Unexpected Benzylic Carbon−Carbon Bond Cleavage by Transfer Epizirconation:  Indications of an SET Pathway and Implications for Alkane Metathesis¹

In addition to the zirconation of benzylic hydrocarbons, Ar−CH₃, by di-n-butylzirconium diethoxide and the ensuing C−C bond formation from (Ar−CH₂)₂Zr(OEt)₂ to yield Ar−CH₂−CH(ZrH(OEt)₂)−Ar, it has now been found that Bu₂Zr(OEt)₂ in ethers can also cleave the C−C bond in bibenzylic hydrocarbons, Ar−CH₂−CH₂−Ar‘, into benzylic zirconium fragments, (Ar−CH₂)(Ar‘−CH₂)Zr(OEt)₂, as fostered by LiOEt and donor solvents. The role of SET processes in such C−C bond cleavages and the potential relevance to practical alkane metathesis are considered.