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Syntheses, Structural Characterizations, and Catalytic Behavior of ansa-Metallocene Complexes Derived from 1,1-Dicyclopentadienyl-1-silacycloalkanes

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journal contribution
posted on 15.09.2003, 00:00 by Sung-Joon Kim, Young-Joo Lee, Eugene Kang, Sang Hern Kim, Jaejung Ko, Byunyeol Lee, Minserk Cheong, Il-Hwan Suh, Sang Ook Kang
1,1-Dicyclopentadienyl-1-silacycloalkanes (2) were prepared by condensation of cyclopentadiene with appropriate 1,1-dichloro-1-silacycloalkanes [(cycl)SiCl2 (1); cycl = CnH2n, n = 3, 4, 5]. Dilithium salts of 2 were subsequently transformed into the corresponding ansa-metallocene complexes [{η:5η5-Cp2-(cycl)Si}MCl2] (M = Ti (3), Zr (4), Hf (5)). The molecular structures of 3b, 3c, 4b, and 4c were determined by X-ray crystallography. As a result of the formation of the siladicyclopentadienyl ring, the metal atoms in 35 exhibit distorted tetrahedral configurations with the two chloride atoms. DFT calculations established that the size of the bridge ring influenced the catalytic activity. Thus, the catalytic activity of the ansa-titanocene complexes was remarkably enhanced by the silacycloalkyl bridge due to their increased conformational stability (14 × 103 kg PE molcat-1 h-1 for 3c). In addition, polyethylenes with high molecular weight such as Mw = (1.3−2.6) × 106 (Mw/Mn = 1.6−2.0 by GPC) were obtained with 3.