Bimetallic zirconium heterocycles supported by boron-oxygen ligands

Reaction between bis(cyclopentadienyl)dimethylzirconium, ZrCP2(CH3)(2), and phenylboronic anhydride, (PhBO)(3), resulted in the formation of the heterocyclic dimer [ZrCp2{mu-O2BPh}](2) (1); no reaction was observed with the mesityl derivative, (mesBO)(3). Compound 1 was also synthesized from the protonolysis reaction between ZrCP2(CH3)(2) and in situ generated phenylboronic acid, PhB(OH)(2). This approach was extended to afford the analogous complexes [ZrCp2{mu-O2BAr}](2) (2, Ar = mes; 3, Ar = C6F5) from the corresponding isolable arylboronic acids, ArB(OH)(2). The molecular structures of 1-3, determined by X-ray diffraction techniques, revealed a common, dimeric motif consisting of a central Zr2B2O4 metallacycle. Variations in the bond parameters within the heterocycle are attributed to the differing steric and electronic properties of the aryl substituents at boron.