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Enantioselective epoxidation of (Z)-stilbene using a chiral Mn(III)-salen complex: effect of immobilisation on MCM-41 on product selectivity

Piaggio, Paola, McMorn, Paul, Murphy, Damien ORCID:, Bethell, D., Page, P. C. B., Hancock, F. E., Sly, C., Kerton, Owain J. and Hutchings, Graham John ORCID: 2000. Enantioselective epoxidation of (Z)-stilbene using a chiral Mn(III)-salen complex: effect of immobilisation on MCM-41 on product selectivity. Journal of the Chemical Society - Perkins Transactions 2 2000 (10) , pp. 2008-2015. 10.1039/B005752P

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Manganese-exchanged Al-MCM-41 modified by the chiral salen ligand [(R,R)-(−)-N,N ′-bis(3,5-di-tert-butylsalicylidene)cyclohexane-1,2-diamine] has been investigated as a heterogeneous catalyst for the enantioselective epoxidation of (Z )-stilbene using iodosylbenzene as oxygen donor, with particular interest in the effect of reaction conditions on the cis∶trans ratio of the epoxide product. Immobilisation of the chiral Mn–salen complex in Al-MCM-41 increases the cis∶trans ratio of the epoxide product when compared to the non-immobilised complex under the same conditions. Increasing the level of Mn-exchange in the Al-MCM-41 increases the amount of trans-epoxide, whereas increasing the iodosylbenzene∶substrate ratio increases the amount of cis product formed. Increasing the reaction temperature also increases the amount of trans-epoxide for the homogeneous Mn-complex under the same conditions. A series of experiments is described in which the external ion-exchange sites on Al-MCM-41 are preferentially silanised, which enables the cis/trans selectivity for external and internal sites to be determined. Mn–salen immobilised on the external surface of Al-MCM-41 gives the same cis∶trans ratio as that observed with the non-immobilised Mn–salen complex in solution, whereas Mn–salen immobilised within the pores gives the cis-epoxide preferentially. The enantioselection of the immobilised chiral Mn–salen complex is shown to decrease with reaction time at −10 °C, but the cis∶trans epoxide ratio remains unchanged; whereas for the non-immobilised complex in solution the enantioselection is independent of reaction time. Iodobenzene, a decomposition product formed from iodosylbenzene, is found to act as a poison for the immobilised catalyst, leading to a slower reaction and lower enantioselection.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Cardiff Catalysis Institute (CCI)
Subjects: Q Science > QD Chemistry
Publisher: Royal Society of Chemistry
ISSN: 1364-5471
Last Modified: 10 Nov 2023 12:45

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