Allyl derivatives of (cyclo-octatetraene)(η- pentamethylcyclopentadienyl)-zirconium: X-ray crystal structure of [Zr(η-C5Me5)(1–4-η-C8H8)(η-C3H5)]

Abstract

Reaction of [Zr(η-C₅Me₄R¹)(η-C₈H₈)Cl] with MgCl(CH₂CR²CHR³)(R¹= Me, R²= R³= H; R²= H, R³= Me or Ph; R²= Me, R³= H; R¹= Et, R²= R³= H; R²= Me, R³= H) affords a series of complexes of general formula [Zr(C₅Me₄R¹)(C₈H₈)(CH₂CR²CHR³)]. Both the C₃H₅ complexes are intense purple and the pentamethylcyclopentadienyl derivative is shown by a single crystal X-ray diffraction study to have an η-C₃H₅ ligand and a 1–4-η-C₈H₈ ligand attached to zirconium [mean Zr-C: C₃H₅, 2.480; C₈H₈(co-ordinated C), 2.457; C₅Me₅, 2.510 Å] and is therefore formally a complex of zirconium(II). This complex undergoes rapid interchange of syn and anti allyl hydrogen atoms at 20 °C (from n.m.r. measurements) and reacts readily with H₂(1 atm) affording a mixture of [Zr(η-C₅Me₅)(η-C₈H₈)(σ-C₃H₇)] and [Zr(η-C₅Me₅)(η-C₈H₈) H]. Those complexes with substituted allyl ligands are pale yellow and have σ-CH₂CR²CHR³ and η-C₈H₈ ligands and are formally derivatives of Zr^IV. Despite the formal co-ordinative saturation of the yellow complexes, the 2-methylallyl derivatives undergo a rapid 1,3 shift.