Density Functional Study on the Mechanisms of the Reactions of Gas-Phase OsO_n⁺ (n = 1−4) with Methane

Abstract

The sextet, quartet, and doublet potential energy surfaces (PESs) of the reactions of methane with gas-phase OsO n + (n=1−4) have been explored via density functional calculations to investigate the mechanisms of these reactions. For the reactions of OsO n + (n = 1−2) with methane, the minimum energy reaction paths are found to involve two spin inversions in the entrance and exit channels. Specifically, they are most likely to proceed through the following steps: 4OsO+ + CH4 → 2OOsCH4 + → 2OOs(H)CH3 + → 2OOsH(H)(CH2)+ → 4OOs(CH2)+ + H2; and 4OsO2 + + CH4 → 2O(O)OsCH4 + → 2O(O)Os(H)CH3 + → 2O(HO)Os(CH3)+ → 2O(HO)Os(H)(CH2)+ → 2OOs(H2O)(CH2)+ → 4OOs(CH2)+ + H2O, respectively. Along the minimum energy pathway the exothermicity of the overall reaction would be 17.3 kcal/mol for OsO+ + CH4 → OOs(CH2)+ + H2, and 24.0 kcal/mol for OsO2 + + CH4 → OOs(CH2)+ + H2O. For the reaction of OsO3 + with methane, it is found to be kinetically unfavorable at room temperature because the intermediate generated by the activation of the first C−H bond has a significantly positive Gibbs free energy relative to the reactants. For OsO4 +, our calculations suggest that it can readily react with methane on the doublet PES by a direct hydrogen atom abstraction process, and the whole reaction is exothermic by 31.8 kcal/mol. These results agree with the experimental observation that OsO n + (n = 1−2, 4) can readily activate methane but OsO3 + cannot.

Theoretical study on the gas‐phase reaction mechanism between palladium monoxide and methane

“…[25] In fact, these DFT results are fully consistent with the qualitative consideration. [8,21,23,25] On the other hand, in contrast to the cation reaction systems, the reactions between neutral metal oxides and methane have not yet received enough attention, partially because of the experimental challenges faced in detecting neutral species in the gas phase. Theoretically, Broclawik's and Hwang's groups have studied the reaction mechanism of neutral metal oxides, MOs (M ¼ Be, Sc, Ni, Pd, Pt, and Rh) with methane.…”

“…[17][18][19][20][21][22][23][24] The experimentally observed reaction efficiency and methanol/ methyl product branching ratio can be rationalized in terms of the calculated barrier heights at the transition states (TSs). [21,23] Li and coworkers [25] have theoretically explored the reaction mechanism of methane with OsO þ . They suggested that the most likely reaction path proceeds via the following:…”

A systematic quantum chemical investigation of the CH bond activation in methane by gas phase vanadium oxide cation VO+

“…[2][3][4][5] An activation of the C H bond is obviously the very first step in all such processes. However, already the interaction between a metal oxide cation MO + with methane is supposed to undergo a variety of different reaction paths leading to different products.…”

Theoretical study on the gas-phase reaction mechanism between rhodium monoxide cation and methane

“…Li et al have theoretically explored the reaction mechanism of methane with OsO ? [46]. They suggested that the most likely reaction paths is the following: ?…”