Carbon-hydrogen and carbon-carbon bond activation with highly electrophilic transition metal complexes

Abstract

Highly electron deficient scandocene derivatives of the types (η^5-C_5Me_5)_2ScR, {(η^5-C_5Me_4)_2SiMe_2}ScR and {(η^5-C_5H_3CMe_3)_2SiMe_2}ScR catalyze the polymerization of ethylene, the head-to-tail dimerization of α olefins, the cyclization of α,ω dienes to methylene cycloalkanes, and the branching of 1,4 pentadienes to isoprenes. The mechanisms of the individual steps have been studied. Key steps involve sequential and reversible olefin insertion/β H elimination/β alkyl elimination, the last of which is particularly facile in these systems. [((η^5-C_5Me_4)Me_2Si(η^1-NCMe_3)(PMe_3)Sc(µ-H)]_2, catalyzes the polymerization of α olefins. Evidence is presented in support of a well defined, one component catalyst system with all scandium centers functioning alike.

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