Propene polymerization using ansa-metallocenium ions:: Excess activator effects on polymerization activity and polymer microstructure

The initial and steady-state rates of propene polymerization using the metallocene complexes Me2X-(Cp)IndZrMe(2) (1, X = C, Si) and Me2C(Cp)FluZrMe(2) (2) activated with B(C6F5)(3) increase in the presence of excess borane; the kinetic data are consistent with two different forms of the propagating catalyst in equilibrium with each other in the presence of excess borane. The ratio k(p)/k(i) for the ion pair [Me2C(Cp)IndZrMe][MeB(C6F5)(3)] (3) is sensitive to the presence of excess borane, while the molecular structure of 3 reveals strong ion pairing in the solid state. Variable-temperature NMR spectra of [Me2C(Cp)IndZr(13)Me][MMeB(C6F5)(3)] in the presence of excess borane are consistent with the doubly activated intermediate Me2C(Cp)IndZr{mu-Me-13)B(C6F5)(3)}(2) (4) being present.