Preparation and reactions of Cp₂HfRCl, Cp₂HfRR′ and hafnacyclopent-2-enes

Reaction of Cp₂HfCl₂ with R₃Al (R = Et, n-Pr, or n-Bu) in hexane selectively produced monoalkylhafnocene complexes, Cp₂HfRCl (1), in high yields. Cp₂HfMeCl (1a) was prepared by the reaction of oxo-bridged hafnocene complex (Cp₂HfCl)₂(μ-O) with Me₃Al. The treatment of 1 with alkylating reagents such as R′Li or EtMgBr afforded unsymmetrical dialkylhafnocene complexes Cp₂HfRR′ (3) in good to excellent yields. The kinetic study of thermolysis of Cp₂HfEtR (R = Me, Et, n-Bu, sec-Bu, t-Bu or Ph) suggested that decomposition of Cp₂HfEt(sec-Bu) was much faster than the others. Cp₂Hf(sec-Bu)₂ (2e) can be used as a good precursor of Cp₂Hf(II) species. Hafnacyclopent-2-enes (4) were prepared in good yields by the reaction of Cp₂HfEt₂ (2b) with alkynes.