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Enantioselective epoxidation of β-methylstyrene catalyzed by immobilized Mn(salen) catalysts in different mesoporous silica supports

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Abstract.
Mesoporous silica-supported chiral Mn(salen) catalysts were prepared and evaluated in the heterogeneous
asymmetric epoxidation of β-methylstyrene with NaClO as an oxidant. Homogeneous and immobilized
Mn(salen) catalysts exhibit similar cis/trans ratios and ee values when trans-substrate is used but
different cis/trans ratios and ee values when cis-substrate is used. The production of trans-epoxides is
favored in the heterogeneous asymmetric epoxidation of cis-β-methylstyrene, whereas the production of
cis-epoxides is favored in homogeneous reaction. In addition, the cis/trans ratio and ee value of transepoxides produced from cis-β-methylstyrene change sequentially with changes in support materials, but
the ee value of cis-epoxides does not. The textural properties of immobilized Mn(salen) catalysts can be
sequentially adjusted by changing pore dimension and channel length, after which the motion restriction
and confinement effect in nanochannels of immobilized Mn(salen) catalysts can be adjusted sequentially.
Our results reflect that the collapse step of trans-intermediates is considerably affected by the confinement
effect, whereas the rotation step of cis-intermediates is greatly influenced by motion restriction.
The motion restriction in nanochannels increases the likelihood of rotation for the C–C single bond of
cis-intermediates and favors the production of trans-epoxides.

Keywords:
Chiral catalysis
Mn(salen)
Asymmetric epoxidation
Motion restriction
Confinement effect
Mesoporous
Immobilization

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Informasi Detail

Judul Seri

Journal of Catalysis

No. Panggil

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Penerbit

London : Elsevier Inc.., 2008

Deskripsi Fisik

Journal of Catalysis 256 (2008) 226–236

Bahasa

English

ISBN/ISSN

00219517

Klasifikasi

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Tipe Isi

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Tipe Media

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Tipe Pembawa

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Edisi

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Subjek

KIMIA

Info Detail Spesifik

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Pernyataan Tanggungjawab

agus

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