Thorium-mediated ring-opening of tetrahydrofuran and the development of a new thorium starting material: preparation and chemistry of ThI4(DME)2

Abstract

The thorium(IV) tetraiodide complex ThI₄(DME)₂ (3) (DME = 1,2-dimethoxyethane) has been prepared in high yield by reacting the corresponding chloride complex ThCl₄(DME)₂ with an excess of trimethylsilyl iodide (Me₃SiI) in toluene. This new route avoids the use of thorium metal as a reagent. ThI₄(DME)₂ (3) exhibits excellent thermal stability compared to ThI₄(THF)₄ (1), which undergoes rapid ring-opening of THF at ambient temperature to yield the iodobutoxide complex ThI₃[O(CH₂)₄I](THF)₃ (2). Subsequent ligand-exchange between 2 and DME affords ThI₃[O(CH₂)₄I](DME)₂ (11), which can be converted to 3 with Me₃SiI. Salt metathesis between 2 and K(L^Me) (L^Me = (2,6-ⁱPr₂C₆H₃)NC(Me)CHC(Me)N(2,6-ⁱPr₂C₆H₃)) cleanly gives (L^Me)ThI₂[O(CH₂)₄I](THF) (10), which is a rare example of a thorium β-diketiminate complex. Complexes 2, 10, and 11 represent the first reported examples of THF ring-opening mediated by thorium. The synthetic utility of ThI₄(DME)₂ (3) is demonstrated by preparation of thorium(IV) alkoxide, amide, and organometallic compounds.