P. Wójcik, A.M. Trzeciak
AppliedCatalysisA,General560(2018)73–83
Scheme 1. The aminocarbonylation of 1,2-diiodobenzene with aniline.
2.2. Instrumental methods
was moved to another glass flask using a stainless steel tube (catheter
tubing), and only the palladium residue was left in the Schlenk flask.
Then, the palladium residue was washed with diethyl ether and dried in
vacuum. After that, the Schlenk flask was charged again with reagents:
1,2-diiodobenzene (1 mmol), aniline (2 mmol), K2CO3 (3 mmol), DMF
(5 ml), and dodecane (0.076 ml). The yellow mixture was frozen in li-
quid nitrogen, the air was evacuated from the Schenk flask. Next, the
Schlenk tube was filled again with carbon monoxide from a balloon
(three times). The balloon was disconnected. The mixture was heated to
100 °C and stirred for 4 h. After that, the reaction mixture was cooled,
and the organic products were separated by extraction with diethyl
ether (3 times with 7 ml) and analyzed by GC with dodecane as the
internal standard.
1H NMR and 13C NMR were recorded on a Bruker Avance 500 MHz
spectrometer (1H NMR 500 MHz, 13C NMR 125 MHz) using TMS as the
internal reference. IR and FIR measurements were performed in KBr or
Nujol with a Bruker 113 V FTIR. Elemental analyses were performed on
a 2400 CHNS Vario EL III apparatus. TEM measurements were carried
out using a FEI Tecnai G2 20 X-TWIN electron microscope operating at
200 kV. XRD measurements were carried out with a Bruker D8 Advance
diffractometer operating with a Cu-Kα radiation line and equipped with
a Vantec detector.
GC and GC–MS analyses of organic products were performed using a
Hewlett Packard 5890 Series II gas chromatograph connected to a HP
5971 A mass selective detector. Separation was achieved on a capillary
HP-5 column coated with a diphenyl (5%) dimethylsiloxane (95%)
copolymer film. Helium was used as the carrier gas. Organic products
were separated by flash chromatography (CombiFlash Rf 200) on silica
gel.
3. Results and discussion
3.1. Catalytic activity of Pd(1-BI)2Cl2 in aminocarbonylation of 1,2-
diiodobenzene with aniline
2.3. General procedure for aminocarbonylation
The coupling of 1,2-diiodobenzene with aniline under a CO atmo-
sphere was selected as a model reaction to study (Scheme 1).
A lot of experiments were carried out to optimize the reaction
conditions, such as the solvent, the base, the temperature, the time, the
amount of amine, and the catalyst. The obtained results are presented in
First, the effects of the solvent and the base were studied (Table 1,
entries 1–9). The highest yield of N-phenylphthalamide (1A) was ob-
tained in DMF with K2CO3 as the base (Table 1, entry 8). Moreover, the
application of an organic base (Et3N) instead K2CO3 provided a lower
yield of the desired product (Table 1, entry 9).
A 50 cm3 Schlenk flask was charged with an ortho-substituted io-
doarene (1 × 10−3 mol), an amine (1.1–5 × 10−3 mol), K2CO3
(2 × 10−3 mol), a catalyst (5 × 10-6 mol), and a stirring bar. Next, 5
cm3 of DMF was added. Under balloon pressure of CO, the reaction
mixture was stirred at 100 °C for 1–6 h. After the reaction, the Schlenk
flask was cooled down, and the organic products were extracted with
3 × 7 cm3 of diethyl ether (3 × 15 min with stirring) and then GC
analyzed with dodecane as the internal standard (0.076 cm3, 5.46 × 10-
4
mol). Each reaction was repeated minimum twice and the average
value from two experiments was reported. The difference between two
results was below 5%.
After the solvents were evaporated, the crude product was purified
by flash chromatography on silica gel using hexane/ethyl acetate (10:4)
as the eluent, and the corresponding N-substituted phthalimides were
obtained.
Further studies focused on the examination of the effect of the
temperature and the amount of amine on the reaction course (Table 1,
entries 10–12). Both lowering the temperature and the use of almost
equimolar amounts of the substrates led to the decrease of 1A yield
(Table 1, entries 10 and 12). Furthermore, a reduction of the tem-
perature from 100 °C to 70 °C resulted in the formation of 2-iodo-N-
phenylbenzamide (12%) as a byproduct (Table 1, entry 12). As regards
the amount of the catalyst (Table 1, entries 13–15), 100% of 1A was
formed in the presence of 0.5 mol% of the catalyst. With a smaller
amount of the catalyst (0.25 mol%), a longer reaction time is required
to receive a reasonable conversion (Table 1, entry 15).
2.4. Catalytic experiments in an autoclave
In a typical experiment, an ortho-substituted iodoarene (1 × 10−3
mol), a catalyst (5 × 10-6 mol), an amine (2 × 10−3 mol), K2CO3
(2 × 10−3 mol), and DMF (5 ml) were transferred under an inert at-
mosphere into a stainless steel autoclave. It was charged with carbon
monoxide (10 atm) and heated with stirring at 100 °C for 1–4 h. The
reaction mixtures were analyzed by gas chromatography (Hewlett
Packard 5890). Conversions and the selectivities of the reactions were
determined by GC using dodecane as the internal standard. After the
solvents were evaporated, the crude products were purified by flash
chromatography on silica gel using hexane/ethyl acetate (1 : 2) as the
eluent, and the corresponding ketocarboxamide-carboxamide deriva-
tives were obtained.
After the optimization of the reaction conditions, we tested another
palladium complex with imidazole ligands Pd(1-BI)2Cl2 (Scheme 2) and
other palladium precursors in order to estimate the effect of the imi-
dazole ligand on the reaction course (Table 2).
The obtained results showed that the complex Pd(1-BI)2Cl2 was the
most catalytically active, forming 100% of 1A after 4 h (Table 2, entry
1). The complex Pd(1-MI)2Cl2 was slightly less active (Table 2, entry 2).
When precursors without an imidazole ligand, Pd(cod)Cl2 and PdCl2,
were applied, the yield of the desired product was not higher than 71%
(Table 2, entries 3 and 5). However, upon the addition of the imidazole
ligand to Pd(cod)Cl2 or to PdCl2, the yield of N-phenylphthalimide in-
creased from 71% to 82% for Pd(cod)Cl2 and from 54% to 70% for
PdCl2 (Table 2, entries 4 and 6). The same effect was also observed after
a shorter reaction time (2 h), where the addition of the imidazole ligand
increased the yield of the product from 38% to 51% (Table 2, entries 7
2.5. Procedure for catalyst recycling
After the first catalytic cycle, the organic products were separated
by extraction (with diethyl ether). The liquid phase with the reagents
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