H. Mei et al. / Applied Catalysis A: General 475 (2014) 40–47
43
Table 1
3
42.4 eV and 337.1 eV, respectively, and were similar to the bind-
Optimization of the aminocarbonylation reaction using heterogeneous Pd catalysts.a
II
ing energies of Pd @Y [35] (Fig. 2b). Note, however, that there
was a minor chemical shift of 0.5 eV for PdCl (phen)@Y, which we
attribute to the difference in coordination environments between
the Pd confined in the cages and of the Pd @Y construct.
The UV–vis result is consistent with FTIR spectra of the cata-
lyst (FTIR; see Fig. S1 in Supporting information). The N2 sorption
isotherm of PdCl (phen)@Y displays the type I-like behavior of
microporous materials, which indicates that the zeolite framework
was not destroyed during encapsulation (N sorption isotherm; see
O
2
I
H
N
Pd cat.
base, DMAc
N
II
+
+ CO
1
2
3
.
2
Entry
Base
Solvent
T
(
PCO
(MPa)
Yieldb
(%)
TOFc
◦
−1
C)
(h
)
2
Fig. S2 in Supporting information). This result agrees with XRD
patterns of the sample, which corresponds well to that of highly
crystalline Y zeolite (XRD; see Fig. S3 in Supporting information).
1
2
3
4
None
DMAc
DMAc
DMAc
DMAc
DMAc
NMP
Toluene
DMAc
DMAc
DMAc
DMAc
DMAc
DMAc
DMAc
130
130
130
130
130
130
130
85
110
130
130
130
130
130
2
2
2
2
2
2
2
2
–
–
84
Pyridine
K2CO3
Et3N
59
96
97
88
96
49
10
63
28
51
93
94
93
137
139
126
137
70
14
90
40
73
The Pd content of PdCl (phen)@Y was 2.1 wt.%, as measured by AAS.
d
2
5
6
7
8
9
1
1
Et N
3
Considerable loss of surface area and pore volume was observed for
Et N
3
the PdCl (phen)@Y construct, which is direct evidence supporting
Et3N
2
e
f
Et3N
Et3N
Et3N
Et3N
Et3N
the presence of Pd complexes generally occurring inside the zeolite
cages rather than on the external surface (AAS, BET and pore vol-
ume; see Table S1 in Supporting information). Thermal behaviors
of the prepared [PdCl (phen)] and PdCl (phen)@Y were studied by
2
0
1
0.5
1.0
2
2
2
g
h
i
12
13
155
134
133
2
2
◦
Et N
TG and DTA in the air at 200–800 C (TG and DTA; see Fig. S4 in
Supporting information). The obvious enhancement to the ther-
mal stability of the Pd complex caused by encapsulation, verified
through a comparative thermal analysis, providing another bit of
3
14
Et3N
a
Reaction conditions: PdCl2(phen)@Y (0.7 mol%), PhI (10 mmol), Et2NH
(
20 mmol), Et3N (30 mmol), solvent (15 ml), 1 h.
b
GC yield.
strong evidence in support of the inclusion of [PdCl (phen)] in Y
c
2
TOF (moles of N,N-diethylbenzamide per mol of palladium per hour).
Et3N (15 mmol).
Selectivity for N,N-diethylbenzamide is 23%.
Selectivity for N,N-diethylbenzamide is 78%.
PdCl2(phen)@Y (0.2 mol%), 3 h.
Pd/C (0.7 mol%).
zeolite.
d
e
f
3.2. Catalytic activity
g
h
i
Carbonylation of aryl iodides with amines usually gives rise to
Pd/Y (0.7 mol%).
mixture of mono- and dicarbonylated products [36]. Chemoselec-
tivity of the reaction is greatly dependent on the reaction conditions
(
N,N-diethyl-2-oxo-2-phenylacetamide) which was confirmed by
[
37]. Therefore, in the first stage of our study, the aminocarbony-
GC–MS analysis became a significant side reaction. This result is
consistent with literatures [40–42] in which reporters claimed that
low temperature (60–80 C) favored double carbonylation reac-
lation of iodobenzene with diethylamine was selected as a model
reaction, and the influence of various reaction parameters such as
bases, solvents, temperature, pressure and Pd loadings were stud-
ied (Table 1).
◦
◦
tions of aryl iodide, while up to 100 C the main products are
the amides. The influence of CO pressure was also studied and
the results demonstrated that increasing pressure obviously ben-
efited the aminocarbonylation rates with improved yield and TOF
of amides (Table 1, entries 4, 10 and 11). Encouraged by the high
reactivity of this palladium-catalyzed system, we tried to employ
a low catalyst loading. On performing the reaction with 0.2 mol%
Previous studies had showed that bases and solvents had
remarkable influences on the reactivity of the aminocarbonylation
reaction [26]. To confirm the influence of bases in reaction progress,
initially reaction was tried in absence of base, but no desired
amides product was observed that indicates vital role of base on
the reaction (Table 1, entry 1). The widely used bases for aminocar-
bonylation including pyridine, K CO and Et N were examined and
−
1
PdCl (phen)@Y resulted in 93% yield of amide and TOF of 155 h
2
2
3
3
after a prolonged reaction time to 3 h (Table 1, entry 12). Other het-
erogeneous catalysts like Pd/C (wt. 5%) and Pd/Y with the same Pd
loadings were also investigated for the aminocarbonylation reac-
tion and they also resulted in high yields of the desired product
with 94% and 93%, respectively (Table 1, entries 13,14).
the results revealed that Et N or K CO were both suitable for this
3
2
3
reaction given 97% and 96% yields of the desired amide, respectively
in comparing with poor activity of pyridine (Table 1, entries 2–4).
Although K CO and Et N performed almost equally well, consid-
2
3
3
ering of the economy of organic amines over potassium salts, Et N
3
was chosen for further optimization. Notably, lowering the amount
of Et N deteriorated the reaction rate and resulted in only 88% yield
3.3. Substrate scope
3
of the desired amide (Table 1, entry 5). Initial attempts to carry out
the reaction in DMF as solvent resulted in a mixture of amides due
to release of dimethylamine from the solvent [38,39]. Therefore,
DMAc was used as a solvent and afforded unexpected fine result
Furthermore, we investigated the activity of PdCl (phen)@Y for
various substrates in aminocarbonylation and the results are sum-
marized in Table 2.
2
(
Table 1, entry 4). Although other polar aprotic solvents such as N-
methylpyrrolidone (NMP) demonstrated similarly superior result
Table 1, entry 6), DMAc was chosen as a solvent owing to its
In general, various substituted aryl iodides and amines were
well tolerated to afford the desired amides 4a-n in good to excel-
lent yields. In all cases, we observed that aryl iodides consumed
completely giving the desired amide products and ˛-ketoamide as
the main byproducts. With diethylamine 2 as the amine, p-OMe, p-
Me, o-Me and p-COMe substituted aryl iodides afforded high yields
(93%, 90.0%, 90% and 88%, respectively) (Table 2, entries 1, 2, 4 and
5), while slightly lower yields were obtained with m-Me, p-Cl and
p-NO2 substituted aryl iodides (84%, 83% and 75%, respectively)
(Table 2, entries 3, 6 and 7). It is worth noting that the TOF reached
(
lower toxicity as a green solvent. On the contrary, non-polar solvent
like toluene furnished lower yield of the desired product (Table 1,
entry 7).
The effect of temperature on reactions was examined at
◦
8
5–130 C (Table 1, entries 4, 8 and 9). Increasing the temperature
favored selectivity to the desired amides and afforded satisfac-
tory yields without significant dehalogenation. However, in lower
temperature the double carbonylation yielding the ˛-ketoamide
−
1
103 h in the case of p-iodoanisole.