Halogeno, hydrido, and hydrocarbyl derivatives of (η-cyclo-octatetraene)(η-pentamethylcyclopentadienyl)zirconium(IV): X-ray crystal structure of [Zr(η-C5Me5)(η-C8H8)H]

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Abstract
The sequential addition of K2(C8H8) and Li(C5Me4R)(R = Me or Et) to ZrCl4 affords [Zr(η-C5Me4R)(η-C8H8)Cl] which further reacts with MR′(M = MgCl or Li; R′= Me, Et, CH2Ph, C6H4Me-4, CMeCH Me, C2Me, or C2Ph) to afford the corresponding hydrocarbyl derivatives [Zr(η-C5Me4R)(η-C8H8)R′]. Reaction of [Zr(η-C5Me4R)(η-C8H8)Cl] with LiAIH4 or Mg(Cl)CHMe2 affords [Zr(η-C5Me4R)(η-C8H8) H]. Both i.r. and n.m.r. data suggest that the compounds [Zr(η-C5Me4R)(η-C8H8)X](X = Cl, H, or R′) have a ‘planar’ 1–8-η-C8H8 ligand and should therefore be regarded as 18-electron complexes of ZrIV. An X-ray diffraction study of [Zr(η-C5Me5)(η–C8H8) H] has shown that the molecule is monomeric and has one terminal hydride ligand. All eight carbon atoms of the C8 ring are within bonding distance of the Zr atom, with Zr–C varying from 2.43(4) to 2.68(4)Å and the ring itself slightly folded into an envelope conformation. It is bonded to the metal atom on the convex face. Crystals of [Zr(η-C5Me5)(η-C8H8)H] are orthorhombic, space group Pbc21, with two crystallographically distinct molecules in the asymmetric unit. Surprisingly, although the two molecules appear to be related by a pseudo-glide plane, in fact one molecule is twisted in its crystal siting relative to the other, though their molecule symmetry is identical. The structure could not be very accurately determined; it has been refined to R 0.066 (R′ 0.055) for 1 019 reflections measured at 210 K to 2θ= 50°.

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