Synthesis with Structural and Electronic Characterization of Homoleptic Fe(II)- and Fe(III)-Fluorinated Phenolate Complexes

Four Fe(III) compounds and one Fe(II) compound containing mononuclear, homoleptic, fluorinated phenolate anions of the form [Fe(OAr)m]n− have been prepared in which ArF = C6F5 and Ar′ = 3,5-C6(CF3)2H3: (Ph4P)2[Fe(OArF)5], 1, (Me4N)2[Fe(OArF)5], 2, {K(18-crown-6)}2[Fe(OArF)5], 3a, {K(18-crown-6)}2[Fe(OAr′)5], 3b, and {K(18-crown-6)}2[Fe(OArF)4], 6. Two dinuclear Fe(III) compounds have also been prepared: {K(18-crown-6)}2[(OArF)3Fe(μ2-O)Fe(OArF)3], 4, and {K(18-crown-6)}2[(OArF)3Fe(μ2-OArF)2Fe(OArF)3], 5. These compounds have been characterized with UV–vis spectroscopy, elemental analysis, Evans method susceptibility, and X-ray crystallography. All-electron, geometry-optimized DFT calculations on four [Ti(IV)(OAr)4] and four [Fe(III)(OAr)4]− species (Ar = 2,3,5,6-C6Me4H, C6H5, 2,4,6-C6Cl3H2, C6F5) with GGA-BP and hybrid B3LYP basis sets demonstrated that, under D2d symmetry, π donation from the O 2p orbitals is primarily into the dxy and dz2 orbitals. The degree of donation is qualitatively consistent with expectations based on ligand Brønsted basicity and supports the contention that fluorinated phenolate ligands facilitate isolation of nonbridged homoleptic complexes due to their reduced π basicity at oxygen.