Selectivity and reactivity in reactions of methylaryltitanium(IV) complexes with electrophiles

Article abstract of DOI:10.1021/om50004a026

Methyl or phenyl for halogen-exchange reactions occur between [TiMe₂(η-C₅H₅)₂] or [TiPh₂(η-C₅H₅)₂] with [TiX₂(η-C₅H₅)₂], X = halogen, to give [TiXMe(η-C₅H₅)₂] or [TiXPh(η-C₅H₅)₂], respectively. The reactions are complicated by parallel decomposition of the methyl- or phenyltitanium complexes, which is catalyzed by [TiX₂(η-C₅H₅)₂] or [TiXR(η-C₅H₅)₂]. In general, there is little difference in the rates of reaction of [TiMe₂(η-C₅H₅)₂] and [TiPh₂(η-C₅H₅)₂] toward the symmetrization reactions. These reagents also transfer a methyl group or phenyl group to platinum(II) or gold(III), but there are again side reactions. The complex [TiMePh(η-C₅H₅)₂] reacts with electrophiles HCl, HOAc, HgCl₂, and MeHgCl to give cleavage of both methyl- and phenyltitanium bonds with little selectivity. In cleavage of [TiMe(C₆H₄X)(η-C₅H₅) ₂] there is a correlation of the selectivity for cleavage of the aryl group by electrophiles HCl or HgCl₂ with the σ⁺ parameters of substituents X. A mechanism of reaction involving electron transfer from the complex to the electrophile followed by rapid cleavage is tentatively suggested.