Carbometallation reactions zirconium compounds

Hydroalumination of terminal alkenes using EtjAl as the hydride source must be carried out with titanium catalysts [24], since zirconium compounds lead to the formation of alumacyclopentanes [60, 61] (Scheme 2-11) and carbometallated products [62]. Suitable substrates for hydroalumination include styrene, allylnaphthalene and vinylsilanes. Only one of the ethyl groups in EtjAl takes part in these reactions, allowing the synthesis of diethylalkylalanes, which are difficult to obtain by other methods. 

In the addition reaction of Grignard reagents to a carbon-carbon unsaturated bond, the yields and selectivities become higher by using transition metal catalysts, and so these reactions came to public notice. Metal compounds of Ti, Ni, Cu and Zr are used for the catalysts [55,56,99]. For example, the adduct is obtained in a high yield by a carbometalation reaction with zirconium catalysts as shown in eq. (4.36) [100]. On the other hand, cyclization proceeds in a high yield by using a diene as shown in eq. (4.37) [101]. 

Alkynes are carbometallated with several organometallic compounds under mild conditions [3] but carbocupration has probably the greatest synthetic possibilities [4], associated with the zirconium-catalyzed methylalumination [5] reaction both proceed with very high stereoselectivity and afford the syn addition product as described in Scheme 7-2. 

Yasuda H, Okamoto T, Matsuoka Y, Nakamura A, Kai Y, Kanehisa N, Kasai N (1989) Diverse reaction courses in the controlled carbometalation of heterocumulenes with zirconium-diene complexes and molecular structures of carbon dioxide, isocyanate and ketene 1 1 and 1 2 inserted compounds. Organometallics 8 1139-1152... 

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