Synthesis of (alkoxymethyl)zirconocene chlorides: Stereochemistry of carbon-carbon bond formation in a zirconocene-Wittig rearrangement

Article abstract of DOI:10.1021/om00109a002

A series of (alkoxymethyl)zirconocene chlorides (1, Cp₂Zr(Cl)CH₂OR, Cp = ν⁵-C₅H₅) has been prepared by treatment of Cp₂ZrCl₂ with (alkoxymethyl)lithium reagents. Compound 1c, Cp₂Zr(Cl)CH₂OCH₂C₆H₅, crystallizes in the orthorhombic space group Pbca, with a = 15.417 (9) A?, b = 18.249 (9) A?, c = 11.746 (8) A?, and Z = 8. The X-ray crystal structure shows that the alkoxymethyl ligand is ν², with a significant Zr-O interaction. Compounds 1 with R = benzyl or substituted benzyl undergo a Wittig rearrangement when heated to give products 3 (Cp₂Zr(Cl)OCH₂R). The activation parameters that were determined for the transformation, the effects of substituents on the rate of the reaction, the identity of the reaction's side products, and the retention of configuration at the benzylic carbon are all consistent with the formation of a short-lived radical pair intermediate.