Methane to Methanol Conversion Facilitated by Transition-Metal Methyl and Methoxy Units: The Cases of FeCH₃ ⁺ and FeOCH₃ ⁺

The conversion of methane to methanol (MTM) catalyzed by FeOCH₃ ⁺ and FeCH₃ ⁺ is investigated by means of multireference configuration interaction (MRCI), single-reference coupled clusters (CC), and density functional theory (DFT) approaches. Our dual purpose is the assessment of the applied methodologies and the performance of the proposed catalytic cycle, which involves both of the titled units. The investigated cycle aims to bypass the limitations of metal-oxide catalysts and offers an alternative promising method for efficient MTM transformation. From the technical viewpoint, we found that generally accurate electron correlation treatment is more important than accurately calculated geometries. The combination of optimal DFT geometries with MRCI and CC energetics provides a good compromise between accuracy and efficiency, although there are cases where multireference calculations must be used to obtain correct structures.