Science of Synthesis

Negishi, E.-i.; Takahashi, T., Science of Synthesis, (2003) 2, 718.

Chlorobis(η5-cyclopentadienyl)monoorganozirconium derivatives, where the monoorgano group is an alkyl, allyl, allenyl (or propargyl), or alkynyl group, are now widely available via transmetalation, hydrozirconation, or oxidative addition. At the time of writing, those containing a benzyl or aryl group are less readily available, and their chemistry as well as that of (alk-1-ynyl)chlorobis(η5-cyclopentadienyl)zirconium complexes remains largely unexplored. The majority of known chlorobis(η5-cyclopentadienyl)monoorganozirconium compounds are thermally stable at ambient temperatures; however, they are sensitive to both air and moisture, and should be handled under an inert atmosphere of argon or nitrogen. The structure of chlorobis(η5-cyclopentadienyl)monoorganozirconium complexes is distorted tetrahedral. For example, the Cp—Zr—Cp and Me—Zr—Cl angles of chlorobis(η5-cyclopentadienyl)methylzirconium(IV) (‌51‌) are 134 and 95°, respectively, and the Zr—Me and Zr—Cl bond lengths are 2.36 and 2.49 Å, respectively.[‌135‌] An empty valence shell orbital, which can act as an electrophilic center, may be available in any of the three regions indicated by the orbital lobes lying in the plane defined by the methyl carbon, zirconium, and chlorine (‌Scheme 42‌). This empty orbital plays a pivotal role in the reactions of bis(η5-cyclopentadienyl)zirconium derivatives including chlorobis(η5-cyclopentadienyl)monoorganozirconium complexes.

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