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 catalyst/cocatalyst interactions, chain propagation, and chain termination, 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-butyl-6-hepten-1-yl)titanocene chloride with (2-propyl-6-hepten-1-yl)aluminum dichloride:diethyl etherate produced 78% cyclization of the titanocene 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 dichloride:diethyl etherate again produced only intramolecular insertion of the titanium ligand (58%). Based on these results, equilibration of ligands through transmetallation between titanium and aluminum did not occur under these reaction conditions, and selective insertion into the titanium-carbon bond was confirmed for this process. Similarly, ligand cyclization with Cp(2)Ti(Cl)R/MgX(2) also occurred through insertion 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 resulted from ligand transposition/chain transfer of the titanium ligand.