Mn(III) based binapthyl cSchiff base complex hetrogenized over organo-modified
SBA-15
Priti Sharma, A.P. Singh*
Catalysis Division, National Chemical Laboratory, Pune 411008, India.
Tel.: +91 20 2590 2497; fax: +91 20 2590 2633.
e-mail: ap.singh@ncl.res.in

Abstract
Heterogenized organocatalyst was synthesized by the covalent anchoring of the complex Schiff base manganese(III)over modified mesoporous surface of SBA-15 through the reactive 3-aminopropyl trimethoxysilane (3-APTMS) group.
The XRD and N2 sorption measurement, UV reflectance and CP MAS NMR spectroscopy (13C and 29Si) of the catalyst
confirmed the structural integrity of the mesoporous hosts and the spectroscopic characterization technique proved thesuccessful anchoring of the metal complex over the modified mesoporous support. The screening of the catalyst Mn(III)L-SBA-15 and neat Mn(III)-L complexes were done in the oxidation reaction of thioanisole (methyl phenyl sulfide) byusing TBHP as an oxidant. Mn(III)-L-SBA-15 catalyst shows higher activities and exhibit enhanced enantiomeric excess
comparable to homogeneous catalyst [Mn(III)-L].

Keywords: Chiral Schiff-base, Binaphthyl ligand, Immobilization, Post grafting synthesis.

1. Introduction
The discovery of efficient method for catalytic epoxidation
is an important goal in synthetic chemistry as there is a
growing interest in using epoxide as a building block inorganic synthesis [1]. Mn(III) Schiff-base complexes havebecome highly valuable catalysts in homogeneous
alkene epoxidation reactions by using readily available
oxygen donors. In separation science SBA-15 has
became the most popular member of the grouppossessed extremely high surface areas, easily
accessible, uniform pore sizes and stability. Herein we
described the covalent bonding of the Schiff base(homogeneous system) complex on modified SBA-15
surface. The immediate goal of our study was to evaluate
the heterogenization method of the salen binapthyl Schiffbase ligand over SBA-15 and to determine the extent of
the increased stability of the catalyst with regard to thehomogeneous catalyst as well as their recycling
properties.

2. Materials and Methods
The synthesis of mesoporous SBA-15 was carried outhydrothermally under the autogeneous pressure in anautoclave. Surface modification of SBA-15 was achievedby a post synthesis grafting method with 3-aminoproply
trimethoxysilane. The unsymmetrical Schiff base wasprepared by the reported procedure. The surface
modified SBA-15 was added to a solution of theunsymmetrical Schiff base in dry toluene and theresulting suspension was refluxed for 48 h under inert
atmosphere (Fig. 1).

3. Results and Discussion
The synthesized catalysts were analyzed by a series ofcharacterization techniques. The presence of (110)reflection [2] in the XRD pattern confirms the retention ofhexagonal ordering of SBA-15 even afterfunctionalization and metal complex anchoring. The
resulting materials were subjected to different
characterization techniques, such as XRD, FT-IR, TGADTA, solid state 13C NMR and XPS, which reveal that themetal complexes are firmly attached to modified SBA-15
support. In heterogeneous catalyst Mn(III)-L-SBA-15
XPS spectra[3] showing two clear band at 641.7 eV andat 652.6 eV, which corresponds to Mn(III)2p3/2 andMn(III)2p1/2 binding energy of the Mn metal respectively;
where as in homogeneous neat catalyst [Mn(III)-L] XPS
spectra showing two resolved peak at 642 eV and 653.1
eV. This indicates the oxidation state of Mn ion is +3 inboth of the catalysts (Fig. 2). The effect of Neat Mn(III)-Lcomplex loading on the physical properties of SBA-15

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013

(surface area and pore size parameter) was explored bynitrogen sorption [4].

applied for the liquid phase sulfoxidation of methyl phenyl
sulfide with TBHP as an oxidant at room temperature(25ºC). Immobilized Mn(III)-L-SBA-15 shows enhanced
catalytic activity with 94% conversion of thioanisole alongwith 95% selectivity of sulfoxide (main product) in 5 hrs.
Finally Mn(III)-L-SBA-15 gave high activity, TON andselectivity compared to homogeneous counterpart
Mn(III)-L complex.
Further recyclability test was done upto 4th cycle andresult shows almost similar conversion and selectivity
form 2nd to 4th cycles (~71 % conversion at the end of
4th cycle). The observed reactivity and data aresupporting the heterogeneity of the synthesized catalyst
Mn(III)-L-SBA-15. The ICP analysis of the filtrate after acatalytic reaction shows the loss of Mn element from theheterogeneous catalyst Mn(III)-L-SBA-15 is less than 2%
compared with the total amount of the Mn(III)-L complex
grafted over the modified surface of the SBA-15.

4. Conclusions

According to IUPAC classification, type IV isotherms
relate to capillary condensation steps, characteristic ofthe mesoporous materials. It is well known that theintroduction of homogenous catalysts or metals on
porous supports shows a decrease in its specific surface
areaand pore volume. After metal complex
functionalization, the surface area gets reduced to 232
m2/gm and pore volume 0.437 cc/gm for Mn(III)-L-SBA15. The decrease in total mesoporous pore volume(20.55%) and surface area (34.88%) after metal
immobilization is indicative of the grafting of complex
inside the channels of mesoporous calcined SBA-15(Fig.3). Thus The progressive change with different
modification on type IV isotherms Confirms that theimmobilization of Mn(III)-L complex causes porenarrowing, which resulted decrease in the mesoporosityof SBA-15.
The present synthesized and characterized materials
Neat Mn(III)-L complex and Mn(III)-LSBA-15 were

In conclusion covalent functionization of Mn(III)-Lcomplex over modified surface of SBA-15 wassuccessfully achieved by multiple synthetic procedures.
The presence of (110) reflection in the XRD patternconfirms the retention of hexagonal ordering even after
functionization and metal complex anchoring. The effectof Neat Mn(III)-L complex loading on the physicalproperties of SBA-15 (surface are and pore parameter)
was explored by nitrogen sorption. The resulting
materials were subjected to different characterization
techniques, which reveal that the metal complexes arefirmly attached to modified SBA-15 support. The
screening of the catalyst Mn(III)-L-SBA-15 was done insulfoxidation reaction of thioanisole. Results reveal
catalyst Mn(III)-L-SBA-15 shows high activity andselectivity compared to homogeneous Mn(III)-L complex
counterpart. During recycling conversion of thioanisole
decreases from 94 to 71% after use from fresh to fourth
recycle over Mn(III)-L-SBA-15.

References[1] M. Dusi, T. Mallat, A. Baiker, Catal. Rev. Sci. Eng. 42(2000) 213–278.
[2]Chengzhong Yu, J. Bozhi Tian, Fan, D. Galen, Stucky,Dongyuan Zhao, J. Am. Chem.Soc.124 (2002) 4556–4557.
[3] G. Zampieri, M. Abbate, F. Prado, A. Caneiro, Solid
State Commun. 123 (2002) 81–85.
[4] D. Zhao, J. Feng, Q. Huo, N. Melosh, G.H.
Fredrickson, B.F. Chmelka, G.D. Stucky, Science. 279(1998) 548–552.

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013