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DOI: 10.1055/sos-SD-002-00797

Negishi, E.-i.; Takahashi, T.Science of Synthesis, (20032707.

Carbometalation converts one organometallic complex into another containing the same metal (e.g., see Scheme 1). It is, in principle, applicable to the synthesis of monoalkyl- and monoalkenylbis(η5-cyclopentadienyl)metal complexes. In reality, the scope of carbozirconation as a method for the synthesis of discrete chlorobis(η5-cyclopentadienyl)monoorganozirconium compounds is rather limited for various reasons: Firstly, carbozirconation must be a process of higher activation energy than the corresponding hydrozirconation reaction. It normally requires either a bimetallic reagent system consisting of zirconium and aluminum compounds, or strained zirconacycles, including zirconacyclopropanes. The latter leads to the formation of five-membered zirconacycles discussed in Section 2.11.5. In the former reaction involving zirconiumaluminum reagents, the carbozirconation products are usually converted into organoaluminum compounds. Therefore, back-transmetalation from aluminum to zirconium is necessary to obtain organozirconium derivatives, as shown in Scheme 26. The in situ transmetalation from zirconium to aluminum can be exploited in developing zirconium-catalyzed carboalumination reactions, as discussed in Sections and For these reasons, the current scope of discrete carbozirconation to give bis(η5-cyclopentadienyl)monoorganozirconium complexes is rather limited, even though it is believed to occur widely in zirconium-catalyzed carbometalation reactions including the ZieglerNatta polymerization.[‌469‌] The reaction of alkynylaluminum 62 with chlorobis(η5-cyclopentadienyl)methylzirconium(IV) (51) to give the monoorganozirconium compound 63 (Scheme 27)[‌126‌] is a prototypical example of carbozirconation producing discrete organozirconium derivatives.

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