Zirconocene compounds derived from boratastilbene, 4-boratastyrylstilbene, and 1,4-bis(boratastyryl)benzene and their reactivities to the ethylene polymerization

(η6-Boratastilbene)(η5-pentamethylcyclopentadienyl)zirconium dichloride (1), (η6-4-boratastyrylstilbene)(η5-pentamethylcyclopentadienyl)zirconium dichloride (2), [1,4-bis(boratastyryl)benzene]bis[(dichloro)(pentamethylcyclopentadienyl)zirconium] (3), and bis(η6-boratastilbene)zirconium dichloride (4) were synthesized. The crystal structure of 1 was determined by X-ray crystallography. These zirconium complexes show activities in the presence of methylaluminoxane (MAO) for the polymerization of ethylene. The activities are in the following order: 1>2>Cp2ZrCl2>3>4. The activity of 1 is three times higher than that of Cp2ZrCl2 under similar conditions.