Sulfide Oxidation by 2,6-Bis[hydroxyl(methyl)amino]-4-morpholino-1,3,5-triazinatodioxomolybdenum(VI): Mechanistic Implications with DFT Calculations for a New Class of Molybdenum(VI) Complex
Sulfide Oxidation by 2,6-Bis[hydroxyl(methyl)amino]-4-morpholino-1,3,5-triazinatodioxomolybdenum(VI): Mechanistic Implications with DFT Calculations for a New Class of Molybdenum(VI) Complex
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DOI：
10.1021/acs.inorgchem.1c00145
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发表时间：
2021-05-13
影响因子：
4.6
通讯作者：
Kuo, Louis Y.
中科院分区：
文献类型：
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作者：
Bullock, Cayden X.;Jamieson, Cooper S.;Kuo, Louis Y.
硫化物氧化是通过一类新型二氧代钼 (VI) 催化剂 (1) 完成的，该催化剂使用三齿 2,6-双[氢酰基（甲基）氨基]-4-吗啉代-1,3,5-三嗪配体形成五配位钼 (VI) 中心。共振拉曼光谱显示，Mo(VI) 氧上的二氧代基团很容易与乙腈介质中的水交换，从而可以对催化剂 1 进行 O-18 标记。模型氧化反应是使用等摩尔量的 H2O2，将苯硫醚 (2) 转化为相应的含 4% 1 的亚砜。在 MeCN-d(3) 中。使用 O-18 标记的 1 或 O-18 标记的 H2O2 进行的 Oxygen-18 标记实验与使用 eta(1)-Mo(OOH) 羟基过氧基物质的硫化物氧化途径一致 (3)。假设的中间体 3 最初是在 1 和 H2O2 之间的质子转移反应中形成的。假设氧化是通过硫化物对 3 的亲核攻击进行的，这得到了 2 对位衍生物的哈米特线性自由能关系的支持。获得了 -1.2 +/- 0.2 的哈米特反应常数 (rho)，这与之前在第 6 族配合物的硫化物氧化反应中发现的其他 rho 值一致。 2 被 1 氧化的 Eyring 图给出了 63.0 +/- 5.2 kJ/mol 的 E-a，略高于钼 (VI) 络合物氧化二过氧化 (吡啶-2-羧基) 钼酸 (VI) 双(吡啶-2-羧酸) 一水合物 (5) 对 2 的类似氧化。使用密度泛函理论 (DFT) 对完整反应曲线进行计算建模，得到的活化焓和活化熵（分别为 64 kJ/mol 和 -120 J/mol.K）在实验值的 1 个标准差范围内，进一步支持了假设的机制。
Sulfide oxidation is accomplished by a new class of dioxomolybdenum(VI) catalyst (1) that uses the tridentate 2,6-bis[hydroryl(methyl)amino]-4-morpholino-1,3,5-triazine ligand to form a five-coordinate molybdenum(VI) center. Resonance Raman spectra show that the dioxo groups on the Mo(VI) oxygens readily exchange with water in an acetonitrile media that allows O-18 labeling of catalyst 1. The model oxidation reaction was the conversion of thioanisole (2) to the corresponding sulfoxide with 4% of 1 using an equimolar amount of H2O2. in MeCN-d(3). Oxygen-18 labeling experiments with either O-18-labeled 1 or O-18-labeled H2O2 are consistent with a sulfide oxygenation pathway that uses a eta(1)-Mo(OOH) hydroxoperoxyl species (3). The hypothesized intermediate 3 is initially formed in a proton transfer reaction between 1 and H2O2. Oxidation is hypothesized via nucleophilic attack of the sulfide on 3 that is supported from a Hammett linear free-energy relationship for para-derivatives of 2. A Hammett reactivity constant (rho) of -1.2 +/- 0.2 was obtained, which is consistent with other rho values found in prior sulfide oxidation reactions by group 6 complexes. An Eyring plot of the 2 oxidation by 1 gives an E-a of 63.0 +/- 5.2 kJ/mol, which is slightly higher than that of a similar oxidation of 2 by the molybdenum(VI) complex, oxodiperoxo (pyridine-2-carboxylato)molybdate(VI) bis(pyridine-2-carboxylic acid) monohydrate (5). Computational modeling with density functional theory (DFT) of the complete reaction profile gave enthalpy and entropy of activations (64 kJ/mol and -120 J/mol.K, respectively) within 1 standard deviation of the experimental values, further supporting the hypothesized mechanism.