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

TL;DR

Iron and manganese complexes with N4Py can activate oxygen to oxidize α-pinene, producing various products with high turnover numbers.

Contribution

The study introduces N4Py-based iron(II) and manganese(II) complexes as efficient dioxygen activators for α-pinene oxidation.

Findings

Iron(II) and manganese(II) complexes with N4Py activate O2 for α-pinene oxidation in acetonitrile.

The iron catalyst achieves a turnover number of approximately 400 with 20% α-pinene conversion.

Manganese catalyst shows similar product selectivity but slightly lower effectiveness than iron.

Abstract

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)FeII]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)MIV=O]2+, M–Fe or Mn, during the simultaneous combination of a catalyst, O2, and substrate, and its subsequent reactions toward the observed products.

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