STEREOCHEMICAL NONRIGIDITY IN METALLOCENIUM IONS

Dynamic NMR spectroscopy of the MeB(C6F5)(3)(-) salts of a series of r ing-substituted zirconium- and hafnium-containing metallocenium ions, exemplified by (RCp)(2)ZrCH3+, reveals two exchange processes. One, ha ving the lower free energy of activation, involves shift of the CH3 gr oup from one lateral equatorial orbital to the other. The second resul ts from exchange between the metal-CH3 and B-CH3 groups. Effects of st ructural variations on exchange barriers are discussed and related to metallocenium ion-catalyzed olefin polymerization.