Novel Type of Aromatic Silicon Compound, Experiment & Theory

用两个硅原子取代两个碳原子，通过影响所有这三个因素来减小能隙。首先，据估计，硅取代苯的芳香性不如苯。其次，硅可以很容易地采用大约90ﾟ的角度，而C基本上更喜欢四面体的角度。第三，与Si=C或Si=Sipi键相比，Si更倾向于形成Si-C和Si-Si单键。计算表明，1，4-二硅苯比杜瓦式更稳定，但热差比苯小得多。B3LYP计算表明，9，10-二硅杂菲(SA)的稳定性比杜瓦异构体差-12.1kcal/mol。在全碳体系(20kca1/mol)和二硅铝体系(26kcal/mol)中，芳香族对杜瓦异构体相对稳定性的变化规律相似。SA具有C2H对称性，其中中心的二硅苯环采用略微非平面的椅型结构(Si-C-C-Si二面角为5.5ﾟ)。这是Con…更符合这一环中较小程度的芳香性。SA的平面形式(即具有d2h对称性)是连接两个同分异构体C2H-极小值的过渡态，但其能量仅高0.02kcal/mol，表明SA本质上是一个平面分子。我们强调了硅和碳之间的相似性。相应的双硅环丙烯可生成二硅苯、杜瓦硅苯、硅苯瓦烯和硅丙烷。3，3‘-双环丙烯(BC)在L50ﾟC下热分解得到重排产物苯并戊烯(82%)。它可以被认为是中间体杜瓦苯和1，4-二硅苯的初始形成和随后的苯并茂的异构化。为了评价BC的稳定性，通过6-3lg^&lt；**&gt；分子轨道计算确定了相应的价异构体的相对能量。因此，苯并二硅苯和杜瓦苯具有相似的能级，其稳定性略低于1，4-二硅苯。由于大的基组和电子相关性的包含通常倾向于三环而不是双环或单环的几何构型可能具有非常相似的能量；稳定性顺序甚至可能颠倒。实际上，甲基取代的BC是以杜瓦硅苯的形式排列的。然而，在该反应条件下未分离出二硅苯。由二氢-9，10-二硅杂菲与锂反应生成的SA二聚体与过量的锂或钾反应生成了9，10-碱-9，10-二硅杂菲。在α，omega-二氯聚硅烷处理下，二阴离子被转化为相应的环状硅化合物。二阴离子与电子受体反应生成SA二聚体，在二苯乙炔存在下生成[2+4]加成产物。结果表明，二阴离子氧化过程可生成SA。较少

The replacement of two carbon atoms by two silicon atoms reduces the energy gap by influence all three factors. First, silasubstituted benzenes are estimated to be less aromatic than benzene. Second, silicon can easily adopt angles of around 90ﾟ while C prefers essentially tetrahedral angles. Third, Si prefers to form Si-C and Si-Si single bonds over Si=C or Si=Si pi bonds. The calculations reveal that 1,4-disilabenzene is more stable than its Dewar form but the enthalpy difference is much small than for benzene. The B3LYP calculations show that 9,10-disilaanthracene (SA) is less stable than the Dewar isomer by -l2.1 kcal/mol. The change in relative stability of the aromatic vs.the Dewar isomer is similar on going from benzene to anthracene in the all carbon system (20kca1/mol) and in the disila-systems (26 kcal/mol). SA possesses C2h-symmetry, in which the central disilabenzene ring adopts a slightly nonplanar chair-type structure (with a Si-C-C-Si dihedral angle of 5.5ﾟ). This is con … More sistent with the smaller degree of aromaticity in this ring. The planar form of SA (i.e., possessing D2h -symmetry) is a transition state that connects the two isomeric C2h-minima, but it is by only 0.02kcal/mol higher in energy, suggesting that SA is essentially a planar molecule. We underlined the similarities between silicon and carbon. The formation of disilabenzene as well as Dewar-silabenzene, silabenzvalene, and silaprismane could be obtained from corresponding bissilayclopropenes. Thermolysis of 3,3'-biscyclopropenyl (BC) at l50ﾟC afforded the rearranged product benzvalene (82%). It could be considered the initial formation of an intermediate either Dewar benzene and 1,4-disilabenezene and their subsequent isomerization to benzvalene.To evaluate the stabilities of BC,the relative energies of the corresponding valence isomers were determined by 6-3lG^<**> molecular orbital calculations. As a result, the benzvalene and the Dewar benzene have similar energy levels and are slightly less stable than 1,4-disilabenzene. Since large basis sets and inclusion of electron correlation generally tend to favor tricyclic over bicyclic or monocyclic geometries may have quite similar energies ; the stability order may even be reversed. Actually, methyl substituted BC arranged to Dewar-silabenzene. However, disilabenzene was not isolated under the reaction conditions. SA dimer prepared from the reaction of dihydro-9,10-disilaanthracene with lithium was treated with excess lithium or potassium resulted in formation of the 9,10-alkali-9,10-disilaanthracene. On treatment with a, omega-dichloropolysilanes, the dianion was converted into the corresponding cyclic silicon compounds. Oxidation of dianion with electron acceptors gave the SA dimer and in the presence of diphenylacetylene gave [2+4] addition product. The results show that SA could be generated from dianion oxidation process. Less