Organic ligand-free carbonylation reactions with unsupported bulk Pd as catalyst

Article abstract of DOI:10.1039/c8gc00740c

Herein, surprising results for bulk Pd-catalyzed carbonylation reactions are presented. Three types of carbonylation reactions can be realized efficiently under organic ligand-free conditions, namely, hydroaminocarbonylation of olefins, aminocarbonylation of aryl iodides and oxidative carbonylation of amines, which almost cover all the known mechanisms in carbonylation reactions. Notably, the bulk Pd catalyst system exhibited better catalytic activity than the classical homogeneous PdCl₂/(2-OMePh)₃P catalyst system. This study will create a momentous and new field of green carbonylation reactions.

Full text of DOI:10.1039/c8gc00740c

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COMMUNICATION
Organic Ligand Free Carbonylation Reactions with Unsupported
Bulk Pd as Catalyst
Shujuan Liu,[a,b] Hongli Wang,[a]* Xingchao Dai,[a,b] and Feng Shi[a]*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
and is emerging as especially useful and versatile tools for organic
synthesis.[23, 24] It is widely used for converting various chemicals into a
diverse set of value-added and important carbonyl compounds, such as
aldehydes, ketones, esters, amides and others, which have been widely
applied in production of commodity chemicals, pharmaceuticals, and
agrochemicals. However, the development of general and versatile
Here, surprising results are presented in bulk Pd catalyzed
carbonylation reactions. Three types of carbonylation reactions
can be realized efficiently under organic ligand-free conditions, i.e.,
hydroaminocarbonylation of olefins, aminocarbonylation of aryl
iodides and oxidative carbonylation of amines, which almost
covers all the known mechanisms in carbonylation reactions.
Noteworthy, the bulk Pd catalyst system exhibited better catalytic
activity than the classical homogeneous PdCl2/(2-OMePh)3P
catalyst system. This study will create a momentous and new field
in green carbonylation reactions.
heterogeneous catalyst for carbonylation reactions constitutes
significant challenge.
a
Based on the above discussions, we envisaged that bulk palladium
self-supported nano-Pd would be useful for the establishment of
general carbonylation reactions. Exactly, the first example of general
and versatile organic ligand-free carbonylation reactions that include
mainly three types of carbonylation reactions enabled by bulk
palladium particle catalyst is realized (Scheme 1).
In general, molecular catalysts have better catalytic activity and
selectivity than heterogeneous catalysts. However, the difficulties in
catalysts separation and recycling hinder their applications in industry.
Heterogeneous catalysts are widely used in industry because it could be
easily separated and recovered from reaction medium after reaction.[1-2]
For heterogeneous catalysts, the size of metal particles is one of the
most important factors in determining the catalytic performance of the
catalyst.[3-5] Given that low-coordination, unsaturated atoms usually
function as catalytically active sites and the catalytic activity of
heterogeneous catalyst normally increased with the decreasing of the
size of the metal particles. Recent results demonstrated that nano
This work:
O
CO/KI/R1R2NH
H3PO4
(a)
H-Pd-X
R
NR1R2
R
Pd
Pd
Pd
Pd
Pd
Pd
Pd
O
CO/KI/R1R2NH
K2HPO4
Ar-I
Bulk Pd
Ar-Pd-I
Ar
NR1R2
(b)
(c)
Pd
Pd
Pd
[5-19]
[4, 10, 11]
catalyst, subnano catalyst
and single atom catalyst
have
Self-supported nano-Pd
better catalytic activity than bulk catalyst. In contrast, the potential of
bulk metal as the catalyst may be tremendous and is worthy of
investigation as the real structure of bulk metal catalyst may be
composed by bulk particle body, and the self-supported nano-particles
on the surface, as the surface of the bulk catalyst is usually crude.
Therefore, the bulk metal particles might possess multi-metallic
catalytic centers on the surface of the catalyst, in which the metal itself
as support might exhibits unimaginable catalytic performance.
O
CO/KI/R1R2NH
O2
R1R2
N
NR1R2
PdXy
Scheme 1. The carbonylation reactions enabled by self-supported nano-Pd.
Initially, the palladium catalyst with different sizes including 148 nm
610 nm, and 1540 nm Pd powders (Alfa Aesar, item No. 043715, 000776,
and 012068) were used in hydroaminocarbonylation reaction,[25-29] and
the size of the palladium particles was determined by SEM images. The
palladium catalysts are denoted as Pd-148, Pd-610, and Pd-1540,
respectively. Following, the hydroaminocarbonylation reaction of
styrene (1a) and aniline (2a) was used to optimize the reaction
conditions with Pd-148 as catalyst, and the impact of different acidic
additives including, Brønsted acids and Lewis acids on the reaction was
investigated first (Table 1). Clearly, with the increase of acid strength of
the acid additives, the conversion of aniline was improved, and a 91%
conversion of aniline with 98% products selectivity was achieved when
H3PO4 was used. However, the conversion of aniline was slightly
decreased when the acid strength of the additives was further
Carbonylation reaction is currently recognized as one of the most
important industrial applications in the area of homogeneous catalysis
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increased. The reason might be attributed to the fact that the key
h
-1 are obtained for Pd-610. Noteworthy, it has been found that the TOF
palladium hydride species was difficult to form when the acid strength numbers of Pd-610 are ~23 times higher than classical homogeneous
was too strong. Lewis acids such as Sc(OTf)3 and Yb(OTf)3•XH2O have PdCl2/(2-OMePh)3P and Pd(acac)2/L catalyst systems. Even if don't take
also been examined under the same condition, and no better results the dispersity into consideration, the homogeneous and heterogeneous
were obtained. These results showed that H3PO4 has a suitable acid system are similar. Therefore, the self-supported nano-Pd is indeed has
strength for the formation of palladium hydride species which was a particular catalytic performance. This will give enlightenment for the
considered to be a key reactive species in these processes for initiating application of bulk metal as a catalyst in catalytic transformations.
the hydroaminocarbonylation.
Table 2. The comparison of TON and TOF between homogeneous and heterogeneous
carbonylation reaction of styrene with aniline.a
Table 1. Effect of acids for the carbonylation of styrene with aniline. a
O
H
[Cat.] H3PO4
KI, 130oC, CO
N
Ph NH2
Ph
Ph
Ph
Ph
Ph
N
H
O
3a
4a
linear
1a
2a
branched
Based on
Conv.
/%[b]
Sel./%[
Based on all of Pd
Entry
Cat.
Acid
[I]
b/l
dispersion
b]
dispersion
(%)
Con.b
(%)
Entry
Pd
TOF(h-
1
1
2
3
4
5
6
7
8
9
Pd-148
Pd-148
Pd-148
Pd-148
Pd-148
Pd-148
Pd-148
Pd-148
Pd-148
2-naphthol
B(OH)3
HOAc
KI
KI
KI
KI
KI
KI
KI
KI
KI
TON
TOF(h-1
)
TON
--
--
--
)
4
>99
--
71:29
--
1
2
Pd-148
Pd-610
Pd-1580
Pd-610
6.628
3.897
4.372
3.897
91
95
16
11
96
101
17
8.0
8.4
1.4
4.9
1455
2584
388
121.3
215.3
32.3
--
H3PO4
91
30
84
59
44
67
98
92
97
89
90
94
46:54
40:60
51:49
28:72
54:46
43:57
54:46
3
TsOH
4c
58
1496
124.7
HCl
PdCl2/(2-
OMePh)P
5d
6e
--
--
95
99
19
9.5
9.9
---
---
---
---
H2SO4
Pd(acac)2
/L
CF3SO3H
Sc(OTf)3
198
aReaction conditions: 1a (4.0 mmol), 2a (1.0 mmol), Pd (1.0 mg), H3PO4 (5.0
mol%), KI (5.0 mol%), CO (40 bar), dioxane (2.0 mL), 130 oC, 12 h. bDetermined by
GC-MS. c 2a (5.0 mmol).d reference 30. e reference 27.
Yb(OTf)3-
XH2O
10
11
Pd-148
Pd-148
KI
KI
16
41
--
--
trace
--
Subsequently, the effects of other parameters such as temperature,
iodide compounds, solvent, pressure of the CO, amounts of H3PO4 and
KI were also investigated. However, no improvement was observed
(Table S2-7). Finally, the reducing of styrene to 2.0 equiv., had a
negligible impact on the reaction (Table S2).
aReaction conditions: 1a (4.0 mmol), 2a (1.0 mmol), Pd-148 (1.0 mg), acid additive
(5.0 mol%), KI (5.0 mol%), CO (40 bar), dioxane (2.0 mL), 130 oC, 12 h.
bDetermined by GC-MS.
Furthermore, the catalytic performance of palladium with different
sizes including Pd-148, Pd-610 and Pd-1540 were studied in details
under the identical reaction conditions (Fig. 1 and Table S1). Clearly,
91% conversion of aniline with >99% selectivity was observed if Pd-148
was used as the catalyst. With the increasing of palladium sizes, the
catalytic performance was slightly improved and 95% conversion of
aniline with 98% selectivity (b/l = 35:65) was achieved when Pd-610 was
employed as the catalyst. However, the conversion of aniline was
decreased if the palladium size was further increased. The conversion
was only 16% and selectivity was >99% if Pd-1540 was employed.
With the optimized conditions in hand, the scope of this bulk Pd
catalyzed hydroaminocarbonylation reaction was investigated (Table 3).
In general, both electro-donating and -withdrawing substituents on the
benzene ring of aromatic amines were well-tolerated under the current
conditions. Unfortunately, currently it is difficult to modulate the
regioselectivity with this bulk Pd catalyst. With electron-rich methyl-,
tertbutyl-, and methoxy-substituted anilines as starting materials, good
to excellent yields (83–99%) with moderate regioselectivities (b/l = 56 :
44 – 71:29) were achieved (3a-3g, 4a-4g). Electron-deficient anilines
bearing fluoro, chloro and ester groups also proceeded well, affording
their corresponding products in 70-97% yields with moderate
regioselectivities (b/l = 50 : 50 – 62 : 38) (3h-3j, 4h-4j). In addition, the
reaction of 8-aminoquinoline, as an example of heterocyclic substrate,
provided the corresponding product in 91% yield with moderate
regioselectivity (b/l = 60:40) (3k, 4k). No conversion was observed when
aliphatic amine, i.e., hexylamine, was employed as substrate, which
might be ascribed to the competition of the amine with the alkene for
surface sites of Pd. Next, reactions of aniline with different olefins were
examined. It was noted that the electronic nature on the phenyl ring of
the styrene had a strong influence on the reactivity and regioselectivity.
For comparison of the catalytic activities of palladium powder and
homogeneous palladium catalysts, the TON (turnover numbers) and
TOF (turnover frequencies) numbers were shown in Table 2. Firstly, the
Pd dispersions of Pd-148, Pd-610 and Pd-1540 catalyst determined with
H2 titration technique are 6.6%, 3.9%, and 4.4%, respectively (Table 2).
Based on the Pd dispersions of different bulk catalysts, the TON and
TOF of Pd-148, Pd-610 and Pd-1540 are 1455, 2584, 388, and 121, 215,
32 h-1, which are related to the active Pd species. It is clear that the
catalytic activity of the bulk palladium is strongly dependent on the size
of the bulk particles, and that the highest TON of 2584 and TOF of 215
2 | J. Name., 2012, 00, 1-3
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In general, styrenes bearing an electro-withdrawing group on their aryl
In order to test if the active species are palladium leached from the
ring exhibited higher reactivity than electro-donating group. For bulk phase during the reaction, a control reaction was performed. The
example, the reaction of 4-bromostyrene with aniline provided the reaction mixture was filtered after reacted for 3 h and the filtrate was
corresponding product in 99% yield while only 74% yield was obtained allowed to react for another 9 h. Indeed, we found that reaction
with 4-methylstyrene as starting material. It is noteworthy that the stopped without further progressing (Fig. 1). Therefore, the self-
bromo group could survive the reaction conditions, which is useful supported nano-Pd is the real catalyst and no catalytically active
handles for further synthetic elaborations with transition metal catalysis. palladium species is dissolved in the solution. Moreover, the Hg
Furthermore, we turned our attention to more challenging aliphatic poisoning experiment was performed in order to provide further
alkenes. Gratifyingly, allylbenzene and terminal aliphatic alkenes with evidence of the nature of the catalytic system (homogeneous vs.
long chains furnished the desired hydroaminocarbonylation products in heterogeneous). First, the reaction mixture was detected after reacted
excellent yields with ratio of b/l from 50 : 50 to 42 : 58 (3p-3s, 4p-4s). for 3 h and the conversion of aniline was 12%. Then, 550 mg Hg metal
We suppose that the l/b ratio should be decided by several factors, such (275 equiv.) was added into the reaction mixtures and allowed to react
as the electrophilicity of amine and the steric hindrance of Pd-CO- for another 9 h, and the final conversion of aniline was 11%. As control
alkene intermediate. The l/b ratio would be close to 50 : 50 if the reaction, the Hg poisoning experiment of homogeneous Pd catalyst was
electrophilicity of amine is weak, i.e., o-F-aniline, or the steric hindrance performed following the typical operation in ref. 30. First, A mixture of
of Pd-CO-alkene intermediate is lower. In reverse, the more linear styrene (11.0 mmol), aniline (1 mmol), PdCl2 (5 mol% based on aniline),
products would be obtained.
P(2-OMePh)3 (0.12 mmol) and THF 10 mL were added a glass tube
which was placed in an 100 mL autoclave. Then the autoclave was
purged and charged with CO (50 atm). The reaction mixture was stirred
at 125 oC. Then the reaction mixture was detected after being reacted
for 1 h and the conversion of aniline was 45%. Then, 550 mg Hg metal
was added into the reaction mixtures and allowed to further react for
another 1 h, and the final conversion of aniline was 76%. So the Hg
poisoning experiment clearly proved that large excess of Hg didn’t
affect the activity of the homogeneous palladium catalyst system and
the heterogeneous nature of the Pd power catalyst in this work can be
confirmed. [31]
Table 3. Bulk Pd catalyzed aminocarbonylation of olefins with amines.a
1 mg Pd, 5 mol% H3PO4
5 mol% KI, CO (40 bar)
,
O
NH2
NH
R2
R1
R1
R2
R2
R1
NH
dioxane,130 οC, 12 h
O
1
2
3
4
O
O
O
O
NH
NH
NH
NH
3
3a+4a
3b+4b
Yield: 99%
3b/4b: 62:38
3c+4c
3d+4d
Yield: 83%
3d/4d: 56:44
Yield: 89%
Yield: 87%
3c/4c: 67:33
3a/4a: 71:29
O
O
O
O
F
NH
NH
NH
NH
t-Bu
OMe
3h+4h
Yield: 70%
3h/4h: 50:50
3e+4e
Yield: 86%
3e/4e: 67:33
3f+4f
Yield: 99%
3f/4f: 62:38
3g+4g
Yield: 89%
3h/4h: 71:29
O
O
O
O
N
NH
NH
NH
NH
CO2Et
Cl
3i+4i
Yield: 90%
3i/4i: 62:38
3k+4k
Yield: 91%
3k/4k: 60:40
3l+4l
Yield: 74%
3l/4l: 59:41
3j+4j
[d] Yield: 97%
3j/4j: 50:50
O
O
O
O
NH
NH
NH
NH
t-Bu
F
Br
3n+4n
Yield: 94%
3n/4n: 67:33
3o+4o
Yield: 99%
3o/4o: 71:29
3p+4p
Yield: 99%
3p/4p: 50:50
3m+4m
[d] Yield: 99%
3m/4m: 50:50
O
O
O
NH
NH
NH
9
5
3q+4q
3r+4r
3s+4s
[d] Yield: 99%
[d] Yield: 99%
3r/4r: 46:54
[d] Yield: 99%
3s/4s: 42:58
3q/4q: 50:50
Fig.
1
Leaching
experiment
in
self-supported
nano-Pd
catalyzed
hydroaminocarbonylation of styrene with aniline by GC-MS.
aReaction conditions: alkenes (2.0 mmol), amines (1.0 mmol), Pd-610 (1 mg), KI (5
mol%), H3PO4 (5 mol%), CO (40 bar), dioxane (2.0 mL), 130 ℃, 24 h. bYield of
isolated. cRegioselectivity was determined by yield of isolated. dPd-610 (4 mg), KI
(5 mol%), H3PO4 (20 mol%).
It
is
well
known
that
transition
metal-catalyzed
aminocarbonylations of C–X bonds with amines is an important strategy
for the synthesis of amides which represent a ubiquitous functional
group in pharmaceutically relevant compounds.[32-35] Given the
To demonstrate the potential synthetic utility of this protocol, we robustness of above aminocarbonylations of alkenes with amines, we
performed the reaction on a gram scale and desired products were investigated the aminocarbonylation of aryl iodides and amines with
obtained in 82% NMR yields, thus demonstrating the scalability of this the bulk Pd catalyst by slightly changing the reaction conditions (Table
reaction (Scheme 2). Importantly, the catalyst could be reused in the
S8-S10). At first, aminocarbonylation reactions of iodobenzene with
hydroaminocarbonylation of styrene with aniline for at least 3 times amines were studied. A variety of amines, including aliphatic primary
without deactivation.
amines, aromatic primary amines, cyclic secondary amines, and acyclic
secondary amines are all readily converted into the desired amides in
88-99% yields (Table 4, 7a-7e). Importantly, the catalyst could be
reused for the aminocarbonylation reactions of iodobenzene with
aniline at least three catalytic cycles with keeping its good catalytic
performance (7a). Furthermore, we investigated the scope of aryl
iodides. In generally, both electron-donating and electron-withdrawing
50 mg Pd-610, 5 mol% H3PO4,
5 mol% KI, CO (65 bar)
O
Ph
Ph NH2
Ph
N
Ph
H
dioxane,130 οC, 12 h
1st run: 82% yield
3rd run: 82% yield
10.4 g (100 mmol) 4.65 g (50 mmol)
Scheme 2. Gram scale hydroaminocarbonylation of styrene with aniline.
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groups in aryl iodides were all compatible with these these palladium particles were characterized by XPS, XRD, SEM and
aminocarbonylation conditions, affording the desired products in 81- TEM. Initially, XPS characterization was employed to investigate the
99% yields (7f-7j). Substituent at the ortho position slightly decreased variations of binding energy of fresh and used three times bulk Pd-610
the product yield, which might arise from steric hindrance (7h). As catalysts (Fig. S2 and Table S10). The Pd 3d5/2 peak at 335.4 eV is
expected, naphthalene substrate also underwent this transformation attributed to Pd(0) (metallic palladium). According to XPS data, metallic
smoothly, giving the desired product in excellent yield (7k).
palladium was mainly formed on the surface of the fresh catalyst, and
PdO was also observed, as the surface palladium is easy to be oxidized
in air The XPS spectra of catalyst sample Pd-610 used three times did
not detect palladium peaks and the content of surface oxygen species
of the used catalyst is much higher than fresh catalyst (Fig. S2). This
observation should be reasonable, because oxidative addition of H3PO4
to Pd(0) gives the palladium hydride species which have higher content
of surface oxygenic species after water washing than bulk palladium. In
addition, the palladium particle surface was covered by carbon
materials, which might be formed via the polymerization of olefin.
However, the formation of carbon layer on the catalyst surface does not
influence it activity. Next, the Pd-610 catalyst before and after being
used for 3 times were characterized by XRD (Fig. S3 and Table S11).
From the analysis of the XRD patterns, the fresh Pd-610 catalyst shows
diffraction peaks at 40.1°, 46.7°, 68.1°, 82.1° and 86.7°, which can be
ascribed to the diffraction peaks of Pd (111), Pd (200), Pd (220), Pd
Table 4. Bulk Pd-catalyzed aminocarbonylation of aryl iodides and amines.a
O
1 mg Pd-610, 5 mol %KI,
I
R3
H
2 equiv. K2HPO4
N
R2
R1
N
R2
R3
R1
dioxane, CO,130 ο
C
5
6
7
O
O
O
O
N
N
N
5
N
H
H
O
7a
7c
7d
7b
Yield: 88%
Yield: 99%(88%)[c]
O
Yield: 99%
Yield: 99%
O
F
O
O
N
N
N
N
O
O
O
MeO
7e
7f
7g
7h
Yield: 96%
Yield: 99%
Yield: 99%
Yield: 88%
O
O
O
N
N
N
O
O
O
Cl
NC
7j
Yield: 81%
7k
7i
Yield: 99%
Yield: 99%
aReaction conditions: amines (1.5 mmol), aryl iodides (1.0 mmol), Pd-610 (1 mg),
K2HPO4 (2.0 mmol ), CO (5 bar), dioxane (2.0 mL), 130 ℃, 12 h. bYield of isolated.
cCatalyst was recovered and reused at the third run.
(311), and Pd (222). Besides above Pd diffraction peaks,
a new
diffraction peak at 18.1° was observed after Pd-610 catalyst being used
for three times. However, the attribution of this peak is still not
determined. It can not be attributed to the diffraction patterns of KI,
PdI2, KH2PO4 and K2HPO4. Meanwhile, some small diffraction peaks can
be observed at 29.3° and 31.5°, which might belong to K2HPO4 and
K2HPO4 in situ generated from KI and H3PO4 during the reaction.
As it is known, the oxidative carbonylation of amines is considered
as an important strategy for synthesis of the symmetric ureas[36-39]
,
which are useful intermediates for the production of pharmaceuticals,
agricultural chemicals and phosgene-free synthesis of isocynates. The
robustness of above aminocarbonylations of alkenes and aryl iodides
has promoted us to further investigate the possibility of using bulk Pd as
catalyst to realize the oxidative carbonylation of the amines. As shown
in Table 5, oxidative carbonylation of aliphatic primary amines such as
n-hexylamine, n-heptanamine and benzylamine proceeded well,
providing the corresponding products in excellent yields (9a-9c). In
addition, bulky substituted cyclohexylamine also underwent this
transformation smoothly to afford the desired product in 99% yield (9d).
Moreover, aromatic primary amines were converted into the
corresponding products in excellent yields (9e-9i). Furthermore, cyclic
secondary amine also reacted smoothly to give the corresponding urea
in 94% yield (9j).
Table 5. Bulk Pd -catalyzed aminocarbonylation of amines.a
O
1 mg Pd-610, 5 mol% KI
H
N
R1
R1
N
N
R1
R2
dioxane, CO/O2,130 ο
C
R2 R2
8
9
O
O
O
O
N
H
N
H
N
N
N
N
N
N
5
4
4
5
H
H
H
H
H
H
9a
9b
9c
Yield: 99%
9d
Yield: 99%
Yield: 99%
Yield: 99%
O
O
Fig. 2 SEM images of catalysts. (a) Pd-148, (c) Pd-610, (e) Pd-1540. TEM images of
catalyst. (b) Pd-148, (d) fresh Pd-610. (f) Pd-1540, (g) Pd-610 used one time, (h) Pd-610
used three times.
O
N
N
H
N
N
N
N
H
H
H
H
H
9g
9e
Yield: 99%
9f
Yield: 99%
Yield: 99%
O
O
O
Cl
N
H
N
H
Cl
O
N
N
O
n-Bu
N
H
N
n-Bu
H
Furthermore, SEM and TEM were used to reveal the microstructure
of the Pd-148, Pd-1540, fresh and used bulk Pd-610 catalyst. SEM image
(Fig. 2a, 2c, 2e) showed that the size of the different bulk palladium
particles is about 148 nm, 610 nm, and 1540 nm, which is confirmed by
the TEM image in Fig. S1. TEM image (Fig. 2b) showed that the Pd-148
particles are formed by accumulation of smaller-sized Pd particles.
According to the TEM images shown in Fig. 2d, the fresh catalyst Pd-610
is composed by bulk particle body, and the nano-Pd layer are self-
supported on the surface of the bulk Pd catalyst. The catalyst sample
9i
9j
Yield: 94%
9h
Yield: 99%
Yield: 99%
aReaction conditions: amines (2.0 mmol), Pd-610 (1 mg), CO (35 bar), O2 (5 bar),
dioxane (2.0 mL), 130℃, 24 h. Yield of isolated.
Based on the above discussions, it can be seen that the bulk Pd
exactly possess superior activity in the carbonylation reactions.
However, we still need to verify the structure of the bulk Pd. Therefore,
4 | J. Name., 2012, 00, 1-3
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2009, 48, 2218-2220; Angew. Chem. 2009, 121, 2252-2254.
used one to three times was further characterized by TEM. As can be
seen from Fig. 2g and 6h the body of bulk Pd still is bulk particles and
the nano-Pd particles are evidently self-supported on the bulk Pd
surface after being used.
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Conclusions
In summary, we have successfully developed the general and
versatile carbonylation reactions using a bulk Pd catalyst under organic
ligand free conditions. By applying an acid additive, aminocarbonylation
of wide range of olefins with amines are efficiently transformed into the
corresponding amides in good to excellent yields. Moreover, the
aminocarbonylation of aryl iodides with amines could also be
established when K2HPO4 was addition to the reaction. In addition, the
oxidative carbonylation of a variety of amines for symmetric urea
synthesis could also be realized by this catalyst. Such general and
versatile catalytic activation may be attributed to the formation of
multi-metallic active sites with multidimensional cooperative activation
function of the self-supported nano-Pd on the bulk palladium surface.
The study should be provided useful inspiration to apply bulk catalysts
in catalysis and synthetic chemistry.
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Financial supports from the NSFC (21633013, 91745106), National Key
Research and Development Program of China (2017YFA0403100) and
Key Research Program of Frontier Sciences of CAS (QYZDJ-SSW-SLH051)
are gratefully acknowledged. Additional optimization and
characterization data are provided in the supplementary materials.
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Table of Contents
Unsupported bulk Pd catalyzed carbonylation reactions have been developed for the
first time under organic ligand free condition without the addition of organic ligand.