4401-18-7Relevant articles and documents
Iron(II) Active Species in Iron-Bisphosphine Catalyzed Kumada and Suzuki-Miyaura Cross-Couplings of Phenyl Nucleophiles and Secondary Alkyl Halides
Daifuku, Stephanie L.,Kneebone, Jared L.,Snyder, Benjamin E. R.,Neidig, Michael L.
, p. 11432 - 11444 (2015)
While previous studies have identified FeMes2(SciOPP) as the active catalyst species in iron-SciOPP catalyzed Kumada cross-coupling of mesitylmagnesium bromide and primary alkyl halides, the active catalyst species in cross-couplings with phenyl nucleophiles, where low valent iron species might be prevalent due to accessible reductive elimination pathways, remains undefined. In the present study, in situ M?ssbauer and magnetic circular dichroism spectroscopic studies combined with inorganic syntheses and reaction studies are employed to evaluate the in situ formed iron species and identify the active catalytic species in iron-SciOPP catalyzed Suzuki-Miyaura and Kumada cross-couplings of phenyl nucleophiles and secondary alkyl halides. While reductive elimination to form Fe(η6-biphenyl)(SciOPP) occurs upon reaction of FeCl2(SciOPP) with phenyl nucleophiles, this iron(0) species is not found to be kinetically competent for catalysis. Importantly, mono- and bis-phenylated iron(II)-SciOPP species that form prior to reductive elimination are identified, where both species are found to be reactive toward electrophile at catalytically relevant rates. The higher selectivity toward the formation of cross-coupled product observed for the monophenylated species combined with the undertransmetalated nature of the in situ iron species in both Kumada and Suzuki-Miyaura reactions indicates that Fe(Ph)X(SciOPP) (X = Br, Cl) is the predominant reactive species in cross-coupling. Overall, these studies demonstrate that low-valent iron is not required for the generation of highly reactive species for effective aryl-alkyl cross-couplings.
General C(sp2)-C(sp3) Cross-Electrophile Coupling Reactions Enabled by Overcharge Protection of Homogeneous Electrocatalysts
Hamby, Taylor B.,Sevov, Christo S.,Truesdell, Blaise L.
, p. 5884 - 5893 (2020/04/10)
Cross-electrophile coupling (XEC) of alkyl and aryl halides promoted by electrochemistry represents an attractive alternative to conventional methods that require stoichiometric quantities of high-energy reductants. Most importantly, electroreduction can readily exceed the reducing potentials of chemical reductants to activate catalysts with improved reactivities and selectivities over conventional systems. This work details the mechanistically-driven development of an electrochemical methodology for XEC that utilizes redox-active shuttles developed by the energy-storage community to protect reactive coupling catalysts from overreduction. The resulting electrocatalytic system is practical, scalable, and broadly applicable to the reductive coupling of a wide range of aryl, heteroaryl, or vinyl bromides with primary or secondary alkyl bromides. The impact of overcharge protection as a strategy for electrosynthetic methodologies is underscored by the dramatic differences in yields from coupling reactions with added redox shuttles (generally >80%) and those without (generally 20%). In addition to excellent yields for a wide range of substrates, reactions protected from overreduction can be performed at high currents and on multigram scales.
Cross-Coupling Reactions of Alkyl Halides with Aryl Grignard Reagents Using a Tetrachloroferrate with an Innocent Countercation
Hashimoto, Toru,Maruyama, Tsubasa,Yamaguchi, Takamichi,Matsubara, Yutaka,Yamaguchi, Yoshitaka
supporting information, p. 4232 - 4236 (2019/08/16)
Bis(triphenylphosphoranylidene)ammonium tetrachloroferrate, (PPN)[FeCl4] (1), was evaluated as a catalyst for cross-coupling reactions. 1 exhibits high stability toward air and moisture and is an effective catalyst for the reaction of secondary alkyl halides with aryl Grignard reagents. The PPN cation is considered as an innocent counterpart to the iron center. We have developed an easy-to-handle iron catalyst for “ligand-free” cross-coupling reactions. (Figure presented.).
