Molecular modeling studies of the intramolecular twist mechanisms of racemization for tris chelate complexes

The preferred mechanisms of racemization for three tris chelate complexes, Co(acac)3, Fe(phen)3 3+ and Fe[S2CN(CH2)4]3, were investigated by molecular modeling. The transition states for both a Bailar twist and a Rây-Dutt twist were considered; semi-empirical calculations (PM3) yielded activation energies. The preferred mechanism was the Bailar twist for Co(acac)3 and Fe[S2CN(CH2)4]3 with activation energies of 83.2 and 7.3 kcal mol−1, respectively, and the Rây-Dutt twist for Fe(phen)3 3+ with an activation energy of 114.4 kcal mol−1. These results are compared with those of geometrical models.