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

Abstract

Two iron catalysts ([Fe(bpc)Cl-2][ELIN] (la) and [Fe(Me(2)bpb)Cl2][Et3NFI] (lb)) 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. la having an electron-withdrawing group showed a little better catalytic activity than that of lb with an electron-donating group. The mechanistic studies through Hammett plot, deuterium isotope effect, and the use of 2-methyl-1-phenylprop2-yl hydroperoxide (MPPH) as a mechanistic probe suggested that the reactive oxidants responsible for the alcohol oxidation possibly involved Fe-lv=0 species, alkoxy radical (Ra), and phthalimide N-oxyl radical (PINO center dot). On the other hand, the presence of imidazole increased the heterolytic cleavage of Fe-OOR intermediate to form Fe-v=0 species and accelerated its O-O bond cleavage rate. In particular, the formation of Fev=0 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. (C) 2016 Elsevier B.V. All rights reserved.