Intramolecular electron transfer between doubly six sigma-bond-linked trialkyldiazenium cation and diazenyl radical units
Intramolecular electron transfer between doubly six sigma-bond-linked trialkyldiazenium cation and diazenyl radical units
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DOI：
10.1021/ja9634177
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发表时间：
1997-07-23
影响因子：
15
通讯作者：
RogersCrowley, S
中科院分区：
文献类型：
--
作者：
Nelsen, SF;Trieber, DA;RogersCrowley, S
二聚体2-叔丁基-2，3-二氮杂双环[2.2.2]辛基二氮阳离子自由基阳离子的还原和氧化二氮烯单元之间的分子内电子转移速率常数k（ESR）由它们在CH 3CN、二甲基甲酰胺和CH 2Cl 2中的变温ESR谱确定。这些阳离子显示溶剂敏感的电荷转移吸收带的垂直电子转移激发能，λ，和电子耦合，V-J，通过模拟，使用振动耦合理论确定。溶剂和λ的振动成分之间的分配是假设与电子转移耦合的振动模式的平均能量hv（v）为3.15 kcal/ mol（1100 cm（-1））。所观察到的速率常数内插到298 K的系数为4.7-5.8，大于从电子振动耦合理论分析的电荷转移带，k（cal），在乙腈和DMF中的电子转移参数计算得到的系数，对于sB 6 σ（+）在CH 2Cl 2中的系数为2.5。在CH 3CN和DMF中，k（ESR）（350）/k（ESR）（250）比k（cal）（350）/k（cal）（250）大1.0-1.6倍，在CH 2Cl 2中大0.9倍。与双-二氮鎓的理论一致性远好于双四σ键连接的双-肼自由基阳离子（J. Am.化学分析1997，119，2000）。双二氮鎓（6.5-7.6）的电子振动耦合常数S = lambda（v）/h（v）明显小于双肼（13.6-17.5）的耦合常数，这可能是理论与实验不一致的主要原因。
Rate constants k(ESR) for intramolecular electron transfer between the reduced and oxidized diazene units of dimeric 2-tert-butyl-2,3-diazabicyclo[2.2.2]octyldiazenium radical cations cations which are doubly linked through the bicyclic units by six a-bonds, sB6 sigma(+) and aB6 sigma(+), were determined from their variable temperature ESR spectra in CH3CN, dimethylformamide, and CH2Cl2. These cations show solvent-sensitive charge transfer absorption bands from which the vertical electron transfer excitation energy, lambda, and the electronic coupling, V-J, were determined by simulation, using vibronic coupling theory. The partitioning between solvent and vibrational components of lambda were made assuming that the average energy of the vibrational modes coupled to the electron transfer, hv(v), is 3.15 kcal/ mol (1100 cm(-1)). The observed rate constants interpolated to 298 K are factors of 4.7-5.8 larger than those calculated from the electron transfer parameters obtained from vibronic coupling theory analysis of the charge transfer bands, k(cal), in acetonitrile and DMF, and for sB6 sigma(+) in CH2Cl2 the factor is 2.5. The ratios k(ESR)(350)/k(ESR)(250) are 1.0-1.6 times larger than k(cal)(350)/k(cal)(250)in CH3CN and DMF and 0.9 times larger in CH2Cl2. The agreement with theory for the bis-diazeniums is far better than that obtained for doubly four sigma-bond-linked bis-hydrazine radical cations (J. Am. Chem. Sec. 1997, 119, XXXX). It is suggested that the significantly smaller vibronic coupling constants S = lambda(v)/h(v) for the bis-diazeniums (6.5-7.6) compared to those of the bis-hydrazines (13.6-17.5) might be principally responsible for the difference in agreement of theory with experiment.