Gas-Phase Ion Chemistry of TiCl4 and CH3TiCl3. Reaction of CH3TiCl2+ with Ethylene

Article abstract of DOI:10.1021/ja00393a005

TiCl4⁺ and TiCl3⁺ are the principal ions produced by electron-impact ionization of TiCl4.Both react with TiCl4 to give Ti2Cl7⁺.Reactions of this and other species of the form TiCl3(ligand)⁺ allow the determination of an order of relative ligand binding energies to TiCl3⁺ of MeF+ than TiCl4.Study of halide-transfer and proton-transfer reactions leads to determination of the thermochemical results: D(TiCl3⁺-Cl^-) = 217+/-11 kcal/mol, D(TiCl3⁺-F^-) = 254+/-4 kcal/mol, and PA(TiCl4) = D(TiCl4-H⁺) = 157+/-11 kcal/mol.Chloride transfer from CH3TiCl3 to TiCl3⁺ yields CH3TiCl2⁺ as the major ion at intermediate times in the ion chemistry of CH3TiCl3.CH3TiCl2⁺ reacts with C2H4 to give C3H5TiCl2⁺ with H2 elimination.C3H5TiCl2⁺ does not react further with ethylene.With C2D4, HD elimination predominates (>85percent).A mechanism involving insertion of C2D4 into the Ti,C bond in CH3TiCl2⁺ followed by 1,2-elimination of HD at the β- and γ-carbons is inferred.This demonstrates carbon-carbon bond formation and chain growth in a Zigler-Natta catalyst site model system, but this gas-phase bimolecular process does not lead to continued polymerization because disposal of the excess internal energy of the complex results in chain termination by unimolecular decomposition.