-heteroleptic NHC‒Pd‒allyl complexes
[(NHC)Pd(allyl)(EPh3)]ClO4 (E = As, Sb) (3a‒3h)
2. Results and Discussion
2.1 Synthesis of the [(NHC)Pd(allyl)(EPh3)]ClO4 (E = As, Sb) complexes
The [(NHC)Pd(allyl)(EPh3)]ClO4 complexes were prepared in one pot based on anion
metathesis and then ligand replacement with EPh3 (NHC: IMes = N,N′-bis-

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(2,4,6-trimethylphenyl)imidazol-2-ylidene;
IPr
=
N,N′-bis-
N,N′-bis-
N,N′-bis-
(2,6-di(isopropyl)phenyl)imidazol-2-ylidene;
(2,4,6-trimethylphenyl)imidazolidin-2-ylidene;
SIMes
SIPr
=
=
(2,6-di(isopropyl)phenyl)imidazolidin-2-ylidene; E = As, Sb). As shown in Scheme 1,
following the synthetic route reported previously, the (NHC)Pd(allyl)Cl complexes
were easily obtained from reaction of imidazolium salts, [Pd(allyl)Cl]2 and KOtBu in
dry THF.[7] The anion metathesis of (NHC)Pd(allyl)Cl with AgClO4 in CH3CN
generated the solvated complexes [(NHC)Pd(allyl)(CH3CN)]ClO4 (2a‒2d) in almost
quantitative yields. The obtained complexes subsequently reacted with EPh3 through
ligand replacement to afford the above-mentioned products (3a‒3h). Complexes
1
3a‒3h have been fully characterized by H NMR, 13C NMR, elemental analysis,
HR-MS and X-ray single-crystal diffraction. The formation of the heteroleptic
complexes is evident from the characteristic proton signal resonances of NHC, allyl
moiety (one heptet and four doublets) and EPh3 in 1H NMR spectra. Furthermore, the
13C NMR spectra revealed the appearance of the carbonic carbons as diagnostic
singlet peaks (156.3‒156.1 ppm for IMes and IPr-bearing complexes; 187.1‒186.5
ppm for SIMes and SIPr-bearing complexes). All of the complexes were further
characterized by X-ray single-crystal diffraction and the structures were depicted in
Figure 1. In all cases the common distorted square-planar coordination around the
palladium center with an environment of an NHC, the allyl moiety and an As or Sb
donor was observed. The allyl moiety is η3-coordinated to the palladium with one
terminal carbon trans to the carbene and the second terminal carbon trans to EPh3.
Among the eight complexes, the Pd‒CNHC bond lengths were in a range of
2.041(7)‒2.087(8) Å with the shortest distance is found for 3a and the longest for 3d,
which suggested a single bond of σ-bond character. The Pd‒Callyl bond lengths were
in a range of 2.124(10)‒2.192(10) Å with the shortest distance is found for 3e and the
longest for 3d. In all complexes, the Pd‒CNHC bond lengths were slightly longer than
that of the Pd‒Callyl bonds. In addition, the Pd‒As(Sb) bond lengths, which were in
narrow ranges [2.4338(12)‒2.4506(13) Å for Pd‒As bonds and 2.572(2)‒2.5888(12)
Å for Pd‒Sb bonds], were significantly longer than the Pd‒C bonds.

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Figure 1. ORTEP diagrams of complexes 3a‒3h with thermal displacement
‒
parameters drawn at 30% probability. The anions (ClO4 ), solvent molecules (CH2Cl2
or CHCl3) and parts of the hydrogen atoms have been omitted for clarity.
2.2 The catalytic activities of complexes 3a‒3h for Sonogashira coupling reaction
The traditional palladium-catalyzed Sonogashira reaction often requires an amount of
copper salt as co-catalyst, which led to the formation of air-sensitive copper acetylide
species. However, the copper acetylides often participate in the Glaser-Hay
homo-coupling, which reduced the yields of the Sonogashira reaction.[8] In this
connection, the Sonogashira reaction performed under Cu-free conditions resulted in a
significant improvement in the performance of these reactions. In recently years,
modified protocols have mainly focused on the development of new Pd-catalysts for
the reaction and a number of examples of Sonogashira reaction catalyzed by NHC‒Pd
catalysts have been reported.[9] In order to demonstrate the utility of these
tri-heteroleptic Pd-complexes, complexes 3a‒3h were subjected to the Cu-free
Sonogashira reaction of phenylacetylene with aryl bromides. Initially, complex 3b
(1.0 mol%) was selected as the model catalyst, the reaction of 4-bromoanisole (0.5
mmol) with phenylacetylene (0.6 mmol) as a model reaction to test the reaction
conditions and in particular the solvent and base. As shown in Table 1, using DMF as
solvent and Cs2CO3 as base gave the best yield at 100 °C in 6 h (Table 1, entry 1).
Under the same conditions, using K2CO3 as the base could also give a similar result.

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However, other inorganic bases, like Na2CO3, KHCO3, KOH and KOtBu have been
tested to lead to relatively poor yields. The solvent was then investigated and the role
of the solvent appeared to be crucial in the reaction with complex 3b as catalyst. With
regard to reaction solvent, DMF is found to be a superior solvent for this process.
Moreover, products can also be obtained in high yields when DMA was used as
solvent. A plausible reason is that the catalytically active Pd(0) species could be
generated readily from the precatalysts [(NHC)Pd(allyl)(EPh3)]ClO4 and remain
stable in DMF or DMA. However, in the presence of other solvents such as DMSO,
moderate yield was obtained. When 1,4-dioxane, CH3CN and THF were used, no
reaction occurred. The catalyst loading and reaction temperature were then tested.
When the catalyst loading was reduced to 0.5 mol%, the yield lowered to 65% (Entry
12). However, the yields could be increased slightly when the time was prolonged
(Entry 13). Furthermore, the reaction temperature was also investigated and the
o
optimum reaction temperature was found to be 100 C. With the increase of
temperature, the catalytic activity of complex 3b decreased gradually which indicated
that the catalysts suitable for the coupling reaction but tend to decompose at higher
temperatures. Moreover, the model reaction was performed in the presence of a
nitrogen atmosphere, complex 3b showed a similar performance of the reaction as
that in air atmosphere (Entry 16). However, an oxygen atmosphere could result into
lower yield of the product (Entry 17), which probably indicated that the oxidative
decomposition of the catalyst in the presence of oxygen. On the basis of the extensive
screening, DMF and Cs2CO3 were proved to be the efficient solvent and base,
respectively, with 1.0 mol % complex 3b at 100 °C for 6 h, thus giving the optimal
coupling result. Under the same conditions, other complexes were also tested, the
(S)IPr-based complexes 3b, 3d, 3f and 3h with the sterically bulky substituent groups
gave high yields, however, the (S)IMes-based complexes 3a, 3c, 3e and 3g gave very
low yields in both cases.
Table 1. Study of the reaction conditions for complex 3b catalyzed Sonogashira
reaction of 4-bromoanisole with phenylacetylenea

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Entry
1
[Pd] [%]
3b (1.0%)
3b (1.0%)
3b (1.0%)
3b (1.0%)
3b (1.0%)
3b (1.0%)
3b (1.0%)
3b (1.0%)
Solvent
DMF
DMF
DMF
DMF
DMF
DMF
DMA
DMSO
Base
Yieldb (%)
91
Cs2CO3
K2CO3
Na2CO3
KHCO3
KOH
2
87
3
64
4
52
5
40
6
KOtBu
Cs2CO3
Cs2CO3
45
7
88
8
65
9
3b (1.0%) 1,4-dioxane Cs2CO3
20
10
11
12
13c
14d
15e
16f
17g
18
19
20
21
22
23
24
3b (1.0%)
3b (1.0%)
3b (0.5%)
3b (0.5%)
3b (1.0%)
3b (1.0%)
3b (1.0%)
3b (1.0%)
3a (1.0%)
3c (1.0%)
3d (1.0%)
3e (1.0%)
3f (1.0%)
3g (1.0%)
3h (1.0%)
CH3CN
THF
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
trace
trace
65
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
72
80
72
92
54
50
42
90
40
88
35
85
a
Reaction conditions: 4-bromoanisole (0.5 mmol), phenylacetylene (0.6 mmol), complex 3b
(0.005 mmol), base (0.6 mmol), solvent (2.0 mL), 100 °C, 6 h. b Isolated yield. c Reaction time is
d
o
e
o
f
12h. Reaction temperature is 130 C. Reaction temperature is 80 C. Under nitrogen
atmosphere. g Under oxygen atmosphere.

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The coupling reactions of a wide range of aryl bromides with terminal alkynes
were further studied in the presence of complexes 3b, 3d, 3f and 3h, the results for
this reaction are reported in Table 2. Usually, electron-withdrawing groups have an
effect on increasing the reactivity of substrates. In this case, gratifyingly, all
complexes were found to be able to efficiently convert activated aryl bromides in 6 h.
The couplings of activated aryl bromide (such as 4-bromoacetophenone and
4-bromonitrobenzene) with phenylacetylene afforded excellent yields (Table 2,
entries 1−8). Thus, to investigate the effects of the catalytic system with an
electron-donating substrate and neutral aryl bromide, we performed the reaction
between phenylacetylene with 4-bromotoluene and bromobenzene under similar
reaction condition, respectively. The corresponding products were obtained in
moderate yields when 4-bromotoluene or bromobenzene was used (Entries 9−16),
which are inferior to the reactions of activated aryl bromides. The system also proved
to be tolerant of sterically hindered substrates, while with an ortho or meta-substituted
aryl bromide, a relatively lower yield was isolated under the present reaction
conditions owing to steric hindrance put by substituents. Furthermore, the coupling
reactions of substituted aryl acetylenes with aryl and alkyl bromides were also
attempted. For example, the couplings of 4-methoxyphenylacetylene with aryl
bromides (such as 4-bromotoluene and 4-bromoanisole) afforded good to excellent
yields (Entries 25–32). Moreover, the couplings of 4-methoxyphenylacetylene with
1-bromohexane also gave relatively good yields (Entries 33–36). However, this
catalytic system was no longer effective for aryl chlorides. No desired Sonogashira
coupling product was obtained for the reaction of aryl chloride with phenylacetylene.
As can be seen from the results above, the reactivities of the obtained complexes
are not limited to para-substituted aryl bromides, ortho- or meta-substituted aryl
bromides and alkyl bromides can be also employed. Yields are somewhat lower
compared with para-substituted aryl bromides, and are found to significantly depend
on the steric hindrance of the substituent. Furthermore, the electronic properties of the
substituent of aryl bromides also influence the reaction yield to some extent. On the
other hand, the reaction fails when aryl chlorides are employed as substrates.

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Consequently, the substrate scope of these obtained Pd-catalysts appears somewhat
lower activities in comparison with some recently reported Pd-catalysts. With the
results in hand and in every case studied, the catalysts 3b and 3d (with As donor) are
slightly more active than the catalysts 3f and 3h (with Sb donor). We attributed these
performance differences to the well-balanced property between NHC and As donor in
the catalytic cycle. As the ancillary ligand, it is known that despite the Sb-donor can
form very similar complexes with P and As-donors, the stibine owned the poorer
donor properties compared to arsine ligand as well as an increased tendency to
dissociation in solution in contrast with their arsine homologues.[10] Furthermore, the
(S)IPr-based complexes with the sterically bulky substituent groups shown more
efficient catalytic activities than the (S)IMes-based complexes. This suggests that the
well-balanced property between NHC and As (Sb) donor do not influence the reaction
yield to a great extent, whereas the steric effects of the NHC ligands are more
important.
Table 2 Sonogashira coupling reaction of aryl bromides with alkynesa,b
Entry Catalyst
Alkynes
Aryl bromides
Yield (%) b
1
2
3b
3d
3f
94
92
88
88
96
94
91
90
84
87
82
80
80
82
77
75
86
3
4
3g
3b
3d
3f
5
6
7
8
3g
3b
3d
3f
9
10
11
12
13
14
15
16
17
3g
3b
3d
3f
3g
3b

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18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
3d
3f
84
80
80
74
72
65
62
90
90
85
85
96
95
92
90
85
82
78
80
3g
3b
3d
3f
3g
3b
3d
3f
3g
3b
3d
3f
3g
3b
3d
3f
3g
a Reaction conditions: aryl bromide (0.5 mmol), terminal alkyne (0.6 mmol), NHC‒Pd (0.005
mmol), Cs2CO3 (0.6 mmol), DMF (2.0 mL) at 100 oC for 6 h. b Isolated yield.
3. Conclusions
In summary, a series of triphenylarsine and triphenylstibine-stabilized tri-heteroleptic
NHC‒Pd‒allyl complexes were synthesized and fully characterized. Analyses of
crystal structures show that each palladium centre was coordinated by an
N-heterocyclic carbene, the allyl moiety and an As or Sb donor. The investigation of
catalytic activities of the obtained complexes shown that the (S)IPr-based complexes
with the sterically bulky substituent groups can effectively catalyze the Sonogashira
coupling reaction of aryl bromide with terminal alkynes. Further studies on the
well-defined NHC‒Pd complexes, as well as their applications in organic synthesis is
currently undergoing in our laboratory.
4. Experimental section
4.1 General considerations
The chemicals were purchased from commercial suppliers and were used without
purification prior to use unless otherwise indicated. NMR spectra were recorded at

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400 MHz (for 1H NMR) and 100 MHz (for 13C NMR) on a Bruker Avance 400 NMR
spectrometer. All 1H, and 13C NMR were performed in CDCl3 with tetramethylsilane
(TMS) as an internal standard. The C, H, and N analyses were performed with a Vario
El III elementar. Complexes (NHC)Pd(allyl)Cl (2a‒2d) were prepared according to
the literature.[11]
4.2 Synthesis of complexes 3a–3h
A round-bottom flask equipped with a stir bar was charged with the (NHC)Pd(allyl)Cl
(0.5 mmol), AgClO4 (0.55 mmol, 104 mg) and CH3CN (5.0 mL). The reaction
mixture was stirred at room temperature for 1 h and a solution of AsPh3 or SbPh3 (0.5
mmol) in CH2Cl2 (5.0 mL) was added dropwise with stirring. The reaction mixture
was stirred for a further 4 h. The solvents were removed under reduced pressure and
the residue was purified by flash chromatography on short silica gel and recrystallized
from n-hexane–CH2Cl2 to afford the desired products. Single crystals of the
complexes for X-ray diffraction analysis were obtained from evaporation of their
n-hexane/CH2Cl2 or CHCl3 solutions.
[(IMes)Pd(Allyl)(AsPh3)]ClO4 (3a)
1
The procedure yielded 385 mg (90%) of the pure 3a as a white powder. H NMR
(CDCl3, 400 MHz) δ (ppm) = 7.43 (t, J = 7.2 Hz, 3H, p-CH-phenyl), 7.34 (s, 2H,
m-CH-aniline), 7.32 (t, J = 7.2 Hz, 6H, m-CH-phenyl), 6.96 (br, 4H, N-CH=CH-N
and m-CH-aniline), 6.90 (d, J = 6.8 Hz, 6H, o-CH-phenyl), 5.08 (sept, J = 6.8 Hz, 1H,
CH-allyl), 4.22 (dd, J = 6.8 and 1.6 Hz, 1H, CH2-allyl), 3.35 (dd, J = 7.2 and 1.6 Hz,
1H, CH2-allyl), 2.47 (d, J = 13.2, 1H, CH2-allyl), 2.33 (s, 6H, p-CH3-aniline), 2.29 (d,
J = 13.6 Hz, 1H, CH2-allyl), 1.99 (s, 12H, o-CH3-aniline). 13C NMR (CDCl3,100
MHz): δ (ppm) = 178.39 (Ccarbene), 139.48 (Caniline), 134.47 (Cphenyl), 132.65 (o-Cphenyl),
130.46 (Caniline), 129.45(p-Cphenyl), 129.15 (m-Cphenyl), 125.09 (N-CH=CH-N), 119.01
(Caniline), 71.04 (CH-allyl), 67.59 (CH2-allyl), 20.89 (p-CH3-aniline), 18.36
(o-CH3-aniline), 18.02 (o-CH3-aniline). HR-MS (ESI): calcd for C42H44AsN2Pd [M –
‒ +
ClO4 ] 757.1755; found 757.1784. Calcd. for [(IMes)Pd(Allyl)(AsPh3)]ClO4
(C42H44AsClN2O4Pd): C, 58.82; H, 5.17; N, 3.27%. Found: C, 58.55; H, 5.33; N,
3.56%.

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[(IPr)Pd(Allyl)(AsPh3)]ClO4 (3b)
1
The procedure yielded 410 mg (87%) of the pure 3b as a white powder. H NMR
(CDCl3, 400 MHz) δ (ppm): 7.61 (s, 2H, N-CH=CH-N), 7.41 (t, J = 7.0 Hz, 3H,
p-CH-phenyl), 7.29 (t, J = 7.5 Hz, 6H, m-CH-phenyl), 7.27‒7.26 (m, 2H,
p-CH-aniline), 7.18 (br, 3H, m-CH-aniline), 6.93 (d, J = 6.0 Hz, 6H, m-CH-phenyl),
6.73 (br, 1H, m-CH-aniline), 5.13 (sept, J = 6.5 Hz, 1H, CH-allyl), 4.27 (d, J = 7.0 Hz,
1H, CH2-allyl), 3.29 (d, J = 7.5 Hz, 1H, CH2-allyl), 2.96 (br, 2H, CH(CH3)2), 2.52 (br,
2H, CH(CH3)2), 2.29 (d, J = 13.5 Hz, 1H, CH2-allyl), 2.09 (d, J = 13.0 Hz, 1H,
CH2-allyl), 1.32 (br, 6H, CH(CH3)2), 1.15 (br, 6H, CH(CH3)2), 1.02 (br, 6H,
13
CH(CH3)2), 0.70 (br, 3H, CH(CH3)2), 0.24 (br, 3H, CH(CH3)2). C NMR (CDCl3,
100 MHz) δ (ppm): 181.54 (Ccarbene), 145.14 (Caniline), 133.56 (Cphenyl), 133.52
(o-Caniline), 132.51 (Caniline), 131.01 (p-Cphenyl), 130.55 (Caniline), 129.35 (m-Cphenyl),
127.01 (N-CH=CH-N), 119.19 (Caniline), 73.11 (CH-allyl), 67.95 (CH2-allyl), 28.72
(CH(CH3)2), 28.50 (CH(CH3)2), 26.96 (CH(CH3)2), 25.73 (CH(CH3)2), 22.60
‒ +
(CH(CH3)2), 22.52 (CH(CH3)2). HR-MS (ESI): calcd for C48H56AsN2Pd [M – ClO4 ]
841.2694;
found
841.2687.
Calcd.
for
[(IPr)Pd(Allyl)(AsPh3)]ClO4
(C48H56AsClN2O4Pd): C, 61.22; H, 5.99; N, 2.97%. Found: C, 60.96; H, 5.73; N,
3.18%.
[(SIMes)Pd(Allyl)(AsPh3)]ClO4 (3c)
1
The procedure yielded 390 mg (91%) of the pure 3c as a white powder. H NMR
(CDCl3, 400 MHz) δ (ppm): 7.42 (t, J = 7.2 Hz, 3H, p-CH-phenyl), 7.32 (t, J = 7.6 Hz,
6H, m-CH-phenyl), 7.00 (s, 1H, m-CH-aniline), 6.96 (s, 1H, m-CH-aniline), 6.89 (d, J
= 7.6 Hz, 6H, o-CH-phenyl), 6.80 (s, 1H, m-CH-aniline), 6.51 (s, 1H, m-CH-aniline),
4.93 (sept, J = 6.8 Hz, 1H, CH-allyl), 4.33 (d, J = 6.4 Hz, 1H, CH2-allyl), 4.15 (s, 4H,
N-CH2-CH2-N), 3.19 (d, J = 7.2 Hz, 1H, CH2-allyl), 2.42 (s, 3H, o-CH3-aniline), 2.40
(d, J = 13.2, 1H, CH2-allyl), 2.31 (s, 6H, p-CH3-aniline), 2.23 (s, 3H, o-CH3-aniline),
2.16 (d, J = 13.2 Hz, 1H, CH2-allyl), 2.02 (s, 3H, o-CH3-aniline), 1.64 (s, 3H,
o-CH3-aniline). 13C NMR (CDCl3, 100 MHz) δ (ppm): 208.13 (Ccarbene), 138.62
(Caniline), 138.34 (Caniline), 135.56 (Cphenyl), 135.02 (Caniline), 134.55 (Caniline), 132.72
(o-Cphenyl), 130.43 (Caniline), 129.43 (p-Cphenyl), 129.11 (m-Cphenyl), 118.86 (Caniline),

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71.70 (CH-allyl), 67.33 (CH2-allyl), 52.17 (N-CH2-CH2-N), 51.99 (N-CH2-CH2-N),
20.92 (p-CH3-aniline), 18.69 (o-CH3-aniline), 18.19 (o-CH3-aniline), 18.09
(o-CH3-aniline), 17.84 (o-CH3-aniline). HR-MS (ESI): calcd for C42H46AsN2Pd [M –
‒ +
ClO4 ] 759.1912; found 759.1923. Calcd. for [(SIMes)Pd(Allyl)(AsPh3)]ClO4
(C42H46AsClN2O4Pd): C, 58.68; H, 5.39; N, 3.26%. Found: C, 58.94; H, 5.21; N,
3.49%.
[(SIPr)Pd(Allyl)(AsPh3)]ClO4 (3d)
1
The procedure yielded 420 mg (89%) of the pure 3d as a white powder. H NMR
(CDCl3, 400 MHz) δ (ppm): 7.42 (t, J = 7.0 Hz, 3H, p-CH-phenyl), 7.34 (br, 6H,
m-CH-phenyl), 7.28 (t, J = 7.0 Hz, 2H, p-CH-aniline), 7.19‒7.17 (m, 2H,
m-CH-aniline), 7.12 (t, J = 7.5 Hz, 2H, o-CH-phenyl), 7.12 (br, 3H, o-CH-phenyl),
7.01‒7.00 (br, 2H, m-CH-aniline), 6.61 (d, J = 7.5 Hz, 1H, o-CH-phenyl), 5.01 (sept,
J = 6.5 Hz, 1H, CH-allyl), 4.68 (q, J = 11.0 Hz, 1H, N-CH2-CH2-N), 4.59 (td, J = 11.0
and 5.5 Hz, 1H, N-CH2-CH2-N), 4.26 (td, J = 11.0 and 5.5 Hz, 1H, N-CH2-CH2-N),
4.09 (q, J = 11.0 Hz, 1H, N-CH2-CH2-N), 4.01 (d, J = 7.0 Hz, 1H, CH2-allyl), 3.51
(sept, J = 6.5 Hz, 1H, CH(CH3)2), 3.34 (sept, J = 6.5 Hz, 2H, CH(CH3)2), 3.22 (sept, J
= 6.5 Hz, 1H, CH(CH3)2), 3.18 (d, J = 7.0 Hz, 1H, CH2-allyl), 2.23 (d, J = 13.5 Hz,
1H, CH2-allyl), 1.86 (d, J = 13.0 Hz, 1H, CH2-allyl), 1.49 (d, J = 6.5 Hz, 3H,
CH(CH3)2), 1.36 (d, J = 6.5 Hz, 3H, CH(CH3)2), 1.34 (d, J = 7.0 Hz, 3H, CH(CH3)2),
1.24 (d, J = 7.0 Hz, 3H, CH(CH3)2), 1.11 (d, J = 6.5 Hz, 3H, CH(CH3)2), 1.07 (d, J =
6.5 Hz, 3H, CH(CH3)2), 0.71 (d, J = 6.5 Hz, 3H, CH(CH3)2), 0.19 (d, J = 6.5 Hz, 3H,
13
CH(CH3)2). C NMR (CDCl3, 100 MHz) δ (ppm): 210.37 (Ccarbene), 146.92 (Caniline),
146.74 (Caniline), 146.18 (Caniline), 145.78 (Caniline), 136.55 (Cphenyl), 135.54 (Caniline),
132.64 (Caniline) 130.51 (o-Cphenyl), 130.06 (Caniline), 129.84 (p-Cphenyl), 129.34
(m-Cphenyl), 125.02 (Caniline), 124.67 (Caniline), 124.55 (Caniline), 124.04 (Caniline), 119.21
(Caniline), 73.83 (CH-allyl), 67.37 (CH2-allyl), 55.63 (N-CH2-CH2-N), 55.19
(N-CH2-CH2-N), 28.97 (CH(CH3)2), 28.62 (CH(CH3)2), 28.50 (CH(CH3)2), 28.30
(CH(CH3)2), 27.09 (CH(CH3)2), 27.03 (CH(CH3)2), 26.94 (CH(CH3)2), 26.23
(CH(CH3)2), 23.84 (CH(CH3)2), 23.75 (CH(CH3)2), 23.35 (CH(CH3)2), 22.54
‒ +
(CH(CH3)2). HR-MS (ESI): calcd for C42H46AsN2Pd [M – ClO4 ] 843.2851; found

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843.2842. Calcd. for [(SIPr)Pd(Allyl)(AsPh3)]ClO4 (C48H58AsClN2O4Pd): C, 61.09;
H, 6.19; N, 2.97%. Found: C, 60.84; H, 5.91; N, 3.22%.
[(IMes)Pd(Allyl)(SbPh3)]ClO4 (3e)
1
The procedure yielded 395 mg (87%) of the pure 3e as a white powder. H NMR
(CDCl3, 400 MHz) δ (ppm): 7.44 (t, J = 7.2 Hz, 3H, p-CH-phenyl), 7.36 (t, J = 7.2 Hz,
6H, m-CH-phenyl), 7.34 (s, 2H, m-CH-aniline), 7.04 (d, J = 7.2 Hz, 6H,
o-CH-phenyl), 6.95 (s, 2H, N-CH=CH-N), 6.82 (s, 2H, m-CH-aniline), 5.09 (sept, J =
6.8 Hz, 1H, CH-allyl), 4.49 (d, J = 6.4 Hz, 1H, CH2-allyl), 3.69 (d, J = 6.8 Hz, 1H,
CH2-allyl), 2.62 (d, J = 13.2, 1H, CH2-allyl), 2.27 (d, J = 13.6 Hz, 1H, CH2-allyl),
2.26 (s, 6H, p-CH3-aniline), 2.04 (s, 6H, o-CH3-aniline), 1.80 (s, 6H, o-CH3-aniline).
13C NMR (CDCl3, 100 MHz) δ (ppm): = 178.29 (Ccarbene), 139.60 (Caniline), 135.22
(Cphenyl), 134.34 (Caniline), 131.49 (o-Cphenyl), 130.61 (Caniline), 129.61 (p-Cphenyl),
129.57 (m-Cphenyl), 124.95 (N-CH=CH-N), 118.11 (Caniline), 71.50 (CH-allyl), 64.95
(CH2-allyl), 20.92 (p-CH3-aniline), 18.40 (o-CH3-aniline), 17.98 (o-CH3-aniline).
‒ +
HR-MS (ESI): calcd for C42H44N2PdSb [M – ClO4 ] 803.1578; found 803.1586.
Calcd. for [(IMes)Pd(Allyl)(SbPh3)]ClO4 (C42H44ClN2O4PdSb): C, 55.78; H, 4.90; N,
3.10%. Found: C, 55.56; H, 5.23; N, 3.36%.
[(IPr)Pd(Allyl)(SbPh3)]ClO4 (3f)
1
The procedure yielded 435 mg (88%) of the pure 3f as a white powder. H NMR
(CDCl3, 400 MHz) δ (ppm): 7.64 (s, 2H, N-CH=CH-N), 7.42 (t, J = 7.2 Hz, 3H,
p-CH-phenyl), 7.35 (t, J = 7.6 Hz, 2H, p-CH-aniline), 7.31 (t, J = 7.2 Hz, 6H,
m-CH-phenyl), 7.19 (d, J = 7.6 Hz, 2H, m-CH-aniline), 7.05 (d, J = 7.6 Hz, 2H,
m-CH-aniline), 7.02 (d, J = 7.2 Hz, 6H, m-CH-phenyl), 4.98 (sept, J = 6.4 Hz, 1H,
CH-allyl), 4.27 (d, J = 5.6 Hz, 1H, CH2-allyl), 3.64 (d, J = 7.2 Hz, 1H, CH2-allyl),
3.12 (sept, J = 6.8 Hz, 2H, CH(CH3)2), 2.74 (sept, J = 6.8 Hz, 2H, CH(CH3)2), 2.24 (d,
J = 13.6 Hz, 1H, CH2-allyl), 2.14 (d, J = 13.2 Hz, 1H, CH2-allyl), 1.16 (d, J = 6.8 Hz,
6H, CH(CH3)2), 1.05 (d, J = 6.8 Hz, 6H, CH(CH3)2), 1.01 (d, J = 6.4 Hz, 6H,
13
CH(CH3)2). 0.83 (br, 6H, CH(CH3)2). C NMR (CDCl3, 100 MHz) δ (ppm): 181.37
(Ccarbene), 145.22 (Caniline), 145.11 (Cphenyl), 135.10 (Caniline), 134.99 (Caniline), 130.86
(o-Cphenyl), 130.70 (Caniline), 130.63 (Caniline), 129.64 (p-Cphenyl), 126.85 (m-Cphenyl),

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124.69 (N-CH=CH-N), 124.27 (N-CH=CH-N), 117.63 (Caniline), 71.65 (CH-allyl),
66.81 (CH2-allyl), 28.82 (CH(CH3)2), 28.51 (CH(CH3)2), 26.82 (CH(CH3)2), 25.74
(CH(CH3)2), 22.61 (CH(CH3)2), 22.53 (CH(CH3)2). HR-MS (ESI): calcd for
‒ +
C48H56N2PdSb [M
–
ClO4 ]
887.2517; found 887.2529. Calcd. for
[(IPr)Pd(Allyl)(SbPh3)]ClO4 (C48H56ClN2O4PdSb): C, 58.32; H, 5.71; N, 2.83%.
Found: C, 58.58; H, 5.96; N, 3.15%.
[(SIMes)Pd(Allyl)(SbPh3)]ClO4 (3g)
1
The procedure yielded 412 mg (91%) of the pure 3g as a white powder. H NMR
(CDCl3, 400 MHz) δ (ppm): 7.43 (t, J = 7.2 Hz, 3H, p-CH-phenyl), 7.35 (t, 6H, J =
7.2 Hz, m-CH-phenyl), 7.02 (d, J = 7.2 Hz, 6H, o-CH-phenyl), 6.87 (br, 2H,
m-CH-aniline), 6.58 (br, 2H, m-CH-aniline), 4.94 (sept, J = 6.8 Hz, 1H, CH-allyl),
4.60 (d, J = 6.4 Hz, 1H, CH2-allyl), 4.15 (s, 4H, N-CH2-CH2-N), 3.52 (d, J = 7.2 Hz,
1H, CH2-allyl), 2.61 (d, J = 13.2 Hz, 1H, CH2-allyl), 2.22 (s, 12H, o-CH3-aniline),
13
2.13 (d, J = 13.2 Hz, 1H, CH2-allyl), 1.68 (s, 6H, p-CH3-aniline). C NMR (CDCl3,
100 MHz) δ (ppm): 207.83 (Ccarbene), 138.47 (Caniline), 135.27 (Cphenyl), 135.16 (Caniline),
131.46 (o-Cphenyl), 130.50 (Caniline), 129.52 (p-Cphenyl), 129.44 (m-Cphenyl), 117.92
(Caniline), 70.94 (CH-allyl), 65.41 (CH2-allyl), 51.89 (N-CH2-CH2-N), 20.77
(p-CH3-aniline), 17.84 (o-CH3-aniline). HR-MS (ESI): calcd for C42H46N2PdSb [M –
‒ +
ClO4 ] 805.1734; found 805.1725. Calcd. for [(SIMes)Pd(Allyl)(SbPh3)]ClO4
(C42H46ClN2O4PdSb): C, 55.65; H, 5.12; N, 3.09%. Found: C, 55.87; H, 5.37; N,
3.26%.
[(SIPr)Pd(Allyl)(SbPh3)]ClO4 (3h)
1
The procedure yielded 420 mg (85%) of the pure 3h as a white powder. H NMR
(CDCl3, 400 MHz) δ (ppm): 7.41 (t, J = 7.2 Hz, 3H, p-CH-phenyl), 7.34 (t, 6H, J =
7.2 Hz, m-CH-phenyl), 7.23 (t, J = 7.6 Hz, 2H, p-CH-aniline), 7.12‒7.11 (m, 8H,
o-CH-phenyl and m-CH-aniline), 6.98 (br, 2H, m-CH-aniline), 4.88 (sept, J = 6.8 Hz,
1H, CH-allyl), 4.45 (s, 4H, N-CH2-CH2-N), 4.21 (d, J = 6.4 Hz, 1H, CH2-allyl), 3.55
(d, J = 7.2 Hz, 1H, CH2-allyl), 3.43 (br, 2H, CH(CH3)2), 3.28 (sept, J = 6.4 Hz, 2H,
CH(CH3)2), 2.03 (d, J = 13.2 Hz, 1H, CH2-allyl), 1.98 (d, J = 13.6 Hz, 1H, CH2-allyl),
1.22 (br, 6H, CH(CH3)2), 1.18 (d, J = 6.4 Hz, 12H, CH(CH3)2), 1.02 (br, 6H,

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13
CH(CH3)2). C NMR (CDCl3, 100 MHz) δ (ppm): 210.27 (Ccarbene), 146.46 (Caniline),
146.38 (Caniline), 135.77 (Cphenyl), 135.15 (Caniline), 130.88 (o-Cphenyl), 130.60 (Caniline),
129.80 (p-Cphenyl), 129.60 (m-Cphenyl), 124.83 (Caniline), 124.42(Caniline), 117.64(Caniline),
71.40 (CH-allyl), 67.07 (CH2-allyl), 55.27 (N-CH2-CH2-N), 28.72 (CH(CH3)2), 28.38
(CH(CH3)2),
26.93
(CH(CH3)2),
26.57
(CH(CH3)2),
23.58(CH(CH3)2),
‒ +
23.16(CH(CH3)2). HR-MS (ESI): calcd for C48H58N2PdSb [M – ClO4 ] 887.2517;
found 887.2529. Calcd. for [(SIPr)Pd(Allyl)(SbPh3)]ClO4 (C48H58ClN2O4PdSb): C,
58.20; H, 5.90; N, 2.83%. Found: C, 58.47; H, 6.24; N, 3.19%.
4.3 General procedure for [(NHC)Pd(Allyl)(EPh3)]ClO4 (E =As or Sb) catalyzed
Sonogashira coupling reaction
A Schlenck tube containing a stirring bar was charged with aryl bromide (0.5 mmol),
terminal alkyne (0.6 mmol), [(NHC)Pd(Allyl)(EPh3)]ClO4 (0.005 mmol), Cs2CO3 (0.6
mmol) and DMF (2.0 mL) under air. The mixture was stirred at 100 oC for 6 h. After
completion of the reaction, the filtrate was concentrated and the residue was subjected
to purification via column chromatography to give the corresponding product.
4.5 X-Ray crystallography
Data collection was performed on a Bruker-AXS SMART CMOS area detector
diffractometer at 296 K using ω rotation scans with a scan width of 0.5° and Mo-Kα
radiation (λ = 0.71073 Å). Multi-scan corrections were applied using SADABS.[12]
Structure solutions and refinements were performed with the SHELX-2014 package.[13]
All non-hydrogen atoms were refined anisotropically by full-matrix least-squares on
F2. The hydrogen atoms to carbon were included in idealized geometric positions with
thermal parameters equivalent to 1.2 times those of carbon atoms. A summary of the
crystallographic data, data collection, and refinement parameters for complexes
3a–3h were provided in Table S1. CCDC 1880562–1880569 contain the
supplementary crystallographic data for this paper.
5. Acknowledgments
Financial support from the Scientific Research Project of Anhui Provincial Education

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Department (KJ2015TD002) is gratefully acknowledged.
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Highlights
•
Triphenylarsine and triphenylstibine-stabilized tri-heteroleptic NHC‒Pd‒allyl
complexes were synthesized.
• Molecular structures have been elucidated by X-ray single-crystal diffraction.
• The catalytic activities of the complexes were examined in Sonogashira coupling
reaction.