A palladium nanoparticle-catalyzed aryl-amine coupling reaction: High performance of aryl and pyridyl chlorides as the coupling partner

Article abstract of DOI:10.1039/c7nj03447d

Carbon nitride (CN)-supported nanosized palladium particles, Pd-CN, have been found to be an active catalyst system for the amination of aryl and pyridyl chloride moieties in the presence of dialkyl amine under mild reaction conditions. The recyclability study of the reaction shows the stable performance of the catalyst without a significant loss of catalytic activity for a couple of cycles.

Full text of DOI:10.1039/c7nj03447d

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Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Palladium nanoparticle catalyzed aryl-amine coupling reaction: High
performance of aryl and pyridyl chlorides as the coupling partner
Debkumar Nandi1, Rafique Ul Islam1, 2, Nishu Devi1, Samarjeet Siwal1, Kaushik Mallick1*
Received 00th January 20xx,
Accepted 00th January 20xx
Carbon nitride (CN) supported nanosized palladium particles, Pd-CN, have been found to be an active catalyst system for
the amination of aryl and pyridyl chloride moieties in presence of dialkyl amine under mild reaction condition. The
recyclability study of the reaction shows the stable performance of the catalyst without the significant loss of catalytic
activity for the couple of cycles.
DOI: 10.1039/x0xx00000x
www.rsc.org/
Construction of aryl-amine containing molecules through transition solution to address these existing problems.
metal catalyzed cross coupling reaction has been received Due to the interesting and versatile chemical properties, palladium
considerable attention due to their applicability in diverse branches nanoparticle have been implied in a diverse range of cross coupling
2
of science and technology.1,
The palladium-catalyzed cross- reaction. Due to the interesting and versatile chemical properties,
coupling reaction of the aryl halides and the amines for the palladium nanoparticle have been implied in a diverse range of
synthesis of arylamine molecule was initially reported by Migita, cross coupling reaction. It has been reported that nafion-graphene
whereas, the major breakthrough in this field was attributed by composite film Pd nanoparticles showed C-C and C-N cross-coupling
Buchwald and Hartwig.3-5
reaction.17 Zinc oxide supported palladium nanoparticle catalyzed C-
The development of improved ligands and catalysts remained a O and C-N bond formation has been evidenced with satisfactory
major focus to address general and reliable applicability of this amount of yields.18 Report has also been published on the Pd
protocol.6 Phosphine containing symmetrical monodentate ligand catalyzed Buchwald-Hartwig C-N cross coupling reaction on silica-
and the ligands with different alkyl substituents has been reported starch substrate with excellent recycling performance.19 A tandem
for the title reaction.7 Reports are also available on bidentate reaction of C-H halogenation and cross-coupling (C-N, C-C, and C-S
phosphine, sterically hindered and electron-rich phosphines and bond formation) was successfully established using controlled
non-phosphine ligands for the effective and successful oxidation of metallic Pd, where the role of the palladium was as a
implementation of the reactions with wide range of substrate catalyst.20 Application of palladium nanoparticle is also evident in
scope.8 Synthesis of palladium catalysts has been reported using enantioselective allylic alkylation21 and hydrogenation22 reactions.
various phosphines and N-heterocyclic carbene ligands for the aryl- Two major factors effecting the catalytic activity of palladium
amine coupling reaction.9 Besides that varieties of palladacycles,10 nanoparticle are particle size and the presence of active atom on
pyridine-containing palladium complexes11 and π-allyl palladium solid support of composite materials.23 Mesoporous layered
complexes12 has been used for the rapid generation of active structured carbon nitride with high chemical and thermal stability
catalyst in the reaction mixture for the successful demonstration of could be a promising support material for the nanocatalysts for the
the title reaction. Copper based material also showed the catalytic heterogeneous catalysis process where the nitrogen moiety could
role for construction of arylamine moiety. Several classes of mono- give the additional stability of the nanoparticles. The recent
and bidentate chelators, such as, diamines13, diols14, amino acids literatures show the unique role of carbon nitride as a support
and alcohols15 are also found as effective catalytic system for material of the metal nanoparticles for heterogeneous oxidation
construction of arylamine moiety.
and hydrogenation reactions.24 The catalyst made of Pd
Regardless of these well versed and reliable progress for the aryl- nanoparticles supported on a mesoporous carbon nitride was
amines cross coupling reaction in presence of homogeneous shown to be highly active for the selective formation of
transition metal catalyst, few major drawbacks, such as, cyclohexanone from phenol under atmospheric pressure of
regeneration and recyclability of the catalyst, contamination of hydrogen in aqueous media.25 An identical system also showed
metal ions in the product, tedious ligand synthesis protocol, excellent catalytic performance for the selective hydrogenation of
moisture sensitivity of the catalyst,16 causes severe limitation for nitrogen heterocycles where quinoline is converted to
the success of the reaction. Apart from that, the aggregation and tetrahydroquinoline with high selectivity under mild temperature
precipitation of metal catalyst in homogeneous catalysis system and pressure (hydrogen) condition.26. Hydrogenation of nitriles is
causes the poor performance of the reaction and in order to avoid one of the most common methods to prepare amines and the
that phenomenon a heterogeneous route could be an attractive carbon nitride supported palladium was employed for the chemical
transformation of butyronitrile to tri-n-butylamine.27 Recent
publication described the hydrogenation of nitrophenol by
mesoporous carbon nitride supported noble metal catalysts. The
1
Department of Chemistry, University of Johannesburg, P.O. Box: 524,
Auckland Park 2006, South Africa.
ultrafine noble metal nanoparticles were homogeneously
2
Department of Chemistry, School of Physical and Material Sciences,
distributed inside the meso-channels and all the catalysts
Mahatma Gandhi Central University, Motihari, Bihar, India.
demonstrated high conversions.28 Carbon nitride supported gold
* E-mail: kaushikm@uj.ac.za (K. Mallick)
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nanoparticle was demonstrated as an effective catalyst for the reaction between 1-chloro-4-nitrobenzene and piperidine [entry: 9
transformation from cyclohexane to cyclohexanone with 100% and 13-15]. An optimum temperature of 80⁰C was selected for the
selectivity.29
reaction because further increase or decrease (not included in the
In connection with our ongoing research on the development of table) of temperature does not have any positive impact on the
effective catalysts for synthetic organic transformations,30 we have yield of the reaction [entry: 7-9]. We also found that the quantity of
also found the possibility of using carbon nitride as the support 5 mg of Pd-CN with 5 wt% of Pd loading was ideal for the reaction
material for the various reactions. Carbon nitride supported [entry: 8-10]. The optimization study also showed the better
palladium was used as an active catalyst for the mono arylation of performance of Pd-CN system as compared with the Pd(OAc)2 and
imidazo [1, 2-a] pyridine and 1, 2-dimethyl imidazole and also for Pd(PPh3)4 catalyst [entry: 11, 12].
the reduction of aromatic nitro-compounds.31 Copper catalyzed N- Based on the above optimized conditions we were interested to
arylation of hetero-aromatic compounds32 and light-induced check the general applicability of the title reaction with a set of aryl
triazole synthesis33 were also reported and proved the versatility of or pyridyl chloride and different dialkyl substituted amine
the carbon nitride as a support material.
compounds (Table: 1). When 1-chloro-4-nitrobenzene (1a) was used
In this manuscript we like to report the cross coupling reaction for as the as the coupling partner for wide range of dialkyl compounds
the amination of aryl and pyridyl chloride moieties using such as diethylamine (2a), dibutylamine (2b), pyrrolidine (2c) and
dialkylamine under the mild reaction condition using carbon nitride piperidine (2d), the corresponding products N,N-diethyl-4-
supported palladium nanoparticles as a catalyst with the scope of nitroaniline (3aa), N,N-dibutyl-4-nitroaniline (3ab), 1-(4-
recyclability of the catalyst.
nitrophenyl)pyrrolidine (3ac) and 1-(4-nitrophenyl)piperidine (3ad)
The synthesis of polymeric form of carbon nitride (CN) and the were obtained with an isolated yield of 75%, 88%, 93% and 95%,
carbon nitride supported metal nanoparticles (M-CN, where, M = respectively. The above mentioned dialkyl compounds also
Pd and Cu) has been previously reported elsewhere.31, 33 The detail produced the aryl-amine coupled products of N,N-diethylpyridin-2-
synthesis method, of the carbon nitride and the carbon nitride amine (3ba), N,N-dibutylpyridin-2-amine (3bb), 2-(pyrrolidin-1-
supported palladium nanoparticles, has also been described in the yl)pyridine (3bc) and 2-(piperidin-1-yl)pyridine (3bd), with an
supplementary document (page: S8). The electron microscopic isolated yield of 83, 91, 92 and 94%, respectively, when combined
image shows a small area of the synthesized carbon nitride (figure with 2-chloropyridine (1b) in the presence of Pd-CN catalyst. The
1A) and carbon nitride supported palladium nanoparticles (dark nitro-substituted pyridyl chloride, 2-chloro-3-nitropyridine (1c), was
spots), where the particles are dispersed on the CN support within also sensitive for the coupling reaction with the above dialkyl
the size rage of 5-20 nm (figure 1B).
compounds and forms N,N-diethyl-3-nitropyridin-2-amine (3ca),
N,N-dibutyl-3-nitropyridin-2-amine (3cb), 3-nitro-2-(pyrrolidin-1-
yl)pyridine (3cc) and 3-nitro-2-(piperidin-1-yl)pyridine (3cd) with the
individual yield of 79, 83, 89 and 87%, respectively.
The title reaction was further extended for 2, 5-dichloropyridine
(1d), as the coupling partner, with the dialkyl compounds (2, a-d)
and resulted to the formation of 5-chloro-N,N-diethylpyridin-2-
amine (3da), N,N-dibutyl-5-chloropyridin-2-amine (3db), 5-chloro-2-
(pyrrolidin-1-yl)pyridine
(3dc)
and
5-chloro-2-(piperidin-1-
yl)pyridine (3dd) successfully with the regiospecific mono-
amination at the C-2 position leaving the chloro-functionality (C-5)
undisturbed. In a similar fashion, 2-chloro-4-nitropyridine (1e) also
underwent the coupling reactions with diethylamine (2a),
dibutylamine (2b), pyrrolidine (2c) and piperidine (2d) with the
formation of the alkyl-amine coupling products, such as, N,N-
diethyl-4-nitropyridin-2-amine (3ea), N,N-dibutyl-4-nitropyridin-2-
amine (3eb), 4-nitro-2-(pyrrolidin-1-yl)pyridine (3ec) and 4-nitro-2-
(piperidin-1-yl)pyridine (3ed), respectively, and more than 90%
yield of the coupling products were achieved when carbon nitride
supported palladium was used as a catalyst. A yield comparison of
present work with few earlier reported similar compounds is also
available as a ready reference in the supplementary document,
page: S3, table: S2.
The design and synthesis of recoverable catalysts is highly
challenging. Recyclability of the catalyst is one of the important
parameter of heterogeneous catalysis to reduce the chemical waste
and make the system economically viable. In this current report, the
recyclability study was performed for the aryl-amine coupling
between the reactants 1-chloro-4-nitrobenzene (1a) and piperidine
(2d), with the formation of 1-(4-nitrophenyl) piperidine (3ad) as a
product, using Pd-CN as catalyst. By maintaining the identical
optimized reaction conditions, the amount of two substrates and
Figure 1: TEM image of the carbon nitride and carbon nitride
supported palladium nanoparticles (indicated by the arrows).
In this current experiment, aryl or pyridyl chloride (1 mmol), aryl
dialkylamine (1.0 mmol), CF3SO3Li (234 mg, 1.5 mmol), and 5.0 mg
of Pd-CN (5.0 wt% of Pd) catalyst were added in 2 mL of N-Methyl-
2-pyrrolidone (NMP).
To find out the optimum reaction condition for aryl and amine
coupling reaction, 1-chloro-4-nitrobenzene (1a) and piperidine (2d)
was chosen as coupling partners [table S1: supporting information].
Initially we focused to screen the performance of various bases (1.5
equivalent of each), such as, K2CO3, Cs2CO3, KOAc, K3PO4, KOtBu,
Et3N and CF3SO3Li [entry: 1-6 and 7-10], for the suitability of the
above reaction. Among them, CF3SO3Li showed the best
performance and produces the yield of 95% of the coupling product
1-(4-nitrophenyl) piperidine (3ad). We also have optimize the
reaction condition by using different solvent system, such as, N,N-
dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N-
methyl-2-pyrrolidine (NMP) and tetrahydrofuran (THF) where we
found that the NMP served as the best solvent for the coupling
other reagents have been increased ten times so that
a
simultaneous study of recyclability of the catalyst and scaling up of
the reaction could be performed.
2 | J. Name., 2012, 00, 1-3
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could be explained in terms of Ostwald ripening effect,34 a growth
mechanism phenomenon, for which the effective surface area or
Table 1: Synthesized aryl-amine coupled product using the Pd-CN the active sites of the catalyst was decreased and that could be the
catalyst. a, b
R
other reason for the deactivation of the catalyst over the cycles.
The kinetics of aryl-amine coupling between the reactants 1-chloro-
4-nitrobenzene (1a) and piperidine (2d) revealed the response of
the reaction under the influence of catalyst. The graphical
representation (figure 2C), percentage of conversion (from reactant
to product, 3ad) as a function of time (for the period of 12h),
showed that in the first 2h the rate of the reaction was very slow
and could be considered as the induction period for the reaction. A
faster and steady rate of product formation was noticed within the
time range between 4-7h. At the end of eighth hour, slightly higher
than 80% of product was achieved. For the last four hours, a fatigue
behaviour in the kinetic graph was noticed which indicates the
passivation of the catalyst due to the blocking of active sites by the
deposition of solid product formed during the reaction.
R
Pd-CN, CF3SO3Li (1.2 equiv)
NMP, 80 o C, 12h
HN
+
n
X
Cl
X
N
2a-2d
3
1a-1e
n
N
N
N
N
N
N
N
N
NO2
NO2
NO2
NO2
3ac, 93%
3bb, 91%
3ad, 95% 3ba, 83%
3aa, 75%
3ab, 88%
NO2
N
N
N
N
N
N
O2N
O2N
N
N
N
N
3cc, 89%
3bc, 92%
3bd, 94%
3ca, 79%
3cb, 83%
N
N
N
N
Cl
N
N
N
N
O2N
N
N
Cl
Cl
Cl
3dc, 98%
3dc, 87%
3db, 95%
3dd, 98%
3da, 79%
O2N
N
N
N
N
N
N
N
N
O2N
O2N
O2N
3ed, 97%
3eb, 92%
3ec, 96%
3ea, 90%
(a) Reaction conditions: aryl or pyridyl chloride, 1, (1.0 mmol),
dialkylamino, 2, (1.0 mmol), CF3SO3Li (234 mg, 1.5 mmol), Pd-CN
catalyst (5 mg, 5 wt% of Pd loading) and NMP (2mL). (b) Isolated
yield.
An isolated yield of 95% of the product (3ad) was achieved after
completion of the first cycle. At the end of sixth cycle a moderate
deactivation of reaction with an isolated yield of 83% of the product
was noticed. After the completion of every cycle, the catalyst was
recovered by filtration technique and used for next cycle. The
graphical representation (figure 2A) shows the recycling
performance of the catalyst in terms of product yield (%) as a
function of cycle number. The gradual decrease of the yield in each
cycle could be associated with the loss of the catalyst during the
filtration and washing process. It is also important to mention that
the loss of catalyst (palladium species) due to the leaching process
was not observed in this study as the inductively coupled plasma
mass spectrometry (ICP-MS) analysis of the filtrate, collected during
the recyclability study, did not record any palladium species within
the detection limit of the instrument and that could be due the
presence of intercalated structure and amine functionality of the
support which makes the support-particle binding system more
stronger.33 At the end of the sixth cycle the recovered catalyst was
characterized by transmission electron microscopy technique and a
significant amount of particle enlargement, within the range of 14-
35 nm, was observed (figure 2B). The enlargement of the particles
Figure 2: (A) The histogram from the recyclability study of the Pd-
CN catalyst system. (B) The TEM image of the used catalyst (Pd-CN),
at the end of the sixth cycle. (C) The graphical representation of the
kinetic study for the aryl-amine coupling reaction as a function of
time.
The schematic diagram (scheme: S1, supporting information) shows
the synthesis route for the formation of Pd-CN (A). The catalyst
combines with aryl or pyridyl chloride to generate the intermediate
complex (B) due to oxidative addition. On the other hand, the alkyl
amine molecule (B′) forms the lithium salt of the corresponding
amine (B′′) due to the acid-base reaction with lithium trifluoro-
methanesulfonate with the release of trifluoro-methanesulfonic
acid. In the next step, lithium salt of amine (B′′) due to
transmetallation reaction forms the intermediate (C) with the
elimination of lithium chloride salt. Further reductive elimination
resulted to the aryl-amine cross coupling product (D) and
regenerate the active metallic palladium species for the next cycle.
It is also important to mention that in the current experiment we
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