Piaggio, P., McMorn, P., Murphy, D., Bethell, D., Bulman Page, P. C. B., Hancock, F. E., Sly, C., Kerton, O. J. and Hutchings, G. J. (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-Perkin Transactions 2 (10). pp. 2008-2015. ISSN 1470-1820
Full text not available from this repository. (Request a copy)Abstract
Manganese-exchanged Al-MCM-41 modified by the chiral salen ligand [(R,R)-(-)-N,N'-bis(3,5-di-tert-butylsalicylidene)cyclohexane-1,2-diamin e] 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 degrees 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 |
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Uncontrolled Keywords: | electron-spin-echo,cis-olefins,asymmetric epoxidation,alkenes,trans-epoxides,(salen)manganese(iii) complexes,molecular-sieves,zeolite,heterogeneous aziridination,catalyst |
Faculty \ School: | Faculty of Science > School of Chemistry |
Depositing User: | Rachel Smith |
Date Deposited: | 21 Jun 2011 11:49 |
Last Modified: | 24 Oct 2022 03:55 |
URI: | https://ueaeprints.uea.ac.uk/id/eprint/32816 |
DOI: |
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