Photochemical Isomerization of Me₂Si-Bridged Zirconocene Complexes. Application to Stereoselective Syntheses of <i>ansa</i>-Zirconocene Binaphtholate Stereoisomers^,¹

Abstract

Upon irradiation in toluene solution, meso-racemate mixtures of Me2Si(2-Me-4-tBu-C5H2)2ZrCl2 or Me2Si(2-Me-4-phenyl-C5H2)2ZrCl2 react with 1 equiv of the dilithium salt of racemic binaphthol quantitatively to the racemic binaphtholate complex. Analogous reactions with 1 equiv of the R(+) enantiomer of dilithium binaphtholate give a near-quantitative yield of the enantiomerically pure ansa-zirconocene binaphtholate complex. The structures of the racemic binaphtholate complex, Me2Si(2-Me-4-tBu-C5H2)2Zr(binaphtholate), and of a monodentate binaphtholate complex with a meso configurated zirconocene moiety, Me2Si(3-tBu-C5H3)2Zr(binaphtholate) chloride, were crystallographically determined.