Dehydrogenation of Methane by Gas-Phase Os+: A Density Functional Study
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- 作者：Ganbing Zhang ; Shuhua Li ; and Yuansheng Jiang
- 刊名：Organometallics
- 出版年：2003
- 出版时间：September 15, 2003
- 年：2003
- 卷：22
- 期：19
- 页码：3820 - 3830
- 全文大小：264K
- 年卷期：v.22,no.19(September 15, 2003)
- ISSN：1520-6041
文摘
Density functional calculations have been performed to explore the sextet, quartet, anddoublet potential energy surfaces of methane dehydrogenation by gas-phase Os+ for understanding the reaction mechanism. The minimum energy reaction path is found to involvethe spin inversion three times in the different reaction steps. Totally, three spin states (sextet,quartet, and doublet) are involved in the whole reaction. Specifically, the reaction is mostlikely to proceed through the following steps: 6Os+ + CH4 
OsCH4+ (61) HOsCH3 (42) HOsH(CH2)+ (23) (H2)Os(CH2)+ (44) Os(CH2)+ (45) + H2. The overall reaction is calculatedto be exothermic by 4.2 kcal/mol, which is in good agreement with the available experimentalresults. The first spin inversion, from the sextet state to the quartet state, makes theactivation of the first C-H bond energetically spontaneous. The second transition from thequartet state to the doublet state facilitates the cleavage of the second C-H bond, loweringthe barrier from 25.9 kcal/mol to 16.1 kcal/mol. The third spin inversion occurs from thedoublet state to the quartet state in the reductive elimination step of H2, and this spininversion leads to a decrease in the barrier height from 41.0 to 30.4 kcal/mol.
OsCH4+ (61) HOsCH3 (42) HOsH(CH2)+ (23) (H2)Os(CH2)+ (44) Os(CH2)+ (45) + H2. The overall reaction is calculatedto be exothermic by 4.2 kcal/mol, which is in good agreement with the available experimentalresults. The first spin inversion, from the sextet state to the quartet state, makes theactivation of the first C-H bond energetically spontaneous. The second transition from thequartet state to the doublet state facilitates the cleavage of the second C-H bond, loweringthe barrier from 25.9 kcal/mol to 16.1 kcal/mol. The third spin inversion occurs from thedoublet state to the quartet state in the reductive elimination step of H2, and this spininversion leads to a decrease in the barrier height from 41.0 to 30.4 kcal/mol.