Synthesis of zirconium, hafnium, and tantalum complexes with sterically demanding hydrazide ligands

The bulky hydrazine t-BuN(H)NMe2 was synthesized via hydrazone and t-BuN(H)N(H)Me intermediates as the major component in a 90:5:5 mixture consisting of t-BuN(H)NMe2, t-BuN(Me)N(H)Me, and t-BuN(Me)NMe2. Reacting the mixture with n-BuLi followed by distillation and fractional crystallization led to the isolation of the ligand precursor LiN(t-Bu)NMe2. Lithium hydrazides, LiN(R)NMe2, were reacted with metal chlorides to afford the hydrazide complexes M(N(Et)NMe2)(4) (M = Zr or Hf), MCl(N(R)NMe2)(3) (M = Zr, R = i-Pr or t-Bu; M = Hf, R = t-Bu), and TaCl3(N(i-Pr)NMe2)(2). The X-ray crystal structures of [LiN(i-Pr)NMe2](4), [LiN(t-Bu)NMe2 center dot THF](2), ZrCl(N(R)NMe2)(3) (R = i-Pr or t-Bu), and TaCl3(N(i-Pr)NMe2)(2) were determined. The structural analyses revealed that the hydrazide ligands in ZrCl(N(R)NMe2)(3) (R = i-Pr or t-Bu) and TaCl3(N(i-Pr)NMe2)(2) are eta(2) coordinated.