Highly Efficient Alkane Oxidation Catalyzed by [MnV(N)(CN)4]2鈥?/sup>. Evidence for [MnVII(N)(O)(CN)4]2鈥?/sup> as an Active Intermediate

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• 作者：Li Ma ; Yi Pan ; Wai-Lun Man ; Hoi-Ki Kwong ; William W. Y. Lam ; Gui Chen ; Kai-Chung Lau ; Tai-Chu Lau
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：May 28, 2014
• 年：2014
• 卷：136
• 期：21
• 页码：7680-7687
• 全文大小：418K
• 年卷期：v.136,no.21(May 28, 2014)
• ISSN：1520-5126

文摘

The oxidation of various alkanes catalyzed by [Mn^V(N)(CN)₄]^{2鈥?/sup> using various terminal oxidants at room temperature has been investigated. Excellent yields of alcohols and ketones (>95%) are obtained using H₂O₂ as oxidant and CF₃CH₂OH as solvent. Good yields (>80%) are also obtained using (NH₄)₂[Ce(NO₃)₆] in CF₃CH₂OH/H₂O. Kinetic isotope effects (KIEs) are determined by using an equimolar mixture of cyclohexane (c-C₆H₁₂) and cyclohexane-d₁₂ (c-C₆D₁₂) as substrate. The KIEs are 3.1 卤 0.3 and 3.6 卤 0.2 for oxidation by H₂O₂ and Ce(IV), respectively. On the other hand, the rate constants for the formation of products using c-C₆H₁₂ or c-C₆D₁₂ as single substrate are the same. These results are consistent with initial rate-limiting formation of an active intermediate between [Mn(N)(CN)₄]2鈥?/sup> and H₂O₂ or CeIV, followed by H-atom abstraction from cyclohexane by the active intermediate. When PhCH₂C(CH₃)₂OOH (MPPH) is used as oxidant for the oxidation of c-C₆H₁₂, the major products are c-C₆H₁₁OH, c-C₆H₁₀O, and PhCH₂C(CH₃)₂OH (MPPOH), suggesting heterolytic cleavage of MPPH to generate a Mn鈺怬 intermediate. In the reaction of H₂O₂ with [Mn(N)(CN)₄]2鈥?/sup> in CF₃CH₂OH, a peak at m/z 628.1 was observed in the electrospray ionization mass spectrometry, which is assigned to the solvated manganese nitrido oxo species, (PPh₄)[Mn(N)(O)(CN)₄]鈭?/sup>路CF₃CH₂OH. On the basis of the experimental results the proposed mechanism for catalytic alkane oxidation by [MnV(N)(CN)₄]2鈥?/sup>/ROOH involves initial rate-limiting O-atom transfer from ROOH to [Mn(N)(CN)₄]2鈥?/sup> to generate a manganese(VII) nitrido oxo active species, [MnVII(N)(O)(CN)₄]2鈥?/sup>, which then oxidizes alkanes (R鈥睭) via a H-atom abstraction/O-rebound mechanism. The proposed mechanism is also supported by density functional theory calculations.}