Chromium Salen Mediated Alkene Epoxidation: A theoretical and Experimental Study Indica

Kaare Brandt Petersen, Per-Ola Norrby, Adrian M. Daly, Declan G. Gilheany

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The mechanism of alkene epoxidation by chromium(v) oxo salen complexes has been studied by DFT and experimental methods. The reaction is compared to the closely related Mn-catalyzed process in an attempt to understand the dramatic difference in selectivity between the two systems. Overall, the studies show that the reactions have many similarities, but also a few critical differences. In agreement with experiment, the chromium system requires a change from low- to high-spin in the catalytic cycle, whereas the manganese system can proceed either with spin inversion or entirely on the high-spin surface. The low-spin addition of metal oxo species to an alkene leads to an intermediate which forms epoxide either with a barrier on the low-spin surface or without a barrier after spin inversion. Supporting evidence for this intermediate was obtained by using vinylcyclopropane traps. The chromium(v) oxo complexes can adopt a stepped shape or form a more concave surface, analogous to previous results on manganese salen complexes.
Original languageEnglish
JournalChemistry - A European Journal
Issue number18
Pages (from-to)4299-4307
Publication statusPublished - 2002


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