Zirconium and hafnium complexes with (allylsilyl)(η-amidosilyl)-η5-cyclopentadienyl ligands: synthesis, structure and reactivity

Abstract

The disubstituted cyclopentadiene C5H4(SiMe2Cl)[SiMe2(CH2CH=CH2)] was isolated by reaction of the lithium salt [Li{C5H4SiMe2(CH2CH=CH2)}] with SiMe2Cl2. It was then treated with NH2tBu and LiNH(2,6-Me2C6H3) to give the (aminosilyl)cyclopentadienes C5H4[SiMe2(CH2CH=CH2)][SiMe2(NHR)], which were further deprotonated to their dilithium salts [Li2{1-SiMe2NR-3-SiMe2(CH2CH=CH2)C5H3}] (R = tBu, 2,6-Me2C6H3). Reactions of the metal halides ZrCl4(THF)2 and HfCl4 with these dilithium salts, followed by alkylation of the resulting dichloro complexes, afforded the (η1-amidosilyl)-η5-cyclopentadienyl complexes [M{η5-C5H3(SiMe2-η1-NR)[SiMe2(CH2CH=CH2)]}X2] (R = tBu, 2,6-Me2C6H3; X = Cl, Me, CH2Ph; M = Zr, Hf). Only the bis(iminoacyl) complexes [M{η5-C5H3(SiMe2-η1-NtBu)[SiMe2(CH2CH=CH2)]}{η2-CR=N(2,6-Me2C6H3)}2] (M = Zr, Hf; R = Me, CH2Ph) could be isolated when the dialkylzirconium and -hafnium complexes were treated with CN(2,6-Me2C6H3); these were slowly transformed into the C–C-coupled diazametallacyclopentene compounds [M{η5-C5H3(SiMe2-η1-NtBu)[SiMe2(CH2CH=CH2)]}{η1-N(2,6-Me2C6H3)-CR=CR-η1-N(2,6-Me2C6H3)}] (R = Me, CH2Ph, M = Zr; R = Me, M = Hf) when their toluene solutions were heated to 70 °C–80 °C for long periods (2–4 d). The structural characterisation of all of the new compounds is described and the molecular structure of the dimeric dichlorozirconocene [ZrCl(μ-Cl){η5-C5H3(SiMe2-η1-NtBu)[SiMe2(CH2CH=CH2)]}]2, was determined by X-ray diffraction methods. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)