Magnetic Field Effects on Chemical Reactions of Organometallic Compounds

磁场对自由基对和双自由基化学反应的影响已被广泛研究。然而，关于硅、S、锗和锡等含有比Ne更重的原子的自由基的影响的报道很少。最近，我们发现芳基和/或烷基取代基14元素(Si或Ge)化合物在环己烷中的光解产生14族元素中心自由基，芳基取代锗的光解是通过它们的三重激发态进行的。因此，我们研究了磁场对四苯基硅烷、四苯基锗、甲基三苯锗和二甲基二苯锗在Briji 35胶束溶液和油乳剂中分解的影响。我们用激光闪光光解技术发现，随着磁场从0T增加到1T，产生的三重态自由基对的寿命缩短了52-80%，逃逸自由基产率增加了5-18%。这是第一次直接观察到磁场对Germyl自由基动力学行为的影响。这些效应可以用超精细机制和弛豫机制相结合来解释。我们还研究了六甲基二硅烷和芳香腈之间的光诱导电子转移反应的磁场效应。对于对二氰基苯和邻二氰基苯，随着电场从0T增加到1.35T，逃逸阴离子的产率分别增加了23%和18%。对于1，2，4，5-四氰基苯和9，10-二氰基苯，由于生成的自由基离子对具有较高的电子亲和力而不能发生背电子转移，因此没有观察到磁场效应。

Magnetic field effects on chemical reactions through radical pairs and biradicals have been studied extensively. There have been few reports, however, on the effects of radicals involving heavier atoms than Ne such as Si, S, Ge, and Sn. Recently, we have found that the photolysis of aryl and/or alkyl substituted group 14 element (Si or Ge) compounds in cyclohexane gives group 14 element centered radicals and that the photodecomposition of aryl substituted germanes occurs through their triplet excited states.Thus, we have studied the magnetic field effects on the decomposition of tetraphenyl silane, tetraphenyl germane, methyltriphenyl germane, and dimethyldiphenyl germane in Briji 35 micellar solution and oil emulsion. We have found with the aid of a laser flash photolysis technique that the lifetimes of the generated triplet radical pairs decrease by 52-80 % with increasing magnetic field from 0 T to 1 T, and that the yields of the escaping radicals increase by 5-18 %. This is the first direct observation of the magnetic field effect on the dynamic behavior of germyl radicals. These effects can be explained by a combination of the hyperfine and relaxation mechanisms.Magnetic field effects have also been studied for the photoinduced electron transfer reactions between hexamethydisilane and aromatic nitriles. For p- and o-dicyanobenzenes, the yields of the escaping anion radicals increase by 23 and 18 %, respectively, with increasing field from 0 T to 1.35 T. For 1, 2, 4, 5-tetracyanobenzene and 9, 10-dicyanoanthracene, no magnetic field effect has been observed, because the back electron transfer from the generated radical ion pairs cannot occur on account of their high electron affinities.