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[Molecules: None] [Related articles/posters: 036 117 006 004 035 ] |
Quantum mechanical and force field modelling leads to a new theory for the
origin of stereoselection in Jacobsen epoxidations. Ab initio DFT calculations
predict a triplet ground state for simple analogues of manganese oxo compounds
which are intermediates in the Jacobsen oxidation. Examination of several
approaches of olefins to the oxo derivative of Jacobsen's catalyst by empirical
force field modelling show that there is a preferred direction of approach
of alkene to the oxygen. Semi-empirical PM3(tm) methods accurately reproduce
DFT and crystal structure data. Analysis of steric issues involved in the approach
of the olefin with either of two enantiotopic faces towards the catalyst
results in an explanation for the cause of stereoselectivity in Jacobsen
type epoxidation reactions.
