Uranium(iv) amide and halide derivatives of two tripodal tris(N-arylamido-dimethylsilyl)methanes

Abstract

Reaction of three equivalents of ArNH₂ (Ar = 3,5-Me₂C₆H₃) with HC(SiMe₂Br)₃ in the presence of the auxiliary base NEt₃ afforded the tripodal tris(N-arylamine-dimethylsilyl)methane HC{SiMe₂N(H)Ar}₃ (1) in 83% yield. Three-fold deprotonation of 1 with n-butyllithium afforded the corresponding tri-lithium tris(N-arylamido-dimethylsilyl)methane etherate [HC{SiMe₂N(Li)Ar}₃(OEt₂)] (2) in 92% yield. Salt elimination reactions between 2 or the known complex [HC{SiMe₂N(Li)Ar′}₃(OEt₂)₂] (3) (Ar′ = 4-MeC₆H₄) with one equivalent of uranium(IV) tetrachloride afforded the corresponding tris(N-arylamido-dimethylsilyl)methane uranium(IV) chloride complexes as monomeric [U(Cl){HC(SiMe₂NAr)₃}(THF)] (4) and dinuclear [{HC(SiMe₂NAr′)₃}U(Cl)(μ-Cl)U(THF)₂{(Ar′NSiMe₂)₃CH}] (5) species in 70 and 90% crystalline yields, respectively. Treatment of 4 and 5 with one equivalent of trimethylsilyl iodide resulted in halide exchange and formation of [U(I){HC(SiMe₂NAr)₃}(THF)₂] (6) and [U(I){HC(SiMe₂NAr′)₃}(THF)] (7) in 85 and 90% yields, respectively. The heteroleptic amide [U(NCy₂){HC(SiMe₂NAr)₃}(THF)] (8) was prepared from the reaction between 4 and one equivalent of lithium dicyclohexylamide and was isolated in 78% yield. Analogous attempts to prepare [U(NCy₂){HC(SiMe₂NAr′)₃}(THF)] (9) from 5 consistently resulted in intractable mixtures of products. Complexes 1–8 have been characterised by X-ray crystallography, NMR spectroscopy, FTIR spectroscopy, room temperature Evans method solution magnetic moments, and CHN micro-analyses.