Enantioselective Epoxidation of Alkenes by Jacobsen Catalyst Anchored onto Aminopropyl-functionalised Laponite, MCM-41 a
- PDF / 279,510 Bytes
- 9 Pages / 595.276 x 790.866 pts Page_size
- 35 Downloads / 190 Views
Enantioselective Epoxidation of Alkenes by Jacobsen Catalyst Anchored onto Aminopropyl-functionalised Laponite, MCM-41 and FSM-16 Pankaj Das Æ Ana Rosa Silva Æ Ana P. Carvalho Æ Joa˜o Pires Æ Cristina Freire
Received: 17 January 2008 / Accepted: 20 November 2008 / Published online: 5 December 2008 Ó Springer Science+Business Media, LLC 2008
Abstract The Jacobsen catalyst derivative, (R,R)[Mn(3,5-dtButsalhd)]ClO4–CAT 2, was immobilized through axial coordination of the metal center onto a Laponite, MCM-41 and FSM-16 functionalized with 3aminopropyltriethoxysilane. The catalytic activity of the Mn-based materials was screened for the enantioselective epoxidation of three olefins: styrene, a-methylstyrene and 6-CN-2,20 -dimethychromene, using m-CPBA/NMO as oxidant, and the results were compared with the corresponding homogenous complex (CAT 2) and with the Jacobsen’s catalyst, (R,R)-[Mn(3,5-dtButsalhd)Cl]–CAT 1. The results indicate that under comparable condition, the Laponite-based materials show both, higher epoxide yield
and enantiomeric excess (ee%) compared to MCM-41 and FSM-16-based materials. The best ee% value was obtained for the substrate 6-CN-2,20 -dimethylchromene (64%) which is very close to that obtained with CAT 2 (67%) in homogeneous phase; for the two regular mesoporous materials (MCM-41 and FSM-16) the catalytic results were more favorable for the FSM-16 samples. Keywords Enantioselective epoxidation Chiral Mn(III) salen complex Laponite MCM-41 FSM-16 Covalent anchoring
1 Introduction
Electronic supplementary material The online version of this article (doi:10.1007/s10562-008-9793-x) contains supplementary material, which is available to authorized users. P. Das A. R. Silva C. Freire (&) REQUIMTE/Departamento de Quı´mica, Faculdade de Cieˆncias, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal e-mail: [email protected] A. P. Carvalho J. Pires Departamento de Quı´mica e Bioquı´mica and CQB, Faculdade de Cieˆncias, Universidade de Lisboa, Ed. C8, Campo Grande, 1749-016 Lisbon, Portugal Present Address: P. Das Department of Chemistry, Dibrugarh University, Dibrugarh, Assam 786 004, India Present Address: A. R. Silva Unilever R&D, Port Sunlight, Bebington, UK
Chiral manganese(III) salen complexes are highly efficient homogeneous catalysts in the asymmetric epoxidation of several un-functionalized alkenes [1–3]. Conversely, chiral epoxides are extremely useful building blocks in the synthesis of chiral compounds for the pharmaceutical as well as for agrochemical industries [1–3]. Therefore, chemical sustainability of this homogeneous catalyst has been attracting attention of researchers [4–6], since it can not be recycled. One of the solutions that has been extensively researched is the immobilization of the chiral manganese(III) salen complexes into/onto insoluble supports, which prevents the formation of inactive dimeric Mn(IV) (the main deactivation process in homogeneous phase) and allows for their recovery by simple filtration [4–6]. Initially organic polymers
Data Loading...
