Alkene and alkyne complexes of zirconocene. Their preparation, structure, and novel transformations

Dialkylzirconocenes in situ generated such as Cp2Zr(n-Bu)(2), Cp2ZrEt2, and Cp2Zr(t-Bu)(i-Bu) are thermolyzed to afford zirconocene-alkene complexes. In the cases of Cp2Zr(n-Bu)(2) and Cp2Zr(t-Bu)(i-Bu), Cp2Zr-alkene complexes generated from them tend to act as a "Cp2Zr" equivalent, since the initially generated alkene is often replaced by another re-bond containing compound. In the presence of alkynes, for example, alkyne complexes may be generated. On the other hand, Cp2Zr(ethylene) tends to serve as an intermediate since the ethylene moiety is often incorporated in the final organic products. Ring expansion and contraction, ligand substitution, transmetallation, migratory insertion, stereoisomerization, regioisomerization, oxidative addition involving these Cp2Zr-alkene and Cp2Zr-alkyne complexes as well as their structures are reviewed.