Olefination of esters using dimethyltitanocene is proposed to proceed via the titanium carbene, Cp2Ti=CH2, on the basis of the following evidence: (1) No H/D exchange or 13C scrambling occurs in the reactions of ethyl acetate or dodecyl acetate using either labeled ester or labeled dimethyltitanocene, (2) kinetics are zero order in ester and first order in Cp2TiMe2, (3) the reactions of ethyl acetate and dodecyl acetate with Cp2Ti(CD3)2 produce substantial kinetic isotope effects of 9-10, (4) esters of differing electronic and steric environments have similar reactivity, and (5) there is regiochemical preference for the least stable exo-methylene product. These findings are inconsistent with the methyl addition mechanism proposed in the literature.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry