Appearance white solid | Pubchem 10891641 | |
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Zirconocene dichloride is an organozirconium compound composed of a zirconium central atom, with two cyclopentadienyl and two chloro ligands. It is a colourless diamagnetic solid that is somewhat stable in air.
Contents
Preparation and structure
Zirconocene dichloride may be prepared from zirconium(IV) chloride-THF complex and sodium cyclopentadienide:
ZrCl4(THF)2 + 2 NaCp → Cp2ZrCl2 + 2 NaCl + 2 THFThe closely related compound Cp2ZrBr2 was first described by Birmingham and Wilkinson.
The compound is a bent metallocene: the Cp rings are not parallel, the average Cp(centroid)-M-Cp angle being 128°. The Cl-Zr-Cl angle of 97.1° is wider than in niobocene dichloride (85.6°) and molybdocene dichloride (82°). This trend helped to establish the orientation of the HOMO in this class of complex.
Schwartz's reagent
Zirconocene dichloride reacts with lithium aluminium hydride to give Cp2ZrHCl Schwartz's reagent:
(C5H5)2ZrCl2 + 1/4 LiAlH4 → (C5H5)2ZrHCl + 1/4 LiAlCl4Since lithium aluminium hydride is a strong reductant, some over-reduction occurs to give the dihydrido complex, Cp2ZrH2; treatment of the product mixture with methylene chloride converts it to Schwartz's reagent.
Negishi reagent
Zirconocene dichloride can also be used to prepare the Negishi reagent, Cp2Zr(η2-butene) which is used as a source for Cp2Zr in oxidative cyclisation reactions. This reagent is prepared by treating zirconacene dichloride with n-BuLi leading to replacement of the two chloride ligands with butyl. The dibutyl compound subsequently undergoes beta-hydrogen abstraction to give one η2-butene ligand, eliminating the other butyl ligand as butane.