Low temperature reaction of [Fe(TPA)(CH3CN)2]2+ with excess 3-chloroperoxybenzoic acid in semi-frozen acetonitrile; EPR detection of an acylperoxo iron(III) adduct

Treatment of [(TPA)FeII(CH3CN)2]2+ (TPA = tris(2-pyridylmethyl)amine) with excess (≥ 2 Eq) of 3-chloroperoxybenzoic acid (mCPBA) in semi-frozen acetonitrile in liquid N2 vapour generates a rhombic EPR signal assigned to the S = ½ low spin acylperoxoiron(III) species [(TPA)Fe(O3CC6H4-3Cl)(CH3CN)]2+ 5; the elusive precursor on the pathway to [(TPA)FeIII(5-chlorosalicylate)]+ 4 via putative [(TPA)FeV(O)(O2CC6H4-3Cl)]2+. Formation of cyclohexene epoxide in the presence of added cyclohexene at low temperatures (<−40 °C) suggests that intermolecular alkene epoxidation competes successfully with the intramolecular reactions involving 5 to generate 4.