Bimetallic Zirconium Heterocycles Supported by Boron−Oxygen Ligands

Reaction between bis(cyclopentadienyl)dimethylzirconium, ZrCp(2)(CH(3))(2), and phenylboronic anhydride, (PhBO)(3), resulted in the formation of the heterocyclic dimer [ZrCp(2)[mu-O(2)BPh]](2) (1); no reaction was observed with the mesityl derivative, (mesBO)(3). Compound 1 was also synthesized from the protonolysis reaction between ZrCp(2)(CH(3))(2) and in situ generated phenylboronic acid, PhB(OH)(2). This approach was extended to afford the analogous complexes [ZrCp(2)[mu-O(2)BAr]](2) (2, Ar = mes; 3, Ar = C(6)F(5)) 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 "Zr(2)B(2)O(4)" metallacycle. Variations in the bond parameters within the heterocycle are attributed to the differing steric and electronic properties of the aryl substituents at boron.