Unique ansa-bis(indenyl)metallocene dichlorides: The quest for catalysts.

Abstract

The background, methodology, design, and synthesis of these four metallocenes will be discussed. In addition, other less successful attempts will be discussed as regards limits to this new methodology. Uniquely tethered metallocene propylene-bridged-1-(4-methylinden-7-yl)-3-(inden-1-yl)zirconium dichloride and ethylene-bridged-1-(4-methylinden-7-yl)-2-(inden-2-yl)zirconium dichloride were also synthesized. The propylene-bridged zirconocene has significant mobility in its bridging unit which allows it to interconvert between conformers rapidly. The ethylene-bridged zirconocene forms enantiomers. The formation of these two metallocenes is due in large part to the methodology of combining a Stetter Reaction and a Erker Cyclization to generate a 3-(4-methylinden-7-yl)propanoic acid from a starting diacid, ketoglutaric acid. Ethylene-bridged-1,2-bis(2-menthylinden-1-yl)zirconium and -titanium dichlorides have been synthesized from ansa-1,2-bis(2-menthylinden-1-yl)ethane 79. The known ansa-1,2-bis(2-bromoinden-1-yl)ethane reacted with the organozinc reagent formed from menthylmagnesium chloride and zinc chloride in the presence of palladium in order to provide ligand 79. The dilithium salt of this ligand was formed and reacted with zirconium(IV)chloride and titanium(III)chloride to give the respective metallocenes.