Interplay of Experiment and Theory in Elucidating Mechanisms of Oxidation Reactions by a Nonheme RuIVO Complex

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• 作者：Sunder N. Dhuri ; Kyung-Bin Cho ; Yong-Min Lee ; Sun Young Shin ; Jin Hwa Kim ; Debasish Mandal ; Sason Shaik ; Wonwoo Nam
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：July 8, 2015
• 年：2015
• 卷：137
• 期：26
• 页码：8623-8632
• 全文大小：599K
• ISSN：1520-5126

文摘

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)鈥搊xo 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 Ru^IVO complex to the C鈺怌 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鈥揌 bond oxidation, with a high KIE value of 38(3). The preference for H atom abstraction over C鈺怌 double bond epoxidation in the oxidation of cyclohexene by 1 is elucidated by DFT calculations, which show that the energy barrier for C鈥揌 activation is 4.5 kcal mol^鈥? lower than the energy barrier for epoxidation. In the oxidation of sulfides, sulfoxidation by the electrophilic Ru鈥搊xo 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.