Reversible Transformation of a Stable Monomeric Silicon(II) Compound into a Stable Disilene by Phase Transfer: Experimental and Theoretical Studies of the System {[(Me3Si)2N](Me5C5)Si}n with n=1,2
Reversible Transformation of a Stable Monomeric Silicon(II) Compound into a Stable Disilene by Phase Transfer: Experimental and Theoretical Studies of the System {[(Me3Si)2N](Me5C5)Si}n with n=1,2
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DOI：
10.1021/ja902153u
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发表时间：
2009-09-02
影响因子：
15
通讯作者：
Rozhenko, A. B.
中科院分区：
文献类型：
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作者：
Jutzi, Peter;Mix, Andreas;Rozhenko, A. B.
(eta(5)-五甲基环戊二烯基)硅(II)四(五氟苯基)硼酸盐(5)在-78℃下与二(三甲基甲硅烷基)氨基锂在二甲氧基乙烷(DME)溶剂中反应，定量得到无色粘稠状化合物[双(三甲基甲硅烷基)氨基][五甲基环戊二烯基]硅(11)6A油。在-40℃下进行的反应生成硅(IV)化合物7，它是6A与DME的正式氧化加成产物。在 6A 与 2,3-二甲基丁二烯的反应中观察到环加成反应，得到硅（IV）化合物 8。尝试从己烷、THF 或甲苯等有机溶剂中结晶 6A 时，得到深黄色化合物反式-1, 2-双[双（三甲基甲硅烷基）氨基]-1,2-双（五甲基环戊二烯基）二硅烯（6B），它是如图6A所示，从无色溶液中结晶，但仅在几天甚至几周后才结晶。当尝试将二硅烯6B溶解在所述有机溶剂中时，在长时间剧烈摇动或超声处理后获得无色溶液。溶剂蒸发后可从该溶液中回收纯6A。这个转变过程可以重复多次。在6B的质谱研究中，观察到Si=Si键断裂，给出具有6A组成的分子离子作为具有最高质量的片段。二硅烯 6B 的 X 射线晶体结构分析支持具有短 Si=Si 键（2.168 埃）的分子，该分子具有有效堆积的刚性 σ 键环戊二烯基取代基和甲硅烷基氨基。后者的构象不允许向中心硅原子提供电子。密度官能团水平（RI-BP86 和 B3LYP、TZVP 基组）的理论计算证实了 6B 的结构，并揭示了亚硅基 6A 存在 eta(2) 键合的环戊二烯基配体和处于防止电子回馈构象的甲硅烷基氨基。对硅(II)化合物6A、二硅烯6B以及源自6A的两种物质11和11（星形）（源自Si=Si键断裂）的进一步理论计算支持了实验结果。 6A和6113之间的可逆相依赖转变是由(a) 6A和6B中的五甲基环戊二烯基团施加的不同立体电子和空间效应引起的，(b) 6B的固态结构中的一些能量存储(盒子中的分子杰克)，(c) 6A和6B之间的小能量差，(d)平衡过程的低活化势垒，以及(e)单体形成后熵增加。
The salt (eta(5)-pentamethylcyclopentadienyl)silicon(II) tetrakis(pentafluorophenyl)borate (5) reacts at -78 degrees C with lithium bis(trimethylsilyl)amide in dimethoxyethane (DME) as solvent to give quantitatively the compound [bis(trimethyl silyl)amino] [pentamethylcyclopentadienyl]silicon (11) 6A in the form of a colorless viscous oil. The reaction performed at -40 degrees C leads to the silicon(IV) compound 7, the formal oxidative addition product of 6A with DME. Cycloaddition is observed in the reaction of 6A with 2,3-dimethylbutadiene to give the silicon(IV) compound 8. Upon attempts to crystallize 6A from organic solvents such as hexane, THF, or toluene, the deep yellow compound trans-1, 2-bis[bis(trimethylsilyl)ami no]-1,2-bis(pentamethylcyclopentadienyl)disilene (6B), the formal dimer of 6A, crystallizes from the colorless solution, but only after several days or even weeks. Upon attempts to dissolve the disilene 6B in the described organic solvents, a colorless solution is obtained after prolonged vigorous shaking or ultrasound treatment. From this solution, pure 6A can be recovered after solvent evaporation. This transformation process can be repeated several times. In a mass spectroscopic investigation of 6B, Si=Si bond cleavage is observed to give the molecular ion with the composition of 6A as the fragment with the highest mass. The X-ray crystal structure analysis of the disilene 6B supports a molecule with a short Si=Si bond (2.168 angstrom) with efficiently packed, rigid sigma-bonded cyclopentadienyl substituents and silylamino groups. The conformation of the latter does not allow electron donation to the central silicon atom. Theoretical calculations at the density functional level (RI-BP86 and B3LYP, TZVP basis set) confirm the structure of 6B and reveal for silylene 6A the presence of an eta(2)-bonded cyclopentadienyl ligand and of a silylamino group in a conformation that prevents electron back-donation. Further theoretical calculations for the silicon(II) compound 6A, the disilene 6B, and the two species 11 and 11(star) derived from 6A (which derive from Si=Si bond cleavage) support the experimental findings. The reversible phase-dependent transformation between 6A and 6113 is caused by (a) different sterecielectronic and steric effects exerted by the pentamethylcyclopentadienyl group in 6A and 6B, (b) some energy storage in the solid state structure of 6B (molecular jack in the box), (c) a small energy difference between 6A and 6B, (d) a low activation barrier for the equilibration process, and (e) the gain in entropy,upon monomer formation.