Synthesis of N-heterocyclic carbene-Pd(II)-5-phenyloxazole complexes and initial studies of their catalytic activity toward the Buchwald-Hartwig amination of aryl chlorides

Article abstract of DOI:10.1016/j.jorganchem.2021.121683

Three new N-heterocyclic carbene (NHC)-Pd(II) complexes using 5-phenyloxazole as the ancillary ligand have been obtained in moderate to good yields by a one-pot reaction of the corresponding imidazolium salts, palladium chloride and 5-phenyloxazole under mild conditions. Initial studies showed that one of the complexes is an efficient catalyst for the Buchwald-Hartwig amination of aryl chlorides with various secondary and primary amines under the varied catalyst loading of 0.01-0.05 mol%, thus it will enrich the chemistry of NHCs and give an alternative catalyst for the coupling of challenging while cost-low aryl chlorides.

Full text of DOI:10.1016/j.jorganchem.2021.121683

Journal of Organometallic Chemistry 940 (2021) 121683
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis of N-heterocyclic carbene-Pd(II)-5-phenyloxazole complexes
and initial studies of their catalytic activity toward the
Buchwald-Hartwig amination of aryl chlorides
Zhi-Mao Zhang, Yu-Ting Xu, Li-Xiong Shao∗
College of Chemistry and Materials Engineering, Wenzhou University, Chashan University Town, Zhejiang Province 325035, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three new N-heterocyclic carbene (NHC)-Pd(II) complexes using 5-phenyloxazole as the ancillary ligand
have been obtained in moderate to good yields by a one-pot reaction of the corresponding imidazolium
salts, palladium chloride and 5-phenyloxazole under mild conditions. Initial studies showed that one of
the complexes is an efficient catalyst for the Buchwald-Hartwig amination of aryl chlorides with various
secondary and primary amines under the varied catalyst loading of 0.01-0.05 mol%, thus it will enrich
the chemistry of NHCs and give an alternative catalyst for the coupling of challenging while cost-low aryl
chlorides.
Received 30 September 2020
Revised 22 November 2020
Accepted 4 January 2021
Available online 7 January 2021
Keywords:
N-heterocyclic carbene
Palladium complex
Buchwald-Hartwig amination
Amines
© 2021 Elsevier B.V. All rights reserved.
Aryl chlorides
Synthetic method
1. Introduction
lary ligand in most cases. Through the hard research during the
recent years, a new and convenient strategy for the synthesis of
Traditionally, palladium-phosphine ligands system-catalyzed
Buchwald-Hartwig amination is popular methodology for
NHC-palladium complexes has been developed by our group. That
is, the strategy that keeping the NHC skeleton as IPr and sim-
ply changing the ancillary ligands was performed. In the reactions,
the ancillary ligands can be used only in equivalents amounts and
all complexes can be achieved in good to high yields by a one-
pot procedure from IPr.HCl, PdCl2 and the ancillary ligands under
mild conditions, providing an impressive method for the develop-
ment of NHC-palladium complexes kept high catalytic activities via
simple pathways [25–32]. Initial studies showed that they were
also efficient catalysts for the cross-coupling reactions involving
the challenging aryl chlorides and aryl sulfonates [33–52]. Encour-
aged by such successful results, we then continued this investiga-
tion by trying other easily available ancillary ligand to find out new
NHC-palladium complexes. In this case, 5-phenyloxazole was cho-
sen as the ancillary ligand, and some novel NHC-palladium com-
plexes were then developed. Initial studies showed that they were
also efficient catalysts for the Buchwald-Hartwig amination of aryl
chlorides with various amines under very low catalyst loadings.
In addition, comparison with some well-defined NHC-Pd(II) com-
plexes were also performed under the same conditions and similar
results were achieved, thus will give at least an alternative catalyst
for the coupling of aryl chlorides. Herein, we report these results
in detail.
a
the formation of N-containing compounds [1–4]. Compared to
their tertiary phosphine counterparts, N-heterocyclic carbenes
(NHCs) are usually more air-, thermal and moisture-stable. Con-
sequently, during the past years, many NHC-palladium com-
plexes have also been developed and applied in the Buchwald-
Hartwig amination of aryl chlorides with various amines [5–24].
In these cases, development of highly efficient NHC-palladium
complexes can be divided into two main different pathways:
one is the modification of the NHC moieties usually using
pyridines as the ancillary ligands [5–8,17–20,24]; the other
is the changement of the ancillary ligands using 1,3-bis(2,6-
diisopropylphenyl)imidazol-2-ylidene (IPr) as the NHC skeleton
[12,13,16,21], and it seems that main interest was paid on the
modification of NHC skeletons. However, besides some simple NHC
moieties such as 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene
(IPr), 1,3-bis(2,6-dimethylphenyl)imidazol-2-ylidene (IXy) and 1,3-
bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), lengthy path-
ways were necessary for most other NHC skeletons. In addition,
pyridines seemed to be the sole choice as the solvent and ancil-
∗
Corresponding author.
E-mail addresses: Shaolix@wzu.edu.cn, shaolix@163.com (L.-X. Shao).
https://doi.org/10.1016/j.jorganchem.2021.121683
0022-328X/© 2021 Elsevier B.V. All rights reserved.

Z.-M. Zhang, Y.-T. Xu and L.-X. Shao
Journal of Organometallic Chemistry 940 (2021) 121683
Table 1
Synthesis of NHC-Pd(ll)-5-phenyloxazole complexes 2.
Entrya
1 (R) (equiv)
Yield (%)b
1
2
3
1a (2,6-iPr) (1.2)
1b (2,6-Me2) (1.5)
1c (2,4,6-Me3) (1.5)
2a, 74
2b, 85
2c, 80
a
All reactions were carried out using 1, PdCl2 (0.15 mmol), 5-phenyloxazole (1.0 equiv) and
K2CO3 (1.2 equiv) in THF (2.0 mL) under reflux for 12 h.
b
Isolated yields.
Table 2
Repersentative results for the NHC-Pd(ll) complex 2a catalyzed reaction of
chlorobenzene 3a with morpholine 4a.
Entrya
[X]
Solvent
Temp (°C)
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
0.1
toluene
THF
90
1
93
60
76
11
96
12
66
75
92
0.1
90
1
0.1
dioxane
toluene
toluene
toluene
toluene
toluene
toluene
90
1
0.05
0.05
0.03
0.03
0.03
0.03
90
1
90
6
90
6
90
12
12
12
110
130
Fig. 1. The molecular structure of complex 2a showing 30% probability ellipsoids;
˚
all hydrogen atoms are omitted for clarity. Selected bond lengths (A) and bond an-
a
Reaction conditions: 3a (0.70 mmol), 4a (0.84 mmol), KOtBu (0.91 mmol), 2a (X
gles (o): Pd(1)-C(1) = 1.963(3), Pd(1)-N(3) = 2.113(3), Pd(1)-Cl(1) = 2.2813(9), Pd(1)-
Cl(2) = 2.3018(9); C(1)-Pd(1)-N(3) = 177.75(13), Cl(1)-Pd(1)-Cl(2) = 179.65(4), C(1)-
Pd(1)-Cl(1) = 88.58(9), C(1)-Pd(1)-Cl(2) = 91.36(9), N(3)-Pd(1)-Cl(1) = 90.13(8), N(3)-
Pd(1)-Cl(2) = 89.92(8).
mol%), solvent (1.0 mL)
b
Isolated yields.
the structure of complex 2a, some representative bond distances
and angles are also given in the Figure.
2. Results and discussion
2.1. Synthesis of NHC-Pd(II)-5-phenyloxazole complexes 2
2.2. Buchwald-Hartwig amination of aryl chlorides
First, the synthesis of NHC-Pd(II)-5-phenyloxazole complexes 2
was carried out using imidazolium salts 1, PdCl2 (0.15 mmol) and
5-phenyloxazole (1.0 equiv) in the presence of K2CO3 (1.2 equiv) in
refluxing THF (2.0 mL) in a one-pot procedure for 12 h. All reac-
tions performed well to give the desired complexes 2 in moderate
to good yields (Table 1). The equivalents of the imidazolium salts
have some effect on the reactions. For example, 1.2 equiv amounts
of IPr.HCl are enough for the synthesis of complex 2a, while 1.5
equiv amounts of IXy.HCl and IMes.HCl are necessary for the good
yields of complexes 2b and 2c.
The evaluation of the catalytic activity of complexes 2 was in-
vestigated choosing the Buchwald-Hartwig amination of aryl chlo-
rides. Initially, using complex 2a (0.1 mol%) as the catalyst, the
reaction between chlorobenzene 3a (0.7 mmol) and morpholine
4a (0.84 mmol) was carried out in toluene (1.0 mL) at 90 °C for
1 h to test various inorganic bases (0.91 mmol). In these cases,
the best yield was achieved when potassium tert-butoxide was
used, giving the desired product 5a in 93% yield (Table 2, entry
1). In the presence of sodium tert-butoxide and potassium hydrox-
ide, only 18 and 12% yields were observed, respectively. In addi-
tion, no reaction occurred once some other bases such as lithium
tert-butoxide, lithium hydroxide, sodium hydroxide, lithium car-
bonate, sodium carbonate, potassium carbonate, cesium carbonate,
sodium bicarbonate, potassium bicarbonate and potassium phos-
phate were added. Subsequently, using potassium tert-butoxide as
the base, the reaction was then performed in various other sol-
vents. For example, in non-polar solvents such as tetrahydrofuran
and dioxane, 60 and 76% yields were found, respectively (Table
2, entries 2 and 3). In polar solvents such as dimethyl sulfox-
To confirm the structure of complexes 2, besides normal meth-
ods such as 1H and 13C NMR, MS and elemental analysis, the sin-
gle crystal of complex 2a was also achieved and was fully ana-
lyzed by single crystal diffraction. As similar as those NHC-Pd(II)
complexes using other N-containing ancillary ligands developed by
our group [25–32], the central Pd atom in complex 2a is also C,N-
coordinated by the carbene carbon atom and the N-atom from 5-
phenyloxazole, together with two chlorine atoms, showing a very
slightly distorted square-planar geometry (Fig. 1). To further clarify
2

Z.-M. Zhang, Y.-T. Xu and L.-X. Shao
Journal of Organometallic Chemistry 940 (2021) 121683
ide, N,N-dimethylformamide and N,N-dimethylacetamide, no reac-
tion occurred. Based on the satisfactory result shown in Table 2,
entry 1, the catalyst loading was then lowered to 0.05 mol%. Dis-
appointingly, the yield drastically lowered from 93 to 11% within
1 h (Table 2, entry 1 vs 4). To our delight, 96% yield can be
still given when the reaction time was prolonged to 6 h (Table
2, entry 5). Similarly, by adjusting the reaction temperature and
time, high yield can be still achieved when only 0.03 mol% cata-
lyst was added (Table 2, entry 9). Under such conditions, almost
no desired product 5a can be detected once complexes 2b or 2c
were used as the catalyst. The comparison between some well-
defined NHC-Pd(II) complexes with complex 2a was also carried
out under the identical conditions shown in Table 2, entry 9. As
can be seen from Fig. 2, with NHC-Pd(II) complexes using differ-
ent ancillary ligands such as 1-methylimidazole[25], 2-phenyl-4,5-
dihydrooxazole[27], isoquinoline[28], 2-picolinic acid[30] and 3-
chloropyridine[16] as the catalyst, similar comparable yields were
observed, implying that complex 2a using 5-phenyloxazole as the
ancillary ligand can also be a potential catalyst in organic synthe-
sis.
With the optimal conditions in hand, the reactions between
various aryl chlorides 3 and secondary amines 4 were first inves-
tigated to test the scope and limitation of this methodology. The
results are summarized in Table 3. It seems that all reactions per-
formed well enough to give the desired coupling products 5 in
good to high yields in the presence of 0.03 or 0.05 mol% com-
Fig. 2. Results using other well-defined NHC-pd(11) complexes as the catalyst.
Table 3
NHC-Pd(ll) complex 2a-catalyzed reactions of aryl chlorides 3 with secondary amines 4.a,b
All reactions were carried out with 3 (0.70 mmol), 4 (0.84 mmol), KOtBu (0.91 mmol) and 2a (X mol%) in
a
toluene (1.0 mL) at 130 °C for 12 h.
b
Isolated yields.
3

Z.-M. Zhang, Y.-T. Xu and L.-X. Shao
Journal of Organometallic Chemistry 940 (2021) 121683
Table 4
4. Experimental
NHC-Pd(ll) complex 2a-catalyzed reactions of aryl chlorides 3 with primary amines
6.
4.1. General remarks
NMR spectra were recorded at 500 MHz (for 1H NMR) or
125 MHz (for 13C NMR), respectively. 1H and 13C NMR spectra
recorded in CDCl3 solutions were referenced to TMS (0.00 ppm)
and the residual solvent peak (77.0 ppm), respectively. J-values are
given in Hz. All solvents were dried by standard methods. The
mass analyzer type for the high resolution mass spectra (HRMS)
is Q-TOF. All amines were distilled prior to using. Other commer-
cially obtained reagents were used without further purification.
Flash column chromatography was performed on silica gel (300-
400 mesh).
Entrya 3 (R)
6 (R’)
[X]
Temp (°C) Time (h) Yield (%)b
1
2
3
4
5
6
7
8
a
3b
6a
0.01 110
0.01 110
0.01 110
0.01 110
0.03 130
0.01 110
0.01 110
0.05 110
12
6
7a, 98
7b, 93
7c, 93
7d, 97
7e, 90
7f, 99
7g, 99
7h, 93
(2-Me)
3b
(2-Me)
6b
(2,4-Me2)
6c
3b
3b
3b
6
(2,6-Me2)
6d
12
24
12
24
24
(2,4,6-Me3)
6e
4.2. General procedure for the synthesis of NHC-Pd(II) complexes 2
(2-OMe)
6c
3i
Under N2 atmosphere, a mixture of imidazolium salts 1 (0.18
or 0.225 mmol), PdCl2 (0.15 mmol), K2CO3 (0.18 mmol) and 5-
phenyloxazole (0.15 mmol) was stirred in anhydrous THF (2.0 mL)
under reflux for 12 h. Then the solvent was removed under re-
duced pressure, and the residue was purified by flash column chro-
matography on silica gel to give complexes 2 as yellow solids.
Compound 2a: yellow solid. m.p. 183.3-185.5 °C. 1H NMR
(500 MHz, CDCl3, TMS) δ 8.35 (s, 1H), 7.62 (s, 1H), 7.51-7.47 (m,
4H), 7.36-7.29 (m, 7H), 7.13 (s, 2H), 3.16 (hept, J = 6.5 Hz, 4H), 1.47
(d, J = 6.5 Hz, 12H), 1.12 (d, J = 6.5 Hz, 12H). 13C NMR (125 MHz,
CDCl3) δ 153.8, 152.7, 151.2, 146.7, 135.0, 130.3, 129.1, 128.8, 126.7,
125.1, 124.5, 124.0, 120.2, 28.7, 26.3, 23.2. IR (neat) ν 2964, 2862,
1739, 1593, 1465, 1411, 1382, 1349, 1328, 1235, 1206, 1162, 1108,
1045, 972, 944, 929, 843, 805, 765, 760 cm−1. MS (ESI): 674
[M-Cl]+. HRMS (ESI) calcd for C36H43ClN3OPd [M-Cl]+: 674.2134;
found: 674.2103. Anal. calcd for C36H43Cl2N3OPd.1/3toluene: C,
62.07%; H, 6.21%; N, 5.66%; found: C, 62.16%; H, 6.48%; N, 5.52%.
Compound 2b: yellow solid. m.p. 231.0 °C (decomposed). 1H
NMR (500 MHz, CDCl3, TMS) δ 8.37 (s, 1H), 7.64 (s, 1H), 7.47 (d,
J = 7.5 Hz, 2H), 7.36-7.29 (m, 5H), 7.26-7.24 (m, 4H), 7.12 (s, 2H),
2.42 (s, 12H). 13C NMR (125 MHz, CDCl3) δ 152.8, 151.2, 151.1,
137.4, 136.6, 129.5, 129.1, 128.9, 128.6, 126.6, 124.4, 124.1, 120.1,
19.2. IR (neat) ν 3153, 3133, 2921, 2845, 1733, 1514, 1477, 1441,
1404, 1381, 1331, 1278, 1218, 1165, 1106, 1043, 967, 943, 926, 839,
821, 785, 761, 747 cm−1. MS (ESI): 622 [M+Na]+. HRMS (ESI) calcd
for C28H27Cl2N3OPdNa [M+Na]+: 622.0460; found: 622.0455. Anal.
calcd for C28H27Cl2N3OPd.1/4toluene: C, 57.46%; H, 4.70%; N, 6.76%;
found: C, 57.19%; H, 4.99%; N, 6.40%.
(2,6-Me2)
3j
6c
6c
(2,4,6-Me3)
3k
(2,6-iPr2)
Reaction conditions: 3 (0.70 mmol), 6 (0.84 mmol), KOtBu (0.91 mmol), 2a (X
mol%), toluene (1.0 mL)
b
Isolated yields.
plex 2a. For example, electron-rich, -poor and sterically-hindered
groups substituted aryl chlorides 3 reacted with morpholine 4a
smoothly in the presence of 0.03 mol% complex 2a, giving prod-
ucts 5b-g in good to high yields (Table 3, entries 1-7). Heteroaryl
chloride such as 2-chloropyridine 3h is also suitable substrate
to afford product 5h in 71% yield (Table 3, entry 8). Other sec-
ondary amines such as pyrrolidine 4b, piperidine 4c, N-methyl-1-
phenylmethanamine 4d and N-methylaniline 4e can be also con-
verted to the corresponding N-arylated products 5i-w in 80-98%
yields smoothly (Table 3, entries 9-23).
To further test the compatibility of this methodology, the re-
actions between a variety of aryl chlorides 3 and anilines 6, both
having sterically-hindered substituents, were also investigated un-
der the similar conditions (Table 4). For such challenging trans-
formation, all reactions performed successfully to give the corre-
sponding diarylamines 7 in 90-99% yields. Notably, for most reac-
tions, the catalyst loading can be lowered to 0.01 mol%, giving the
desired products 7 in 93-99% yields (Table 4, entries 1-4, 6 and
7). Compared to secondary amines, it seems that the reactions in-
volving primary amines gave higher yields, affording products 7 in
>90% yields in all cases checked, implying that such complex may
be more efficient catalyst for the coupling of primary amines.
Compound 2c: yellow solid. m.p. 149.7-150.3 °C. 1H NMR
(500 MHz, CDCl3, TMS) δ 8.39 (s, 1H), 7.66 (s, 1H), 7.48 (d,
J = 7.0 Hz, 2H), 7.35 (t, J = 7.5 Hz, 2H), 7.31 (d, J = 7.0 Hz, 1H), 7.07
(s, 2H), 7.05 (s, 4H), 2.36 (s, 18H). 13C NMR (125 MHz, CDCl3) δ
152.8, 151.1, 139.2, 136.2, 135.0, 129.3, 129.1, 128.93, 128.86, 126.7,
124.4, 124.3, 120.2, 21.2, 19.1. IR (neat) ν 3160, 2921, 1676, 1603,
1485, 1444, 1408, 1371, 1335, 1278, 1229, 1166, 1106, 1036, 965,
929, 852, 839, 764, 738 cm−1. MS (ESI): 650 [M+Na]+. HRMS (ESI)
calcd for C30H31Cl2N3OPdNa [M+Na]+: 650.0774; found: 650.0783.
Anal. calcd for C30H31Cl2N3OPd: C, 57.48%; H, 4.98%; N, 6.70%;
found: C, 57.60%; H, 5.04%; N, 6.57%.
3. Conclusion
In conclusion, using 5-phenyloxazole as the ancillary ligand, a
novel type of NHC-Pd(II) complexes can be obtained by the reac-
tion of imidazolium salts, palladium chloride and 5-phenyloxazole
in a one-pot procedure under mild conditions. All complexes are
air- and thermal-stable, and can be kept under air for at least sev-
eral months. Initial studies on the catalytic activities of such NHC-
Pd(II) complexes were performed by the Buchwald-Hartwig reac-
tions of aryl chlorides with a variety of secondary and primary
amines. All amination reactions took place smoothly, giving the
corresponding products in good to almost quantitative yields with
the catalyst loadings varied from 0.01-0.05 mol%, thus new cata-
lysts with efficient activity were developed and will give at least
an alternative for the coupling reactions of challenging while cost-
low aryl chlorides.
4.3. General procedure for the complex 2a-catalyzed
Buchwald-Hartwig amination of aryl chlorides
Under N2 atmosphere, KOtBu (102.1 mg, 1.3 equiv) and a so-
lution of complex 2a (10-50 μL, 0.01-0.05 mol%, prepared from
5.0 mg of complex 2a in 1.0 mL dichloromethane) were added
into a Schlenk reaction tube. The tube was sealed and the sol-
vent was removed under reduced pressure. Then toluene (1.0 mL),
4

Z.-M. Zhang, Y.-T. Xu and L.-X. Shao
Journal of Organometallic Chemistry 940 (2021) 121683
J = 5.5 Hz, 4H), 1.58-1.53 (m, 2H). 13C NMR (125 MHz, CDCl3) δ
152.3, 138.5, 128.8, 120.1, 117.4, 113.6, 50.7, 25.9, 24.3, 21.7.
Compound 5n [25]: colorless liquid. 1H NMR (500 MHz, CDCl3,
TMS) δ 7.14 (t, J = 8.0 Hz, 1H), 6.54 (dd, J = 8.0, 2.0 Hz, 1H), 6.47 (t,
J = 2.5 Hz, 1H), 6.37 (dd, J = 8.0, 2.5 Hz, 1H), 3.77 (s, 3H), 3.14 (t,
J = 5.5 Hz, 4H), 1.68 (quintet, J = 5.5 Hz, 4H), 1.58-1.54 (m, 2H). 13C
NMR (125 MHz, CDCl3) δ 160.5, 153.5, 129.5, 109.2, 103.9, 102.7,
55.0, 50.5, 25.7, 24.3.
Compound 5o [25]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.27 (t, J = 7.5 Hz, 2H), 7.21-7.17 (m, 5H), 6.72 (t,
J = 8.5 Hz, 2H), 6.69 (t, J = 7.5 Hz, 1H), 4.49 (s, 2H), 2.97 (s, 3H). 13C
NMR (125 MHz, CDCl3) δ 149.8, 139.0, 129.1, 128.5, 126.8, 126.7,
116.6, 112.4, 56.6, 38.4.
amines (0.84 mmol) and aryl chlorides (0.70 mmol) were succes-
sively added. The mixture was stirred vigorously at the specified
temperature for 6-24 h. Then the solvent was removed under re-
duced pressure and the residue was purified by flash column chro-
matography on silica gel to give the corresponding products.
Compound 5a [25]: white solid. 1H NMR (500 MHz, CDCl3,
TMS) δ 7.26 (t, J = 7.5 Hz, 2H), 6.90-6.85 (m, 3H), 3.82 (t, J = 4.5 Hz,
4H), 3.12 (t, J = 4.5 Hz, 4H). 13C NMR (125 MHz, CDCl3) δ 151.2,
129.0, 119.9, 115.6, 66.8, 49.3.
Compound 5b [25]: colorless liquid. 1H NMR (500 MHz, CDCl3,
TMS) δ 7.17 (t, J = 7.5 Hz, 2H), 7.02-6.97 (m, 2H), 3.83 (t, J = 4.5 Hz,
4H), 2.89 (t, J = 4.5 Hz, 4H), 2.31 (s, 3H). 13C NMR (125 MHz, CDCl3)
δ 151.3, 132.6, 131.1, 126.6, 123.4, 119.0, 67.4, 52.3, 17.8.
Compound 5c [25]: colorless liquid. 1H NMR (500 MHz, CDCl3,
TMS) δ 7.15 (t, J = 7.5 Hz, 1H), 6.71-6.69 (m, 3H), 3.82 (t, J = 4.5 Hz,
4H), 3.11 (t, J = 4.5 Hz, 4H), 2.31 (s, 3H). 13C NMR (125 MHz, CDCl3)
δ 151.3, 138.7, 128.9, 120.8, 116.4, 112.8, 66.8, 49.4, 21.6.
Compound 5d [25]: white solid. 1H NMR (500 MHz, CDCl3,
TMS) δ 7.07 (d, J = 8.0 Hz, 2H), 6.81 (d, J = 8.0 Hz, 2H), 3.83 (t,
J = 4.5 Hz, 4H), 3.08 (t, J = 4.5 Hz, 4H), 2.26 (s, 3H). 13C NMR
(125 MHz, CDCl3) δ 149.2, 129.6, 129.4, 116.0, 66.9, 49.9, 20.3.
Compound 5e [25]: colorless liquid. 1H NMR (500 MHz, CDCl3,
TMS) δ 7.16 (t, J = 8.0 Hz, 1H), 6.50 (d, J = 8.0 Hz, 1H), 6.43-6.41 (m,
2H), 3.81 (t, J = 4.5 Hz, 4H), 3.76 (s, 3H), 3.11 (t, J = 4.5 Hz, 4H). 13C
NMR (125 MHz, CDCl3) δ 160.5, 152.6, 129.7, 108.3, 104.6, 102.1,
66.7, 55.0, 49.1.
Compound 5p [25]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.36 (d, J = 7.5 Hz, 2H), 7.30 (t, J = 7.5 Hz, 2H), 7.22
(t, J = 7.5 Hz, 1H), 7.18-7.12 (m, 2H), 7.06 (d, J = 7.5 Hz, 1H), 6.96
(t, J = 7.5 Hz, 1H), 4.01 (s, 2H), 2.56 (s, 3H), 2.39 (s, 3H). 13C NMR
(125 MHz, CDCl3) δ 152.4, 139.1, 132.9, 131.1, 128.3, 128.2, 126.9,
126.4, 123.0, 120.1, 60.8, 40.9, 18.3.
Compound 5q [25]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.27 (t, J = 7.5 Hz, 2H), 7.20 (d, J = 7.5 Hz, 3H), 7.08 (t,
J = 8.0 Hz, 1H), 6.57-6.52 (m, 3H), 4.47 (s, 2H), 2.94 (s, 3H), 2.27 (s,
3H). 13C NMR (125 MHz, CDCl3) δ 150.0, 139.1, 138.7, 128.5, 126.77,
126.76, 117.6, 113.1, 109.7, 56.6, 38.3, 21.8.
Compound 5r [25]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.27 (t, J = 7.5 Hz, 2H), 7.22-7.19 (m, 3H), 7.01 (d,
J = 8.0 Hz, 2H), 6.66 (d, J = 8.0 Hz, 2H), 4.45 (s, 2H), 2.93 (s, 3H),
2.23 (s, 3H). 13C NMR (125 MHz, CDCl3) δ 147.9, 139.2, 129.7, 128.5,
126.9, 126.8, 125.8, 112.8, 57.0, 38.5, 20.2.
Compound 5s [25]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.27 (t, J = 7.5 Hz, 2H), 7.19 (d, J = 7.5 Hz, 3H), 7.09 (t,
J = 8.0 Hz, 1H), 6.35 (d, J = 8.0 Hz, 1H), 6.29-6.25 (m, 2H), 4.48 (s,
2H), 3.71 (s, 3H), 2.96 (s, 3H). 13C NMR (125 MHz, CDCl3) δ 160.8,
151.1, 138.9, 129.8, 128.5, 126.8, 126.7, 105.6, 101.4, 99.0, 56.5, 55.0,
38.4.
Compound 5f [29]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.18 (dd, J = 15.5, 8.0 Hz, 1H), 6.64 (dd, J = 8.0,
2.0 Hz, 1H), 6.57-6.52 (m, 2H), 3.82 (t, J = 5.0 Hz, 4H), 3.12
(t, J = 5.0 Hz, 4H). 13C NMR (125 MHz, CDCl3) δ 163.8 (d,
JC-F = 242.0 Hz), 152.9 (d, JC-F = 9.625 Hz), 130.1 (d, JC-F = 9.875 Hz),
110. 7 (d, JC-F = 2.375 Hz), 106.1 (d, JC-F = 21.375 Hz), 102.3 (d,
JC-F = 25.0 Hz), 66.6, 48.7.
Compound 5g [27]: colorless liquid. 1H NMR (500 MHz, CDCl3,
TMS) δ 6.96 (t, J = 8.5 Hz, 2H), 6.85 (dd, J = 8.5, 4.5 Hz, 2H), 3.84
(t, J = 4.5 Hz, 4H), 3.06 (t, J = 4.5 Hz, 4H). 13C NMR (125 MHz,
CDCl3) δ 157.3 (d, JC-F = 237.625 Hz), 147.9 (d, JC-F = 2.0 Hz), 117.4
(d, JC-F = 7.625 Hz), 115.5 (d, JC-F = 22.0 Hz), 66.8, 50.3.
Compound 5t [31]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.28 (t, J = 7.0 Hz, 2H), 7.21 (t, J = 7.5 Hz, 1H),
7.17 (d, J = 7.5 Hz, 2H), 7.08 (dd, J = 16.0, 8.0 Hz, 1H), 6.45 (dd,
J = 7.5, 2.0 Hz, 1H), 6.41-6.35 (m, 2H), 4.47 (s, 2H), 2.96 (s, 3H).
13C NMR (125 MHz, CDCl3) δ 164.2 (d, JC-F = 240.5 Hz), 151.4
(d, JC-F = 10.5 Hz), 138.4, 130.1 (d, JC-F = 10.25 Hz), 128.6, 127.0,
126.6, 107.9 (d, JC-F = 2.0 Hz), 102.9 (d, JC-F = 21.5 Hz), 99.2 (d,
JC-F = 25.875 Hz), 56.4, 38.5.
Compound 5h [25]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 8.20 (d, J = 4.0 Hz, 1H), 7.49 (t, J = 7.5 Hz, 1H), 6.66-
6.62 (m, 2H), 3.81 (t, J = 4.5 Hz, 4H), 3.49 (t, J = 4.5 Hz, 4H). 13C
NMR (125 MHz, CDCl3) δ 159.6, 147.9, 137.4, 113.7, 106.8, 66.7, 45.6.
Compound 5i [28]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.10 (t, J = 7.0 Hz, 2H), 6.87 (d, J = 8.0 Hz, 1H), 6.82
(t, J = 7.5 Hz, 1H), 3.17 (t, J = 6.5 Hz, 4H), 2.31 (s, 3H), 1.91 (quintet,
J = 6.5 Hz, 4H). 13C NMR (125 MHz, CDCl3) δ 149.4, 131.6, 128.7,
126.2, 120.2, 115.8, 51.0, 24.9, 20.4.
Compound 5u [25]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.26-7.23 (m, 4H), 7.00 (d, J = 7.5 Hz, 4H), 6.93 (t,
J = 7.0 Hz, 2H), 3.29 (s, 3H). 13C NMR (125 MHz, CDCl3) δ 149.0,
129.1, 121.2, 120.4, 40.2.
Compound 5j [25]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.11 (t, J = 8.0 Hz, 1H), 6.22 (dd, J = 8.0, 2.5 Hz,
1H), 6.18 (dd, J = 8.0, 2.0 Hz, 1H), 6.10 (t, J = 2.0 Hz, 1H), 3.77 (s,
3H), 3.25 (t, J = 7.0 Hz, 4H), 1.97-1.94 (m, 4H). 13C NMR (125 MHz,
CDCl3) δ 160.7, 149.2, 129.7, 104.9, 100.5, 97.9, 55.0, 47.6, 25.3.
Compound 5k [25]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.25-7.21 (m, 2H), 6.93 (d, J = 8.0 Hz, 2H), 6.81 (t,
J = 7.5 Hz, 1H), 3.14 (t, J = 5.5 Hz, 4H), 1.69 (quintet, J = 5.5 Hz, 4H),
1.58-1.54 (m, 2H). 13C NMR (125 MHz, CDCl3) δ 152.2, 128.9, 119.1,
116.5, 50.6, 25.8, 24.3.
Compound 5l [28]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.17-7.13 (m, 2H), 7.00 (d, J = 8.0 Hz, 1H), 6.94 (t,
J = 7.5 Hz, 1H), 2.83 (t, J = 5.0 Hz, 4H), 2.30 (s, 3H), 1.70 (quintet,
J = 5.5 Hz, 4H), 1.57 (s, 2H). 13C NMR (125 MHz, CDCl3) δ 152.9,
132.7, 130.9, 126.4, 122.6, 119.0, 53.4, 26.6, 24.4, 17.8.
Compound 5v [27]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.24 (dd, J = 8.0, 7.5 Hz, 2H), 7.14 (t, J = 7.5 Hz,
1H), 6.98 (d, J = 8.0 Hz, 2H), 6.91 (t, J = 7.5 Hz, 1H), 6.84-6.82 (m,
2H), 6.77 (d, J = 7.0 Hz, 1H), 3.27 (s, 3H), 2.28 (s, 3H). 13C NMR
(125 MHz, CDCl3) δ 149.1, 149.0, 138.9, 129.1, 129.0, 122.3, 121.4,
120.9, 120.1, 117.9, 40.2, 21.5.
Compound 5w [25]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.27 (t, J = 7.5 Hz, 2H), 7.14 (t, J = 8.0 Hz, 1H), 7.05
(d, J = 8.0 Hz, 2H), 6.97 (t, J = 7.5 Hz, 1H), 6.57 (dd, J = 8.0, 1.5 Hz,
1H), 6.53 (t, J = 2.0 Hz, 1H), 6.47 (dd, J = 8.0, 2.0 Hz, 1H), 3.73 (s,
3H), 3.28 (s, 3H). 13C NMR (125 MHz, CDCl3) δ 160.5, 150.4, 148.8,
129.7, 129.2, 121.9, 121.5, 112.2, 105.9, 105.6, 55.1, 40.2.
Compound 7a [28]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.16 (d, J = 7.5 Hz, 2H), 7.08 (td, J = 8.5, 1.0 Hz, 2H),
6.95 (d, J = 7.5 Hz, 2H), 6.87 (td, J = 7.5, 1.0 Hz, 2H), 5.09 (br, 1H),
2.22 (s, 6H). 13C NMR (125 MHz, CDCl3) δ 142.0, 130.7, 127.5, 126.7,
121.3, 118.3, 17.7.
Compound 5m [28]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.12 (t, J = 7.5 Hz, 1H), 6.75-6.73 (m, 2H), 6.64 (d,
J = 7.5 Hz, 1H), 3.12 (t, J = 5.5 Hz, 4H), 2.30 (s, 3H), 1.69 (quintet,
5

Z.-M. Zhang, Y.-T. Xu and L.-X. Shao
Journal of Organometallic Chemistry 940 (2021) 121683
Compound 7b [28]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.13 (d, J = 7.0 Hz, 1H), 7.04 (t, J = 7.5 Hz, 1H), 7.00
(s, 1H), 6.92 (s, 2H), 6.82-6.79 (m, 2H), 5.01 (s, 1H), 2.27 (s, 3H),
2.22 (s, 3H), 2.18 (s, 3H). 13C NMR (125 MHz, CDCl3) δ 142.9, 138.9,
131.7, 131.5, 130.6, 129.1, 127.2, 126.7, 125.9, 120.5, 120.2, 116.4,
20.6, 17.7, 17.6.
Compound 7c [35]: white solid. 1H NMR (500 MHz, CDCl3,
TMS) δ 7.11-7.09 (m, 3H), 7.05 (dd, J = 8.5, 6.5 Hz, 1H), 6.94 (t,
J = 7.5 Hz, 1H), 6.68 (t, J = 7.5 Hz, 1H), 6.14 (d, J = 8.0 Hz, 1H), 4.88
(s, 1H), 2.30 (s, 3H), 2.16 (s, 6H). 13C NMR (125 MHz, CDCl3) δ
144.1, 138.7, 135.5, 130.2, 128.5, 126.9, 125.5, 122.4, 118.1, 111.7, 18.1,
17.5.
Compound 7d [28]: white solid. 1H NMR (500 MHz, CDCl3,
TMS) δ 7.08 (d, J = 7.5 Hz, 1H), 6.94-6.92 (m, 3H), 6.65 (t, J = 7.5 Hz,
1H), 6.12 (d, J = 8.0 Hz, 1H), 4.80 (s, 1H), 2.29 (s, 3H), 2.28 (s, 3H),
2.12 (s, 6H). 13C NMR (125 MHz, CDCl3) δ 144.5, 136.0, 135.5, 135.1,
130.1, 129.2, 126.9, 122.0, 117.7, 111.4, 20.8, 18.0, 17.5.
Compound 7e [28]: colorless liquid. 1H NMR (500 MHz, CDCl3,
TMS) δ 7.31 (d, J = 8.0 Hz, 1H), 7.20 (d, J = 7.5 Hz, 1H), 7.14 (t,
J = 7.5 Hz, 1H), 7.03 (d, J = 7.5 Hz, 1H), 6.93 (t, J = 7.5 Hz, 1H), 6.89-
6.80 (m, 3H), 5.87 (s, 1H), 3.88 (s, 3H), 2.26 (s, 3H). 13C NMR
(125 MHz, CDCl3) δ 148.0, 140.8, 133.9, 130.8, 129.3, 126.6, 122.1,
120.8, 119.6, 119.3, 114.4, 110.4, 55.6, 17.8.
Compound 7f [28]: white solid. 1H NMR (500 MHz, CDCl3, TMS)
δ 6.96 (d, J = 7.5 Hz, 4H), 6.83 (t, J = 7.5 Hz, 2H), 4.78 (s, 1H), 2.00
(s, 12H). 13C NMR (125 MHz, CDCl3) δ 141.8, 129.5, 128.7, 121.7,
19.0.
Compound 7g [35]: white solid. 1H NMR (500 MHz, CDCl3,
TMS) δ 6.95 (d, J = 7.5 Hz, 2H), 6.80 (s, 3H), 4.70 (s, 1H), 2.25 (s,
3H), 1.98 (s, 12H). 13C NMR (125 MHz, CDCl3) δ 142.2, 139.0, 131.5,
130.5, 129.2, 128.8, 128.5, 121.0, 20.6, 19.1, 19.0.
Compound 7h [35]: pale yellow liquid. 1H NMR (500 MHz,
CDCl3, TMS) δ 7.14-7.09 (m, 3H), 6.92 (d, J = 7.5 Hz, 2H), 6.70 (t,
J = 7.5 Hz, 1H), 4.78 (s, 1H), 3.15 (hept, J = 7.0 Hz, 2H), 1.97 (s, 6H),
1.11 (d, J = 7.0 Hz, 12H). 13C NMR (125 MHz, CDCl3) δ 144.1, 143.1,
138.8, 129.5, 125.6, 124.8, 123.2, 119.6, 28.0, 23.4, 19.3.
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Declaration of Competing Interest
None.
Supplementary materials
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