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 MO 3 L (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 MnO 3 L (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 MO 3 L (M = Tc, Mn, and L = O - ) where the vice versa occurs. In the reaction of both TcO 3 L and MnO 3 L (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 TcO 4 - and MnO 4 - 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 MnO 3 L (L = F - , Cl - , Br - , I - , OH - ) and TcO 3 L (L = F - , Cl - , Br - , I - , OH - ) catalyzed surfaces respectively. In all cases, the TcO 3 L complexes were found to be polar compared to the MnO 3 L complexes. The MnO 4 - (singlet) and MnO 3 F (singlet) are the best catalysts for the exclusive formation of the diols and epoxides respectively.