Methyl-versus-chloride exchange as a measure of electron density at the metal center of ring-substituted zirconocene complexes

Methyl-versus-cloride exchange equilibria between different zirconocene complexes provide a sensitive measure of relative electron densities at the Zr centers of these complexes. As expected, methyl and trimethyl silyl substituents increase the electron density at the Zr center of a bis(cyclopentadienyl) Zr(IV) complex; the same holds for a dimethyl silyl bridge. In bis(indenyl) complexes, on the other hand, electron density at the metal center is reduced and substituent and bridge effects are different from those observed in bis(cyclopentadienyl) Zr(IV) complexes.