Early transition metal complexes with pi donor ligands and their reaction with alkynes.

Abstract

A one step procedure for the preparation of new group 5 amido halides M(NEt₂)ₓCl₅₋ₓ (x = 1, 2, 3), imido halides M(=NAr)Cl₃(L)₂, and group 4 and 5 phenoxide halides. These complexes are obtained easily from the metal halides and trimethylsilyl reagents such as Me₃SiNR₂, Me₃SiNHAr, and Me₃SiOAr. The dimeric amides [M(NEt₂)₂Cl₃]₂ (M = Nb, Ta), the dimeric imide [Ta(=NAr)Cl₃(NH₂Ar)]₂, and the polymeric imide [Ta(=NAr)Cl₃(NH₂Ar)](n) are also prepared in a single step. The use of Me₃SiNR₂ and Me₃SiOAr compounds as amidation and alkoxylation reagents can be extended to prepare the alkoxide amides Ta(NEt₂)(OAr)Cl₃(OEt₂), Ta(NEt₂)(OAr)₂Cl₂(OEt₂), and Ta(OAr)(OAr')Cl₃(OEt₂). When these complexes are reduced using 2 equiv of NaHg in the presence of the appropriate alkyne, the d² alkyne adducts or cycloadducts of the form (alkyne)Ta(NEt₂)(m)X(3-m) (m = 1, 2), (alkyne)Ta(=NAr)X(py)₂, and (R₃CC=CHCH=CCR₃))Ta(=NAr)X(py)₂ (X = OAr, Cl), and (η⁶-C₆Et₆)Ta(OAr)Cl₂, (η⁶-C₆Me₆)Ta(OAr')Cl, (R₃CC=CHCH=CCR₃)Ta(OAr)Cl₂, and (alkyne)Nb(DIPP)₃ are formed. CpTa(NEt₂)₂Cl₂ (Cp = C₅H₅⁻) forms from the reaction of Ta(NEt₂)₂Cl₃(OEt₂) and NaCp. A low yield of [CpTa(NEt₂)₂H₂]₂ is isolated from CpTa(NEt₂)₂Cl₂ and 2 equiv of LiNHAr. The reaction of Ta(NEt₂)₂Cl₃(OEt₂) with various equiv of LiNHAr provides the mono(imido) complex Ta(=NAr)(NEt₂)Cl₂(L)₂, bis(imido) complex Ta(=NAr)₂Cl(py)₂, and tris(imido)complexes [Ta(=NAr)₃(NHAr)]⁻. The analogous complexes of niobium, [Nb(=NAr)(NEt₂)Cl₂(NHEt₂)]₂, Nb(=NAr)₂Cl(py)₂, and [Nb(=NAr)₃(NHAr)]⁻ are prepared from [Nb(NEt₂)₂Cl₃]₂ by a parallel procedure. Preliminary results, not always reproducible, for the syntheses of Li[Ta(=NAr)₃(py)] are also reported. The reaction of MCl₄ (M = Zr, Hf) with 4 equiv of LiNHAr in the presence of donor solvents provides the imido complexes M(=NAr)(NHAr)₂(L)₂.