Structural and Dynamic Features of Bis[2-(2-furyl)indenyl]zirconium Derivatives<sup>†</sup>

Treatment of 2-indanone with 2-lithio-5-methylfuran, followed by hydrolysis, dehydration, deprotonation with <i>n</i>-butyllithium, and transmetalation, gave bis[2-(5-methyl-2-furyl)indenyl]zirconium dichloride (<b>6a</b>). The dynamic 600 MHz <sup>1</sup>H 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 <b>6a</b> was determined at Δ<i>G</i><sup>⧧</sup><sub>rot</sub> = 7.0 ± 0.4 kcal mol<sup>-1</sup> 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]ZrR<sub>2</sub> series the metallocene rotational barrier can apparently be frozen on the 600 MHz <sup>1</sup>H NMR time scale for R = CH<sub>2</sub>CMe<sub>3</sub> and R = CH<sub>2</sub>Ph. The di(neopentyl)Zr complex <b>7b</b> shows a metallocene rotational barrier of Δ<i>G</i><sup>⧧</sup><sub>rot(Cp)</sub>(213 K) = 9.0 ± 0.3 kcal mol<sup>-1</sup>, and for the di(benzyl)Zr complex <b>7c</b> a Δ<i>G</i><sup>⧧</sup><sub>rot(Cp)</sub> value of 11.4 ± 0.3 kcal mol<sup>-1</sup> was obtained at 243 K. In the cases of <b>7b</b> and <b>7c</b> only chiral <i>rac</i>-type metallocene conformers were found in solution within the limits of the accuracy of the <sup>1</sup>H NMR method. The complexes bis[2-(5-ethyl-2-furyl)indenyl]ZrCl<sub>2</sub> (<b>8</b>) and bis[2-(5-methyl-2-furyl)indenyl]Zr(neopentyl)<sub>2</sub> (<b>7b</b>) were characterized by X-ray crystal structure analyses. In the solid state both complexes exhibit chiral <i>rac</i>-like metallocene frameworks.