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Issue 28, 2009
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Epoxidation of olefins catalysed by vanadium–salan complexes: a theoretical mechanistic study

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Abstract

Plausible mechanisms of olefin epoxidation catalysed by a V–salan model complex [VIV([double bond, length as m-dash]O)(L)(H2O)] (1, L = (CH2NHCH2CH[double bond, length as m-dash]CHO)2) in the presence of H2O2 are investigated and compared by theoretical methods using density functional theory. Three main routes, i.e. the Mimoun, Sharpless and biradical mechanisms, were examined in detail, and the Sharpless pathway was found to be the most favourable one. The reaction starts from the formation of an active catalytic species [VV([double bond, length as m-dash]O)(OO)(LH)] (3c) upon interaction of 1 with H2O2, then concerted, highly synchronous attack of the olefin to 3c occurs yielding the epoxide and catalyst [VV([double bond, length as m-dash]O)2(LH)], the latter being oxidized by H2O2 to 3c. The activation barrier strongly depends on the proton location in the catalyst molecule and is the lowest when one of the oxygen atoms of the salan ligand is protonated and the vanadium atom is penta-coordinated with one vacant coordination position (complex 3c). The olefin in this reaction acts as an electron donor (nucleophile) rather than as an electron acceptor (electrophile).

Graphical abstract: Epoxidation of olefins catalysed by vanadium–salan complexes: a theoretical mechanistic study

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Publication details

The article was received on 06 Feb 2009, accepted on 20 Apr 2009 and first published on 29 May 2009


Article type: Paper
DOI: 10.1039/B902424G
Citation: Dalton Trans., 2009,0, 5460-5468
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    Epoxidation of olefins catalysed by vanadium–salan complexes: a theoretical mechanistic study

    M. L. Kuznetsov and J. C. Pessoa, Dalton Trans., 2009, 0, 5460
    DOI: 10.1039/B902424G

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