Incorporation of redox-inactive cations promotes iron catalyzed aerobic C–H oxidation at mild potentials

摘要: The synthesis and characterization of the Schiff base complexes Fe(II) (2M) Fe(III)Cl (3M), where M is a K+ or Ba2+ ion incorporated into ligand, are reported. Fe(III/II) redox potentials positively shifted by 440 mV (2K) 640 (2Ba) compared to Fe(salen) (salen = N,N′-bis(salicylidene)ethylenediamine), 70 (3K) 230 (3Ba) Fe(Cl)(salen), which likely due an electrostatic effect (electric field) from cation. catalytic activity 3M towards aerobic oxidation allylic C–H bonds was explored. Prior studies on iron salen modified through conventional electron-donating withdrawing substituents found that only most oxidizing derivatives were competent catalysts. In contrast, complexes, significantly less oxidizing, both active. Mechanistic comparing indicate proximal cation contributes overall reactivity in rate determining step. cationic charge also inhibits oxidative deactivation formation corresponding Fe2-μ-oxo isolated characterized. This study demonstrates how non-redox active Lewis acidic cations secondary coordination sphere can be used modify catalysts order operate at milder with minimal impact reactivity, unattainable tuning catalyst traditional substituent effects ligand.