Homoleptic hydroxylamides of titanium, zirconium and hafnium

Abstract

The homoleptic N,N-dimethylhydroxylamides of titanium (1), zirconium (2) and hafnium (3), M(ONMe₂)₄, have been prepared in high yield by the reactions of the corresponding metal tetrakis(dimethylamides) and N,N-dimethylhydroxylamine in diethyl ether. The compounds have been characterised by ¹H and ¹³C NMR and IR spectroscopy as well as by nominal and high-resolution mass spectrometry and elemental analysis. Compounds 1 and 2 are crystalline solids, which dissolve in ethers and hydrocarbons. They can be sublimed at 90 and 100 °C (0.1 mbar) respectively. These volatility data are discussed in comparison to those of the isoelectronic titanium and zirconium tetra(isopropoxides) and Ti(ONEt₂)₄ and in the context of their molecular complexities and structures. Compounds 1 and 2 are monomeric both in benzene solution and in the solid state, as shown by cryoscopy and single-crystal X-ray diffraction, respectively. The Ti and Zr atoms occupy an eight-co-ordinate environment with the ONMe₂ ligands co-ordinated in a bidentate fashion. Crystallographic C₂ axes pass through the metal atoms in 1 and 2. The non-equivalent ONMe₂ ligands in one molecule have been found to exhibit markedly different geometries, which are discussed in the context of the molecular geometry of free Me₂NOH.