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 ([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 Fe^IV[Formula presented]), and phthalimide N-oxyl radical [Formula presented]. On the other hand, the presence of imidazole increased the heterolytic cleavage of Fe-OOR intermediate to form Fe^V[Formula presented] species and accelerated its [Formula presented] bond cleavage rate. In particular, the formation of Fe^V[Formula presented] 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.