The asymmetric Schrock olefin metathesis catalyst. A computational study

The mechanism of the transition metal catalyzed olefin metathesis reaction with the Schrock catalyst is investigated with pure (BP86) and hybrid (B3LYP) density functional theory. On the free-energy surface there is no adduct between ethylene and model catalyst (MeO)₂Mo(CH₂)NH but instead a single transition on a flat surface giving a metallacyclobutane with a trigonal bipyramidal conformation that has a sizable barrier for conversion to the square pyramidal form. The model was expanded to the active asymmetric Schrock catalyst and investigated with QM/MM, using BP86 for the QM part and AMBER 95 for the MM part, for the experimentally known ring-closing metathesis of a symmetrical triene. The factors effecting chiral induction to the observed product are delineated.