Theoretical evidence of persistent chirality in D3 homoleptic hexacoordinate complexes with monodentate ligands

A theoretical study of the enantiomer interconversion pathway relevant to racemization reactions of hexacoordinate transition-metal complexes is presented based on density functional calculations. The potential-energy surface for the trigonal twist pathway of the [Zr(SH)(6)](2-) model compound has been explored. The optimum structure reproduces, to a very good approximation, the experimental geometry of the analogous compound in which the thiolato groups have C6H4-4-OMe substituents instead of H atoms. A barrier of about 19 kcal mol(-1) is estimated for the racemization of [Zr(SH)(6)](2-) and exploratory calculations for [Zr(SC6H4-4-OMe)(6)](2-) indicate that a larger barrier should be expected. For the chiral homoleptic organometallic complexes [ZrMe6](2-) and [RhMe6](3-) no significant racemization barrier is expected.