Synthesis, characterization and catalytic property of chiral oxo-vanadium (+)-pseudoephedrine complex supported on magnetic nanoparticles Fe3O4 in the cyanosilylation of carbonyl compounds

Article abstract of DOI:10.1016/j.catcom.2014.08.029

Vanadium complex of pseudoephedrine immobilized on magnetic nanoparticle Fe₃O₄[VO(Pseudoephedrine)@MNPs] was prepared and characterized by UV-vis, SEM, XRD, TGA, EDX, FT-IR, AGFM and elemental analysis techniques. VO(Pseudoephedrine)

Full text of DOI:10.1016/j.catcom.2014.08.029

Catalysis Communications 58 (2015) 80–84
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Synthesis, characterization and catalytic property of chiral oxo-vanadium
(+)-pseudoephedrine complex supported on magnetic nanoparticles
Fe3O4 in the cyanosilylation of carbonyl compounds
a
Amin Rostami a,b, , Bahareh Atashkar
⁎
a
Department of Chemistry, Faculty of Science, University of Kurdistan, 66177-15175 Sanandaj, Iran
Research Centre of Nanotechnology, University of Kurdistan, P.O. Box 416, Sanandaj, Iran
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 June 2014
Received in revised form 19 August 2014
Accepted 21 August 2014
Available online 30 August 2014
Vanadium complex of pseudoephedrine immobilized on magnetic nanoparticle Fe3O4[VO(Pseudoephedrine)
@MNPs] was prepared and characterized by UV–vis, SEM, XRD, TGA, EDX, FT-IR, AGFM and elemental analysis
techniques. VO(Pseudoephedrine)@MNPs was found to catalyze the cyanosilylation of carbonyl compounds
using TMSCN in good yields with 8–25% enantiomeric excesses under solvent-free conditions at room tempera-
ture. The catalyst was recycled up to 15 times with little loss of activity and enantioselectivity.
© 2014 Elsevier B.V. All rights reserved.
Keywords:
Carbonyl compounds
TMSCN
Oxovanadium–(+)-pseudoephedrine complex
Magnetically catalyst
1. Introduction
silylated cyanohydrins is the addition reaction of TMSCN to carbonyl
compounds. The reaction is mostly catalyzed by Lewis acids or base
Magnetic nanoparticles (MNPs) have gained a significant place in
catalysis as a magnetically separable catalyst. The separation of magnet-
ic nanoparticles from the reaction mixtures is driven by an external
magnet, which makes the recovery and reusability of the catalyst easier
and avoids loss of catalyst associated with traditional methods. Also, the
activity and selectivity of magnetic nanocatalysts can be manipulated by
their surface modification. In addition to these points, the magnetic
properties of nanoparticles are stable and can tolerate the chemical
environment except those that are acidic/corrosive [1–3].
catalysts [13–20], although these protocols represent considerable
progress, however recover and reuse of catalysts are difficult.
In continuation of our studies on magnetic nanocatalysts [21–23],
herein, we report the synthesis, characterization and catalytic property
of new chiral VO(Pseudoephedrine)@MNPs in the cyanosilylation of
carbonyl compounds.
2. Experimental
Recently, an increasing interest has been focused on catalytic activity
of the vanadium Schiff base complexes derived from chiral and achiral
amino alcohols [4–9]. The main disadvantage of a catalyst based on
vanadium is their separation from the products which needs tedious
work-up processes in many reactions. This drawback can be overcome
by immobilizing these catalysts on MNPs, which can be easily removed
from the reaction mixture by magnetic separation.
The cyanosilylation of carbonyl compounds to form new C–C
bonds and to protect alcohol functions is an important reaction as the
O-protected cyanohydrins can be transformed into a wide range of
important intermediates such as α-hydroxy acids, α-amino acids,
β-amino alcohols, vicinal diols, 1,2-diamines and other valuable build-
ing blocks [10–12]. The main synthetic route for the preparation of
2.1. Instruments
The X-ray powder diffraction (XRD) data were collected on an
X 'Pert MPD Philips diffractometer. The SEM image was obtained by
VEGA TESCAN. The thermogravimetric analysis (TGA) was carried out
on a Bähr STA 503 instrument (Germany). The magnetic measurements
were carried out in an Alternating Gradient Force Magnetometer
(AGFM). UV–vis spectra were recorded on a JASCOV-550 UV–vis
spectrophotometer. The conversion and optical rotation were deter-
mined by an Agilent GC system and a Perkin Elmer Model 341 Polarim-
eter respectively.
2.2. General procedure for the cyanosilylation of carbonyl compounds
⁎
Corresponding author at: Research Centre of Nanotechnology, University of
VO(Pseudoephedrine)@MNPs (50 mg, 1.75 mol%) was added to a
mixture of carbonyl compound (1 mmol) and TMSCN (0.119 g,
Kurdistan, P.O. Box 416, Sanandaj, Iran. Tel.: +98 9183730910; fax: +98 8716624004.
E-mail address: a_rostami372@yahoo.com (A. Rostami).
http://dx.doi.org/10.1016/j.catcom.2014.08.029
1566-7367/© 2014 Elsevier B.V. All rights reserved.

A. Rostami, B. Atashkar / Catalysis Communications 58 (2015) 80–84
81
Scheme 1. Synthesis of VO(Pseudoephedrine)@MNPs.
1.2 mmol) under solvent-free conditions at room temperature and
stirred for the appropriate time. The progress was monitored by TLC.
After completion of the reaction, the catalyst was separated by an exter-
nal magnet and the mixture was washed with CH2Cl2 (2 × 5 mL). The
evaporation of CH2Cl2 under reduced pressure gave the pure products
in 75–99% yields.
UV–vis spectroscopy was applied to the characterization of
oxovanadium N-(3-trimethoxysilane) propyl pseudoephedrine
[VO(TMSP-Pseudoephedrine)] complex. UV–vis spectrum of the
VO(TMSP-Pseudoephedrine) complex (Fig. 1) shows three bands at
265–312 (π–π* transition of phenyl ring on ligand), 320–420 (may
be assigned as a ligand-to-metal charge transfer (LMCT) transition
originating from the oxygen and nitrogen on pseudoephedrine ligand
to the empty d orbital at the vanadium center) and 420–650 nm (d–d
transition), this band is not always observed, being often buried
3. Results and discussions
3.1. Preparation and characterization of VO(Pseudoephedrine)@MNPs
To prepare the catalyst, first, (+)-Pseudoephedrine hydrochlo-
ride was reacted with (3-chloropropyl)-trimethoxysilane to
give N-(3-trimethoxysilane) propyl pseudoephedrine (TMSP-Pseu-
doephedrine) ligands. The resulting TMSP-Pseudoephedrine ligand
was then allowed to react with vanadium acetyl acetonate to pro-
duce the VO(TMSP-Pseudoephedrine) complex. Finally, the reaction
of silica-coated Fe3O4 (Fe3O4@SiO2, SMNPS) which can be easily
prepared according to the reported procedure [24] with ob-
tained VO(TMSP-Pseudoephedrine) complex nanoparticles led to
VO(Pseudoephedrine)-functionalized magnetic Fe3O4@SiO2 nano-
particles [VO(Pseudoephedrine)@MNPs]. The process of the prepa-
ration of VO(Pseudoephedrine)@MNPs is shown in Scheme 1
(experimental details were provided in the Supplementary data).
The characterization of the catalyst was carried out by UV–vis,
SEM, XRD, TGA, EDX, FT-IR, AGFM and elemental analysis (see Supple-
mentary data).
Fig. 2. FTIR spectra of (a) (+)-Pseudoephedrine hydrochloride, (b) TMSP-Pseudoephedrine,
(c) VO(acac)2, (d) VO(TMSP-Pseudoephedrine) complex and (e) VO(Pseudoephedrine)
@MNPs.
Fig. 1. UV–vis spectra of a) VO(acac)2 and b) VO(Pseudoephedrine)@MNP complex.

82
A. Rostami, B. Atashkar / Catalysis Communications 58 (2015) 80–84
Scheme 2. VO(Pseudoephedrine)@MNPs catalyzed the synthesis of silylated cyanohydrins.
beneath a high intensity charge transfer band (or more accurately
the low energy tail of that band), and when it is observed it is generally
a shoulder [25]. These bands differ from that of the VO(acac)2
(Fig. 1) [26].
The SEM image of VO(Pseudoephedrine)@MNPs confirmed that the
catalyst was made up of uniform nanometer-sized particles 28–32 nm
(Fig. S1).
All together, the aforementioned results confirmed the formation
of a silica layer around the Fe3O4 nanoparticles and the VO(Pseudo-
ephedrine)-functionalization of this core–shell structure. Unfortunately,
due to the magnetic properties of VO(Pseudoephedrine)@MNPs it is
actually impossible to further characterize this material by using solid-
state NMR spectroscopy.
The position and relative intensities of all peaks in the XRD pattern
of VO(Pseudoephedrine)@MNPs conform well with the standard XRD
pattern of Fe3O4 (Fig. S2) [27], indicating retention of the crystalline
cubic spinel structure during functionalization of MNPs. The interlayer
spacing (dhkl), calculated using the Bragg equation, agrees well with
the data for standard magnetic (Table S1).
The TGA curve of the VO(Pseudoephedrine)@MNPs shows a weight
loss of about 19% from 260 to 600 °C, resulting from the decomposition
of the complex grafting to the silica-coated magnetic nanoparticle
(SMNP) surface (Fig. S3). The loading of the complex in VO(Pseudo-
ephedrine)@MNPs can be calculated from TGA and quantitative
elemental analysis, which confirmed a loading of approximately
0.35 mmol/g.
3.2. The catalytic applications of VO(Pseudoephedrine)@MNPs in
the cyanosilylation of carbonyl compounds
VO(Pseudoephedrine)@MNPs was tested as a magnetically separable
heterogeneous nanocatalyst for the cyanosilylation of carbonyl com-
pounds using TMSCN under solvent-free conditions at room temperature
(Scheme 2).
In order to optimize the reaction conditions, we evaluated the
influence of different amounts of catalyst on the cyanosilylation of benz-
aldehyde as a model compound under solvent-free conditions at room
temperature (Table 1). As shown in Table 1, the reaction was incom-
plete in the absence of a catalyst even after 24 h (Table 1, entry 1).
50 mg of VO(Pseudoephedrine)@MNPs was found to be ideal for
complete reaction of benzaldehyde with TMSCN (1.2 mmol).
In order to generalize the scope of the reaction, a series of structur-
ally diverse carbonyl compounds was subjected to the cyanosilylation
reaction under the optimized reaction conditions, and the results are
presented in Table 2. The overall yields of products are in the range
of 75–99% and an enantiomeric excess (ee) of 8–25% silylated cyano-
hydrins was obtained (Table 2, entries 1–17). The effect of temperature,
solvents and different amounts of catalyst and TMSCN in the cyano-
silylation of benzaldehyde on the enantiomeric excess were evaluated;
in all cases the observed enantiomeric excess was low.
The ability to easily recover and recycle of VO(Pseudoephedrine)
@MNPs was investigated. We have found that this catalyst was rapidly
recovered and demonstrated remarkably excellent recyclability; after
the first use of catalyst in the cyanosilylation reaction of benzaldehyde,
the catalyst was separated by an external magnet (Fig. 3), washed thor-
oughly with ether, and reused for subsequent experiments under simi-
lar reaction conditions. As shown in Fig. 4, the catalyst was reusable
without any significant loss of activity and enantioselectivity for the
15th recycling experiment (corresponding to a total TON = 850).
The comparison of the activity and enantioselectivity of soluble
oxo-vanadium complex bearing pseudoephedrine ligand [VO(TMSP-
Pseudoephedrine)] and VO(Pseudoephedrine)@MNPs (heterogenized
complex) in the model reaction was investigated (Table 3).
EDX spectrum shows the elemental composition (V, O, C, N, Si
and Fe) of the VO(Pseudoephedrine)@MNPs (Fig. S4).
Successful functionalization of the SMNPs can be inferred from FT-IR
techniques. The FTIR spectrum of VO(Pseudoephedrine)@MNPs shows
peaks that are characteristic of a functionalized VO(Pseudoephedrine)
group, which clearly differs from that of the (+)-Pseudoephedrine
hydrochloride, TMSP-Pseudoephedrine, VO(acac)2 and VO(TMSP-Pseu-
doephedrine) complex (Fig. 2). The interpretation of FTIR spectra has
been provided in the Supplementary data.
Superparamagnetic particles are beneficial for magnetic separation,
the magnetic measurements of MNPs and VO(Pseudoephedrine)
@MNPs were carried out in an AGFM (Fig. S5). As expected, the bare
MNPs showed the higher magnetic value (saturation magnetization,
Ms) of 74.3 emug−1 [28], and the Ms value of VO(Pseudoephedrine)
@MNPs is decreased due to the silica coating and the layer of the grafted
catalyst (30.4 emug−1). It has been reported that the Fe3O4 nanoparti-
cles with a value of coercivity (coercive field, Hc) lower than 20 Oe
could be called superparamagnetic. VO(Pseudoephedrine)@MNPs
have an Hc of 1.12 Oe and the remanent magnetization (Mr) of
1.23 emug−1 respectively. As a result, the modified MNPs have a typical
superparamagnetic behavior [29] and can be efficiently attracted with a
small magnet.
As shown in Table 3, the homogeneous complex shows more activity
and selectivity than the heterogenized complex. However, two major
advantages of the magnetically heterogenized complex as catalyst are:
(a) easily separation and (b) high reusability.
Table 1
Evaluation of the effect of the catalyst on the cyanosilylation reaction between benzaldehyde
(1 mmol) and TMSCN (1.2 mmol) under solvent-free conditions at room temperature.
Entry
Catalyst (mg)
Time/min
Converted yield (%)a
1
2
3
4
5
6
7
Catalyst-free
Fe3O4 NP (50)
24 h
24 h
300
250
180
180
175
20
30
4. Conclusion
VO(Pseudoephedrine)@MNPs (40)
VO(Pseudoephedrine)@MNPs (45)
VO(Pseudoephedrine)@MNPs (50)
VO(Pseudoephedrine)@MNPs (55)
VO(Pseudoephedrine)@MNPs (60)
100
100
100
100
100
In conclusion, the first magnetic nanoparticle-supported VO(Pseu-
doephedrine) for use as a robust heterogeneous catalyst was designed.
The VO(Pseudoephedrine)@MNPs was used as an efficient and reusable
catalyst in the cyanosilylation of carbonyl compounds using TMSCN
under solvent-free conditions at room temperature. In these reactions,
a
Conversion was determined by GC.

A. Rostami, B. Atashkar / Catalysis Communications 58 (2015) 80–84
Table 2 (continued)
83
Table 2
VO(Pseudoephedrine)@MNPs (50 mg) catalyzed the cyanosilylation of aldehydes and
ketones using TMSCN (1.2 mmol) under solvent-free conditions at room temperature.
Entry
Substrate
Time
(min)
Isolated
ee (%)b
yield (%)a
Entry
Substrate
Time
Isolated
ee (%)b
(min)
yield (%)a
1
180
200
97
96
25
15
190
96
8
2
3
18
20
16
17
180
300
75
85
15
17
195
182
92
99
4
22
18
220
88
–
(continued on next page)
5
6
205
240
95
94
20
19
7
540
89
9
8
9
180
180
98
97
23
20
10
11
190
205
98
89
18
18
Fig. 3. A reaction mixture in the absence (left) or presence of a magnetic field (right).
12
13
180
180
97
98
15
20
14
195
90
10
(continued on next page)
Fig. 4. The recycling experiment of VO(Pseudoephedrine)@MNPs for the cyanosilylation of
benzaldehyde (1 mmol) using TMSCN (1.2 mmol) under solvent-free conditions at room
temperature.

84
A. Rostami, B. Atashkar / Catalysis Communications 58 (2015) 80–84
Table 3
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Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2014.08.029.