Mechanistic Insights into the Dicopper-Complex-Catalyzed Hydroxylation of Methane and Benzene Using Nitric Oxide: A DFT Study

Abstract

Although hydrocarbons are known to act as reductants for the catalytic reduction of nitric oxides (NO x ) over copper-based catalysts, the reaction mechanism requires clarification. Herein, density functional theory (DFT) calculations were carried out to investigate the reduction mechanisms of NO x to dinitrogen coupled to the hydroxylation of methane or benzene using the dicopper complex reported by Zhang and co-workers [J. Am. Chem. Soc.20191411015910164]. The B3LYP functional was used to optimize the (μ-oxo)­(μ-nitrosyl)­dicopper complex in the quartet state and the (μ-η2:η2-NO2)­dicopper complex in the doublet state, the latter of which was found to be the ground state. Then, we investigated the reactivities of the (μ-η2:η2-NO2)­dicopper complex toward methane and benzene by considering the conversions of N2O to N2 in the presence and the absence of methane or benzene. In the presence of methane and benzene, the calculated activation energies were 27.0 and 21.0 kcal/mol, respectively, whereas that with N2O alone was prohibitively high (61.9 kcal/mol). Thus, the (μ-η2:η2-NO2)­dicopper complex prefers the reactions with methane and benzene to that with N2O. The reaction of the (μ-η2:η2-NO2)­dicopper complex with methane or benzene generated the (μ-nitrosyl)­dicopper complex. The (μ-nitrosyl)­dicopper complex then reacted with N2O to regenerate the (μ-η2:η2-NO2)­dicopper complex and N2 with an activation barrier of 31.5 kcal/mol. The overall reactions for methane and benzene hydroxylation were calculated to be exothermic by 41.7 and 54.1 kcal/mol, respectively. These results suggest that the catalytic reduction of NO x using hydrocarbons is feasible at certain operating temperatures. Thus, our calculations provide new insights into the design of catalysts for NO x purification.

Mixed Anion Control of the Partial Oxidation of Methane to Methanol on the β-PtO2Surface

“…A preceding PBE study for this reaction provided the overall energy change of about −38 kcal/mol, which is consistent with our result. Could one use a hybrid functional, the energy difference would get closer to the experimental enthalpy difference, but there would still be a deviation of about 10 kcal/mol from the experimental value …”

“…Could one use a hybrid functional, the energy difference would get closer to the experimental enthalpy difference, but there would still be a deviation of about 10 kcal/mol from the experimental value. 77 3.6. Comparison with IrO 2 .…”

Two-State Hydrogen Atom Transfer Reactivity of Unsymmetric [Cu2(O)(NO)]2+ Complexes

“…These doublet/quartet splitting energies are much smaller compared to those predicted by DFT. 32 However, they are still higher than the experimental values, perhaps due to the solid-state or solution environment of the [ H LCu 2 (O)(NO)] 2+ structure, zero-point vibrational effects, and approximations in the SC-NEVPT2/SA-CASSCF method. Analysis of the SA-CASSCF spin density for the S = 1/2 and S = 3/2 states shows that the unpaired electron is localized on the bridging oxo ligand (Figure 4).…”

“…However, a recent computational study by Yoshizawa and Shiota proposed an alternative S = 3/2 state for the [ H LCu 2 (O)(NO)] 2+ complex. 32 Encouraged by their work, we further examined the EPR of [ H LCu 2 (O)(NO)] 2+ at low temperature (5 K) and high microwave power (2.0 mW) and observed an S = 3/2 signal at g = 1.95. Spectral simulation of the S = 3/2 signal allowed us to determine zero-field splitting parameters of D = 0.2 cm −1 and E/D = 0.3 (Figure 2, red).…”

Theoretical insights into the antiradical activity and copper-catalysed oxidative damage of mexidol in the physiological environment

“…In evaluating the antioxidant activity of MD, one has to also consider that pyridines are very good coordinating ligands and therefore it is highly likely that MD forms chelates with trace metals [5,6]. Previous studies showed that the presence of transition metals such as Cu(I) can produce hydroxyl radicals via the Fenton-like reaction (1.1) [7][8][9][10][11]:…”