Chemistry of (η-Phenoxide)Cr(CO)₃Ligands

(η⁶-Phenol) tricarbonylchromium complexes are conveniently converted to [(η⁶-phenoxide)Cr(CO)₃]^- species on treatment with aqueous base. The phenoxide chromium anions, which are readily isolated as crystalline tetraethylammonium salts, react with main-group electrophiles ((p-tol)SO₂Cl or CF₃COCl) to produce new sulfonate-and carboxylate-substituted arene chromium complexes. Similar reactions between the phenoxide anions and metal electrophiles (CpFe(CO)₃⁺ or Cp₂ZrCl₂) result in electron-transfer reactions that consume the starting arene complexes. Transition-metal complexes bearing (η-phenoxide)Cr(CO)₃ ligands are conveniently prepared through alcoholysis reactions with metal alkoxide and metal dimethylamide precursors. An X-ray crystallographic study of Cp₂Zr{(η-OC₆H₅)Cr(CO)₃}₂ was carried out. For 1403 unique intensity data collected by using Cu Kα radiation in a θ–2θ scan procedure, the space group for the molecule was determined to be Pnma with unit cell parameters a = 15.023 (3) Å, b = 21.864 (5) Å, and c = 8.073 (2) Å. The refinement converged to an R(F) of 0.078 and an R_W(F) of 0.089. The molecule shows general structural features common to other bent zirconocene and π-arene chromium complexes but shows some unexpected features associated with the Zr-aryloxide bonding. Little evidence is found for either steric interactions between the (η-OC₆H₅)Cr(CO)₃ units or for Zr-O π bonding. The O-arene bond does show a small degree of multiple-bond character. This observation is supported by the deviation of the O-C arene vector from the least-squares arene plane, suggesting that a small degree of a cyclohexadienone resonance form is contributing to Zr-arene bonding.