Abstract
The spontaneous reduction of Ti IV to Ti III in soluble Ziegler—Natta catalysts of type Cp 2RTiCl·R’AlCl 2 (Cp = h 5 -cyclopentadienyl, R and R’ = methyl or ethyl) was studied both spectrally and chromatographically. Varied were R, R’, Al/Ti ratio, total concentration, solvent, and added olefin. Kinetic order in [Ti] could be varied from zero to second order by changing solvent. This can be explained by a mechanism in which a Cp 2 RTiCl—R’AlCl 2—olefin complex forms in the rate determining step and ligand R is expelled as half alkane half olefin. The expelled olefin may either polymerize or catalyze reduction by forming the rate-determining complex. Different apparent kinetic orders arise from differences in the olefin competitive reactions. The reaction products appear to form in a rapid bimolecular reaction following the rate-determining step. Evidence is presented that neither free radicals nor Cp 2RR’Ti are reduction intermediates. The intermediate is postulated to be a Ti IV transient hydride formed by a reverse insertion step.
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