Polymerization of ethylene by silica-supported dinuclear Cr(III) sites through an initiation step involving C-H bond activation.

摘要: The insertion of an olefin into a preformed metal–carbon bond is common mechanism for transition-metal-catalyzed polymerization. However, in one important industrial catalyst, the Phillips not present precatalyst. CrO3 dispersed on silica, polymerizes ethylene without activator. Despite 60 years intensive research, active sites and way first CrC formed remain unknown. We synthesized well-defined dinuclear CrII CrIII silica. Whereas material was poor polymerization active. Poisoning studies showed that about 65 % were active, far higher proportion than typically observed catalyst. Examination spent catalyst isotope labeling experiments formation Si–(μ-OH)–CrIII species, consistent with initiation involving heterolytic activation at CrIIIO bonds.