Highly selective monofunctionalization of zirconacyclopentanes and dialkylzirconocene complexes

Selective monofunctionalization was investigated for symmetrical zirconacyclopentanes or symmetrical dialkylzirconocenes. Reaction of zirconacyclopentanes, which were prepared by intermolecular coupling of two alkenes, or intramolecular cyclization of dienes, trienes or tetraenes on zirconium, with PPh₂Cl or SnR₃Cl (R = Me, Ph) gave monofunctionalized products in good to high yields with high selectivities. Even in the presence of 2 equiv. of PPh₂Cl or SnR₃Cl, only one Zr-carbon bond reacted. Treatment of zirconacyclopentanes with methanol yielded monoprotonated complexes. Subsequent addition of halogen such as Br₂ and I₂ to these monoprotonated complexes gave highly selective monohalogenated products. Similar monoprotonation reactions proceeded for dialkylzirconocene or-hafnocene complexes. Reaction of Cp₂MR₂ (M = Zr or Hf, R = alkyl or aryl) with alcohols afforded alkylalkoxyzirconocene or -hafnocene complexes, Cp₂MR(OR′) (M = Zr or Hf, R′ = alkyl or aryl) in high yields with high selectivities. High selectivity of monofunctionalization using PPh₂Cl, SnR₃Cl or alcohols can be attributed to the different reactivities between monoalkylzirconocenes which are monofunctionalized products and zirconacyclopentanes or dialkylzirconocenes.