Structural and Dynamic Features of Bis[2-(2-furyl)indenyl]zirconium Derivatives

Abstract

Treatment of 2-indanone with 2-lithio-5-methylfuran, followed by hydrolysis, dehydration, deprotonation with n-butyllithium, and transmetalation, gave bis[2-(5-methyl-2-furyl)indenyl]zirconium dichloride (6a). The dynamic 600 MHz 1H NMR spectroscopic analysis in the temperature range between 253 and 128 K revealed the presence of two metallocene conformational isomers in a 60:40 ratio. It is likely that this observed feature just originates from freezing out the indenyl−furyl rotation. The corresponding activation barrier of 6a was determined at ΔG⧧rot = 7.0 ± 0.4 kcal mol-1 by a line shape analysis. A series of analogous 5-methyl-2-furyl- and 5-methyl-2-thienyl-substituted bis(indenyl)zirconium dibromides and dichlorides show analogous conformational behavior and almost identical rotational activation energies. In the bis[2-(5-methyl-2-furyl)indenyl]ZrR2 series the metallocene rotational barrier can apparently be frozen on the 600 MHz 1H NMR time scale for R = CH2CMe3 and R = CH2Ph. The di(neopentyl)Zr c...