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 ThI(4)(DME)(2) (3) (DME = 1,2-dimethoxyethane) has been prepared in high yield by reacting the corresponding chloride complex ThCl(4)(DME)(2) with an excess of trimethylsilyl iodide (Me(3)SiI) in toluene. This new route avoids the use of thorium metal as a reagent. ThI(4)(DME)(2) (3) exhibits excellent thermal stability compared to ThI(4)(THF)(4) (1), which undergoes rapid ring-opening of THF at ambient temperature to yield the iodobutoxide complex ThI(3)[O(CH(2))(4)I](THF)(3) (2). Subsequent ligand-exchange between 2 and DME affords ThI(3)[O(CH(2))(4)I](DME)(2) (11), which can be converted to 3 with Me(3)SiI. Salt metathesis between 2 and K(L(Me)) (L(Me) = (2,6-(i)Pr(2)C(6)H(3))NC(Me)CHC(Me)N(2,6-(i)Pr(2)C(6)H(3))) cleanly gives (L(Me))ThI(2)[O(CH(2))(4)I](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 ThI(4)(DME)(2) (3) is demonstrated by preparation of thorium(IV) alkoxide, amide, and organometallic compounds.

A Rare Tetranuclear Thorium(IV) μ4‐Oxo Cluster and Dinuclear Thorium(IV) Complex Assembled by Carbon–Oxygen Bond Activation of 1,2‐Dimethoxyethane (DME)

“…Performing this sequence three times gave 2 in 85 % yield. 1g In our hands, deviating from this protocol resulted in incomplete halide exchange to give the mixed‐halide compound ThCl 4− x I x (DME) 2 ( 3 ; Scheme ).…”

“…For example, UBr 4 (CH 3 CN) 4 does not react with tetrahydrofuran (THF), but UI 4 (CH 3 CN) 4 does react with THF to form the bis(iodobutoxide) uranium complex, UI 2 [O(CH 2 ) 4 I] 2 (OPPh 3 ) 2 2. In another example, ThI 4 (THF) 4 readily undergoes ring opening of THF at room temperature in benzene, toluene, or in the solid state to give the iodobutoxide thorium complex, ThI 3 [O(CH 2 ) 4 I](THF) 3 , whereas ThI 4 (DME) 2 ( 2 ; DME=1,2‐dimethoxyethane) is thermally stable under identical conditions 1g…”

“…We have been developing new routes to thorium halide starting materials that avoid the use of thorium metal as a reagent 1e,g. 3 Recently, we demonstrated that 2 can be prepared in high yield by halide exchange between ThCl 4 (DME) 2 ( 1 ) and trimethylsilyl iodide (Me 3 SiI) 1g.…”

“…We have been developing new routes to thorium halide starting materials that avoid the use of thorium metal as a reagent 1e,g. 3 Recently, we demonstrated that 2 can be prepared in high yield by halide exchange between ThCl 4 (DME) 2 ( 1 ) and trimethylsilyl iodide (Me 3 SiI) 1g. We now report that if this halide exchange is incomplete, a mixed‐halide compound ThCl 4− x I x (DME) 2 ( 3 ) is produced (Scheme ), and that 3 spontaneously reacts with DME in methylene chloride (CH 2 Cl 2 ) to form the tetranuclear thorium(IV) μ 4 ‐oxo cluster Th 4 (μ 4 ‐O)(μ‐Cl) 2 I 6 [κ 2 ( O,O’ )‐μ‐O(CH 2 ) 2 OCH 3 ] 6 ( 4 ; Scheme ).…”

Insertion, protonolysis and photolysis reactivity of a thorium monoalkyl amidinate complex

“…The Th(1)–O(1) distance of 2.504(2) Å is in the range observed for other THF-bonded thorium complexes. 87 – 90 The second equivalent of THF can be removed under high vacuum. The 1 H NMR spectrum of dried 13 in CDCl 3 displays equivalent amidinate resonances, the aromatic peaks of the BPh 4 anion, and one set of resonances corresponding to coordinated THF.…”