Intermolecular electron-transfer mechanisms via quantitative structures and ion-pair equilibria for self-exchange of anionic (dinitrobenzenide) donors.
Intermolecular electron-transfer mechanisms via quantitative structures and ion-pair equilibria for self-exchange of anionic (dinitrobenzenide) donors.
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通过定量结构和离子对平衡的分子间电子转移机制，用于阴离子（二硝基苯化物）供体的自交换。
DOI：
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发表时间：
2005
影响因子：
15
通讯作者：
J. Kochi
中科院分区：
文献类型：
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作者：
S. Rosokha;J. Lü;M. Newton;J. Kochi
“分离”与“接触”离子对的X射线结构及其光谱（UV-NIR，ESR）表征为评价对二硝基苯自由基阴离子钾盐（DNB（-））的络合平衡和本征（自交换）电子转移速率提供了定量依据。三种主要类型的离子对，K（L）（+）DNB（-），通过K（+）与不同的大环聚醚配体（L）的特异性连接被指定为S类、M类和C类。对于S类，分离离子对（SIP）的自交换速率常数与“自由”阴离子的自交换速率常数基本相同，并且我们得出结论，当分离离子对中的离子间距离为r（SIP）时，二硝基苯反应性不受影响。或=6埃。对于M类，接触离子对（r（CIP）= 2.7埃）和其分离的离子对之间的动态平衡进行了定量评价，而SIP的小部分仍然是整体电子转移动力学的主要贡献者。对于C类，SIP速率受CIP右箭头相对于左箭头SIP互变的慢速率限制，并且自交换默认经由接触离子对进行。从理论上讲，分离的离子对的电子转移速率常数是由马库斯/苏廷两态配方时，方案2中的前体被确定为“分离的”内球复合物（IS（SIP））的共面DNB（-）/DNB二联体。相比之下，通过接触离子对的显著较慢的自交换速率需要缔合机制（方案3），其中根据方案4中的动力学，电子转移速率强烈地受“接触”前体络合物（IS（CIP））内K（L）（+）的阳离子迁移率控制。
Definitive X-ray structures of "separated" versus "contact" ion pairs, together with their spectral (UV-NIR, ESR) characterizations, provide the quantitative basis for evaluating the complex equilibria and intrinsic (self-exchange) electron-transfer rates for the potassium salts of p-dinitrobenzene radical anion (DNB(-)). Three principal types of ion pairs, K(L)(+)DNB(-), are designated as Classes S, M, and C via the specific ligation of K(+) with different macrocyclic polyether ligands (L). For Class S, the self-exchange rate constant for the separated ion pair (SIP) is essentially the same as that of the "free" anion, and we conclude that dinitrobenzenide reactivity is unaffected when the interionic distance in the separated ion pair is r(SIP) > or =6 Angstroms. For Class M, the dynamic equilibrium between the contact ion pair (with r(CIP) = 2.7 Angstroms) and its separated ion pair is quantitatively evaluated, and the rather minor fraction of SIP is nonetheless the principal contributor to the overall electron-transfer kinetics. For Class C, the SIP rate is limited by the slow rate of CIP right arrow over left arrow SIP interconversion, and the self-exchange proceeds via the contact ion pair by default. Theoretically, the electron-transfer rate constant for the separated ion pair is well-accommodated by the Marcus/Sutin two-state formulation when the precursor in Scheme 2 is identified as the "separated" inner-sphere complex (IS(SIP)) of cofacial DNB(-)/DNB dyads. By contrast, the significantly slower rate of self-exchange via the contact ion pair requires an associative mechanism (Scheme 3) in which the electron-transfer rate is strongly governed by cationic mobility of K(L)(+) within the "contact" precursor complex (IS(CIP)) according to the kinetics in Scheme 4.