En route to zirconium hydrazides(2−)

Abstract

The structures and properties of a series of new zirconium hydrazido(1−) complexes and the possibility of converting them to the respective hydrazido(2−) species are reported. Reaction of complex [Zr(N₂^TBSN_py)Cl₂] (1) with the monolithiated hydrazide LiNHNMe₂ gave the hydrazido(1−) complex [Zr(N₂^TBSN_py)(NHNMe₂)Cl] (2) which exists as two isomeric forms (2a and 2b) in solution. All attempts to convert a mixture of 2a and 2b to the respective hydrazido(2−) compound by reaction with the bulky base lithium hexamethyldisilazide or via the alkyl/hydrazido(1−) complex [Zr(N₂^TBSN_py)(CH₂SiMe₃)(NHNMe₂)] (3) and subsequent thermal alkane elimination failed. Reaction of 1 with LiHNNPhMe gave a mixture of stereoisomers of [Zr(N₂^TBSN_py)(NHNMePh)Cl] (4a and 4b), in which the hydrazido unit is end-on bound in solution and η²-bonded in the solid state. Reaction of this mixture with lithium hexamethyldisilazide in the presence of pyridine selectively yielded the hydrazido(2−) complex [Zr(N₂^TBSN_py)(NNPhMe)(py)] (5) which aggregated upon attempts to isolate it. Reaction of the insoluble precipitate with 4-dimethylaminopyridine (dmap) selectively gave the corresponding hydrazido(2−) complex [Zr(N₂^TBSN_py)(NNPhMe)(dmap)] (6), which could be obtained in a one-pot reaction directly from 1 and which was analytically and spectroscopically fully characterized. It appears that the isolation of stable hydrazido(2−) complexes of zirconium depends on the type of substituents at the N_β atom as well as the co-ligands coordinated to the metal centre.