Abstract
The study describes the first catalytic application of iron phosphinooxazoline complexes and Fe(OTf) 2 in oxidation reactions. New iron phosphinooxazoline (PHOX) complexes of the general formulation [Fe(PHOX) 2] 2+[OTf] 2 ( 3, OTf = CF 3SO 3 −) were synthesized in virtually quantitative yield from anhydrous Fe(OTf) 2 and the corresponding PHOX ligands. The new complexes 3 as well as previously synthesized iron PHOX complexes of the general formula [Fe(Cp)(CO)(PHOX)] +[I] − ( 2) were employed as catalysts in the oxidation of benzylic CH 2 groups to the corresponding ketones. Whereas 3 showed catalytic activity at room temperature (about two equivalents t-BuOOH as the oxidant, 2 mol% catalyst, pyridine solvent, 12 h, 38–93% isolated yields), complexes of 2 were only active at elevated temperatures. The product profile is in accordance with a mechanism previously described as “oxygenated Fenton chemistry”, which is further corroborated by UV–vis investigations. They showed that an iron alkylperoxo species [Fe–OO tBu] might be involved in the catalytic cycle. The reaction follows a pseudo zero order rate law in substrate.
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