Manganeseporphyrin catalyzed cyclohexene epoxidation by iodosylbenzene -: The remarkable effect of the meso-phenyl ortho-OH substituent

Catalytic cyclohexene epoxidation with iodosylbenzene by the following Mn-porphyrins bearing ortho substituents on a meso group: MnTTP, MnM2-OHPTTP(5-(2-hydroxyphenyl)-10,15,20-tritolylporphyrin) and MnM2-BrPTTP(5-(2-(3-bromo-1-propoxy)phenyl)-10,15,20-tritolylporphyrin), has been studied. The effect of dioxygen and imidazole axial ligand on the yields of epoxide and allylic oxidation products, i.e. alcohol and ketone, was investigated. It was observed that the product selectivity is strongly dependent on the distribution of the Im/MnP species (M, MIm and MIm(2) obtained by spectrophotometric titrations). For MnTPP at Im/MnP = 1 the best epoxide yield associated with the maximum MIm concentration was observed. The presence of the -OH substituent produced a remarkable effect on the reactivity and catalytic properties of the porphyrin system, i.e. drastic reduction in allylic oxidation, slight increase on the epoxide yield, a decrease on the formation of the MnP/Im complexes and change of the reactivity of the Mn center with PhIO. These results are discussed in terms of a possible electronic interaction of the oxygen ortho substituent and the porphyrin ring. (C) 2001 Elsevier Science B.V. All rights reserved.