Titanium and Zirconium Bent-Sandwich Complexes with the New [2-(Diisopropylamino)ethyl]cyclopentadienyl Ligand: Catalysts for the Polymerization of Ethylene and the Dehydrocoupling of Phenylsilane

Abstract

Titanium(IV) and zirconium(IV) bent-sandwich complexes containing the new donor substituted [2-(diisopropylamino)ethyl]cyclopentadienyl (Cp(N)) ligand are described. Cp(N)H (1; (C5H5CH2CH2NPr2)-Pr-i) is prepared from sodium cyclopentadienide and 2-chloro-1-(diisopropylamino)ethane. The highly moisture-sensitive metallocene dichlorides Cp(2)(N)TiCl(2) (2) and Cp(2)(N)ZrCl(2) (3) are synthesized by reaction of Cp(N)Li with TiCl4 and ZrCl4, respectively. In combination with the cocatalyst methylaluminoxane (MAO) they are precursors for ethylene polymerization catalysts. Compounds 2 and 3 react with 2 equiv of HCl with protonation of the amino groups to give the air- and moisture-stable metallocene dichloride dihydrochlorides Cp(2)(N)TiCl(2) . 2HCl (4) and Cp(2)(N)ZrCl(2) . 2HCl (5), which also are found to be precatalysts for the polymerization of ethylene. The dimethyl compounds Cp(2)(N)TiMe(2) (6) and Cp(2)(N)ZrMe(2) (7) can be obtained by reaction of 2 and 3 with 2 equiv of methyllithium. The dibenzyl complexes Cp(2)(N)TiBz(2) (8) and Cp(2)(N)ZrBz(2) (9) are formed analogously with a stoichiometric amount-of benzylmagnesium bromide. The diphenoxy complex Cp(2)(N)Ti(OPh)(2) (10) is synthesized by reaction of 2 with 2 equiv of lithium phenoxide. The dialkyl compounds 6-8 and the diphenoxy compound 10 show a remarkable activity in the catalytic dehydrocoupling of phenylsilane. Zr(NMe(2))(4) reacts with 2 equiv of Cp(N)H (1) to give the zirconocene derivative Cp(2)(N)Zr(NMe(2))(2) (11) in quantitative yield. The structure of 2 has been determined by a single-crystal X-ray diffraction study. The effects of the (dialkylamino)- and (dialkylammonio)ethyl substituents in metallocene-type compounds of titanium and zirconium are described.