Halide induced epimerization of meso-1,2-dihalo-1,2-diaryl-1,2-dimethyldisilanes

Kinetic data were obtained for the halide induced epimerization of meso-X[(p-RC6H4)MeSi]2X (halide=Cl− where X=F, R=H, CH3O, CH3, F, CF3; halide=Br− where X=Cl, R=H) to a 1:1 meso:racemic mixture of diastereomers. A Hammett plot demonstrates a correlation of the rate of epimerization of the fluorinated derivatives with electropositive character at silicon. In order to extend the series of para-substituted derivatives, F[(p-RC6H4)MeSi]2F (R=CF3) was prepared by treatment of H[(p-RC6H4)MeSi]2H (R=CF3) with CuCl2/CuI/KF in THF and the meso diastereomer was resolved via crystallization induced asymmetric transformation and the structure verified by X-ray crystallography. Possible mechanisms for the halide induced epimerization are discussed.