Multifunctional phosphine stabilized gold nanoparticles: An active catalytic system for three-component coupling reaction

Article abstract of DOI:10.1166/jnn.2013.7576

Multifunctional phosphine based ligands, 1,1,1- tris(diphenylphosphinomethyl)ethane [CH₃C(CH₂ PPh ₂)₃][P₃] and 1,1,1- tris(diphenylphosphinomethyl)ethane trisulphide [CH₃C(CH ₂P(S)Ph₂)₃][P₃S₃] have been introduced to stabilize Au°-nanoparticles having small core diameter and narrow size distribution. The Au°-nanoparticles were synthesized by the reduction of HAuCl₄ precursor with NaBH₄ in the presence of ligand P₃ or P₃S₃ using two phases, one pot reaction at room temperature. The Au°-nanoparticles exhibit face centered cubic (fcc) lattice having different crystalline shape i.e., single crystallite stabilized by P₃ while P₃S₃ forms decahedral shapes. Surface plasmon bands at ~520 nm and TEM study indicate particle size below 2 and 4 nm for Au°-nanoparticles stabilized by P₃ and P₃S₃ respectively, which are attributable to the stronger interaction of Au° (Soft) with P (Soft) than Au° (Soft) with S (less Softer than P). Au°-nanoparticles stabilized by P₃S₃ shows higher thermal stability than that of P₃. The synthesized Au°-nanoparticles serve as an efficient catalyst for one-pot, three-component (A³) coupling of an aldehyde, an amine and an alkyne via C H alkyne-activation to synthesize propargylamines (85-96%) without any additives and precaution to exclude air. Copyright

Full text of DOI:10.1166/jnn.2013.7576

Copyright © 2013 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 13, 5080–5087, 2013
Multifunctional Phosphine Stabilized Gold
Nanoparticles: An Active Catalytic System
for Three-Component Coupling Reaction
Bibek Jyoti Borah, Subrat Jyoti Borah, and Dipak Kumar Dutta∗
Materials Science Division, CSIR-North East Institute of Science and Technology, Jorhat, 785 006, Assam, India
Multifunctional phosphine based ligands, 1,1,1-tris(diphenylphosphinomethyl)ethane [CH3C(CH2
PPh2ꢀ3][P3] and 1,1,1-tris(diphenylphosphinomethyl)ethane trisulphide [CH3C(CH2P(S)Ph2ꢀ3][P3S3]
have been introduced to stabilize Auꢀ-nanoparticles having small core diameter and narrow size dis-
tribution. The Auꢀ-nanoparticles were synthesized by the reduction of HAuCl4 precursor with NaBH4
in the presence of ligand P3 or P3S3 using two phases, one pot reaction at room temperature.
The Auꢀ-nanoparticles exhibit face centered cubic (fcc) lattice having different crystalline shape i.e.,
single crystallite stabilized by P3 while P3S3 forms decahedral shapes. Surface plasmon bands at
∼ 520 nm and TEM study indicate particle size below 2 and 4 nm for Auꢀ-nanoparticles stabilized
by P3 and P3S3 respectively, which are attributable to the stronger interaction of Auꢀ (Soft) with
P (Soft) than Auꢀ (Soft) with S (less Softer than P). Auꢀ-nanoparticles stabilized by P3S3 shows
higher thermal stability than that of P3. The synthesized Auꢀ-nanoparticles serve as an efficient cat-
alyst for one-pot, three-component (A3ꢀ coupling of an aldehyde, an amine and an alkyne via C
H
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alkyne-activation to synthesize propargylamines (85–96%) without any additives and precaution to
IP: 50.63.25.41 On: Sun, 25 Oct 2015 07:17:02
exclude air.
Copyright: American Scientific Publishers
Keywords: Auꢀ-Nanoparticles,
Decahedral,
Propargylamines, C H Activation.
Single
crystallite,
Surface
Plasmon,
1. INTRODUCTION
their donor sites affinity towards nanoparticles and also
structural suitability. The physico-chemical properties of
metal nanoparticles can be tuned by variations in both the
nature of the ligand and size of the metal core. Phos-
phine stabilized metal nanoparticles are excellent building
blocks possessing well organized metallic cores. Schmid
et al.5 reported the Ph3P stabilized Auꢀ-nanoparticles pre-
pared by reduction of Ph3PAuCl with diborane. After
the development of biphasic reduction procedure,4a the
synthesis of phosphine stabilized Auꢀ-nanoparticles (d ∼
1ꢁ5 nm) is further improved4b by reduction of HAuCl4
precursor with NaBH4. The biphosphine ligands having
different skeletons are also reported for the synthesis of
Pdꢀ- and Auꢀ-nanoparticles having narrow size distribution
and their catalytic applications.4cꢀd Recently, our group
has introduced tripodal phosphine based ligands system
for stabilization of Pdꢀ- and Auꢀ-nanoparticles.6 In case
of Pdꢀ-nanoparticles, a details study including catalytic
activity in C C bond formation coupling reactions were
reported.6a but for Auꢀ-nanoparticles, a very preliminary
investigation was presented.6b In this present study, we
In the recent years, there has been increasing interest
in gold for using as catalysts in organic transformations,
though gold was traditionally considered to be chemically
inert and regarded as a poor catalyst.1 The development
of facile synthetic methods and choice of suitable sup-
port towards the synthesis of Auꢀ-nanoparticles having
uniform size (less than 5 nm) and controllable prepara-
tion of nanocrystals with different shapes and exposed
surfaces appear to be of key importance for their spe-
cific applications.1ꢀ2 Different types of supports like meso-
porous materials, activated carbons, polymers, dendrimers,
metal oxides, organic ligands, etc. have been employed
to stabilize nanoparticles.3 Among the different supports,
organic ligands have aroused much attention recently
as supports because they provide important building
blocks to construct nano-organised systems with different
shape and size.4 The ligands are choosen by considering
∗Author to whom correspondence should be addressed.
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1533-4880/2013/13/5080/008
doi:10.1166/jnn.2013.7576

Borah et al.
Multifunctional Phosphine Stabilized Gold Nanoparticles
have reported the detail study of Auꢀ-nanoparticles having
different sizes and shapes stabilized by tripodal phosphine
based ligands and their catalytic activities for one-pot
synthesis of propargylamines with excellent yields and
selectivity under mild reaction conditions.
Elemental S
PPh2
S
Toluene, r.t., Stirring
Ph2P
S
PPh2
Ph2P
PPh2
PPh2
Propargylamines are versatile intermediates for the
preparation of various nitrogen-containing compounds and
are key components of biologically active pharmaceuti-
cals and natural products and also for the synthesis of
polyfunctional amino derivatives.7 Recently, considerable
afford has also been devoted to the application of var-
ious metal nanoparticles such as Cu, Fe, Au, In, etc.
for the synthesis of propargylamines via C H alkyne-
activation.8 Among the different metals, gold based cat-
alysts are highly explored in this regards because of
alkynophilicity nature of gold.3aꢀ7cꢀ8a In the recent time,
gold nanoparticles stabilized on various supports have been
extensively used for three component coupling reactions
and therefore, there is a high scope of introduction of
new catalytic system.3aꢀ7ꢀ8a Herein, we have reported a
well-defined catalytic system by preparing monodispersed,
tripodal phosphine based ligands capped Auꢀ-nanoclusters
having different crystalline properties and their catalytic
activities for one-pot synthesis of propargylamines.
(i) HAuCl4 (aq.)
S
P3
(ii) TOAB (Toluene)
(iii) NaBH4 (aq.)
P3S3
X = P
X
XX
X = S
X
X
Auo
X
X
X
X
X
X
X
Scheme 1. Synthesis of sulfur functionalized tripodal ligand and phos-
phine based ligands stabilized Auꢀ-nanoparticles.
layer took place. The complete transfer was confirmed by
the color changes that occurred in the two phases i.e., the
initial light yellow color of aqueous layer became com-
pletely colorless, while the organic phase turned into deep
red. The ligand P3 or P3S3 (0.253 mmol) in 10 ml toluene
was added to the organic phase and the resulting mixture
was stirred for about 1 h (stirring was done under nitro-
gen atmosphere for P3 since the ligand is air sensitive).
2. EXPERIMENTAL DETAILS
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3
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2.1. Syntheses
but for P S3, no color change was observed. 10 ml aqueous
solution of NaBH4 (134 mg, 3.54 mmol) was then added
Copyright: American Scientific3Publishers
2.1.1. Synthesis of 1,1,1-TrisꢂDiphenylphosphinomethylꢃ
Ethane Trisulphide ꢄCH3C(CH2P(S)Ph2ꢃ3ꢅP3S3
Ligand
slowly to the organic phase, the reaction started immedi-
ately and the organic phase turned into dark purple. The
reaction mixture was stirred for another 2 h at r.t. The
organic phase was separated and washed with water and
the solvent was removed in vacuo to yield a black solid
product. The washing of the crude solid was repeated until
no free ligand or phase transfer catalyst was detected by
[CH3C(CH2PPh2ꢃ3]P3 (1 g, 1.6 mmol) was dissolved in
50 ml of toluene and the solution was stirred at room tem-
perature (r.t.) under nitrogen atmosphere. Three fold excess
of elemental sulphur (155 mg, 4.85 mmol) was added to
the stirred solution over a period of 30 min. After the addi-
tion of sulphur was complete, the solution was stirred for
another 2 h at room temperature. The solvent was evapo-
rated under vacuum and the white product so obtained was
recrystallized from dichloromethane/n-hexane to obtain
[CH3C(CH2P(S)Ph2ꢃ3, P3S3]. The synthesized ligand is
characterized by different analytical techniques.
TLC and H NMR spectroscopy. The synthesized Auꢀ-
1
nanoparticles were designated as Auꢀ–P3 and Auꢀ–P3S3
respectively for P3 and P3S3 ligands and they were eval-
uated as catalyst precursors for one-pot three-component
coupling reaction.
2.1.3. General Procedure for the One-Pot
Synthesis of Propargylamines
2.1.2. Synthesis of Auꢀ-Nanoparticles
Aldehyde (1 mmol), amine (1 mmol), alkyne (1.2 mmol),
25 mg catalyst and 7 ml toluene were taken in a 25 ml
round bottom flask and reaction mixture was refluxed at
110 ꢀC for stipulated time period. The progress of the
reactions was monitored by TLC. After completion of the
reaction, the solvent was removed under low pressure in a
rotavapour. The crude product obtained was then purified
by silica gel column chromatography using ethyl acetate
and hexane as eluents. The products were characterized by
1H, 13C NMR and mass spectrometry.
The Auꢀ-nanoparticles stabilized by phosphine and its
sulphur functionalized one were synthesized by follow-
ing a slightly modified procedure reported by Hutchison
et al.4b (Scheme 1). 10 ml aqueous solution of HAuCl4 ·
3H2O (100 mg, 0.254 mmol) and 15 ml of toluene solu-
tion of tetra-n-octylammonium bromide (TOAB) (160 mg,
0.293 mmol) were taken into a two necked round bot-
tom flask and after vigorous stirring for about 45 min, the
transfer of [AuCl4]− anion from aqueous layer to organic
J. Nanosci. Nanotechnol. 13, 5080–5087, 2013
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Multifunctional Phosphine Stabilized Gold Nanoparticles
Borah et al.
3. RESULTS AND DISCUSSION
size histogram for ligands P3 and P3S3 stabilized Auꢀ-
nanoparticles (Auꢀ–P3 and Auꢀ–P3S3ꢃ showed narrow size
distribution of particles of 1ꢁ6 0ꢁ4 nm and 3ꢁ0 0ꢁ7 nm
respectively.
3.1. Characterization of Auꢀ-Nanoparticles
During the preparation of Auꢀ-nanoparticles, addition of
ligand P3 turns the organic layer white and cloudy because
of partial reduction of Au(III) to Au(I) state by triva-
lent phosphorous atom of ligand P3. Au(I) forms some
stable complex through phosphorus donor of triphos lig-
and, which on reduction with NaBH4 generates Auꢀ-
nanoparticles. The formation of Au(I) triphos complex is
substantiated by 31P NMR data, a downfield shift in the
31P NMR peak of ligand by trivalent phosphorous atom
of ligand P3 from −21 ppm to 29 ppm, indicates that the
ligand ligand P3 is coordinated to Au(I)9 through its triva-
lent phosphorous atom. On the other hand, in case of the
ligand P3S3, no color change was observed in the organic
layer and the partial reduction could not be possible due
to presence of pentavalent phosphorous atom (Scheme 1).
Finally, reduction was carried out with NaBH4 to generate
Auꢀ-nanoparticles.
The XRD pattern of Auꢀ–P3S3 [Fig. 3(A)] shows broad
peaks of 2ꢆ values at 38.4, 43.5, 64.65 and 78.27ꢀ assigned
to the corresponding (111), (200), (220) and (311) planes
and a broad peak appears at around 2ꢆ value at 38ꢀ for
Auꢀ–P3 [Fig. 3(B)], which corresponding to the fcc lattice
of gold. The average particle sizes of Au-1 and Au-2 were
calculated by the Scherrer equation, using the FWHM of
the intense (111) plane reflection and the average sizes are
found to be 1.27 and 3.27 nm respectively.
The microstructure of Auꢀ-nanoparticles were further
characterized by HRTEM and SAED. The HRTEM pat-
tern of Auꢀ–P3 shows that the lattice planes continuously
extended to the whole particles without stacking faults or
twins, indicating their single-crystal nature [Fig. 4(A)].10
The inset of Figure 4(A) shows the corresponding SAED
pattern obtained by directing the electron beam perpen-
dicularly to one of the particles. The hexagonal symmetry
of this pattern also proved the single crystalline nature of
the particles. Auꢀ-nanoparticles stabilized by ligand P3S3
(Auꢀ–P3S3ꢃ exhibit decahedral shape [Fig. 4(B)]. The dec-
ahedral is one of the basic multiply twinned structures,
which consists of five tetrahedral crystallites with (111) sur-
faces and found in many fcc lattice.2ꢀ10a The Figure 4(B)
shows the HRTEM image of an individual decahedral
The immediate evidence for the formation of Auꢀ-
nanoparticles was obtained by UV-Visibe spectroscopy.
The pattern of surface plasmon resonance bands at around
∼ 520 nm of Auꢀ–P3 and Auꢀ–P3S3 signifies different
characteristics [Fig. 1]. A broad surface plasmon band
for ligand P3S3 reveals the formation of Auꢀ-nanoparticles
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having the particles size below 4 nm (also substantiated
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by TEM and XRD studies) and for P3 ligand, shows no
nanoparticle where the five triangular facets of the gold
decahedron can be clearly observed. This image also dis-
plays symmetric lattice fringe images against the twin
boundary, where a few parallel layers are observed. Each
triangular face represents a single crystalline nature by con-
tinuous lattice fringes.2ꢀ10a The complex SAED pattern,
inset of Figure 4(B) may be interpreted by five twinned
subunits with their common (110) axis along a 5-fold axis.2
The Auꢀ-nanoparticles were analyzed by XPS in order
to determine the electronic state of the atom. The Auꢀ–P3
shows Au 4f doublet (4f5/2, 88.5 ev and 4f7/2, 84.8 ev) and
peak-to-peak distance (3.7 ev) [Fig. 5(A)] which is in good
agreement with the value due to Auꢀ oxidation state.11
The core-level Au 4f7/2 is shifted to a value +0.8 ev, rel-
ative to the bulk value of Au (84.0 ev), and this posi-
tive shift can be attributed due to smaller cluster size of
Auꢀ-nanoparticles.11a–c In case of Auꢀ–P3S3 [Fig. 5(B)],
exhibits Au 4f doublet at 4f5/2, 87.5 ev and 4f7/2, 83.8 ev
with peak-to-peak distance (3.7 ev) which is also in good
agreement with the value due to Auꢀ oxidation state.11 The
core-level Au 4f7/2 is shifted to a value −0.2 ev, relative
to the bulk value of Au (84.0 ev), and this negative shift
may be due to faceted nature of Auꢀ-nanoparticles.11cꢀd
The presence of ligands on the surface of metal nanopar-
ticles are determined by FTIR study.3bꢀ4e The IR spectra
of ligands P3 and P3S3 after and before stabilization gives
slightly different band assignments [Figs. 6(A) and (B)].
Some of the characteristic bands, e.g., in case of ligand P3,
Copyright: American Scientific Publishers
significant plasmon resonance band at ∼ 520 nm (consis-
tent with its smaller particles size having diameter < 2 nm
and narrower distribution). This is due to the lack of quasi
delocalized electrons that are necessary for the interaction
with visible light.4b–d
The core size and size distribution of the stabilized
Auꢀ-nanoparticles were examined by TEM [Figs. 2(A)
and (B)]. The TEM images of both the ligands stabi-
lized Auꢀ-nanoparticles show that the particles are uni-
formly distributed. The TEM images along with particles
(B)
(A)
Wavelength (nm)
Fig. 1. UV-Visible spectra of (A) Auꢀ–P3 and (B) Auꢀ–P3S3 in toluene.
5082
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Borah et al.
Multifunctional Phosphine Stabilized Gold Nanoparticles
(B)
(A)
60
40
20
0
40
30
20
10
0
1.2
1.6
2.0
1
2
3
4
5
Particles size (nm)
Particles size (nm)
Fig. 2. Representative TEM images and their particles size histogram of (A) Auꢀ–P3 and (B) Auꢀ–P3S3.
sharp peak at 1433.1 cm−1, ascribed to the P–C stretch-
ing vibration mode is shifted to 1436.8 cm−1 and also
(A)
the most characteristic ꢇp=s bands of ligand P3S3 at 624.4
and 611.0 cm−1 are shifted to 624.0 and 610.6 cm−1
(A)
(111)
1500
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1000
500
(200)
(311)
(220)
5 nm
30
40
50
60
70
80
90
(B)
Two Theta (degree)
(B)
(111)
1000
800
600
400
200
1 nm
20
30
40
50
60
70
80
90
Two Theta (degree)
Fig. 4. Representative HRTEM images and their corresponding SAED
pattern (inset) of Auꢀ–P3 and (B) Auꢀ–P3S3 showing reticular planes
inside the particle.
Fig. 3. Powder XRD patterns of Auꢀ-nanoparticles stabilized by ligands
(A) P3 and (B) P3S3.
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Multifunctional Phosphine Stabilized Gold Nanoparticles
Borah et al.
(A)
(A)
84.8
24000
23000
22000
21000
20000
88.5
80
82
84
86
88
90
92
Binding Energy (ev)
(B)
83.8
110000
100000
90000
80000
70000
1800
1500
1200
900
600
87.5
Wavenumber (cm–1
)
(B)
624.4
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611
88Cop9y0right: American Scientific Publishers
80
82
84
86
92
94
Binding Energy (ev)
Fig. 5. XPS spectra of Auꢀ-nanoparticles stabilized by ligands (A) P3
and (B) P3S3.
610.6
624
900
respectively. These observations give the evidence that the
ligands are grafted on the surface of Auꢀ-nanoparticles
through phosphorous and sulphur atom for ligands P3 and
P3S3 respectively.
1800
1500
1200
600
Wavenumber (cm–1
)
Fig. 6. FTIR spectra (A) of ligand P3 and Auꢀ–P3 nanocomposite and
(B) ligand P3S3 and Auꢀ–P3S3 nanocomposite. The upper and lower spec-
trums are for pure ligand and Auꢀ-ligands nanocomposite respectively.
The Thermogravimetric Analyses (TGA) data
[Figs. 7(A) and 6(B)] indicate that Auꢀ-nanoparticles sta-
bilized by P3 and P3S3 started decomposition of the ligand
ꢀ
at lower temperature i.e., at 170 and 190 C respectively
substantiated by TGA data that ligand P3S3 forms ther-
mally more stable Auꢀ-nanoparticles than ligand P3.
compared to the corresponding free ligands i.e., at ∼ 300
and ∼ 380 ꢀC.12 The lower decomposition temperature
of Auꢀ–P3 may be attributed to stronger and symmetri-
cal interaction of ligand P3 on the nanoparticles surface
compared to the ligand P3S3, where a weaker surface
interaction is likely due to its structural characteristics.
In general, the multi-twinned particles (MTPs) includ-
ing five-fold twinned decahedral shaped Auꢀ-nanoparticles
are theoretically more stable than those of single crys-
talline counterparts.2b However, the MTPs are chem-
ically more reactive than single crystalline structures
because of high defect density on their surfaces.2b There-
fore, Auꢀ-nanoparticles stabilized by ligand P3S3 should
be thermally more stable than ligand P3. This is well
The ligand P3 forms relatively smaller sized particles
than P3S3, which may be due to the stronger interac-
tion of Auꢀ (Soft) with P (Soft) of P3 than Auꢀ (Soft)
with S (less Softer than P) of P3S3. In addition, the ter-
tiary phosphorous atom has a strong affinity towards the
surface of Auꢀ-nanoparticles and therefore, the symmet-
rical tripodal ligands (P3ꢃ13 interacts very strongly with
Auꢀ-nanoparticles and could lead to formation of lig-
and stabilized stable small size and orderly core structure
nanoparticles. Also, such ligand-metal (atom) interac-
tion is responsible for determining the size and shape
of metal nanoparticles.14 On the other hand, in case
of P3S3 ligand, which is bulkier than P3 and having
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Borah et al.
Multifunctional Phosphine Stabilized Gold Nanoparticles
(A)
100
(B)
Ligand P3S3
Ligand P3
100
50
0
170 ºC
190 ºC
Auº-P3 composite
50
0
Auº-P3S3 composite
120
220
320
520
100
200
300
420
500
400
600
Temperature (ºC)
Temperature (ºC)
Fig. 7. TGA plots (A) of ligand P3 and Auꢀ–P3 nanocomposite and (B) ligand P3S3 and Auꢀ–P3S3 nanocomposite.
unsymmetrical tripodal character,15 interact with the sur-
face of the Auꢀ-nanoparticles through sulphur atom only
and make less stronger interaction than that of P-atom
because of two factors: (i) the latter atom exhibits much
stronger interaction with the metal surface and (ii) steric
hindrance of bulky ligand (P3S3ꢃ and as a result lead to
formation of bigger size nanoparticles with multi facet
decahedral shape particles.
Table I. Three-component coupling of aldehyde, alkyne and amine for the synthesis of propargylamine.
R2
R1
N
Auº-P3 or Auº-P3S3
R1
R2
+
CHO
+
N
H
R
Toluene, 110 ºC, 3 h
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Entry
Alkyne
Aldehyde
Amine
Products
Catalyst
Auº-P3
Yield* (%)
89
N
CHO
1
N
H
Auº-P3S3
Auº-P3
94
87
90
91
N
CHO
CHO
H3CO
2
3
N
H
Auº-P3S3
Auº-P3
H3CO
N
Cl
N
H
Auº-P3S3
96
Cl
Auº-P3
85
88
N
CHO
N
H
4
Auº-P3S3
Notes: Reaction conditions: Aldehyde (1.0 mmol), amine (1.0 mmol), alkyne (1.2 mmol), 25 mg catalyst (Auꢀ–P3 or Auꢀ–P3S3) and toluene (7 ml) stirred at 110 ꢀC for
3 h. ∗Isolated yields based on aldehyde after silica gel column chromatography.
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5085

Multifunctional Phosphine Stabilized Gold Nanoparticles
Borah et al.
3.2. Catalytic Activity
4. CONCLUSION
The main theme of this three component coupling is the
The effect of donor site environment of the ligands P3 and
P3S3 towards the stability of Auꢀ-nanoparticles and their
bonding capabilities are demonstrated. These ligands are
found to be excellent stabilizer of Auꢀ-nanoparticles hav-
ing small core diameter (less than 4 nm) and narrow size
distribution and also these ligands allow the isolation of
Auꢀ-nanoparticles as solid materials that can be redispesed
in appropriate solvents for further utilities. The ligand P3
forms relatively smaller size Auꢀ-nanoparticles than P3S3
ligand. The ligands P3 and P3S3 form single-crystalline and
decahedral shape Auꢀ-nanoparticles respectively. The Auꢀ-
nanoparticles show good to excellent catalytic activities for
one-pot three-component coupling reaction for synthesis of
propargylamines. The work reported here points towards
a new direction in the design of new ligands for the sta-
bilization of metal nanoparticles for an alternative catalyst
for three component coupling reactions.
C
H alkyne-activation, which can be accomplished by
using late transition metals in both complexes as well
as nano form catalyst. These metals are well known
to form ꢈ complexes with terminal alkynes and hence
increase the acidity of the C H bond. Among the
transition-metal based catalysts, gold exhibits excellent
alkynophilicity.3aꢀ7cꢀ8a Therefore, it is obvious that in the
present case also the surface of Au(0) only is responsi-
ble for the activation of C H alkyne bond. The gold-
alkylide complex thus formed, react with iminium ions
which are formed in situ from reaction between aldehyde
and amine, to give corresponding desired propargylamine
product. This is further substantiated by the catalytic reac-
tion conducted only in presence of the ligands molecules,
where no product was observed.
In order to determine the best reaction condition (i.e.,
solvent, reaction time etc.) that are required to afford
excellent yields of propargylamines, a series of three-
component reactions were carried out using benzaldehyde,
piperidine and phenylacetylene as the model substrates.
After screening a wide range of reactions, we have found
that our catalytic system (Auꢀ–P3 and Auꢀ–P3S3ꢃ is most
efficient for the three-component coupling reaction in
toluene as a solvent at refluxing temperature. The reactions
Acknowledgments: The authors are grateful to
Dr. P. G. Rao, Director, CSIR-North East Institute of
Science and Technology, Jorhat, Assam, India, for his
kind permission to publish the work. The authors appre-
ciate the opportunity for a preliminary exploration under
the CSIR XII Five Year Plan project: Chemical Science
Cluster (CSC-0125). The authors are thankful to CSIR,
New Delhi for financial support (In-house Project: MLP-
6000/01). The author Subrat Jyoti Borah is grateful to
UGC, New Delhi for providing JRF.
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required 3 h time for completion. Using optimized reac-
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tion conditions, we explored the versatility and limitations
of various substrates as well as efficiency of our catalyst
for the said one-pot three-component coupling to synthe-
sise propargylamines and the results are summarized in
Table I. In this study, we used phenylacetylene as alkyne,
various electronically diverse aldehydes e.g., benzalde-
hyde, 4-methoxybenzaldehyde, 4-chlorobenzaldehyde and
amines e.g., piperidine, diethylamine and all the sub-
strates produce the expected propargylamines with very
good to excellent yields and selectivity irrespective of
nature of the substrates. The model reaction, i.e., cou-
pling between benzaldehyde, phenylacetylene and piperi-
dine gives maximum 94% isolated yield (entry 1). It is
observed that the aromatic aldehyde containing electron
withdrawing group (entry 3) gives slightly higher yield
than that bearing electron donating group (entry 2). Again,
the aliphatic amine i.e., diethylamine (entry 4) shows
lower conversion than the cyclic amine i.e., piperidine
(entry 1).
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Received: 31 October 2012. Accepted: 14 February 2013.
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Copyright: American Scientific Publishers
J. Nanosci. Nanotechnol. 13, 5080–5087, 2013
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