A DFT study on the reaction mechanisms of the oxidation of ethylene mediated by technetium and manganese oxo complexes

The oxidation of ethylene catalyzed by manganese and technetium oxo complexes of the type MO₃L (M = Tc, Mn, and L = O⁻, Cl⁻, F⁻, OH⁻, Br⁻, I⁻) on both singlet and triplet potential energy surfaces (PESs) have been studied. All molecular structures were stable on the singlet PES except for the formation of the dioxylate intermediate for the MnO₃L (L = O⁻, Cl⁻, F⁻, OH⁻, Br⁻, I⁻) catalyzed pathway. Frontier molecular orbital calculations showed that electrons flow from the HOMO of ethylene into the LUMO of the metal-oxo complex for all complexes studied except for MO₃L (M = Tc, Mn, and L = O⁻) where the vice versa occurs. In the reaction of both TcO₃L and MnO₃L (L = O⁻, Cl⁻, F⁻, OH⁻, Br⁻, I⁻) with ethylene, it was observed that the formation of the dioxylate intermediate along the [3 + 2] addition pathway on the singlet reaction surface is both kinetically and thermodynamically favorable over its formation via the [2 + 2] pathway. Furthermore, it was observed that TcO₄⁻ and MnO₄⁻ catalyzed pathways exclusively form diols on the singlet PES. The formation of epoxides on the singlet surface is kinetically favorable through the [2 + 1] and [2 + 2] channel for the MnO₃L (L = F⁻, Cl⁻, Br⁻, I⁻, OH⁻) and TcO₃L (L = F⁻, Cl⁻, Br⁻, I⁻, OH⁻) catalyzed surfaces respectively. In all cases, the TcO₃L complexes were found to be polar compared to the MnO₃L complexes. The MnO₄⁻ (singlet) and MnO₃F (singlet) are the best catalysts for the exclusive formation of the diols and epoxides respectively. Graphical abstract: [Figure not available: see fulltext.]