Reversible σ-Dimerizations of Persistent Organic Radical Cations
Reversible σ-Dimerizations of Persistent Organic Radical Cations
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DOI：
10.1002/anie.201207412
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发表时间：
2013-01-01
影响因子：
16.6
通讯作者：
Power, Philip P.
中科院分区：
文献类型：
--
作者：
Chen, Xiaoyu;Wang, Xingyong;Power, Philip P.
CÀC 键的形成和断裂是有机化学中的基本事件。涉及 CÀC 偶联的共轭芳族体系的氧化 σ-二聚在有机合成中起着至关重要的作用，[1] 例如氧化寡聚和聚合，[2] 其中 σ-二聚二聚体被认为是关键中间体。[2-4] 快速扫描循环伏安法和 NMR 光谱研究表明溶液中存在双电荷 σ-二聚体。[3] Effenberger 及其同事于 1969 年成功分离出 1, 3, 5-三吡咯烷苯二聚体 σ- 络合二聚体，并证明了 σ-二聚体在固态下的存在。 [4]随后分离出了更多二聚体复合物的例子。 [5]然而，在之前报道的氧化二聚化过程中，由于自由基阳离子的寿命较短，尚未被直接观察到并得到充分证实。[4, 5]事实上，在固态下观察到的π共轭体系持久[6]自由基阳离子的二聚结构都是π二聚体。[3b,7,8]另一方面，多氟烷氧基铝酸盐超弱阴离子[Al(ORF)4]À (ORF= OC (CF3) 3) 已被证明不仅可以通过氟-阳离子接触使正电荷离域来稳定有趣的阳离子物种，而且由于其半径较大，还可以增加形成的盐的溶解度。[9a, b] 通过使用这种阴离子，我们最近成功分离了
CÀC bond formation and cleavage are basic events in organic chemistry. The oxidative σ-dimerization of conjugated aromatic systems involving CÀC coupling plays an essential role in organic syntheses,[1] such as oxidative oligo-and polymerization,[2] where a σ-dimeric dication is suggested as a key intermediate.[2–4] Fast-scan cyclic voltammetry and NMR spectroscopic studies have suggested the existence of a doubly charged σ-dimeric species in solution.[3] Effenberger and co-workers succeeded in isolating a dimeric σ-complexed dication of 1, 3, 5-tripyrrolidinobenzene in 1969 and proved the existence of the σ-dimer in the solid state.[4] More examples of dimeric complexes have been isolated subsequently.[5] In the previously reported oxidative dimerizations, however, the radical cations have not been directly observed and well confirmed owing to their short lifetime.[4, 5] In fact, all of the dimerized structures of persistent [6] radical cations of πconjugated systems observed in the solid state are πdimers.[3b, 7, 8]On the other hand, the polyfluoroalkoxy aluminate superweak anion [Al (ORF) 4] À (ORF= OC (CF3) 3) has been shown to be effective not only in stabilizing intriguing cationic species by delocalization of their positive charges through fluorine–cation contacts, but also in increasing solubility of formed salts owing to its large radius.[9a, b] By using this anion, we recently have successfully isolated radical cations of