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

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)(4)I](THF)(3) (2). Subsequent ligand-exchange between 2 and DME affords ThI3[O(CH2)(4)I](DME)(2) (11), which can be converted to 3 with Me3SiI. Salt metathesis between 2 and K(L-Me) (L-Me = (2,6-(Pr2C6H3)-Pr-i)NC(Me)CHC(Me)N(2,6-(Pr2C6H3)-Pr-i)) cleanly gives (L-Me) ThI2[O(CH2)(4)I](THF) (10), which is a rare example of a thorium beta-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.