Hydrazido(1-), 1,2-Hydrazido(2-), and Hydrazido(4-) Complexes of Tungsten(VI)

Abstract

We have found (Rocklage, Schrock, 1982) that niobium or tantalum neopentylidene complexes of the type M(CHCMe₃)(THF)₂Cl₃ react with 0.5 eq of an azine such as PhCH=N-N=CHPh to yield cis and trans-Me₃CCH=CHPh and sparingly soluble orange (M = Ta) or plum-colored (M = Nb) complexes of the composition [MCl₃(THF)₂]₂ (μ-N₂). The THF ligands in [TaCl₃(THF)₂]₂₋ (μ-N₂) can be replaced by phosphine ligands such as PMe₂Ph or PEt₃ to give related complexes of the type [TaCl₃L₂] ₂(μ-N₂). If one equivalent (per Ta) of PBZ₃ (Bz = CH₂Ph) is employed a product having the composition [TaCl₃(THF)(PBz₃)] ₂(µ-N₂) can be isolated. An x-ray structural study (Churchill, Wasserman, 1982, 218) shows it to have the structure in Figure 1. The Ta=N distance (1.796(5)Å) compares favorably with that (1.765(5)Å) found in the analogous imido complex, Ta(NPh)Cl₃(THF)(PEt₃) (Churchill, Wasserman, 1982, 223). The rather long N-N distance (1.282(6)Å) and essentially linear Ta-N-N arrangement (178.9(4)°) suggest that the µ-N₂ ligand is essentially a µ-hydrazido(4−) ligand. In keeping with this description this and similar complexes react readily with excess HC1 in ether to produce 85–90% of the expected hydrazine dihydrochloride. They also react with acetone to give Me₂C=N−N=CMe₂ in ~50% yield, an unprecedented type of reaction of a μ-N₂ complex, but one which is analogous to the reaction of related phenylimido complexes with acetone to give Me₂C=NPh in high yield. Treatment of the [MCl₃(THF)₂]₂(μ-N₂) complexes with Mg(CH₂CMe₃)₂ or KOCMe₃ yields neopentyl and t-butoxy complexes of the type [Ta(CH₂CMe₃)₃(THF)] ₂(μ-N₂) and [Ta (OCMe ₃) ₃ (THF)] ₂ (μ-N₂), respectively, in good yield.