Silica functionalized Cu(II) acetylacetonate Schiff base complex: An efficient catalyst for the oxidative condensation reaction of benzyl alcohol with amines

Article abstract of DOI:10.1016/j.jssc.2017.06.012

Silica functionalized Cu(II) acetylacetonate Schiff base complex via the one pot reaction of silica functionalized 3-aminopropyltriethoxysilane with acetyl acetone and copper acetate has been reported. The synthesized material was well characterized by analytical techniques such as FT-IR, UV-DRS, XRD, SEM-EDX, HR-TEM, EPR, ICP-AES and BET analysis. The characterization results confirmed the grafting of Cu(II) Schiff base complex on the silica surface. The catalytic activity of synthesized silica functionalized Cu(II) acetylacetonate Schiff base complex was evaluated through the oxidative condensation reaction of benzyl alcohol to imine.

Full text of DOI:10.1016/j.jssc.2017.06.012

Author’s Accepted Manuscript
Silica functionalized Cu(II) acetylacetonate Schiff
base complex: An efficient catalyst for the
oxidative condensation reaction of benzyl alcohol
with amines
G. Anbarasu, M. Malathy, P. Karthikeyan, R.
Rajavel
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PII:
S0022-4596(17)30234-7
http://dx.doi.org/10.1016/j.jssc.2017.06.012
YJSSC19830
DOI:
Reference:
To appear in: Journal of Solid State Chemistry
Received date: 23 February 2017
Revised date: 12 June 2017
Accepted date: 15 June 2017
Cite this article as: G. Anbarasu, M. Malathy, P. Karthikeyan and R. Rajavel,
Silica functionalized Cu(II) acetylacetonate Schiff base complex: An efficien
catalyst for the oxidative condensation reaction of benzyl alcohol with amines
Journal of Solid State Chemistry, http://dx.doi.org/10.1016/j.jssc.2017.06.012
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Silica functionalized Cu(II) acetylacetonate Schiff base complex: An efficient catalyst for
the oxidative condensation reaction of benzyl alcohol with amines
G. ANBARASU, M. MALATHY, P. KARTHIKEYAN, R. RAJAVEL*
Department of Chemistry, Periyar University, Periyar Palkalai Nagar, Salem – 636 011, Tamil Nadu, India,
Corresponding author E mail: drrajavelpu@gmail.com
Tel: +91-427-234-5271; Fax: +91-427-234-5124
Abstract:
Silica functionalized Cu(II) acetylacetonate Schiff base complex via the one pot
reaction of silica functionalized 3-aminopropyltriethoxysilane with acetyl acetone and copper
acetate has been reported. The synthesized material was well characterized by analytical
techniques such as FT-IR, UV-DRS, XRD, SEM-EDX, HR-TEM, EPR, ICP-AES and BET
analysis. The characterization results confirmed the grafting of Cu(II) Schiff base complex on
the silica surface. The catalytic activity of synthesized silica functionalized Cu(II)
acetylacetonate Schiff base complex was evaluated through the oxidative condensation
reaction of benzyl alcohol to imine.
Keywords:
Silica; Cu(II) acetylacetonate Schiff base complex; 3-Aminopropyltriethoxysilane;
Oxidative condensation.
1
. Introduction
In recent years, functionalization of silica material with metal complexes are very
active area of research in the fields of organic synthesis, catalysis, adsorption, separation and
sensing [1-5]. Because, these heterogenized metal complexes of their easy separation from the
reaction mixture and minimal product contamination caused by metal leaching [6-9], as well
as the recyclability of catalyst [10], it is well known that Schiff base metal complexes have
been widely employed as an efficient catalyst in a variety of oxidation reactions [11-14]. Due
to their environmental issue arises from homogeneous catalyst and newer development in
chemistry, which cannot be well suitable for large scale process, recent researchers are very
much interested in the transformation of homogeneous catalytic reaction into heterogeneous
process. Generally, heterogeneous catalyst has been prepared by anchoring homogeneous
catalysts onto insoluble supports like, metal oxides [15], aluminophosphates [16], MCM-41
[
17], silica [18], SBA-16 [19], SBA-15 [20], montmorillonite [21], Zeolite-X [22], and zeolite-
Y [23].
Oxidation of alcohols to the corresponding carbonyl compounds is one of the most
important transformations in organic synthesis [24-26]. In particular, the oxidation of benzyl
1

alcohol to benzaldehyde is an important organic reaction due to the widespread applications of
benzaldehyde in perfumery, dyestuff and agro-chemical industries [27-29]. There are
numerous methods available in the literature for the oxidation of benzyl alcohols to their
corresponding benzaldehydes. Gao et al [30]. reported that functionalized
dioxomolybdenum(VI) complex with bidendate Schiff base type CPS-[MoO (ALGl) ]
2
2
microsphere is efficient catalyst for the oxidation of benzyl alcohol to benzaldehyde From the
background of this, herein we have reported the design and characterization of silica
functionalised Cu(II) Schiff base metal complexes bearing acetyl acetone group. In addition,
we have also studied the catalytic properties of these complexes in the oxidative condensation
reaction of benzyl alcohol with variety of amines to corresponding Schiff bases.
2
. Experimental
2
.1. Materials and instruments
3
-aminopropyltriethoxysilane (3-APTES) was procured from Sigma Aldrich and all
the other reagents and solvents were purchased from Loba Chemie. FT-IR spectra of the
-1
samples were recorded in the region of 4000-400 cm on Shimadzu spectrophotometer using
KBr pellet technique. Diffuse reflectance spectra were obtained on an UV-DRS Ocean Optics
px-2 spectrometer with pulsed xenon light source. Powder X-ray diffraction (XRD) patterns
were recorded on a Rigaku Mini Flex II diffractometer. The surface morphology of the
synthesized material was analyzed by using High Resolution Transmission Electron
Microscope (HRTEM, JEOL JEM 2100) scanning electron microscope (HRSEM, JSM 840A,
1
13
JEOL.) equipped with EDX. H (300.13 MHz) and C (75.47 MHz) NMR spectra were taken
in DMSO-d or CDCl at room temperature with a Bruker AV400 instrument with chemical
6
3
1
13
shifts relative to tetramethylsilane ( H, C). EPR spectrum was recorded on a JEOL model
JES FA200 EPR spectrometer at liquid nitrogen temperature operating at X-band frequency
(9.45 GHz). The Cu loading in the catalyst were determined using inductively coupled plasma
atomic emission spectroscopy (ICP-AES) analysis on a Thermo Electron IRIS Intrepid II XSP
DUO. BET Surface area was calculated by Brunauer Emmett and Teller Equation using
multipoint adsorption in the P/Po range 0.05-0.33. Micro pore size distribution was calculated
using Horvath-Kawazoe and BJH method. The Surface area has been measured by using
Micromeritics ASAP 2020 surface area analyzer. The surface area analysis condition such as
sample mass: 0.2478 g, analysis bath temp: -195 °C, degassing temperature and duration 150
°
C & 12 h respectively.
2

2
.2. Functionalization of silica gel with 3-aminopropyltriethoxysilane
Initially, the silica gel was activated by refluxing silica gel (3.0 g) with 6 mol L HCl
-1
for 8 h. After cooling, solid was filtered off and washed with doubly distilled water until free
of acid. After complete removal of acid, the crude solid was dried for 12 h in a furnace at 120
°
C and finally the unwanted gases were removed by vacuum at 100 °C for 8 h. Then the
amino functionalized silica gel (SiO -NH ) was prepared by refluxing silica gel (3.0 g) with 3-
2
2
aminopropyltriethoxysilane (10 mmol) in dry dichloromethane for 24 h. The resultant solid
was filtered and washed three time with dichloromethane and dried under vacuum at 50 °C.
2
.3. Preparation of silica supported Cu(II) Schiff base complex [SiO -NH -Cu(II)]
2 2
A mixture of acetyl acetone (10 mmol) and copper acetate (5 mmol) in ethanol (30 ml)
was added to the suspended solution of amino functionalized silica gel (SiO -NH ) (3.0 g)
2
2
and the mixture was refluxed for 5 h. After cooling, the solid was filtered and washed with hot
ethanol to remove the unreacted copper acetate. Finally, the resultant solid was dried under
vacuum at 60 °C and labelled as SiO -NH -Cu(II) (Scheme 1).
2
2
2
.4. General experimental procedure for the oxidative condensation reaction
A mixture of benzyl alcohol (1.5 equiv) and aromatic amine (1 equiv) in the presence
of SiO -NH -Cu(II) complex (50 mg) as a catalyst in toluene (10 ml) was refluxed until the
2
2
completion of the reaction as evidenced by TLC. After completion, the reaction mixture was
cooled to room temperature and the catalyst was removed by simple filtration. Then the filtrate
was evaporated under reduced pressure. The pure products were obtained by recrystallization
1
of crude product with ethanol. The Product was confirmed by H NMR Spectroscopy.
3
. Results and discussion
3
.1. Characterization of synthesized silica functionalised Cu(II) Schiff base complex
The synthesized silica functionalised Cu(II) Schiff base complex was completely
characterized by FT-IR, UV-DRS, XRD, SEM-EDX, HRTEM and EPR, BET analysis.
.1.1. FT-IR study
Fig. 1 Shows the FT-IR spectra of the activated silica (1a), amino functionalised silica
1b) and silica functionalised Cu(II) Schiff base complex (1c). In FT-IR spectra of activated
3
(
-1
silica, a broad band appeared at 3442 cm was due to the symmetric stretching vibration of
-1
water molecule and the band appeared at 1651 cm correspond to –OH bending vibration. The
bands observed nearly in the region of 1085 and 804 correspond to the asymmetric and
-1
symmetric stretching vibrations of Si-O-Si, respectively. The band at 462 cm correspond to
the bending vibrations of O-Si-O groups present in the silica framework. Upon
3

functionalization with 3-APTES, the intensity of the -OH band was decreased and a new band
-1
appeared at 1512 cm corresponds to the bending vibration of NH group which confirms the
2
successful functionalization of 3-APTES on silica surface [31]. But, the FT-IR spectrum of
SiO -NH -Cu(II) complex was something different than that of parent materials and showed
2
2
-1
two new bands at 1604 and 1512 cm which may be attributed to the C=N stretching vibration
-
1
and the band at 1739 cm corresponds to the C=O present in the acetylacetonate ring of metal
complex [32]. This indicates that the amino group present in functionalised silica was almost
reacted with acetyl acetone to form a Schiff base. Moreover, some other peaks observed in the
-1
range of 1600-1340 cm due to the C-O and C-N vibrations, indicates the formation of silica
functionalized Cu(II) Schiff base complex.
3
.1.2. UV-vis DRS
The electronic spectrum of pure SiO showed three peaks at λmax = 220, 260 and 334
2
nm (Fig. 2a). When the SiO was functionalized with 3-APTES, we observed that the peak
2
obtained for pure silica was shifted to the higher wavelength (238, 326 and 402 nm) with band
broadening (Fig. 2b). But, in the case of silica functionalized Cu(II) Schiff base complex some
additional peaks appeared at 442, 498 and 541 nm. This may lead to the charge transfer
between the ligand and the metallic ion [33].
3
.1.3. XRD Characterization
The XRD patterns of activated silica and silica functionalized Cu(II) Schiff base
complex are shown in Fig. 3. The XRD pattern of pure SiO exhibited a broad peak centred at
2
2
θ = 22.37° indicating the amorphous nature of the silica [34]. Whereas, silica functionalized
copper(II) Schiff base complex showed a peak at 2θ = 21.71° which suggests that there is only
a small change in the centre of peak position but the intensity of the peak reduced slightly. It is
clear from the XRD patterns, that there was essentially no major changes occurred during the
functionalization of silica with Cu(II) Schiff base complex.
3
.1.4. SEM –EDX and High resolution TEM analysis
The SEM images (Fig. 4a, 4b) of activated pure silica and the functionalized Cu(II)
Schiff base complex clearly indicates the changes in the surface morphology of the catalyst
before and after introduction of metal complex on silica surface. It was seen from the Fig. 4
that the morphology of the both samples are quite similar in appearance with well dispersed
stone like structure. Fig. 4c & 4d shows different morphology compare to pure activated silica
surface, its indicates that the Cu(II) complex bind with silica surface. This type of morphology
to possess good catalytic behavior [35]. Furthermore, EDX spectrum of silica functionalized
Cu(II) Schiff base complex (Fig. 4c,4d) confirms the presence of copper (Fig. 4e), which is in
4

good agreement with the value determined by ICP-AES technique. The Cu(II) amount of the
−
1
immobilized catalyst on SiO was found to be 0.373 mmol g or 50 mg.
2
The high resolution transition electron microscopy images of SiO revealed that all the
2
particles have stone like structure with well definite pore structure. (Fig. 5a, 5b) The TEM
image of SiO -NH -Cu(II) complex shows a thick grey colour core and the surface region
2
2
indicates the presence of inorganic Cu (II) moieties that completely cover the SiO resulting
2
the formation of SiO -NH -Cu (II) complex.
2
2
3
.1.5. EPR spectroscopy.
EPR spectra also proved the presence of Cu(II) ion in the silica functionalized Cu(II)
Schiff base complex. The EPR spectra of the powdered silica functionalized Cu(II) Schiff base
complex was recorded on X-band at frequency 9.45 GHz and the g & g values were intended
||

from the obtained spectrum. The calculated g & g values for the complex were found to be
||

2
.27 and 2.05 indicating the formation of Cu(II) complex (Fig. 6) [32].
3
.1.6. N adsorption-desorption isotherm
2
The N adsorption and desorption isotherms of SiO and SiO -NH -Cu(II) complex are
2
2
2
2
shown in Fig. 7. This study provided the information about the specific surface area and
porosity of the prepared samples. The isotherms of both the samples followed typical type IV
patterns according to IUPAC classification with a typical hysteresis loop, featuring
mesoporous material with highly uniform pore size distribution [36] Cu(II) complex on porous
supports shows decrease in its specific surface area and pore volume. The support SiO shows
2
2
-1
3
a high surface area of 387m g ; and pore volume of 0.4215 cm /g; after Cu(II) complex
2
-1
immobilization, the surface area and pore volume gets reduced to 151m g , respectively, with
pore radius of 28Å and 18Å, respectively. A considerable decrease in the BET surface area,
pore volume and pore radius suggested that Cu(II) complex have been anchored on the inner
surface of the pores.
3
.2. Catalytic properties
The catalytic activity of the silica functionalized Cu(II) Schiff base complex was
evaluated for the oxidative condensation reaction of benzyl alcohol with different
aromatic/aliphatic amines affording the corresponding imines in good yields (Scheme 2).
In order to optimize the suitable reaction conditions for this oxidative condensation
reaction, we have chosen benzyl alcohol and aniline as model reactants. Initially, we have
started our investigation under neat condition under refluxing toluene, where no reaction was
observed to produce the corresponding product (Table 1, entry 1) even after prolonged time
5

(
24 h). So we have added SiO -NH -Cu(II) complex (50 mg) as a catalyst, interestingly the
2 2
reaction was going well and produce the corresponding product in excellent yields (94%)
Table 1, entry 5) in shorter time (10 h). Next, we have find out the suitable solvents for this
(
reaction, same reaction was performed with different solvents (10 ml) like ethanol, methanol,
dichloromethane, toluene, chlorobenzene, nitrobenzene and acetonitrile under refluxing
conditions and found that toluene was most efficacious one in the terms of yield and time.
After that, we have to fix the amount of catalyst required for this reaction, we have
carried out the reaction with different quantity of catalyst like 10 mg, 20 mg, 30 mg, 40 mg,
5
0 mg and 100mg. The reaction rate as well as product yield was increased with increasing the
catalyst amount from 10 mg to 50 mg and decreases the reaction time. By increasing the
catalyst above 50 mg, there is no change in reaction rate and yield. This optimization results
suggested the 50 mg of catalyst and toluene were found to be most suitable for this reaction
(Table 2).
Under this optimized conditions, differently substituted amines were made to react
with benzyl alcohol and the results are summarized in Table 3.
From the table we noted that the aromatic amines having electron donating group
required shorter reaction time to produce the corresponding product in better yield than that of
electron withdrawing counter parts (Table 3, entries 3,4 and 9). Aliphatic amines also reacted
well and provided the good yields (Table 3, entries 10 and 11).
Next, the reusability of the new SiO -NH -Cu(II) catalyst has been checked using the
2
2
reaction of benzyl alcohol with aniline under optimized reaction conditions. After extracting
the reaction mixture, the catalyst was recovered by simple filtration, washed twise with hot
ethanol and dried. Then the recovered catalyst can be effectively reused for five consecutive
runs with slight decrease in activity (Table 4).
The catalytic efficiency of the synthesized silica functionalized Cu(II) Schiff base
complex was compared with the other earlier reported catalysts and the results are presented in
the Table 5. From this comparison Table 3, we suggested that the efficiency of the SiO -NH -
2
2
Cu(II) catalyst is comparable or better than the reported catalysts.
3
.2.1. Plausible mechanism for the oxidative condensation reaction
A proposed mechanism for this reaction has given in (Scheme 3), in which the
catalysts accept hydrogen from alcohols and oxidize them to aldehydes in the first step. In the
second step, the carbonyl moiety undergoes condensation with arylamine and form
azomethine functionality, ie. Imine compounds.
6

4
. Conclusion
We have successfully synthesized the silica functionalized Cu(II) Schiff base complex
bearing acetylacetone group in a stepwise manner. SiO -NH -Cu(II) complex was confirmed
2
2
by FT-IR, UV-DRS, XRD, SEM-EDX, HR-TEM, EPR, ICP-AES and BET analysis. In
addition, to this the material has been employed as an efficient heterogeneous catalyst for the
oxidative condensation reaction of benzyl alcohol with aniline, resulting to high yield of
imines compounds. Moreover the obtained catalyst could be recovered and reused for five
times with slight decrease in activity.
Reference:
[
[
[
[
1] D.E.D. Vos, M. Dams, F.S. Bert, P.A. Jacobs, Chem. Rev. 102 (2002) 3615−3640.
2] A. Taguchi, F. Schüth, Microporous Mesoporous Mater. 77 (2005) 1–45.
3] R.K. Sharma, A. Pandey, S. Gulati, Polyhedron. 45 (2012) 86–93.
4] S. Yajima, T. Nakajima, M. Higashi, K Kimura, Chem. Commun. 46 (2010) 1914–
1
916.
5] G. Anbarasu, M. Malathy, R. Rajavel,
0.1007/s10934-017-0366-5.
[
J
Porous Mater. (2017) DOI
1
[
[
6] M. Heitbaum, F. Glorius, I. Escher, Angew. Chem. Int. Ed. 45 (2006) 4732 – 4762.
7] F. Fache, E. Schulz, M.L. Tommasino, M. Lemaire, Chem. Rev. 100 (2000)
2
159−223.
[
[
[
8] R.T. Baker, W. Tumas, To ward greener chemistry. Science. (1999) 1477-1479.
9] A. Zsigmond, K. Bogar, F. Nothessz, Catal Lett. 83 (2002) 1-2.
10] C.G.l. Arellano, A. Corma, M. Iglesias, F. Sancheza, Adv. Synth Catal. 346 (2004)
1
758 – 1764.
[
[
[
11] X. Yuan, G. Shan, L. Li, J. Wu, H. Luo, Catal. Lett. 145 (2015) 868-874.
12] M. Nandi, P. Roy, H. Uyama, A. Bhaumik, Dalton Trans. 40 (2011) 12510–12518
13] R. Antony, T. David, S. Manickam, K. Karuppasamy, P. Kollu, P.V. Chandrasekar,
S. Balakumar, RSC Adv. 4 (2014) 42816–42824.
[
[
[
[
[
14] K.I.O. Connor, S.J. Wey, C.J. Burrows, Tetrahedron Lett. 23 (1992) 1001-1004.
15] S. Imamura, H. Sasaki, M. Shono, H. Kanai, J. Catal. 177 (1998) 72–81.
16] M.S. Rigutto, H.V. Bekkum, J. Mol. Catal. 81(1993) 77-98.
17] S. Jana, S. Bhunia, B. Dutta, S. Koner, Appl. Catal. A. 81 (2011) 225–232.
18] F. Rajabi, R. Luque, J. H. Clark, B. Karimi, D. Macquarrie, J. Catal. Commun. 12
(2011) 510–513.
7

[
[
[
19] H. Yang, L. Zhang, W. Su, Q. Yang, C. Li, Journal of Catal. 248 (2007) 204–212.
20] D. Bek, R. Gawin, K. Grela, H, Balcar, Catal. Commun. 21 (2012) 42–45.
21] C. Pereira, A.R. Silva, A.P. Carvalho, J. Pires, C. Freire, J. Mol. Catal. A: Chem:
Chemical. 283 (2008) 5–14.
[
22] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. M. Baltork, M. Moosavifar, J.
Mol. Catal. A: Chem. 302 (2009) 68–75.
[
[
23] V.K. Bansal, P.P. Thankachan, R. Prasad, Appl. Catal., A. 381 (2010) 8–17.
24] Y. Hou, X. Ji, G. Liu, J. Tang, J. Zheng, Y. Liu, W. Zhang, M. Jia, Catal.
Commun. 10 (2009) 1459–1462.
[
[
[
[
25] T. Orbegozo, I. Lavandera, W.M.F. Fabian, B. Mautner, J.G.D. Vries, W. Kroutil,
Tetrahedron. 65 (2009) 6805–6809.
26] Y. Guo, J. Zhao, J. Xu, W. Wang, F. Tian, G. Yang, M. Song, J. Nat. Gas
Chemistry. 16 (2007) 210–212.
27] V.R. Choudhary, P.A. Chaudhari, V.S. Narkhede, Catal. Commun. 4 (2003) 171–
1
75.
28] Y. Su, L.C. Wang, Y.M. Liu, Y. Cao, H.Y. He, K.N. Fan, Catal. Commun. 8
2007) 2181–2185.
(
[
[
[
[
29] E. Sindhuja, R. Ramesh, Tetrahedron Letters. 55 (2014) 5504-5507.
30] B. Gao, M. Wan, J. Men, Y. Zhang, Appl. Catal., A. 439 (2012) 156– 162.
31] C. Sarmah, D. Sahu, P. Das, Catal. Today. 198 (2012) 197– 203.
32] A.R. Silva, K. Wilson, A.C. Whitwood, J.H. Clark, C. Freire, Eur. J. Inorg. Chem.
(2006) 1275–1283.
[
[
[
[
33] J.G. Tojal, A. G. Orad, J.L. Serra, J.L. Pizarro, L. Lezama, M.I. Arriortua, T. Rojo,
J. Inorg. Biochem. 75 (1999) 45-54.
34] J.R. Martinez, S.P. Sanchez, G.O. Zarzosa, F. Ruiz, Y. Chumakov, Mater. Let. 60
(
2006) 3526–3529.
35] S. Urus, M. Ozdemir, G. Ceyhan, M. Tumer, Synth. React. Inorg. Met.-Org. 42
2012) 382–391.
36] V.D Chaube, S. Shylesh, A.P. Singh., Journal of Molecular Catalysis A: Chemical
41 (2005) 79-87.
(
2
[
[
[
37] L. Tang, H. Sun, Y. Li, Z. Zha, Z. Wang, Green Chem. 14 (2012) 3423- 3428.
38] Q. Kang, Y. Zhang, Green Chem. 14 (2012) 1016–1019.
39] J. Xu, R. Zhuang, L. Bao, G. Tang Y. Zhao, Green Chem. 14 (2012) 2384–2387.
8

[
[
40] M.S. Kwon, S. Kim, S. Park, W. Bosco R.K. Chidrala, J. Park, J. Org. Chem. 74
2009) 2877–2879.
41] M. Tamura, K. Tomishige, Angew. Chem. Int. Ed. 54 (2015) 864 –867.
(
Scheme captions
Scheme 1: Synthesis of silica supported Cu(II) Schiff base complex [SiO -NH -Cu(II)].
2
2
Scheme 2: Oxidative condensation reaction of benzyl alcohol with amines.
Scheme 3: Plausible mechanism for the oxidative condensation reaction.
Figure captions
Figure 1: FTIR-Spectra of (a) SiO , (b) SiO -NH , (c) SiO -NH -Cu(II) complex.
2
2
2
2
2
Figure 2: UV-vis adsorption spectra of (a) SiO , (b) SiO -NH and (c) SiO -NH -Cu(II)
2
2
2
2
2
Figure 3: X-ray diffraction patterns of patterns of SiO and SiO -NH -Cu(II) complex
2
2
2
Figure 4: SEM images (a & b) SiO , (c & d) SiO -NH -Cu(II) complex, (e) EDX spectrum of SiO -NH -
2
2
2
2
2
Cu(II) Schiff base complex.
Figure 5: HRTEM images (a) SiO , (b) SiO -NH -Cu(II) complex.
2
2
2
Figure 6: EPR spectrum of silica functionalized Cu(II) Schiff base complex.
Figure 7: N Adsorption-Desorption isotherms and pore size distributions inset. Of: (a) activated SiO and
2
2
(
b) SiO -NH -Cu(II) complex.
2
2
Table Captions
a
Table 1: Effect of solvents on oxidative condensation reaction .
Table 2: Effect of catalyst amount and temperature.
a
Table 3: Substrate scope of oxidative condensation reaction
a
Table 4: Reusability of the catalyst
Table 5: Comparison of efficiency of the prepared catalysts with some reported catalysts.
9

Scheme 1:
Scheme 2:
Scheme 3:
1
0

Fig 1:
Fig 2:
Fig 3:
1
1

Fig 4:
Fig 5:
(a)
(b)
1
2

Fig 6:
Fig 7:
Table 1:
c
d
e
-1
Entry
Solvent
Reaction time (h) Yield (%) TON TOF (h )
b
1
2
3
4
5
6
7
8
Toluene
Ethanol
24
24
24
24
10
14
18
12
-
-
-
55
63
45
94
79
73
81
147
168
120
251
211
195
216
6
Methanol
7
Dichloromethane
Toluene
5
25
15
11
18
Chlorobenzene
Nitrobenzene
Acetonitrile
1
3

a
Oxidative condensation reaction of aromatic amines (1 equiv) with benzyl alcohol (1.5 equiv) using SiO2-
NH -Cu(II) Schiff base complex (50 mg, 0.375% Cu) in different solvents (10 ml) under refluxing
2
conditions.
b
Reaction carried out under neat conditions (without catalyst)
c
Isolated yield.
d
Turnover number (TON) = (mmol of product)/(mmol of catalyst) after time t.
e
TOF = TON/time
Table 2:
b
c
-1
Entry Catalyst amount
Temperature
(°C)
Reaction time Yield TON TOF (h )
a
(
mg, mol%)
-
(h)
24
20
18
15
12
10
10
24
20
13
(%)
-
1
2
3
4
5
6
7
8
9
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
RT
-
-
10, 0.075
20, 0.15
30, 0.225
40, 0.3
50, 0.375
100, 0.75
50, 0.375
50, 0.375
50, 0.375
21
30
64
72
94
94
18
45
80
280
200
284
240
251
125
48
14
11
19
20
25
12
2
50
80
120
213
6
16
1
0
Oxidative condensation reaction of aromatic amines (1 equiv) with benzyl alcohol (1.5 equiv) using SiO2-
NH -Cu(II) Schiff base complex (50 mg, 0.375% Cu) in different temperature under refluxing toluene.
2
a
Isolated yield.
b
Turnover number (TON) = (mmol of product)/(mmol of catalyst) after time t.
TOF = TON/time
c
Table 3:
Time Yield
b
d
e
-1
Entry
Amine
Product (3(a-k))
TON
TOF (h )
c
(h)
(%)
1
10
9
94
251
25
2
3
4
92
96
95
245
256
253
27
32
32
8
8
1
4

5
6
7
10
11
10
75
78
91
200
208
245
20
19
24
8
9
15
8
73
92
195
245
13
31
1
0
1
16
14
83
89
221
237
14
17
1
a
Oxidative condensation reaction of aromatic amines (1 equiv) with benzyl alcohol (1.5 equiv) using SiO2-
NH -Cu(II) Schiff base complex (50 mg, 0.375% Cu) in toluene (10 ml) under refluxing condition.
2
b
All the compounds are known compounds and physical and spectral data are good agreement with
literature.
c
Isolated yield.
d
Turnover number (TON) = (mmol of product)/(mmol of catalyst) after time t.
TOF = TON/time
e
Table 4:
Cycle
Fresh
94
1
2
3
4
5
b
Yield (%)
94
93
92
90
88
a
Oxidative condensation reaction of aromatic amines (1 equiv) with benzyl alcohol (1.5 equiv) using SiO2-
NH -Cu(II) Schiff base complex (50 mg) in different solvents (10 ml) under refluxing conditions.
2
b
Isolated yield.
1
5

Table 5:
Entry
Catalyst
Condition
Time (h) Yield (%) Reference
Pd/DNA
a
1
H O, N balloon, 50 °C
12
96
[37]
2
2
LiOH.H O
2
Cu(ClO ) .H O
KOH, Toluene, 70 °C
4
2
2
b
2
3
4
19
20
20
97
92
90
[38]
[39]
[40]
(5 mol%)
O balloon
2
b
b
KOH
Air, Toluene, 90 °C
Pd/AlO(OH)
4 mol%)
1 atm O , heptane
2
(
90 °C
Mesitylene (1.5 g)
c
5
CeO (50 mg)
24
10
93
94
[41]
2
6
0 °C, 24 h, air
SiO -NH -Cu(II)
2
2
c
6
Toluene, Reflux
This work
(50 mg)
a
Determined by GC-MS.
Yields were determined by H NMR.
Isolated yield.
b
1
c
1
6

Highlights


We successfully synthesized the silica functionalized Cu(II) Schiff base complex.
The immobilization of the Cu(II) Schiff base complex on the surface of the silica
material was confirmed by various physicochemical studies.


The catalytic activity of the synthesized material was studied through the oxidative
condensation reaction of benzyl alcohol with aromatic amines.
Operational simplicity, activity under mild reaction conditions, excellent product
yields with greater substrate scope are the advantages of this methods
1
7