COMPETITIVE INTRAMOLECULAR TI-C VERSUS AL-C ALKENE INSERTIONS - EXAMINING THE ROLE OF LEWIS-ACID COCATALYSTS IN ZIEGLER-NATTA ALKENE INSERTION AND CHAIN TRANSFER-REACTIONS

Mechanistic aspects of Ziegler-Natta olefin insertion, which include c atalyst/cocatalyst interactions, chain propagation, and chain terminat ion, have been examined for systems which model the Cp(2)Ti(Cl)R/RAlCl (2) and Cp(2)Ti(Cl)R/MgX(2) catalyst complexes. The reaction of (2-but yl-6-hepten-1-yl)titanocene chloride with (2-propyl-6-hepten-1-yl)alum inum dichloride:diethyl etherate produced 78% cyclization of the titan ocene ligand, while less than 2% of the ligand originating on aluminum cyclized. In a complementary experiment, the reaction of (2-propyl-6- hepten-1-yl)titanocene chloride and (2-butyl-6-hepten-1-yl)aluminum di chloride:diethyl etherate again produced only intramolecular insertion of the titanium ligand (58%). Based on these results, equilibration o f ligands through transmetallation between titanium and aluminum did n ot occur under these reaction conditions, and selective insertion into the titanium-carbon bond was confirmed for this process. Similarly, l igand cyclization with Cp(2)Ti(Cl)R/MgX(2) also occurred through inser tion into the titanium-carbon bond. The product distribution generated by the MgX(2) was highly solvent dependent. Cyclization in CH2Cl2 was very efficient, while reaction in toluene generated numerous products . Included in the toluene reaction mixture were compounds that resulte d from ligand transposition/chain transfer of the titanium ligand.