Cationic titanium(IV) complexes via halide abstraction from [Ti(C5H5)Cl3]: crystal and molecular structure of [Ti(C5H5)(MeCN)5][SbCl6]3·2MeCN

Abstract

Treatment of [Ti(cp)Cl₃](cp =η⁵-C₅H₅) with SbCl₅ as chloride abstractor in acetonitrile provided hexachloroantimonate(V) salts of [Ti(cp)Cl₂]⁺, [Ti(cp)Cl]²⁺ and [Ti(cp)]^{3 +} respectively. With 1 : 1 stoichiometry red-brown crystals of [Ti(cp)Cl₂(MeCN)₃][SbCl₆]1 are obtained and with 1 : 2 stoichiometry light blue crystals of [Ti(cp)Cl(MeCN)₄][SbCl₆]₂2. Complete removal of chloride ion from [Ti(cp)Cl₃] requires a six-fold excess of SbCl₅ when purple-blue crystals of [Ti(cp)(MeCN)₅][SbCl₆]₃3 can be isolated. These products were characterised by analytical and spectroscopic (IR, ¹H NMR) data and, in the case of 3, by a crystal structure determination. Proton NMR studies indicate the presence of intermediate halide-bridged [Ti(µ-Cl)₂Sb] species in solution during the sequential halide abstractions 1→2→3. Crystals of complex 3, obtained as the bis(solvate) from recrystallisation in acetonitrile, are monoclinic and X-ray structural analysis confirmed the formulation. The crystal structure [space group Cc, a= 19.650(4), b= 19.182(4), c= 12.958(3)Å, β= 91.612(3)°, Z= 4, R= 0.0386, R′= 0.0406] shows discrete cations and anions and a pseudo-octahedral co-ordination sphere for the Ti^IV. A significant trans influence of the cyclopentadienyl ligand affects Ti–N bond lengths in the complex.