Oxidations of NADH analogues by cis-[RuIV(bpy)2(py)(O)]2+ occur by hydrogen-atom transfer rather than by hydride transfer
Oxidations of NADH analogues by cis-[RuIV(bpy)2(py)(O)]2+ occur by hydrogen-atom transfer rather than by hydride transfer
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DOI：
10.1021/ic048170q
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发表时间：
2005-04-04
影响因子：
4.6
通讯作者：
Mayer, JM
中科院分区：
文献类型：
--
作者：
Matsuo, T;Mayer, JM
研究了cis-[Ru-IV（bpy）（2）（PY）（O）]（2+）（（RUO ~（2+））-O-IV）对NADH类似物10-甲基-9，10-二氢吖啶（AcrH（2））和N-苄基1，4-二氢烟酰胺（BNAH）的氧化反应，探讨了C-H键氧化的氢原子转移机制和氢化物转移机制。超过20分钟后，AcrH 2和（RuO 2+）-O-IV的完全反应的H-1 NMR谱显示主要产物为10-甲基吖啶酮（AcrO）和顺式[Ru-11（bPY）（2）（PY）（MeCN）]（2+）。然而，在反应的前几秒钟，如通过停流光谱法监测的，观察到10-甲基吖啶鎓阳离子（AcrH（+））。AcrH+是从AcrH 2中净去除氢化物的产物，但氢化物转移不能是主要途径，因为AcrH+仅以40-50%的产率形成，并且其随后氧化成AcrO相对缓慢。动力学研究表明，Ru（IV）O2（+）和AcrH（2）中的反应均为一级反应，k =（5.7 +/- 0.3）x 103 M-1 s（-1），25摄氏度，AW = 5.3 +/- 0.3 kcalmol（-1）和Delta S-双匕首= -23 +/- 1 calmol（-1）K-1。观察到大的动力学同位素效应，k（AcrH 2）/k（AcrD 2）= 12 +/- 1。该反应的动力学受O-2的显著影响。AcrH_2和BNAH氧化反应的速率常数与（RuO_2 ~+）-O-IV氧化一系列碳氢化合物C-H键的速率常数有很好的相关性。这些数据表明了初始氢原子提取的机制。吖啶基自由基，AcrH（中心点），然后通过电子转移（产生AcrH+）或通过C-O键形成（导致AcrO）快速反应。热化学分析表明，H-中心点和从AcrH（2）到（RuO 2）-O-IV+的H-转移是放热的：Δ G度= -10 +/-2 kcal mol（-1）（H-中心点）和-6 +/-5 kcal mol（-1）（H-）。氢原子转移是优选的动力学表明，这种机制具有等于或低于氢化物转移途径的固有势垒。
Oxidations of the NADH analogues 10-methyl-9,10-dihydroacridine (AcrH(2)) and N-benzyl 1,4-dihydronicotinamide (BNAH) by cis-[Ru-IV(bpy)(2)(PY)(O)](2+) ((RUO2+)-O-IV) have been studied to probe the preferences for hydrogen-atom transfer vs hydride transfer mechanisms for the C-H bond oxidation. H-1 NMR spectra of completed reactions of AcrH2 and (RuO2+)-O-IV, after more than similar to 20 min, reveal the predominant products to be 10-methylacridone (AcrO) and cis[Ru-11(bPY)(2)(PY)(MeCN)](2+). Over the first few seconds of the reaction, however, as monitored by stopped-flow optical spectroscopy, the 10-methylacridinium cation (AcrH(+)) is observed. AcrH+ is the product of net hydride removal from AcrH2, but hydride transfer cannot be the dominant pathway because AcrH+ is formed in only 40-50% yield and its subsequent oxidation to AcrO is relatively slow. Kinetic studies show that the reaction is first order in both Ru(IV)O2(+) and AcrH(2), with k = (5.7 +/- 0.3) x 103 M-1 s(-1) at 25 degrees C, AW = 5.3 +/- 0.3 kcal mol(-1) and Delta S-double dagger = -23 +/- 1 cal mol(-1) K-1. A large kinetic isotope effect is observed, k(AcrH2)/k(AcrD2) = 12 +/- 1. The kinetics of this reaction are significantly affected by O-2. The rate constants for the oxidations of AcrH2 and BNAH correlate well with those for a series of hydrocarbon C-H bond oxidations by (RuO2+)-O-IV. The data indicate a mechanism of initial hydrogenatom abstraction. The acridinyl radical, AcrH(center dot), then rapidly reacts by electron transfer (to give AcrH+) or by C-O bond formation (leading to AcrO). Thermochemical analyses show that H-center dot and H- transfer from AcrH(2) to (RuO2)-O-IV+ are comparably exoergic: Delta G degrees = -10 +/- 2 kcal mol(-1) (H-center dot) and -6 +/- 5 kcal mol(-1) (H-). That a hydrogen-atom transfer is preferred kinetically suggests that this mechanism has an equal or lower intrinsic barrier than a hydride transfer pathway.