Kinetic UV-Vis Spectroscopic and DFT Mechanistic Study of the Redox Reaction of [OsVIIIO4(OH)n]n- (n = 1, 2) and Methanol in a Basic Aqueous Matrix.
Kinetic UV-Vis Spectroscopic and DFT Mechanistic Study of the Redox Reaction of [OsVIIIO4(OH)n]n- (n = 1, 2) and Methanol in a Basic Aqueous Matrix.
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[OsVIIIO4(OH)n]n- (n = 1, 2) 和甲醇在碱性水基体中氧化还原反应的动力学紫外-可见光谱和 DFT 机理研究。
DOI：
10.1021/acs.inorgchem.0c02799
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发表时间：
2021
影响因子：
4.6
通讯作者：
Wilhelmus J Gerber
中科院分区：
文献类型：
--
作者：
D. V. van Niekerk;Theodor E Geswindt;Wilhelmus J Gerber
这种结合的实验和计算研究建立在我们以前的研究，阐明甲醇氧化OsVIII氧化/羟基物种（在碱性水介质中）的反应机制，同时占OsVII物种通过OsVIII和OsVI之间的comproportionation反应的同时形成。以CH_3OH或氘代类似物CD_3OH为还原剂的紫外-可见光谱动力学分析表明，甲醇的α-碳氢转移是部分限速步骤。由此产生的相对较大的KIE值约为11.82，是一次和二次同位素效应的组合。在相同的反应条件下，这些甲醇同位素体氧化的Eyring图相互平行，因此具有相同的活化焓[Δ H° = 14.4 ± 1.2 kcal mol-1（CH_3OH）和14.5 ± 1.3 kcal mol-1（CD_3OH）]，但活化熵（Δ S°）从-12.5 ± 4.1 kcal mol-1 K-1（CH_3OH）降低到-12.5 ± 4.1 kcal mol-1 K-1（CD_3OH）。17.1 ± 4.4 cal mol-1 K-1（CD3OH）。在PBE-D3水平上用QZ 4P（Os）和pVQZ（O和H）基组进行的DFT计算研究提供了明确的证据来支持来自实验动力学工作的数据和解释。在模拟水相（COSMO）的比较DFT机制的调查表明，甲醇和OsVIII第一关联，形成一个非共价加合物结合在一起的分子间氢键相互作用。随后通过HAT从甲醇到OsVIII发生自旋禁戒的α-碳氢转移（而不是O-H转移），这被认为是部分限速步骤。在整个逐步氧化还原反应期间没有有机和无机片段彼此解离的情况下（为了避免形成高能量上不利的单体物质），HAT步骤之后是PT，然后是ET，之后是最终产物单体甲醛和OsVI彼此解离。DFT计算的Δ Δ H°在实验获得的值的5 kcal mol-1范围内，而DFT Δ Δ S°比实验发现的大三倍。
This combined experimental and computational study builds on our previous studies to elucidate the reaction mechanism of methanol oxidation by OsVIII oxido/hydroxido species (in basic aqueous media) while accounting for the simultaneous formation of OsVII species via a comproportionation reaction between OsVIII and OsVI. UV-Vis spectroscopy kinetic analyses with either CH3OH or the deuterated analogue CD3OH as a reducing agent revealed that transfer of α-carbon-hydrogen of methanol is the partial rate-limiting step. The resulting relatively large KIE value of approximately 11.82 is a combination of primary and secondary isotope effects. The Eyring plots for the oxidation of these isotopologues of methanol under the same reaction conditions are parallel to each other and hence have the same activation enthalpy [Δ⧧H° = 14.4 ± 1.2 kcal mol-1 (CH3OH) and 14.5 ± 1.3 kcal mol-1 (CD3OH)] but lowered activation entropy (Δ⧧S°) from -12.5 ± 4.1 cal mol-1 K-1 (CH3OH) to -17.1 ± 4.4 cal mol-1 K-1 (CD3OH). DFT computational studies at the PBE-D3 level with QZ4P (Os) and pVQZ (O and H) basis sets provide clear evidence to support the data and interpretations derived from the experimental kinetic work. Comparative DFT mechanistic investigations in a simulated aqueous phase (COSMO) indicate that methanol and OsVIII first associate to form a noncovalent adduct bound together by intermolecular H-bonding interactions. This is followed by spin-forbidden α-carbon-hydrogen transfer (not O-H transfer) from methanol to OsVIII by means of HAT, which is found to be the partial rate-limiting step. Without the organic and inorganic fragments dissociating from each other during the entire stepwise redox reaction (in order to avoid formation of highly energetically unfavorable monomer species), the HAT step is followed by PT and then ET before the final product monomers formaldehyde and OsVI dissociate from each other. DFT-calculated Δ⧧H° is within 5 kcal mol-1 of the experimentally obtained value, while the DFT Δ⧧S° is three times larger than that found from the experiment.