D. Yang et al. / Journal of Catalysis 371 (2019) 236–244
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Table 2
The recycling uses of the PdCl2(MeCN)2-L20 catalytic system in [Bmim]BF4 and [Bmim]NTf2 respectively for methoxycarbony-
lation of phenylacetylene.a
RTIL: [Bmim]BF4
Conv. (%)b
RTIL: [Bmim]NTf2
Conv. (%)b
Run
Sel.
(%)b
B/Lc
Sel.
(%)b
a,b-esters
B/Lc
a,b-esters
1
2
3
4
5
6
7
90
89
89
85
84
73
Undone
100
100
100
100
100
100
–
95/5
95/5
91/9
90/10
91/9
90/10
–
93
92
93
91
90
91
88
100
100
100
100
100
100
100
95/5
95/5
93/7
91/9
93/7
91/9
90/10
a
PdCl2(MeCN)2 0.05 mmol (Pd 2 mol%), P/Pd = 6 M ratio, phenylacetylene 2.5 mmol, H2O 2 mmol, CO 3.0 MPa, MeOH 1 mL,
RTIL 3.0 mL, temp. 110 °C, reaction time 5 h.
b
Determined by GC and GC-Mass.
B/L = the ratio of branched methyl 2-phenylacrylate to the linear methyl cinnamate.
c
optical emission spectrometer (ICP-OES) on an Optima 8300
instrument (PE Corporation).
1-(2,5-Bis(diphenylphosphanyl)thiophen-30-yl)-2-
(diphenylphosphanyl)-3-methyl-1H-imidazol-3-ium
trifluoromethanesulfonate (L20)
A solution of L2 (0.70 g, 1 mmol) in dry CH2Cl2 (30 mL) was
cooled to ꢁ78 °C, then methyl-trifluoromethanesulfonate (0.18 g,
1.1 mmol) was added dropwise. The solution was stirred overnight
with the reaction temperature increasing to ambient. After evapo-
ration of the solvent under vacuum, the residue was recrystallized
from CH2Cl2/Et2O to yield L20 as white solids (0.71 g, 82%). 1H NMR
(d, ppm, CD2Cl2): 7.54–7.26 (m, 30H, 6C6H5), 7.11 (s, 1H, NCH), 7.02
(t, 2H, SCHCH, J = 10 Hz), 3.32 (s, 3H, CH3). 31P NMR (d, ppm, CD3-
COCD3): ꢁ20.49 to ꢁ20.61 (dd, P2Ph2, J1 = 13.04 Hz, J2 = 6.52 Hz),
ꢁ30.56 to ꢁ30.80 (ABd, P3Ph2, J1 = 26.08 Hz, J2 = 13.04 Hz),
ꢁ31.54 to ꢁ31.74 (ABd, P1Ph2, J1 = 20.68 Hz, J2 = 6.52 Hz). CHN-
elemental analysis (%, found): C 62.47, H 4.65, N 3.26 (calcd., C
62.35, H 4.19 N 3.23).
3.2. Synthesis
2-(Diphenylphosphanyl)-1-(2-(diphenylphosphanyl)thiophen-30-yl)-
1H-imidazole (L1)
L1 was prepared according to the procedures reported by us
[25] with some modifications.
Under N2 atmosphere, a solution of 1-(thiophen-30-yl)-1H-
imidazole (1.50 g, 10 mmol) in dry CH2Cl2 (100 mL) was cooled
to ꢁ78 °C, then N, N, N0, N0-tetramethylethylenediamine (TMEDA,
3.0 mL, 20 mmol) and n-BuLi (2.5 M in hexane, 8.8 mL, 22 mmol)
were added dropwise. After stirring vigorously for 1 h, the obtained
reaction mixture was added with chlorodiphenylphosphine (PPh2-
Cl, 4.60 g, 22 mmol) dropwise. The resultant mixture was stirred
for another 1 h then warmed up to room temperature. After
quenching the excess n-BuLi with deionized water (100 mL), the
mixture was extracted with ethyl acetate (3 ꢂ 80 mL) and the com-
bined organic phase was concentrated by vacuum. The residue was
purified by column chromatography on silica gel, using pure
dichloromethane as eluant, to give product of L1 as a yellow solid
(2.38 g, yield of 48%). The sample suitable for X-ray diffraction
analysis was obtained by slow volatilization of an ethyl acetate
solution containing L1. 1H NMR (d, ppm, CD3COCD3): 7.68 (s, 1H,
SCH), 7.44 (s, 1H, SCCH), 7.42–7.32 (m, 20H, 4C6H5), 7.29 (s, 1H,
2NCH), 6.99 (s, 1H, NCCH). 31P NMR (d, ppm, CD3COCD3): ꢁ29.12
(d, J = 9.78 Hz, P1Ph2), ꢁ29.82 (d, J = 8.15 Hz, P2Ph2). CHN-
elemental analysis (%, found): C 70.96, H 5.65, N 5.36 (calcd., C
71.80, H 4.67, N 5.40).
1-(2,5-Bis(diphenylphosphanyl)thiophen-30-yl)-2,5-bis
(diphenylphosphanyl)-1H-imidazole (L3)
L3 was obtained with the yield of 26% according to the prepara-
tion procedures for L2. 1H NMR (d, ppm, CD3COCD3): 7.45–7.12 (m,
40H, 6C6H5), 7.19–7.15(m, 1H, SCCH), 7.14 ꢃ 7.11 (m, 1H, 1NCH).
31P NMR (d, ppm, CD3COCD3): ꢁ17.73 (s, P4Ph2), ꢁ27.58 (t, P1Ph2,
J = 21.19 Hz), ꢁ28.04 to ꢁ28.22 (ABd, P3Ph2, J1 = 21.19 Hz,
J2 = 8.15 Hz), ꢁ33.70 to ꢁ33.88 (ABd, P2Ph2, J1 = 21.19 Hz,
J2 = 8.15 Hz). CHN-elemental analysis (%, found): C 74.52, H 5.23,
N 2.91 (calcd., C 74.48, H 4.77, N 3.16).
1-(2,5-Bis(diphenylphosphanyl)thiophen-30-yl)-2,5-bis
(diphenylphosphanyl)-3-methyl-1H-imidazol-3-ium
trifluoromethanesulfonate (L30)
1-(2,5-Bis(diphenylphosphanyl)thiophen-30-yl)-2-
(diphenylphosphanyl)-1H-imidazole (L2)
L30 was obtained with the yield of 79% after the quaternization
of L3 by MeOTf according to the preparation procedures for L20. 1H
NMR (d, ppm, CD3COCD3) 7.54–7.17 (m, 40H, 6C6H5), 7.16–7.14 (m,
1H, SCCH), 7.13–7.10 (m, 1H, 1NCH), 3.48 (s, 3H, CH3). 31P NMR (d,
ppm, CD3COCD3): ꢁ16.77 (s, P4Ph2), ꢁ19.23 to ꢁ19.36 (ABd, P2Ph2,
J1 = 14.67 Hz, J1 = 6.52 Hz), ꢁ28.55 to ꢁ28.81 (ABd, P3Ph2,
J1 = 27.71 Hz, J2 = 14.67 Hz), ꢁ32.48 to ꢁ32.74 (dd, P1Ph2,
J1 = 27.71 Hz, J2 = 9.78 Hz). CHN-elemental analysis (%, found): C
64.04, H 4.30, N 2.39 (calcd., C 65.14, H 4.32, N 2.67).
L2 was obtained with the yield of 39% according to the prepara-
tion procedures for L1. 1H NMR (d, ppm, CD3COCD3): 7.67–7.21 (m,
30H, 6C6H5), 7.17 (t, 2H, SCHCH, J = 10 Hz), 6.90 (s, 1H, NCH). 31P
NMR (d, ppm, CD3COCD3): ꢁ28.80 to ꢁ28.97 (ABd, P3Ph2,
J1 = 19.56 Hz, J2 = 8.15 Hz), ꢁ29.27 (t, P1Ph2, J1 = 19.56 Hz),
ꢁ34.35 to ꢁ34.50 (ABd, P2Ph2, J1 = 17.93 Hz, J2 = 6.52 Hz). CHN-
elemental analysis (%, found): C 73.43, H 5.05, N 3.39 (calcd., C
73.49, H 4.73, N 3.99).