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Abstract

Heterogeneous chromium catalysts are used to prep. much of the polyethylene manufd. industrially. Related homogeneous catalysts have received less attention and have never found com. use. A new family of phosphinoalkyl-​substituted cyclopentadienyl chromium compds. which, after activation with methylaluminoxane, give highly active homogeneous catalysts for the oligomerization and polymn. of ethylene are prepd.; the degree of oligomerization is controlled by the size of the substituents on the P-​atom. By varying the substituent the catalysis can be directed to give mainly dimers and trimers, oligomers or polymer. D. functional calcns. indicate that this effect is the consequence of an unusually selective steric destabilization of the transition state for termination which proceeds by β-​hydrogen transfer to the incoming ethylene in a reaction involving spin inversion.