- Email: [email protected]
Ternary hybrid TiO2-PANI-AuNPs for photocatalytic A3-coupling of aldehydes, amines and alkynes: First photochemical synthesis of propargyl amines
Accepted Manuscript Ternary hybrid TiO2-PANI-AuNPs for photocatalytic A3-coupling of aldehydes, amines and alkynes: First photochemical synthesis of propargyl amines
Vineeta Panwar, Suman L. Jain PII: DOI: Reference:
S0928-4931(18)31777-6 https://doi.org/10.1016/j.msec.2019.01.085 MSC 9343
To appear in:
Materials Science & Engineering C
Received date: Revised date: Accepted date:
22 June 2018 14 January 2019 20 January 2019
Please cite this article as: V. Panwar and S.L. Jain, Ternary hybrid TiO2-PANI-AuNPs for photocatalytic A3-coupling of aldehydes, amines and alkynes: First photochemical synthesis of propargyl amines, Materials Science & Engineering C, https://doi.org/ 10.1016/j.msec.2019.01.085
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Ternary hybrid TiO2-PANI-AuNPs for photocatalytic A3-coupling of aldehydes, amines and alkynes: first photochemical synthesis of propargyl amines
T
Vineeta Panwara,b and Suman L. Jaina* a
IP
Chemical Sciences Division, CSIR-Indian Institute of Petroleum, Mohkampur, Dehradun-248005 (India) b
CR
Academy of Scientific and Industrial Research (AcSIR), New Delhi, India
US
*Corresponding author: Suman L. Jain
AN
Email: [email protected]
AC
CE
PT
ED
M
Tel. 91-135-2525788; Fax: 91-135-2660202;
1
ACCEPTED MANUSCRIPT ABSTRACT The present paper describes the successful synthesis and application of a ternary hybrid consists of gold nanoparticles decorated on titania-polyaniline (TiO2-PANI-AuNPs) for A3-coupling between aldehydes, terminal alkynes and amines under visible irradiation. The synthesis of
T
ternary hybrid involved the coating of PANI on TiO2 via an oxidative polymerization method
IP
followed by the deposition of AuNPs on TiO2-PANI using trisodium citrate as a reducing agent.
CR
The synthesized photocatalyst was characterized by various techniques like FT-IR, SEM, HRTEM, XRD, UV-VIS, ICP-AES, TGA, XPS and PL spectroscopy. The synthesized photocatalyst
US
exhibited higher efficiency which was presumed due to the suppressed electron-hole
AN
recombination and better electron mobility at the surface of the photocatalyst. In the hybrid, polyaniline was found to enhance the activity as well as stability of the photocatalyst owing to its
M
chemical interaction with titania and gold. Furthermore, after the reaction, the photocatalyst
ED
could readily be recovered and recycled for several runs with consistent photoactivity. Key words: Photocatalyst, multi-component coupling, gold nanoparticles, ternary hybrid, A3-
AC
CE
PT
coupling.
2
ACCEPTED MANUSCRIPT Introduction Visible light driven photocatalytic organic transformations provide novel avenues for well established reactions under mild conditions with or without altering the mechanistic pathways [1]. Particularly, light induced metal oxide catalyzed organic transformations are associated with
T
free radical non-selective reaction pathways and have been extensively used for various reactions
IP
such as oxidation of alkanes [2-3], hydroxylation of aromatics [4-5], epoxidation of alkenes [6],
CR
C-N [7-8] and C-C [9-10] coupling reactions. Among the known metal oxides, titanium dioxide
US
(TiO2) owing to its inherent properties such as higher photo-stability, non-toxicity, insolubility in aqueous media, chemically and biologically inertness, low cost and easy availability has been
AN
extensively used for organic transformations [11-12]. However, owing to the wide band gap of titania (3.0-3.2 eV), it does not show absorption in the visible region (λ > 400 nm) which
M
constitutes the major part of the solar spectrum [13]. A number of surface modifications of
ED
titania including doping of heteroatoms [14] and dye sensitization [15-16] have been well
PT
explored in order to reduce the band gap and to prevent the electron-hole recombinations. In addition, materials such as graphene oxide have been used to prepare heterostructures with TiO2
CE
to provide wide surface for reaction and prolonged charge separation [17-21]. Furthermore, some conjugate molecules, such as porphyrins and perylene diimide have been reported to enhance the
AC
photocatalytic activity of the metal oxide photocatalysts [22-25]. Conjugated polymers such as polyaniline (PANI) [26-27], polythiophene (PPTH) [28-29] and their derivatives due to their visible light absorbance, higher stability and better mobility of charge carriers have shown great deal of interest in recent years. In addition these polymers have been effectively used to combine with wide band gap inorganic semiconductors such as TiO2 to 3
ACCEPTED MANUSCRIPT improve the photo-catalytic performance and to shift the spectral absorption towards visible region. Furthermore, the conjugated structure of such polymer molecules can capture more photo-excited electrons to delay the recombination of electron-hole pairs [30]. In addition, the deposition of noble metal nanoparticles (Au, Pt and Pd) to these composites further increase the
T
photocatalytic activity due to the surface plasmon resonance (SPR) effect that improves the light
CR
IP
absorption as well as charge separation during the photocatalytic process.
Propargylamines are an important class of compounds which have widely been used as
US
precursors in the synthesis of heterocyclic compounds and as intermediates in the preparation of biologically active compounds including drugs [31-34]. Traditionally these compounds have
AN
been synthesized by using strong bases such as butyl lithium, organo-magnesium reagents or
M
lithium diisopropylamide (LDA) which initially form alkynyl metal compounds followed by their nucleophilic attack to imines or their derivatives [35]. However these reagents are used in
ED
stoichiometric amounts, hence produce large amounts of undesired waste and require strictly
PT
controlled experimental conditions. Catalytic coupling of alkyne, aldehyde and amine by C-H activation known as A3-coupling is an alternative atom-economical approach for their synthesis
CE
where water is the only by-product [36]. Among the recently reported several metal based
AC
catalysts such as gold salts (AuBr3 or AuCl3) [37], gold complexes [38], silver salts [39], copper salts [40-41], Hg2Cl2 [42] and a Cu/RuII bimetallic system [43-45], cationic gold has shown best activity for this transformation [46]. However, besides the potential limitations i.e. tedious recovery and non-recycling ability of homogeneous catalysis, the rapid reduction of cationic gold species into inactive metallic atoms is unavoidable when gold salts/ complexes activate alkynes/alkenes [47-48]. Furthermore, photocatalytic reactions are considered to be more promising owing to their cost effectiveness, use of renewable solar energy, mild reaction 4
ACCEPTED MANUSCRIPT conditions and higher atom efficiency. To the best of our knowledge so far there is no report known on the photocatalytic A3-coupling of aldehydes, amines and alkynes. In continuation to our on-going research on photocatalytic chemical transformations [49-50], herein we report the first successful example of photocatalytic A3-coupling of aldehydes, amines
IP
T
and alkynes using water as a solvent under visible light irradiation by employing a functional
CR
ternary hybrid, which include in-situ polymerization of aniline on TiO2 and grafting of gold
US
nanoparticles to yield TiO2-PANI-AuNPs composite (Scheme 1).
CHO R
+
N
Visible light
+ N H
AN
Water, 48h
R
TiO2-PANI-AuNPs
M
Scheme 1: Visible light driven photocatalytic A3-coupling of aldehydes, amines and alkynes
ED
Results and discussion
PT
Synthesis and characterization of catalyst The desired photocatalyst was synthesized by coating of TiO2 (anatase) on PANI during in-situ
CE
oxidative polymerization of aniline in the presence of potassium persulphate as an oxidant in
AC
acidic medium. In the second step gold nanoparticles as prepared via in situ reduction of HAuCl4 using trisodium citrate as a reducing agent grafted to TiO2-PANI to give ternary TiO2-PANIAuNPs as shown in Scheme 2. The Au and Ti contents in the synthesized hybrid were found to be 2 wt% and 3.5 wt%, respectively as determined by ICP-AES analysis.
5
ACCEPTED MANUSCRIPT
Aniline monomer
Titanium isopropoxide Hydrothermal Method
APS
Anatase TiO2
T
TiO2-PANI
US
CR
IP
HAuCl4
AN
TiO2-PANI-AuNPs
ED
M
Scheme 2: Schematic representation for the synthesis of TiO2-PANI-AuNPs
The changes in the chemical functionalities during the synthesis of hybrid are determined by
PT
FTIR spectroscopy. Figure 1 shows the FTIR spectra of PANI, TiO2-PANI and TiO2-PANI-
CE
AuNPs, respectively. In Figure 1a, the bands at 1571 and 1488 cm-1 are attributed to C=N and C=C stretching mode of vibration for the quinoid and benzenoid units of PANI. The peaks
AC
appearing at 1301 and 1232 cm-1 are assigned to C–N stretching mode of benzenoid ring [51]. In plane and out of plane bending vibration of C–H mode appears at 1120 cm-1and 813 cm-1 respectively. In FTIR spectrum of the TiO2-PANI (Figure 1b), the broad absorption of TiO2 centered at 3400 cm-1 is ascribed to the O-H stretching vibration of surface hydroxyl arising from the TiO2 [52]. In addition, the Ti–O stretching and Ti–O–Ti bridging vibration are appeared at ∼590 and ∼516 cm-1 respectively, which are characteristic bands of TiO2 [52]. More 6
ACCEPTED MANUSCRIPT importantly, TiO2-PANI exhibits the characteristic IR signature of both PANI (700-1600 cm-1) and TiO2 (400-700 cm-1), demonstrating the successful synthesis of TiO2-PANI composite. It is also worth mentioning that the characteristic peaks corresponding to pure PANI were found to be shifted towards longer wavelength to 1568 and 1481 cm-1 which indicated the chemical
T
interaction between the amine or imine groups of the PANI chains and the TiO2 [53]. This
IP
interaction may weaken the bond strengths of C=N, C=C and C-N in PANI macromolecule,
CR
which can be further confirmed by comparing the peak intensity of PANI and TiO2-PANI. Further, the π-π interactions shift the FT-IR peaks to lower frequencies due to the deformation of
US
the bonds. Therefore, in TiO2-PANI, the peaks related to quinoid rings were found to be shifted
AN
towards lower frequencies as compared to the pure PANI [53]. The FTIR of TiO2-PANI-AuNPs
AC
CE
PT
ED
M
(Figure 1c) was found to be almost similar to TiO2-PANI, except slight sharpness of the peaks.
7
M
AN
US
CR
IP
T
ACCEPTED MANUSCRIPT
ED
Figure 1: FTIR Spectra of a) PANI; b) TiO2-PANI; c) TiO2-PANI-AuNPs
PT
Figure 2 shows the TEM images of TiO2-PANI and TiO2-PANI-AuNPs to examine the inner nanostructure of the prepared materials. Spherical TiO2 nanoparticles (Figure 2a) having 3–4 nm
CE
size are randomly distributed in the PANI matrix and tend to line up along with the cross linked
AC
PANI chains. The ternary hybrid TiO2-PANI-AuNPs (Figure 2b) clearly shows the uniform distribution of gold nanoparticles having size in the range of 20-30 nm to the TiO2-PANI surface. The SAED pattern exhibited a distinct diffraction pattern with the appearance of dark and bright fringes, which are characteristic of the polycrystalline structures of both TiO2-PANI and TiO2PANI-AuNPs (Figure 2c, d). TEM images clearly indicate intimate contact among TiO2, PANI and Au, which would facilitate the electron transfer within the ternary hybrid to improve the photo-generated charge separation on the surface. Furthermore, elemental mapping (Figure 3) 8
ACCEPTED MANUSCRIPT confirms the homogeneous distribution of the elements in the ternary hybrid. Moreover, the presence of gold and other desired elements in EDAX confirmed the successful formation of
AC
CE
PT
ED
M
AN
US
CR
IP
T
ternary hybrid nanocomposite TiO2-PANI-AuNPs (Figure 3b).
Figure 2: TEM image and SAED pattern of a,c) TiO2-PANI; b,d) TiO2-PANI-AuNPs
9
M
AN
US
CR
IP
T
ACCEPTED MANUSCRIPT
Figure 3: EDAX pattern of a) TiO2-PANI and b) TiO2-PANI-AuNPs and elemental mapping of
ED
TiO2-PANI-AuNPs
PT
The crystalline phases of TiO2 and Au in TiO2-PANI and TiO2-PANI-AuNPs were examined by X-ray diffraction (XRD) pattern as shown in Figure 4. Characteristic diffraction peaks
CE
corresponding to anatase TiO2 (101), (004), (200), (105), (211), (204), (220) and (301) are found
AC
at 2θ = 25.28, 37.80, 48.05, 53.89, 55.06, 62.69, 70.31 and 76.02, respectively that matches well with JCPDS card 21-1272 (Figure 3a) [54]. The relatively sharp peaks indicated the highly crystalline nature of anatase TiO2. However, relatively weak peaks at 2θ = 44.37, 64.68, and 77.55 (Figure 3b) corresponding to fcc gold (200), (220) and (311), respectively, indicated the lower loading of AuNPs in the ternary hybrid (JCPDS card 02-1095).
10
AN
US
CR
IP
T
ACCEPTED MANUSCRIPT
M
Figure 4: XRD pattern of a) TiO2-PANI; b) TiO2-PANI-AuNPs
ED
UV-vis spectra of PANI, TiO2, TiO2-PANI, and TiO2-PANI-AuNPs are shown in Figure 5 [5556]. Pure polyaniline displayed two absorption bands centered at 330-370 nm ascribing to the n-
PT
л* transitions in PANI and a broad band at around 630 nm represents the transition of the
CE
quinoid rings in polyaniline chains (Figure 5a). Neat TiO2 owing to the wide band gap (3.2-3.4 eV) absorbs in the UV range between 380–400 nm. In case of TiO2-PANI composite (Figure 5b)
AC
an additional strong intensity band observed in the region of 570–800 nm is attributed to the PANI [57]. In TiO2-PANI-AuNPs the absorption band of polyaniline was found to be merged with Au at 520 nm and shifted the absorption towards lesser wavelength. This shifting can be assumed due to the bonding of Au with PANI in ternary hybrid (Figure 5c).
11
M
AN
US
CR
IP
T
ACCEPTED MANUSCRIPT
ED
Figure 5: UV-Vis spectra of a) PANI; b) TiO2-PANI; c) TiO2-PANI-AuNPs Figure 6 shows the PL emission spectra of PANI, TiO2-PANI and TiO2-PANI-AuNPs. PL was
PT
carried out to determine the charge recombination and migration efficiency of TiO2-PANI and TiO2-PANI-AuNPs. The excitation wavelength for TiO2-PANI and TiO2-PANI-AuNPs falls
CE
within the visible light region, showing that they are visible light active [58]. Photoluminescence
AC
spectrum of PANI shows a sharp peak near 450 nm due to the polaronic band in PANI [59]. In the PL spectra of TiO2-PANI-AuNPs, the emission peak showed a lesser intensity which indicated a lower recombination rate of TiO2-PANI-AuNPs than TiO2-PANI (Figure 6).
12
US
CR
IP
T
ACCEPTED MANUSCRIPT
Figure 6: Photoluminescence emission spectra of PANI, TiO2-PANI and TiO2-PANI-AuNPs
AN
The thermal stability and degradation pattern of the synthesized hybrid photocatalyst was
M
examined by TGA (Figure 7) [60]. In case of PANI, the first weight loss up to 100 oC was assigned to the evaporation of free water molecules and other volatile impurities. The weight loss
ED
from ~100 to 400 oC was attributed to the removal of water and dopant molecules adsorbed on
PT
PANI as well as initial degradation of PANI chains. The third degradation step was assigned to decomposition of the molecular chains of PANI (Figure 7a). Thermogram of TiO2-PANI showed
CE
two major weight losses attributed to the decomposition of organic polyaniline chains. An
AC
additional weight loss due to the disassociation of PANI from TiO2 was also observed (Figure 7b). As expected, TiO2-PANI-AuNPs ternary hybrid became more resistant to thermal degradation and revealed a major weight loss around at 570 oC possibly due to the strong interactions between the components in the hybrid (Figure 7c).
13
AN
US
CR
IP
T
ACCEPTED MANUSCRIPT
M
Figure 7: TGA thermogram of a) PANI; b) TiO2-PANI; c) TiO2-PANI-AuNPs
ED
XPS was performed to analyze the chemical composition of the PANI−TiO2-AuNPs on the surface. The survey scan reveals the presence of C, N, O, Ti and Au in PANI−TiO2-AuNPs as
PT
shown in Figure 8. The peak at 284.72 eV is related to C1s corresponding to the C-C of aromatic
CE
rings of PANI. The C1s peak at 285.75 is attributed to the C−N group and at 288.40 eV attributed to the electronic transition on PANI ring. The N1s peak at 399.62 eV assigned to the
AC
positively charged quinoid and benzenoid amine. The binding energies for O1s located at 530.01, 531.05 and 532.58 eV are ascribed to the oxygen of TiO2 in hybrid. The core-level spectrum of Ti 2p split into spin−orbit doublets of Ti 2p1/2 and Ti 2p3/2 at 464.50 and 458.72 eV, respectively [61-62]. Furthermore, two peaks related to Au 4f separated by 3.7 eV corresponding to Au 4f5/2 and Au 4f7/2 are observed at 87.21 eV and 83.51 eV, respectively [63].
14
AN
US
CR
IP
T
ACCEPTED MANUSCRIPT
M
Figure 8: XPS Spectra of TiO2-PANI-AuNPs
ED
Photocatalytic activity
PT
The synthesized ternary hybrid photocatalyst TiO2-PANI-AuNPs was evaluated for the synthesis of propargylamines by A3-coupling reaction of aldehydes, amines and alkynes at room
CE
temperature under visible light irradiation. At first, benzaldehyde, piperidine and
AC
phenylacetylene were chosen as model substrates to perform the optimization study using different solvents (Table 1, entries 1-7). As shown, the non polar solvents such as toluene and chloroform were found to be less effective and afforded poor product yield (Table 1, entries 1, 2). However, the polar aprotic solvents such as dimethylformamide (DMF), dimethylsulfoxide (DMSO), acetonitrile (CH3CN) and dichloromethane (DCM) were found to be promising and provided moderate product yield under similar reaction conditions (Table 1, entries 3-6). Interestingly, water was found to be most effective reaction medium and afforded almost 15
ACCEPTED MANUSCRIPT quantitative yield of the desired product (Table 1, entry 7). The use of water as a “green” reaction medium is a remarkable advantage, which makes the developed protocol a greener and attractive from both environmental and economical viewpoints. Therefore, further experiments were conducted using water as a solvent of choice. Further in the absence of the photocatalyst,
T
there was no reaction observed even in prolonged reaction time (Table 1, entry 8). However,
IP
when 20 mg of photocatalyst was used, the reaction was found to be slow and afforded 70 %
CR
conversion in prolonged reaction time (72 h) (Table 1, entry 7). Further increase in photocatalyst amount to 50 mg, enhanced the reaction rate significantly and afforded 95% conversion in 48h.
US
Further increase in photocatalyst amount to 70 mg although did not provide any significant
AN
change in the conversion and yield of the product, albeit the reaction completed in shorter time (42 h). Based on these controlled experiments, we selected 50 mg photocatalyst as the optimum
M
amount for the reaction (Table 1, entry 8). Furthermore, the reaction afforded best results in 48h
ED
of visible, irradiation; the lesser time gave poor conversion, whereas longer reaction time did not provide any significant enhancement in the yield of the desired product under optimized reaction
PT
conditions. In order to confirm the photocatalytic nature of the reaction, following blank
CE
experiments were carried out: i) no reaction occurred in the absence of photocatalyst (Table 1, entry 8) under visible light irradiation for 48 h.; ii) a very poor conversion (10% by GC) was
AC
observed in case of dark condition using hybrid photocatalyst under otherwise identical conditions.; iii) no reaction occurred using either PANI, TiO2 and TiO2-PANI as photocatalysts under identical conditions (Table 1, entry 9-11). These results confirmed that light and gold are essentially required for the reaction to occur.
Based on these experiments; the optimized
reaction conditions should include photocatalyst 50 mg, water as reaction medium, reaction time 48h, visible light and temperature 25 oC. 16
ACCEPTED MANUSCRIPT In order to establish the synergistic effect of the components in ternary hybrid TiO 2-PANIAuNPs, we performed the reaction with Au, Au-TiO2, Au-PANI under described reaction conditions. In case of neat AuNPs the reaction did occur but afforded poor product yield, which is attributed to the fast recombination of the electron-hole pairs on the surface (Table 1, entry
T
12). However, no reaction was occurred in subsequent recycling experiment, which is mainly
IP
due to the agglomeration and deactivation of the AuNPs. In case of Au-TiO2 and Au-PANI,
CR
almost similar activity was obtained (Table 1, entry 13-14), which is attributed to the better charge separation and suppressed recombination rates, resulting from the activation and
US
stabilization of AuNPs on the photoactive supports. Among all combinations, ternary hybrid,
AN
TiO2-PANI-AuNPs provided the ideal synergistic effect between AuNPs and the support TiO2PANI for this transformation. This enhancement is presumed to the combined participation of
M
TiO2-PANI in supplying the electrons in the CB of AuNPs as well as in the alkyne addition to
AC
CE
PT
ED
the interface.
17
ACCEPTED MANUSCRIPT Table 1: Results of the optimization experiments[a] Yield
(%)[b]
(%)[c]
Toluene
75
72
TiO2-PANI-AuNPs
CHCl3
70
68
3
TiO2-PANI-AuNPs
DMF
80
78
4
TiO2-PANI-AuNPs
CH3CN
85
5
TiO2-PANI-AuNPs
DMSO
84
82
6
TiO2-PANI-AuNPs
DCM
90
88
7
TiO2-PANI-AuNPs
H2O
95
92
-[d],70[e],
-[d], 65[e],
71[f]
67[f]
H2O
-
-
H2O
-
-
H2O
-
-
H2O
35, -g
32, -g
TiO2-PANI-AuNPs
2
IP
1
CR
Solvent
US
Catalyst
82
8
TiO2-PANI-AuNPs
9
PANI
10
TiO2
11
TiO2-PANI
12
Au NPs
13
Au-TiO2
H2O
80
78
14
Au-PANI
H2O
82
80
PT
ED
M
AN
H2O
T
Conv.
Entry
[a]
AC
CE
Reaction conditions: benzaldehyde (1.0 mmol), piperidine (1.2 mmol), phenylacetylene (1.2 mmol), H2O (4.0 mL) and photocatalyst (50 mg, 0.005 mmol Au) at 25 oC for 48 h in visible light; [b]Conversion was determined by GC-MS; [c]Isolated yields; [d]blank without photocatalyst; [e]when 20 mg of photocatalyst is used for 72h; [f]when 70 mg of photocatalyst is used, reaction was found to be completed in 42h; [g]recycling experiment.
After having the optimized reaction conditions in hand, we investigated the reaction scope with a variety of substrates and the results are summarized in Table 2. Both aromatic and aliphatic aldehydes provided the desired products in high yields (Table 2, entries 1–8). Among the various aromatic aldehydes studied, benzaldehydes having electron donating groups were found to be more reactive (Table 2, entry 2-3) as compared to those having electron withdrawing ones (Table 18
ACCEPTED MANUSCRIPT 2, entry 4-5). Notably, aliphatic aldehydes such as cyclohexane carboxaldehyde and nbutyraldehyde also displayed higher reactivity and afforded excellent product yields (entries 67). Long chain aldehyde such as n-decanal provided poor product yield (Table 1, entry 8). Furthermore, secondary amines were also showed comparable efficiency as shown in the Table 2
T
(entry 9-11). The reaction with primary amines, i.e. n-butyl amine and n-hexylamine under the
IP
described reaction conditions did not afford the desired propargylamine even after the prolonged
CR
reaction time. However, corresponding Schiff bases generated from the corresponding aldehyde and primary amine were obtained as the predominant products at the end of the reaction. Good
US
to excellent yields were obtained for aryl alkynes (Table 2, entries 11-12), whereas, the reactivity
AC
CE
PT
ED
M
AN
was found to be little lower in the case of aliphatic alkynes (Table 2, entries 13-14).
19
ACCEPTED MANUSCRIPT Table 2: Visible light assisted TiO2-PANI-AuNPs catalyzed A3 -coupling of aldehydes, alkynes, and amines[a] NR2R3
Visible light
1
R CHO + R2R3NH + R4
H
R1
Water, 48h
R4
TiO2-PANI-AuNPs
R1
R2R3NH
R4
1
Ph
piperidine
Ph
92
2
4-CH3C6H4
piperidine
Ph
85
3
4-OCH3C6H4
piperidine
Ph
87
4
4-ClC6H4
piperidine
Ph
90
5
4-NO2C6H4
piperidine
Ph
40
6
Cyclohexyl
piperidine
Ph
90
7
propyl
piperidine
Ph
88
8
decanal
piperidine
Ph
55
9
Ph
pyrrolidine
Ph
85
10
Ph
morpholine
Ph
80
11
Ph
piperidine
4-OCH3C6H4
90
12
Ph
piperidine
4-ClC6H4
84
Ph
piperidine
(CH3)3C
40
Ph
piperidine
Butyl
70
[a]
IP
CR
US
AN
M
ED
PT
14
CE
13
Yield[b]
T
Entry
AC
Reaction conditions: benzaldehyde (1.0 mmol), piperidine (1.2 mmol), and phenylacetylene (1.2 mmol), H2O (4.0 mL) and catalyst (50 mg, 0.005 mmol Au) at room temp for 48 h in visible light; [b] Isolated yields.
In order to determine the stability and recycling ability of the photocatalyst TiO 2-PANI-AuNPs, the reaction between benzaldehyde, piperidine and phenylacetylene was carried out under the optimized reaction conditions. After completion of the reaction, the photocatalyst was separated by centrifugation and washed with water, methanol, dried in vacuum, and then reused with a 20
ACCEPTED MANUSCRIPT fresh charge of reactants for subsequent runs under identical conditions. The recycling ability of the recovered photocatalyst was tested for five consecutive runs and the results are summarized in Figure 9. The results demonstrate that the photocatalyst could be efficiently used for five runs without noticeable deactivation, suggesting its good reusability and stability under the light
T
irradiation in A3-coupling of benzaldehyde, piperidine and phenylacetylene. Furthermore, to
IP
evaluate the leaching and to establish the heterogeneous nature of the reaction, the photocatalyst
CR
was removed by filtering when the conversion reached to 50 % as determined by GC in A3coupling reactions, and then the resulting reaction mixture was continued under the same
US
conditions. The conversion of the benzaldehyde did not significantly increase further, which
AN
suggested that the reaction was truly heterogeneous in nature. Furthermore, the reaction mixture was subjected to ICP-AES in order to determine the leaching of active metal content during the
M
reaction. There was no detectable metal content observed in the reaction mixture, further
ED
confirmed that the developed photocatalyst was highly stable and leaching had not occurred
AC
CE
PT
during the reaction.
Figure9: Results of recycling experiments
21
ACCEPTED MANUSCRIPT To check the structural stability of the photocatalyst, we analyzed the recycled photocatalyst recovered after fifth run by XRD and HR-TEM as shown in the Figure 10. As can be seen, that the XRD and TEM image of the recovered photocatalyst remained almost unchanged that suggested the higher stability of the photocatalyst without any morphological change during the
AC
CE
PT
ED
M
AN
US
CR
IP
T
photocatalytic reaction conditions.
Figure 10: a,b) HR-TEM images of Fresh and recovered photocatalyst; c,d) XRD of fresh and recovered photocatalyst. Based on the existing prior art we depicted a plausible mechanism of the reaction as shown in Scheme 3. Based on the experimental results (Table 1), the ternary hybrid TiO2-PANI-AuNPs exhibited higher photocatalytic activity than other components such as, AuNPs, AuNps-TiO2 and Au-PANI which is attributed to the synergistic effect of all components (PANI, TiO2 and 22
ACCEPTED MANUSCRIPT AuNPs) in hybrid providing efficient electron transfer for the reaction. In the ternary hybrid, PANI has an extended π-delocalized conjugated structure and acted as a photosensitizer, which strongly absorbs the visible light (PANI + hʋ → h+ + e−) to induce π - π* transition and transport the excited electrons to the π* orbital. These electrons can be transferred to the conduction band
T
of TiO2 and AuNPs; hence PANI can provide electrons to both TiO2 and AuNPs as shown in
IP
Scheme 3. The electrons and holes on the Au interface activate the substrates and take part in the
CR
reaction. It is believed that the first step involves the adsorption of the alkyne on the AuNPs surface due to the alkynophilicity displayed by gold nanoparticles on TiO2-PANI [64-65]. Then,
US
the enamine formed from the reaction between aldehyde and the amine interacts with the
AC
CE
PT
ED
M
AN
alkynyl–[Au-PANI-TiO2] complex to afford the desired propargylamine (Scheme 3).
Scheme 3: Possible mechanism of the photocatalytic coupling reaction 23
ACCEPTED MANUSCRIPT Conclusion In conclusion, we have demonstrated the first report on photocatalytic A3-coupling of aldehydes, amines and alkynes using water as green reaction media under mild conditions using visible irradiation. A novel ternary hybrid photocatalyst synthesized by coupling of TiO2 with PANI
T
followed by immobilization of gold nanoparticles has been developed for the said reaction. The
IP
developed photocatalyst showed enhanced activity mainly due to the better electron-hole
CR
separation, higher electron mobility and electron transfer at the surface. At the end of the reaction, the photocatalyst was removed by centrifugation and used for subsequent runs. The
US
photocatalyst showed efficient recycling without any significant loss in activity and leaching of
AN
the active metal during the reaction. We believe that this report will open new avenues for developing other hybrid photocatalysts for light assisted greener organic transformations.
M
Experimental
ED
Materials
All the chemicals were commercially available and used without further purification. Aniline
PT
(≥99.5 %), potassium persulfate (PPs) (≥99.99 %), gold chloride (≥99.99 %), trisodium
CE
citrate dihydrate and titanium isopropoxide (TiOP) (≥ 99.7 %), were purchased from Sigma Aldrich. Acetic acid, 2-butanol, hydrochloric acid, ammonia solution (35%), ethanol,
AC
methanol and acetone were purchased from Merck (India). All chemicals and solvents are of analytical grade and used as received. Deionised water was used throughout the synthesis. Techniques used The FTIR spectra were recorded on a Nicolet 8700 FTIR spectrometer. Phase structure and crystalline state of the materials was determined on Bruker D8 Advance diffractometer at 40 kV and 40 mA with Cu Kα radiation (λ= 0.15418 nm). For XRD, the samples were prepared on glass 24
ACCEPTED MANUSCRIPT slide by adding well dispersed catalyst in slot and drying properly. Scanning electron microscopy (SEM) was done using FESEM, Quanta 200 F (Netherland) at a voltage of 10-30kV. Inner fine structure of samples was determined with high resolution transmission electron microscopy using JEOL-JEM 2100 electron microscope operating at an acceleration voltage of 200 kV. The
T
samples for TEM analysis were made by depositing very dilute aqueous suspension of samples
IP
on carbon coated TEM grid. Thermo gravimetric analyses (TGA) were done using a thermal
CR
analyzer TA-SDT Q-600. Loading of gold on TiO2-PANI composite was determined using an inductively coupled plasma atomic emission spectrometer (ICP-AES, PS-3000UV, Leeman
US
Labs). Solid UV–visible spectra of samples were collected on Perkin Elmer lambda-19UV–vis–
AN
NIR spectrophotometer using a 10 mm quartz cell, using BaSO4 as reference. X-ray photoelectron microscopy using ESCA+, (omicron nanotechnology, Oxford Instrument
M
Germany) equipped with monochromatic aluminium source (Al ka radiation hv =1486.7ev). The
ED
instrument was operated at 15kv and 20mA. Sample were taken in powder / pellet and deposited on cu tape and degassed for overnight in XPS FEL chamber to minimize the air contaminator at
PT
sample surface as well as degasing in main chamber. To overcome the charging problem a
CE
charge neutralizer of 2 keV is applied and binding energy of C1s core (284.6ev) was taken as reference The PL measurements of catalysts were carried out at room temperature using
AC
Fluoromax-4C spectrofluorometer, from HORIBA Scientific at an excitation wavelength of 330 nm. Photocatalytic experiments were performed under visible light by using 20 W white cold LED flood light (model no. HP-FL- 20W-F-Hope LED Opto-Electric Co., Ltd.). Intensity of the light at vessel was measured by intensity meter and was found to be 75 Wm-2. Product identification was carried out by GCMS using HP 5972 MSD coupled with HP 5890 GC, HP
25
ACCEPTED MANUSCRIPT (USA) 1998. 1H-NMR and 13C NMR spectra of the products were recorded at 500 MHz by using Bruker Avance-III 500 MHz instrument. Synthesis of TiO2-PANI composites Anatase TiO2 was prepared by hydrothermal treatment. In brief, 20 mmol of titanium
T
isopropoxide (IV) was added in the solution containing of 20 ml acetic acid and 5ml 2-butanol.
IP
The resulting mixture was vigorously stirred at 60 oC for 5 h and then autoclaved at 180 oC for
CR
24 h. The product was filtered and dried for further use. The as-prepared TiO2 (0.5g) was first dispersed in 50 ml of water-ethanol (1:1) mixture by ultra-sonication followed by the addition of
US
aniline monomer (0.5 ml) and 10 ml of HCl solution (1.2 M) which contained 0.4 g of
AN
ammonium peroxydisulfate (APS). The polymerization reaction was carried out under ice bath condition for 24 h. The colour of the reaction mixture turned green and the resulting dark green
M
product was separated by filtration, washed with deionized water, methanol and dried at 80 oC
ED
for 12 h.
Synthesis of TiO2-PANI-AuNPs ternary hybrid
PT
In brief 5 mM HAuCl4 aqueous solution (5 mL) was added to 20 mL of deionized water and
CE
mixed for 5 min before addition of suspension containing 500 mg of TiO2-PANI composite in 10 ml of water. Resulting reaction mixture was heated until it reached to the desired temperature in
AC
the range 50–100 °C and then the preheated 1 mL of 0.5% trisodium citrate solution was added to this mixture. The reaction mixture was heated until evident colour change had occurred and then it allowed cooling to room temperature. In order to remove unattached AuNPs to TiO2PANI surface, the reaction mixture was subjected to a few washing steps by centrifugation and re-dispersion in 0.5% solution of trisodium citrate. The loading of Au and Ti in the synthesized
26
ACCEPTED MANUSCRIPT hybrid TiO2-PANI-AuNPs was found to be 2 wt% and 3.5 wt% respectively, as determined by ICP-AES. General experimental procedure In a typical experiment, all the substrates and photocatalyst, i.e. aldehyde (1.0 mmol), amine (1.2
T
mmol), alkyne (1.2 mmol), TiO2-PANI-AuNPs (50 mg, 0.005 mmol Au) and water (4 mL) were
IP
added into a dried borosil round bottom flask equipped with magnetic bar under stirring to give a
CR
well-dispersed solution. After sealing with a rubber septum the sealed and evacuated flask was placed in front of 20 W white cold LED flood light (visible light source) to carry out visible light
US
induced coupling at room temperature under nitrogen atmosphere. The progress of the reaction
AN
was monitored by TLC (SiO2). After completion of the reaction, ethyl acetate (2 mL) was added to the resulting mixture, followed by filtration and washing with additional ethyl acetate (4 mL).
M
The crude reaction product was purified by column chromatography (silica gel, hexane/EtOAc)
ED
and identified by GC-MS and 1H-NMR spectroscopy. Acknowledgements
PT
We acknowledge Director, CSIR-Indian Institute of Petroleum (IIP) for his kind permission to
CE
publish these results. VP thanks Council of Scientific and Industrial Research (CSIR), New
in analysis.
AC
Delhi for providing fellowship. Analytical division is kindly acknowledged for providing support
27
ACCEPTED MANUSCRIPT REFERENCES [1].
J. M. R. Narayanam, C. R. J. Stephenson, Visible light photoredox catalysis: applications in organic synthesis, Chem. Soc. Rev. 40 (2011) 102–113. https://doi.org/10.1039/B913880N J. She, Z. Fu, J. Lia, B. Zeng, S. Tang, W. Wu, H. Zhao, D. Yin, S. R. Kirk, Visible light-
T
[2].
IP
triggered vanadium-substituted molybdophosphoric acids to catalyze liquid phase
404. https://doi.org/10.1016/j.apcatb.2015.09.048
W. Zhong, T. Qiao, J. Dai, L. Mao, Q. Xu, G. Zou, X. Liu, D.Yin F. Zhao, Visible-light-
US
[3].
CR
oxygenation of cyclohexane to KA oil by nitrous oxide. Appl. Catal. B, 182 (2016) 392-
AN
responsive sulfated vanadium-doped TS-1 with hollow structure: Enhanced photocatalytic
10.1016/j.jcat.2015.06.013
P. Devaraji, N. K. Sathu, C. S. Gopinath, Ambient oxidation of benzene to phenol by
ED
[4].
M
activity in selective oxidation of cyclohexane, J. Catal. 330 (2015) 208-221.
photocatalysis on Au/Ti0.98V0.02O2: Role of holes, ACS Catal. 4 (2014) 2844-2853.
P. Zhang, Y. Gong, H. Li, Z. Chen, Y. Wang, Selective oxidation of benzene to phenol by
CE
[5].
PT
https://doi.org/10.1021/cs500724z
FeCl3/mpg-C3N4 hybrids, RSC Adv. 3 (2013) 5121–5126.
[6].
AC
https://doi.org/10.1039/C3RA23357J K. Yasutaka, M. Yasuhiro, Y. Hiromi, Photocatalytic epoxidation of olefins using molecular O2 by TiO2 incorporated in hydrophobic Y- zeolite, Rapid Commun. Photosci. 4 (2015) 19-21. https://doi.org/10.5857/RCP.2015.4.1.19
28
ACCEPTED MANUSCRIPT [7].
Y. –L Cui, X. –N. Guo, Y. –Y. Wang. X. –Y. Guo, Visible-light-driven photocatalytic Narylation of imidazole derivatives and arylboronic acids on Cu/graphene catalyst, Sci. Rep. 5 (2015) 1-9. https://doi.org/10.1038/srep12005
[8].
Y. W. Zheng, B. Chen , P. Ye, K. Feng, W. Q. Wang, Y. Meng, L. –Z. Wu, C. -H. Tung,
IP
hydroxylation, J. Am. Chem. Soc. 138(32) (2016) 10080–10083.
CR
https://doi.org/10.1021/jacs.6b05498 [9].
T
Photocatalytic hydrogen-evolution cross-couplings: Benzene C–H amination and
X. –H. Li, M. Baar, S. Blechert, M. Antonietti, Facilitating room-temperature Suzuki
US
coupling reaction with light: Mott-Schottky photocatalyst for C-C-coupling, Sci. Rep.
[10].
AN
3(1743) (2013) 1-6. https://doi.org/10.1038/srep01743
T. Lei, W. –Q. Liu, J. Li, M. –Y. Huan, B. Yang, Q. Y. Meng, B. Chen, C. –H. Tung, L. –
M
Z. Wu, Visible light initiated Hantzsch synthesis of 2,5-diaryl-substituted pyrroles at
ED
ambient conditions, Org. Lett. 18 (2016) 2479–2482. https://doi.org/10.1021/acs.orglett.6b01059 A. Pu, J. Deng, M. Li, J. Gao, H. Zhang, Y. Hao, J. Zhong, X. Sun, Coupling Ti-doping
PT
[11].
CE
and oxygen vacancies in hematite nanostructures for solar water oxidation with high efficiency, J. Mater. Chem. A. 2 (2014) 2491–2497.
[12].
AC
https://doi.org/10.1039/C3TA14575A W. J. Ong, L. Tan, P. Chai, S. T Yong, A. R. Mohamed, Highly reactive {001} facets of TiO2-based composites: synthesis, formation mechanism and characterization, Nanoscale. 6 (2014) 1946–2008. https://doi.org/10.1039/C3NR04655A
29
ACCEPTED MANUSCRIPT [13].
T. Kawahara, Y. Konishi, H. Tada, N. Tohge, J. Nishii, S. A. Ito, A patterned TiO2 (Anatase)/TiO2 (Rutile) bilayer-type photocatalyst: Effect of the Anatase/Rutile Junction on the photocatalytic activity, Angew. Chem. Int. Ed. 41 (2002) 2811−2813.
[14].
R. Beranek, B. Neumann, S. Sakthivel, M. Janczarek, T. Dittrich, H. Tributsch, H. Kisch,
T
Exploring the electronic structure of nitrogen-modified TiO2 photocatalysts through
[15].
CR
https://doi.org/10.1016/j.chemphys.2007.05.022
IP
photocurrent and surface photovoltage studies, Chem. Phys. 339 (2007) 11–19.
A. Morandeira, I. Lopez-Duarte, B. O'Regan, M. V. Martinez-Diaz, A. Forneli, E.
US
Palomares, T. Torres, J. R. Durrant, Ru(II)-phthalocyanine sensitized solar cells: the
AN
influence of co-adsorbents upon interfacial electron transfer kinetics, J. Mater. Chem. 19 (2009) 5016-5026. https://doi.org/10.1039/B904179F Y. H. Yum, S. R. Jang, R. Humphry-Baker, M. Grätzel, J. J. Cid, T. Torres, M. K.
M
[16].
ED
Nazeeruddin, Effect of co-adsorbent on the photovoltaic performance of zinc pthalocyanine-sensitized solar cells, Langmuir. 24(10) (2008) 5636-5640.
N. Zhang, M. Q. Yang, Z. R. Tang, Y. –J Xu, CdS–graphene nanocomposites as visible
CE
[17].
PT
https://doi.org/10.1021/la800087q
light photocatalyst for redox reactions in water: A green route for selective transformation
AC
and environmental remediation, J. Catal. 303 (2013) 60-69. https://doi.org/10.1016/j.jcat.2013.02.026 [18].
M. Nasrollahzadeh, S. M. Sajadi, Green synthesis, characterization and catalytic activity of the Pd/TiO2 nanoparticles for the ligand-free Suzuki–Miyaura coupling reaction, J. Colloid Interf. Sci. 465 (2016) 121. https://doi.org/10.1016/j.jcis.2015.11.038.
30
ACCEPTED MANUSCRIPT [19].
M. Nasrollahzadeh, S. M. Sajadi, Euphorbia heterophylla leaf extract mediated green synthesis of Ag/TiO2 nanocomposite and investigation of its excellent catalytic activity for reduction of variety of dyes in water, J. Colloid Interf. Sci. 462 (2016) 272. https://doi.org/10.1016/j.jcis.2015.09.073. M. Nasrollahzadeh, Z. Issaabadi, M. M. Tohidi, S. M. Sajadi, Recent developments in the
T
[20].
CR
in the chemical reactions, Chem. Rec. 18 (2018) 165. https://doi.org/10.1002/tcr.201800069
S. G. Babu, R. Vinoth, D. P. Kumar, Influence of electron storing, transferring and
US
[21].
IP
biosynthesis of Cu-based recyclable nanocatalysts using plant extracts and their application
AN
shuttling assets of reduced graphene oxide at the interfacial copper doped TiO2 p–n heterojunction for increased hydrogen production, Nanoscale. 7(2015) 7849-7857.
Q. Liu, Y. Yang, H. Li, R. Zhu, Q. Shao, S. Yang, J. Xu, NiO nanoparticles modified with
ED
[22].
M
https://doi.org/10.1039/c5nr00504c
5,10,15,20-tetrakis(4-carboxyl pheyl)-porphyrin: Promising peroxidase mimetics for H2O2 glucose
detection,
PT
and
Biosens.
Bioelectron.
64
(2015)
147–153.
[23].
CE
https://doi.org/10.1016/j.bios.2014.08.062 Q. Liu, Y. Yang, X. Lv, Y. Ding, Y. Zhang, J. Jing, C. Xu, One-step synthesis of uniform
AC
nanoparticles of porphyrin functionalized ceria with promising peroxidase mimetics for H2O2 and glucose colorimetric detection, Sensors and Actuators B: Chemical, 240 (2017) 726–734, https://doi.org/10.1016/j.snb.2016.09.049. [24].
Q. Liu, P. Chen, Z. Xu, M. Chen, Y. Ding, K. Yue, J. Xu, A facile strategy to prepare porphyrin functionalized ZnS nanoparticles and their peroxidase-like catalytic activity for
31
ACCEPTED MANUSCRIPT colorimetric sensor of hydrogen peroxide and glucose, Sensors and Actuators B: Chemical, 251, 2017, 339-348, https://doi.org/10.1016/j.snb.2017.05.069. [25].
M. Chen, L. Sun, Y. Ding, Z. Shi, Q. Liu, N,N′-Di-carboxymethyl perylene diimide functionalized magnetic nanocomposites with enhanced peroxidase-like activity for
T
colorimetric sensing of H2O2 and glucose, New J. Chem., 41 (2017) 5853-5862,
G. Z. Liao, S. Chen, X. Quan, Y. B. Zhang, H. M. Zhao, Remarkable improvement of
CR
[26].
IP
10.1039/C7NJ00292K
visible light photocatalysis with PANI modified core–shell mesoporous TiO2
Y. J. Wang, J. Xu, W. Z. Zong, Y. F. Zhu, Enhancement of photoelectric catalytic activity
AN
[27].
US
microspheres, Appl. Catal. B. 102 (2011) 126−131. 10.1016/j.apcatb.2010.11.033
of TiO2 film via Polyaniline hybridization, Solid State Chem. 184 (2011) 1433−1438.
D. Wang, J. Zhang, Q Luo, X. Li, Y. Duan, J. An, Characterization and photocatalytic
ED
[28].
M
https://doi.org/10.1016/j.jssc.2011.04.001
activity of poly (3-hexylthiophene)-modified TiO2 for degradation of methyl orange under
PT
visible light, J. Hazardous Mat. 169 (2009) 546–550.
[29].
CE
https://doi.org/10.1016/j.jhazmat.2009.03.135 Y. Zhu, S. Xu, D. Yi, Photocatalytic degradation of methyl orange using
AC
polythiophene/titanium dioxide composites, React. Funct. Poly. 70 (2010) 282–287. https://doi.org/10.1016/j.reactfunctpolym.2010.01.007 [30].
J. Zhu, X. Huo, X. Liu, H. Ju, Gold nanoparticles deposited polyaniline−TiO2 nanotube for surface plasmon resonance enhanced photoelectrochemical biosensing, ACS Appl. Mater. Interfaces. 8 (2016) 341−349. https://doi.org/10.1021/acsami.5b08837
32
ACCEPTED MANUSCRIPT [31].
T. Naota, H. Takaya, S. I. Murahashi, Ruthenium-catalyzed reactions for organic synthesis, Chem. Rev. 98 (1998) 2599-2660. https://doi.org/10.1021/cr9403695
[32].
T. Murai, Y. Mutoh, Y. Ohta, M. Murakami, Synthesis of tertiary propargylamines by sequential reactions of in situ generated thioiminium salts with organolithium and
T
magnesium reagents, J. Am. Chem. Soc. 126 (2004) 5968-5969.
G. Dyker, Transition metal catalyzed coupling reactions under C−H activation, Angew.
CR
[33].
IP
https://doi.org/10.1021/ja048627v
Chem. Int. Ed. 38 (1999) 1698-1712.
C. Wei, C. –J. Li, A Highly efficient three-component coupling of aldehyde, alkyne, and
US
[34].
AN
amines via C−H activation catalyzed by gold in water, J. Am. Chem. Soc. 125 (2003) 9584-9585. https://doi.org/10.1021/ja0359299
M. Nasrollahzadeh, S. M Sajadi, Preparation of Au nanoparticles by Anthemis xylopoda
M
[35].
ED
flowers aqueous extract and their application for alkyne/aldehyde/amine A3-type coupling reactions, RSC Adv. 5 (2015) 46240. https://doi.org/10.1039/C5RA08927A M. Nasrollahzadeh, S. M. Sajadi, A. Rostami-Vartooni, Green synthesis of CuO
PT
[36].
CE
nanoparticles by aqueous extract of Anthemis nobilis flowers and their catalytic activity for the A³ coupling reaction, J. Colloid Interf. Sci. 459 (2015) 183-188.
[37].
AC
https://doi.org/10.1016/j.jcis.2015.08.020 M. Nasrollahzadeh, M. Sajjadi, F. Ghorbannezhad, S. M. Sajadi, A Review on recent advances in the application of nanocatalysts in A3 coupling reactions, Chem. Rec. 18(10) (2018) 1409-1473. https://doi.org/10.1002/tcr.201700100.
33
ACCEPTED MANUSCRIPT [38].
V. K.-Y. Lo, Y. Liu, M –K Wong, C. –M. Che, Gold(III)salen complex-catalyzed synthesis of propargylamines via a three-component coupling reaction, Org. Lett. 8 (2006) 15291532. https://doi.org/10.1021/ol0528641
[39].
C. Wei, Z. Li, C. –J. Li, The first silver-catalyzed three-component coupling of aldehyde,
L Shi, Y. Q. Tu, M. Wang, F. –M. Zhang, C.–A. Fan, Microwave-promoted three-
IP
[40].
T
alkyne and amine, Org. Lett. 5 (2003) 4473-4475. https://doi.org/10.1021/ol035781y
CR
component coupling of aldehyde, alkyne and amine via C−H activation catalyzed by copper in water, Org. Lett. 6 (2004) 1001-1003. https://doi.org/10.1021/ol049936t H. Z. S. Huma, R. Halder, S. S. Karla, J. Das, J. Iqbal, Cu(I)-catalyzed three component
US
[41].
AN
coupling protocol for the synthesis of quinoline derivatives, Tetrahedron Lett. 43 (2002) 6485-6488. https://doi.org/10.1016/S0040-4039(02)01240-6 L P. Hua, W. Lei, Mercurous chloride catalyzed Mannich condensation of terminal alkynes
M
[42].
ED
with secondary amines and aldehydes, Chin. J. Chem. 23 (2005) 1076-1080. https://doi.org/10.1002/cjoc.200591076 C. J. Li, C. Wei, Highly efficient Grignard-type imine additions via C–H activation in and
under
solvent-free
conditions,
Chem.
Commun.
(2002)
268-269.
CE
water
PT
[43].
https://doi.org/10.1039/B108851N L. Zhang, C. Wei, R. S Varma, C.–J. Li, Three-component coupling of aldehyde, alkyne,
AC
[44].
and amine catalyzed by silver in ionic liquid, Tetrahedron Lett. 45 (2004) 2443-2446. https://doi.org/10.1016/j.tetlet.2004.01.044 [45].
K. M. Reddy, N. S. Babu, I. Suryanarayana, P. S. S. Prasad, N. Lingaiah, The silver salt of 12-tungstophosphoric acid: an efficient catalyst for the three-component coupling of an aldehyde, an amine and an alkyne, Tetrahedron Lett. 47 (2006) 7563-7566. 34
ACCEPTED MANUSCRIPT https://doi.org/10.1016/j.tetlet.2006.08.094 [46].
Y. Zhang, A. M. Santos, E. Herdtweck, J. Mink, F. E. Kuhn, Organonitrile ligated silver complexes with perfluorinated weakly coordinating anions and their catalytic application for coupling reactions, New J. Chem. 29 (2005) 366-370.
X. Zhang, A. Corma, Effective Au(III)–CuCl2-catalyzed addition of alcohols to alkenes,
IP
[47].
T
https://doi.org/10.1039/B414060E
[48].
CR
Chem. Commun. (2007) 3080-3082. https://doi.org/10.1039/B706961H X. Zhang, A. Corma, Efficient addition of alcohols, amines and phenol to unactivated
US
alkenes by AuIII or PdII stabilized by CuCl2, Dalton Trans. (2008) 397-403.
[49].
AN
https://doi.org/10.1039/B714617E
P. Kumar, A. Kumar, B. Sreedhar, B. Sain, S. S. Ray, S. L. Jain, Cobalt phthalocyanine
M
immobilized on graphene oxide: an efficient visible-active catalyst for the photoreduction
ED
of carbon dioxide, Chem. Eur. J. 20 (2014) 6154–6161. https://doi.org/10.1002/chem.201304189 A. Kumar, P. Kumar, C. Joshi, M. Manchanda, R. Boukherroub, S. L Jain, Nickel
PT
[50].
CE
decorated on phosphorous-doped carbon nitride as an efficient photocatalyst for reduction of nitrobenzenes, Nanomaterials. 6(59) (2016) 1-14.
[51].
AC
https://doi.org/10.3390/nano6040059 V. Panwar, P. Kumar, S. S Ray, S. L Jain, Organic inorganic hybrid cobalt phthalocyanine/polyaniline as efficient catalyst for aerobic oxidation of alcohols in liquid phase, Tetrahedron Lett. 56 (2015) 3948–3953. https://doi.org/10.1016/j.tetlet.2015.05.003
35
ACCEPTED MANUSCRIPT [52].
M. R. Karim, J. H. Yeum, M. S. Lee, K. T. Lim, Preparation of conducting polyaniline/TiO2
composite
submicron-rods
by
the
gamma-radiolysis
oxidative
polymerization method, React. Funct. Poly. 68 (2008) 1371-1376. https://doi.org/10.1016/j.reactfunctpolym.2008.06.016 Q. Wang, X. Qian, S. Wang, W. Zhou,H. Guo, X. Wua, J. Li, X. Wang, Conductive
T
[53].
https://doi.org/10.1016/j.synthmet.2014.11.007
Z. Cai, Z. Xiong, X. Lu, J. Teng, In situ gold-loaded titania photonic crystals with
US
[54].
CR
walled carbon nanotube, Synthetic Metals. 199 (2015) 1-7.
IP
polyaniline composite films from aqueous dispersion: Performance enhancement by multi-
https://doi.org/10.1039/C3TA13878J
H. Xia, Q. Wang, Synthesis and characterization of conductive polyaniline nanoparticles
M
[55].
AN
enhanced photocatalytic activity, J. Mater. Chem. A. 2 (2014) 545-553.
ED
through ultrasonic assisted inverse microemulsion polymerization, J. Nanopart Res. 3 (2001) 399–409.
A. B. Rohom, P. U. Londhe, N. B. Chaure, Enhancement of optical absorption by
PT
[56].
CE
incorporation of plasmonic nanoparticles in PANI films, Nanosci. Nanotech. 6 (2016) 8387. https://doi.org/10.5923/c.nn.201601.16 A. Katoch, M. Burkhart, T. Hwang, S. S. Kim, Synthesis of polyaniline/TiO2 hybrid
AC
[57].
nanoplates via a sol–gel chemical method, Chem. Eng. J. 192 (2012) 262–268. https://doi.org/10.1016/j.cej.2012.04.004 [58].
M. O. Ansari, M. M. Khan, S. A. Ansari, J. Lee, M. H. Cho, Enhanced thermoelectric behaviour and visible light activity of Ag@TiO2/polyaniline nanocomposite synthesized by biogenic-chemical route, RSC Adv. 4 (2014) 23713-23719. 36
ACCEPTED MANUSCRIPT https://doi.org/10.1039/C4RA02602K [59].
D. Geethalakshmi, N. Muthukumarasamy, R. Balasundaraprabhu, Effect of dopant concentration on the properties of HCl-doped PANI thin films prepared at different temperatures, Optik-International Journal for Light and Electron Optics. 125 (2014) 1307-
M. O. Ansari, F. Mohammad, Thermal stability and electrical properties of dodecyl-
IP
[60].
T
1310. https://doi.org/10.1016/j.ijleo.2013.08.014
CR
benzene-sulfonic-acid doped nanocomposites of polyaniline and multi-walled carbon nanotubes, Composites. Part B.43 (2012) 3541-3548.
N. Parveen, M. O. Ansari, M. H. Cho, Correction to “Route to high surface area,
AN
[61].
US
https://doi.org/10.1016/j.compositesb.2011.11.031
mesoporosity of polyaniline−titanium dioxide nanocomposites via one pot synthesis for
M
energy storage applications, Eng. Chem. Res. 55 (2016) 2277–2277.
[62].
ED
https://doi.org/10.1021/acs.iecr.6b00362
R. Kumar, R. M. E. Shishtawy, M. A. Barakat, Synthesis and characterization of Ag-
PT
Ag2O/TiO2@polypyrrole heterojunction for enhanced photocatalytic degradation of
[63].
CE
methylene blue, Catalysts. 6 (2016) 76. https://doi.org/10.3390/catal6060076 H. Wang, R. Liu, Z. Cui, X. Lü, Y. Li, X. Li, S. Xin, R. Zhang, M. Lei, Z. Lin, Durable
AC
and Efficient Hollow Porous Oxide Spinel Microspheres for Oxygen Reduction, Joule, 2 (2018) 337-348 [64].
M. G. Bejar, K. Peters, G. L. H. Tapley, M. Grenier, J. C. Scaiano, Rapid one-pot propargylamine synthesis by Plasmon mediated catalysis with gold nanoparticles on ZnO under ambient conditions, Chem. Commun. 49 (2013) 1732. https://doi.org/10.1039/C3CC38287G 37
ACCEPTED MANUSCRIPT K. Yang, Y. Li, K. Huang, X. Chen, X. Fu, W. Dai, Promoted effect of PANI on the preferential oxidation of CO in the presence of H2 over Au/TiO2 under visible light irradiation, Int. J. hydrogen energy. 39 (2014) 18312-18325.
CE
PT
ED
M
AN
US
CR
IP
T
https://doi.org/10.1016/j.ijhydene.2014.09.053
AC
[65].
38
ACCEPTED MANUSCRIPT
AC
CE
PT
ED
M
AN
US
CR
IP
T
Table of content entry
39
ACCEPTED MANUSCRIPT Highlights
First report on photocatalytic A3- coupling of aldehyde, amine and alkyne using goldpolyanilne-titania nanocomposite photocatalyst.
Visible light assisted methodology for the formation of propargylamines under mild
Enhanced performance of photocatalyst due to the slower electron-hole recombination
IP
T
conditions.
CR
and better electron mobility.
Environmentally benign coupling methodology using H2O as a green solvent.
Facile recovery and efficient recycling of photocatalyst for several runs with consistent
US
AC
CE
PT
ED
M
AN
activity.
40
Vineeta Panwar, Suman L. Jain PII: DOI: Reference:
S0928-4931(18)31777-6 https://doi.org/10.1016/j.msec.2019.01.085 MSC 9343
To appear in:
Materials Science & Engineering C
Received date: Revised date: Accepted date:
22 June 2018 14 January 2019 20 January 2019
Please cite this article as: V. Panwar and S.L. Jain, Ternary hybrid TiO2-PANI-AuNPs for photocatalytic A3-coupling of aldehydes, amines and alkynes: First photochemical synthesis of propargyl amines, Materials Science & Engineering C, https://doi.org/ 10.1016/j.msec.2019.01.085
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Ternary hybrid TiO2-PANI-AuNPs for photocatalytic A3-coupling of aldehydes, amines and alkynes: first photochemical synthesis of propargyl amines
T
Vineeta Panwara,b and Suman L. Jaina* a
IP
Chemical Sciences Division, CSIR-Indian Institute of Petroleum, Mohkampur, Dehradun-248005 (India) b
CR
Academy of Scientific and Industrial Research (AcSIR), New Delhi, India
US
*Corresponding author: Suman L. Jain
AN
Email: [email protected]
AC
CE
PT
ED
M
Tel. 91-135-2525788; Fax: 91-135-2660202;
1
ACCEPTED MANUSCRIPT ABSTRACT The present paper describes the successful synthesis and application of a ternary hybrid consists of gold nanoparticles decorated on titania-polyaniline (TiO2-PANI-AuNPs) for A3-coupling between aldehydes, terminal alkynes and amines under visible irradiation. The synthesis of
T
ternary hybrid involved the coating of PANI on TiO2 via an oxidative polymerization method
IP
followed by the deposition of AuNPs on TiO2-PANI using trisodium citrate as a reducing agent.
CR
The synthesized photocatalyst was characterized by various techniques like FT-IR, SEM, HRTEM, XRD, UV-VIS, ICP-AES, TGA, XPS and PL spectroscopy. The synthesized photocatalyst
US
exhibited higher efficiency which was presumed due to the suppressed electron-hole
AN
recombination and better electron mobility at the surface of the photocatalyst. In the hybrid, polyaniline was found to enhance the activity as well as stability of the photocatalyst owing to its
M
chemical interaction with titania and gold. Furthermore, after the reaction, the photocatalyst
ED
could readily be recovered and recycled for several runs with consistent photoactivity. Key words: Photocatalyst, multi-component coupling, gold nanoparticles, ternary hybrid, A3-
AC
CE
PT
coupling.
2
ACCEPTED MANUSCRIPT Introduction Visible light driven photocatalytic organic transformations provide novel avenues for well established reactions under mild conditions with or without altering the mechanistic pathways [1]. Particularly, light induced metal oxide catalyzed organic transformations are associated with
T
free radical non-selective reaction pathways and have been extensively used for various reactions
IP
such as oxidation of alkanes [2-3], hydroxylation of aromatics [4-5], epoxidation of alkenes [6],
CR
C-N [7-8] and C-C [9-10] coupling reactions. Among the known metal oxides, titanium dioxide
US
(TiO2) owing to its inherent properties such as higher photo-stability, non-toxicity, insolubility in aqueous media, chemically and biologically inertness, low cost and easy availability has been
AN
extensively used for organic transformations [11-12]. However, owing to the wide band gap of titania (3.0-3.2 eV), it does not show absorption in the visible region (λ > 400 nm) which
M
constitutes the major part of the solar spectrum [13]. A number of surface modifications of
ED
titania including doping of heteroatoms [14] and dye sensitization [15-16] have been well
PT
explored in order to reduce the band gap and to prevent the electron-hole recombinations. In addition, materials such as graphene oxide have been used to prepare heterostructures with TiO2
CE
to provide wide surface for reaction and prolonged charge separation [17-21]. Furthermore, some conjugate molecules, such as porphyrins and perylene diimide have been reported to enhance the
AC
photocatalytic activity of the metal oxide photocatalysts [22-25]. Conjugated polymers such as polyaniline (PANI) [26-27], polythiophene (PPTH) [28-29] and their derivatives due to their visible light absorbance, higher stability and better mobility of charge carriers have shown great deal of interest in recent years. In addition these polymers have been effectively used to combine with wide band gap inorganic semiconductors such as TiO2 to 3
ACCEPTED MANUSCRIPT improve the photo-catalytic performance and to shift the spectral absorption towards visible region. Furthermore, the conjugated structure of such polymer molecules can capture more photo-excited electrons to delay the recombination of electron-hole pairs [30]. In addition, the deposition of noble metal nanoparticles (Au, Pt and Pd) to these composites further increase the
T
photocatalytic activity due to the surface plasmon resonance (SPR) effect that improves the light
CR
IP
absorption as well as charge separation during the photocatalytic process.
Propargylamines are an important class of compounds which have widely been used as
US
precursors in the synthesis of heterocyclic compounds and as intermediates in the preparation of biologically active compounds including drugs [31-34]. Traditionally these compounds have
AN
been synthesized by using strong bases such as butyl lithium, organo-magnesium reagents or
M
lithium diisopropylamide (LDA) which initially form alkynyl metal compounds followed by their nucleophilic attack to imines or their derivatives [35]. However these reagents are used in
ED
stoichiometric amounts, hence produce large amounts of undesired waste and require strictly
PT
controlled experimental conditions. Catalytic coupling of alkyne, aldehyde and amine by C-H activation known as A3-coupling is an alternative atom-economical approach for their synthesis
CE
where water is the only by-product [36]. Among the recently reported several metal based
AC
catalysts such as gold salts (AuBr3 or AuCl3) [37], gold complexes [38], silver salts [39], copper salts [40-41], Hg2Cl2 [42] and a Cu/RuII bimetallic system [43-45], cationic gold has shown best activity for this transformation [46]. However, besides the potential limitations i.e. tedious recovery and non-recycling ability of homogeneous catalysis, the rapid reduction of cationic gold species into inactive metallic atoms is unavoidable when gold salts/ complexes activate alkynes/alkenes [47-48]. Furthermore, photocatalytic reactions are considered to be more promising owing to their cost effectiveness, use of renewable solar energy, mild reaction 4
ACCEPTED MANUSCRIPT conditions and higher atom efficiency. To the best of our knowledge so far there is no report known on the photocatalytic A3-coupling of aldehydes, amines and alkynes. In continuation to our on-going research on photocatalytic chemical transformations [49-50], herein we report the first successful example of photocatalytic A3-coupling of aldehydes, amines
IP
T
and alkynes using water as a solvent under visible light irradiation by employing a functional
CR
ternary hybrid, which include in-situ polymerization of aniline on TiO2 and grafting of gold
US
nanoparticles to yield TiO2-PANI-AuNPs composite (Scheme 1).
CHO R
+
N
Visible light
+ N H
AN
Water, 48h
R
TiO2-PANI-AuNPs
M
Scheme 1: Visible light driven photocatalytic A3-coupling of aldehydes, amines and alkynes
ED
Results and discussion
PT
Synthesis and characterization of catalyst The desired photocatalyst was synthesized by coating of TiO2 (anatase) on PANI during in-situ
CE
oxidative polymerization of aniline in the presence of potassium persulphate as an oxidant in
AC
acidic medium. In the second step gold nanoparticles as prepared via in situ reduction of HAuCl4 using trisodium citrate as a reducing agent grafted to TiO2-PANI to give ternary TiO2-PANIAuNPs as shown in Scheme 2. The Au and Ti contents in the synthesized hybrid were found to be 2 wt% and 3.5 wt%, respectively as determined by ICP-AES analysis.
5
ACCEPTED MANUSCRIPT
Aniline monomer
Titanium isopropoxide Hydrothermal Method
APS
Anatase TiO2
T
TiO2-PANI
US
CR
IP
HAuCl4
AN
TiO2-PANI-AuNPs
ED
M
Scheme 2: Schematic representation for the synthesis of TiO2-PANI-AuNPs
The changes in the chemical functionalities during the synthesis of hybrid are determined by
PT
FTIR spectroscopy. Figure 1 shows the FTIR spectra of PANI, TiO2-PANI and TiO2-PANI-
CE
AuNPs, respectively. In Figure 1a, the bands at 1571 and 1488 cm-1 are attributed to C=N and C=C stretching mode of vibration for the quinoid and benzenoid units of PANI. The peaks
AC
appearing at 1301 and 1232 cm-1 are assigned to C–N stretching mode of benzenoid ring [51]. In plane and out of plane bending vibration of C–H mode appears at 1120 cm-1and 813 cm-1 respectively. In FTIR spectrum of the TiO2-PANI (Figure 1b), the broad absorption of TiO2 centered at 3400 cm-1 is ascribed to the O-H stretching vibration of surface hydroxyl arising from the TiO2 [52]. In addition, the Ti–O stretching and Ti–O–Ti bridging vibration are appeared at ∼590 and ∼516 cm-1 respectively, which are characteristic bands of TiO2 [52]. More 6
ACCEPTED MANUSCRIPT importantly, TiO2-PANI exhibits the characteristic IR signature of both PANI (700-1600 cm-1) and TiO2 (400-700 cm-1), demonstrating the successful synthesis of TiO2-PANI composite. It is also worth mentioning that the characteristic peaks corresponding to pure PANI were found to be shifted towards longer wavelength to 1568 and 1481 cm-1 which indicated the chemical
T
interaction between the amine or imine groups of the PANI chains and the TiO2 [53]. This
IP
interaction may weaken the bond strengths of C=N, C=C and C-N in PANI macromolecule,
CR
which can be further confirmed by comparing the peak intensity of PANI and TiO2-PANI. Further, the π-π interactions shift the FT-IR peaks to lower frequencies due to the deformation of
US
the bonds. Therefore, in TiO2-PANI, the peaks related to quinoid rings were found to be shifted
AN
towards lower frequencies as compared to the pure PANI [53]. The FTIR of TiO2-PANI-AuNPs
AC
CE
PT
ED
M
(Figure 1c) was found to be almost similar to TiO2-PANI, except slight sharpness of the peaks.
7
M
AN
US
CR
IP
T
ACCEPTED MANUSCRIPT
ED
Figure 1: FTIR Spectra of a) PANI; b) TiO2-PANI; c) TiO2-PANI-AuNPs
PT
Figure 2 shows the TEM images of TiO2-PANI and TiO2-PANI-AuNPs to examine the inner nanostructure of the prepared materials. Spherical TiO2 nanoparticles (Figure 2a) having 3–4 nm
CE
size are randomly distributed in the PANI matrix and tend to line up along with the cross linked
AC
PANI chains. The ternary hybrid TiO2-PANI-AuNPs (Figure 2b) clearly shows the uniform distribution of gold nanoparticles having size in the range of 20-30 nm to the TiO2-PANI surface. The SAED pattern exhibited a distinct diffraction pattern with the appearance of dark and bright fringes, which are characteristic of the polycrystalline structures of both TiO2-PANI and TiO2PANI-AuNPs (Figure 2c, d). TEM images clearly indicate intimate contact among TiO2, PANI and Au, which would facilitate the electron transfer within the ternary hybrid to improve the photo-generated charge separation on the surface. Furthermore, elemental mapping (Figure 3) 8
ACCEPTED MANUSCRIPT confirms the homogeneous distribution of the elements in the ternary hybrid. Moreover, the presence of gold and other desired elements in EDAX confirmed the successful formation of
AC
CE
PT
ED
M
AN
US
CR
IP
T
ternary hybrid nanocomposite TiO2-PANI-AuNPs (Figure 3b).
Figure 2: TEM image and SAED pattern of a,c) TiO2-PANI; b,d) TiO2-PANI-AuNPs
9
M
AN
US
CR
IP
T
ACCEPTED MANUSCRIPT
Figure 3: EDAX pattern of a) TiO2-PANI and b) TiO2-PANI-AuNPs and elemental mapping of
ED
TiO2-PANI-AuNPs
PT
The crystalline phases of TiO2 and Au in TiO2-PANI and TiO2-PANI-AuNPs were examined by X-ray diffraction (XRD) pattern as shown in Figure 4. Characteristic diffraction peaks
CE
corresponding to anatase TiO2 (101), (004), (200), (105), (211), (204), (220) and (301) are found
AC
at 2θ = 25.28, 37.80, 48.05, 53.89, 55.06, 62.69, 70.31 and 76.02, respectively that matches well with JCPDS card 21-1272 (Figure 3a) [54]. The relatively sharp peaks indicated the highly crystalline nature of anatase TiO2. However, relatively weak peaks at 2θ = 44.37, 64.68, and 77.55 (Figure 3b) corresponding to fcc gold (200), (220) and (311), respectively, indicated the lower loading of AuNPs in the ternary hybrid (JCPDS card 02-1095).
10
AN
US
CR
IP
T
ACCEPTED MANUSCRIPT
M
Figure 4: XRD pattern of a) TiO2-PANI; b) TiO2-PANI-AuNPs
ED
UV-vis spectra of PANI, TiO2, TiO2-PANI, and TiO2-PANI-AuNPs are shown in Figure 5 [5556]. Pure polyaniline displayed two absorption bands centered at 330-370 nm ascribing to the n-
PT
л* transitions in PANI and a broad band at around 630 nm represents the transition of the
CE
quinoid rings in polyaniline chains (Figure 5a). Neat TiO2 owing to the wide band gap (3.2-3.4 eV) absorbs in the UV range between 380–400 nm. In case of TiO2-PANI composite (Figure 5b)
AC
an additional strong intensity band observed in the region of 570–800 nm is attributed to the PANI [57]. In TiO2-PANI-AuNPs the absorption band of polyaniline was found to be merged with Au at 520 nm and shifted the absorption towards lesser wavelength. This shifting can be assumed due to the bonding of Au with PANI in ternary hybrid (Figure 5c).
11
M
AN
US
CR
IP
T
ACCEPTED MANUSCRIPT
ED
Figure 5: UV-Vis spectra of a) PANI; b) TiO2-PANI; c) TiO2-PANI-AuNPs Figure 6 shows the PL emission spectra of PANI, TiO2-PANI and TiO2-PANI-AuNPs. PL was
PT
carried out to determine the charge recombination and migration efficiency of TiO2-PANI and TiO2-PANI-AuNPs. The excitation wavelength for TiO2-PANI and TiO2-PANI-AuNPs falls
CE
within the visible light region, showing that they are visible light active [58]. Photoluminescence
AC
spectrum of PANI shows a sharp peak near 450 nm due to the polaronic band in PANI [59]. In the PL spectra of TiO2-PANI-AuNPs, the emission peak showed a lesser intensity which indicated a lower recombination rate of TiO2-PANI-AuNPs than TiO2-PANI (Figure 6).
12
US
CR
IP
T
ACCEPTED MANUSCRIPT
Figure 6: Photoluminescence emission spectra of PANI, TiO2-PANI and TiO2-PANI-AuNPs
AN
The thermal stability and degradation pattern of the synthesized hybrid photocatalyst was
M
examined by TGA (Figure 7) [60]. In case of PANI, the first weight loss up to 100 oC was assigned to the evaporation of free water molecules and other volatile impurities. The weight loss
ED
from ~100 to 400 oC was attributed to the removal of water and dopant molecules adsorbed on
PT
PANI as well as initial degradation of PANI chains. The third degradation step was assigned to decomposition of the molecular chains of PANI (Figure 7a). Thermogram of TiO2-PANI showed
CE
two major weight losses attributed to the decomposition of organic polyaniline chains. An
AC
additional weight loss due to the disassociation of PANI from TiO2 was also observed (Figure 7b). As expected, TiO2-PANI-AuNPs ternary hybrid became more resistant to thermal degradation and revealed a major weight loss around at 570 oC possibly due to the strong interactions between the components in the hybrid (Figure 7c).
13
AN
US
CR
IP
T
ACCEPTED MANUSCRIPT
M
Figure 7: TGA thermogram of a) PANI; b) TiO2-PANI; c) TiO2-PANI-AuNPs
ED
XPS was performed to analyze the chemical composition of the PANI−TiO2-AuNPs on the surface. The survey scan reveals the presence of C, N, O, Ti and Au in PANI−TiO2-AuNPs as
PT
shown in Figure 8. The peak at 284.72 eV is related to C1s corresponding to the C-C of aromatic
CE
rings of PANI. The C1s peak at 285.75 is attributed to the C−N group and at 288.40 eV attributed to the electronic transition on PANI ring. The N1s peak at 399.62 eV assigned to the
AC
positively charged quinoid and benzenoid amine. The binding energies for O1s located at 530.01, 531.05 and 532.58 eV are ascribed to the oxygen of TiO2 in hybrid. The core-level spectrum of Ti 2p split into spin−orbit doublets of Ti 2p1/2 and Ti 2p3/2 at 464.50 and 458.72 eV, respectively [61-62]. Furthermore, two peaks related to Au 4f separated by 3.7 eV corresponding to Au 4f5/2 and Au 4f7/2 are observed at 87.21 eV and 83.51 eV, respectively [63].
14
AN
US
CR
IP
T
ACCEPTED MANUSCRIPT
M
Figure 8: XPS Spectra of TiO2-PANI-AuNPs
ED
Photocatalytic activity
PT
The synthesized ternary hybrid photocatalyst TiO2-PANI-AuNPs was evaluated for the synthesis of propargylamines by A3-coupling reaction of aldehydes, amines and alkynes at room
CE
temperature under visible light irradiation. At first, benzaldehyde, piperidine and
AC
phenylacetylene were chosen as model substrates to perform the optimization study using different solvents (Table 1, entries 1-7). As shown, the non polar solvents such as toluene and chloroform were found to be less effective and afforded poor product yield (Table 1, entries 1, 2). However, the polar aprotic solvents such as dimethylformamide (DMF), dimethylsulfoxide (DMSO), acetonitrile (CH3CN) and dichloromethane (DCM) were found to be promising and provided moderate product yield under similar reaction conditions (Table 1, entries 3-6). Interestingly, water was found to be most effective reaction medium and afforded almost 15
ACCEPTED MANUSCRIPT quantitative yield of the desired product (Table 1, entry 7). The use of water as a “green” reaction medium is a remarkable advantage, which makes the developed protocol a greener and attractive from both environmental and economical viewpoints. Therefore, further experiments were conducted using water as a solvent of choice. Further in the absence of the photocatalyst,
T
there was no reaction observed even in prolonged reaction time (Table 1, entry 8). However,
IP
when 20 mg of photocatalyst was used, the reaction was found to be slow and afforded 70 %
CR
conversion in prolonged reaction time (72 h) (Table 1, entry 7). Further increase in photocatalyst amount to 50 mg, enhanced the reaction rate significantly and afforded 95% conversion in 48h.
US
Further increase in photocatalyst amount to 70 mg although did not provide any significant
AN
change in the conversion and yield of the product, albeit the reaction completed in shorter time (42 h). Based on these controlled experiments, we selected 50 mg photocatalyst as the optimum
M
amount for the reaction (Table 1, entry 8). Furthermore, the reaction afforded best results in 48h
ED
of visible, irradiation; the lesser time gave poor conversion, whereas longer reaction time did not provide any significant enhancement in the yield of the desired product under optimized reaction
PT
conditions. In order to confirm the photocatalytic nature of the reaction, following blank
CE
experiments were carried out: i) no reaction occurred in the absence of photocatalyst (Table 1, entry 8) under visible light irradiation for 48 h.; ii) a very poor conversion (10% by GC) was
AC
observed in case of dark condition using hybrid photocatalyst under otherwise identical conditions.; iii) no reaction occurred using either PANI, TiO2 and TiO2-PANI as photocatalysts under identical conditions (Table 1, entry 9-11). These results confirmed that light and gold are essentially required for the reaction to occur.
Based on these experiments; the optimized
reaction conditions should include photocatalyst 50 mg, water as reaction medium, reaction time 48h, visible light and temperature 25 oC. 16
ACCEPTED MANUSCRIPT In order to establish the synergistic effect of the components in ternary hybrid TiO 2-PANIAuNPs, we performed the reaction with Au, Au-TiO2, Au-PANI under described reaction conditions. In case of neat AuNPs the reaction did occur but afforded poor product yield, which is attributed to the fast recombination of the electron-hole pairs on the surface (Table 1, entry
T
12). However, no reaction was occurred in subsequent recycling experiment, which is mainly
IP
due to the agglomeration and deactivation of the AuNPs. In case of Au-TiO2 and Au-PANI,
CR
almost similar activity was obtained (Table 1, entry 13-14), which is attributed to the better charge separation and suppressed recombination rates, resulting from the activation and
US
stabilization of AuNPs on the photoactive supports. Among all combinations, ternary hybrid,
AN
TiO2-PANI-AuNPs provided the ideal synergistic effect between AuNPs and the support TiO2PANI for this transformation. This enhancement is presumed to the combined participation of
M
TiO2-PANI in supplying the electrons in the CB of AuNPs as well as in the alkyne addition to
AC
CE
PT
ED
the interface.
17
ACCEPTED MANUSCRIPT Table 1: Results of the optimization experiments[a] Yield
(%)[b]
(%)[c]
Toluene
75
72
TiO2-PANI-AuNPs
CHCl3
70
68
3
TiO2-PANI-AuNPs
DMF
80
78
4
TiO2-PANI-AuNPs
CH3CN
85
5
TiO2-PANI-AuNPs
DMSO
84
82
6
TiO2-PANI-AuNPs
DCM
90
88
7
TiO2-PANI-AuNPs
H2O
95
92
-[d],70[e],
-[d], 65[e],
71[f]
67[f]
H2O
-
-
H2O
-
-
H2O
-
-
H2O
35, -g
32, -g
TiO2-PANI-AuNPs
2
IP
1
CR
Solvent
US
Catalyst
82
8
TiO2-PANI-AuNPs
9
PANI
10
TiO2
11
TiO2-PANI
12
Au NPs
13
Au-TiO2
H2O
80
78
14
Au-PANI
H2O
82
80
PT
ED
M
AN
H2O
T
Conv.
Entry
[a]
AC
CE
Reaction conditions: benzaldehyde (1.0 mmol), piperidine (1.2 mmol), phenylacetylene (1.2 mmol), H2O (4.0 mL) and photocatalyst (50 mg, 0.005 mmol Au) at 25 oC for 48 h in visible light; [b]Conversion was determined by GC-MS; [c]Isolated yields; [d]blank without photocatalyst; [e]when 20 mg of photocatalyst is used for 72h; [f]when 70 mg of photocatalyst is used, reaction was found to be completed in 42h; [g]recycling experiment.
After having the optimized reaction conditions in hand, we investigated the reaction scope with a variety of substrates and the results are summarized in Table 2. Both aromatic and aliphatic aldehydes provided the desired products in high yields (Table 2, entries 1–8). Among the various aromatic aldehydes studied, benzaldehydes having electron donating groups were found to be more reactive (Table 2, entry 2-3) as compared to those having electron withdrawing ones (Table 18
ACCEPTED MANUSCRIPT 2, entry 4-5). Notably, aliphatic aldehydes such as cyclohexane carboxaldehyde and nbutyraldehyde also displayed higher reactivity and afforded excellent product yields (entries 67). Long chain aldehyde such as n-decanal provided poor product yield (Table 1, entry 8). Furthermore, secondary amines were also showed comparable efficiency as shown in the Table 2
T
(entry 9-11). The reaction with primary amines, i.e. n-butyl amine and n-hexylamine under the
IP
described reaction conditions did not afford the desired propargylamine even after the prolonged
CR
reaction time. However, corresponding Schiff bases generated from the corresponding aldehyde and primary amine were obtained as the predominant products at the end of the reaction. Good
US
to excellent yields were obtained for aryl alkynes (Table 2, entries 11-12), whereas, the reactivity
AC
CE
PT
ED
M
AN
was found to be little lower in the case of aliphatic alkynes (Table 2, entries 13-14).
19
ACCEPTED MANUSCRIPT Table 2: Visible light assisted TiO2-PANI-AuNPs catalyzed A3 -coupling of aldehydes, alkynes, and amines[a] NR2R3
Visible light
1
R CHO + R2R3NH + R4
H
R1
Water, 48h
R4
TiO2-PANI-AuNPs
R1
R2R3NH
R4
1
Ph
piperidine
Ph
92
2
4-CH3C6H4
piperidine
Ph
85
3
4-OCH3C6H4
piperidine
Ph
87
4
4-ClC6H4
piperidine
Ph
90
5
4-NO2C6H4
piperidine
Ph
40
6
Cyclohexyl
piperidine
Ph
90
7
propyl
piperidine
Ph
88
8
decanal
piperidine
Ph
55
9
Ph
pyrrolidine
Ph
85
10
Ph
morpholine
Ph
80
11
Ph
piperidine
4-OCH3C6H4
90
12
Ph
piperidine
4-ClC6H4
84
Ph
piperidine
(CH3)3C
40
Ph
piperidine
Butyl
70
[a]
IP
CR
US
AN
M
ED
PT
14
CE
13
Yield[b]
T
Entry
AC
Reaction conditions: benzaldehyde (1.0 mmol), piperidine (1.2 mmol), and phenylacetylene (1.2 mmol), H2O (4.0 mL) and catalyst (50 mg, 0.005 mmol Au) at room temp for 48 h in visible light; [b] Isolated yields.
In order to determine the stability and recycling ability of the photocatalyst TiO 2-PANI-AuNPs, the reaction between benzaldehyde, piperidine and phenylacetylene was carried out under the optimized reaction conditions. After completion of the reaction, the photocatalyst was separated by centrifugation and washed with water, methanol, dried in vacuum, and then reused with a 20
ACCEPTED MANUSCRIPT fresh charge of reactants for subsequent runs under identical conditions. The recycling ability of the recovered photocatalyst was tested for five consecutive runs and the results are summarized in Figure 9. The results demonstrate that the photocatalyst could be efficiently used for five runs without noticeable deactivation, suggesting its good reusability and stability under the light
T
irradiation in A3-coupling of benzaldehyde, piperidine and phenylacetylene. Furthermore, to
IP
evaluate the leaching and to establish the heterogeneous nature of the reaction, the photocatalyst
CR
was removed by filtering when the conversion reached to 50 % as determined by GC in A3coupling reactions, and then the resulting reaction mixture was continued under the same
US
conditions. The conversion of the benzaldehyde did not significantly increase further, which
AN
suggested that the reaction was truly heterogeneous in nature. Furthermore, the reaction mixture was subjected to ICP-AES in order to determine the leaching of active metal content during the
M
reaction. There was no detectable metal content observed in the reaction mixture, further
ED
confirmed that the developed photocatalyst was highly stable and leaching had not occurred
AC
CE
PT
during the reaction.
Figure9: Results of recycling experiments
21
ACCEPTED MANUSCRIPT To check the structural stability of the photocatalyst, we analyzed the recycled photocatalyst recovered after fifth run by XRD and HR-TEM as shown in the Figure 10. As can be seen, that the XRD and TEM image of the recovered photocatalyst remained almost unchanged that suggested the higher stability of the photocatalyst without any morphological change during the
AC
CE
PT
ED
M
AN
US
CR
IP
T
photocatalytic reaction conditions.
Figure 10: a,b) HR-TEM images of Fresh and recovered photocatalyst; c,d) XRD of fresh and recovered photocatalyst. Based on the existing prior art we depicted a plausible mechanism of the reaction as shown in Scheme 3. Based on the experimental results (Table 1), the ternary hybrid TiO2-PANI-AuNPs exhibited higher photocatalytic activity than other components such as, AuNPs, AuNps-TiO2 and Au-PANI which is attributed to the synergistic effect of all components (PANI, TiO2 and 22
ACCEPTED MANUSCRIPT AuNPs) in hybrid providing efficient electron transfer for the reaction. In the ternary hybrid, PANI has an extended π-delocalized conjugated structure and acted as a photosensitizer, which strongly absorbs the visible light (PANI + hʋ → h+ + e−) to induce π - π* transition and transport the excited electrons to the π* orbital. These electrons can be transferred to the conduction band
T
of TiO2 and AuNPs; hence PANI can provide electrons to both TiO2 and AuNPs as shown in
IP
Scheme 3. The electrons and holes on the Au interface activate the substrates and take part in the
CR
reaction. It is believed that the first step involves the adsorption of the alkyne on the AuNPs surface due to the alkynophilicity displayed by gold nanoparticles on TiO2-PANI [64-65]. Then,
US
the enamine formed from the reaction between aldehyde and the amine interacts with the
AC
CE
PT
ED
M
AN
alkynyl–[Au-PANI-TiO2] complex to afford the desired propargylamine (Scheme 3).
Scheme 3: Possible mechanism of the photocatalytic coupling reaction 23
ACCEPTED MANUSCRIPT Conclusion In conclusion, we have demonstrated the first report on photocatalytic A3-coupling of aldehydes, amines and alkynes using water as green reaction media under mild conditions using visible irradiation. A novel ternary hybrid photocatalyst synthesized by coupling of TiO2 with PANI
T
followed by immobilization of gold nanoparticles has been developed for the said reaction. The
IP
developed photocatalyst showed enhanced activity mainly due to the better electron-hole
CR
separation, higher electron mobility and electron transfer at the surface. At the end of the reaction, the photocatalyst was removed by centrifugation and used for subsequent runs. The
US
photocatalyst showed efficient recycling without any significant loss in activity and leaching of
AN
the active metal during the reaction. We believe that this report will open new avenues for developing other hybrid photocatalysts for light assisted greener organic transformations.
M
Experimental
ED
Materials
All the chemicals were commercially available and used without further purification. Aniline
PT
(≥99.5 %), potassium persulfate (PPs) (≥99.99 %), gold chloride (≥99.99 %), trisodium
CE
citrate dihydrate and titanium isopropoxide (TiOP) (≥ 99.7 %), were purchased from Sigma Aldrich. Acetic acid, 2-butanol, hydrochloric acid, ammonia solution (35%), ethanol,
AC
methanol and acetone were purchased from Merck (India). All chemicals and solvents are of analytical grade and used as received. Deionised water was used throughout the synthesis. Techniques used The FTIR spectra were recorded on a Nicolet 8700 FTIR spectrometer. Phase structure and crystalline state of the materials was determined on Bruker D8 Advance diffractometer at 40 kV and 40 mA with Cu Kα radiation (λ= 0.15418 nm). For XRD, the samples were prepared on glass 24
ACCEPTED MANUSCRIPT slide by adding well dispersed catalyst in slot and drying properly. Scanning electron microscopy (SEM) was done using FESEM, Quanta 200 F (Netherland) at a voltage of 10-30kV. Inner fine structure of samples was determined with high resolution transmission electron microscopy using JEOL-JEM 2100 electron microscope operating at an acceleration voltage of 200 kV. The
T
samples for TEM analysis were made by depositing very dilute aqueous suspension of samples
IP
on carbon coated TEM grid. Thermo gravimetric analyses (TGA) were done using a thermal
CR
analyzer TA-SDT Q-600. Loading of gold on TiO2-PANI composite was determined using an inductively coupled plasma atomic emission spectrometer (ICP-AES, PS-3000UV, Leeman
US
Labs). Solid UV–visible spectra of samples were collected on Perkin Elmer lambda-19UV–vis–
AN
NIR spectrophotometer using a 10 mm quartz cell, using BaSO4 as reference. X-ray photoelectron microscopy using ESCA+, (omicron nanotechnology, Oxford Instrument
M
Germany) equipped with monochromatic aluminium source (Al ka radiation hv =1486.7ev). The
ED
instrument was operated at 15kv and 20mA. Sample were taken in powder / pellet and deposited on cu tape and degassed for overnight in XPS FEL chamber to minimize the air contaminator at
PT
sample surface as well as degasing in main chamber. To overcome the charging problem a
CE
charge neutralizer of 2 keV is applied and binding energy of C1s core (284.6ev) was taken as reference The PL measurements of catalysts were carried out at room temperature using
AC
Fluoromax-4C spectrofluorometer, from HORIBA Scientific at an excitation wavelength of 330 nm. Photocatalytic experiments were performed under visible light by using 20 W white cold LED flood light (model no. HP-FL- 20W-F-Hope LED Opto-Electric Co., Ltd.). Intensity of the light at vessel was measured by intensity meter and was found to be 75 Wm-2. Product identification was carried out by GCMS using HP 5972 MSD coupled with HP 5890 GC, HP
25
ACCEPTED MANUSCRIPT (USA) 1998. 1H-NMR and 13C NMR spectra of the products were recorded at 500 MHz by using Bruker Avance-III 500 MHz instrument. Synthesis of TiO2-PANI composites Anatase TiO2 was prepared by hydrothermal treatment. In brief, 20 mmol of titanium
T
isopropoxide (IV) was added in the solution containing of 20 ml acetic acid and 5ml 2-butanol.
IP
The resulting mixture was vigorously stirred at 60 oC for 5 h and then autoclaved at 180 oC for
CR
24 h. The product was filtered and dried for further use. The as-prepared TiO2 (0.5g) was first dispersed in 50 ml of water-ethanol (1:1) mixture by ultra-sonication followed by the addition of
US
aniline monomer (0.5 ml) and 10 ml of HCl solution (1.2 M) which contained 0.4 g of
AN
ammonium peroxydisulfate (APS). The polymerization reaction was carried out under ice bath condition for 24 h. The colour of the reaction mixture turned green and the resulting dark green
M
product was separated by filtration, washed with deionized water, methanol and dried at 80 oC
ED
for 12 h.
Synthesis of TiO2-PANI-AuNPs ternary hybrid
PT
In brief 5 mM HAuCl4 aqueous solution (5 mL) was added to 20 mL of deionized water and
CE
mixed for 5 min before addition of suspension containing 500 mg of TiO2-PANI composite in 10 ml of water. Resulting reaction mixture was heated until it reached to the desired temperature in
AC
the range 50–100 °C and then the preheated 1 mL of 0.5% trisodium citrate solution was added to this mixture. The reaction mixture was heated until evident colour change had occurred and then it allowed cooling to room temperature. In order to remove unattached AuNPs to TiO2PANI surface, the reaction mixture was subjected to a few washing steps by centrifugation and re-dispersion in 0.5% solution of trisodium citrate. The loading of Au and Ti in the synthesized
26
ACCEPTED MANUSCRIPT hybrid TiO2-PANI-AuNPs was found to be 2 wt% and 3.5 wt% respectively, as determined by ICP-AES. General experimental procedure In a typical experiment, all the substrates and photocatalyst, i.e. aldehyde (1.0 mmol), amine (1.2
T
mmol), alkyne (1.2 mmol), TiO2-PANI-AuNPs (50 mg, 0.005 mmol Au) and water (4 mL) were
IP
added into a dried borosil round bottom flask equipped with magnetic bar under stirring to give a
CR
well-dispersed solution. After sealing with a rubber septum the sealed and evacuated flask was placed in front of 20 W white cold LED flood light (visible light source) to carry out visible light
US
induced coupling at room temperature under nitrogen atmosphere. The progress of the reaction
AN
was monitored by TLC (SiO2). After completion of the reaction, ethyl acetate (2 mL) was added to the resulting mixture, followed by filtration and washing with additional ethyl acetate (4 mL).
M
The crude reaction product was purified by column chromatography (silica gel, hexane/EtOAc)
ED
and identified by GC-MS and 1H-NMR spectroscopy. Acknowledgements
PT
We acknowledge Director, CSIR-Indian Institute of Petroleum (IIP) for his kind permission to
CE
publish these results. VP thanks Council of Scientific and Industrial Research (CSIR), New
in analysis.
AC
Delhi for providing fellowship. Analytical division is kindly acknowledged for providing support
27
ACCEPTED MANUSCRIPT REFERENCES [1].
J. M. R. Narayanam, C. R. J. Stephenson, Visible light photoredox catalysis: applications in organic synthesis, Chem. Soc. Rev. 40 (2011) 102–113. https://doi.org/10.1039/B913880N J. She, Z. Fu, J. Lia, B. Zeng, S. Tang, W. Wu, H. Zhao, D. Yin, S. R. Kirk, Visible light-
T
[2].
IP
triggered vanadium-substituted molybdophosphoric acids to catalyze liquid phase
404. https://doi.org/10.1016/j.apcatb.2015.09.048
W. Zhong, T. Qiao, J. Dai, L. Mao, Q. Xu, G. Zou, X. Liu, D.Yin F. Zhao, Visible-light-
US
[3].
CR
oxygenation of cyclohexane to KA oil by nitrous oxide. Appl. Catal. B, 182 (2016) 392-
AN
responsive sulfated vanadium-doped TS-1 with hollow structure: Enhanced photocatalytic
10.1016/j.jcat.2015.06.013
P. Devaraji, N. K. Sathu, C. S. Gopinath, Ambient oxidation of benzene to phenol by
ED
[4].
M
activity in selective oxidation of cyclohexane, J. Catal. 330 (2015) 208-221.
photocatalysis on Au/Ti0.98V0.02O2: Role of holes, ACS Catal. 4 (2014) 2844-2853.
P. Zhang, Y. Gong, H. Li, Z. Chen, Y. Wang, Selective oxidation of benzene to phenol by
CE
[5].
PT
https://doi.org/10.1021/cs500724z
FeCl3/mpg-C3N4 hybrids, RSC Adv. 3 (2013) 5121–5126.
[6].
AC
https://doi.org/10.1039/C3RA23357J K. Yasutaka, M. Yasuhiro, Y. Hiromi, Photocatalytic epoxidation of olefins using molecular O2 by TiO2 incorporated in hydrophobic Y- zeolite, Rapid Commun. Photosci. 4 (2015) 19-21. https://doi.org/10.5857/RCP.2015.4.1.19
28
ACCEPTED MANUSCRIPT [7].
Y. –L Cui, X. –N. Guo, Y. –Y. Wang. X. –Y. Guo, Visible-light-driven photocatalytic Narylation of imidazole derivatives and arylboronic acids on Cu/graphene catalyst, Sci. Rep. 5 (2015) 1-9. https://doi.org/10.1038/srep12005
[8].
Y. W. Zheng, B. Chen , P. Ye, K. Feng, W. Q. Wang, Y. Meng, L. –Z. Wu, C. -H. Tung,
IP
hydroxylation, J. Am. Chem. Soc. 138(32) (2016) 10080–10083.
CR
https://doi.org/10.1021/jacs.6b05498 [9].
T
Photocatalytic hydrogen-evolution cross-couplings: Benzene C–H amination and
X. –H. Li, M. Baar, S. Blechert, M. Antonietti, Facilitating room-temperature Suzuki
US
coupling reaction with light: Mott-Schottky photocatalyst for C-C-coupling, Sci. Rep.
[10].
AN
3(1743) (2013) 1-6. https://doi.org/10.1038/srep01743
T. Lei, W. –Q. Liu, J. Li, M. –Y. Huan, B. Yang, Q. Y. Meng, B. Chen, C. –H. Tung, L. –
M
Z. Wu, Visible light initiated Hantzsch synthesis of 2,5-diaryl-substituted pyrroles at
ED
ambient conditions, Org. Lett. 18 (2016) 2479–2482. https://doi.org/10.1021/acs.orglett.6b01059 A. Pu, J. Deng, M. Li, J. Gao, H. Zhang, Y. Hao, J. Zhong, X. Sun, Coupling Ti-doping
PT
[11].
CE
and oxygen vacancies in hematite nanostructures for solar water oxidation with high efficiency, J. Mater. Chem. A. 2 (2014) 2491–2497.
[12].
AC
https://doi.org/10.1039/C3TA14575A W. J. Ong, L. Tan, P. Chai, S. T Yong, A. R. Mohamed, Highly reactive {001} facets of TiO2-based composites: synthesis, formation mechanism and characterization, Nanoscale. 6 (2014) 1946–2008. https://doi.org/10.1039/C3NR04655A
29
ACCEPTED MANUSCRIPT [13].
T. Kawahara, Y. Konishi, H. Tada, N. Tohge, J. Nishii, S. A. Ito, A patterned TiO2 (Anatase)/TiO2 (Rutile) bilayer-type photocatalyst: Effect of the Anatase/Rutile Junction on the photocatalytic activity, Angew. Chem. Int. Ed. 41 (2002) 2811−2813.
[14].
R. Beranek, B. Neumann, S. Sakthivel, M. Janczarek, T. Dittrich, H. Tributsch, H. Kisch,
T
Exploring the electronic structure of nitrogen-modified TiO2 photocatalysts through
[15].
CR
https://doi.org/10.1016/j.chemphys.2007.05.022
IP
photocurrent and surface photovoltage studies, Chem. Phys. 339 (2007) 11–19.
A. Morandeira, I. Lopez-Duarte, B. O'Regan, M. V. Martinez-Diaz, A. Forneli, E.
US
Palomares, T. Torres, J. R. Durrant, Ru(II)-phthalocyanine sensitized solar cells: the
AN
influence of co-adsorbents upon interfacial electron transfer kinetics, J. Mater. Chem. 19 (2009) 5016-5026. https://doi.org/10.1039/B904179F Y. H. Yum, S. R. Jang, R. Humphry-Baker, M. Grätzel, J. J. Cid, T. Torres, M. K.
M
[16].
ED
Nazeeruddin, Effect of co-adsorbent on the photovoltaic performance of zinc pthalocyanine-sensitized solar cells, Langmuir. 24(10) (2008) 5636-5640.
N. Zhang, M. Q. Yang, Z. R. Tang, Y. –J Xu, CdS–graphene nanocomposites as visible
CE
[17].
PT
https://doi.org/10.1021/la800087q
light photocatalyst for redox reactions in water: A green route for selective transformation
AC
and environmental remediation, J. Catal. 303 (2013) 60-69. https://doi.org/10.1016/j.jcat.2013.02.026 [18].
M. Nasrollahzadeh, S. M. Sajadi, Green synthesis, characterization and catalytic activity of the Pd/TiO2 nanoparticles for the ligand-free Suzuki–Miyaura coupling reaction, J. Colloid Interf. Sci. 465 (2016) 121. https://doi.org/10.1016/j.jcis.2015.11.038.
30
ACCEPTED MANUSCRIPT [19].
M. Nasrollahzadeh, S. M. Sajadi, Euphorbia heterophylla leaf extract mediated green synthesis of Ag/TiO2 nanocomposite and investigation of its excellent catalytic activity for reduction of variety of dyes in water, J. Colloid Interf. Sci. 462 (2016) 272. https://doi.org/10.1016/j.jcis.2015.09.073. M. Nasrollahzadeh, Z. Issaabadi, M. M. Tohidi, S. M. Sajadi, Recent developments in the
T
[20].
CR
in the chemical reactions, Chem. Rec. 18 (2018) 165. https://doi.org/10.1002/tcr.201800069
S. G. Babu, R. Vinoth, D. P. Kumar, Influence of electron storing, transferring and
US
[21].
IP
biosynthesis of Cu-based recyclable nanocatalysts using plant extracts and their application
AN
shuttling assets of reduced graphene oxide at the interfacial copper doped TiO2 p–n heterojunction for increased hydrogen production, Nanoscale. 7(2015) 7849-7857.
Q. Liu, Y. Yang, H. Li, R. Zhu, Q. Shao, S. Yang, J. Xu, NiO nanoparticles modified with
ED
[22].
M
https://doi.org/10.1039/c5nr00504c
5,10,15,20-tetrakis(4-carboxyl pheyl)-porphyrin: Promising peroxidase mimetics for H2O2 glucose
detection,
PT
and
Biosens.
Bioelectron.
64
(2015)
147–153.
[23].
CE
https://doi.org/10.1016/j.bios.2014.08.062 Q. Liu, Y. Yang, X. Lv, Y. Ding, Y. Zhang, J. Jing, C. Xu, One-step synthesis of uniform
AC
nanoparticles of porphyrin functionalized ceria with promising peroxidase mimetics for H2O2 and glucose colorimetric detection, Sensors and Actuators B: Chemical, 240 (2017) 726–734, https://doi.org/10.1016/j.snb.2016.09.049. [24].
Q. Liu, P. Chen, Z. Xu, M. Chen, Y. Ding, K. Yue, J. Xu, A facile strategy to prepare porphyrin functionalized ZnS nanoparticles and their peroxidase-like catalytic activity for
31
ACCEPTED MANUSCRIPT colorimetric sensor of hydrogen peroxide and glucose, Sensors and Actuators B: Chemical, 251, 2017, 339-348, https://doi.org/10.1016/j.snb.2017.05.069. [25].
M. Chen, L. Sun, Y. Ding, Z. Shi, Q. Liu, N,N′-Di-carboxymethyl perylene diimide functionalized magnetic nanocomposites with enhanced peroxidase-like activity for
T
colorimetric sensing of H2O2 and glucose, New J. Chem., 41 (2017) 5853-5862,
G. Z. Liao, S. Chen, X. Quan, Y. B. Zhang, H. M. Zhao, Remarkable improvement of
CR
[26].
IP
10.1039/C7NJ00292K
visible light photocatalysis with PANI modified core–shell mesoporous TiO2
Y. J. Wang, J. Xu, W. Z. Zong, Y. F. Zhu, Enhancement of photoelectric catalytic activity
AN
[27].
US
microspheres, Appl. Catal. B. 102 (2011) 126−131. 10.1016/j.apcatb.2010.11.033
of TiO2 film via Polyaniline hybridization, Solid State Chem. 184 (2011) 1433−1438.
D. Wang, J. Zhang, Q Luo, X. Li, Y. Duan, J. An, Characterization and photocatalytic
ED
[28].
M
https://doi.org/10.1016/j.jssc.2011.04.001
activity of poly (3-hexylthiophene)-modified TiO2 for degradation of methyl orange under
PT
visible light, J. Hazardous Mat. 169 (2009) 546–550.
[29].
CE
https://doi.org/10.1016/j.jhazmat.2009.03.135 Y. Zhu, S. Xu, D. Yi, Photocatalytic degradation of methyl orange using
AC
polythiophene/titanium dioxide composites, React. Funct. Poly. 70 (2010) 282–287. https://doi.org/10.1016/j.reactfunctpolym.2010.01.007 [30].
J. Zhu, X. Huo, X. Liu, H. Ju, Gold nanoparticles deposited polyaniline−TiO2 nanotube for surface plasmon resonance enhanced photoelectrochemical biosensing, ACS Appl. Mater. Interfaces. 8 (2016) 341−349. https://doi.org/10.1021/acsami.5b08837
32
ACCEPTED MANUSCRIPT [31].
T. Naota, H. Takaya, S. I. Murahashi, Ruthenium-catalyzed reactions for organic synthesis, Chem. Rev. 98 (1998) 2599-2660. https://doi.org/10.1021/cr9403695
[32].
T. Murai, Y. Mutoh, Y. Ohta, M. Murakami, Synthesis of tertiary propargylamines by sequential reactions of in situ generated thioiminium salts with organolithium and
T
magnesium reagents, J. Am. Chem. Soc. 126 (2004) 5968-5969.
G. Dyker, Transition metal catalyzed coupling reactions under C−H activation, Angew.
CR
[33].
IP
https://doi.org/10.1021/ja048627v
Chem. Int. Ed. 38 (1999) 1698-1712.
C. Wei, C. –J. Li, A Highly efficient three-component coupling of aldehyde, alkyne, and
US
[34].
AN
amines via C−H activation catalyzed by gold in water, J. Am. Chem. Soc. 125 (2003) 9584-9585. https://doi.org/10.1021/ja0359299
M. Nasrollahzadeh, S. M Sajadi, Preparation of Au nanoparticles by Anthemis xylopoda
M
[35].
ED
flowers aqueous extract and their application for alkyne/aldehyde/amine A3-type coupling reactions, RSC Adv. 5 (2015) 46240. https://doi.org/10.1039/C5RA08927A M. Nasrollahzadeh, S. M. Sajadi, A. Rostami-Vartooni, Green synthesis of CuO
PT
[36].
CE
nanoparticles by aqueous extract of Anthemis nobilis flowers and their catalytic activity for the A³ coupling reaction, J. Colloid Interf. Sci. 459 (2015) 183-188.
[37].
AC
https://doi.org/10.1016/j.jcis.2015.08.020 M. Nasrollahzadeh, M. Sajjadi, F. Ghorbannezhad, S. M. Sajadi, A Review on recent advances in the application of nanocatalysts in A3 coupling reactions, Chem. Rec. 18(10) (2018) 1409-1473. https://doi.org/10.1002/tcr.201700100.
33
ACCEPTED MANUSCRIPT [38].
V. K.-Y. Lo, Y. Liu, M –K Wong, C. –M. Che, Gold(III)salen complex-catalyzed synthesis of propargylamines via a three-component coupling reaction, Org. Lett. 8 (2006) 15291532. https://doi.org/10.1021/ol0528641
[39].
C. Wei, Z. Li, C. –J. Li, The first silver-catalyzed three-component coupling of aldehyde,
L Shi, Y. Q. Tu, M. Wang, F. –M. Zhang, C.–A. Fan, Microwave-promoted three-
IP
[40].
T
alkyne and amine, Org. Lett. 5 (2003) 4473-4475. https://doi.org/10.1021/ol035781y
CR
component coupling of aldehyde, alkyne and amine via C−H activation catalyzed by copper in water, Org. Lett. 6 (2004) 1001-1003. https://doi.org/10.1021/ol049936t H. Z. S. Huma, R. Halder, S. S. Karla, J. Das, J. Iqbal, Cu(I)-catalyzed three component
US
[41].
AN
coupling protocol for the synthesis of quinoline derivatives, Tetrahedron Lett. 43 (2002) 6485-6488. https://doi.org/10.1016/S0040-4039(02)01240-6 L P. Hua, W. Lei, Mercurous chloride catalyzed Mannich condensation of terminal alkynes
M
[42].
ED
with secondary amines and aldehydes, Chin. J. Chem. 23 (2005) 1076-1080. https://doi.org/10.1002/cjoc.200591076 C. J. Li, C. Wei, Highly efficient Grignard-type imine additions via C–H activation in and
under
solvent-free
conditions,
Chem.
Commun.
(2002)
268-269.
CE
water
PT
[43].
https://doi.org/10.1039/B108851N L. Zhang, C. Wei, R. S Varma, C.–J. Li, Three-component coupling of aldehyde, alkyne,
AC
[44].
and amine catalyzed by silver in ionic liquid, Tetrahedron Lett. 45 (2004) 2443-2446. https://doi.org/10.1016/j.tetlet.2004.01.044 [45].
K. M. Reddy, N. S. Babu, I. Suryanarayana, P. S. S. Prasad, N. Lingaiah, The silver salt of 12-tungstophosphoric acid: an efficient catalyst for the three-component coupling of an aldehyde, an amine and an alkyne, Tetrahedron Lett. 47 (2006) 7563-7566. 34
ACCEPTED MANUSCRIPT https://doi.org/10.1016/j.tetlet.2006.08.094 [46].
Y. Zhang, A. M. Santos, E. Herdtweck, J. Mink, F. E. Kuhn, Organonitrile ligated silver complexes with perfluorinated weakly coordinating anions and their catalytic application for coupling reactions, New J. Chem. 29 (2005) 366-370.
X. Zhang, A. Corma, Effective Au(III)–CuCl2-catalyzed addition of alcohols to alkenes,
IP
[47].
T
https://doi.org/10.1039/B414060E
[48].
CR
Chem. Commun. (2007) 3080-3082. https://doi.org/10.1039/B706961H X. Zhang, A. Corma, Efficient addition of alcohols, amines and phenol to unactivated
US
alkenes by AuIII or PdII stabilized by CuCl2, Dalton Trans. (2008) 397-403.
[49].
AN
https://doi.org/10.1039/B714617E
P. Kumar, A. Kumar, B. Sreedhar, B. Sain, S. S. Ray, S. L. Jain, Cobalt phthalocyanine
M
immobilized on graphene oxide: an efficient visible-active catalyst for the photoreduction
ED
of carbon dioxide, Chem. Eur. J. 20 (2014) 6154–6161. https://doi.org/10.1002/chem.201304189 A. Kumar, P. Kumar, C. Joshi, M. Manchanda, R. Boukherroub, S. L Jain, Nickel
PT
[50].
CE
decorated on phosphorous-doped carbon nitride as an efficient photocatalyst for reduction of nitrobenzenes, Nanomaterials. 6(59) (2016) 1-14.
[51].
AC
https://doi.org/10.3390/nano6040059 V. Panwar, P. Kumar, S. S Ray, S. L Jain, Organic inorganic hybrid cobalt phthalocyanine/polyaniline as efficient catalyst for aerobic oxidation of alcohols in liquid phase, Tetrahedron Lett. 56 (2015) 3948–3953. https://doi.org/10.1016/j.tetlet.2015.05.003
35
ACCEPTED MANUSCRIPT [52].
M. R. Karim, J. H. Yeum, M. S. Lee, K. T. Lim, Preparation of conducting polyaniline/TiO2
composite
submicron-rods
by
the
gamma-radiolysis
oxidative
polymerization method, React. Funct. Poly. 68 (2008) 1371-1376. https://doi.org/10.1016/j.reactfunctpolym.2008.06.016 Q. Wang, X. Qian, S. Wang, W. Zhou,H. Guo, X. Wua, J. Li, X. Wang, Conductive
T
[53].
https://doi.org/10.1016/j.synthmet.2014.11.007
Z. Cai, Z. Xiong, X. Lu, J. Teng, In situ gold-loaded titania photonic crystals with
US
[54].
CR
walled carbon nanotube, Synthetic Metals. 199 (2015) 1-7.
IP
polyaniline composite films from aqueous dispersion: Performance enhancement by multi-
https://doi.org/10.1039/C3TA13878J
H. Xia, Q. Wang, Synthesis and characterization of conductive polyaniline nanoparticles
M
[55].
AN
enhanced photocatalytic activity, J. Mater. Chem. A. 2 (2014) 545-553.
ED
through ultrasonic assisted inverse microemulsion polymerization, J. Nanopart Res. 3 (2001) 399–409.
A. B. Rohom, P. U. Londhe, N. B. Chaure, Enhancement of optical absorption by
PT
[56].
CE
incorporation of plasmonic nanoparticles in PANI films, Nanosci. Nanotech. 6 (2016) 8387. https://doi.org/10.5923/c.nn.201601.16 A. Katoch, M. Burkhart, T. Hwang, S. S. Kim, Synthesis of polyaniline/TiO2 hybrid
AC
[57].
nanoplates via a sol–gel chemical method, Chem. Eng. J. 192 (2012) 262–268. https://doi.org/10.1016/j.cej.2012.04.004 [58].
M. O. Ansari, M. M. Khan, S. A. Ansari, J. Lee, M. H. Cho, Enhanced thermoelectric behaviour and visible light activity of Ag@TiO2/polyaniline nanocomposite synthesized by biogenic-chemical route, RSC Adv. 4 (2014) 23713-23719. 36
ACCEPTED MANUSCRIPT https://doi.org/10.1039/C4RA02602K [59].
D. Geethalakshmi, N. Muthukumarasamy, R. Balasundaraprabhu, Effect of dopant concentration on the properties of HCl-doped PANI thin films prepared at different temperatures, Optik-International Journal for Light and Electron Optics. 125 (2014) 1307-
M. O. Ansari, F. Mohammad, Thermal stability and electrical properties of dodecyl-
IP
[60].
T
1310. https://doi.org/10.1016/j.ijleo.2013.08.014
CR
benzene-sulfonic-acid doped nanocomposites of polyaniline and multi-walled carbon nanotubes, Composites. Part B.43 (2012) 3541-3548.
N. Parveen, M. O. Ansari, M. H. Cho, Correction to “Route to high surface area,
AN
[61].
US
https://doi.org/10.1016/j.compositesb.2011.11.031
mesoporosity of polyaniline−titanium dioxide nanocomposites via one pot synthesis for
M
energy storage applications, Eng. Chem. Res. 55 (2016) 2277–2277.
[62].
ED
https://doi.org/10.1021/acs.iecr.6b00362
R. Kumar, R. M. E. Shishtawy, M. A. Barakat, Synthesis and characterization of Ag-
PT
Ag2O/TiO2@polypyrrole heterojunction for enhanced photocatalytic degradation of
[63].
CE
methylene blue, Catalysts. 6 (2016) 76. https://doi.org/10.3390/catal6060076 H. Wang, R. Liu, Z. Cui, X. Lü, Y. Li, X. Li, S. Xin, R. Zhang, M. Lei, Z. Lin, Durable
AC
and Efficient Hollow Porous Oxide Spinel Microspheres for Oxygen Reduction, Joule, 2 (2018) 337-348 [64].
M. G. Bejar, K. Peters, G. L. H. Tapley, M. Grenier, J. C. Scaiano, Rapid one-pot propargylamine synthesis by Plasmon mediated catalysis with gold nanoparticles on ZnO under ambient conditions, Chem. Commun. 49 (2013) 1732. https://doi.org/10.1039/C3CC38287G 37
ACCEPTED MANUSCRIPT K. Yang, Y. Li, K. Huang, X. Chen, X. Fu, W. Dai, Promoted effect of PANI on the preferential oxidation of CO in the presence of H2 over Au/TiO2 under visible light irradiation, Int. J. hydrogen energy. 39 (2014) 18312-18325.
CE
PT
ED
M
AN
US
CR
IP
T
https://doi.org/10.1016/j.ijhydene.2014.09.053
AC
[65].
38
ACCEPTED MANUSCRIPT
AC
CE
PT
ED
M
AN
US
CR
IP
T
Table of content entry
39
ACCEPTED MANUSCRIPT Highlights
First report on photocatalytic A3- coupling of aldehyde, amine and alkyne using goldpolyanilne-titania nanocomposite photocatalyst.
Visible light assisted methodology for the formation of propargylamines under mild
Enhanced performance of photocatalyst due to the slower electron-hole recombination
IP
T
conditions.
CR
and better electron mobility.
Environmentally benign coupling methodology using H2O as a green solvent.
Facile recovery and efficient recycling of photocatalyst for several runs with consistent
US
AC
CE
PT
ED
M
AN
activity.
40