Side-chain oxidation of benzyltrimethylsilanes by iodosylbenzene in the presence of iron and manganese porphyrins

Article abstract of DOI:10.1016/S0040-4020(01)87204-5

Benzyltrimethylsilanes react with iodosylbenzene in the presence of either iron(III) or magnanese(III) tetrakis(pentafluorophenyl)porphyrin (TFPPM, with M = Fe, Mn) to give α-hydroxybenzyltrimethylsilanes, which are then rapidly converted into the corresponding benzaldehydes in the reaction medium. In these reactions the active species is the metal-oxo complex. TFPPM(V) = O, formed by iodosylbenzene and TFPPM. A relative reactivity study for a series of ring substituted benzyltrimethylsilanes has shown that when M = Fe, the reaction is quite selective (ρ = -1.85), with the m-MeO substituent exhibiting a much higher reactivity than expected. When M = Mn, a lower ρ value (-1.15) is observed and no anomalous reactivity is found with the m-MeO group. These result suggest that the side-chain hydroxylation of benzyltrimethylsilane by TFPPMn(V) = O occurs by the well known hydrogen atom transfer mechanism. For the corresponding reactions induced by TFPPFe(V) = O a coupled proton/electron transfer mechanism, which might involve the formation of a charge-transfer complex, seems more likely.