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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.

The mechanism of the rearrangement of diorganylzirconium dialkoxides, such as R1(R2CH2)Zr(OEt)2, into organylzirconium hydride alkoxides of the type R1R2CHZr(OEt)2H, has been investigated as a function of the R1 and R2 substituents and been found to involve optimally an intramolecular migration of R1 to an sp3-hybridized C−H center. A remarkably rapid transfer hydrozirconation between Bun2Zr(OEt)2 and the olefin RCHCH2 now permits the synthesis of (RCH2CH2)2Zr(OEt)2, whose rearrangement offers a route to the linear olefin dimer R(CH2)4R.

Benzylic hydrocarbons of the types Ar−CH3 and Ar2CH2 undergo zirconation at their benzylic C−H bonds by Bun2Zr(OEt)2 at room temperature in Lewis basic solvents and catalyzed by lithium ethoxide. Upon heating, such benzylic organozirconium derivatives can undergo C−C bond formation, either intermolecularly or intramolecularly, with the elimination of zirconium(IV) hydrides of the type H2Zr(OEt)2. Such oxidative dimerizations or cyclizations are exemplified by the conversion of toluene into trans-stilbene or the formation of 9,10-dihydrophenanthrene from 2,2 ‘-dimethylbibenzyl.