Trans-chloro-(1-naphthyl)bis[tris-(4-methoxyphenyl)phosphane]-nickel(II) catalyzed Suzuki-Miyaura coupling of aryl chlorides with phenylboronic acid

Article abstract of DOI:10.1016/j.catcom.2014.08.010

A readily accessible trans-chloro-(1-naphthyl)bis-[tris-(4-methoxyphenyl)phosphine]-nickel(II) [NiCl(MOTPP)₂(1-naphthyl)] complex was prepared and applied successfully to the Suzuki-Miyaura coupling of aryl chlorides with phenylboronic acid. The pre-catalyst readily forms the catalytically active Ni(0) species in situ under mild conditions without an additional reducing reagent. The electron-rich methoxy moieties on the phosphine ligand may increase the electron density of Ni and thus accelerates the reaction rate of oxidative addition. Single crystal X-ray diffraction revealed the NiCl and NiC bonds were lengthened in comparison with those in NiCl(PPh₃)₂(1-naphthyl), presumably owing to the stronger electron donating ability of MOTPP, which would facilitate the oxidative addition step.

Full text of DOI:10.1016/j.catcom.2014.08.010

Trans-Chloro (1-Naphthyl)bis[tris(4-methoxyphenyl)phosphane] nickel(II)
Catalyzed Suzuki-Miyaura Coupling of Aryl Chlorides with Phenylboronic
acid
Xueli Zheng, Qin Yang, Ziyao Li, Zhu Zhu, Xiaoyu Cui, Haiyan Fu,
Hua Chen, Ruixiang Li
PII:
DOI:
Reference:
S1566-7367(14)00314-8
doi: 10.1016/j.catcom.2014.08.010
CATCOM 4009
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
16 June 2014
25 July 2014
5 August 2014
Please cite this article as: Xueli Zheng, Qin Yang, Ziyao Li, Zhu Zhu, Xi-
aoyu Cui, Haiyan Fu, Hua Chen, Ruixiang Li, Trans-Chloro (1-Naphthyl)bis[tris(4-
methoxyphenyl)phosphane] nickel(II) Catalyzed Suzuki-Miyaura Coupling of Aryl
Chlorides with Phenylboronic acid, Catalysis Communications (2014),
0.1016/j.catcom.2014.08.010
doi:
1
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ACCEPTED MANUSCRIPT
Trans-Chloro (1-Naphthyl)bis[tris(4-methoxyphenyl)phosphane]
nickel(II) Catalyzed Suzuki-Miyaura Coupling of Aryl Chlorides
with Phenylboronic acid
Xueli Zheng, Qin Yang, Ziyao Li, Zhu Zhu, Xiaoyu Cui, Haiyan Fu, Hua Chen,
Ruixiang Li*
Key Laboratory of Green Chemistry and Technology of Ministry of Education,
College of Chemistry, Sichuan University, Chengdu 610064, Sichuan, China.
＊
Corresponding Author: Ruixiang Li
Key Laboratory of Green Chemistry and Technology of Ministry of Education, The
Institute of Homogeneous Catalysis, College of Chemistry, Sichuan University, No.29
Wangjiang Road, Chengdu 610064, Sichuan, China.
Tel: +86(28)85412904; Fax: +86(28)85412904;
E-mail: liruixiang@scu.edu.cn
Abstract
A
readily
trans-chloro-(1-naphthyl)bis-[tris-(4-methoxyphenyl)phosphine]-nickel(II)
NiCl(MOTPP) (1-naphthyl)] complex was prepared and applied successfully to the
accessible
[
2
Suzuki-Miyaura coupling of aryl chlorides with phenylboronic acid. The pre-catalyst
readily forms the catalytically active Ni(0) species in situ under mild conditions
without an additional reducing reagent. The electron-rich methoxy moieties on the
phosphine ligand may increase the electron density of Ni and thus accelerates the
reaction rate of oxidative addition. Single crystal X-ray diffraction revealed the Ni-Cl
and Ni-C bonds were lengthened in comparison with those in
NiCl(PPh ) (1-naphthyl), presumably owing to the stronger electron donating ability
3
2
of MOTPP, which would facilitate the oxidative addition step.
Keywords:
Suzuki-Miyaura
coupling;
aryl
chlorides;
nickel;
tris-(4-methoxyphenyl)phosphine
1

ACCEPTED MANUSCRIPT
1
. Introduction
Transition-metal-mediated Suzuki-Miyaura cross-coupling is an extremely efficient
strategy for the construction of biaryl compounds, which traditionally involves aryl
halides as electrophiles, arylboronic acids as nucleophiles, and a Pd catalyst [1-6].
Bearing relatively strong leaving groups, aryl bromides and iodides readily participate
in this cross-coupling. Aryl chlorides, however, are more challenging substrates due
to slow oxidative addition of the catalyst into the C-Cl bond [7, 8], thus
electron-deficient groups on the aryl chloride will benefit the coupling reaction [7].
The relatively low cost and availability of aryl chlorides adds great value to the
pursuit of new cost-effective catalyst systems that allow for their coupling to proceed
smoothly [3]. Nickel-catalyzed cross-coupling reactions have gained substantial
interest since Percec’s first report in 1995 [9-12]. Advantages of Ni over Pd catalysis
lie in the low cost and high reactivity toward aryl chlorides and the Ni atom being
smaller and more nucleophilic than Pd [10]. In the Ni-catalyzed Suzuki aryl-aryl
cross-coupling, the mechanism may follow a Ni(0)-Ni(II) catalytic cycle [11, 13, 14].
NiCl (PPh ) [3, 11, 15, 16], NiCl (PCy ) [12, 15], NiCl (dppf) [15, 17], NiCl (dppe)
2
3 2
2
3 2
2
2
[
15] and NiCl (dppp) [17] are generally regarded as appropriate Ni(II) sources due to
2
their availability and non-hygroscopicity. Ni(II) may be reduced in situ to the active
Ni(0) species, and either a reductant (such as Zn [9] or n-BuLi [16]) or elevated
reaction temperatures [18, 19] or an external ligand [15, 20] is favorable for the
coupling reaction. Recently, a Ni(COD) /PPh system was found to achieve
2
3
cross-coupling of aryl chlorides at room temperature [21], suggesting that
2

ACCEPTED MANUSCRIPT
commercially accessible Ni(COD) might be an alternative solution to the activation
2
of Ni(II) to Ni(0). However, this Ni(0) source is expensive and highly air-sensitive
[
16], and the presence of excess PPh is a necessity for the good yields (yield:
3
8
0-98%) [21]. Chen and Yang discovered that NiCl(PPh ) (1-naphthyl) combining
3 2
with excess of PPh (substrate/pre-catalyst/PPh : 1/0.05/0.1) was highly effective for
3
3
the Suzuki coupling of aryl chlorides under mild conditions (at 60 C in THF) [20].
These pioneering works prompted us to develop an easy-to-activate and
convenient-to-handle Ni pre-catalyst to carry out the Suzuki coupling of aryl chlorides,
including amino-substituted aryl chlorides, which are always regarded as challenging
substrates. It is well known that the improvements in Suzuki-Miyaura coupling
reactions greatly rely on increasing the reactivity and stability of the metal catalysts
by using efficient ligands. Our previous work demonstrated that MOTPP
(tris(4-methoxyphenyl)phosphine) was a good ligand for Ru-catalyzed direct arylation
of 2-phenylpyridine with aryl chlorides [22]. Being more electron-rich than PPh due
3
to the methoxy moieties, MOTPP is expected to increase the electron density of Ni
when employed as the ligand to prepare Ni(II) catalyst, and thus should probably
facilitate the oxidative addition. In this study, NiCl(MOTPP) (1-naphthyl) was
2
synthesized and applied to the Suzuki-Miyaura cross-coupling of aryl chlorides with
phenylboronic acid. Gratifyingly, this catalytic system appears to be highly effective
for various aryl chloride substrates, including those bearing N(CH ) or pyridyl
3
2
groups, in the absence of additional reducing reagents or external ligands.
2
. Experimental
3

ACCEPTED MANUSCRIPT
2
.1 Reagents
Toluene, DMA and dioxane were redistilled from Na/benzophenone prior to use.
Distilled water was degassed by nitrogen. NiCl(PPh ) (1-naphthyl) and
3
2
NiCl(MOTPP) (1-naphthyl) were synthesized according to the literature procedures
2
[
23-25] (see supplementary material).
.2 General Procedure for NiCl(MOTPP) (1-naphthyl) catalyzed cross-coupling
2
2
reaction
An oven-dried reaction tube was charged with Ni(MOTPP) (1-naphthyl)Cl (2
2
mol %, relative to aryl chloride), K PO (3 equiv., relative to aryl chloride),
3
4
phenylboronic acid (1.5 equiv., relative to aryl chloride). Solid aryl chlorides (0.5
mmol) were also added at this time. The tube was evacuated and purged with nitrogen
for three times. 1,4-Dioxane (2 mL) and degassed water (0.2 mL) were added via
syringe. Liquid aryl chlorides were also added via syringe with the solvents. The
mixture was stirred at 100 C for 1 h under a nitrogen atmosphere, and then was
cooled to room temperature. The reaction mixture was extracted with ethyl acetate,
and the organic layers were dried over anhydrous Na SO . The organic phase was
2
4
evaporated under reduced pressure, and the residue was purified by column
chromatography on silica gel with hexane/ethylacetate as the eluent to afford the
desired product. The products were identified by gas chromatograph and NMR
spectra.
2
.3 Characterization
Single crystal X-ray diffraction was conducted on an Oxford Xcalibur,
4

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Eos diffractometer. The crystal was kept at 143.00(10) K during data collection.
Elemental Analysis was conducted on Italy CARLO ERBA 1106.Gas chromatograph
analysis was performed on an Aglient GC 6890 N with an SE-30 column of 30 m ×
1
13
0
.32 mm × 0.25 μm. H and C NMR spectra were recorded on a BrukerAvanceII-400
MHz in CDCl with TMS as internal standard.
3
3
. Results and discussion
3
.1 Optimization of reaction conditions
NiCl(PPh ) (1-naphthyl) and NiCl(MOTPP) (1-naphthyl) were synthesized and
3
2
2
applied to catalyze the cross-coupling reaction. From the outset, the effects of the
solvent, base and temperature on the cross-coupling reaction were investigated using a
model reaction between 4-chlorobenzotrifluoride and phenylboronic acid.
1
,4-Dioxane was chosen as a candidate solvent since it is an aprotic solvent and
miscible with water. More importantly, it was shown to be a good solvent for other
Ni-catalyzed Suzuki-Miyaura coupling reactions [16]. As demonstrated in Table 1,
moderate yield was observed in 1,4-dioxane (70%, Entry 1). Interestingly, the yield
was dramatically increased to 97% when little amounts of H O was added (Entry 2,
2
Vdioxane/Vwater = 10/1). In an attempt to implement more environmentally friendly
coupling reactions [12], water alone was investigated as the solvent, but only a low
yield of 35% was obtained. From Entries 1-3 in Table 1, it can be seen that moisture
had no negative influence on the catalytic activity. Rather, the coupling reaction could
be accelerated by adding a small amount of H O, matching the general assumption
2
that the added water increased the solubility of the inorganic base K PO [20]. Other
3
4
5

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organic solvents (i.e., toluene or DMA) mixed with water were tested, but the results
were inferior to that observed for the dioxane-water mixture (Entries 4 and 5 vs 2,
Table 1), possibly due to their immiscibility with water. Subsequently, the influence of
the base was evaluated in dioxane/H O at 100 C. Apart from the strong base NaOH
2
and the weak base CH COONa (Entries 6 and 9), all other bases tested, including
3
K CO , NaHCO and K PO , gave good yields (Entries 7, 8 and 2). In particular, the
2
3
3
3
4
moderately basic K PO led to the best result (Entry 2), agreeing with previous reports
3
4
that the base can decrease the activation barrier for transmetalation by forming a
potassium aryl boronate salt with phenylboronic acid [26, 27]. A decrease in the
quantity of K PO resulted in a slight decrease in yield (Entries 10, 11 and 2). Based
3
4
on these results, K PO was chosen as the base in the following investigation.
3
4
NiCl(PPh ) (1-naphthyl) was also effective for the cross-couplings of aryl chlorides
3
2
with phenylboronic acid but slightly inferior to NiCl(MOTPP) (1-naphthyl) (Entries
2
1
2 vs 2, yield: 83% vs 97%). However, NiCl(PPh ) (1-naphthyl) combing with an
3 2
excess of PPh was ineffective for catalyzing the model cross-coupling reaction at
3
room temperature (Entry 13), which as previously reported by Chen [20]. Referring to
NiCl(MOTPP) (1-naphthyl), there was very little reactivity at either room temperature
2
or 50 C (Entries 14 and 15); the elevated temperature is one of the key factors
required for generating the catalytically active Ni(0) species in situ [16, 18, 19].
Fortunately, NiCl(MOTPP) (1-naphthyl) did afford an 85% yield of the biaryl when
2
the reaction was heated to 75 C (Entry 16). NiCl(PPh ) (1-naphthyl), in comparison,
3
2
only led to an yield of 22% under 75 C (Entry 17), which suggests that the
6

ACCEPTED MANUSCRIPT
NiCl(MOTPP) (1-naphthyl) catalytic system is capable of generating the catalytically
2
active Ni(0) species in situ at lower temperatures without the need of additional
reducing reagents or excess ligands [18, 19].
3
.2 Expand on different substrates
Under our established reaction conditions (NiCl(MOTPP) (1-naphthyl) as the
2
catalyst, S/C molar ratio 50:1, 10:1 dioxane/H O as the solvent and K PO as the
2
3
4
base), electron-rich or electron-deficient aryl chlorides coupled efficiently with
phenylboronic acid in comparable yields without the need of an additional reducing
reagent. For aryl chlorides bearing electron-withdrawing groups at the para-, meta- or
ortho- position, excellent yields (92-98%) could be obtained within 1 h as shown in
Table 2 (Entries 1-9), indicating that the steric hindrance of electron-deficient
substrate had less influence on this coupling reaction. The yields were comparable to
those achieved by using 4% (Ni(COD) /8% PPh ) [16] (room temperature, 30 h) or
2
3
(
NiCl(Ph PCH CH OH) (H O))Cl [28] (80 C, 4-12 h). Although longer reaction
2
2
2
2
2
times (around 20 h) were required, it is interesting to note that good yields (around
7
1
8-88%) were observed for aryl chlorides with electron-donating substituents (Entries
0-14), hinting that the catalyst has a good stability even in the absence of additional
ligands [15, 20]. Sterically hindered electron-rich aryl chlorides inhibited the reaction
more obviously than electron-deficient substrates (Entry 15 vs 13 vs 11, Entry 16 vs
1
4 vs 10), and only trace amount of coupling product was obtained for more bulky
substrate 2,6-dimethylchlorobenzene (Entry 16). Gratifyingly, pyridyl chloride and
amino-substituted aryl chlorides also successfully coupled with phenylboronic acid in
7

ACCEPTED MANUSCRIPT
this system (Table 2, Entries 7, 12). The Suzuki-Miyaura coupling between
amino-substituted aryl chlorides and phenylboronic acid is always regarded to be
tough given that the electron-rich NR group might coordinate with and deactivate the
2
metal (i.e., Ni) [29, 30]. To our delight, moderate yield (80%) was obtained for
4
-chloro-N,N-dimethylaniline (Entry 12). In addition, upon decreasing the catalyst
loading from 2 mol% to 1 mol% or further to 0.5 mol%, yields remained relatively
steady for electron-deficient aryl chlorides (Entries 3 vs 17 vs 19, yield: 97% vs 95%
vs 88%), but were greatly influenced with respect to the electron-rich aryl chlorides
(Entries 10 vs 18 vs 20, yield: 88% vs 70% vs 32%). A substrate substituted by
electron-withdrawing group might facilitate the oxidative addition of Ni into aryl
chloride [28], which presumably because the electron-drawing groups may help
polarize the C-Cl bond, in turn, electron-donating substituted aryl chloride is
unfavorable for the oxidative addition.
In contrast, with the presence of 0.5 mol% NiCl(PPh ) (1-naphthyl) under the
3
2
similar conditions with 0.5 mol% NiCl(MOTPP) (1-naphthyl), the yields were only
2
1
4
4% and 1.6% for the coupling between phenylboronic acid and
-chlorobenzotrifluoride (Entry 21) or 4-chlorotoluene (Entry 22), respectively, thus
demonstrating
the
superiority
of
NiCl(MOTPP) (1-naphthyl)
over
2
NiCl(PPh ) (1-naphthyl) in regards to catalytic efficiency. We also performed
3
2
NiCl(MOTPP) (1-naphthyl)
catalyzed
and various
Suzuki-Miyaura
arylboronic
coupling
acids,
between
such as
2
4
4
-chlorotrifluorotoluene
-methoxyphenylboronic acid, pyridine-3-boronic acid, 2,6-dimethylphenylboronic
8

ACCEPTED MANUSCRIPT
acid and thiophene-3-boronic acid (see Entries 23-26, Table 2). Unfortunately, except
the former two could give the isolated yield of 38% and 16%, respectively, nearly no
desired products were observed for the latter two.
3
.3 Proposed reason for the superiority of NiCl(MOTPP) (1-naphthyl)
2
In this study, NiCl(MOTPP) (1-naphthyl) (CI) showed much better performance
2
than NiCl(PPh ) (1-naphthyl) (CII). It is well known that increasing the electron
3
2
density of central metal can accelerate the oxidation addition [29]. MOTPP is more
electron-rich than PPh , the electron density of Ni in CI may be higher than that in
3
CII, hence, the oxidative addition of aryl chloride was expected to proceed more
smoothly on species A which was derived from CI than on the corresponding species
derived from CII (Scheme 1). In addition, the characteristic of more electron-rich
MOTPP may in turn influence the Ni-Cl or Ni-C (1-naphthyl) bonds in CI. So, we
expected to seek some supporting information from the structures of CI and CII.
Fortunately, the single crystal X-ray diffraction of CI and CII were obtained
successfully and the data evidenced that the average length of Ni-P bond in CI was
little shorter than that in CII (Figure 1), the Ni-Cl bond in CI is elongated to 2.2280 Å
compared to 2.2238 Å in CII, and accordingly, the Ni-C bond between the Ni atom
and naphthyl moiety is lengthened from 1.899 Å to 1.929 Å, which hint the more
electron-rich MOTPP might increase the electron density of Ni, weaken the Ni-Cl and
Ni-C bonds in CI and make them more prone to dissociate than those in CII.
Although the structure of nickel complex in solution will not be identical to the crystal
state, the information of the crystal structure still clearly revealed the influence from
9

ACCEPTED MANUSCRIPT
electronic effect of phosphine. Based on the above study, it is reasonable to infer that
CI is more likely to generate the catalytically active Ni(0) species (compound A,
Scheme 1), and then proceed into the requisite catalytic cycle (proposed in Scheme 1).
It is also reasonable to suggest that the coordination bonds between Ni and carbon
atoms in species B and C might be weaker due to the electron-rich phosphines
MOTPP (Scheme 1), and the reductive elimination was probably easier to occur with
the presence of CI than CII.
Conclusions
Satisfactory to excellent yields were achieved in NiCl(MOTPP) (1-naphthyl)
2
catalyzed Suzuki-Miyaura cross-coupling of aryl chlorides with phenylboronic acids,
under relatively mild conditions. This catalyst provides a convenient, relatively
efficient and less expensive alternative for the synthesis of biaryls. Owing to MOTPP
ligand, the Ni-Cl and Ni-C bonds in NiCl(MOTPP) (1-naphthyl) were weakened,
2
which play a vital role in improving the whole catalytic cross-coupling process.
Acknowledgements
The authors thank the National Natural Science Foundation of China (Project No.
J1310008, No. 21202104) for financial support of this work. We thank Prof. Jason J.
Chruma (Sichuan University) for his assistance with manuscript preparation.
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The list of Table, Figure, and Scheme captions
Table 1. The optimum of reaction conditions for NiCl(MOTPP) (1-naphthyl)
2
catalyzed Suzuki cross-coupling between 4-chlorobenzotrifluoride and phenylboronic
[
a]
acid.
[
a]
Table 2. Suzuki coupling of a variety of aryl chlorides with arylboronic acids.
Figure 1. ORTEP view of the molecular structure of the two complexes.
Scheme 1. Synthesis of NiCl(MOTPP) (1-naphthyl) and proposed mechanism for the
2
cross coupling of aryl chlorides with phenylboronic acid.
13

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Table 1. The optimum of reaction conditions for NiCl(MOTPP) (1-naphthyl)
2
catalyzed Suzuki cross-coupling between 4-chlorobenzotrifluoride and phenylboronic
[
a]
acid.
NiCl(MOTPP) (1-naphthyl)
2
Cl
CF3
+
B(OH)2
CF3
Base, Solvent
[
b]
Entry
Solvent
Base
Temp. (C) Time (h) Yield (%)
1
2
3
4
5
6
7
8
9
1,4-Dioxane
K PO4
100
100
100
100
100
100
100
100
100
100
100
100
25
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
70
97
3
1,4-Dioxane-H O
K PO4
3
2
H O
2
K PO4
3
35
Toluene-H O
K PO4
3
63
2
DMA- H O
K PO4
3
35
2
1,4-Dioxane-H O
NaOH
Trace
70
2
1,4-Dioxane-H O
K CO3
2
2
1,4-Dioxane-H O
NaHCO3
50
2
1,4-Dioxane-H O
CH COONa
Trace
2
3
[
c]
1
0
1
1,4-Dioxane-H O
K PO4
3
80
2
[
d]
1
1,4-Dioxane-H O
K PO4
3
88
83
2
[
e]
f]
1
1
1
1
1
1
2
3
4
5
6
7
1,4-Dioxane-H O
K PO4
3
2
[
1,4-Dioxane-H O
K PO4
3
NR
2
1,4-Dioxane-H O
K PO4
3
25
NR
NR
85
2
1,4-Dioxane-H O
K PO4
3
50
2
1,4-Dioxane-H O
K PO4
3
75
2
[
e]
1,4-Dioxane-H O
K PO4
3
75
22
2
[
a] Reaction conditions: 4-chlorobenzotrifluoride (0.5 mmol), phenylboronic acid
0.75 mmol), NiCl(MOTPP) (1-naphthyl) (0.01 mmol), K PO , NaOH, K CO ,
(
2
3
4
2
3
NaHCO and CH COONa (1.5 mmol), dioxane (2 mL), H O (0.2 mL). [b] Isolated
3
3
2
yields (average of two runs). [c] K PO (0.5 mmol).[d] K PO (1.0 mmol).[e] the
3
4
3
4
catalyst was NiCl(PPh ) (1-naphthyl) (0.01 mmol). [f] the catalyst was
3
2
NiCl(PPh ) (1-naphthyl)/PPh (0.01 mmol/0.025 mmol).
3
2
3
14

ACCEPTED MANUSCRIPT
[
a]
Table 2. Suzuki coupling of a variety of aryl chlorides with arylboronic acids.
Entry
aryl chloride
arylboronic acid
t
Product
Yield
(
h)
1
1
1
1
1
1
1
1
1
(%)
98
97
97
97
97
95
92
98
93
88
87
80
1
2
3
4
5
6
7
8
9
4-Chlorobenzaldehyde
4-Chlorobenzonitrile
4-Chlorotrifluorotoluene
4-Chloroacetophenone
3-Chlorotrifluorotoluene
3-Chloroacetophenone
3-Chloropyridine
phenylboronic acid
phenylboronic acid
phenylboronic acid
phenylboronic acid
phenylboronic acid
phenylboronic acid
phenylboronic acid
phenylboronic acid
phenylboronic acid
phenylboronic acid
phenylboronic acid
a
b
c
d
e
f
g
h
i
2-Chlorobenzonitrile
2-Fluorochlorobenzene
4-Chlorotoluene
10
1
20
20
20
j
1
4-Chloroanisole
k
l
1
2
4-Chloro-N,N-dimethylanil phenylboronic acid
ine
1
1
1
1
1
1
1
2
2
2
2
3
4
5
6
7
8
9
0
1
2
3
3-Chloroanisole
2-Chlorotoluene
2-Chloroanisole
phenylboronic acid
phenylboronic acid
phenylboronic acid
20
20
20
20
1
m
n
o
p
c
j
85
78
trace
trace
2,6-Dimethylchlorobenzene phenylboronic acid
[
b]
4-Chlorotrifluorotoluene
4-Chlorotoluene
phenylboronic acid
phenylboronic acid
phenylboronic acid
phenylboronic acid
phenylboronic acid
phenylboronic acid
95
70
88
32
[
b]
20
20
20
20
20
[
c]
c]
d]
4-Chlorotrifluorotoluene
4-Chlorotoluene
c
j
[
[
4-Chlorotrifluorotoluene
4-Chlorotoluene
c
j
14
[
d]
1.6
38
4-Chlorotrifluorotoluene
4-methoxyphenylbor 20
onic acid
q
2
2
2
4
5
6
4-Chlorotrifluorotoluene
4-Chlorotrifluorotoluene
4-Chlorotrifluorotoluene
pyridine-3-boronic
acid
20
r
s
t
16
2,6-dimethylphenylb 20
oronic acid
trace
trace
Thiophene-3-boroni 20
c acid
[
a] Reaction conditions: aryl chloride (0.5 mmol), arylboronic acid (0.75 mmol),
NiCl(MOTPP) (1-naphthyl) (0.01mmol), K PO (1.5 mmol), dioxane (2 mL), H O
2
3
4
2
15

ACCEPTED MANUSCRIPT
(0.2 mL), 100 C. [b] the catalyst was 1 mol%. [c] the catalyst was 0.5 mol%. [d] the
catalyst was 0.5 mol% NiCl(PPh ) (1-naphthyl).
3
2
(
CI): NiCl(MOTPP) (1-naphthyl), Ni1-Cl1: 2.2280(8) Å, Ni1-C1: 1.929(4) Å, Ni1-P1:
2
2
.2263(9) Å, Ni1-P2: 2.2114(9) Å
(
CII): NiCl(PPh ) (1-naphthyl), Ni1-Cl1: 2.2238(7) Å, Ni1-C37: 1.899(2) Å, Ni1-P1:
3 2
2
.2179(7) Å, Ni1-P2: 2.2236(7) Å
Figure 1. ORTEP view of the molecular structure of the two complexes.
16

ACCEPTED MANUSCRIPT
MOTPP
Ni Cl
Ar B(OH)2
K PO
MOTPP
3
4
Cl
MOTPP
Zn
Cl-B(OH)2
EtOH
MOTPP
Ni Ar
MOTPP
Ni(II)Cl2
Ar
Ni(0)(MOTPP)2
R
Ar' Ar
(A)
Cl Ar'
R
reductive
elimination
oxidative addition
MOTPP
MOTPP
R
Ar' Ni Ar
MOTPP
R
Ar' Ni Cl
(B)
(
C)
MOTPP
K PO
3
4
transmetalation
Cl B(OH)2
Ar B(OH)2
R = CF , F, CN, CHO, COCH , OCH , CH , N(CH )
3
3
3
3
3 2
Ar' = aryl, pyridyl
Scheme 1. Synthesis of NiCl(MOTPP) (1-naphthyl) and proposed mechanism for the
2
cross coupling of aryl chlorides with phenylboronic acid.
17

ACCEPTED MANUSCRIPT
NiCl(MOTPP) (1-naphthyl) could afford excellent yields (92-98%) within 1 h for the coupling of
2
aryl chlorides bearing electron-withdrawing groups. Around 78-88% yields were observed for aryl
chlorides with electron-donating or amino-substituents.
MOTPP
(1-2 mol%)
Ni Cl
MOTPP
Cl
+
B(OH)2
o
R
K PO , dioxane/H O (10/1), 100 C
R
3
4
2
R = 4-CHO, 4-CN, 4-CF , 4-COCH ,
3
3
yield: 92% to 98%
yield: 78% to 88%
3
-CF , 3-COCH , 2-CN, 2-F
3 3
R = 4-CH , 4-OCH , 4-N(CH ) , 3-OCH , 2-CH ,
3
3
3 2
3
3
NiCl(MOTPP) (1-naphthyl)
2
Graphical abstract
18

ACCEPTED MANUSCRIPT
Highlights




NiCl(MOTPP) (1-naphthyl) was prepared and applied successfully.
Excellent yields were achieved for the coupling of various aryl chlorides.
The impact of MOTPP was studied by single crystal X-ray diffraction.
2
The Ni-C and Ni-Cl bonds in NiCl(MOTPP) (1-naphthyl) were somewhat
2
lengthened.

MOTPP increased the electron density of Ni compared to TPP.
19