Fluxional behavior and polymerization activity of the new a,a?-ortho-xylene-bis-(5,6-dimethyl-1-indenyl)-zirconium dichloride

We synthesize a new ortho-xylenyl-bridged substituted metallocene catalyst which surprisingly affords ethylene-1-hexene copolymers with broad molecular weight distribution (MWD), when activated with methylaluminoxane (MAO). In order to investigate the reasons of this behavior we carry out an indepth study on the metallocene complex. Its structure is determined by X-ray crystallography and found to have C1 symmetry in the solid state. Variable temperature 1H NMR suggests the existence in solution of a slow conformational exchange between two identical C1 structures. Therefore, the broad MWD has been ascribed to the presence of two conformationally blocked, single-site catalysts.