Nonheme iron complex-catalyzed efficient alcohol oxidation by t-BuOOH with N-hydroxyphthalimide (NHPI) as co-catalyst: Implication of high valent iron-oxo species

•Two iron catalysts displayed efficient catalysis in oxidation of various alcohols.•Reactive oxidants are FeIVO species, alkoxy radical (RO), and PINO.•Presence of imidazole increases formation of FeVO intermediate.

Two iron catalysts ([Fe(bpc)Cl2][Et4N] (1a) and [Fe(Me2bpb)Cl2][Et3NH] (1b)) displayed efficient catalysis in oxidation of various alcohols to the corresponding carbonyl products using t-BuOOH as an oxidant in the presence of N-hydroxyphthalimide (NHPI) under mild conditions. 1a having an electron-withdrawing group showed a little better catalytic activity than that of 1b with an electron-donating group. The mechanistic studies through Hammett plot, deuterium isotope effect, and the use of 2-methyl-1-phenylprop-2-yl hydroperoxide (MPPH) as a mechanistic probe suggested that the reactive oxidants responsible for the alcohol oxidation possibly involved FeIVO species, alkoxy radical (RO), and phthalimide N-oxyl radical (PINO). On the other hand, the presence of imidazole increased the heterolytic cleavage of Fe-OOR intermediate to form FeVO species and accelerated its OO bond cleavage rate. In particular, the formation of FeVO intermediate via the heterolytic cleavage of Fe-OOR species in the presence of imidazole in the catalytic oxidation systems of nonheme iron complexes with t-BuOOH was substantialized, for the first time, to the best of our knowledge.

Graphical abstractTwo iron catalysts ([Fe(bpc)Cl2][Et4N] (1a) and [Fe(Me2bpb)Cl2][Et3NH] (1b)) displayed efficient catalysis in oxidation of various alcohols to the corresponding carbonyl products using t-BuOOH as an oxidant in the presence of N-hydroxyphthalimide (NHPI) under mild conditions. The mechanistic studies through Hammett plot, deuterium isotope effect, and the use of 2-methyl-1-phenylprop-2-yl hydroperoxide (MPPH) as a mechanistic probe suggested that the reactive oxidants responsible for the alcohol oxidation possibly involved FeIVO species, alkoxy radical (RO), and phthalimide N-oxyl radical (PINO).Figure optionsDownload full-size imageDownload as PowerPoint slide