ja0681523_si_001.pdf (506.59 kB)

Control of ansa-Zirconocene Stereochemistry by Reversible Exchange of Cyclopentadienyl and Chloride Ligands

Download (506.59 kB)
journal contribution
posted on 28.03.2007 by Richard M. Buck, Nawaporn Vinayavekhin, Richard F. Jordan
The reaction of Li2[Me2Si(3-R-C5H3)2] salts with Zr{Me3SiN(CH2)3NSiMe3}Cl2(THF)2 in THF quantitatively afforded rac-Me2Si(3-R-C5H3)2Zr{Me3SiN(CH2)3NSiMe3} zirconocenes with 100% stereoselectivity. NMR monitoring studies showed that these reactions initially form rac/meso mixtures, which undergo isomerization to pure rac. The isomerization requires Cp−enantioface exchange and is catalyzed by chloride ion, which reversibly displaces Cp- from Me2Si(3-R-C5H3)2Zr{Me3SiN(CH2)3NSiMe3}. Kinetic analyses for selected complexes showed first-order dependence of the isomerization rate on both metallocene and chloride concentrations. Reversible Cp-/Cl- exchange is also facile for {ansa-bis-Cp}ZrCl2 and nonbridged Cp2ZrCl2 complexes.