cis-Dihydroxylation of Alkenes with Oxone Catalyzed by Iron Complexes of a Macrocyclic Tetraaza Ligand and Reaction Mechanism by ESI-MS Spectrometry and DFT Calculations

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• 作者：Toby Wai-Shan Chow ; Ella Lai-Ming Wong ; Zhen Guo ; Yungen Liu ; Jie-Sheng Huang ; Chi-Ming Che
• 刊名：Journal of the American Chemical Society
• 出版年：2010
• 出版时间：September 29, 2010
• 年：2010
• 卷：132
• 期：38
• 页码：13229-13239
• 全文大小：456K
• 年卷期：v.132,no.38(September 29, 2010)
• ISSN：1520-5126

文摘

[Fe^III(L-N₄Me₂)Cl₂]⁺ (1, L-N₄Me₂ = N,N′-dimethyl-2,11-diaza[3.3](2,6)pyridinophane) is an active catalyst for cis-dihydroxylation of various types of alkenes with oxone at room temperature using limiting amounts of alkene substrates. In the presence of 0.7 or 3.5 mol % of 1, reactions of electron-rich alkenes, including cyclooctene, styrenes, and linear alkenes, with oxone (2 equiv) for 5 min resulted in up to >99% substrate conversion and afforded cis-diol products in up to 67% yield, with cis-diol/epoxide molar ratio of up to 16.8:1. For electron-deficient alkenes including α,β-unsaturated esters and α,β-unsaturated ketones, their reactions with oxone (2 equiv) catalyzed by 1 (3.5 mol %) for 5 min afforded cis-diols in up to 99% yield with up to >99% substrate conversion. A large-scale cis-dihydroxylation of methyl cinnamate (9.7 g) with oxone (1 equiv) afforded the cis-diol product (8.4 g) in 84% yield with 85% substrate conversion. After catalysis, the L-N₄Me₂ ligand released due to demetalation can be reused to react with newly added Fe(ClO₄)₂·4H₂O to generate an iron catalyst in situ, which could be used to restart the catalytic alkene cis-dihydroxylation. Mechanistic studies by ESI-MS, isotope labeling studies, and DFT calculations on the 1-catalyzed cis-dihydroxylation of dimethyl fumarate with oxone reveal possible involvement of cis-HO−Fe^V═O and/or cis-O═Fe^V═O species in the reaction; the cis-dihydroxylation reactions involving cis-HO−Fe^V═O and cis-O═Fe^V═O species both proceed by a concerted but highly asynchronous mechanism, with that involving cis-HO−Fe^V═O being more favorable due to a smaller activation barrier.