Air termination of hydrocarbon-reduced Cr(Vi)/silica

Abstract

The initiation of the Phillips commercial polymerization catalyst, comprising simultaneous reduction and self-alkylation of the Cr(VI), has again been examined, this time by using oxygen to terminate live Cr–alkyls formed during reduction. Cr(VI)/silica catalysts were first reduced by an alkane or alkene, then exposed to oxygen, followed by immediate hydrolysis to liberate the species thus formed. The brief exposure to oxygen significantly increased the amount of oxygenated products obtained from Cr(VI) including both monomeric and oligomeric species. This suggests that Cr–alkyls formed during reduction were converted into Cr–alkoxides or other oxygenated terminal species. This approach produces an interesting insight into the state of Cr during and shortly after initiation.