Preparation and reactions of Cp2HfRC1, 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 (la) was prepared by the reaction of oxo-bridged hafnocene complex (Cp2HfCl)(2)(mu-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. (C) 1997 Elsevier Science S.A.