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2.11.4.4.5 Method 5: Miscellaneous Methods

DOI: 10.1055/sos-SD-002-00797

Negishi, E.-i.; Takahashi, T.Science of Synthesis, (20032709.

As discussed in Section 2.11.4.7, there are various alternatives for the synthesis of bis(η5-cyclopentadienyl)monoorganozirconium compounds, where the organo group is an alkyl, alkenyl, or allyl group. However, those containing other organo groups, such as aryl, benzyl, and alkynyl groups, have been much less accessible; thereby, impeding the progress in the chemistry of organozirconium and -hafnium compounds. In contrast with monoorgano-substituted zirconocene derivatives, bis(η5-cyclopentadienyl)diorganozirconium complexes are readily formed by treatment of dichlorobis(η5-cyclopentadienyl)zirconium with 2 equivalents of an organolithium or Grignard reagent, even though many of them are thermally unstable (see Sections 2.11.4.5, 2.11.5, and 2.11.8). Once the bis(η5-cyclopentadienyl)diorganozirconium complex has been generated, it may then be subjected to (i) selective protonolysis,[‌131‌] e.g. using hydrogen chloride, (ii) selective haloge­nolysis,[‌132‌] or (iii) conproportionation with a bis(η5-cyclopentadienyl)zirconium derivative[‌133‌] to give the corresponding bis(η5-cyclopentadienyl)monoorganozirconium compounds as shown in Scheme 30. For example, bis(η5-cyclopentadienyl)dimethylzirconi­um(IV) undergoes conproportionation with bis(η5-cyclopentadienyl)diiodozirconium(IV) to give the corresponding product 71 (Scheme 31).[‌134‌] Despite its potential, this area, however, has not yet been systematically and adequately developed.

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