Air-stable Pd(0) catalyst bearing dual phosphine ligands: a detailed evaluation of air stability and catalytic property in cross-coupling reactions

Article abstract of DOI:10.1039/d0dt02744h

We have synthesised an air-stable Pd(0) catalyst bearing donor and acceptor phosphine ligands (Complex1). This study revealed the long-term air stability and catalytic property of Complex1as a catalyst for cross-coupling reactions, where it was stable in air for eight months. DFT calculations revealed that the acceptor ligands in Complex1decreased the HOMO energy level, which provided the observed air stability. Complex1successfully served as a catalyst for direct C-H arylation reactions and Suzuki-Miyaura cross-coupling reactions, and catalysed the reaction of a relatively inactive substrate, 2-chrolopyridine, which could not be achieved by conventional, air-stable Pd(0) catalysts. Isolating the intermediates of the coupling reactions revealed that each intermediate possessed the donor ligand (PCy₃), which was determined to be responsible for imparting the high catalytic activity exhibited by Complex1.

Full text of DOI:10.1039/d0dt02744h

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Air-stable Pd(0) catalyst bearing dual phosphine
ligands: a detailed evaluation of air stability and
catalytic property in cross-coupling reactions†
Cite this: DOI: 10.1039/d0dt02744h
Ryota Sato, Takaki Kanbara * and Junpei Kuwabara
*
We have synthesised an air-stable Pd(0) catalyst bearing donor and acceptor phosphine ligands (Complex
1). This study revealed the long-term air stability and catalytic property of Complex 1 as a catalyst for
cross-coupling reactions, where it was stable in air for eight months. DFT calculations revealed that the
acceptor ligands in Complex 1 decreased the HOMO energy level, which provided the observed air stabi-
lity. Complex 1 successfully served as a catalyst for direct C–H arylation reactions and Suzuki–Miyaura
cross-coupling reactions, and catalysed the reaction of a relatively inactive substrate, 2-chrolopyridine,
which could not be achieved by conventional, air-stable Pd(0) catalysts. Isolating the intermediates of the
coupling reactions revealed that each intermediate possessed the donor ligand (PCy3), which was deter-
mined to be responsible for imparting the high catalytic activity exhibited by Complex 1.
Received 5th August 2020,
Accepted 28th August 2020
DOI: 10.1039/d0dt02744h
rsc.li/dalton
tor) ligands. In contrast to air stability, electron-sufficient
(donor) ligands are favoured for oxidative addition in the cata-
Introduction
The development of transition-metal-catalysed cross-coupling lytic cycle.2 Therefore, a new molecular design that provides
reactions has accelerated syntheses of natural products, agro- both air stability and good catalytic activity is necessary.
chemicals, materials in organic electronic devices, etc.1–5 Pd, Recently, we have developed an air-stable Pd(0) complex
Ni, and Cu complexes are commonly used as catalysts for that bears acceptor phosphine ligands for stability and a
cross-coupling reactions. Among them, Pd catalyst precursors donor phosphine ligand, PCy3, to impart catalytic activity
and their ligands have been predominantly investigated, as (Complex 1, Scheme 1).22 Complex 1 showed excellent air stabi-
they can achieve high catalytic activity and be employed in a lity during an accelerated deterioration test, and high catalytic
wide range of applications. Bi- or zero-valent Pd catalyst pre- activity in direct C–H arylation reactions.
cursors are generally used for various cross-coupling reactions.
In this paper, we report an extensive investigation of
Pd(II) precatalysts6–9 are stable in air and easy to handle, while Complex 1 regarding its long-term stability and catalytic prop-
a process of forming a catalytically active Pd(0) species causes erty in cross-coupling reactions, the results of which compli-
decomposition of substrates or additive ligands during the ment those of previous works. DFT calculations revealed that
initial stage of cross-coupling reactions.10–13 The use of Pd(0) the origin of the air stability of Complex 1 was the acceptor
catalysts can avoid this because there is no activation process. phosphine ligands, while mechanistic studies and catalytic
However, Pd(0) catalysts are generally unstable in air and reactions demonstrated that the donor ligand coordinates to
difficult to handle.14 Therefore, researchers in the field of cata- the Pd centre during the catalytic reaction and provides high
lytic chemistry aspire to develop air-stable Pd(0) catalysts. catalytic activity.
Precise molecular designs have provided air-stable Pd(0)15–19
and Ni(0) catalysts in recent years,20,21 and the basic concept
behind them is selecting appropriate electron-deficient (accep-
Tsukuba Research Center for Energy Materials Science (TREMS), Graduate School of
Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Ibaraki 305-8573,
Japan. E-mail: kanbara@ims.tsukuba.ac.jp, kuwabara@ims.tsukuba.ac.jp
†Electronic supplementary information (ESI) available. CCDC 1950052. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
d0dt02744h
Scheme 1 Synthesis of Complex 1.
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Results and discussion
Evaluation of long-term air stability
Complex 1 was stored in air for a long time to confirm its long-
term air stability. The 31P NMR spectrum of Complex 1 was
taken before it was stored and then again eight months later
(Fig. 1). Both spectra showed doublet and triplet signals with
an integral ratio of 2 : 1, which correspond to the complex.
This spectroscopic data demonstrated that there was no
decomposition of the complex after long-term storage under
ambient conditions.
The catalytic activity of air-exposed Complex 1 was com-
pared to that of the pristine complex in a direct C–H arylation
reaction. The reaction was carried out under nitrogen atmo-
sphere because Complex 1 was unstable in solution under air.
Time course reactions were performed for both versions of
Complex 1, and consisted of 2-cyanothiophene reacting with
4-bromoanisole in the presence of 0.5 mol% of Complex 1
(Fig. 2). The results of the time courses were almost identical,
demonstrating that there was no degradation of catalytic
activity during storage and Complex 1 displays long-term air
stability. Fig. 2 shows the induction period in a reproducible
fashion. This observation indicates the three-coordinated Pd
(0) complex was stable and slowly converted to the active
species.
Fig. 2 Time courses of the direct C–H arylation reactions by Complex
1. Conditions: Pd, 0.0025 mmol; 4-bromoanisole, 0.50 mmol; 2-cya-
nothiophene, 1.0 mmol; PivOH, 0.15 mmol; K2CO3, 0.75 mmol; toluene,
1.7 mL; and temperature, 100 °C. The yields were determined by 1H
NMR analysis of the crude product with ferrocene as the internal
standard.
DFT calculations
Subsequent density functional theory (DFT) calculations were
performed on the complexes to estimate their HOMO energy
levels, because a low HOMO level is linked to low oxidation
potentials and high air stability. The HOMO and LUMO energy
levels of Complex 1 were compared to those of related com-
plexes: Pd(PCy3)2 and superstable Pd (Pd[P(3,5-(CF3)2C6H3)3]3,
SSPd, Fig. 3).19 Complex 1 and SSPd showed much lower
HOMO levels than Pd(PCy3)2. The two acceptor ligands of
Complex 1 strongly stabilized it, despite the coordination of
the donor ligand.23 These DFT calculations clarified that P(3,5-
(CF3)2C6H3)3 ligand lowered the HOMO level of Complex 1,
providing its air-stability.
Fig. 3 HOMO and LUMO distributions and energy levels of Complex 1,
Pd(PCy3)2, and superstable Pd (SSPd) based on DFT calculations.
Mechanistic study
A previous study22 revealed that Complex 1 showed higher cata-
lytic activity in a direct C–H arylation reaction than SSPd, pre-
sumably due to the presence of the PCy3 ligand in Complex 1.
It is desirable that PCy3 does not dissociate from the Pd centre
during the catalytic cycle to ensure accelerated oxidative
addition and reductive elimination steps. To confirm PCy3
coordination, intermediates from each step of a direct C–H
arylation reaction were isolated (Fig. S1†). We found that one
of the P(3,5-(CF3)2C6H3)3 ligands had selectively dissociated
from the Pd centre due to the weak basicity of the oxidative
addition step (Scheme 2).22 This formed Complex 2, whose
PCy3 ligand does not dissociate during the initial step of the
direct C–H arylation reaction.
The intermediate of the next step is a Pd pivalato complex
(Fig. S1†). The reaction of Complex 2 with silver pivalate gave
Complex 3 (Scheme 3) in a 50% yield.24 The crystal structure of
Complex 3 was determined (Fig. 4), which revealed that both
Fig. 1 31P NMR spectra of Complex 1 before storage (top) and after
being stored for eight months in the solid state in air (bottom; 162 MHz,
acetone-d6, r.t., under N2, external standard: 85% H3PO4 0 ppm).
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Scheme 4 Stoichiometric
reaction
of
Complex
3
with
2-cyanothiophene.
Scheme 2 Synthesis of Complex 2.22
Table 1 Direct C–H arylation reaction by Complex 1
Scheme 3 Synthesis of Complex 3.
Entry
X
Y
Yielda (%)
1
2
3
4
5
−CN
−CN
−CN
−Ac
−OMe
−Me
83
72
40
29
34
−CF3
−OMe
−OMe
−CHO
a Isolated yield.
Direct C–H arylation reaction
In our previous works,22 the catalytic properties of Complex 1
1
had been evaluated by H NMR analysis, where the conversion
of the substrates was monitored. This study determined the
catalytic properties based on the isolated yields of the products
(Table 1).
Fig. 4 ORTEP drawing of Complex 3 with thermal ellipsoids at the 30%
Complex 1 afforded coupling products in moderate to good
probability level. All hydrogen atoms and incorporated molecules were
omitted for clarity. Selected bond lengths (Å): Pd1–P1 = 2.3322(7), Pd1– isolated yields. The yields of reactions with electron-rich bro-
P2 = 2.3160(7), Pd1–O1 = 2.120(2), Pd1–C1 = 2.005(3). Selected bond
angles (°): P1–Pd1–P2 = 176.98(3), P1–Pd–O1 = 88.26(6), P2–Pd1–O1 =
94.53(6), O1–Pd1–C1 = 178.44(9).
moarenes were higher than those of reactions with electron-
poor bromoarenes (entries 1–3). Therefore, the oxidative
addition step may not be the rate-determining step because
the PCy3 ligand promotes faster oxidative addition.2
2-Cyanothiophene showed higher reactivity than acetyl- or
the P(3,5-(CF3)2C6H3)3 and PCy3 ligands were coordinated to formyl thiophenes (entry 1 vs. 4 and 5). Its strong electron-
the Pd centre. The 31P NMR spectrum of Complex 3 exhibited withdrawing nature, or coordination ability, ascribed to its
two doublet signals (J = 388 Hz, Fig. S3†). The signal pattern cyano group, is likely behind this improved direct C–H aryla-
and the J values suggest that the heteroligated complex pos- tion reaction activity. The strong electron-withdrawing nature
sesses the trans configuration and is stable in solution.25,26 provides high reactivity of the C–H bond. In addition, coordi-
These results confirm that the Pd centre maintains coordi- nation ability of the cyano group may promote the dissociation
nation with the PCy3 ligand during the catalytic cycle.
of one of the phosphine ligands in Complex 1 to generate an
The stoichiometric reaction of Complex 3 with 2-cyanothio- active two-coordinate species.
phene was conducted to investigate whether Complex 3 was
Suzuki–Miyaura cross-coupling
the true intermediate during the direct C–H arylation reaction
using Complex 1 (Scheme 4). The reaction gave 5-phenyl-2-cya- Complex 1 was applied to Suzuki–Miyaura cross-coupling reac-
nothiophene as the coupling product, confirming that tions to confirm its catalytic property as a catalyst. Reactions of
Complex 3 is the intermediate of this reaction (Fig. S1†). The 4-bromotoluene with phenylboronic acid in the presence of
low yield of the products is presumably due to the decompo- Complex 1 were conducted under several reaction conditions
sition of a Pd(0) species formed by reductive elimination; (Table S1†). The reaction under suitable conditions afforded
released phosphine ligands from the decomposed Pd species the products in 97% yield (Table 2, entry 1). The other bro-
may inhibit the reaction of Complex 3 with 2-cyanothiophene.
moarenes, bearing electron-donating or electron-withdrawing
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respectively (Fig. S4†).27 Based on the results, the HOMO was
located on the Pd centre in both species, and the HOMO
energy level of Pd(PCy3)P(3,5-(CF3)2C6H3)3 was higher than
that of Pd[P(3,5-(CF3)2C6H3)3]2. The high energy Pd-centred
HOMO would be an origin of high reactivity in the oxidative
addition step because a transition state of oxidative addition
involves interaction between a 4d orbital of a Pd centre and a
σ*(and π*) orbital of a substrate (see ESI†).28–32 The PCy3
ligand is likely to provide high reactivity to plausible active
species from Complex 1, Pd(PCy3)P(3,5-(CF3)2C6H3)3 due to its
strong donor nature.
Table 2 Suzuki–Miyaura cross-coupling reaction by Complex 1
Entry
Ar–X
Yielda (%)
1
2
3
4
4-Bromotoluene
4-Bromoanisole
4-Bromobenzotrifluoride
2-Chloropyridine
97
81
83
66
a Isolated yield.
Conclusion
Table 3 Suzuki–Miyaura cross-coupling reactions of 2-chloropyridine
Complex 1 showed high stability in air for eight months, and
DFT calculations revealed that the low HOMO energy level con-
tributed to this stability. These results also showed the stabilis-
ing effect from the acceptor ligand, P(3,5-(CF3)2C6H3)3.
Isolating the intermediate of the direct C–H arylation reaction
confirmed that PCy3 coordinates to the Pd centre during each
step of the reaction and imparts catalytic activity. Complex 1
showed high catalytic activity for direct C–H arylation reactions
and Suzuki–Miyaura cross-coupling reactions. Moreover,
Complex 1 was able to catalyse the reaction of a relatively inac-
tive substrate, 2-chrolopyridine, which could not be achieved
by conventional, air-stable Pd(0) catalysts, due to the activating
effect of its donor ligand, PCy3. This study clarified the
working principle of Complex 1, which satisfied the demands
for air stability and catalytic activity.
with phenyl boronic acid by various Pd catalysts
Entry
Pd(0)
Yielda (%)
1
2
3
Complex 1
Pd(PCy3)2
SSPd
89
94
9
a The yield was determined by 1H NMR analysis of the crude product
with ferrocene as the internal standard.
substituents, also afforded the corresponding products in high
yields (entries 2 and 3). Even for a relatively inactive substrate,
2-chrolopyridine, Complex 1 proved to be a good catalyst (entry Experimental section
4). The performance of the other Pd(0) catalysts during the
reaction of 2-chloropyridine with phenylboronic acid were
General, measurement, and materials
1H and 31P{1H} NMR spectra were recorded using a Bruker
compared (Table 3), where the catalyst loading was 0.1 mol%.
The reaction with 0.1 mol% of Complex 1 gave 2-phenylpyri-
dine in 89% yield (entry 1), which was similar to that obtained
when Pd(PCy3)2 was used (entry 2). In contrast, the reaction
employing SSPd under the same conditions resulted in a low
yield (9%, entry 3). Soós and co-workers19 have also reported a
low yield (25%) for a similar coupling reaction, where 2-chloro-
pyridine and 4-ethoxy-3-methylphenyldioxaborolane reacted
with 0.33 mol% of SSPd at 110 °C for 24 h. Complex 1 showed
almost the same activity as the unstable Pd(PCy3)2 complex,
but distinctly higher catalytic activity than that of the conven-
tional, air-stable Pd(0) complex used in Suzuki–Miyaura cross-
coupling reactions. These results show that the PCy3 ligand of
Complex 1 can be ascribed to the accelerated oxidative
AVANCE-400 NMR spectrometer. Elemental analyses were
carried out using a PerkinElmer 2400 CHN elemental analyzer.
SSPd was purchased from FUJIFILM Wako Pure Chemical
Corporation. Anhydrous methanol, n-pentane, n-hexane and
toluene were purchased from Kanto Chemical and used as dry
solvents. The density functional theory (DFT) calculations were
performed at the B3LYP/6-31G(d) level with the Gaussian09
Rev. D.01 program (Gaussian, Inc., Wallingford, CT, USA).
Synthetic methods
Complex 1 and 2 were synthesized as previously reported.22
Complex 3
addition that was observed for the inactive C–Cl bond in A solution of Complex 2 (126 mg, 0.10 mmol) and silver piva-
2-chloropyridine. To confirm this, a plausible active species of late (31 mg, 0.15 mmol) was stirred in n-pentane (4 mL) at
Complex 1 and SSPd were analysed by DFT calculations. One 25 °C for 20 h. The resulting mixture was filtered through
of the P(3,5-(CF3)2C6H3)3 ligands may dissociate from the Pd glass filter and concentrated under vacuum. Recrystallization
centre before the oxidative addition step, which would form from n-pentane gave Complex 3 (62 mg, 50%). 1H NMR
two coordinated Pd(0) complexes, Pd(PCy3)P(3,5-(CF3)2C6H3)3 (400 MHz, acetone-d6, room temperature): δ 8.18 (s, 3 H), 8.16
and Pd[P(3,5-(CF3)2C6H3)3]2, from Complex
1
and SSPd, (s, 6 H), 7.06 (br, 2 H), 6.57 (br, 3 H), 1.78–1.66 (m, 16 H),
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1.31–1.07 (m, 14 H), 0.87 (t, 3 H, J = 8.0 Hz), 0.61 (s, 9 H). 31P J = 4 Hz, 1H), 7.59 (d, J = 8.8 Hz, 2H), 7.22 (d, J = 4 Hz, 1H),
{1H} NMR (162 MHz, acetone-d6, room temperature): δ 29.8 (d, 6.94 (d, J = 8.8 Hz, 2H), 3.86 (s, 3H), 2.56 (s, 3H).36
1 P, J = 388 Hz), 24.0 (d, 1 P, J = 389 Hz). Elemental analysis:
Synthesis of 5-(4-methoxyphenyl)-2-formylthiophene (Table 1,
Found: C 51.28%, H 4.67%; Calcd for C52H47F18O2P2Pd: C entry 5). Purification by column chromatography on silica gel
51.53%, H 4.57%.
using a mixture of hexane and ethyl acetate (30 : 1) as an
eluent gave 5-(4-methoxyphenyl)-2-formylthiophene (37 mg,
34%). 1H NMR (400 MHz, CDCl3, room temperature): δ 9.86 (s,
Stoichiometric reaction of Complex 3 with 2-cyanothiophene
A mixture of Complex 3 (67.5 mg, 0.055 mmol), 2-cyanothio- 1H), 7.71 (d, J = 3.6 Hz, 1H), 7.62 (d, J = 8.8 Hz, 1H), 7.30 (d, J =
phene (51.3 μL, 0.55 mmol) and K2CO3 (15.2 mg, 0.11 mmol) 4 Hz, 2H), 6.96 (d, J = 8.8 Hz, 2H), 3.86 (s, 3H).37
was stirred in toluene (1.3 mL) for 20 h at 100 °C under nitro-
Tracking of the direct C–H arylation reaction. A mixture of
gen atmosphere. The reaction mixture was cooled to room Complex 1 (4.3 mg, 0.0025 mmol), pivalic acid (17.5 μL,
temperature and diluted with ethyl acetate. The organic phase 0.15 mmol), 2-cyanothiophene (93 μL, 1.0 mmol), 1-bromo-4-
was washed with water and brine, and dried over Na2SO4. The methoxybenzene (62 μL, 0.50 mmol), K2CO3 (104 mg,
product was isolated by column chromatography on silica gel 0.75 mmol) and ferrocene (18.6 mg, 0.1 mmol) was stirred in
using a mixture of hexane and ethyl acetate (32 : 1) as an toluene (1.7 mL) at 100 °C under a nitrogen atmosphere.
eluent and HPLC. The solvents were removed in vacuo to give A portion of a reaction mixture (ca. 10 μL) was taken out at 0,
1
5-phenyl-2-cyanothiophene (2.2 mg, 22%). H NMR (400 MHz, 3, 6, 9, 21, 24 h. The NMR yield at each reaction time was
CDCl3, room temperature): δ 7.62–7.58 (m, 3H), 7.46–7.38 (m, obtained from the integral value of the signal for the product
3H), 7.28 (d, J = 4.0 Hz, 1H). The NMR data is consistent with at 3.85 ppm on the basis of the internal standard
reported data.33
(ferrocene).22
Suzuki–Miyaura cross-coupling reaction
Synthesis of 4-methylbiphenyl (Table 2, entry 1). A mixture of
Complex 1 (4.3 mg, 0.0025 mmol), phenylboronic acid (64 mg,
General procedure of catalytic reaction
Direct C–H arylation reaction
Synthesis of 5-(4-methoxyphenyl)-2-cyanothiophene (Table 1, 0.53 mmol), 1-bromo-4-methylbenzene (62 μL, 0.50 mmol),
entry 1). A mixture of Complex 1 (4.3 mg, 0.0025 mmol), and K2CO3 (138 mg, 1.0 mmol) was stirred in 1,4-dioxane
pivalic acid (17.5 μL, 0.15 mmol), 2-cyanothiophene (93 μL, (1.0 mL) for 4 h at 100 °C under a nitrogen atmosphere. The
1.0 mmol), 1-bromo-4-methoxybenzene (62 μL, 0.50 mmol), reaction mixture was cooled to room temperature and diluted
and K2CO3 (104 mg, 0.75 mmol) was stirred in toluene with ethyl acetate. The organic phase was washed with NH4Cl
(1.7 mL) for 20 h at 100 °C under a nitrogen atmosphere. The aq. and brine, and dried over Na2SO4. The product was iso-
reaction mixture was cooled to room temperature and diluted lated by column chromatography on silica gel using hexane as
with CHCl3. The organic phase was washed with water and an eluent. The solvents were removed in vacuo to give 4-methyl-
brine, and dried over MgSO4. The product was isolated by biphenyl (82 mg, 97%). 1H NMR (400 MHz, CDCl3, room temp-
column chromatography on silica gel using a mixture of erature): 7.58 (d, J = 7.2 Hz, 2H), 7.49 (d, J = 8.0 Hz, 2H), 7.42
hexane and ethyl acetate (32 : 1) as an eluent. The solvents (t, J = 7.6 Hz, 2H), 7.32 (t, J = 7.2 Hz, 1H), 7.25 (d, J = 8.0 Hz,
were removed in vacuo to give 5-(4-methoxyphenyl)-2-cya- 2H), 2.40 (s, 3H).38
1
nothiophene (89 mg, 83%). H NMR (400 MHz, CDCl3, room
Synthesis of 4-methoxybiphenyl (Table 2, entry 2). Purification
temperature): δ 7.56 (d, J = 4.0 Hz, 1H), 7.53 (d, J = 9.2 Hz, 2H), by column chromatography on silica gel using hexane as an
7.16 (d, J = 4.0 Hz, 1H), 6.95 (d, J = 9.2 Hz, 2H), 3.85 (s, 3H).22 eluent gave 4-methoxybiphenyl (75 mg, 81%). 1H NMR
Synthesis of 5-(4-methylphenyl)-2-cyanothiophene (Table 1, (400 MHz, CDCl3, room temperature): 7.54 (t, J = 5.5 Hz, 4H),
entry 2). Purification by column chromatography on silica gel 7.41 (t, J = 7.6 Hz, 2H), 7.30 (t, J = 7.4 Hz, 1H), 6.98 (d, J = 8.8
using a mixture of hexane and ethyl acetate (30 : 1) as an Hz, 2H), 3.85 (s, 3H).38
eluent gave 5-(4-methylphenyl)-2-cyanothiophene (72 mg,
Synthesis of 4-trifluoromethylbiphenyl (Table 2, entry 3).
72%). 1H NMR (400 MHz, CDCl3, room temperature): δ 7.57 (d, Purification by column chromatography on silica gel using
J = 3.6 Hz, 3H), 7.49 (d, J = 8.4 Hz, 2H), 7.24–7.22 (m, 3H), 2.39 hexane as an eluent gave 4-trifluoromethylbiphenyl (92 mg,
1
(s, 3H).34
83%). H NMR (400 MHz, CDCl3, room temperature): 7.70 (m,
Synthesis
of
5-(4-trifluoromehylphenyl)-2-cyanothiophene 4H), 7.60 (d, J = 6.8 Hz, 2H), 7.48 (t, J = 7.4 Hz, 2H), 7.41 (t, J =
(Table 1, entry 3). Purification by column chromatography on 7.2 Hz, 1H).38
silica gel using a mixture of hexane and ethyl acetate (30 : 1) as
Synthesis of 2-phenylpyridine (Table 2, entry 4). Purification
an eluent gave 5-(4-trifluoromehylphenyl)-2-cyanothiophene by column chromatography on silica gel using ethyl acetate
(51 mg, 40%). 1H NMR (400 MHz, CDCl3, room temperature): δ and hexane (1 : 6) as an eluent gave 2-phenylpyridine (51 mg,
7.71 (m, 4H), 7.63 (d, J = 3.6 Hz, 1H), 7.36 (d, J = 4 Hz, 1H).35
66%). 1H NMR (400 MHz, CDCl3, room temperature): 8.70 (d, J
Synthesis of 5-(4-methoxyphenyl)-2-acetylthiophene (Table 1, = 4.8 Hz, 1H), 8.00 (d, J = 7.2 Hz, 2H), 7.76–7.72 (m, 2H), 7.48
entry 4). Purification by column chromatography on silica gel (t, J = 7.4 Hz, 2H), 7.42 (t, J = 7.2 Hz, 1H), 7.26–7.21 (m, 1H).39
using a mixture of hexane and ethyl acetate (30 : 1) as an
Crystal structure determination. Recrystallization from
eluent gave 5-(4-methoxyphenyl)-2-acetylthiophene (34 mg, toluene/methanol gave a single crystal of Complex 3 for crystal
29%). 1H NMR (400 MHz, CDCl3, room temperature): δ 7.64 (d, structure determination. Intensity data were collected on a
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Bruker SMART APEX II ULTRA with Mo Kα radiation. A full 15 S. I. Aizawa, A. Majumder, Y. Yokoyama, M. Tamai,
matrix least-squares refinement was used for non-hydrogen
D. Maeda and A. Kitamura, Organometallics, 2009, 28,
atoms with anisotropic thermal parameters using the
6067–6072.
SHELXL-97 program. CCDC 1950052† contains the supplemen- 16 N. C. Bruno, M. T. Tudge and S. L. Buchwald, Chem. Sci.,
tary crystallo-graphic data for this paper.
2013, 4, 916–920.
17 H. G. Lee, P. J. Milner and S. L. Buchwald, Org. Lett., 2013,
15, 5602–5605.
Conflicts of interest
18 A. Majumder, R. Gupta, M. Mandal, M. Babu and
D. Chakraborty, J. Organomet. Chem., 2015, 781, 23–34.
19 A. Jakab, Z. Dalicsek, T. Holczbauer, A. Hamza, I. Pápai,
Z. Finta, G. Timári and T. Soós, Eur. J. Org. Chem., 2015,
60–66.
20 L. Nattmann, R. Saeb, N. Nöthling and J. Cornella, Nat.
Catal., 2020, 3, 6–13.
21 V. Tran, Z.-Q. Li, O. Apolinar, J. Derosa, S. Wisniewski,
M. V. Joannou, M. Eastgate and K. M. Engle, Angew. Chem.,
2020, 59, 7409–7413.
There are no conflicts to declare.
Acknowledgements
The authors thank the Chemical Analysis Center of University
of Tsukuba for the measurements of NMR spectra and elemen-
tal analysis, and single crystal X-ray structure analysis. This
study was supported by Grant-in-Aid for Scientific Research
(17K05973, 17H03063) from JSPS.
22 R. Sato, T. Kanbara and J. Kuwabara, Organometallics, 2020,
39, 235–238.
23 A. Weisman, M. Gozin, H. B. Kraatz and D. Milstein, Inorg.
Chem., 1996, 35, 1792–1797.
24 Y. Tan and J. F. Hartwig, J. Am. Chem. Soc., 2011, 133,
3308–3311.
Notes and references
1 C. C. C. Johansson Seechurn, M. O. Kitching, T. J. Colacot
and V. Snieckus, Angew. Chem., Int. Ed., 2012, 51, 5062– 25 J. G. Verkade, Coord. Chem. Rev., 1972, 9, 1–106.
5085.
26 Y. Hayashi, K. Isobe, Y. Nakamura and S. Okeya,
J. Organomet. Chem., 1986, 310, 127–134.
27 E. A. Mitchell, P. G. Jessop and M. C. Baird,
Organometallics, 2009, 28, 6732–6738.
28 P. Vermeeren, X. Sun and F. M. Bickelhaupt, Sci. Rep., 2018,
8, 10729.
2 H. Li, C. C. C. Johansson Seechurn and T. J. Colacot, ACS
Catal., 2012, 2, 1147–1164.
3 L. C. Campeau, D. R. Stuart and K. Fagnou, Aldrichimica
Acta, 2007, 40, 35–41.
4 Applied Cross-Coupling Reactions. Lecture Notes in Chemistry,
ed. Y. Nishihara, Springer, Berlin, Heidelberg, 2013, vol. 80. 29 L. P. Wolters, W. J. Van Zeist and F. M. Bickelhaupt, Chem.
5 K. H. Shaughnessy, Isr. J. Chem., 2020, 60, 180–194. – Eur. J., 2014, 20, 11370–11381.
6 C. J. O’Brien, E. A. B. Kantchev, C. Valente, N. Hadei, 30 N. Pálinkás, L. Kollár and T. Kégl, Dalton Trans., 2017, 46,
G. A. Chass, A. Lough, A. C. Hopkinson and M. G. Organ,
Chem. – Eur. J., 2006, 12, 4743–4748.
15789–15802.
31 A. Ariafard and Z. Lin, Organometallics, 2006, 25, 4030–
7 M. S. Viciu, R. F. Germaneau, O. Navarro-Fernandez,
4033.
E. D. Stevens and S. P. Nolan, Organometallics, 2002, 21, 32 A. Diefenbach and F. M. Bickelhaupt, J. Phys. Chem. A,
5470–5472. 2004, 108, 8460–8466.
8 D. P. Hruszkewycz, J. Wu, N. Hazari and C. D. Incarvito, 33 X. De An and S. Yu, Org. Lett., 2015, 17, 5064–5067.
J. Am. Chem. Soc., 2011, 133, 3280–3283.
9 M. R. Biscoe, B. P. Fors and S. L. Buchwald, J. Am. Chem.
Soc., 2008, 130, 6686–6687.
10 F. Ozawa, A. Kubo and T. Hayashi, Chem. Lett., 1992, 21,
2177–2180.
34 Y. Li, J. Wang, M. Huang, Z. Wang, Y. Wu and Y. Wu, J. Org.
Chem., 2014, 79, 2890–2897.
35 S. I. Gorelsky, D. Lapointe and K. Fagnou, J. Org. Chem.,
2012, 77, 658–668.
36 G. A. Molander, S. L. J. Trice and S. M. Kennedy, J. Org.
Chem., 2012, 77, 8678–8688.
37 D. Zhao, W. Wang, F. Yang, J. Lan, L. Yang,
G. Gao and J. You, Angew. Chem., Int. Ed., 2009, 48, 3296–
3300.
11 Z. Bao, W. K. Chan and L. Yu, J. Am. Chem. Soc., 1995, 117,
12426–12435.
12 C. S. Wei, G. H. M. Davies, O. Soltani, J. Albrecht, Q. Gao,
C. Pathirana, Y. Hsiao, S. Tummala and M. D. Eastgate,
Angew. Chem., Int. Ed., 2013, 52, 5822–5826.
13 J. Kuwabara, M. Sakai, Q. Zhang and T. Kanbara, Org.
Chem. Front., 2015, 2, 520–525.
38 T. Iwai, S. Konishi, T. Miyazaki, S. Kawamorita,
N. Yokokawa, H. Ohmiya and M. Sawamura, ACS Catal.,
2015, 5, 7254–7264.
14 S. Fantasia and S. P. Nolan, Chem. – Eur. J., 2008, 14, 39 X. B. Lan, F. M. Chen, B. B. Ma, D. S. Shen and F. S. Liu,
6987–6993. Organometallics, 2016, 35, 3852–3860.
Dalton Trans.
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