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

Abstract

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 [FeX 2 (SciOPP)]-catalyzed KumadaTamaoCorriu (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 The renaissance of iron-catalyzed cross-coupling reactions in the last decade 15 has been triggered by their unprecedented nonclassical reactivities and selectivities in comparison with conventional Pd and Ni catalysts.6 Recent worldwide interest in practical research applications, based on the utilization of abundant earth elements and the practical advantages of iron catalysts, including low cost, low toxicity, high availability, and easy separation of metal residues, have also demanded a much greater focus on iron-catalyzed cross-coupling reactions.

A DFT Study on FeI/FeII/FeIII Mechanism of the Cross-Coupling between Haloalkane and Aryl Grignard Reagent Catalyzed by Iron-SciOPP Complexes

“…Hence, care should be taken in choosing functional, especially for iron complexes with the small spin-state energy gaps. The DFT method (B3LYP-D3 Functional) used in this work predicted quintet as the ground state for iron(II) complexes, Fe II BrPh(SciOPP) and Fe II Br 2 (SciOPP), which is in agreement with the experimentally known spin state [33,34]. Additionally, the spin state for related iron(I) complex (Fe(η 2 -[TIPS-CC-H])Br(SciOPP)) was also predicted correctly [52].…”

“…A variety of radical mechanisms have been discussed thus far by Hu [ 28 ], Norrby [ 29 ], Bedford [ 30 ], Tonzetich [ 31 ], Fürstner [ 22 ], Neidig [ 32 , 33 ], and us [ 19 , 34 ]. Our group and the Neidig group have independently crystalized iron-bisphosphine complexes, such as Fe II X 2 (SciOPP), Fe II XAr(SciOPP), Fe II Ar 2 (SciOPP), where X = halide and Ar = Ph or Mes [ 32 , 33 , 34 ]. Furthermore, we identified the presence of Fe II BrMes(SciOPP), Fe II Mes 2 (SciOPP) in the reaction mixture of the cross-coupling reaction by using solution-phase synchrotron X-ray absorption spectroscopic (XAS) studies [ 34 ].…”

“…Our group and the Neidig group have independently crystalized iron-bisphosphine complexes, such as Fe II X 2 (SciOPP), Fe II XAr(SciOPP), Fe II Ar 2 (SciOPP), where X = halide and Ar = Ph or Mes [ 32 , 33 , 34 ]. Furthermore, we identified the presence of Fe II BrMes(SciOPP), Fe II Mes 2 (SciOPP) in the reaction mixture of the cross-coupling reaction by using solution-phase synchrotron X-ray absorption spectroscopic (XAS) studies [ 34 ]. According to this study, we proposed an Fe II /Fe II mechanism based on identification of Fe II Ar 2 (SciOPP) ( Figure 1 a, Ar = Mes and X = Br).…”

Iron(II) Active Species in Iron–Bisphosphine Catalyzed Kumada and Suzuki–Miyaura Cross-Couplings of Phenyl Nucleophiles and Secondary Alkyl Halides

“…For iron–SciOPP cross-coupling, it has been proposed that catalysis proceeds through an Fe(II)/Fe(III) radical pathway. 42 , 43 , 49 Recent work from our group investigating iron–SciOPP catalyzed Kumada cross-coupling of mesitylmagnesium bromide (MesMgBr) and primary alkyl halides has identified Fe(Mes) 2 (SciOPP) as the active catalytic species. 50 While an analogous mechanism has been proposed across a range of nucleophiles (e.g., mesityl, phenyl and alkynyl Grignards, as well as aryl-borates) with iron–SciOPP, 42 − 44 the reaction rates, yields, and temperatures vary significantly between reactions, and the possibility that analogous iron(II) active species exist across all of these reactions has not been evaluated in detail.…”

A Physical‐Inorganic Approach for the Elucidation of Active Iron Species and Mechanism in Iron‐Catalyzed Cross‐Coupling

“…While not covered in this review, Nakamura and and Nagashima have previously described the use of XAS in iron-catalyzed cross-coupling reactions. [78–79] …”