The Reactivity of Niobium and Tantalum Pentahalides with Cyclic Ethers and the Isolation and the Characterization of Intermediates of the Polymerization of Tetrahydrofuran

The reactivity of MX5 (M = Nb, Ta; X = F, Cl, Br, I) with controlled amounts of THF allowed the isolation of probable intermediates of the THF polymerization reaction catalyzed by MX5. In particular, the ionic compounds give information of the fact that the polymerization requires, at a certain step, halide migration from one metal center to another, and confirm the generally accepted mechanism known for the cationic polymerization of cyclic ethers, for which an oxonium ion is involved in the chain growth.