Preparation of Pincer Hafnium Complexes for Olefin Polymerization

Pincer-type [C(naphthyl), N(pyridine), N(amido)]HfMe(2) 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(amido), N(pyridine), N(amido)]HfMe(2) complexes were prepared by reacting in situ generated HfMe(4) with the corresponding ligand precursors, and the structure of a complex bearing 2,6-Et(2)C(6)H(3)N(amido) moieties was confirmed by X-ray crystallography. When the ligand precursors of [(CH(3))R(2)Si-C(5)H(3)N-C(H)PhN(H)Ar (R = Me or Ph, Ar = 2,6-diisopropylphenyl) were treated with in situ generated HfMe(4), pincer-type [C(silylmethyl), N(pyridine), N(amido)]HfMe(2) complexes were afforded by formation of Hf-CH(2)Si bond. Pincer-type [C(naphthyl), S(thiophene), N(amido)]HfMe(2) 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(4). Instead, the [S(thiophene), N(amido)]HfMe(3)-type complex was obtained with no formation of the Hf-C(naphthyl) bond. A series of pincer-type [C(naphthyl), N(pyridine), N(alkylamido)]HfMe(2) complexes was prepared where the arylamido moiety in the flagship catalyst was replaced with alkylamido moieties (alkyl = iPr, cyclohexyl, tBu, 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 [(C(18)H(37))(2)N(H)Me](+)[B(C(6)F(5))(4)](−), 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.