Valence-to-Core X-Ray Emission Spectroscopy of Iron-Carbonyl Complexes: Implications for the Examination of Catalytic Intermediates

Valence-to-core X-ray emission spectroscopy (V2CXES) has been applied to a series of compounds relevant to both homogeneous catalysts and intermediates in heterogeneous reactions, namely [Fe(CO)(5)], [Fe-2(CO)(9)], [Fe-3(CO)(12)], [Fe(CO)(3)(cod)] (cod=cyclo-octadienyl), [Fe2Cp2(CO)(4)] (Cp=cyclo-pentadienyl), [Fe2Cp*(2)(CO)(4)] (Cp*=tetramethylcyclopentadienyl), and [FeCp(CO)(2)(thf)][B(ArF)(4)] (ArF=pentafluorophenyl). DFT calculations of the V2CXES spectra show very good agreement with experiment, which allows for an in depth analysis of the origins of the observed spectral signatures. It is demonstrated that the observed spectral features can be broken down into specific ligand and metal fragment contributions. The relative intensities of the observed features are further explained through a quantitative investigation of the metal 3p and 4p contributions to the spectra. The ability to use V2CXES to separate carbonyl, hydrocarbon, and solvent contributions is highlighted.