Iron Catalyzed Competitive Olefin Oxidation and ipso-Hydroxylation of Benzoic Acids: Further Evidence for an FeV=O Oxidant
Iron Catalyzed Competitive Olefin Oxidation and ipso-Hydroxylation of Benzoic Acids: Further Evidence for an FeV=O Oxidant
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DOI：
10.1021/ic101144s
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发表时间：
2010-10-18
影响因子：
4.6
通讯作者：
Que, Lawrence, Jr.
中科院分区：
文献类型：
--
作者：
Das, Parthapratim;Que, Lawrence, Jr.
铁配合物[Fe-II(TPA)(CH3CN)(2)](OTf)(2) (1) [TPA = 三(2-吡啶甲基)胺]与H2O2作为氧化剂在室温下对吸电子苯甲酸进行原羟基化，导致相应酚类的多次转换。在烯烃存在下，内部羟基化与烯烃环氧化和顺式二羟基化竞争，产物比例由苯甲酸、烯烃和水的相对量调节。据推测，苯甲酸和水竞争 [(TPA)Fe-III(OOH)] 中间体上可用的第六个位点，该中间体经历 O-O 键杂解，分别形成 Fe-V(O)(O2CAr) 和 Fe-V(O)(OH) 氧化剂，从而决定产物结果。推定的 Fe-V(O)(O2CAr) 氧化剂通过氧化脱羧和随后的自身羟基化形成观察到的苯酚产物或通过氧化转移至烯烃形成环氧化物而衰变。在所有研究的情况下，当反应混合物中存在吸电子苯甲酸时，观察到苯酚的产率高于环氧化物或顺式二醇，这表明假定的 Fe-V(O)-(O2CAr) 氧化剂的分子内衰变比分子间烯烃氧化更有利。这些结果支持了 Fe(TPA) 氧化催化假设的机理框架，并进一步强化了氧铁 (V) 物质是这些反应中关键氧化剂的观点。
The iron complex [Fe-II(TPA)(CH3CN)(2)](OTf)(2) (1) [TPA = tris(2-pyridylmethyl)amine] with H2O2 as an oxidant performs ipso-hydroxylation of electron-withdrawing benzoic acids at room temperature, leading to multiple turnovers of corresponding phenols. ipso-Hydroxylation competes with olefin epoxidation and cis-dihydroxylation in the presence of olefins, with the product ratios being modulated by the relative amounts of benzoic acid, olefin, and water. It is proposed that benzoic acid and water compete for the available sixth site on the [(TPA)Fe-III(OOH)] intermediate, which undergoes O-O bond heterolysis to form, respectively, the Fe-V(O)(O2CAr) and Fe-V(O)(OH) oxidants that determine the product outcome. The putative Fe-V(O)(O2CAr) oxidant decays either by undergoing oxidative decarboxylation and subsequent ipso-hydroxylation to form the observed phenol product or by oxo-transfer to olefins to form epoxide. The observed higher yield of phenol over epoxide or cis-diol in all cases studied, where an electron-withdrawing benzoic acid is present in the reaction mixture, suggests that intramolecular decay of the putative Fe-V(O)-(O2CAr) oxidant is favored over intermolecular olefin oxidation. These results support the mechanistic framework postulated for Fe(TPA) oxidative catalysis and further strengthens the notion that oxoiron(V) species are the key oxidants in these reactions.