Nano and Sub-nano Gold–Cobalt Particles as Effective Catalysts in the Synthesis of Propargylamines via AHA Coupling

Article abstract of DOI:10.1007/s10562-020-03382-x

Abstract: Titania supported Au–Co catalysts with nano- and sub-nanoparticles, were prepared with 1% Au and different contents of cobalt by one pot deposition precipitation with urea. Monometallic gold and cobalt catalysts were also prepared by the same me

Full text of DOI:10.1007/s10562-020-03382-x

Catalysis Letters
https://doi.org/10.1007/s10562-020-03382-x
Nano and Sub‑nano Gold–Cobalt Particles as Efective Catalysts
in the Synthesis of Propargylamines via AHA Coupling
Meriem Bensaad1 · Amina Berrichi1,2 · Redouane Bachir1 · Sumeya Bedrane1
Received: 6 July 2020 / Accepted: 30 August 2020
© Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Titania supported Au–Co catalysts with nano- and sub-nanoparticles, were prepared with 1% Au and diferent
contents of cobalt by one pot deposition precipitation with urea. Monometallic gold and cobalt catalysts were also prepared
by the same method for a comparative purpose. The characterization of bimetallic catalyst evidenced the presence of sub-
nanoparticles where 50% of cobalt and 40% of gold particles are smaller than 1 nm and the formation Au–Co particles. The
results show a positive efect of cobalt on gold particles size and the catalytic activity. The efectiveness of these catalysts
in the synthesis of several propargylamines via amine, CH2Cl2 and alkyne coupling (AHA coupling) was demonstrated.
Diferent propargylamines were synthesized with very good yields (71%–88%). A comparative study of monometallic gold,
monometallic cobalt and bimetallic gold–cobalt catalysts was investigated. The most efcient catalyst was reused for up to
six reaction cycles without signifcant activity loss.
Graphic Abstract
Keywords Sub-nano · Gold nanoparticles · Bimetallic nanoparticles · Propargylamine · AHA coupling
1 Introduction
* Amina Berrichi
Gold has attracted many researchers because since its sur-
berrichi.amina@yahoo.fr
prising catalytic activity was evidenced in CO oxidation [1].
1
2
However, gold catalytic activity depends widely on the par-
ticles size, with an optimum when gold particles are in the
range of 1–5 nm [2]. The gold catalyst synthesis is conse-
quently a key step to aford nanoparticles smaller than 5 nm
Laboratory of Catalysis and Synthesis in Organic Chemistry,
University of Tlemcen, BP 119, Tlemcen, Algeria
Sciences Institut, University Center Belhadj Bouchaib, BP
284, 46000 Ain Témouchent, Algeria
Vol.:(0123456789)
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M. Bensaad et al.
[3], because of their activity and stability, mono-dispersed
gold NPs were described in the literature, sub-10, sub-5, and
sub-2 nm synthesized with several methods [4].
Barrios and colleagues [13] used the consecutive steps
incipient wetness impregnation to modify TiO2 by three
diferent metals (Ni, Co and Pd) and gold was deposed by
the DP method. All samples have an average particles size
in the range of 3–4 nm. Finally, in Santos’s study [20], the
catalyst was prepared by a three-step process, anodization of
titanium (Ti), electroless cobalt deposition and a spontane-
ous Au displacement from the Au-containing solution. All
preparation methods of gold–cobalt catalysts included two
or three steps leading to Au NPs larger than 2 nm.
Several methods have been investigated for gold sub-
nanoparticles preparation, and it is still difcult because of
the lack of reproducibility despite a high level of control and
specifc reagents. The combination of gold with diferent
metals such as copper [5], silver [6], palladium [7], Nickel
[8], iron [9] and cobalt is an interesting way. Gold based
bimetallic systems are known to exhibit higher catalytic
activity in diferent reactions such as the water–gas shift
reaction [10], Oxidation [11], hydrogenation [12], hydrogen
production and amidation reactions [13, 14].
Furthermore, propargylamines are key intermediate for
the synthesis of several chemicals [21, 22], and biologically
active molecules such as inhibitors of Parkinson’s disease
[23–25]. Diferent propagylamines were synthesized through
the one-pot three- component coupling reactions of amines,
alkynes and aldehydes (A3 coupling) using homogenous
gold [26–30], cobalt [31] and others catalysts [32].
Heterogeneous monometallic gold [33–50] and cobalt
catalysts [51] were also used for this coupling.
Supported Au–Co catalysts have a high activity due to
synergetic efect between Au NPs and cobalt species. The
preparation method is the key parameter of NPs formation.
Gamboa and colleagues [15] prepared Au–Co/CeO2 catalyst
by metals successive deposition on the support. In fact, the
cobalt catalyst was prepared by incipient wetness impregna-
tion (IWI) while gold was introduced by a deposition pre-
cipitation method (DP). The authors showed the Co3O4 par-
ticles with size ranging from 11 to 19 nm. The same catalyst
was prepared by deposition precipitation method (DP) [16];
sub-5 nanoparticles were obtained.
Recently, haloalcanes were used as a source of methylene
fragment for the propargylamines synthesis. The coupling
of amines, haloalcane and alkynes (AHA coupling) remains
limited compared to A3 coupling [52–54] particularly under
heterogeneous conditions, where very few catalysts are
reported, such as Au/CeO2 [55] or SiO2/APTES/DAFO–Fe
[56] and recently Au–Co/CeO2 [57].
Electroless metal deposition [17] was also used, where
the Au(Co)/Ti catalysts were prepared following two-steps:
electroless cobalt deposition and gold displacement from
thetetrachloro-complex solution. The preparation leaded to
Au nanoparticles crystallites with a cubic shape and size
ranging from 30 to 100 nm. Then, Au–Co(III)/SAC [18]
was prepared by the incipient wetness impregnation where
Au nanoparticles have an average size of 4 nm. The authors
showed that the addition of Co result a slight increase of
the particles size. In 2014, Xu and colleagues [11] prepared
Au–Co/SiO2 with an average size of 2.5 nm. They pre-
pared frstly the Au/SiO2 by impregnation, later, the cobalt
was deposited on the parent catalyst. Supported bimetallic
Au–Co/SBA-1 was also prepared by impregnation and depo-
sition–precipitation with urea (DPU) [19]. The characteriza-
tion showed the presence of gold particles and cobalt oxide
Co3O4. The DPU method usually used for the synthesis of
mono sub-5 nm Au NPs on oxides [3].
The main objective of this work is the preparation of
a supported catalyst containing nano and sub-nanopar-
ticles, ideally smaller than 1 nm. The trick is the cobalt
use to increase gold dispersion and obtain gold and cobalt
sub-nanoparticles.
The catalyst was prepared by one pot-DPU method (one
pot deposition precipitation by urea) in a parallel ways and
under the same conditions of pH and it used for amines,
haloalkane and alkyne coupling (AHA coupling) to synthe-
size propargylamines (Scheme 1).
Scheme 1 Synthesis of propargylamines via AHA coupling
1 3

Nano and Sub‑nano Gold–Cobalt Particles as Efective Catalysts in the Synthesis of…
mixed with solvent (3 mL) under N2 at 65 °C. After 24 h,
2 Experimental
the reaction mixture was diluted with CH2Cl2 and the cata-
lyst was recovered by centrifugation.
2.1 Reagents and Characterization Methods
The mixture was extracted with water/CH2Cl2 and dried
over Na2SO4. Evaporation of the solvent furnished the crude
product which was purifed by column chromatography. The
reaction products were known compounds and confrmed by
NMR, GC–MS and FTIR spectroscopy.
HAuCl4.3H2O, Co(NO3)2·6H2O, TiO2 powder, amines, and
phenylacetylene were purchased from Sigma–Aldrich and
used directly as the main starting materials without further
purifcation.
1,4-Diphenylbuta-1,3-diyne
Atomic absorption spectroscopy analysis (AAS) was
carried out with a Perkin Elmer Instrument Analyst 300
with fam.
1H NMR (400 MHz, CDCl3) (δ ppm): 7.42–7.44 (m, 4H),
7.24–7.27 (m, 6H);
13C NMR (100 MHz, CDCl3) (δ ppm): 132.6, 129.3,
128.5, 122.1, 81.8, 75.2;
Powder X-rays difraction (XRD) patterns were col-
lected using an Ultima III Rigaku Monochromatic Dif-
fractometer using Cu Kα radiation (λ = 1.5406 A˚). Angle
powder XRD were obtained at the same scanning rate of
1/min in the 2θ range 20–80°.
MS (EI) m/z: 202, 174, 126, 101, 88.
N,N-Diethyl-3-phenylprop-2-yn-1-amine
1H NMR (400 MHz, CDCl3) (δ ppm): 1.10–1.136 (t,
6H, 2CH3), 2.60–2.66 (q, 4H, 2CH2), 3.643 (s, 2H, CH2),
7.27–7.30 (m, 3Har), 7.41–7.43 (m, 2Har);
13C NMR (100 MHz, CDCl3) (δ ppm): 11.61, 40.44,
46.31, 83.34, 83.96, 122.35, 126.89, 127.20, 130.69;
MS: m/z=188.089, 115.027 (−HN(CH2CH3)2).
IR (ν, cm−1)=760, 689, 1198, 1320;
Difuse refectance spectroscopy (DR‐UV–Vis) meas-
urements were carried at room temperature with Lambda
800 UV/Vis spectrometer in the range of 200–800 nm.
Transmission Electron Microscopy (TEM) was carried
out on a JEM-1230 electron microscope (JEOL, Tokyo)
with an acceleration voltage of 80 kV. All samples were
dispersed in ethanol and sonicated for 20 min.
The results presented in this article are propargylamines
yields, TONAu and TONtot.
TONAu is calculated by considering that Au is the sole
to have a catalytic activity while the TONtot is calculated by
considering that Au and Co are both active.
TONAu = moles of product formed/moles of Au atoms
exposed on the catalyst surface.
2.2 Catalyst Preparation
Monometallic catalysts 1%Au/TiO2 and x%Co/TiO2 were
prepared by DPU (Deposition–Precipitation with Urea).
This method is described elsewhere [9, 57].
TONtot is calculated by considering that Au and Co are
both active.
The bimetallic gold–cobalt catalysts 1%Au–x%Co/TiO2
with diferent cobalt loadings were prepared by one pot
deposition precipitation with urea (one-pot DPU). For
1%Au–1%Co/TiO2, a suspension of 2 g of TiO2 in 200 mL
of distilled water was introduced into a double walls glass
reactor. The suspension was heated at 80 °C, then 4 mL of
HAuCl4.3H2O (aqueous solution at 10 g/L), 62.4 mL of
Co(NO3)2·6H2O (aqueous solution at 10 g/L) and 900 mg
of urea were added in the same time (one pot) under vigor-
ous stirring. The suspension was stirred at 80 °C for 16 h
in the absence of light. The solid obtained was separated
by centrifugation, washed several times with distilled
water and dried at 80 °C overnight.
TONtot =moles of product formed/moles of (Au+cobalt)
atoms exposed on the catalyst surface.
Yield (%)=100* experimental weight of propargylamine/
theoretical weight of propargylamine.
3 Results and Discussion
3.1 Catalysts Characterization
Metal loadings of Au and Co for 1%Au/TiO2 and difer-
ent 1%Au–x%Co/TiO2 catalysts were measured by atomic
absorption spectroscopy (AAS) in order to check the ef-
ciency of Co‐DPU method to deposit both gold and cobalt
on TiO2 in the same time. Results reported in Table 1 show
a good agreement between the amount of gold theoretically
introduced (1% Au) and that actually deposited.
2.3 Synthesis of Propargylamines via AHA Coupling
In this study, the propargylamine was synthesized via the
activation of the C–Cl bond of CH2Cl2 and the terminal
alkynes C–H bond.
For low percentages (1% Co and 2% Co) the experi-
mental values of deposited cobalt are very close to the
theoretical values. However, with a high Co content (4%
and 6%), the amounts actually deposited are lower than
A terminal alkyne (2 mmol), amine (2.2 mmol), CH2Cl2
(3 mL), DABCO (2 mmol), and catalyst (80 mg) were
1 3

M. Bensaad et al.
Table 1 Gold and cobalt loadings as measured by atomic absorption
those theoretically expected. This is probably related to the
saturation of the support surface at such a high metal load.
These results indicate that the Co‐DPU method is very
efcient for the deposition up to 1% Au and 2% Co, how-
ever for high Co contents; the amounts actually deposited
are generally lower than those expected.
spectroscopy (AAS)
Catalyst
Au (wt%)a Au (wt%)b Co (wt%)a Co (wt%)b
Au/TiO2
Co/TiO2
Au–Co/TiO2 (1)
Au–Co/TiO2 (2)
Au–Co/TiO2 (3)
Au–Co/TiO2 (4)
1
0
1
1
1
1
0.80
0
0.86
0.99
0.89
0.71
0
1
1
2
4
6
0
0.80
0.80
2
2.64
3
To evidence the nature of cobalt species, samples were
characterized by XRD. The bimetallic catalysts are com-
pared to the monometallic one in Fig. 1. All samples have
peaks at 2θ values of 25.31°, 37.40°, 37.76°, 37.9°, 48.03°,
53.93°, 55.11°, 62.59°, 62.62°, 68.88°, 70.25°, 75.10° and
76,22° which correspond to the TiO2 difractions planes
(101), (103), (004), (112), (200), (105), (211), (213),
(204), (116), (220), (215) and (301) respectively [58].
However, no gold or cobalt diffraction peaks were
observed in the monometallic and the bimetallic
difractograms.
aTheoretical content
bExperimental content
This fnding indicates that metal particles are smaller
than the XRD detection limit. This shows that both gold
and cobalt particles are well dispersed on the surface of
the support. Unfortunately, this does not inform about
the crystallographic structures of Au and Co or about the
interaction between them.
Thus, Au/TiO2 and Au–Co/TiO2 were characterized by
DR-UV–Vis spectroscopy.
The deconvoluted spectrum of Au/TiO2 (Fig. 2a) shows
a band with a maximum at 600 nm characteristic of the
reduced gold nanoparticles plasmon resonance [55].
Fig.1 XRD patterns of (a) TiO2, (b) 1%Co/TiO2, (c) 1%Au/TiO2, (d)
Au–Co/TiO2 (1) and (e) Au–Co/TiO2(4) 254×190 mm (96×96 DPI)
Fig.2 Difuse-refectance UV–visible spectra of a Au/TiO2 and b Au–Co/TiO2 (4) 346×169 mm (120×120 DPI)
1 3

Nano and Sub‑nano Gold–Cobalt Particles as Efective Catalysts in the Synthesis of…
This band is still visible on the Au–Co/TiO2 spectrum
The histograms of the particles size distribution for Au
(Fig. 2b), thus showing the existence of nanoparticles
in this catalyst. However, the maximum of this band has
shifted towards the lowest values (560 nm) which could be
explained by the modifcation of gold particles environ-
ment probably due to interactions with Co [57] indicating
the possible formation of bimetallic Au–Co nanoparticles.
Nevertheless, the deconvolution of this spectrum reveals
characteristic bands of cobalt oxides at 460 nm for Co3+
and 670 nm, 730 nm for Co2+.
(Fig. 4b) and Co (Fig. 4c) indicate that Au particle sizes
range from 0.2 to 4 nm and. Co particle sizes range from
0.1 to 5 nm.
These results highlight the presence of sub-nano parti-
cles of Au and Co. Indeed, 40% of gold particles and 50%
of cobalt particles are in the sub-nano range (smaller than
1 nm).
This shows deposition and stabilization of sub-nanopar-
ticles of Au and Co on TiO2 can be achieved using Co-DPU
method.
These fndings suggest the existence of Au–Co bimetal-
lic nano alloy but also of separated Co particles. However,
results are insufcient to decide on the nature of the Au–Co
interactions.
In order to confrm the hypothesis of the formation of
bimetallic Au–Co sub-nanoparticles and nanoparticles sug-
gested earlier following the results of the DR-UV–Vis char-
acterization, Au–Co/TiO2 catalysts were characterized by
(HAADF)-STEM microscopy.
In order to rate particles sizes and examine the nature of
Au–Co interactions, various electron microscopy techniques
were used.
Indeed, scanning/transmission electron microcopy
(STEM) using high-angle annular dark feld (HAADF)-
STEM is one of the most important techniques used to
characterize the bimetallic nanoparticles where images with
Z-contrast and high-resolution can be acquired.
Figure 5 shows HAADF-STEM images of the Au–Co/
TiO2 catalyst. The fgure displays the elemental mapping
images for the bimetallic nanoparticle. The blue and red
color images are associated with the Co and Au elements,
respectively. Also the overlap image is shown. It can be
observed that Co (Fig. 5b) and Au (Fig. 5c) are nano and
sub-nano sized and have an almost homogeneous distri-
bution on the support surface. The overlap image Fig. 5a
First, Au/TiO2 and bimetallic Au–Co/TiO2 (4) were char-
acterized by Transmission Electron Microscopy. The results
are shown in Fig. 3 and Fig. 4 respectively.
Figure 3a reveals a homogeneous distribution of gold
nanoparticles on TiO2 surface. The histogram of the parti-
cles size distribution (Fig. 3b) indicates that gold nanopar-
ticle sizes range from 2 to 5 nm.
TEM images of the Au–Co/TiO2 catalyst show a homo-
geneous distribution of Au and Co particles on the TiO2
surface (Fig. 4 a).
To assess the particle sizes of gold and Co separately, the
Avizo software was used.
Fig.3 TEM micrograph of a
Au/TiO2 and b gold particles
size plot 254×190 mm (96×96
DPI)
1 3

M. Bensaad et al.
Fig.4 HAADF STEM micrographs of Au–Co/TiO2 (4), gold and cobalt particles size plot 270×151 mm (120×120 DPI)
Fig.5 HAADF STEM image of Au–Co/TiO2 (4), a EDS overlap mapping of Au and Co, EDS mapping of b Co, c Au and EDS analysis
254×190 mm (96×96 DPI)
1 3

Nano and Sub‑nano Gold–Cobalt Particles as Efective Catalysts in the Synthesis of…
shows some zones where cobalt is segregated (circles) but
also areas where gold and cobalt overlap (squares). These
results clearly show the formation of bimetallic Au–Co
particles but also the segregation of some Co particles.
To better understand the Au–Co interaction, zooms on
the areas where Au and Co overlap were made. It can be
observed on Fig. 6 that the sub nano and nanoparticles
have an alloy structure, where Au and Co atoms are local-
ized in the particles in random form.
Fig.6 HAADF-STEM image
of Au–Co alloy bimetallic nano
and sub-nanoparticles with EDS
mapping of Au, Co and overlap
elements for diiferent zones
254×190 mm (96×96 DPI)
Fig.7 Drift Corrected Frame
Integration (DCFI) combined
with HR-STEM of the bimetal-
lic Au–Co/TiO2 (4) catalyst
254×190 mm (96×96 DPI)
1 3

M. Bensaad et al.
To confrm the above obtained results, HR-STEM com-
bined with Drift Corrected Frame Integration (DCFI) was
made. d-spacings of 0.14 nm and 0.17 nm were obtained
from Fig. 7. Such d-spacings do not perfectly match with any
refection plane distances of pure Au or Co suggesting that
an alloyed Au–Co structure was formed in the particles [59].
Therefore, this confrms the alloy structure of the bimetallic
sub nanoparticles and nanoparticles.
absolutely not equal to the sum of the two monometallic cat-
alysts TONs, even worse it is lower than that of the 1%Au/
TiO2 monometallic catalyst.
However, the TONAu of the bimetallic catalyst is almost
twice that of the 1%Au/TiO2 monometallic catalyst.
In order to verify the efect of Co on Au activity, diferent
catalysts were prepared by keeping gold loading equal to
nearly 1wt-% and increasing the cobalt loading from 1 to 3%.
Results in Table 2 show that yields increase when the
Co contents increases and reaches up to 80% (entries 3–6).
Furthermore, these results confrm the TONAu increases with
yields while the TONtot decreases.
3.2 Synthesis of Propargylamines
First, propargylamine (N,N-Diethyl-3-phenyl-
prop-2-yn-1-amine) was synthesized via AHA coupling of
diethylamine, CH2Cl2 and phenylacetylene (Scheme 1) using
the monometallic catalysts Au/TiO2 and Co/TiO2. Results
are summarized in Table 2.
For comparison, diferent monometallic Co/TiO2 cata-
lysts having the same Co contents as their bimetallic coun-
terpart were prepared and tested. The results shown in the
Fig. 8 indicate that cobalt has very little activity and the
yield does not exceed 18% whatever the Co content.
These observations reasonably suggest that the active
sites in the bimetallic catalyst are the alloyed Au–Co sub-
nano and nano particles. Thus, Co would not be active in
itself, but it improves the activity of Au by decreasing the
particles size, their stabilization in the form of sub-nanopar-
ticles and by modifying their electron density.
With Au/TiO2 and Co/TiO2 catalysts yields of 26%
(entry 1) and 16% (entry 2) respectively were obtained. The
reaction was subsequently carried out using the bimetallic
1%Au–1%Co/TiO2 catalyst. An interesting yield of 53% was
obtained (entry 3).
This improvement in yield could be attributed either to
the summation of Au and Co activities or to an increase in
the Au activity when it alloys with Co in the form of Au–Co
subnano and nano particles.
3.3 Synthesis of Diferent Propargylamines
In order to verify either of these two hypotheses, the TON
of the reaction was calculated according to two ways. The
frst considers the Au and Co particles both to be Active
Sites (TONtot) which means that the TONtot of the Au–Co/
TiO2 catalysts would be comparable to the sum of the two
monometallic catalysts TONs. The second considers that Au
particles are active sites but Co particles are not (TONAu)
which would mean that the TONAu increases when the reac-
tion yield increases although the Au content always remains
equal to 1% in all the catalysts.
When this study started, phenylacetylene, dichloromethane
and diethylamine were used as initial substrates to synthe-
size propargylamine and to compare activities of monome-
tallic and bimetallic catalysts.
This study showed that Au–Co/TiO2 (4) was the best
catalyst reaching a propargylamine yield of 80%. This
catalyst was therefore selected to synthesize diferent pro-
pargylamines, under similar reaction conditions, and using
secondary amines. Very good yields of 77%–88% were
obtained (Table 3). The acyclic secondary amines such as
dibutylamine and diethylamine gave the same yield (80%).
The cyclic secondary amines such as morpholine gave also a
good yield (88%). We also checked the activity of sterically
secondary amine which worked smoothly to give targeted
propargylamines with appreciable yields (Table 3, entry 6).
The catalyst was also successfully used in A3 formal-
dehyde, morpholine and phenylacetylene coupling using
Huang’s reaction conditions [37] leading to 71% of product
(Table 3, entry 3).
The results shown in the Table 2 clearly indicate that
the TONtot of the 1%Au1%Co/TiO2 (entry 3) catalyst is
Table 2 Activity of mono and bimetallic catalysts in AHA coupling
reaction
a
b
Entry
Catalysts
Yield (%)
TONAu
TONtot
1
2
3
4
5
6
Au/TiO2
Co/TiO2
Au–Co/TiO2 (1)
Au–Co/TiO2 (2)
Au–Co /TiO2 (3)
Au–Co /TiO2 (4)
26
16
53
64
70
80
80
0
152
160
194
286
80
15
37
20
18
17
One of the most important criteria in heterogeneous
catalysis is the resistance to deactivation. Consequently, the
reusability of Au–Co/TiO2 (4) catalyst was evaluated in the
propargylamine synthesis by phenylacetylene, CH2Cl2 and
diethylamine coupling under the same reaction conditions.
In addition, the reusability of Au–Co/TiO2 (4) catalyst
was compared with that of the monometallic catalyst Au/
TiO2. After the reaction, the catalysts were centrifugated,
Reaction conditions: Phenylacetylene (2 mmol), diethylamine
(2.2 mmol), CH2Cl2 (3 mL), DABCO (2 mmol), catalyst (80 mg) and
CH3CN (3 mL), N2, 24 h, 65 °C
aTON calculated with Au as the only active site
bTON calculated with (Au+Co) as active sites
1 3

Nano and Sub‑nano Gold–Cobalt Particles as Efective Catalysts in the Synthesis of…
Fig.8 Monometallic and bime-
tallic catalysts activity in AHA
coupling 254×190 mm (96×96
DPI)
Table 3 Diferent propargylamines synthesized by AHA and A3 cou-
pling reactions over Au–Co/TiO2 (4)
Entry
1
Propargylamine
Yield (%)
80
N
2
3
88
N
O
71a
N
O
Fig.9 Reusability of Au/TiO2and Au–Co/TiO2 (4) in AHA coupling
254×190 mm (96×96 DPI)
4
5
77
80
N
washed with acetone and dried at 80 °C. Figure 9 shows
that the bimetallic catalyst is almost stable and reusable
upon six reaction cycles while the reusability of the mono-
metallic decreased after the third cycle. These results show
that cobalt stabilized gold sub-nano and nanoparticles and
improve their activity. This further confrms a benefcial
efect of Co on Au. Finally, according to our earlier and
others studies [55, 60–63], the catalytic mechanism for the
AHA three-component coupling reaction with CH2Cl2, phe-
nylacetylene, and amine is proposed in Scheme 2.
N
6
70
N
Reaction conditions: Phenylacetylene (2 mmol), Amine (2.2 mmol),
CH2Cl2 (3 mL), DABCO (2 mmol), catalyst (80 mg) and CH3CN
(3 mL), N2, 24 h, 65 °C
In the absence of CH2Cl2, the homocoupling product
6 can be aforded following Path I: the C–H band of phe-
nylacetylene activated by gold–cobalt nanoparticles with
aA3 coupling catalyzed by Au–Co/TiO2 (4) (80 mg)
1 3

M. Bensaad et al.
Scheme 2 Proposed AHA reaction mechanism using gold cobalt bimetallic catalyst
generation of the Au–Co acetylide intermediate 1. With
CH2Cl2, the propargylamine is formed via AHA coupling
following Path II. The reaction of CH2Cl2 and amine gives
a chloro-N,N-R1R2- methammonium chloride salt 3. This
compound produces chloro-N,NR1R2-methanamine 4 by
elimination of HCl. Finally, chloro-N,NR1R2-methanamine
reacts with an adsorbed molecule of phenylacetylene 1
on the catalyst surface to give the corresponding propar-
gylamine 5.
Compliance with Ethical Standards
Conflict of interest The authors declare that they have no conficts of
interest.
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Acknowledgements This work was funding by the Algerian DGRSDT-
MESRS, and the University of Tlemcen. The authors thank the com-
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