Polymerization of 1-hexene catalyzed by Cp*TiMe3-B(C6F5)3;: a mechanistic and structural study

Solutions of the Ziegler-Natta system Cp*TiMe3 - B(C6F5)(3) in toluene catalyze the polymerization of 1-hexene to mixtures of atactic poly-1-hexenes and complex oligomeric materials, which were characterized by H-1 and C-13{H-1} NMR spectroscopy and gel permeation chromatography (GPC). The polymer molecular weights and the relative proportions of polymers and oligomers vary with temperature, monomer:catalyst ratios, and degree of dilution and may generally be rationalized in terms of a conventional Ziegler-Natta mechanism. The C-13{H-1} NMR spectra of the polymers exhibit resonances suggesting significant degrees of 2,1-insertions during propagation, while experiments utilizing Cp*Ti((CH3)-C-13)(3) verify that initiation in toluene involves predominantly via 1,2-insertion of the first monomer unit but that 2,1-insertions occur up to 15-20% of the time in CH2Cl2. NMR experiments involving Cp*Ti((CH3)-C-13)(3) demonstrate that both methyl groups in the presumed active species Cp*TiMe2+ are incorporated into polymer.