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 aryliron 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^IIBrMes(SciOPP)] and [Fe^IIMes₂(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.