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Title
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Enantioselective binding of structural epoxide isomers by a chiral vanadyl salen complex: a pulsed EPR, cw-ENDOR and DFT investigation
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Author
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Abstract
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| The mode of chiral interaction between a series of asymmetric epoxides (propylene oxide, butylene oxide, epifluorohydrin and epichlorohydrin) and a chiral vanadyl salen complex, N, N-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diamino-vanadium (IV) oxide, [VO( 1)], was investigated by a range of electron magnetic resonance techniques (EPR, ENDOR, HYSCORE) and DFT. Enantiomer discrimination of the weakly bound epoxides by the vanadyl complex was evident by cw-ENDOR. The origin of this discrimination was attributed to a number of factors including H-bonds, steric properties and electrostatic contributions, which collectively control the outcome of the chiral interaction. DFT revealed the role of a key H-bond, formed between the epoxide oxygen atom (Oepoxide) and the methine proton (Hexo) attached to the asymmetric carbon atom of the chiral vanadyl salen complex, thereby providing a direct pathway for stereochemical communication between complex and substrate. These findings reveal the potential importance of weak outer sphere interactions in stereoselectivities of enantioselective homogeneous catalysis. |
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Language
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English
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Source (journal)
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Physical chemistry, chemical physics / Royal Society of Chemistry [London] - Cambridge, 1999, currens
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Publication
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Cambridge
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The Royal Society of Chemistry
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2009
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ISSN
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1463-9076
[print]
1463-9084
[online]
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DOI
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10.1039/B907807J
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Volume/pages
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11
:31
(2009)
, p. 6757-6769
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ISI
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000268481200022
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Full text (Publisher's DOI)
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