Investigation of Organoiron Catalysis in Kumada-Tamao-Corriu-Type Cross-Coupling Reaction Assisted by Solution-Phase X-ray Absorption Spectroscopy

Solution-phase synchrotron X-ray absorption spectroscopy (XAS) is a powerful tool for structural and mechanistic investigations of paramagnetic organoiron intermediates in solution-phase reactions. For paramagnetic organotransition metal intermediates, difficulties are often encountered with conventional NMR- and EPR-based analyses. By using solution-phase XAS, we succeeded in identifying the organoiron species formed in the reaction of iron bisphosphine with mesitylmagnesium bromide, MesMgBr, and 1-bromodecane in a [FeX2(SciOPP)]-catalyzed Kumada-Tamao-Corriu (KTC)-type cross-coupling reaction. X-ray absorption near-edge structure (XANES) spectra showed that the resulting axyliron species possessed a divalent oxidation state. Extended X-ray absorption fine structure (EXAFS) demonstrated that the solution-phase molecular geometries of these species are in satisfactory agreement with the crystallographic geometries of [Fe(II)BrMes(SciOPP)] and [Fe(II)Mes(2)(SciOPP)]. By combining GC-quantitative analysis and solution-phase XAS, the cross-coupling reactivities of these aryliron species were successfully investigated in the reaction with 1-bromodecane under stoichiometric and catalytic conditions.