Benchmark Study On Methanol C-H And O-H Bond Activation Bly Bare [Fe^ⅣO]²⁺

We present a high-level computational study on methanol C H and O H bondcleavages by bare [FeIVO]2+, as well as benchmarks of various density functionaltheory (DFT)methods. We considered direct and concerted hydrogen transfer(DHTand CHT) pathways, respectively. The potential energy surfaces were constructed atthe CCSD(T)/def2-TZVPP//B3LYP/def2-TZVP level of theory. Mechanistically,(1)the C H bond cleavage is dominant and the O H activation only plays minor role onthe PESs;(2) the DHT from methyl should be the most practical channel; and (3)electronic structure analysis demonstrates the proton and electron transfer couplingbehavior along the reaction coordinates. The solvent effect is evident and playsdistinct roles in regulating the two bond activations in different mechanisms duringthe catalysis. The effect of optimizing the geometries using different densityfunctionals was also studied, showing that it is not meaningful to discuss which DFTmethod could give the accurate prediction of the geometries, especially for transitionstructures. Furthermore, the gold-standard CCSD(T) method was used to benchmark19different density functionals with different Hartree Fock exchange fractions. Theresults revealed that (i) the structural factor plays a minor role in the single pointenergy (SPE) calculations;(ii) reaction energy prediction is quite challenging for DFTmethods;(iii)the mean absolute deviations (MADs) reflect the problematic descriptionof the DFs when dealing with metal oxidation state change, giving a strong correlationon the HF exchange in the DFs. Knowledge from this study should be of great valuefor computational chemistry, especially for the de novo design of transition metalcatalysts.