Structural Elucidation of a Methylenation Reagent of Esters: Synthesis and Reactivity of a Dinuclear Titanium(III) Methylene Complex

Transmetallation of a zinc methylene complex [ZnI(tmeda)]2(μ-CH2) with a titanium(III) chloride [TiCl3(tmeda)(thf)] produced a titanium methylene complex. The X-ray diffraction study displayed a dinuclear methylene structure [TiCl(tmeda)]2(μ-CH2)(μ-Cl)2. Treatment of an ester with the titanium methylene complex resulted in methylenation of the ester carbonyl to form a vinyl ether. The titanium methylene complex also reacted with a terminal olefin, resulting in olefin-metathesis and olefin-homologation. Cyclopropanation by methylene transfer from the titanium methylene proceeded by use of a 1,3-diene. The mechanistic study of the cyclopropanation reaction by the density functional theory calculations was also reported.