Synthesis, Characterization, and Polymerization Properties of Bis(2-menthylindenyl)zirconium Dichloride and Bis(2-menthyl-4,7-dimethylindenyl)zirconium Dichloride

Abstract

The tetrakis(triphenylphosphine)palladium-catalyzed cross coupling of 2-bromoindene or 2-bromo-4,7-dimethylindene with menthylmagnesium chloride gave the novel ligands 2-menthylindene (10) and 2-menthyl-4,7-dimethylindene (11) in 66 and 57% yields. These indenes were deprotonated with n-BuLi to give isolated indenyllithium complexes which were metalated with zirconium tetrachloride to give bis(2-menthylindenyl)zirconium dichloride (14) and bis(2-menthyl-4,7-dimethylindenyl)zirconium dichloride (15) in 40 and 66% yields. Both complexes formed as their single possible stereoisomer and were characterized by X-ray crystallography and MS, NMR, and IR spectroscopy. The variable-temperature 1H NMR spectrum of bis(2-menthyl-4,7-dimethylindenyl)zirconium dichloride (15) showed that it interconverts with a rotational activation barrier of about 12.5 ± 0.5 kcal/mol, and that a 60:40 mixture of C2-symmetric diastereomeric conformations was present at −50 °C. The 1H NMR spectrum of bis(2-menthylindenyl)zirconium dichloride (14) was invariant between −50 and +50 °C. Complexes 14 and 15 polymerized propene in the presence of methylaluminumoxane (MAO) and hydrogen (10 960 and 33 750 g PP/g Zr h, respectively). The molecular weights and stereoregularity of the polymers produced were low.