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

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; C 5 H 5 CH 2 CH 2 N i Pr 2 ) is prepared from sodium cyclopentadienide and 2-chloro-1-(diisopropylamino)ethane. The highly moisture-sensitive metallocene dichlorides Cp N 2 TiCl 2 (2) and Cp N 2 ZrCl 2 (3) are synthesized by reaction of Cp N Li with TiCl 4 and ZrCl 4, 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 N 2 TiCl 2 ·2HCl (4) and Cp N 2 ZrCl 2 ·2HCl (5), which also are found to be precatalysts for the polymerization of ethylene. The dimethyl compounds Cp N 2 TiMe 2 (6) and Cp N 2 ZrMe 2 (7) can be obtained by reaction of 2 and 3 with 2 equiv of methyllithium. The dibenzyl complexes Cp N 2 TiBz 2 (8) and Cp N 2 ZrBz 2 (9) are formed analogously with a stoichiometric amount of benzylmagnesium bromide. The diphenoxy complex Cp N 2 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 N 2 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.