Cycloheptatrienyl-Pentadienyl Complexes of Zirconium (Half-Open Trozircenes): Syntheses, Structures, Bonding, and Chemistry

The reactions of Zr(C7H7)(Cl)(tmeda) (tmeda = tetramethylethylenediamine) with pentadienyl anions lead to formally tetravalent Zr(C7H7)(Pdl) complexes, for Pdl = C5H7, 2,4-C7H11, 6,6-dmch, and c-C7H9 (C7H11 = dimethylpentadienyl, dmch = dimethylcyclohexadienyl, c-C7H9 = cycloheptadienyl). Structural characterizations of the first three have been carried out, revealing much shorter Zr−C distances for the C7H7 ligand and a pattern of Zr−C bond distances for the pentadienyl ligands that is consistent with a formally high (+4) metal oxidation state, which is also supported by DFT calculations. As had been found for the analogous Cp complexes, these 16-electron species are susceptible to Lewis base coordination, and the 2,6-xylyl isocyanide adducts of the 2,4-C7H11 and 6,6-dmch complexes have been isolated and characterized by IR spectroscopy and single-crystal X-ray diffraction studies. The IR spectroscopic studies indicate that the pentadienyl ligands are serving as better net electron donors than Cp ligands, opposite what is typically found for related but lower valent species. At high temperatures the 16-electron Zr(C7H7)(C5H7) complex undergoes slow conversion to the corresponding Cp complex.