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Stabilization of Triplet Diphenylcarbene by Ortho Aryl Groups

邻位芳基对三重态二苯基碳烯的稳定作用

基本信息

批准号：
16550034
负责人：
HIRAI Katsuyuki
金额：
$ 2.18万
依托单位：
Mie University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2005
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-16550034/
关键词：
diazo compound triplet carbene laser flash photolysis steric protection electron spin resonance matrix isolation

项目摘要

Diphenyldiazomethanes (DDMs) having phenyl groups at the ortho positions were prepared and the corresponding diphenylcarbenes photolytically generated from them were characterized not only by product analysis 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 the corresponding fluorenes are formed almost exclusively. Fluorene is most likely produced by the attack of singlet carbene on an ortho carbon of the phenyl substituent to generate isofluorene, followed by 1,5-H shift. Irradiation of the phenylated DDMs in a 2-methyltetrahydrofuran (2-MTHF) matrix at 77 K gave ESR signals ascribable to triplet carbenes. UV/vis spectra of the triplet carbenes were obtained by irradiating the DDMs under identical conditions. However, laser flash photolysis of the DDMs 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. Essentially the same transient band was observed in LFP of the corresponding fluorene. The LFP of the phenylated DDM in non-degassed benzene gave transient absorption bands ascribable to triplet carbene and the corresponding carbonyl oxide. The quenching rate constant of the triplet carbene by oxygen and the lifetime of the triplet carbene in the absence of oxygen were 1.9 x 10^7 M^<-1>s^<-1> and 16 μs, respectively. Similar studies with DDMs having 4-biphenylyl, 3,5-bis (trifluoromethyl) phenyl, 2-fluorophenyl, and 4-pyridyl groups gave essentially identical results, indicating that those substituents exhibit little effect on overall reaction pathway. From those studies, it is suggested that the triplet carbenes are also trapped by the ortho-phenyl ring to give eventually fluorenes.

制备了邻位含苯基的二苯基重氮甲烷（DDMs），并通过产物分析、ESR和UV/维斯光谱表征了它们在低温刚性有机基质中的光解反应，以及在室温溶液中的激光闪光光解反应.产物分析表明，相应的芴几乎完全形成。芴最有可能是通过单重态卡宾攻击苯基取代基的邻位碳以生成异芴，然后进行1，5-H位移而产生的。在2-甲基四氢呋喃（2-MTHF）矩阵在77 K下照射的苯基化的DDMs给出归因于三重态卡宾的ESR信号。三重态卡宾的UV/维斯光谱通过在相同条件下照射DDMs获得。然而，DDMs在脱气苯在室温下的激光闪光光解显示出瞬态吸收带完全不同的光解中观察到的2-MTHF矩阵在77 K。在相应芴的LFP中观察到基本相同的瞬态谱带。苯化DDM在未脱气的苯中的LFP给出了归因于三重态卡宾和相应的羰基氧的瞬态吸收带。氧对三重态卡宾的猝灭速率常数和无氧条件下三重态卡宾的寿命分别为1.9 × 10^7 M^<-1>s^<-1>和16 μs。用具有4-联苯基、3，5-双（三氟甲基）苯基、2-氟苯基和4-吡啶基的DDM进行的类似研究给出了基本上相同的结果，表明这些取代基对整个反应途径几乎没有影响。从这些研究中，有人建议，三重态卡宾也被捕获的邻苯基环，最终得到芴。