Density Functional Study on the Mechanisms of the Reactions of Gas-Phase OsOn+ (n = 1-4) with Methane
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- 作者：Ganbing Zhang ; Shuhua Li ; and Yuansheng Jiang
- 刊名：Organometallics
- 出版年：2004
- 出版时间：July 19, 2004
- 年：2004
- 卷：23
- 期：15
- 页码：3656 - 3667
- 全文大小：337K
- 年卷期：v.23,no.15(July 19, 2004)
- ISSN：1520-6041
文摘
The sextet, quartet, and doublet potential energy surfaces (PESs) of the reactions ofmethane with gas-phase OsOn+ (n=1-4) have been explored via density functionalcalculations to investigate the mechanisms of these reactions. For the reactions of OsOn+ (n= 1-2) with methane, the minimum energy reaction paths are found to involve two spininversions in the entrance and exit channels. Specifically, they are most likely to proceedthrough 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 17.3kcal/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 kineticallyunfavorable at room temperature because the intermediate generated by the activation ofthe 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 doubletPES by a direct hydrogen atom abstraction process, and the whole reaction is exothermicby 31.8 kcal/mol. These results agree with the experimental observation that OsOn+ (n =1-2, 4) can readily activate methane but OsO3+ cannot.
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 17.3kcal/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 kineticallyunfavorable at room temperature because the intermediate generated by the activation ofthe 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 doubletPES by a direct hydrogen atom abstraction process, and the whole reaction is exothermicby 31.8 kcal/mol. These results agree with the experimental observation that OsOn+ (n =1-2, 4) can readily activate methane but OsO3+ cannot.