A Continuum of Proton-Coupled Electron Transfer Reactivity.
A Continuum of Proton-Coupled Electron Transfer Reactivity.
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DOI：
10.1021/acs.accounts.8b00319
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发表时间：
2018-10-16
影响因子：
18.3
通讯作者：
Mayer JM
中科院分区：
文献类型：
--
作者：
Darcy JW;Koronkiewicz B;Parada GA;Mayer JM
质子耦合电子转移涵盖了涉及电子和质子转移(S)的一系列反应。最著名的PCET反应，氢原子转移(HAT)，已经被详细研究了一个多世纪。HAT通常被描述为氢原子(H·≡H++e−)从一个基团Y+H−X→Y−H+X的协同转移，但很难建立一个严格的定义。当“H·”的转移涉及e−和H+转移到空间上不同的地点或甚至完全分开的试剂(多地点协同质子−电子转移，MS-CPET)时，区分更具挑战性。MS-CPET的反应性在生物和合成环境中被越来越多地提出，一些通常被描述为HAT的反应更类似于MS-CPET。尽管HAT和MS-CPET反应“看起来不同”，但我们在这里认为，这些反应位于反应性连续体上，并且它们受到许多相同的关键参数的支配。这一描述带领读者了解了PCET的反应连续体，使用了一系列研究来展示以似乎不同的方式移动质子和电子的反应的强烈相似性。为了为我们的漫步做准备，我们描述了HAT和MS-CPET的热化学和动力学框架。溶液HAT反应的驱动力最容易被讨论为反应物和产物的键解离自由能(BDFE)的差异。BDFE可以分析为电子和质子转移步骤的总和，因此可以从pKa和E°值获得。尽管MS-CPET反应不会以与HAT相同的方式生成和断裂H-−X键，但引入有效的BDFE(BDFEff)也可以使用相同的热化学描述。还原剂/酸对的BDFEff是该对形成H·的自由能，它可以用类似于标准BDFE的方式从pKa和E°值获得。当PCET热化学已知时，HAT和PCET速率常数可以用线性自由能关系(Brnsted催化定律)和Marcus理论类型的方法来理解和预测。在此背景下，我们将向读者介绍PCET反应性的连续体。我们的旅程从研究金属介导的HAT从碳氢化合物底物到金属氧络合物，再到反应光谱的MS-CPET端，涉及H+和e−从羟胺TEMPOH转移到两个完全独立的分子。这些例子，以及介于两者之间的例子，都是在相同的热力学和动力学框架内分析的。对具有C−H键的MS-CPET的第一个例子的描述使用了相同的框架，并强调了氢键和预组织的重要性。这些例子和分析表明，沿着PCET连续体的反应更相似，而不是不同，试图将这些反应分成子类别可能会模糊许多基本的化学。我们希望，开发这些反应的许多共同特征将有助于专家和新手探索PCET反应性的令人兴奋的新领域。
Proton-coupled electron transfer (PCET) covers a wide range of reactions involving the transfer(s) of electrons and protons. The best-known PCET reaction, hydrogen atom transfer (HAT), has been studied in detail for more than a century. HAT is generally described as the concerted transfer of a hydrogen atom (H• ≡ H+ + e−) from one group to another, Y + H−X → Y−H + X, but a strict definition of HAT has been difficult to establish. Distinctions are more challenging when the transfer of “H•” involves e− and H+ that transfer to/from spatially distinct sites or even completely separate reagents (multiple-site concerted proton−electron transfer, MS-CPET). MS-CPET reactivity is increasingly proposed in biological and synthetic contexts, and some reactions typically described as HAT more resemble MS-CPET. Despite that HAT and MS-CPET reactions “look different,” we argue here that these reactions lie on a reactivity continuum, and that they are governed by many of the same key parameters. This Account walks the reader across this PCET reactivity continuum, using a series of studies to show the strong similarities of reactions that move protons and electrons in seemingly different ways. To prepare for our stroll, we describe the thermochemical and kinetic frameworks for HAT and MS-CPET. The driving force for a solution HAT reaction is most easily discussed as the difference in the bond dissociation free energies (BDFEs) of the reactants and products. BDFEs can be analyzed as sums of electron and proton transfer steps and can therefore be obtained from pKa and E° values. Even though MS-CPET reactions do not make and break H−X bonds in the same way as HAT, the same thermochemical description can be used with the introduction of an effective BDFE (BDFEeff). The BDFEeff of a reductant/acid pair is the free energy of that pair to form H•, which can be obtained from pKa and E° values in an analogous fashion to a standard BDFE. When the PCET thermochemistry is known, HAT and PCET rate constants can be understood and often predicted using linear free energy relationships (the Brønsted catalysis law) and Marcus theory type approaches. After this background, we walk the reader through a continuum of PCET reactivity. Our journey begins with a study of metalmediated HAT from hydrocarbon substrates to a metal-oxo complex and travels to the MS-CPET end of the reactivity spectrum, involving the transfer of H+ and e− from the hydroxylamine TEMPOH to two completely separate molecules. These examples, and those in between, are all analyzed within the same thermodynamic and kinetic framework. A description of the first examples of MS-CPET with C−H bonds uses the same framework and highlights the importance of hydrogen bonding and preorganization. The examples and analyses show that the reactions along the PCET continuum are more similar than they are different, and that attempts to divide these reactions into subcategories can obscure much of the essential chemistry. We hope that developing the many common features of these reactions will help experts and newcomers alike to explore exciting new territories in PCET reactivity.
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影响因子：
62.1
作者：
Dempsey, Jillian L.;Winkler, Jay R.;Gray, Harry B.
通讯作者：
Gray, Harry B.
影响因子：
15
作者：
Mayer, JM;Hrovat, DA;Borden, WT
通讯作者：
Borden, WT
DOI：
10.1073/pnas.0708967105
发表时间：
2008-06-17
影响因子：
11.1
作者：
Markle, Todd F.;Rhile, Ian J.;Mayer, James M.
通讯作者：
Mayer, James M.
影响因子：
4.6
作者：
Bryant, JR;Matsuo, T;Mayer, JM
通讯作者：
Mayer, JM
影响因子：
15
作者：
Schrauben, Joel N.;Cattaneo, Mauricio;Day, Thomas C.;Tenderholt, Adam L.;Mayer, James M.
通讯作者：
Mayer, James M.