Preparation of Pincer Hafnium Complexes for Olefin Polymerization.

Pincer-type [C, N, N]HfMe complex is a flagship among the post-metallocene catalysts. In this work, various pincer-type Hf-complexes were prepared for olefin polymerization. Pincer-type [N, N, N]HfMe complexes were prepared by reacting in situ generated HfMe with the corresponding ligand precursors, and the structure of a complex bearing 2,6-EtCHN moieties was confirmed by X-ray crystallography. When the ligand precursors of [(CH)RSi-CHN-C(H)PhN(H)Ar (R = Me or Ph, Ar = 2,6-diisopropylphenyl) were treated with in situ generated HfMe, pincer-type [C, N, N]HfMe complexes were afforded by formation of Hf-CHSi bond. Pincer-type [C, S, N]HfMe complex, where the pyridine moiety in the flagship catalyst was replaced with a thiophene unit, was not generated when the corresponding ligand precursor was treated with HfMe. Instead, the [S, N]HfMe-type complex was obtained with no formation of the Hf-C bond. A series of pincer-type [C, N, N]HfMe complexes was prepared where the arylamido moiety in the flagship catalyst was replaced with alkylamido moieties (alkyl = iPr, cyclohexyl, Bu, adamantyl). Structures of the complexes bearing isopropylamido and adamantylamido moieties were confirmed by X-ray crystallography. Most of the complexes cleanly generated the desired ion-pair complexes when treated with an equivalent amount of [(CH)N(H)Me][B(CF)], which showed negligible activity in olefin polymerization. Some complexes bearing bulky substituents showed moderate activities, even though the desired ion-pair complexes were not cleanly afforded.