Mono- and Bi-nuclear anionic derivatives of methyltitanium trichloride and methyltitanium tribromide and related complexes

Abstract

Treatment of methyltitanium trichloride or methyltitanium tribromide with tetra-alkylammonium halides in dichloromethane at 0 °C yields three different series of complex salts depending on the mole ratios of the reactants. They are: type A, R[Me₂Ti₂X₇] or R[Me₂Ti₂X₆Y]; type B, [R]₂[Me₂Ti₂X₈] or [R]₂[Me₂Ti₂X₆Y₂]; type C, [R]₂[MeTiX₅] or [R]₂[MeTiX₃Y₂], where X, Y = Cl or Br. The complexes are deeply coloured solids, very sensitive to air and moisture; although they are much more stable thermally than methyltitanium trichloride or methyltitanium tribromide themselves, they are nevertheless only stable for short periods at room temperature. On the basis of i.r. spectral studies and other considerations, the type A complexes are believed to contain, in the solid state, anions of the Ti₂Cl₉^– type (i.e. two octahedra with a shared face), the type B complexes anions of the Ti₂Cl₁₀^2– type (i.e. two octahedra with a shared edge), and the type C complexes mononuclear octahedral anions. The structures of the complexes in solution are discussed with reference to temperature-range n.m.r. studies. The TiC stretching frequencies in the complex anions occur in the range 461–504 cm^–1, and the titanium–methyl group n.m.r. resonances in the range τ 7·28–7·60 (dichloromethane solutions). This resonance occurs at τ 7·09 for methyltitanium trichloride and τ 7·45 for methyltitanium tribromide (dichloromethane solutions). The new complex Et₄N[Ti₂Br₉] is reported. Brief reports of both oxygen and sulphur dioxide insertions into titanium–carbon bonds are included. The structure of methyltitanium trichloride in the solid state is discussed.