Iron(II) and Manganese(II) Complexes with N4Py as Dioxygen Activators for α-Pinene Oxidation in Acetonitrile

Iron(II) and manganese(II) complexes with N4Py [N4Py-N,N-bis(2-pyridylmethyl)-N-(bis-2-pyridylmethyl)amine] have been found to activate O₂ for the oxidation of α-pinene in acetonitrile. For example, for 1 M α-pinene, 0.5 mM [(N4Py)Fe^II]²⁺, and dioxygen as an oxidant, 90 mM α-pinene epoxide, 48 mM verbenol, and 50 mM verbenone have been formed, which, taking into account the concentrations of the minor products (myrtenol and myrtenal), gives a turnover number approximately equal to 400. Based on the amounts of products formed, the conversion of α-pinene is approximately 20% and 18% for iron and manganese catalysts, respectively. Although the manganese catalyst is somewhat less effective than the iron catalyst, the selectivity of the products is similar for both catalysts. Replacement of dioxygen with air as the oxidant causes the reaction yield to be lower. The proposed mechanism assumes the formation of a metal(IV)-oxo complex [(N4Py)M^IV=O]²⁺, M-Fe or Mn, during the simultaneous combination of a catalyst, O₂, and substrate, and its subsequent reactions toward the observed products.