Intramolecular and intermolecular reactivity of localized singlet diradicals: The exceedingly long-lived 2,2-diethoxy-1,3-diphenylcyclopentane-1,3-diyl
Intramolecular and intermolecular reactivity of localized singlet diradicals: The exceedingly long-lived 2,2-diethoxy-1,3-diphenylcyclopentane-1,3-diyl
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DOI：
10.1021/ja992507j
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发表时间：
2000-03-08
影响因子：
15
通讯作者：
Zhang, XY
中科院分区：
文献类型：
--
作者：
Abe, M;Adam, W;Zhang, XY
二乙氧基取代的二氮烯3在非质子性溶剂(如正己烷、苯和乙腈)中直接和二苯甲酮敏化的光脱氮反应，通过中间体2，2-二乙氧基-1，3-二苯基环戊烷1，3-二基二自由基2b得到了唯一的环己烷4。在甲醇存在下，通过捕获烯丙基阳离子5竞争形成加合物6。双氮烯3的激光-闪光光解实验证实了中间体的干预作用。双基中间体在545 nm处具有强的瞬时吸收，在微秒范围内衰减为一级寿命。双自由基寿命依次为正己烷(0.52亩S)、苯(0.88亩S)、乙腈(1.01亩S)、氯仿(3.73万亩S)。以2，2-二乙氧基-1，3-二苯基-L，3-环戊二基为模型，通过对2，2-二乙氧基-1，3-二苯基-2，2-二乙氧基-1，3-二苯基-2，2-二乙氧基-1，3-二苯基-2，2-二乙氧基-1，3-二苯基-2，2-二乙氧基-1，3-二苯基-2，3-二苯基-2，3-环戊二基的(UB3LYP/6-31G~(**))的计算，提出了2，2-二乙氧基-1，3-二苯基2b的单重态基态。没有观察到外部添加剂，如烯烃、二烯和TEMPO对1，3-二自由基2b的捕获作用。在质子型溶剂中，随着酸度的增加，双自由基寿命缩短，如在醋酸中寿命降至70 ns。此外，还发现在酸性溶剂中伴随有一个470 nm处的附加瞬变峰，它被归属为烯丙基阳离子5。讨论了影响局域单重态二自由基2b分子内和分子间化学反应活性的因素。
The direct and benzophenone-sensitized photodenitrogenation of the diethoxy-substituted diazene 3 in nonprotic solvents, e.g. n-hexane, benzene, and acetonitrile, afforded exclusively the housane 4 through the intermediary 2,2-diethoxy-1,3-diphenylcyclopentane 1,3-diyl diradical 2b. Alternatively, in the presence of methanol, the formation of the adduct 6 competed through trapping of the allylic cation 5. The intervention of the intermediates was corroborated by laser-flash photolysis experiments of the diazene 3. The diradical intermediate was characterized by its strong transient absorption at 545 nm, which decayed with a first-order lifetime in the microsecond range. The diradical lifetimes increased in the order n-hexane (0.52 mu s), benzene (0.88 mu s), acetonitrile (1.01 mu s), and chloroform (3.73 mu s). The singlet ground state of the 2,2-diethoxy-substituted 1,3-diradical 2b is suggested by the absence of EPR signals at,low temperature, the lack of quenching by molecular oxygen, and the calculated (UB3LYP/6-31G*) singlet preference of ca. 4 kcal mol(-1) for 2,2-dihydroxy- 1,3-diphenyl-l,3-cyclopentanediyl as a model. Trapping of the 1,3-diradical 2b by external additives, e.g., olefins, dienes, and TEMPO, was not observed. In protic solvents, a decrease of the diradical lifetimes with increasing acidity was noted, e.g., the lifetime in acetic acid dropped to 70 ns. Moreover, a concomitant growth of an additional transient at 470 nm was found in acidic solvents, which was assigned to the allylic cation 5. The factors governing the intramolecular and intermolecular chemical reactivity of the localized singlet diradical 2b are discussed.