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Interplay of Experiment and Theory in Elucidating Mechanisms of Oxidation Reactions by a Nonheme (RuO)-O-IV Complex
- Interplay of Experiment and Theory in Elucidating Mechanisms of Oxidation Reactions by a Nonheme (RuO)-O-IV Complex
- Dhuri, Sunder N.; Cho, Kyung-Bin; Lee, Yong-Min; Shin, Sun Young; Kim, Jin Hwa; Mandal, Debasish; Shaik, Sason; Nam, Wonwoo
- Ewha Authors
- 남원우; 이용민
- SCOPUS Author ID
- 남원우; 이용민
- Issue Date
- Journal Title
- JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
- vol. 137, no. 26, pp. 8623 - 8632
- AMER CHEMICAL SOC
- SCI; SCIE; SCOPUS
- A comprehensive experimental and theoretical study of the reactivity patterns and reaction mechanisms in alkane hydroxylation, olefin epoxidation, cyclohexene oxidation, and sulfoxidation reactions by a mononuclear nonheme ruthenium(IV)-oxo complex, [Ru-IV(O)(terpy)-(bpm)](2+) (1), has been conducted. In alkane hydroxylation (i.e., oxygen rebound vs oxygen non-rebound mechanisms), both the experimental and theoretical results show that the substrate radical formed via a rate-determining H atom abstraction of alkanes by 1 prefers dissociation over oxygen rebound and desaturation processes. In the oxidation of olefins by 1, the observations of a kinetic isotope effect (KIE) value of 1 and styrene oxide formation lead us to conclude that an epoxidation reaction via oxygen atom transfer (OAT) from the (RuO)-O-IV complex to the C=C double bond is the dominant pathway. Density functional theory (DFT) calculations show that the epoxidation reaction is a two-step, two-spin-state process. In contrast, the oxidation of cyclohexene by 1 affords products derived from allylic C-H bond oxidation, with a high KIE value of 38(3). The preference for H atom abstraction over C=C double bond epoxidation in the oxidation of cyclohexene by 1 is elucidated by DFT calculations, which show that the energy barrier for C-H activation is 4.5 kcal mol(-1) lower than the energy barrier for epoxidation. In the oxidation of sulfides, sulfoxidation by the electrophilic Ru-oxo group of 1 occurs via a direct OAT mechanism, and DFT calculations show that this is a two-spin-state reaction in which the transition state is the lowest in the S = 0 state.
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