Trialkyl imido niobium and tantalum compounds: synthesis, structural study and migratory insertion reactions

Abstract

Trialkyl imido niobium and tantalum complexes [MR₃(NtBu)] (M = Nb, R = Me 2, CH₂CMe₃3, CH₂CMe₂Ph 4, CH₂SiMe₃5; M = Ta, R = Me 6, CH₂CMe₂Ph 7, CH₂SiMe₃8) have been prepared by treatment of solutions containing [MCl₃(NtBu)py₂] (M = Nb 1a, Ta 1b) with three equivalents of magnesium reagent. By an unexpected hydrolysis reaction of the tris-trimethylsilylmethyl imido tantalum compound 8a, a μ-oxo derivative [(Me₃SiCH₂O)(Me₃SiCH₂)₃Ta(μ-O)Ta(CH₂SiMe₃)₂(NtBu)] (8a) was formed and its structure was studied by X-ray diffraction methods. Reactions of trialkyl imido compounds with two equivalents of isocyanide 2,6-Me₂C₆H₃NC result in the migration of two alkyl groups, leading to the formation of a series of alkyl imido bisiminoacyl derivatives [MR(NtBu){C(R)NAr}₂] (Ar = 2,6-Me₂C₆H₃; M = Nb, R = Me 9, CH₂CMe₃10, CH₂CMe₂Ph 11, CH₂SiMe₃12, CH₂Ph 13; M = Ta, R = CH₂CMe₃14, CH₂CMe₂Ph 15, CH₂SiMe₃16). All compounds were studied by IR and NMR (¹H, ¹³C and ¹⁵N) spectroscopy.