Improved synthesis and crystal structure of TiCl3(tmeda)(thf): A highly stereoselective pinacol coupling reagent for aromatic aldehydes

A monomeric titanium(III) complex, TiCl3(tmeda)(thf) (1), has been prepared by a reaction of TICl4 with TMEDA, Zn, and a catalytic amount of PbCl2 in an almost quantitative yield. The solid state structure of 1 is revealed by X-ray crystallographic analysis. The complex 1 couples aromatic aldehydes under mild conditions to give 1,2-diols in good to excellent yields with hi gh dl-selectivities.