Preparation and properties of the tungsten tris(imido) functional group

Abstract

The first tris(imido) complex of a group 6 transition metal, [Li(THF)₄][W(=NAr)₃Cl] (8) (Ar = 2,6 iPr-C₆H₃) was prepared from W(=NAr)₂Cl₂(THF)₂ (2) and 2 equiv of the corresponding lithium amide, LiNHAr in THF. Complex (8) crystallizes in the monoclinic space group P2(1/n) with a = 13.787 (4) Å, b = 17.348 (5) Å, c = 22.781 (8) Å, and β = 90.43 (3)° with Z = 4. The crystal contains discrete C₃ᵥ [W(=NAr)₃Cl]⁻ anions with imido W-N-C(ipso) angles averaging 170.8 (15)° and imido W-N bonds averaging 1.782 (15) Å. The neutral imido species W(=NAr)₃(PMe₃) (15) was made by adding 10 equiv of PMe₃ to (8). "Coupling" of the imido ligand in (15) with CO₂ and O=C=NR (R = Ph, ᵗBu) gave W[NArC(O)O] (=NAr)₂ PMe₃ (20) and W[NArC(O)NR](=NAr)₂PMe₃ (19) respectively. 2,6 Diisopropylaniline was added to (8) to give the complex W(=NAr)₂(NHAr)₂ (9). The chloride ligand of complex (8) was replaced by Li alkyl reagents to yield alkylated product [Li(THF)₄][W(=NAr)₃R] (R = Me, ᵗBu and Np') (11-13). The cation of (8) was substituted by adding ⁿBu₄NBr to afford [ⁿBu₄N][W(=NAr)₃Br] (10). These and related synthetic and reactivity studies will be described.