Partial Methane Oxidation to Methanol on Ru-Porphyrins - on the Role of Non-Innocent Ligands and Spin Crossover

The partial oxidation reaction of CH4 led to the formation of CH3OH in the presence of Ru-porphyrin oxo complexes (denoted as POR, POR-O and POR-OH where in the case of the last two, oxygen atom and the OH group were attached to the active site, respectively), in which Ru was present on different oxidation states. The simulations were performed based on Density Functional Theory (DFT) with extended geometric and electronic structure analyses of each reaction step. Moreover, the reaction pathways were investigated in different spin states. The Spin Crossover (SCO) phenomenon was found to play an important role in the kinetics of the reaction in the presence of POR and POR-O. Harmonic Oscillator Model of Aromaticity (HOMA) index was applied for different spin states to estimate the aromaticity changes of the pyrrole rings in the Ru-porphyrin complexes. In order to characterize the nature of bonding, the Natural Bond Orbitals (NBO) analysis including the Wiberg Bond Index (WBI) and Natural Population Analysis (NPA) was carried out. Finally, the Non-Covalent Interactions (NCI) index was employed to gain insight into interactions between the components of the reaction. It was found that the non-covalent interactions cannot be neglected in the studied reaction paths. Partial oxidation of methane to methanol using Ru-porphyrin complexes as catalysts was investigated theoretically. The Spin Crossover (SCO) phenomenon was shown to play a significant role in the reaction kinetics of complexes denoted as POR and POR-O. Analysis of electronic structure changes during the reaction course, revealed that non-covalent interactions play a significant role in the study of this type of reaction.image

Automated summary

The theoretical investigation of partial oxidation of methane to methanol using Ru-porphyrin complexes as catalysts revealed the significant role of the Spin Crossover phenomenon in the reaction kinetics, and the impact of non-covalent interactions on the electronic structure during the reaction.