Synthesis of 1-ethyl-l,2,2-trimethyl-l,2-disilacyclobutane and its spontaneous polymerization and copolymerization with 1,1,2,2 -tetramethyl-1,2 -disilacyclobutane

Dehalogenation of 1-[(chloro)(ethyl)(methyl)silyl]-2-[chloro(climethyl)silyl]ethane with the alkali metal vapors gave l-ethyl-l,2,2-trimethyl-1,2-disilacyclobutane. Its spontaneous ring-opening polymerization at room temperature afforded an amorphous linear polymer with T _g = −75 °C, M _w = 454 200–512 800, and M _w/M_n = 1.87–2.82. According to NMR data, the backbone of the polymer consists of alternating monomeric units linked in the “head-to-tail” (SiMe ₂CH₂CH₂SiMeEtSiMe₂CH₂CH₂SiMeEt) and “head-to-head” ways (SiMeEtCH₂CH₂SiMe₂SiMe₂CH₂CH₂SiMeEt) in a ratio of 1: 0.96. Spontaneous copolymerization of the above disilacyclobutane with 1,1,2,2-tetramethyl-l,2-disilacyclobutane gave partially crystalline copolymers with different glass transition and melting temperatures, depending on the ratio of the components in the reaction mixture. The compositions of the copolymers were examined by ¹H, ¹³C, and ²⁹Si NMR spectroscopy.     

1,1,2,2-四甲基-1,2-二氯二硅烷裂解机理的研究

利用量子化学知识对典型的二硅烷高沸物1,1,2,2-四甲基-1,2-二氯二硅烷的裂解机理进行理论研究。结果表明,在无催化剂和常温常压下,1,1,2,2-四甲基-1,2-二氯二硅烷以CHCl3作为裂解气的反应分为两步进行,均为放热反应,其速控步第一步的正反应活化能为352.949kJ/mol。     

三氯化铝催化1,1,2,2-四甲基-1,2-二氯二硅烷的裂解机理研究

采用DFT和MP2方法对1,1,2,2-四甲基-1,2-二氯二硅烷的催化裂解机理进行了研究. 结果表明, 催化剂三氯化铝先与二硅烷反应, 生成中间产物后再与裂解气三氯甲烷作用并生成产物. 反应分3步进行, 各步活化能分别为: 152.543, 79.322和128.889 kJ•mol^－1. 速控步为第一步反应, 3步的焓变分别为: 83.785, －275.771和－120.712 kJ•mol^－1, 总焓变为－312.698 kJ•mol^－1, 即为放热的. 反应的标准摩尔吉布斯自由能为－306.462 kJ•mol^－1, 裂解反应的平衡常数 ＝4.9295×10⁵³, 在常温常压下反应的理论产率较高, 与实验结果一致.     

Counterattack reagents:hexamethyldisilane and 1,2-dimethyl-1,1,2,2-tetraphenyldisilane in the synthesis of polysilylated hydrazines

Polysilylated hydrazines have wide applicability. It is tedious to prepare these compounds by classic means. However, using hexamethyldisilane and 1,2-dimethyl-1,1,2,2-tetraphenyldisilane as counterattack reagents, we synthesized polysilylated hydrazines under alkaline conditions in good to excellent yields. This one-pot method is expedient and more efficient than other procedures. Polysilylated hydrazines were found to react with aldehydes or ketones in the presence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate to give the corresponding hydrazones under anhydrous conditions.     

A Retro-Diels Alder route to Tetramethyldisilene Me2Si=SiMe2 revisited: Flow Pyrolysis of 1,1,2,2-Tetramethyl-1,2-disilacyclohex-4-ene

Reinvestigation of the flow pyrolysis of 1,1,2,2-tetramethyl-1,2-disilacyclohex-4-ene did not identify conditions under which the retro-Diels Alder reaction was the exclusive process. Extrusion of Me₂Si=SiMe₂was confirmed, but dimerization of directly extruded Me₂Si: contributes significantly to its formation. Rearrangement of 1,1,2,2-tetramethyl-1,2-disilacyclohex-4-ene to 1,1,3,3-tetramethyl-1,3-disilacyclohex-4-ene is a major process under a variety of conditions. Computational studies reduced the number of viable pathways. Both experimental and computational results point to stepwise extrusion of Me₂Si=SiMe₂ via a diradical intermediate and to linkage by one or more common intermediates of the extrusion pathway and the pathway leading to rearranged disilacyclohexene. Such a mechanism receives support from the formation of 1,2- and 1,3-disilacyclohex-4-enes, that is both the Diels-Alder product and the rearrangement product, in the addition of Me₂Si=SiMe₂ to butadiene. Dedicated to Professor Mitsuo Kira on the occasion of his being honored for his inspiring work as the recipient of the 2005 Wacker Silicon Award.     

Synthesis and ionic polymerization of 1,2-epoxy-3-nitropropane

The synthesis of 1,2-epoxy-3-nitropropane (ENP) was improved so that this monomer could be obtained in a pure, stable form with an acceptable yield. Anionic polymerization even using milder conditions causes isomerization of ENP into nitroallylic alcohol. Cationic polymerization using a classical initiator produces a mixture of compounds of low molecular weight. We have studied in detail the cationic polymerization of ENP in the presence of a diol such as ethylene glycol (“Activated Monomer Mechanism”): only the first two steps follow this latter, but a competitive mechanism takes over rapidly which limits severely the molecular weight of the products: this mechanism was analyzed.     

Ruthenium-catalyzed cycloisomerization of 1,1,2,2-tetramethyl-1,2-divinyldisilane: Selective formation of a five-membered silacycle

The cycloisomerization of 1,1,2,2-tetramethyl-1,2-divinyldisilane (1) in the presence of ruthenium-diphosphine complexes has been examined. A ruthenium-dppe (8) or a ruthenium-dppv (12) complex selectively catalyzed the reaction and 1,1,2,3,3-pentamethyl-1,3-disilycyclopent-4-ene (3) was isolated as the major product. The reaction was also carried out in the presence of a deuterated ruthenium-PⁱPr₃ complex and the incorporation of deuterium to 1,1,4,4-tetramethyl-1,4-disilacyclohex-2-ene (2) was observed. The mechanism of this reaction has been proposed.     

Synthesis and oxidation of 1,1,2,2-tetramethyl-3,4,5,6-tetraphenyl-1,2-disila-3,4-cyclohexadiene

The synthesis of 1,1,2,2-tetramethyl-3,4,5,6-tetraphenyl-1,2-disila-3,4-cyclohexadiene, (I), from 1,4-dilithiotetrapheynylbutadiene and 1,2-dichlorotetramethyldisilane is described. (I) is reluctant to react with singlet oxygen, in contrast to its carbon analogue, but the SiSi bond of(I) is readily oxidized to give 2,2,7,7-tetramethyl- 3,4,5,6-tetrapheynyl-1-oxo-2,7-disila-3,5-cycloheptadiene. The mechanism of the formation of this siloxane is discussed, and a peroxy radical shown to act as an important intermediate in the oxidation.     

Silicon-carbon unsaturated compounds: XXXIX. Photolysis of 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobutene

Photolysis of 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobutene gives a silene which can be trapped by t-butyl alcohol and acetone in high yields.     

Derivatives of 1,1,2,2-tetraaminoethane: I. Condensation of 1,2-diacetoxy-1,2-bis(acylamino)ethanes with nitrogen-containing nucleophiles

Reaction of 1,2-diacetoxy-1,2-bis(acylamino)ethanes with acetamide and urethane gave rise to 1,2-bis(acetylamino)-1,2-bis(acylamino)ethanes and 1,2-bis(acylamino)-1,2-bis(ethoxycarbonylamino)ethanes respectively. Condensation products were isolated of reactions between 1,2-diacetoxy-1,2-bis-(acylamino)ethanes with acetonitrile, diaminofurazan, and 4-phenylfurazan-3-ylamine.     

1,1,2,2-Tetrahydroperoxy-1,2-Diphenylethane: An efficient and high oxygen content oxidant in various oxidative reactions

Several oxidative approaches namely thiocyanation of aromatic compounds, epoxidation of alkenes, amidation of aromatic aldehydes, epoxidation of α, β-unsaturated ketones, oxidation of sulfides to sulfoxides and sulfones, bayer-villeger reaction, bromination and iodation of aniline and phenol derivatives oxidative esterification, oxidation of pyridines and oxidation of secondary, allylic and benzyllic alcohols were carried out using 1,1,2,2-Tetrahydroperoxy-1,2-Diphenylethane as the potential solid oxidant which can be stored for several months without any loss in its activity. All of the procedures were accomplished via mild reaction conditions and the products were afforded in high yields and short reaction times.     

Synthesis and polymerization of methyl 3-methylenecyclobutene-1-carboxylate and dimethyl 3-methylenecyclobutene-1,2-dicarboxylate

The two title monomers were synthesized. In both cases the key cyclobutane intermediates were obtained by cycloaddition of allene to acrylonitrile or chloromaleic anhydride. These two new monomers proved to be highly reactive in free radical polymerization, and each polymerized spontaneously in air at room temperature. Linear polymers were prepared in dimethyl sulfoxide solution at 35° with AIBN and UV light. At higher temperatures crosslinking became a problem in some instances. The structure of the polymers derived from 1,4 polymerization in the diene portion of the monomers was confirmed by ¹³C-NMR, ¹H-NMR and IR spectra. Copolymers were prepared with methyl methacrylate, styrene, and p-methoxystyrene and were always rich in the methylene-cyclobutene monomers used. Films of homopolymers and copolymers could be cast from chloroform solution.     

Effective synthesis of non-racemic prenalterol based on spontaneous resolution of 3-(4-hydroxyphenoxy)propane-1,2-diol

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Synthesis and thermal reactions of 3-trimethylsilyl-1-pyrazoline

The compound 3-trimethylsilyl-1-pyrazoline has been synthesized by addition of diazomethane to vinyltrimethylsilane at room temperature. In contrast, addition of trimethylsilyldiazomethane to ethylene at 55°C yields 1-trimethylsilyl-2-pyrazoline exclusively. The thermal isomerization of 3-trimethylsilyl-1-pyrazoline to 1-trimethylsilyl-2-pyrazoline has been followed kinetically by proton NMR spectroscopy and the reverse reaction has been detected by gas phase pyrolysis. Thermal elimination of nitrogen from either pyrazoline leads to cyclopropyltrimethylsilane, allyltrimethylsilane and E- and Z-1-propenyltrimethylsilane. The relative rates of methylene-H migration to radical centers α and γ to silicon are approximately equal.     

Synthesis of 1-phenylbut-3-ene-1,2-dione and its attempted radical polymerization

1,2-Diketone moiety-bearing monomer 1-phenylbut-3-ene-1,2-dione, an analogue of phenyl vinyl ketone, was synthesized from 4-chlorobutyryl chloride in a 29 % overall yield in five steps. Following acylation of benzene with 4-chlorobutyryl chloride, the resulting α-methylene group was oxidized to 1,2-diketone in three steps: successive bromination, substitution with lithium hydroxide, and oxidation of α-hydroxyketone with potassium dichromate. The final step was dehydrochlorination of 4-chloro-1-phenyl-butane-1,2-dione. The attempted copolymerization of this monomer with styrene, using AIBN as the initiator, was unsuccessful.     

Synthesis and polymerization studies of 1,2-dimethyleneoctafluorocyclohexane

1,2-Dimethyleneoctafluorocyclohexane has been prepared by the pyrolysis of 2-chloro-methyl-1-methyloctafluorocyclohexane. Free radicals initiate the polymerization of the diene in both bulk and emulsion systems to give a highly crystalline (mp 214–218°C) polymer that has an all-cis 1,4-structure. The polymer is insoluble in common laboratory solvents, but will dissolve in perfluorokerosene above 175°C and in 2,5-dichlorobenzo-trifluoride above 150°C. This diene is not polymerized by cationic, anionic, or Ziegler-Natta catalysts. The diene is readily copolymerized with many common monomers to give soluble, high molecular weight polymers. Relative reactivity ratios have been measured with styrene by the Fineman and Ross method and Q–e parameters for the diene have been calculated.