Triplet diphenylcarbenes protected by o-Aryl groups.
Triplet diphenylcarbenes protected by o-Aryl groups.
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DOI：
10.1021/ja047738r
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发表时间：
2004-09
影响因子：
15
通讯作者：
Kyoko Monguchi;T. Itoh;Katsuyki Hirai;H. Tomioka
中科院分区：
文献类型：
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作者：
Kyoko Monguchi;T. Itoh;Katsuyki Hirai;H. Tomioka
合成了邻位含苯基的二苯基重氮甲烷(2a-N(2))，并用传统的产物分析方法表征了它们光解生成的二苯基卡宾(2a)，还用低温刚性有机基质中的ESR和UV/Vis光谱以及室温溶液中的激光闪光光解对其进行了表征.产物分析表明，荧烯4a几乎完全形成。荧烯很可能是通过单线态卡宾(1)2a攻击苯基取代基的邻位碳生成异荧烯，然后1，5-H移动而产生的。在77K下，2a-N(2)在2-甲基四氢呋喃(2-MTHF)基质中的ESR信号可归因于三重态卡宾((3)2a)。在相同的条件下，用2a-N(2)辐照得到了(3)2a的UV/Vis光谱。在室温下，2a-N(2)在脱气苯中的激光闪光光解表现出与77K下2-甲基四氢呋喃基质中的光解完全不同的瞬时吸收峰，瞬时吸收带呈一级衰减，速率常数为7.6x10(4)S(-1)，这一现象不受邻苯基氢的氚取代的抑制。在荧烯4a的LFP中也观察到了基本相同的暂态带。2a-N(2)在非脱气苯中的LFP给出了可归因于三重卡宾(3)2a和相应的羰基氧化物的瞬时吸收带。通过绘制(3)2a生成的准一级速率常数与氧浓度的关系图，估算了氧猝灭(3)2a的速率常数和(3)2a在无氧条件下的寿命。它们分别为1.9×10~(-7)M(-1)、S(~(-1))和16微米。对于邻苯环上有一系列取代基(4-Ph，3，5-(Cf(3))(2)和2-F)的二苯基重氮甲烷进行了类似的研究，得到了基本相同的结果，表明这些取代基对整个反应路径几乎没有影响。从这些研究表明，三重卡宾(3)2也被邻苯环捕获，最终得到荧烯。
Diphenyldiazomethanes (2a-N(2)) having phenyl groups at the ortho positions were prepared and the corresponding diphenylcarbenes (2a) photolytically generated from them were characterized not only by the traditional product analysis method but also by ESR and UV/vis spectroscopy in a rigid organic matrix at low temperature and in laser flash photolysis in solution at room temperature. Product analysis indicated that fluorenes 4a are formed almost exclusively. Fluorene is most likely produced by the attack of singlet carbene (1)2a on an ortho carbon of the phenyl substituent to generate isofluorene, followed by 1,5-H shift. Irradiation of 2a-N(2) in a 2-methyltetrahydrofuran (2-MTHF) matrix at 77 K gave ESR signals ascribable to triplet carbenes ((3)2a). UV/vis spectra of (3)2a were obtained by irradiating 2a-N(2) under identical conditions. However, laser flash photolysis (LFP) of 2a-N(2) in degassed benzene at room temperature showed transient absorption bands completely different from those observed in photolysis in the 2-MTHF matrix at 77 K. The transient band decayed in first-order with a rate constant of 7.6 x 10(4) s(-1), which was not retarded by deuterium substitution of o-phenyl hydrogens. Essentially the same transient band was observed in LFP of fluorene 4a. The LFP of 2a-N(2) in nondegassed benzene gave transient absorption bands ascribable to triplet carbene (3)2a and the corresponding carbonyl oxide. The quenching rate constant of (3)2a by oxygen and the lifetime of (3)2a in the absence of oxygen were estimated by plotting the observed pseudo-first-order rate constant of the formation of the carbonyl oxide against the concentration of oxygen. They were 1.9 x 10(7) M(-1)s(-1) and 16 micros, respectively. Similar studies with diphenyldiazomethanes having a series of substituents (4-Ph, 3,5-(CF(3))(2), and 2-F) on the ortho-phenyl rings gave essentially identical results, indicating that those substituents exhibit little effect on overall reaction pathway. From those studies, it is suggested that triplet carbenes (3)2 are also trapped by the ortho-phenyl ring to give eventually fluorenes.