Preparation, properties, and crystal structures of the monochlorotris[bis(trimethylsilyl)amido]-compounds of titanium, zirconium, and hafnium

The monomeric compounds [MCl{N(SiMe₃)₂}₃] (M = Ti, Zr, or Hf) have been prepared by the reaction of MCl₄ with excess of Li[N(SiMe₃)₂]. Mass and i.r. spectra have been obtained, together with variable-temperature ¹H n.m.r. spectra which shows evidence of fluxional behaviour of the bulky ligands. Molecular structures have been determined by single-crystal X-ray diffraction for the whole series. The three compounds are isostructural in space group R3c with lattice parameters (hexagonal setting) a = b = 18.076, 18.317, 18.304 and c = 17.208, 17.078, and 17.085 Å respectively for Ti, Zr, and Hf. Structure analysis by the heavy-atom method and refinement by full-matrix least-squares has given R values of 0.048, 0.029, and 0.053 based on 577, 1 182, and 1 195 unique data for Ti, Zr, and Hf respectively. The structural and spectroscopic results are discussed in terms of steric effects and the nature of the metal-ligand bonding.