Pd-PEPPSI Complexes bearing bulky [(1,2-Di-(tert-butyl)acenaphthyl] (DtBu-An) on N-heterocarbene backbones: Highly efficient for suzuki-miyaura cross-coupling under aerobic conditions

Article abstract of DOI:10.1021/acs.organomet.6b00723

With the goal of achieving highly efficient palladium-catalyzed cross-coupling reactions under mild reaction conditions, the Pd-PEPPSI complexes C1 and C2 bearing 1,2-di(tert-butyl)acenaphthyl (DtBu-An) backbones were synthesized and characterized, and their use in Suzuki-Miyaura cross-coupling was investigated. The effects of catalyst structure and reaction conditions on the cross-coupling efficiency were evaluated in detail. The significant differences in catalytic activity compared with classical PEPPSI-IPr and PEPPSI-IPr^An precatalysts are discussed, where the axial sterics on the backbone play an important role. At low palladium loadings of 0.05-0.1 mol % and upon the addition of the relatively weak base K₃PO₄, the palladium complex C1 was found to be highly efficient for the coupling of (hetero)aryl chlorides with arylboronic acids under aerobic conditions, affording the corresponding biaryls in excellent yields.

Full text of DOI:10.1021/acs.organomet.6b00723

Article
pubs.acs.org/Organometallics
Pd-PEPPSI Complexes Bearing Bulky [(1,2-Di‑(tert-butyl)acenaphthyl]
(DtBu-An) on N‑Heterocarbene Backbones: Highly Efficient for
Suzuki−Miyaura Cross-Coupling under Aerobic Conditions
Xiao-Bing Lan,† Fu-Min Chen,† Bei-Bei Ma,† Dong-Sheng Shen,† and Feng-Shou Liu*,†,‡
†School of Chemistry and Chemical Engineering, Guangdong Pharmaceutical University, Zhongshan, Guangdong 528458, China
‡Guangdong Cosmetics Engineering & Technology Research Center, Zhongshan, Guangdong 528458, China
S
* Supporting Information
ABSTRACT: With the goal of achieving highly efficient palladium-
catalyzed cross-coupling reactions under mild reaction conditions, the Pd-
PEPPSI complexes C1 and C2 bearing 1,2-di(tert-butyl)acenaphthyl
(DtBu-An) backbones were synthesized and characterized, and their use
in Suzuki−Miyaura cross-coupling was investigated. The effects of catalyst
structure and reaction conditions on the cross-coupling efficiency were
evaluated in detail. The significant differences in catalytic activity
compared with classical PEPPSI-IPr and PEPPSI-IPrAn precatalysts are
discussed, where the axial sterics on the backbone play an important role.
At low palladium loadings of 0.05−0.1 mol % and upon the addition of
the relatively weak base K3PO4, the palladium complex C1 was found to
be highly efficient for the coupling of (hetero)aryl chlorides with
arylboronic acids under aerobic conditions, affording the corresponding biaryls in excellent yields.
Suzuki−Miyaura reaction.12 For example, the use of bulky
INTRODUCTION
■
palladium complexes such as Pd-PEPPSI-IPr,13 particularly in
Palladium-catalyzed cross-coupling reactions are now recog-
Pd-PEPPSI-IPent12a and Pd-PEPPSI-IPr*12e precatalysts
(Scheme 1), has resulted in significant improvements in
Negishi,3 and Suzuki4 for their considerable contributions to
Scheme 1. Bulky Pd-PEPPSI Precatalysts on Backbones and
the field. Among them, the Suzuki−Miyaura reaction, which
N-Aryl Moieties
nized as highly versatile tools for C−C bond formation.1 In
2010, the Nobel Prize in Chemistry was awarded to Heck,2
involves the cross-coupling of aryl halides with arylboronic
acids to construct the respective biaryl structure, has emerged
as one of the most valuable synthetic methodologies.1c,e,4,5
Since the isolation and structural characterization of the first
stable free N-heterocyclic carbenes (NHCs) by Arduengo in
1991,6 this class of ligands has been recognized as excellent
candidates for palladium-catalyzed cross-coupling reactions.7
NHCs behave as strong σ-electron donors and are less sensitive
to oxidation than alkyl phosphines, leading to greater stability
of the precatalysts and the catalytic species. As a result, even
sterically hindered substrates have been used as coupling
partners with readily available aryl chlorides following these
protocols due to the facile cleavage of the carbon−chlorine
bond upon employing NHC-Pd species.8,9
In view of their increasing popularity in scientific and
industrial applications, developing efficient precatalysts with
low palladium loadings remains a significant interest.10
Therefore, considerable effort has been focused on under-
standing the electronic as well as the steric properties of ligands
to guide catalyst design.11 For PEPPSI (Pyridine Enhanced
Precatalyst Preparation Stabilization and Initiation) palladium
complexes, it was found that increasing the steric bulk at the
Received: September 13, 2016
ortho-position of the N-aryl moiety on NHC can benefit the
© XXXX American Chemical Society
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catalytic performance.13 Relative to the extensively studied N-
aryl moiety, modification of the backbone derived from NHCs
has been of less focus and is, therefore, limited in the
literature.14 Nevertheless, this strategy has emerged as a
powerful tool because such modification would greatly enhance
the steric and electronic ability of the palladium center.15 Tu
revealed that the acenaphthyl-based Pd-PEPPSI-IPrAn precata-
lyst exhibited a much higher efficiency than the classical Pd-
PEPPSI-IPr precatalyst.15a,16 Under a moderate palladium
loading of 0.5 mol %, a variety of biaryls including tetra-
ortho-substituted biaryls can be conveniently synthesized.
Scheme 2. Synthetic Route of Pd-PEPPSI-IPrDtBu‑An
Complexes
Moreover, a new type of Pd-PEPPSI-IPr(NMe ) precatalyst
developed by Cesar and Lavigne, wherein NMe2 groups were
2
2
́
introduced on the skeleton, showed broad applicability and
efficiency toward aryl chlorides in C−N amination.15f,17 The
NHCs-Pd precatalysts were very stable under aerobic
conditions; however, their catalytic species Pd(0) was highly
air-sensitive,18 as a low level of dissolved oxygen in
commercially available anhydrous solvent would terminate the
reaction.11c Therefore, most of the NHCs-Pd catalyzed cross-
couplings were performed in an environment free of oxygen.
Moreover, in these catalytic systems, strong bases (such as
KOtBu, KOH, and NaOH) were indispensable when aryl
chlorides were used as substrates, casting limitation on the
functional group tolerance.19 In contrast, relatively weak bases
(such as K3PO4 and K2CO3) generally led to much lower
efficiency.20 Until now, only in rare instances could weaker
bases be successfully used in aerobic conditions.21 An exception
(DtBu-An)-based Pd-PEPPSI complexes in this study were
readily prepared from the one-pot reaction between imidazo-
lium salt and PdCl2 in pyridine or 3-chloropyridine. The
resulting palladium complexes were purified by silica-gel
chromatography in dichloromethane and isolated in satisfactory
yields of 73% and 61%, respectively. These two complexes are
is the reaction with Pd-PEPPSI-SIMesPhNO , which contained a
2
1
air- and moisture-stable and were characterized by H and 13C
nitrophenyl group on the backbone (Scheme 1), wherein the
catalytic activity was greatly increased.21d
NMR. The characteristic signals of Pd−Ccarbene were observed
at δ = 160.6 ppm for C1 and δ = 159.0 ppm for C2, consistent
with literature data for Pd-PEPPSI-IPrAn.16
Considering both academic and potential industrial applica-
tions, we have focused on the development of highly efficient
palladium catalysts that do not necessitate the use of air- and
moisture-free techniques.15o Taking into account that modify-
ing the backbone is a very useful strategy to elevate the catalytic
efficiency, we surmised that bulky substituted acenaphthyl
groups combined with sterically hindering N-aryl moieties can
protect the Pd(0) species effectively. Therefore, a great
improvement in the catalytic efficiency could be achieved.
Herein, we report the results of 1,2-di(tert-butyl)acenaphthyl
(DtBu-An)-based Pd-PEPPSI complexes for the Suzuki−
Miyaura reaction of aryl chlorides with arylboronic acids
using relatively weak bases under aerobic conditions.
Single crystals of these synthesized Pd-PEPPSI complexes
were obtained by slowly evaporating a concentrated solution of
dichloromethane and hexane (v/v = 1/2), and the structures
were unambiguously confirmed by X-ray diffraction analysis.
Figures 1 and 2 display the molecular structures of C1 and C2,
respectively. The palladium complexes are structurally similar,
in which palladium is coordinated by two chlorides in a trans
arrangement, an NHC ligand, and pyridine or 3-chloropyridine
as the ancillary ligand in a pseudo-square-planar geometry. The
bond lengths lie within the same range as those observed for
analogous Pd-PEPPSI complexes.11 For instance, the lengths of
the Pd−Ccarbene bonds are 1.981(7) Å (for C1) and 1.970(6) Å
(for C2), while those of the Pd−N bonds are 2.090(6) Å (for
C1) and 2.093(6) Å (for C2). Nevertheless, it is noteworthy
that the bulky 1,2-di-tert-butyl groups on the backbone lie
above and below the coordination plane, which retards N-aryl
rotation. Moreover, the N-aryl moiety on NHC is almost
perpendicular to the coordination plane, with dihedral angles of
87.60° and 80.00° in C1 and 86.96° and 82.53° in C2. It is
reasonable to assume that the steric bulk derived from both the
N-aryl group and the backbone provides axial protection for the
palladium center and is believed to stabilize the Pd(0) species
in the process of the catalytic reaction.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of α-Diimine Palla-
dium Complexes. As an access to bulky Pd-PEPPSI
complexes on the backbone, acenaphthyl α-diimine was first
synthesized via the acid-catalyzed condensation reaction
between acenaphthenequinone and 2,6-diisopropylaniline.15a
Then, 2 equiv of tert-butyllithium was added to a hexane
solution of acenaphthyl α-diimine, affording the bulky 1,2-
di(tert-butyl)acenaphthyl α-diimine, 2, in high yield (Scheme
2).22 The desired imidazolium salt of 3 was subsequently
obtained by the cyclization of 1,2-di(tert-butyl)acenaphthyl α-
diimine (2) with chloromethyl ethyl ether, giving a moderate
yield of 68%. The formation of the NCHN bond in the
imidazolium salt was confirmed by characteristic signals in the
1H NMR spectrum, in which the resonance of imidazolium C−
H protons appeared at δ = 11.71 ppm.
Suzuki−Miyaura Cross-Coupling Promoted by Palla-
dium Complexes. The catalytic performance of precatalysts
C1 and C2 in the Suzuki−Miyaura cross-coupling reaction was
then explored. Unless otherwise specified, the reaction was
performed under aerobic conditions, and the solvent did not
undergo any further purification. We began this study by
choosing to examine the coupling between 1-chloro-2-methyl-
Unlike the synthesis of Pd-PEPPSI-IPr(NMe ) , which requires
2
2
the use of strong bases such as butyllithium (nBuLi),15f the
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whereas other bases led to minor yields for this cross-coupling.
Considering that K3PO4 is readily available, relatively
inexpensive, and tolerant toward a variety of functional groups,
it was chosen for further study. We next screened the solvents,
and a significant acceleration effect was observed when ethanol
was used, while THF, MeOH, and iPrOH afforded moderate to
high yields (runs 13−15, Table 1). Unexpectedly, water,
dioxane, and toluene, which are frequently used with NHC-Pd
catalytic systems, were totally inactive (runs 10−12, Table 1).
On the basis of the optimized reaction conditions, C2 was
also tested in the cross-coupling reaction for comparison. In a
previous report, a chlorine atom at the 3-position of pyridine
further favors the dissociation of the Pd(0)−N bond and
thereby promotes the oxidation process in the Suzuki−Miyaura
reaction.13 However, in this study, an almost identical result of
98% was obtained with C2. In an effort to further understand
the effects of “throw away” ligand on the catalytic efficiency,
kinetic experiments were performed. As can be seen in Figure 3,
the cross-coupling reactions turned over immediately and were
complete within 40 min. A comparison of the rate of cross-
coupling reaction between C1 and C2 demonstrated that they
possess very similar catalytic activities, indicating minor
differences in performance of the “throw away” ligands in this
study. To additionally investigate the backbones on our NHC
ligand design, coupling reactions employing classical Pd-
PEPPSI-IPr and Pd-PEPPSI-IPrAn were also subjected under
the current reaction conditions (also seen in runs 18 and 19 in
Table 1). We found that significant, but much lower, yields of
84% and 91% were afforded for Pd-PEPPSI-IPr and Pd-
PEPPSI-IPrAn, respectively. Significantly, no induction period
was observed for these palladium complexes, and the reaction
rates were almost the same in the initial 20 min. These results
indicated that backbones derived from the NHCs do not play a
key role on their activation as well as activities. However, the
classical palladium complexes of Pd-PEPPSI-IPr and Pd-
PEPPSI-IPrAn stalled at approximately 25 and 30 min,
respectively, with no increased products when extending the
reaction time. In contrast, the catalyst lifetime of C1 and C2
was much longer than that of these classical palladium
complexes, therefore leading to a much higher catalytic
efficiency. On accounting the catalytic properties of these Pd-
PEPPSI complexes, the stability of the palladium(0) species
(catalyst lifetime) would become an important issue in the
cross-coupling when exposed to air.
Figure 1. Molecular structure of C1 depicted with 30% thermal
ellipsoids. Hydrogen atoms have been omitted for clarity. Selected
bond distances (Å) and angles (deg): Pd(1)−C(1) 1.981(7), Pd(1)−
N(3) 2.090(6), Pd(1)−Cl(1) 2.2977(18), Pd(1)−Cl(2) 2.2793(18),
N(3)−Pd(1)−C(1) 176.7(3), N(3)−Pd(1)−Cl(1) 90.4(2), C(1)−
Pd(1)−Cl(1) 88.97(19), N(3)−Pd(1)−Cl(2) 88.3(2), C(1)−Pd(1)−
Cl(2) 92.53(19), Cl(1)−Pd(1)−Cl(2) 177.45(7).
To shed further light onto the performance of these
palladium complexes, an extremely low palladium concen-
tration of 0.01 mol % was conducted. The cross-coupling
product was obtained in a satisfying yield of 72% and 74% for
C1 and C2, respectively (runs 20 and 21, Table 1). In contrast,
much lower yields of 43% and 56% were given by Pd-PEPPSI-
IPr and Pd-PEPPSI-IPrAn, respectively (runs 22 and 23, Table
1). At this stage, the kinetic experiment of the C1 and C2
demonstrated somewhat higher activities than that of Pd-
PEPPSI-IPr and Pd-PEPPSI-IPrAn. Nevertheless, on assuming
that the palladium(0) species would be easily deactivated at a
low palladium concentration in aerobic conditions, we cannot
conclude such comparison simply. Therefore, we conducted
some other control experiments. It was found that, in the
presence of 1 atm of oxygen and at a palladium loading of 0.05
mol %, the reactions were completely shut down and only
amount of ca. 20% biphenyl was obtained by these four Pd-
PEPPSI complexes. It can be inferred from these investigations
that the NHCs-Pd(0) would be captured by oxygen, forming
Figure 2. Molecular structure of C2 depicted with 30% thermal
ellipsoids. Hydrogen atoms have been omitted for clarity. Selected
bond distances (Å) and angles (deg): Pd(1)−C(1) 1.970(6), Pd(1)−
N(3) 2.093(6), Pd(1)−Cl(1) 2.3223(17), Pd(1)−Cl(2) 2.3054(18),
N(3)−Pd(1)−C(1) 178.9(3), N(3)−Pd(1)−Cl(1) 89.55(18), C(1)−
Pd(1)−Cl(1) 90.56(18), N(3)−Pd(1)−Cl(2) 87.72(18), C(1)−
Pd(1)−Cl(2) 92.21(18), Cl(1)−Pd(1)−Cl(2) 176.86(7).
benzene and phenylboronic acid as a model reaction in the
presence of 0.05 mol % C1. Initially, a variety of reaction
parameters, such as bases and solvents, were screened. As
illustrated in Table 1, among the bases screened, the use of
K3PO4 resulted in near completion, giving quantitative yield of
the product (run 2, Table 1). Other bases, such as K2CO3,
NaOH, KOH, and KOtBu, were inferior (runs 1, 7−9, Table 1),
C
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a
Table 1. Screening of the Palladium Precatalysts on Suzuki−Miyaura Cross-Coupling Reaction
b
run
Pd
loading (%)
base
solvent
EtOH
yield (%)
1
2
C1
C1
C1
C1
C1
C1
C1
C1
C1
C1
C1
C1
C1
C1
C1
C2
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.01
0.01
0.01
0.01
K2CO3
K3PO4
KOAc
93
c
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
H2O
100 (98)
NR
7
3
4
NaHCO3
Na2CO3
Cs2CO3
NaOH
KOH
5
16
6
8
7
89
8
98
9
KOtBu
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
88
10
11
12
13
14
15
16
17
18
19
20
21
22
23
NR
NR
NR
36
1,4-dioxane
toluene
THF
MeOH
iPrOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
86
91
98
PdCl2
NR
84
PEPPSI-IPr
PEPPSI-IPrAn
C1
91
72
C2
74
PEPPSI-IPr
PEPPSI-IPrAn
43
56
a
Reaction conditions: 1-chloro-2-methylbenzene (1.0 mmol), phenylboronic acid (1.2 mmol), base (1.5 mmol), solvent: 3 mL in aerobic
b
environment. The GC yield was determined by GC-FID using the (trifluoromethyl)benzene as internal standard. Two parallel reactions were
performed, and the yield was given in average. Isolated yields in parentheses.
c
same N-aryl moiety, the observed differences in catalytic activity
can be mostly ascribed to the steric hindrance on the backbones
for their protection on Pd(0) species. With only two hydrogen
atoms on the backbone, the decreased bulk of Pd-PEPPSI-IPr
led to a much less efficient reaction. Although Pd-PEPPSI-IPrAn
contains a large acenaphthyl backbone, it exists in a planar
geometry and thus has less of an effect on protecting the axial
site of the metal center. Consequently, the catalytic species
NHC-Pd(0) can be captured by oxygen molecules to form
NHC-Pd(O-O) complexes, ultimately resulting in catalyst
deactivation. In comparison, as seen in the solid structure
analysis in Figures 1 and 2, the 1,2-di-tert-butyl groups on Pd-
PEPPSI-IPrDtBu‑An provide steric hindrance to the axial positions
above and below the acenaphthyl on the backbone, which
retards CAr−N bond rotation and, therefore, protects the
catalytic species from exposure to air. It can be reasonable that
sterically encumbered substituents on the backbone would
extend the catalyst life and, therefore, improve the efficiency of
the cross-coupling reaction. In order to further clarify the bond
strength of NHCs-Pd(0) in our study, the poison experiments
were performed to determine the possibility of the palladium
nanoparticles involved as catalytic species. Upon the addition of
one drop of Hg(0) to the reaction mixture, the reaction was not
affected and nearly quantitative yield of the product was
observed (both for C1 and C2). Obviously, the result indicated
a homogeous nature involved in the reaction, and the bulky
NHCs ligand would strongly coordinate on the Pd(0). In
addition, the formation of the expected biphenyl byproducts,
which can be derived from the oxidative homocoupling of
Figure 3. Kinetic profiles for the Suzuki−Miyaura cross-coupling
reaction of 1-chloro-2-methylbenzene with phenylboronic acid
performing in Table 1.
the unreactive NHCs-Pd(O-O) peroxo complexes.18c,g,h More-
over, the cross-coupling reactions were also carried out at lower
temperature (25, 60, and 70 °C) in air. Beyond expectation,
neither the desired cross-coupling product nor biphenyl was
observed. Although the role of the reaction temperature is still
not fully understood, Cazin recently revealed that the oxygen
binding of peroxo complex IPr-Pd(O-O) is reversible, which
would revert back to IPr-Pd(0) at 80 °C (threshold
temperature) at a high vacuum.18f
With these viewpoints, the catalytic performances of the
PEPPSI palladium complexes in this study are discussed below.
Because C1, C2, Pd-PEPPSI-IPr, and Pd-PEPPSI-IPrAn bear the
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phenylboronic acid, was suppressed under the reaction
conditions (<1%). Thus, based on the screening conditions,
optimized reaction conditions were obtained at a palladium
loading of 0.05 mol %, K3PO4 as the base, and EtOH as the
solvent in an aerobic environment. Moreover, C1 was selected
as the palladium source for its easily accessible.
Table 3. Suzuki−Miyaura Cross-Coupling Reaction of Aryl
a
Chlorides with Arylboronic Acids
With the established optimized reaction conditions, the
scope of the aryl chloride substrates was then examined in the
cross-coupling reaction with phenylboronic acid. As shown in
Table 2, all of the reactions proceeded with excellent yield, and
Table 2. Suzuki−Miyaura Cross-Coupling Reaction of Aryl
a
Chlorides with Phenylboronic Acids
a
Reaction conditions: aryl chloride (1.0 mmol), arylboronic acid (1.2
mmol), K3PO4 (1.5 mmol); EtOH: 3 mL in aerobic environment, C1
b
(0.05 mol %). Isolated yields. Reaction conditions: C1 (0.1 mol %)
was performed.
functional groups was successful, giving the corresponding
products (5bb−5gc) in 91−99% yields. Moreover, challenging
cross-couplings involving sterically hindered 2,6-dimethyl-
phenyl chloride with several ortho-substituted arylboronic
acids were tested. Indeed, 2-MeO, 2-Me, and 2,4-dimethyl
phenylboronic acids are readily coupled, affording the tri-ortho-
substituted biaryls of 5db−5dd in very high yields of 98, 91,
and 93%, respectively. To further gauge the potential
application in functional molecule formation, the cross-coupling
of 2-nitrochlorobenzene and 4-chlorophenylboronic acids
proceeded at a satisfying yield of 88% (5if), providing a key
intermediate of boscalid, which is used in agricultural chemicals.
Furthermore, 2-chlorobenzonitrile and 4-methylphenylboronic
acids were also coupled to provide an important intermediate of
the Sartan family in 91% yield (5jg).
a
Reaction conditions: aryl chloride (1.0 mmol), phenylboronic acid
(1.2 mmol), K3PO4 (1.5 mmol); EtOH: 3 mL in aerobic environment,
C1 (0.05 mol %). Isolated yields. Reaction conditions: C1 (0.1 mol
%) was performed.
b
various functional groups, such as −MeO, −CN, −NO2,
−CH3CO, and −CHO, were tolerated under the standard
conditions. Meanwhile, neither electron-donating (5ba−5da,
Table 2) nor electron-withdrawing (5ea−5ja, Table 2) groups
on the aryl chloride affected the corresponding biaryls and gave
good to excellent yields. It is important to note that aryl
chlorides with ortho-substituents, such as 2-Me, 2-OMe, 2-CN,
2-NO2, 2-CHO, and even bulky 2,6-dimethyl, were also
compatible and furnished the product in good to excellent
yields. Encouraged by the excellent performance of the
palladium complexes, we set out to explore the synthesis of
heterobiaryls, which are commonly found in the structure of
pharmaceuticals, natural products, and functional materials.23
To our delight, heteroaromatic chlorides, such as 2-chloro-
pyridine, 3-chloropyridine, and 2-chlorothiophene, also reacted
efficiently to afford 5ka−5ma in high yields at a palladium
loading of 0.1 mol %.
CONCLUSION
■
In summary, we have developed well-defined and air-stable Pd-
PEPPSI-IPrDtBu‑An complexes for the Suzuki−Miyaura cross-
coupling reaction by incorporating bulky 1,2-di(tert-butyl)-
acenaphthene (DtBu-An) into the catalyst backbone. Com-
pared with the classical Pd-PEPPSI-IPr and Pd-PEPPSI-IPrAn
precatalysts, the introduction of steric bulk to the axial positions
on the skeleton provided significant enhancements in Pd-
catalyzed cross-coupling. Upon optimizing the reaction
conditions, Pd-PEPPSI-IPrDtBu‑An-(Py) (C1) was found to be
highly efficient in the presence of the relatively weak base
K3PO4, allowing the reaction to be performed under aerobic
conditions at low palladium loadings of 0.05−0.1 mol %.
Notably, substrates with electron-deficient, electron-rich, and
The remarkable activities encouraged us to extend the scope
further. We next examined the coupling with various
arylboronic acids. As shown in Table 3, the coupling of
arylboronic acid with 2-MeO, 2,4-dimethyl, 2-Me, and 4-MeO
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MHz, CDCl3) δ 11.71 (s, NCHN, 1H), 7.60 (m, Ar-H, 2H), 7.39 (m,
Ar-H, 4H), 7.16 (m, Ar-H, 1H), 7.11−7.05 (m, Ar-H, 1H), 6.60−6.35
(m, Ar-H, 1H), 6.03 (d, J = 5.6 Hz, Ar-H, 1H), 2.74−2.59 (m,
CH(CH3)2, 4H), 2.33 (s, CH, 2H), 1.34 (m, CH3, 9H), 1.25 (m, CH3,
3H), 1.19 (m, CH3, 3H), 1.16−1.10 (m, CH3, 9H), 0.94 (s, CH3, 3H),
0.77 (s, CH3, 6H), 0.76 (s, CH3, 6H), 0.68 (s, CH3, 3H). 13C NMR
(101 MHz, CDCl3) δ 147.2, 145.0, 143.5, 140.7, 139.6, 136.0, 134.1,
133.4, 133.0, 132.0, 131.1, 130.4, 129.2, 128.1, 124.9, 124.8, 124.7,
123.6, 122.3, 116.4, 115.9, 47.8, 45.9, 37.8, 36.2, 36.0, 35.0, 31.1, 29.6,
29.4, 29.3, 28.7, 27.7, 27.5, 27.3, 24.5, 23.5, 23.3, 22.7. Anal. Calcd for
C45H59ClN2, C, 81.47; H, 8.96; N, 4.22. Found: C, 81.39; H, 9.03; N,
4.18.
sterically bulky aryl and heteroaryl chlorides were compatible.
This study further illustrated the potential of this synthetic
strategy for pharmaceuticals, agrochemicals, and functional
materials.
EXPERIMENTAL SECTION
■
Physical Measurements and Materials. All aryl halides and
arylboronic acids were purchased from Aldrich Chemical. Palladium
chloride, chloromethyl ethyl ether, and tert-butyllithium (1.6 M,
hexane) were purchased from Aldrich Chemical. Pyridine, 3-
chloropyridine, and the solvents, were purchased from Guangzhou
Chemical Reagent Factory and were used as received. The
acenaphthenequinone, bases, and 2,6-diisopropylaniline were pur-
chased from Darui Chemical Reagent Factory. The α-diimine
compound of [2,6-(iPr)2-C6H3)-NC(An)C(An)N-(2,6-(iPr)2-
C6H3)] (1) was prepared according to the previous report.15a Pd-
PEPPSI-IPr and Pd-PEPPSI-IPrAn were synthesized according to
literature methods.12,15a
General Procedures for the Synthesis of Pd-PEPPSI
Compounds. A mixture of imidazolium salt (1 mmol), palladium
dichloride (0.177 g, 1 mmol), and K2CO3 (0.690 g, 10 mmol) in
pyridine or 3-chloropyridine (4 mL) was stirred at 80 °C for 24 h.
When having reached the determined time, the solution was cooled to
room temperature and 20 mL of dichloromethane was added, and
then the reaction mixture was added into a short silica-gel column
washing with substantial dichloromethane. Evaporation of the filtrate
provided the yellow/brown solid. The solid was then washed and
stirred with hexane (15 mL) for 1 h. The precipitate was isolated by
filtration. The yellow solid was slowly treated with dichloromethane
until it was dissolved completely; then, massive Et2O was added,
causing the formation of a white precipitate. The suspension was
filtered through a sintered funnel. Drying the solid in vaccuo produced
the desired palladium complexes as a yellowish powder.
The NMR data of compounds were obtained on a Varian Mercury-
Plus 400 MHz spectrometer at ambient temperature with the
decoupled nucleus, using CDCl3 as solvent and referenced versus
TMS as standard. Elemental analyses were determined with a Vario EL
Series Elemental Analyzer from Elementar. The X-ray diffraction data
of single crystals were obtained with the ω-2θ scan mode on a Bruker
SMART 1000 CCD diffractometer with graphite-monochromated Mo
Kα radiation (λ = 0.71073 Å) at 173 K for C1, C2. The structure was
solved using direct methods, and further refinement with full-matrix
least-squares on F2 was obtained with the SHELXTL program package.
All non-hydrogen atoms were refined anisotropically. Hydrogen atoms
were introduced in calculated positions with the displacement factors
of the host carbon atoms. CCDC 1501896 (C1) and 1501895 (C2)
contain the supplementary crystallographic data for this paper.
Synthesis of {[2,6-(iPr)2-C6H3)-NC(DtBu-An)C(DtBu-An)
N-(2,6-(iPr)2-C6H3)]} (2). According to a modified literature
procedure, [2,6-(iPr)2-C6H3)-NC(An)C(An)N-(2,6-(iPr)2-
C6H3)] (4 mmol) was diluted in hexane under a nitrogen atmosphere,
and tert-butyllithium (5 mL, 1.6 M) was added using a syringe at
ambient temperature. Then, the reaction was heated to 70 °C for 48 h.
When having reached the determined time, the addition of water
added to the dark purple solution resulted in the slow formation of a
clear red colored solution. The latter hexane solution was extracted by
means of a separatory funnel and dried over anhydrous magnesium
sulfate. Concentration of the hexane solution afforded a mixture of
products that was washed with hexane to remove impurities. The
crude product was then extracted into a dichloromethane solution and
recrystallized by slow vapor diffusion of hexane into the dichoro-
methane solution, which, in turn, resulted in the formation of a crop of
red crystals (1.572 g, 64%). 1H NMR (400 MHz, CDCl3) δ 7.19 (d, J
= 11.4 Hz, Ar-H, 5H), 7.15−7.09 (m, Ar-H, 1H), 7.03 (d, J = 7.4 Hz,
Ar-H, 1H), 6.85 (m, Ar-H, 1H), 6.17 (d, J = 7.7 Hz, Ar-H, 1H), 5.35
(d, J = 5.2 Hz, Ar-H, 1H), 3.20−2.85 (m, CH(CH3)2, 4H), 2.59 (s,
CH, 1H), 2.27 (d, J = 5.5 Hz, CH, 1H), 1.27 (d, J = 6.6 Hz, CH3, 3H),
1.20 (m, CH3, 9H), 1.17−1.13 (m, CH3, 6H), 0.95 (d, J = 6.6 Hz,
CH3, 6H), 0.75 (s, CH3, 9H), 0.64 (s, CH3, 9H). 13C NMR (101
MHz, CDCl3) δ 161.8, 159.4, 147.9, 147.6, 141.0, 135.6, 135.4, 135.3,
134.5, 133.7, 133.0, 132.0, 129.0, 127.5, 123.9, 123.7, 123.4, 123.3,
123.0, 122.9, 46.3, 45.6, 36.9, 35.7, 28.8, 28.6, 28.4, 28.2, 27.6, 27.1,
23.5, 23.4, 23.4, 23.3, 23.1, 23.0, 22.6, 22.5. Anal. Calcd for
C44H58Cl2N2, C, 85.94; H, 9.51; N, 4.56. Found: C, 85.91; H, 9.57;
N, 4.50.
Pd-PEPPSI-IPr(DtBu‑An)-Py (C1). C1 was obtained as a yellowish
1
powder (0.645 g, 73%). H NMR (400 MHz, CDCl3) δ 8.61 (d, J =
5.5 Hz, Ar-H, 2H), 7.66−7.51 (m, Ar-H, 3H), 7.47 (d, J = 7.7 Hz, Ar-
H, 1H), 7.43 (d, J = 7.7 Hz, Ar-H, 2H), 7.35 (m, Ar-H, 1H), 7.11 (m,
Ar-H, 2H), 6.94−6.72 (m, Ar-H, 2H), 6.11 (d, J = 7.1 Hz, Ar-H, 1H),
5.61 (d, J = 5.4 Hz, Ar-H, 1H), 3.86−3.59 (m, CH(CH3)2, 2H), 3.30
(m, 6.6 Hz, CH(CH3)2, 1H), 2.93 (m, CH(CH3)2, 1H), 2.67 (s, CH,
1H), 2.56 (d, J = 5.5 Hz, CH, 1H), 1.53 (d, J = 6.4 Hz, CH3, 6H), 1.43
(m, CH3, 6H), 1.13 (d, J = 6.7 Hz, CH3, 3H), 1.07 (d, J = 6.8 Hz, CH3,
3H), 0.98 (d, J = 6.7 Hz, CH3, 3H), 0.94 (s, CH3, 3H), 0.77 (s, CH3,
9H), 0.69 (s, CH3, 9H). 13C NMR (101 MHz, CDCl3) δ 160.6, 151.5,
147.4, 147.2, 147.1, 146.8, 143.9, 137.3, 135.9, 135.0, 134.0, 133.8,
133.3, 130.3, 129.3, 128.4, 126.5, 125.6, 125.0, 124.9, 124.4, 124.1,
123.9, 115.9, 47.5, 45.8, 37.7, 35.7, 29.8, 29.0, 28.8, 28.7, 28.6, 28.1,
27.1, 26.1, 26.0, 25.4, 25.1, 24.8, 24.3, 23.4. Anal. Calcd for
C50H63Cl2N3Pd, C, 67.98; H, 7.19; N, 4.76. Found: C, 67.76; H,
7.23; N, 4.72.
Pd-PEPPSI-IPr(DtBu‑An)-3ClPy (C2). C2 was obtained as a yellowish
1
powder (0.560, 61%). H NMR (400 MHz, CDCl3) δ 8.66 (s, Ar-H,
1H), 8.57 (m, Ar-H, 1H), 7.57 (m, Ar-H, 3H), 7.46 (m, Ar-H, 3H),
7.38 (d, J = 7.7 Hz, Ar-H, 1H), 7.10−7.04 (m, Ar-H, 1H), 6.94−6.83
(m, Ar-H, 2H), 6.12 (d, J = 7.1 Hz, Ar-H, 1H), 5.62 (d, J = 5.5 Hz, Ar-
H, 1H), 3.78−3.55 (m, CH(CH3)2, 2H), 3.30 (m, CH(CH3)2, 1H),
2.92 (m, CH(CH3)2, 1H), 2.68 (s, CH, 1H), 2.56 (m, CH, 1H), 1.53
(d, J = 6.4 Hz, CH3, 3H), 1.43 (d, J = 5.4 Hz, CH3, 9H), 1.13 (d, J =
6.5 Hz, CH3, 3H), 1.07 (d, J = 6.6 Hz, CH3, 3H), 0.99 (d, J = 6.3 Hz,
CH3, 3H), 0.79 (d, J = 8.6 Hz, CH3, 12H), 0.70 (s, CH3, 9H). 13C
NMR (101 MHz, CDCl3) δ 159.0, 151.2, 150.5, 149.5, 147.4, 147.2,
147.1, 146.8, 144.0, 137.4, 136.0, 135.0, 133.9, 133.7, 133.3, 131.8,
130.5, 130.4, 129.4, 128.4, 126.6, 125.6, 124.9, 124.5, 124.2, 116.0,
47.6, 45.8, 37.6, 35.7, 29.0, 28.8, 28.7, 28.6, 28.1, 27.1, 26.1, 26.0, 25.4,
25.1, 24.7, 24.4, 24.3, 23.4. Anal. Calcd for C50H62Cl3N3Pd, C, 65.43;
H, 6.81; N, 4.58. Found: C, 65.12; H, 6.73; N, 4.47.
General Procedure for the Suzuki−Miyaura Reaction. Unless
otherwise noted, the Suzuki−Miyaura reaction was carried out under
aerobic conditions. All solvents were used as received, and no further
purification was needed. A parallel reactor containing a stir bar was
charged with Pd-PEPPSI complexes (0.05% mmol), aryl halides (1.0
mmol), boronic acid (1.2 mmol), base (1.5 mmol), and 3 mL of
solvent. The reaction mixture was carried out at 80 °C for 4 h. After
completion of the reaction, the reaction mixture was cooled to ambient
temperature and 20 mL of water was added. The mixture was diluted
with dichloromethane (5 mL), followed by extraction three times (3 ×
Synthesis of Imidazolium Salts IPr(DtBu‑An)·HCl (3). α-Diimine
compound of 2 (1 mmol) and chloromethyl ethyl ether (6 mL) were
combined under a nitrogen atmosphere at room temperature, and then
the reaction was heated to 100 °C for 24 h. When having reached the
determined time, the solution was cooled to room temperature, and
the reaction mixture was treated with Et2O and stirred for 1 h, causing
the formation of a great deal of precipitate. The solid was isolated by
filtration and wash with Et2O three times. The resulting crude was
1
obtained as a yellowish white powder (0.451g, 68%). H NMR (400
F
DOI: 10.1021/acs.organomet.6b00723
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
5 mL) with dichloromethane. The organic layer was dried with
anhydrous magnesium sulfate, filtered, and evaporated under reduced
pressure. The crude cross-coupling products were purified by silica-gel
column chromatography using petroleum ether−dichloromethane
(20/1) as eluent, and the isolated yield was then calculated based
on the feeding of the aryl halides. The isolated cross-coupling products
were characterized by 1H NMR and 13C NMR, and the spectra can be
found in the Supporting Information.
General Information for NMR Data. The NMR data of
compounds were obtained on a Varian Mercury-Plus 400 MHz
spectrometer at ambient temperature, using CDCl3 as solvent and
referenced versus TMS as standard. Chemical shifts are reported in
ppm, and coupling constants are reported in Hz.
7.11 (m, Ar-H, 1H). 13C NMR (101 MHz, CDCl3) δ 144.4, 134.4,
128.9, 128.0, 127.4, 126.0, 124.8, 123.1.
2,2′-Dimethoxy-1,1′-biphenyl (5bb).24d 1H NMR (400 MHz,
CDCl3) δ 7.32 (m, Ar-H, 2H), 7.23 (m, Ar-H, 2H), 7.07−6.89 (m,
Ar-H, 4H), 3.76 (s, Ar-OCH3, 6H). 13C NMR (101 MHz, CDCl3) δ
157.1, 131.4, 128.6, 127.9, 120.3, 111.1, 55.7.
2′-Methoxy-2,4-dimethyl-1,1′-biphenyl (5bc).24e 1H NMR (400
MHz, CDCl3) δ 7.37 (m, Ar-H, 1H), 7.19 (d, J = 7.3 Hz, Ar-H, 1H),
7.13 (s, Ar-H, 2H), 7.11−6.98 (m, Ar-H, 3H), 3.80 (s, Ar-OCH3, 3H),
2.41 (s, CH3, 3H), 2.16 (s, CH3, 3H). 13C NMR (101 MHz, CDCl3) δ
156.7, 136.8, 136.6, 135.7, 131.1, 130.8, 130.4, 129.9, 128.4, 126.2,
120.4, 110.6, 55.3, 21.1, 19.8.
1-(2-Methoxyphenyl)naphthalene (5cb).19a 1H NMR (400 MHz,
CDCl3) δ 7.89 (m, Ar-H, 2H), 7.60 (d, J = 6.1 Hz, Ar-H, 1H), 7.54
(m, Ar-H, 1H), 7.42 (m, Ar-H, 4H), 7.30 (d, J = 5.3 Hz, Ar-H, 1H),
7.08 (m, Ar-H, 2H), 3.71 (s, Ar-OCH3, 3H). 13C NMR (101 MHz,
CDCl3) δ 157.2, 137.0, 133.5, 132.1, 131.9, 129.5, 129.0, 128.1, 127.6,
127.3, 126.4, 125.6, 125.5, 125.3, 120.5, 111.0, 55.5.
2-Methyl-1,1′-biphenyl (5aa).9j 1H NMR (400 MHz, CDCl3) δ
7.45 (m, Ar-H, 2H), 7.37 (m, Ar-H, 3H), 7.32−7.24 (m, Ar-H, 4H),
2.31 (s, CH3, 3H). 13C NMR (101 MHz, CDCl3) δ 141.9, 135.3,
130.3, 129.8, 129.2, 128.0, 127.2, 126.7, 125.7, 125.5, 20.5.
2-Methoxy-1,1′-biphenyl (5ba).19a 1H NMR (400 MHz, CDCl3) δ
7.61 (s, Ar-H, 2H), 7.48 (d, J = 5.2 Hz, Ar-H, 2H), 7.43−7.33 (m, Ar-
H, 3H), 7.14−6.98 (m, Ar-H, 2H), 3.86 (s, Ar-OCH3, 3H). 13C NMR
(101 MHz, CDCl3) δ 156.4, 138.5, 130.8, 130.6, 129.5, 128.6, 127.9,
126.9, 120.8, 111.1, 55.5.
1-(2,4-Dimethylphenyl)naphthalene (5cc).24f 1H NMR (400
MHz, CDCl3) δ 7.94 (m, Ar-H, 2H), 7.63−7.50 (m, Ar-H, 3H),
7.48−7.34 (m, Ar-H, 2H), 7.21 (m, Ar-H, 3H), 2.50 (s, CH3, 3H),
2.08 (s, CH3, 3H). 13C NMR (101 MHz, CDCl3) δ 139.8, 137.3,
137.1, 136.6, 133.5, 132.1, 130.6, 130.3, 128.1, 127.3, 126.7, 126.2,
126.1, 125.9, 125.6, 125.4, 21.2, 20.0.
1-Phenylnaphthalene (5ca).19a 1H NMR (400 MHz, CDCl3) δ
7.97−7.83 (m, Ar-H, 3H), 7.60−7.48 (m, Ar-H, 6H), 7.47−7.40 (m,
Ar-H, 3H). 13C NMR (101 MHz, CDCl3) δ 140.7, 140.2, 133.7, 131.6,
130.0, 128.2, 127.6, 127.2, 126.9, 126.0, 125.7, 125.4.
1-(o-Tolyl)naphthalene (5cd).21d 1H NMR (400 MHz, CDCl3) δ
7.93 (m, Ar-H, 2H), 7.67−7.48 (m, Ar-H, 3H), 7.46−7.22 (m, Ar-H,
6H), 2.08 (s, CH3, 3H). 13C NMR (101 MHz, CDCl3) δ 140.2, 139.7,
136.8, 133.5, 132.0, 130.3, 129.8, 128.2, 127.5, 127.4, 126.6, 126.1,
125.9, 125.7, 125.5, 125.3, 20.0.
2,6-Dimethyl-1,1′-biphenyl (5da).9q 1H NMR (400 MHz, CDCl3)
δ 7.47 (m, Ar-H, 2H), 7.38 (m, Ar-H, 1H), 7.23−7.18 (m, Ar-H, 3H),
7.16 (d, J = 7.0 Hz, Ar-H, 2H), 2.09 (s, CH3, 6H). 13C NMR (101
MHz, CDCl3) δ 141.9, 141.1, 136.0, 129.0, 128.4, 127.3, 127.0, 126.6,
20.8.
1-(4-Methoxyphenyl)naphthalene (5ce).21d 1H NMR (400 MHz,
CDCl3) δ 7.95 (m, Ar-H, 2H), 7.87 (d, J = 7.9 Hz, Ar-H, 1H), 7.61−
7.40 (m, Ar-H, 6H), 7.12−7.03 (m, Ar-H, 2H), 3.92 (s, Ar-OCH3,
3H). 13C NMR (101 MHz, CDCl3) δ 158.9, 139.9, 133.8, 133.1, 131.8,
131.1, 128.2, 127.3, 126.9, 126.0, 125.9, 125.7, 125.4, 113.7, 55.3.
2′-Methoxy-2,6-dimethyl-1,1′-biphenyl (5db).9o 1H NMR (400
MHz, CDCl3) δ 7.41−7.32 (m, Ar-H, 1H), 7.20 (m, Ar-H, 1H), 7.14
(d, J = 7.4 Hz, Ar-H, 2H), 7.09−6.99 (m, Ar-H, 3H), 3.76 (s, Ar-
OCH3, 3H), 2.05 (s, CH3, 6H). 13C NMR (101 MHz, CDCl3) δ
156.6, 138.2, 136.6, 130.7, 129.6, 128.4, 127.0, 127.0, 120.7, 110.9,
55.4, 20.4.
4-Nitro-1,1′-biphenyl (5ea).20b 1H NMR (400 MHz, CDCl3) δ
8.29 (d, J = 8.9 Hz, Ar-H, 2H), 7.74 (d, J = 8.9 Hz, Ar-H, 2H), 7.63 (d,
J = 6.9 Hz, Ar-H, 2H), 7.49 (m, Ar-H, 3H). 13C NMR (101 MHz,
CDCl3) δ 147.6, 147.1, 138.7, 129.1, 128.9, 127.7, 127.3, 124.0.
[1,1′-Biphenyl]-4-carbonitrile (5fa).9o 1H NMR (400 MHz,
CDCl3) δ 7.70 (m, Ar-H, 4H), 7.59 (d, J = 7.3 Hz, Ar-H, 2H), 7.45
(m, Ar-H, 3H).13C NMR (101 MHz, CDCl3) δ 145.6, 139.1, 132.5,
129.0, 128.6, 127.6, 127.1, 118.8, 110.9.
1-([1,1′-Biphenyl]-4-yl)ethanone (5ga).9j 1H NMR (400 MHz,
CDCl3) δ 8.04 (d, J = 8.5 Hz, Ar-H, 2H), 7.69 (d, J = 8.5 Hz, Ar-H,
2H), 7.63 (d, J = 7.3 Hz, Ar-H, 2H), 7.48 (m, Ar-H, 2H), 7.41 (m, Ar-
H, 1H), 2.64 (s, CH3, 3H). 13C NMR (101 MHz, CDCl3) δ 197.7,
145.8, 139.9, 135.9, 135.6, 128.9, 128.2, 127.9, 127.2, 26.6.
[1,1′-Biphenyl]-2-carbaldehyde (5ha).24a 1H NMR (400 MHz,
CDCl3) δ 9.99 (s, CHO, 1H), 8.04 (m, Ar-H, 1H), 7.64 (m, Ar-H,
1H), 7.54−7.43 (m, Ar-H, 5H), 7.41−7.37 (m, Ar-H, 2H). 13C NMR
(101 MHz, CDCl3) δ 192.4, 146.0, 137.8, 133.7, 133.5, 130.7, 130.1,
128.5, 128.4, 128.1, 127.8, 127.6.
2,2′,4,6′-Tetramethyl-1,1′-biphenyl (5dc).24g 1H NMR (400 MHz,
CDCl3) δ 7.21−7.07 (m, Ar-H, 5H), 6.93 (d, J = 7.6 Hz, Ar-H, 1H),
2.40 (s, CH3, 3H), 1.98 (s, CH3, 6H), 1.96 (s, CH3, 3H). 13C NMR
(101 MHz, CDCl3) δ 141.1, 137.4, 136.4, 136.1, 135.3, 131.5, 130.7,
128.7, 127.1, 126.8, 21.1, 20.3, 19.3.
2,2′,6-Trimethyl-1,1′-biphenyl (5dd).9q 1H NMR (400 MHz,
CDCl3) δ 7.25 (m, Ar-H, 3H), 7.16 (m, Ar-H, 1H), 7.10 (d, J = 7.3
Hz, Ar-H, 2H), 7.04−6.97 (m, Ar-H, 1H), 1.96 (s, CH3, 3H), 1.94 (s,
CH3, 6H). 13C NMR (101 MHz, CDCl3) δ 141.1, 140.6, 135.9, 135.6,
130.0, 128.9, 127.2, 127.0, 126.9, 126.0, 20.3, 19.3.
2-Nitro-1,1′-biphenyl (5ia).24b 1H NMR (400 MHz, CDCl3) δ 7.86
(m, Ar-H, 1H), 7.62 (m, Ar-H, 1H), 7.52−7.40 (m, Ar-H, 5H), 7.33
(m, Ar-H, 2H). 13C NMR (101 MHz, CDCl3) δ 149.3, 137.4, 136.3,
132.2, 131.9, 128.6, 128.2, 128.1, 127.9, 124.0.
2,4-Dimethyl-4′-nitro-1,1′-biphenyl (5ec).24h 1H NMR (400 MHz,
CDCl3) δ 8.27 (d, J = 8.8 Hz, Ar-H, 2H), 7.48 (d, J = 8.8 Hz, Ar-H,
2H), 7.20−7.02 (m, Ar-H, 3H), 2.39 (s, CH3, 3H), 2.26 (s, CH3, 3H).
13C NMR (101 MHz, CDCl3) δ 148.9, 138.3, 137.4, 136.8, 134.8,
131.5, 130.1, 129.4, 126.8, 123.3, 21.0, 20.2.
[1,1′-Biphenyl]-2-carbonitrile (5ja).24c 1H NMR (400 MHz,
CDCl3) δ 7.77 (m, Ar-H, 1H), 7.65 (m, Ar-H, 1H), 7.60−7.55 (m,
Ar-H, 2H), 7.54−7.50 (m, Ar-H, 2H), 7.49−7.42 (m, Ar-H, 3H). 13C
NMR (101 MHz, CDCl3) δ 145.5, 138.1, 133.7, 132.7, 130.0, 128.7,
128.7, 127.5, 118.6, 111.3.
2′,4′-Dimethyl-[1,1′-biphenyl]-4-carbonitrile (5fc).24i 1H NMR
(400 MHz, CDCl3) δ 7.69 (d, J = 8.4 Hz, Ar-H, 2H), 7.43 (d, J =
8.4 Hz, Ar-H, 2H), 7.11 (d, J = 12.4 Hz, Ar-H, 3H), 2.38 (s, CH3, 3H),
2.24 (s, CH3, 3H). 13C NMR (101 MHz, CDCl3) δ 146.82 (s), 138.1,
137.2, 134.8, 131.9, 131.4, 130.0, 129.3, 126.8, 118.9, 110.5, 21.0, 20.2.
1-(2′,4′-Dimethyl-[1,1′-biphenyl]-4-yl)ethanone (5gc).24j 1H
NMR (400 MHz, CDCl3) δ 8.01 (d, J = 8.2 Hz, Ar-H, 2H), 7.43
(d, J = 8.2 Hz, Ar-H, 2H), 7.11 (m, Ar-H, 3H), 2.65 (s, CH3, 3H), 2.39
(s, CH3, 3H), 2.26 (s, CH3, 3H). 13C NMR (101 MHz, CDCl3) δ
197.8, 147.0, 146.2, 142.3, 137.6, 134.9, 131.3, 129.5, 128.2, 126.6,
126.0, 26.5, 21.0, 20.3.
2-Phenylpyridine (5ka).9j 1H NMR (400 MHz, CDCl3) δ 8.70 (d, J
= 4.7 Hz, Ar-H, 1H), 8.11−7.92 (m, Ar-H, 2H), 7.79−7.66 (m, Ar-H,
2H), 7.48 (m, Ar-H, 2H), 7.45−7.39 (m, Ar-H, 1H), 7.24−7.19 (m,
Ar-H, 1H). 13C NMR (101 MHz, CDCl3) δ 157.4, 149.6, 139.4, 136.7,
128.9, 128.7, 126.9, 122.0, 120.5.
3-Phenylpyridine (5la).9q 1H NMR (400 MHz, CDCl3) δ 8.85 (s,
Ar-H, 1H), 8.59 (d, J = 4.5 Hz, Ar-H, 1H), 7.88 (m, Ar-H, 1H), 7.59
(d, J = 7.5 Hz, Ar-H, 2H), 7.48 (m, Ar-H, 2H), 7.43−7.34 (m, Ar-H,
2H). 13C NMR (101 MHz, CDCl3) δ 148.4, 148.3, 137.8, 136.7, 134.4,
129.1, 128.1, 127.1, 123.5.
4′-Chloro-2-nitro-1,1′-biphenyl (5if).24k 1H NMR (400 MHz,
CDCl3) δ 7.88 (d, J = 8.1 Hz, Ar-H, 1H), 7.62 (m, Ar-H, 2H),
7.58−7.47 (m, Ar-H, 2H), 7.40 (d, J = 8.8 Hz, Ar-H, 3H). 13C NMR
2-Phenylthiophene (5ma).21d 1H NMR (400 MHz, CDCl3) δ 7.65
(d, J = 7.2 Hz, Ar-H, 2H), 7.40 (m, Ar-H, 2H), 7.32 (m, Ar-H, 3H),
G
DOI: 10.1021/acs.organomet.6b00723
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(101 MHz, CDCl3) δ 149.1, 139.9, 138.8, 136.7, 132.4, 131.8, 129.3,
129.0, 128.9, 124.2.
teaching demonstration center of chemistry & chemical
engineering.
4′-Methyl-[1,1′-biphenyl]-2-carbonitrile (5jg).24k 1H NMR (400
MHz, CDCl3) δ 7.75 (m, Ar-H, 1H), 7.63 (m, Ar-H, 1H), 7.51 (m, Ar-
H, 1H), 7.47 (d, J = 8.1 Hz, Ar-H, 2H), 7.42 (m, Ar-H, 1H), 7.31 (d, J
= 7.9 Hz, Ar-H, 2H), 2.43 (s, CH3, 3H). 13C NMR (101 MHz,
CDCl3) δ 145.5, 138.6, 135.3, 133.7, 132.7, 129.9, 129.4, 128.6, 127.2,
118.8, 111.2, 21.2.
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ASSOCIATED CONTENT
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S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00723.
Details of NMR spectra of all α-diimines, N-hetero-
carbene salts, Pd-PEPPSI complexes, and cross-coupling
products (PDF)
Crystallographic data (CIF)
Organometallics 2015, 34, 381−394. (n) Garrido, R.; Hernan
́
dez-
́
Montes, P. S.; Gordillo, A.; Gom
́
ez-Sal, P.; Lop
́
ez-Mardomingo, C.; de
AUTHOR INFORMATION
Jesus, E. Organometallics 2015, 34, 1855−1863. (o) Serrano, J. L.;
́
■
́ ́
Perez, J.; García, L.; Sanchez, G.; García, J.; Lozano, P.; Zende, V.;
Corresponding Author
*E-mail: fengshou2004@126.com.
Kapdi, A. Organometallics 2015, 34, 522−533. (p) Steeples, E.; Kelling,
A.; Schilde, U.; Esposito, D. New J. Chem. 2016, 40, 4922−4930.
(q) Seva, L.; Hwang, W.-S.; Sabiah, S. J. Mol. Catal. A: Chem. 2016,
418−419, 125−131. (r) Marchenko, A.; Koidan, G.; Hurieva, A. N.;
Vlasenko, Y.; Kostyuk, A.; Biffis, A. Organometallics 2016, 35, 762−
770. (s) Mikhaylov, V. N.; Sorokoumov, V. N.; Korvinson, K. A.;
Novikov, A. S.; Balova, I. A. Organometallics 2016, 35, 1684−1697.
(t) Alam, K.; Kim, S. M.; Kim, D. J.; Park, J. K. Adv. Synth. Catal. 2016,
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Foundation for Distinguished
Young Talents in Higher Education of Guangdong (No.
Yq2013101), and the Project of Innovation for Enhancing
Guangdong Pharmaceutical University, provincial experimental
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DOI: 10.1021/acs.organomet.6b00723
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