Magnetic Field Effects on Chemical Reactions of Organometallic Compounds

点击翻译按钮获取中文摘要

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.