Mono- and double carbonylation of aryl iodides with amine nucleophiles in the presence of recyclable palladium catalysts immobilised on a supported dicationic ionic liquid phase

Article abstract of DOI:10.1039/c7ra04680d

Silica modified with organic dicationic moieties proved to be an excellent support for palladium catalysts used in the aminocarbonylation of aryl iodides. By an appropriate choice of the reaction conditions, the same catalyst could be used for selective mono- or double carbonylations leading to amide and α-ketoamide products, respectively. The best catalyst could be recycled for at least 10 consecutive runs with a loss of palladium below the detection limit. By the application of the new support, efficient catalyst recycling could be achieved under mild reaction conditions (under low pressure and in a short reaction time). Palladium-leaching data support a mechanism with dissolution - re-precipitation of the active palladium species.

Full text of DOI:10.1039/c7ra04680d

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Mono- and double carbonylation of aryl iodides
with amine nucleophiles in the presence of
recyclable palladium catalysts immobilised on
a supported dicationic ionic liquid phase†
a
Cite this: RSC Adv., 2017, 7, 44587
M. Papp,a P. Szabo,‡b D. Sranko,c G. Safran,d L. Kollare and R. Skoda-Foldes
*
´
´
´ ´
´
¨
Silica modified with organic dicationic moieties proved to be an excellent support for palladium catalysts
used in the aminocarbonylation of aryl iodides. By an appropriate choice of the reaction conditions, the
same catalyst could be used for selective mono- or double carbonylations leading to amide and a-
ketoamide products, respectively. The best catalyst could be recycled for at least 10 consecutive runs
with a loss of palladium below the detection limit. By the application of the new support, efficient
catalyst recycling could be achieved under mild reaction conditions (under low pressure and in a short
reaction time). Palladium-leaching data support a mechanism with dissolution—re-precipitation of the
active palladium species.
Received 26th April 2017
Accepted 8th September 2017
DOI: 10.1039/c7ra04680d
rsc.li/rsc-advances
synthesis of carboxamides via monocarbonylation reactions.
Some recent examples include the use of palladium nano-
particles dispersed on metal–organic8 or zeolitic imidazole
Introduction
Palladium-catalysed aminocarbonylation involves the reaction
of aryl/alkenyl halides (or halide equivalents) with amines using
carbon monoxide as carbonyl source.1–5 The process leads to
amides and a-ketoamides via mono- and double carbonylation,
respectively. Both the amide and a-ketoamide functionalities
are important motifs in a great variety of natural and non-
natural biologically active compounds.6,7 Also, a-ketoamides
can be used as starting material in Mannich-type reactions and
in the synthesis of heterocycles.7
In the past few years, there is an increasing interest in the
development of new, heterogeneous catalysts in order to reduce
the metal content of the products and to make catalyst recycling
possible. There is an intense ongoing research aiming at the
frameworks,9,10 carbon nanotubes11 or on a siliceous meso-
cellular foam.12 Several carboxamides were synthesised using
palladium complexes, such as palladium–phosphine,13 palla-
dium–Schiff base14 or palladium–bisoxazoline15 derivatives
anchored on polymers14,15 or silica,13 as well as in the presence
of a palladium-1,10-phenanthroline complex encaged in Y
zeolite.16 Palladium immobilised on a silica support with graf-
ted imidazolium ions was also shown to be suitable catalyst by
ourselves17 and others.18 Although some catalysts showed good
activity even under atmospheric conditions,8,12,17 effective recy-
cling could usually be achieved using 2–20 bar CO pressure.
Much fewer examples have been reported for heterogeneous
double carbonylation reactions.
A silica-supported poly-
titazane–palladium (Ti–N–Pd) compound,19 a Pd/C + PPh3
catalyst system20 and palladium–phosphine complexes graed
onto mesoporous silica (SBA-15)21 were proved to be selective
catalysts. In recent studies, heterogeneous double carbonyla-
tion was carried out in the presence of palladium nanoparticles
that were supported on a cross-linked functional polymer22 or
on a triazine framework.23 With the exception of the last
example,23 when atmospheric conditions were used, selective
double carbonylation was achieved at high pressure (30–40
bar).19–22
Beside CO pressure, the selectivity of the amino-
carbonylation is affected by a number of other parameters, such
as temperature, solvent and added base, as well as by the
structure of the reaction partners. Under homogeneous condi-
tions, it is also possible to use the same catalyst either for mono-
aUniversity of Pannonia, Institute of Chemistry, Department of Organic Chemistry, P.
´
O. Box 158, H-8201 Veszprem, Hungary. E-mail: skodane@almos.uni-pannon.hu; Fax:
+36-88-624469; Tel: +36-88-624719
bUniversity of Pannonia, Department of Analytical Chemistry, Hungary
cHungarian Academy of Sciences, Centre for Energy Research, Department of Surface
Chemistry and Catalysis, P. O. Box 49, H-1525 Budapest 114, Hungary
dHungarian Academy of Sciences, Research Institute for Technical Physics and
Materials Science, P. O. Box 49, H-1525 Budapest, Hungary
e
´
University of Pecs, Department of Inorganic Chemistry, MTA-PTE Research Group for
´ ´
´
Selective Chemical Syntheses, Iusag u. 6. (P. O. Box 266), H-7624 Pecs, Hungary
† Electronic supplementary information (ESI) available: Preparation of the
catalysts, general procedure for aminocarbonylation reactions, 29Si CP MAS
NMR spectrum of 3, TEM images and XPS spectra of catalysts, data of recycling
experiments with CAT-1 and CAT-2, characterisation of products, and 1H and
13C-NMR spectra of isolated products, references. See DOI: 10.1039/c7ra04680d
˚
‡ Present address: Department of Engineering Science and Mathematics, Lulea
˚
University of Technology, 97187 Lulea, Sweden.
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or double carbonylation by a simple change in the temperature The resulting aminopropyl silica (1) was reacted with glyoxal,
of the reaction.24 formaldehyde and NH4Cl to construct the imidazole ring.32 Then,
In case of supported catalysts, there are only two reports modied silica 2 was reuxed in the presence of 1-(2-bromoethyl)-
demonstrating the applicability of the same catalysts in the 3-methylimidazolium bromide33 in acetonitrile for
days.
5
selective production of either amides or ketoamides: with According to the weight increase in the last step, 55% of the
palladium immobilised on a mesoporous poly-melamine- imidazole groups were converted into the corresponding bis(imi-
formaldehyde material25 or on silica functionalised with imi- dazolium) bromide.
dazolium ions.26 Although both catalysts showed good recycla-
The procedure was followed by FT-IR and solid phase NMR
bility, relatively long reaction time (8–12 h) had to be used to measurements. In the FT-IR spectrum of 1 the appearance of
achieve total conversion25 or to ensure effective reuse.26,27 There N–H stretching (3292 and 3362 cmꢀ1) and N–H bending
are no data for metal leaching in case of the polymer supported (1560 cmꢀ1) vibrations34 showed the presence of the amine
catalyst,25 but in the other case, an average of 2–4% loss of the functionality on the surface of silica (Fig. 1). The disappearance
original load of palladium was still observed in recycling of N–H stretching vibrations and the new bands at 1565, 1515,
studies.26,27
1450 and 1410 cmꢀ1
, attributed to the imidazole ring, are in
35
Di- and tricationic ionic liquids are known to have some accordance with the formation of modied silica 2. The vibra-
advantageous properties compared to the monocationic tions of the imidazole ring became stronger in the FT-IR spec-
versions, such as better thermal properties, lower miscibility trum of 3. 13C CP MAS NMR spectra of the solid materials also
with conventional organic solvents and more efficient stabili- supported the formation of structures 2 and 3 (Fig. 2). The
sation of transition metals.28 The introduction of imidazolium signals at 124 and 136 ppm in the spectrum of compound 2
functionalities into polymeric supports, providing multiple proved the formation of the heterocycle. The new signals at 37
ionic liquid-like structures, was found to enhance catalyst and 43 ppm were assigned to the methyl group and the meth-
stability in Heck coupling.29 Supported palladium–carbene ylene linkers between the two imidazole rings,36 respectively, in
complexes obtained from dicationic ionic liquids also showed case of dicationic phase 3. In the 29Si CP MAS NMR spectrum of
good performance in the same reaction.30 Dicationic triazolium 3, the peaks around ꢀ60 ppm show the presence of organo-
salts anchored on halloysite was found to be useful for immo- siloxane moieties (Fig. S1†) that conrms the formation of
bilisation of a palladium catalyst for a Suzuki coupling.31
At the same time, to the best of our knowledge, there is no
covalent bonds between the ionic liquid and silica.37
The catalysts were obtained from the SILP phase and
example for the use of silica-graed dicationic ionic liquids as Pd2(dba)3 (ref. 27) or Pd(OAc)2 precursors17 as reported previ-
supports in carbonylation reactions.
ously. The palladium content of the catalysts was determined by
In the present paper we report the results of mono- and ICP-AES (Table 1).
double carbonylation reactions of iodoarenes with amines as
TEM measurements (Fig. S2†) proved the formation of
nucleophiles in the presence of the catalysts mentioned above. palladium nanoparticles in both cases with an average diameter
of 6.6 ꢁ 0.9 nm (CAT-1) and 4.6 ꢁ 0.8 nm (CAT-2).
The catalysts were investigated by X-ray photoelectron spec-
Results and discussion
Preparation and characterisation of the catalysts
troscopy (XPS) analysis (Table 2). Bands at 335.0 eV and 340.3 eV
were assigned to the Pd0 (3d5/2 and 3d3/2 respectively), and the
ones at around 337.0 eV and 342.3 eV to Pd(II) (3d5/2 and 3d3/2
respectively). These results are typical for Pd(II) in similar
The dicationic ionic liquid phase 3 was prepared as shown in
Scheme 1. Silica gel was treated with 3-aminopropyltriethoxysilane.
Scheme 1 Preparation of SILP catalysts.
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Fig. 2 13C CP MAS NMR spectrum of 2 and 3.
Fig. 1 FT-IR spectra of ligand, Pd precursors, supported phases 1, 2
and 3, fresh and spent catalysts (aspent catalyst in the amino-
carbonylation reaction of iodobenzene (4a) with morpholine (5a) in
DMF).
monocationic SILP catalyst reported earlier.27 Amino-
carbonylation in less polar solvents led to lower conversion of
iodobenzene (4a) (Table 3, entries 3, 4). In toluene the mono-
carbonylated 6a was formed as the main product in the pres-
ence of triethylamine as the base. (Formation of the a-
ketoamide is usually favoured in more polar solvents, as double
carbonylation is thought to proceed via ionic intermediates. At
the same time, the participation of neutral complexes is
supposed in the catalytic cycle of monocarbonylation41) aer
changing the base to DBU, 7a was obtained selectively, and full
conversion of 4a was achieved aer 8 hours (Table 3, entries 5,
6). CAT-2 catalyst was tested under 5, 10 and 20 bar CO pressure
and with the exception of the reaction at 5 bar, iodobenzene was
totally consumed and good to excellent selectivity towards a-
ketoamide 7a was observed (Table 3, entries 8–10).
conditions.17,26,38–40 The ratios for the Pd, Si and C are presented
in the Table 2.
Interestingly, Pd(II)/Pd0 ratio is a bit higher for CAT-1 that
might be attributed to an oxidative addition of the surface
organic moieties to Pd0 accompanied by deliberation of dba
that can be observed also by FTIR measurements (Fig. 1). In case
of CAT-2, the low Pd(II) content is probably a result of the
reducing ability of the ethanol solvent used during
immobilisation.
Aminocarbonylation of iodobenzene (4a) with morpholine
(5a) in the presence of catalysts CAT-1 and CAT-2
Recirculation experiments and palladium leaching
The aminocarbonylation of iodobenzene (4a, Scheme 2) with
morpholine (5a) as nucleophile was used as the model reaction. A main advantage of heterogeneous catalysts is the possibility of
First, carbonylation was carried out at atmospheric pressure catalyst reuse. Accordingly, recycling experiments were carried
(Table 3, entries 1, 7). Full conversion of iodobenzene could not out under different conditions with catalysts CAT-1 and CAT-2.
be achieved even aer 8 hours and the selectivity for 7a was low. Atmospheric carbonylation of 4a with morpholine reagent (5a)
At the same time, under 30 bar pressure of CO iodobenzene was in the presence of CAT-1 led to 74%, 40% and 26% conversion
totally consumed aer 3 hours, and a-ketoamide 7a was formed in three successive runs. Then, the recyclability of this catalyst
with excellent selectivity in the presence of both catalysts, CAT-1 in different solvents was compared at 30 bar CO pressure
and CAT-2 (Table 3, entries 2, 11). As a comparison, 88% (Fig. 3). In acetonitrile it could be reused with a small loss of
conversion was observed aer 3 hours in the presence of the activity, while in DMF (using triethylamine as base) and in
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Table 1 Supported palladium catalysts used during the carbonylation
reactions
Pd-Contenta
Catalyst Pd-Precursor
Additive Solvent
[%]
CAT-1
CAT-2
Pd2(dba)3$CHCl3
Pd(OAc)2
—
tBuOK
THF/Acetonitrile 2.64
EtOH 1.66
a
(mg Pd/mg catalyst) ꢂ 100.
Table 2 XPS Pd 3d5/2 binding energies (eV), Pd(II)/Pd0, Pd/Si and Pd/C
surface atomic ratios of as prepared and used Pd catalysts
Fig. 3 Recycling experiments with CAT-1 (0.2 mmol 4a, 0.5 mmol 5a,
0.25 mmol base, 1.0 ml solvent, CAT-1 (1.4 mol% Pd), 100 ꢃC,
a
conversion determined by GC. With Et3N. bWith DBU).
Position of
the peak Pd
3d5/2
Ratio of the atomic concentrations
In DMF, better results were obtained during the recycling
experiments with CAT-2 catalyst (Fig. 4) than with CAT-1,
surpassing even the efficiency of the CAT-1/toluene/DBU system
(Fig. 3, Table S1,† entry 6). The effect of recycling on the catalytic
features of the CAT-2 catalyst was studied under 5, 10, 20 and 30
bar CO pressure, and the pressure could be decreased to 20 bar
without a signicant loss in activity and selectivity (Fig. 4, Table
S3†).
Pd0
(eV)
Pd(II)
(eV)
Sample
Pd(II)/Pd0
Pd/Si
Pd/C
CAT-1 fresh 335.0 336.9 5.72 ꢂ 10ꢀ1 5.79 ꢂ 10ꢀ2 3.87 ꢂ 10ꢀ2
CAT-1 spent 335.4 337.4 1.77 ꢂ 10ꢀ1 5.81 ꢂ 10ꢀ2 5.83 ꢂ 10ꢀ2
CAT-2 fresh 335.1 336.9 2.32 ꢂ 10ꢀ1 4.00 ꢂ 10ꢀ2 5.12 ꢂ 10ꢀ2
CAT-2 spent 335.3 337.1 4.60 ꢂ 10ꢀ1 5.21 ꢂ 10ꢀ2 5.70 ꢂ 10ꢀ2
The FT-IR spectra of fresh and spent catalysts were compared
(Fig. 1). The FT-IR spectrum of fresh CAT-1 showed the immo-
bilisation of Pd2(dba)3 on the surface and the presence of some
free dba (1650 cmꢀ1) could be observed. In case of CAT-2, no
stretching vibrations of the carboxylate moiety of the AcOꢀ ion
could be detected even in the fresh catalyst. The IR spectra of
spent CAT-1 and CAT-2 were very similar, preserving the bands
attributed to the imidazolium cations at 1565, 1515, 1450 and
1410 cmꢀ1. (In the case of spent catalysts, the DMF solveꢀn1t
could not be removed completely26 and the signal at 1660 cm
can be assigned to the amide band).
Scheme 2 Aminocarbonylation of iodobenzene with morpholine.
According to XPS measurements (Table 2), the Pd contents
were similar for both of the samples before and aer the cata-
lytic cycle. At the same time, Pd(II)/Pd0 ratio slightly differs – in
the case of CAT-1 Pd0 is enriched on the surface upon the
catalytic reaction, while in CAT-2 the amount of Pd(II) increased.
The catalytic cycle has no major effect on the Pd/Si and Pd/C
toluene (using DBU as base) it could be recycled in 5 runs
without signicant change in the catalytic activity (Fig. 3,
Table 4). The catalyst was also reused in further 5 runs and
a drop in the activity was observed only aer the 8th run in
toluene (Table S1†).
Table 3 Aminocarbonylation of iodobenzene with morpholinea
Entry
Catalyst
CO pressure [bar]
R. time [h]
Solvent
Base
Conversionb [%]
Ratio of 6a : 7ab
1
2
3
4
5
6
7
8
CAT-1
CAT-1
CAT-1
CAT-1
CAT-1
CAT-1
CAT-2
CAT-2
CAT-2
CAT-2
CAT-2
1
8
3
3
3
3
8
8
3
3
3
3
DMF
DMF
Et3N
Et3N
Et3N
Et3N
DBU
DBU
Et3N
Et3N
Et3N
Et3N
Et3N
74
100
88
53
90
100
31
79
100
100
100
76 : 24
5 : 95
5 : 95
72 : 28
13 : 87
11 : 89
78 : 22
35 : 65
14 : 86
5 : 95
30
30
30
30
30
1
Acetonitrile
Toluene
Toluene
Toluene
DMF
DMF
DMF
DMF
DMF
5
9
10
11
10
20
30
3 : 97
a
Reaction conditions: 0.2 mmol 4a, 0.5 mmol 5a, 0.25 mmol base, 1.0 ml solvent, catalyst (2.8 mmol Pd, 1.4 mol%), 100 ꢃC. b Determined by GC.
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Table 4 Selectivity of aminocarbonylation of iodobenzene with morpholine during recycling experiments in the presence of CAT-1a
Selectivity for 7ab
Entry
CO pressure [bar]
R. time [h]
Solvent
Base
Run 1
Run 2
Run 3
Run 4
Run 5
1
2
3
4
5
6
30
1
30
30
30
30
3
8
3
3
3
8
DMF
DMF
Acetonitrile
Toluene
Toluene
Toluene
Et3N
Et3N
Et3N
Et3N
DBU
DBU
95
76
95
28
87
89
94
61
94
29
87
91
97
50
95
26
86
88
98
n.d.
96
27
84
96
n.d.
98
30
85
89
87
a
Reaction conditions: 0.2 mmol 4a, 0.5 mmol 5a, 0.25 mmol base, 1.0 ml solvent, CAT-1 (2.8 mmol Pd, 1.4 mol%), 100 ꢃC. b Determined by GC.
The amount of palladium loss during the amino-
carbonylation reaction was determined by ICP measurements.
In the reactions with CAT-1, a relatively high palladium leaching
was detected in DMF, with a loss of 4.9% and 5.9% of the
original load in the rst two runs, respectively (Table 5, entry 1).
At the same time, the use of toluene as solvent (entry 2) or CAT-2
as catalyst (entries 3, 4) led to a considerable decrease in
palladium leaching that remained below the detection limit.
To get some information about the homogeneous or heteroge-
neous nature of the catalytic reaction, hot ltration and mercury
poisoning tests were carried out with the catalysts (Table 6). In the
rst experiments (entries 1, 2) the reaction mixture was ltered aer
a half an hour. The ltrate was divided into 2 portions, (a small
sample was analysed by GC) and one half of the mixture was heated
for 3 hours at 20 or 30 bar. To the second portion a small amount of
mercury was added and it was heated under similar conditions.
Some iodobenzene (4a) was consumed aer the removal of the
heterogeneous phases (Table 6, entries 1, 2) but the reaction was
slower compared to the usual catalytic experiments (Table 3,
entries 2, 10). Addition of mercury slowed down the reaction
considerably, so it can be concluded that the catalytically active
palladium species, leached into the mixture, are mainly nano-
particles. It should be mentioned that despite the relatively high
conversion observed aer the removal of the heterogeneous phase,
the palladium leaching was below the detection limit (<30 ppm)
aer a 3 hour-long reaction in the presence of catalyst CAT-2 (Table
5, entry 3). It is supposed, that aer the completion of the reaction
the leached palladium species re-precipitate onto the solid phase.
To prove this, a modied hot ltration test was carried out
(Table 6, entry 3). The reaction mixture was ltered aer 3 hours
Fig. 4 Recycling experiments with CAT-2 under different CO pres-
sures (0.2 mmol 4a, 0.5 mmol 5a, 0.25 mmol Et3N, 1.0 ml DMF, CAT-2
(1.4 mol% Pd), 100 ꢃC, 3 h, conversion determined by GC).
ratios. Small amount of bromine can be detected on the “fresh”
but not on the “spent” catalysts. However the lines appeared at
ꢄ620.0 eV are assigned to I 3d and therefore to the presence of
iodine (ꢄ1 at%)42 aer the catalytic cycle. This can be attributed
to a Br / I exchange with the ammonium salt formed from
Et3N base and deliberated HI. Nitrogen content was detected at
peak energies that are typical for an organic environment. The
peak at ꢄ400.0 eV is assigned to the N 1s in organic nitrogen
species.42
TEM measurements (Fig. S2†) showed no aggregation of Pd
nanoparticles aer the reaction (average diameter 7.0 ꢁ 1.3 nm
(CAT-1) and 3.8 ꢁ 0.4 nm (CAT-2)).
Table 5 Palladium leaching in the aminocarbonylation of iodobenzene (4a) with morpholine (5a)a
Pd leachingb [%]
Run 1
Entry
Catalyst
CO pressure [bar]
R. time [h]
Solvent
Base
Run 2
1
2
3
CAT-1
CAT-1
CAT-2
CAT-2
CAT-2
30
30
30
20
5
3
8
3
3
3
DMF
Toluene
DMF
DMF
—
Et3N
DBU
Et3N
Et3N
4.9
5.9
<1.0c
<1.3c
<1.3c
<2.3c
<1.1c
<1.6c
<1.3c
<2.2c
4
5d
DABCO
a
Reaction conditions: 0.2 mmol 4a, 0.5 mmol 5a, 0.25 mmol base, 1.0 ml solvent, catalyst (2.8 mmol Pd, 1.4 mol%), 100 ꢃC. b Determined by ICP.
c
Below the detection limit. d 120 ꢃC.
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Table 6 Filtration and mercury poisoning testsa
First step
R. time
0.5
Second step
Entry
Catalyst
CAT-1
CAT-2
CAT-2
CAT-2
CAT-2
Solvent
DMF
Pressure (bar)
Temp. (ꢃC)
100
Conv.
49
Ratio of 6a : 7ab
7 : 93
Hg
R. time
Conv.
Ratio of 6a : 7ab
1
2
3
4
5
30
20
20
5
ꢀ
+
3
3
80
55
80
44
50
50
99
75
49
49
6 : 94
7 : 93
5 : 95
5 : 95
6 : 94
6 : 94
85 : 15
84 : 16
99 : 1
99 : 1
DMF
100
0.5
3
38
3 : 97
ꢀ
3
+
3
DMF
100
100
43
6 : 94
ꢀ
+
3c
3c
3
d
—
120
0.5
3
98 : 2
ꢀ
+
3
e
—
5
120
100
99 : 1
ꢀ
+
3f
3f
a
b
c
Reaction conditions: 0.2 mmol 4a, 0.5 mmol 5a, 0.25 mmol Et3N, 1.0 ml DMF, catalyst (2.8 mmol Pd, 1.4 mol%). Determined by GC. Aer
d
ltration fresh reagents were added to the ltrate (0.2 mmol 4a, 0.5 mmol 5a, 0.25 mmol Et3N). Solvent-free reaction (0.8 mmol 4a, 2.0 mmol
5a, 1.0 mmol DABCO, catalyst with 5.4 mmol Pd, 0.7 mol%). Solvent-free reaction (0.4 mmol 4a, 1.0 mmol 5a, 0.5 mmol DABCO, catalyst with
2.7 mmol Pd, 0.7 mol%) it was extracted with toluene and the extract was heated in the second step. Aer ltration fresh reagents were added
e
f
to the toluene extract (0.4 mmol 4a, 1.0 mmol 5a, 0.5 mmol DABCO).
(aer 100% conversion) and fresh reagents were added to the
ltrate. One half of the resulting mixture was heated under 20
bar CO pressure at 100 C for 3 hours and to the second half,
a small amount of mercury was added before heating (Table 6,
entry 3). GC analysis of both of the reaction mixtures showed
the presence of 50% iodobenzene and 50% of carbonylation
products that means that no conversion of iodobenzene took
place in the ltrate. Aer the removal of the solid phase, the
reaction completely stopped proving the dissolution—re-
precipitation theory.43
Double carbonylation with other nucleophiles/substrates
Based on the results discussed above, catalyst CAT-2 was chosen
for aminocarbonylations carried out with other substrates. It was
found effective in the double carbonylation of iodobenzene with
other aliphatic amines (Table 7, entries 1–5) at 20 bar CO pressure
in DMF. The catalyst was tested in two consecutive runs and the
a-ketoamides were isolated in good to excellent yields.
ꢃ
The double carbonylated products could be obtained in
moderate to good yields in the reaction of other aryl iodides and
Table 7 Double carbonylation of other substratesa
Run 1
Run 2
Entry
R
5
Conv.b [%]
Ratio of 6 : 7b
Conv.b [%]
Ratio of 6 : 7b
Yield of 7c [%]
1
2
3
4
5
6
7
8
Ph
Ph
Ph
Ph
Morpholine
Piperidine
100
100
95
5 : 95
4 : 96
14 : 86
17 : 83
7 : 93
100
100
98
7 : 93
3 : 97
10 : 90
24 : 76
8 : 92
90
91
82
71
86
86
48
84
85
50
61
41g
Pyrrolidine
Diethylamine
Morpholine
Morpholine
Morpholine
Morpholine
Morpholine
Morpholine
Morpholine
Morpholine
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
4-CH3O–C6H4
3,4-(CH3)2–C6H3
1-Naphthyl
3-F–C6H4
4-Cl–C6H4
3-Br–C6H4
4-Br–C6H4
4-NO2–C6H4
4 : 96
4 : 96
40 : 60
11 : 89
11 : 89
4 : 91d
3 : 78e
48 : 0f
34 : 66
10 : 90
7 : 93
9
10
11
12
2 : 95d
3 : 66e
56 : 0f
a
b
Reaction conditions: 0.2 mmol 4, 0.5 mmol 5, 0.25 mmol Et3N, 1.0 ml DMF, CAT-2 (2.8 mmol Pd, 1.4 mol%), 100 ꢃC, 3 h. Determined by GC.
c
d
Isolated yield from the combined reaction mixtures of the rst two runs. Side products: 8b, 9b and 10b formed with a total yield of 5% and
3% (GC) in the rst and 2nd runs, respectively. Side products: 8c, 9c and 10c formed with a total yield of 19% and 31% (GC) in the rst and
2
e
f
nd runs, respectively. Side product: morpholino(4-aminophenyl)methanone. g Isolated yield for 6.
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Scheme 3 Aminocarbonylation of bromoiodobenzenes with morpholine.
Table 8 Aminocarbonylation of iodobenzene with aromatic aminesa
4-bromoiodobenzene (entry 12) were used as substrates, bis-
carbonylated side products were formed (Scheme 3). However,
no conversion of 1-bromo-4-chlorobenzene, 1-bromo-3-
chlorobenzene, 1-bromo-4-uorobenzene or bromobenzene
was observed under identical conditions.
No formation of the corresponding a-ketoamide could be
detected by GC-MS in the reaction of 1-iodo-4-nitrobenzene
(Table 7, entry 12). Beside the expected amide product, the
corresponding 4-amino-substituted amide, morpholino(4-
aminophenyl)methanone was formed in a yield of 52% and
44% in the rst and 2nd runs, respectively (determined by GC),
via the reduction of the nitro group.
In the reaction of iodobenzene with aromatic amines no
double carbonylation was observed, the amide product was
formed selectively (Table 8). The catalyst was reused 4 times
with full conversion of iodobenzene with the exception of p-
anisidine (Table 8, entry 4). The corresponding substituted N-
phenylbenzamides could be isolated in good to excellent yields.
Conversion of 4ab [%]
Entry
R
Run 1 Run 2 Run 3 Run 4 Yield of 6c [%]
1
2
3
4
5
H
4-CH3
4-nBu
100
100
100
100
100
100
97
100
100
100
98
100
100
100
100
100
88
91
92
92
85
4-CH3O 100
4-NO2 100
100
100
a
Reaction conditions: 0.2 mmol 4, 0.5 mmol 5, 0.25 mmol Et3N, 1.0 ml
DMF, CAT-2 (2.8 mmol Pd, 1.4 mol%), 100 ꢃC, 3 h. b Determined by GC.
c
Isolated yield from the combined reaction mixtures of the rst four
runs.
Monocarbonylation of iodobenzene with morpholine
Aer the success of double carbonylations, reaction conditions
were optimised to achieve selective formation of amide prod-
ucts even with aliphatic amines as nucleophiles. Reactions were
carried out in toluene that usually favours formation of
morpholine as well (Table 7, entries 6–13). In the case of uoro
and chloro derivatives only the iodide functionality reacted
(entries 9–10). When 3-bromoiodobenzene (entry 11) and
Table 9 Optimisation of reaction conditions for monocarbonylation of iodobenzene with morpholine in the presence of CAT-2a
Conversionb [%]/selectivity for 6ab [%]
Entry
Base
Solvent
Pressure [bar]
Temp. [ꢃC]
R. time [h]
Run 1
Run 2
Run 3
1
2
3
4
5
6
7
8
Et3N
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
30
30
30
30
30
30
30
1
1
1
1
1
100
100
120
100
100
100
100
100
100
100
100
120
120
120
120
8
8
8
8
8
8
8
8
8
8
8
8
8
8
3
91/71
72/66
99/89
87/81
73/75
79/51
88/70
59/100
60/100
90/97
85/98
100/99
100/96
100/96
100/98
84/68
61/48
63/85
78/72
37/65
58/59
78/70
32/100
66/97
77/100
75/98
76/100
100/96
100/100
100/100
79/63
n.d.
61/86
n.d.
n.d.
n.d.
80/71
14/100
11/100
n.d.
67/98
81/100
96/92
100/98
100/98
Et3Nc
Et3N
Na2CO3
K2CO3
Cs2CO3
DABCO
Et3N
Na2CO3
DBU
DABCO
DABCO
Et3N
d
—
d
9
—
d
10
11
12
13
14
15
—
d
—
d
—
d
—
5
5
5
d
DABCO
DABCO
—
d
—
a
Reaction conditions: 0.2 mmol 4a, 0.5 mmol 5a, 0.25 mmol base, 1 ml solvent, CAT-2 (2.8 mmol Pd, 1.4 mol%). b Determined by GC. c 0.5 mmol
Et3N. d Solvent-free reaction 0.4 mmol 4, 1.0 mmol 5, 0.5 mmol base, CAT-2 (2.8 mmol Pd, 0.7 mol%).
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a solid phase decorated with imidazolium ions.26 In toluene
(Table 9, entry 1) the main product was indeed amide 6a,
however, the conversion of iodobenzene was lower than in DMF
even aer a longer reaction (8 h instead of 3 h in DMF (Table 3,
entry 11)). An increase in the amount of the base to 0.5 mmol
ꢃ
lowered the activity of the catalyst (Table 9, entry 2). At 120 C
(entry 3) good selectivity for 6a and almost full conversion of
iodobenzene was observed, but the latter decreased to 63% and
61% in the 2nd and 3rd runs, respectively, when the catalyst was
recycled. The use of inorganic (Na2CO3, K2CO3, Cs2CO3) bases
or DABCO did not lead to better results (Table 9, entries 4–7).
In the absence of a solvent, the monocarbonylated product
6a was formed in 59–87% yield in the presence of a variety of
bases (Et3N, Na2CO3, DBU, DABCO) at atmospheric pressure of
CO (Table 9, entries 8–11), but much lower conversions could be
observed upon catalyst reuse. Under atmospheric conditions,
the most efficient recycling could be achieved with DABCO as
Fig. 5 Recycling experiments with CAT-2 under solvent-free condi-
tions (0.4 mmol 4a, 1.0 mmol 5a, 0.5 mmol DABCO, CAT-2 (2.8 mmol
Pd, 0.7 mol%), 120 ꢃC, 5 bar, 3 h, conversion determined by GC).
ꢃ
base at 120 C (Table 9, entry 12).
By the increase of the CO pressure to 5 bar, better results
were obtained (Table 9, entries 13–15). In the presence of
DABCO as base, full conversion of iodobenzene was achieved
monocarbonylated products (Table 3, entry 4) or in the absence
of a solvent. The latter condition had been found to lead to
amides in good yields with a similar catalyst immobilised on
Table 10 Solvent-free carbonylation of other substratesa
Run 1
Run 2
Entry
R
5
Conv.b [%]
Ratio of 6 : 7b
Conv.b [%]
Ratio of 6 : 7b
Yield of 6c [%]
1
2
3
Ph
Ph
Ph
Morpholine
Piperidine
Pyrrolidine
100
100
99
98 : 2
95 : 5
99 : 1
100
100
99
100 : 0
97 : 3
95 : 5
91
93
86
4
5
6
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Diethylamine
n-Propylamine
t-Butylamine
Aniline
100
100
89
43
98
74 : 26
85 : 0d
75 : 25
100 : 0
100 : 0
100 : 0
100 : 0
100 : 0
100 : 0
97 : 3
94
100
84
49
100
32
98
100
92
100
100
100
79
78 : 22
93 : 0d
84 : 16
100 : 0
100 : 0
100 : 0
100 : 0
97 : 0
100 : 0
97 : 3
93 : 7
100 : 0
39 : 0f
19 : 0g
37 : 1i
50 : 0j
100 : 0
72
75
63
n.d.
89
n.d.
90
87
93
95
7
8e
9
Aniline
4-Methylaniline
4-Methylaniline
Morpholine
Morpholine
Morpholine
Morpholine
Morpholine
Morpholine
Morpholine
Morpholine
Morpholine
2-Morpholinoethylamine
83
10e
11
12
13
14
15
16
17e
18
19e
20
100
100
100
100
100
100
94
99
94
100
100
4-CH3O–C6H4
3,4-(CH3)2–C6H3
1-Naphtyl
3-F–C6H4
4-Cl–C6H4
3-Br–C6H4
3-Br–C6H4
4-Br–C6H4
4-Br–C6H4
4-Cl–C6H4
97 : 3
91
96
100 : 0
37 : 1f
11 : 0g
72 : 1i
17 : 0j
100 : 0
31
93
82
97
99
73h
48
58k
90
a
Reaction conditions: 0.4 mmol 4, 1.0 mmol 5, 0.5 mmol DABCO, CAT-2 (2.8 mmol Pd, 0.7 mol%), 120 ꢃC, 5 bar, 3 h. b Determined by GC. c Isolated
yield from the combined reaction mixtures of the rst two runs. d Side product: 11d (see Scheme 4) formed with a yield of 15% and 7% (GC) in the
rst and 2nd runs, respectively. e 8 h. f Side products: 8b, 9b and 10b (see Scheme 3) formed with a total yield of 58% and 48% (GC) in the rst and
g
2nd runs, respectively. Side products: 8b, 9b and 10b (see Scheme 3) formed with a total yield of 88% and 75% (GC) in the rst and 2nd runs,
h
i
respectively. Isolated yield for 8b. Side products: 8c, 9c and 10c (see Scheme 3) formed with a total yield of 25% and 51% (GC) in the rst
j
and 2nd runs, respectively. Side products: 8c, 9c and 10c (see Scheme 3) formed with a total yield of 83% and 49% (GC) in the rst and 2nd
k
runs, respectively. Isolated yield for 8c.
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even in 3 hour-long reactions. The catalyst could be reused
In the solvent-free aminocarbonylation reaction of 4-chlor-
efficiently leading to the selective formation of amide 6a and oiodobenzene and 4-(2-aminoethyl)morpholine, the antide-
total conversion of iodobenzene (4a) in the rst 9 cycles (Fig. 5). pressant agent Moclobemide44 was synthesised with 90%
Filtration and mercury poisoning tests were also carried out isolated yield (Table 10, entry 20).
under solvent-free conditions (Table 6, entries 4, 5). The results
were in good agreement with those in DMF. Catalytically active
palladium species leached into the reaction mixture, and the
Conclusions
presence of both nanoparticles and complexes could be detec-
ted (Table 6, entry 4). At the same time, when the mixture was
extracted with toluene aer completion of the reaction and
fresh reagents were added to the extract, no conversion of
iodobenzene could be observed (entry 5). This proves that
similarly to the results obtained in DMF (entry 3), the leached
palladium particles re-precipitated on the solid support at the
end of the reaction.
Modication of silica with dicationic organic moieties was
shown to result in palladium catalysts with higher activity and
better recyclability compared to similar derivatives immobilised
on monocationic SILP phases. The use of Pd(OAc)2 as
a precursor led to a more stable catalyst than that obtained with
Pd2(dba)3$CHCl3 ensuring excellent recyclability as well as
palladium leaching below the detection limit. The better
performance can be attributed to the formation of smaller and
more evenly distributed Pd-nanoparticles on the surface as
shown by TEM measurements.
Monocarbonylation with other nucleophiles/substrates
N,N-Dialkyl-phenylglyoxylamide derivatives could be
produced in excellent yield via double carbonylation reactions
at 20 bar and 100 ꢃC in DMF solvent with Et3N base. By a change
in the reaction conditions (5 bar CO pressure, 120 ꢃC in toluene,
with DABCO as base) selective monocarbonylation took place
resulting in the formation of N-alkyl- or N,N-dialkyl-
benzamides. N-aryl benzamides were obtained as the only
products in aminocarbonylation of iodobenzene with aniline
derivatives even at higher pressure.
The CAT-2 catalyst was found to be efficient in the mono-
carbonylation of iodobenzene with other secondary amines as
well (Table 10, entries 1–4). During carbonylations with primary
aliphatic amines the amide products were isolated in acceptable
yields (Table 10, entries 5–6). In the reaction of n-propylamine the
corresponding imine (11d, Scheme 4) was obtained as side
product instead of the expected a-ketoamide, via the condensa-
tion of the latter with the excess of the amine reagent. In the
presence of aromatic amines lower conversion of iodobenzene
was obtained (Table 10, entries 7, 9) under identical conditions.
However, the N-arylbenzamides were isolated in good yields by
the application of a longer reaction time (Table 10, entries 8, 10).
In the reaction of iodobenzene derivatives, the mono-
carbonylated products were formed in good to excellent yield
(Table 10, entries 11–15). In the case of 3-bromoiodobenzene
and 4-bromoiodobenzene, the disubstituted products 8b and 8c
were formed in considerable amounts (Table 10, entries 16, 18).
When a longer reaction time was applied, the ratio of 8b and 8c
increased in the reaction mixtures and they were isolated in
73% and 58% yield, respectively. Unfortunately, no carbonyla-
tion was observed using 1-bromo-4-chlorobenzene, 1-bromo-3-
chlorobenzene, 1-bromo-4-uorobenzene, 4-bromoacetophe-
none or bromobenzene as substrates, even in the presence of
iodide ions added as KI or Bu4NI.
Dissolution — re-precipitation of active palladium species
was proved by hot ltration tests.
Experimental
Preparation of 3-(2-bromoethyl)-1-methylimidazolium
bromide
The 3-(2-bromoethyl)-1-methylimidazolium bromide was
prepared according to a literature procedure.33 1,2-Dibromo-
ethane (3.2 ml, 36.25 mmol) was added to a solution of 1-meth-
ylimidazole (500 ml, 6.13 mmol) in diethyl ether (3.5 ml) under Ar
atmosphere, and the resulting mixture was stirred at room
temperature for 4 days. During this time, a white precipitate was
formed. It was collected by ltration and washed with diethyl
ether (3 ꢂ 1 ml) and dried in vacuo. The ltrate was stirred at
room temperature for further 24 hours to give a second crop of
crystals. 3-(2-Bromoethyl)-1-methylimidazolium bromide was
isolated as a hygroscopic white solid (0.90 g, 53%) and it was
stored under argon. 1H NMR (400 MHz, DMSO-d6) d 9.23 (s, 1H),
7.87–7.81 (m, 1H), 7.78–7.73 (m, 1H), 4.63 (t, J ¼ 5.8 Hz, 2H), 3.95
(t, J ¼ 5.8 Hz, 2H), 3.89 (s, 3H).
Preparation of imidazole functionalised silica
Compound 2 was prepared by a modied method described in
the literature.32 To a solution of (3-aminopropyl)triethoxysilane
(2.3 ml, 10 mmol) in inert toluene (36 ml), 5.0 g silica (pre-
treated by heating for 5 h at 250 ꢃC) was added. The mixture
was reuxed for 72 h. Then the white material was ltered and
washed with toluene (3 ꢂ 5 ml) and diethyl ether (3 ꢂ 5 ml). The
solid was dried to constant weight (8 h) in vacuo to produce 1.
Scheme 4 Aminocarbonylation of iodobenzene (4a) with n-propyl-
amine (0.4 mmol 4a, 1.0 mmol n-propylamine, 0.5 mmol DABCO,
CAT-2 (2.8 mmol Pd, 0.7 mol%), 120 ꢃC, 5 bar, 3 h).
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The aminopropyl group content of the silica was determined by reaction mixture was analysed by GC and the catalyst was
measuring the weight increase of the material (0.73 mmol gꢀ1 reused.
modied silica). 1.0 g of 1 was suspended in 10 ml methanol
General procedure for solvent-free reactions. The catalyst (with
and 2.8 mmol glyoxal (40% solution in water) was added and 2.8 mmol Pd content) was placed in a Schlenk tube. The atmo-
was stirred overnight. 5.6 mmol NH4Cl and 5.6 mmol formal- sphere was changed to carbon monoxide. 0.4 mmol (45 ml)
dehyde were added and it was diluted with 30 ml methanol. iodobenzene, 1.0 mmol (87 ml) morpholine and 0.5 mmol (70 ml)
This was reuxed for an hour and H3PO4 (0.5 ml, 85%) was triethylamine was added via septum. The mixture was stirred in
slowly added to the mixture before heating to reux for 12 an oil bath for 8 hours at 100 ꢃC. Aer cooling to room
hours. The resulting material was ltered and washed with temperature, the products were extracted with 3 ꢂ 1 ml toluene.
methanol (3 ꢂ 10 ml) and diethyl ether (3 ꢂ 10 ml). It was then The reaction mixture was analysed by GC and the catalyst was
dried in vacuo at 60 ꢃC to constant weight (8 h) to give reused.
a yellowish solid product with 0.72 mmol gꢀ1 imidazole func-
Catalytic reactions at elevated pressure. In a typical experi-
tionality (determined by elemental analysis from the nitrogen ment the catalyst (with 2.8 mmol Pd content) was placed in
content of the solid material: calculated for 0.72 mmol gꢀ1 a stainless steel autoclave. A solution of 0.2 mmol (22 ml)
C8H14N2OSi: C: 6.93; H: 1.01; N: 2.02; found C: 6.34; H: 0.90; N: iodobenzene, 0.5 mmol (44 ml) morpholine and 0.25 mmol (35
2.02).
ml) triethylamine in 1 ml DMF was added via syringe. The
autoclave was charged with carbon monoxide (5–30 bar) and
was heated with stirring in an oil bath for 3 and 8 hours at
100 ꢃC. Aer cooling to room temperature, the liquid phase was
removed with a syringe. The reaction mixture was analysed by
gas chromatography and the catalyst was reused.
Preparation of SILP phase 3
To
a
solution of 3-(2-bromoethyl)-1-methylimidazolium
bromide (405 mg, 1.5 mmol) in 20 ml acetonitrile, 685 mg of
2 was added and the resulting mixture was reuxed for 5 days.
Then the solid was ltered and washed with acetonitrile (3 ꢂ 5
ml), methanol (3 ꢂ 5 ml), acetone (3 ꢂ 5 ml) and diethyl ether (3
ꢂ 5 ml). The solid was dried to constant weight (8 h) in vacuo to
produce 3, with 0.40 mmol gꢀ1 dicationic moieties (determined
by measuring the weight increase of the material). Elemental
analysis: C: 9.28; H: 1.21; N: 3.11.
General procedure for solvent-free reactions. In a typical
experiment the catalyst (with 2.8 mmol Pd content) was placed in
a stainless steel autoclave. 0.4 mmol (45 ml) iodobenzene,
1.0 mmol (87 ml) morpholine and 0.5 mmol (56.1 mg) DABCO
was added. It was charged with carbon monoxide (5–30 bar) and
was heated with stirring in an oil bath for 3 and 8 hours at
ꢃ
120 C. Aer cooling to room temperature, the products were
extracted with 3 ꢂ 1 ml toluene. The reaction mixture was
Preparation of CAT-1
analysed by GC and the catalyst was reused. The catalyst was
29.0 mmol (30.0 mg) Pd2(dba)3$CHCl3 was dissolved in a mixture washed with 2 ꢂ 1 ml methanol before recycling in every two
of 2 ml acetonitrile and 2 ml THF. The mixture was stirred for runs to remove the ammonium salt formed during the reaction.
15 min at room temperature. Then 200 mg of 3 was added and
the resulting mixture was stirred overnight. The solvents were
removed in vacuo and the residue was dried in vacuo at 35 ꢃC for
Analytical measurements
3 h and the catalyst was obtained as a dark grey solid. Palladium Reaction mixtures were analysed by gas chromatography
content of the catalyst: 2.64% (determined by ICP).
(Hewlett Packard 5890) and GC-MS (Hewlett Packard 5971A GC-
MSD, HP-1 column).
The palladium-content of the catalysts and palladium
leaching were determined by ICP.
Preparation of CAT-2
To a solution of Pd(OAc)2 (13.0 mg, 58.0 mmol) and potassium
tert-butoxide (6.5 mg, 58.0 mmol) in 4 ml ethanol, 200 mg of 3
was added and the resulting mixture was stirred at room
temperature overnight. It was ltered and washed with ethanol
(3 ꢂ 2 ml) and diethyl ether (3 ꢂ 2 ml). The catalyst was dried in
vacuo at 35 ꢃC for 3 h and was obtained as a brown solid.
Palladium content of the catalyst: 1.66% (determined by ICP).
FT-IR spectra were measured on a BRUKER Vertex 70 type
spectrometer with a Bruker Platinum ATR adapter without
sample preparation. The spectra were recorded at a resolution
of 2 cmꢀ1 with a room temperature DTGS detector (512 scans
were co-added).
Surface compositions of CAT-1 and CAT-2 before (“fresh”)
and aer (“spent”) the catalytic test reactions were determined
by X-ray photoelectron spectroscopy (XPS) performed by a KRA-
TOS XSAM 800 XPS instrument. Al Ka characteristic X-ray line,
General procedure for aminocarbonylation reactions
Catalytic reactions at atmospheric pressure. In a typical 40 eV pass energy and FAT mode were applied for recording the
experiment the catalyst (with 2.8 mmol Pd content) was placed in XPS lines of Pd 3d, C 1s, O 1s, Br 3d, I 3d, N 1s and Si 2p. C 1s
a Schlenk tube. The atmosphere was changed to carbon binding energy at 284.8 eV was used as reference for charge
monoxide. A solution of 0.2 mmol (22 ml) iodobenzene, compensation. The surface concentrations of the elements were
0.5 mmol (44 ml) morpholine and 0.25 mmol (35 ml) triethyl- calculated from the integral intensities of the XPS lines using
amine in 1 ml DMF was added via septum. The mixture was sensitivity factors given by the manufacturer.
stirred in an oil bath for 8 hours at 100 ꢃC. Aer cooling to room
temperature, the liquid phase was removed with a syringe. The were carried out by a JEOL 3010 high resolution TEM operating
Transmission Electron Microscope (TEM) investigations
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Conflicts of interest
´
¨
´
24 E. Takacs, C. S. Varga, R. Skoda-Foldes and L. Kollar,
There are no conicts of interest to declare.
Tetrahedron Lett., 2007, 48, 2453–2456.
25 R. A. Molla, M. A. Iqubal, K. Ghosh, A. S. Roy, Kamaluddin
and S. M. Islam, RSC Adv., 2014, 4, 48177–48190.
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