The mechanism of the zirconium catalysed ethyl- and 2-magnesioethyl-magnesiation of unactivated alkenes

Article abstract of DOI:10.1016/0040-4020(94)01139-Q

Deuterium labelling experiments prove that the zirconocene dichloride catalysed ethylmagnesiation of alkenes occurs via a zirconocene η²-ethylene complex and allow a deuterium isotope effect for a key β-hydride transfer to be estimated (k(H)/k(D) = 2.5). Transmetallation from zirconium to magnesium to form 1,4-dimagnesiated reagents is shown to be an intramolecular process. Kinetic studies show that the reaction between η²-ethylene zirconocene and the alkene is rate limiting and that Lewis bases inhibit the reaction by decreasing the amount of η²-ethylene zirconocene in equilibrium with the 'ate' complex [Cp₂Zr(CH₂=CH₂)Et]^-.[MgX.Base]⁺.