Hafnium chloride and hafnium methyl complexes bearing substituted pyrrolyl ligands: synthesis, characterization, and ethylene polymerization

Reactions of HfCl4 with 2 and 3 equiv. of Li[C4H3N(CH2NMe2)-2] in toluene afford HfCl2[C4H3N(CH2NMe2)-2]2 (1) and HfCl[C4H3N(CH2NMe2)-2]3 (2), respectively. Transmetallation reaction of 1 with 2 equiv. of MeLi results in a hafnium dimethyl compound HfMe2[C4H3N(CH2NMe2)-2]2 (3). A variable-temperature 1H NMR spectroscopic study shows that the activation energy for the dissociation/association of the NMe2 units of compound 2 in solution is ca. 13.6 kcal/mol. Compounds 1–3 are characterized by NMR spectroscopy and single crystal X-ray diffraction. A polymerization study shows that compounds 1 and 3 exhibit moderate activity toward ethylene in the presence of TIBA and MAO.