Titanium reduction in a soluble ziegler—natta catalyst |
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Authors: | JA Waters GA Mortimer |
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Institution: | Monsanto Polymers and Petrochemicals Company, Texas City, Texas 77590 U.S.A. |
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Abstract: | The spontaneous reduction of TiIV to TiIII in soluble Ziegler—Natta catalysts of type Cp2RTiCl·R’AlCl2 (Cp = h5 -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 Cp2 RTiCl—R’AlCl2—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 Cp2RR’Ti are reduction intermediates. The intermediate is postulated to be a TiIV transient hydride formed by a reverse insertion step. |
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