Ethylene polymerization and ethylene/1-octene copolymerization using group 4 half-metallocenes containing aryloxo ligands, Cp*MCl2(OAr) [M = Ti, Zr, Hf; Ar = O-2,6-R2C6H3, R = tBu, Ph]—MAO catalyst systems

Effect of the centered metal toward the catalytic activity as well as comonomer incorporation has been explored in ethylene (co)polymerization using a series of Cp*MCl2(O-2,6-R2C6H3) [M = Ti (1), Zr (2), Hf (3); R = Ph (a), tBu (b), iPr (c)] in the presence of methylaluminoxane (MAO) cocatalyst. Complexes 2a, 3a,b were prepared and identified, and the structures for 2–3a,b were determined by X-ray crystallography as a distorted tetrahedral geometry around the metal center. The catalytic activity in ethylene polymerization was affected by the centered metal employed [Ti > Zr > Hf]; the complexes containing 2,6-diphenylphenoxy ligand (1–3a) showed higher catalytic activities than the complexes containing 2,6-di-tert-butylphenoxy analogues (1–3b). The molecular weights in the resultant polymers prepared by the Zr and the Hf analogues were lower than those prepared by the Ti–Ph (1a) and the Ti–iPr (1c) analogues. Although the copolymerizations of ethylene with 1-octene afforded the copolymers with uniform molecular weight distributions (except 1b), both the catalytic activities and the 1-octene incorporation were highly affected by the centered metal employed; the Ti–iPr analogue (1c) seems to be the most suited in terms of both the catalytic activity and the 1-octene incorporation. The attempted copolymerization of ethylene with 2-methyl-1-pentene using 2a,b and 3a—MAO catalysts afforded linear polyethylene.

Graphical abstractEffect of the centered metal in ethylene (co)polymerization using a series of Cp*MCl2(O-2,6-R2C6H3) in the presence of MAO cocatalyst have been explored; the catalytic activities as well as comonomer (1-octene) incorporations were highly affected by the centered metal employed rather than the phenoxy substituents.Figure optionsDownload full-size imageDownload as PowerPoint slide