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{-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{-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.