S.J. Sabounchei et al. / Journal of Molecular Catalysis A: Chemical 383–384 (2014) 249–259
257
Table 9
Catalytic activity of some palladacycles complexes that promote the Heck coupling between olefins and aryl halides.
Entry
Ar-X
R
CH CH2
[Pd] catalyst
Mol%
Conditions
Yield (%)
Ref.
NaOAc, DMAa, under nitrogen, 175 ◦C, 1 h
NaOAc, DMA, under nitrogen, 175 ◦C, 1 h
LDAb (TBAB), H2O, under air, 100 ◦C, 4.5 h
K2CO3, MeOH, under nitrogen, 80 ◦C, 20 h
Cs2CO3, DMF, [nBu4N]Br, under air, 140 ◦C, 4 h
NaOAc, NMP, under nitrogen, 140 ◦C, 24 h
KF (TBAB), DMA, under argon, 140 ◦C, 30 h
KF (TBAB), DMA, under argon, 140 ◦C, 30 h
K2CO3, NMP, under air, 130 ◦C, 24 h
100
100
99
92
66
60
76
99
76
85
[70]
[70]
[71]
[74a]
[74b]
[75]
[76]
[76]
ˆ
1
2
3
4
5
6
7
8
9
Ph-Br
R = Ph
R = Ph
R = Ph
R = CO2-t-Bu
R = Ph
[(CC)PdCl2]
0.5
0.5
0.5
0.2
0.001
0.001
0.001
0.001
0.001
0.001
ˆ
4-COMe-Ph-Br
4-COMe-Ph-Br
4-COMe-Ph-Br
4-Me-Ph-Br
Ph-Br
Ph-Br
4-COMe-Ph-Br
Ph-Br
[(CC)PdCl2]
ˆ
[(NN)PdCl2]
ˆ
[(PS)PdCl2]
ˆ
[(PN)PdCl2]
ˆ
R = Ph
[(CN)Pd(PPh3)Cl]
ˆ
R = CO2-Me
R = CO2-t-Bu
R = CO2-Et
R = CO2-Et
[(CC)PdI2]
ˆ
[(CC)PdI2]
ˆ
[(PC)PdCl2]
This work
This work
10
Ph-Br
K2CO3, NMP, under air, 130 ◦C, 24 h
ˆ
[(CC)PdCl2]
a
Dimethylacetamide.
Lithium diisopropylamide.
b
dioxane as solvent at 80 ◦C). By comparison, we can see that pal-
good yields in lower catalyst loading under air in comparison with
similar systems (Table 8, entries 1–4 and 7–8). Also, high reactivity
with aryl chloride with these palladacycle relative to similar Pd
reported has been shown (Table 8, entries 2, 6 and 8). Other factors
a significant influence on the catalytic performance.
reaction mixture was then cooled to room temperature. The com-
bined organic extracts were washed with brine and dried over CaCl2
and Na2SO4. The liquid residues were purified by silica gel column
chromatography (n-hexane:EtOAc, 80:20) and the solid residues
were purified by re-crystallization from ethanol and water.
3.2.1. Characterization of Suzuki coupling products [34a]
3.2.1.1. 4-Ethyl-biphenyl (3a). M.p. 34–35 ◦C. 1H NMR (ppm):
ı = 7.43–7.48 (m, phenyl, 4H), 7.18–7.32 (m, phenyl, 5H), 2.59 (q,
CH2, 3J = 8.5 Hz, 2H), 1.24 (t, CH3, 3J = 8.0 Hz, 3H). 13C NMR (ppm):
ı = 138.4, 136.5, 133.7, 129.3, 128.3, 127.7, 127.9, 127.8, 32.4 (s,
Also, the comparison of the conditions of palladacycle
1
tions are presented in Table 9. Of note is that the satisfactory
results for the coupling of olefins with aryl halides were
obtained with using of (L)PdX2 precatalysts such as diylidene
palladium bromide [70], di(2-pyridyl)methylamine[PdCl2]
3.2.1.2. 4-Carboxaldehyde-4ꢀ-ethyl-biphenyl (3b). M.p. 81–82 ◦C. IR
(KBr, cm−1): ꢀ = 3024, 2965, 2936, 1682 (C O), 1605, 881, 835, 808.
1H NMR (ppm): ı = 10.04 (s, CHO, 1H), 7.24–7.59 (m, phenyl, 8H),
2.68 (q, CH2, 3J = 7.9 Hz, 2H), 1.30 (t, CH3, 3J = 7.4 Hz, 3H). 13C NMR
(ppm): ı = 191.8 (s, C O), 147.0, 144.7, 136.8, 134.8, 130.1, 128.4,
127.3, 127.1.
[71],
[PdCl2{P(OCMe2CMe2O)OCMe2CMe2NH2}]
acetylferrocenyloxime palladacycle [75]
[{(-OC10H6(-S)C10H6O-)P(O)-P,S}PdCl2]
[74a],
[74b],
and
{1,1ꢀ-(1,1ꢀ-
Binaphthyl)-3,3ꢀ-dimethyldibenzimidazolium}[PdI2] [76]. From
Table 9, it is appear that palladacycles 1 and 2 (entries 9–10)
showed good catalytic activities for the Heck coupling reaction in
the presence of 0.001 mol% catalysts compared with the others
(0.2–0.5 mol%) (entries 1–4) and also working under air atmo-
are similar to those of related bidentate complexes (Table 9, entries
5–8). From an industrial view point, the low catalyst loading and
stable phosphine ligands provide an indisputable advantage than
the other catalytic systems [24b,77–79].
3.2.1.3. 4-Nitro-4ꢀ-ethyl-biphenyl (3c). M.p. 82–83 ◦C. 1H NMR
(ppm): ı = 7.28–8.34 (m, phenyl, 8H), 2.70 (q, CH2, 3J = 7.5 Hz, 2H),
1.30 (t, CH3, 3J = 7.4 Hz, 3H). 13C NMR (ppm): ı = 149.9, 148.6, 141.3,
128.8, 127.6, 127.4, 126.9, 124.1, 28.69 (s, CH2), 15.43 (s, CH3).
3.2.1.4. 4-Methyl-4ꢀ-ethyl-biphenyl (3d). M.p. 59–61 ◦C. 1H NMR
(ppm): ı = 7.21–7.82 (m, phenyl, 8H), 2.71 (q, CH2, 3J = 7.9 Hz, 2H),
2.45 (s, CH3, 3H), 1.30 (t, CH3 (Ethyl), 3J = 8.1 Hz, 3H). 13C NMR
(ppm): ı = 143.0, 138.4, 138.2, 136.6, 129.4, 128.2, 126.85, 126.80,
28.4 (s, CH2), 21.0 (s, CH3), 15.6 (s, CH3 (Ethyl)).
3. Experimental
3.2.1.5. 4-Acetyl-4ꢀ-ethyl-biphenyl (3e). IR (KBr, cm−1): ꢀ = 3060,
3019, 2976, 1655 (C O), 1611, 815, 789, 751. 1H NMR (ppm):
ı = 7.25–8.01 (m, phenyl, 8H), 2.59 (q, CH2, 3J = 7.3 Hz, 2H), 2.51 (s,
CH3, 3H), 1.24 (t, CH3, 3J = 8.0 Hz, 3H). 13C NMR (ppm): ␦ = 190.8 (s,
3.1. Physical measurements and materials
The required chemicals were of analytical reagent grade and
were purchased from Merck and Aldrich. Melting points were mea-
sured on a SMPI apparatus and are reported without correction.
NMR Spectra were recorded on a 90 MHz Jeol spectrometer (1H at
89.60 MHz) or 400 MHz Bruker spectrometer (13C at 100.62 MHz)
in CDCl3 as solvent at 25 ◦C. The splitting of proton resonances in
the 1H and 13C NMR spectra is shown as, s = singlet, d = doublet,
t = triplet and m = multiplet.
C
O), 140.9, 138.4, 135.7, 133.7, 129.3, 128.3, 127.8, 127.7, 33.4 (s,
CH2), 30.3 (s, CH3), 15.9 (s, CH3).
3.2.1.6. 1-(4-ethylphenyl)naphthalene (3f). 1H NMR (ppm):
ı = 7.11–8.50 (m, phenyl, 11H), 2.83 (q, CH2, 3J = 7.6 Hz, 2H),
1.45 (t, CH3, 3J = 7.3 Hz, 3H). 13C NMR (ppm): ı = 143.1, 140.2,
137.9, 133.7, 131.6, 129.9, 128.2, 127.7, 127.3, 126.8, 126.0, 125.8,
125.6, 125.3, 28.6 (s, CH2), 15.5 (s, CH3).
3.2. General procedure for Suzuki cross-coupling reactions
3.2.1.7. 2-(4-Ethylphenyl)thiophene (3g). M.p. 48–49 ◦C. 1H NMR
(ppm): ı = 6.91–7.80 (m, phenyl, 7H), 2.62 (q, CH2, 3J = 8.1 Hz, 2H),
1.16 (t, CH3, 3J = 7.2 Hz, 3H). 13C NMR (ppm): ı = 131.8, 128.3, 128.2,
127.8, 126.8, 125.9, 124.2, 122.5, 28.5 (s, CH2), 15.5 (s, CH3).
A mixture of an aryl halide (0.75 mmol), phenyl boronic acid
(1 mmol), palladacycle complex (0.001 mol%), Cs2CO3 (1.5 mmol),
and DMF (2 ml) was heated to 110 ◦C for specified time (see Table 3).
The reactions were monitored by thin-layer chromatography. The