Multiple Bonds between Main-Group Elements and Transition Metals. 130. (Cyclopentadienyl)trioxorhenium(VII): Synthesis, Derivatives, and Properties

(η⁵-Cyclopentadienyl)trioxorhenium(VII) and ring-substituted derivatives are conveniently synthesized from (trifluoroacetyl)perrhenate and substituted (cyclopentadienyl)tin compounds. As shown by cyclovoltammetry, peralkylated (cyclopentadienyl)tin derivatives undergo redox reactions with Re(VII) precursor compounds such as (trifluoroacetyl)trioxorhenium(VII). The reduction potentials of peralkylated CpRe^VII systems differ significantly from those of the nonalkylated forms. Thermal stabilities of CpReO₃ derivatives increase with the number of methyl groups in the Cp ring, reflecting increasing Re-C bond strengths resulting from the electron density of the π-bonded ligands. Increasing π-donor capability of the Cp ligands with increasing substitution by alkyl groups is documented in the IR and ¹⁷O NMR spectra. As shown by a single-crystal X-ray diffraction analysis of (C₅H₅)ReO₃, the Cp ligand is η⁵-bonded to the metal. Crystal data: monoclinic P2₁/m, a = 5.984(1) Å, b = 9.179(1) Å, c = 6.099(1) Å, β = 116.30(1)°, R = 0.021 for 559 reflections.