Generation of Unsaturated silicon species from acylpolysianes and investigation on their chemical behaviors

1.酰基聚硅烷的异构化反应在硅化学中具有重要意义，是一种生产硅烯的简便方法。然而，人们对异构化的机理知之甚少。为了了解反应机理，我们测定了不同取代基聚硅烷的热异构化反应动力学参数，分别为ΔH^≠=25.7-29.3kcal molt；-1&gt；和ΔS^≠=-11.5-17.5cal molt；-1&gt；负大的活化内窥量和在羰基碳上引入一个吸电子基团促进了异构化，清楚地表明了分子内的协同机制。模型体系的分子轨道计算也表明了四中心过渡态。酰基聚硅烷与2，3-二甲基丁二烯反应时，热生成的硅烯总是以[2+4]加合物为主。此外，在羰基碳上含有芳基的酰基聚硅烷中的硅烯作为次要产物生成了烯加合物。2.研究了2，2-二(酰基)三硅烷和1，2-二(酰基)二硅烷的热异构化反应，发现这些反应生成了硅烯中间体。

1.Isomerization of acylpolysilanes of importance in silicon chemistry as a convenient method to produce silenes. However, little is known for the mechanism of the isomerization. To know about the mechanism, we determined the kinetic parameters of the thermal isomerization of variously substituted acylpolysilanes, as being ΔH^≠=25.7-29.3 kcal mol^<-1> and ΔS^≠=-11.5--17.5 cal mol^<-1> K^<-1>. The negatively large activation entoropies and the fact that introduction of an electron-withdrawing group on the carbonyl carbon facilitated the isomerization, clearly indicated the intramolecular concerted mechanism. The molecular orbital calculations on a model system also suggested the four-centered transition state. The silenes thermally generated from acylpolysilanes always gave [2+4] adducts as the major products by the reactions with 2,3-dimethylbutadiene. In addition to these, silenes from acylpolysilanes bearing an aryl group on the carbonyl carbon gave ene-adducts as the minor products. However, in contrast to this, silenes from alkyl-substituted acylpolysilanes afforded [2+2] cycloadducts as the minor products.2.Thermal and photocheical isomerization of 2,2-bis(acyl)trisilanes and 1,2-bis(acyl)disilanes was investigated, and it was found that these reactions gave products arising from silene intermediates.