Novel zirconocene hydride complexes in homogeneous and in SiO2-supported olefin-polymerization catalysts modified with diisobutylalundnum hydride or triisobutylaluminum

摘要

Reactive species in SiO2-supported, zirconocene-based olefin-polymerization catalysts have been characterized by comparison of their UV-vis spectra with those of related, NMR-spectroscopically identified catalyst species in homogeneous solution. Neutral zirconocene dihydride complexes are found to arise in hydrocarbon solutions as well as on SiO2 supports when catalyst systems that contain rac-Me2Si(ind)(2)ZrCl2 and methylaluminoxane (MAO) are modified by addition of diisobutylaluminum hydride or triisobutylaluminum. These complexes, tentatively formulated as adducts with Lewis-acidic alkylaluminum species AlR2X, rac-Me2Si(ind)(2)ZrH2 center dot {nAlR(2)X}, are reconverted into the initial reactive zirconocene cations upon addition of isobutene to these reaction systems.