Lewis Acid Coupled Electron Transfer of Metal-Oxygen Intermediates
Lewis Acid Coupled Electron Transfer of Metal-Oxygen Intermediates
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DOI：
10.1002/chem.201502693
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发表时间：
2015-12-01
影响因子：
4.3
通讯作者：
Nam, Wonwoo
中科院分区：
文献类型：
--
作者：
Fukuzumi, Shunichi;Ohkubo, Kei;Nam, Wonwoo
氧化还原不活跃的金属离子和作为Lewis酸的Bronsted酸在调节金属-氧中间体的氧化还原反应活性方面起着关键作用，如金属-氧和金属-过氧络合物。在三氟酸(HOTf)和Sc(OTf)(3)存在下，甲苯衍生物的氧化C-H键断裂、硫代苯甲醚衍生物的亚磺氧化和单核非血红素铁(IV)-氧配合物环氧化苯乙烯衍生物的机理被统一为铁(III)-氧配合物结合Lewis酸(HOTf和Sc(OTf)(3)的速率决定电子转移耦合机制。在考虑前驱体形成常数差异的情况下，Lewis酸促进的铁(IV)-氧络合物的氧化C-H键断裂、亚硫氧化和环氧化反应的二级速率常数的所有对数都与质子耦合电子转移(PCET)和金属离子耦合电子转移(MCET)的驱动力具有显著的一致性。证实了Mn-IV-OTO络合物中HOTf和Sc(OTf)(3)与金属-氧基部分的结合。随着氧化还原非活性金属离子的Lewis酸度的增加，与Lewis酸结合的金属氧络合物的电子转移活性增强。金属离子也能与单核非血红素铁(III)-过氧基配合物结合，导致电子转移还原加速，电子转移氧化速度减慢。这种通过Lewis酸结合来控制金属-氧中间体的反应活性的方法，为深入了解钙离子在光系统II中放氧复合体将水氧化为氧气中的作用提供了有价值的见解。
Redox-inactive metal ions and Bronsted acids that function as Lewis acids play pivotal roles in modulating the redox reactivity of metal-oxygen intermediates, such as metal-oxo and metal-peroxo complexes. The mechanisms of the oxidative C-H bond cleavage of toluene derivatives, sulfoxidation of thioanisole derivatives, and epoxidation of styrene derivatives by mononuclear nonheme iron(IV)-oxo complexes in the presence of triflic acid (HOTf) and Sc(OTf)(3) have been unified as rate-determining electron transfer coupled with binding of Lewis acids (HOTf and Sc(OTf)(3)) by iron(III)-oxo complexes. All logarithms of the observed second-order rate constants of Lewis acid-promoted oxidative C-H bond cleavage, sulfoxidation, and epoxidation reactions of iron(IV)-oxo complexes exhibit remarkably unified correlations with the driving forces of proton-coupled electron transfer (PCET) and metal ion-coupled electron transfer (MCET) in light of the Marcus theory of electron transfer when the differences in the formation constants of precursor complexes were taken into account. The binding of HOTf and Sc(OTf)(3) to the metal-oxo moiety has been confirmed for Mn-IV-oxo complexes. The enhancement of the electron-transfer reactivity of metal-oxo complexes by binding of Lewis acids increases with increasing the Lewis acidity of redox-inactive metal ions. Metal ions can also bind to mononuclear nonheme iron(III)-peroxo complexes, resulting in acceleration of the electron-transfer reduction but deceleration of the electron-transfer oxidation. Such a control on the reactivity of metal-oxygen intermediates by binding of Lewis acids provides valuable insight into the role of Ca2+ in the oxidation of water to dioxygen by the oxygen-evolving complex in photosystem II.