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

Abstract

Reactions of HfCl 4 with 2 and 3 equiv. of Li[C 4H 3N(CH 2NMe 2)-2] in toluene afford HfCl 2[C 4H 3N(CH 2NMe 2)-2] 2 ( 1) and HfCl[C 4H 3N(CH 2NMe 2)-2] 3 ( 2), respectively. Transmetallation reaction of 1 with 2 equiv. of MeLi results in a hafnium dimethyl compound HfMe 2[C 4H 3N(CH 2NMe 2)-2] 2 ( 3). A variable-temperature 1H NMR spectroscopic study shows that the activation energy for the dissociation/association of the NMe 2 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.