An ab initio study on thermal rearrangement reactions of 1-silylprop-2-en-1-ol H3SiCH(OH)CH=CH2

The thermal rearrangement reactions of 1-silylprop-2-en-1-ol H3SiCH(OH)CH=CH2 were studied by ab initio calculations at the G2(MP2) and G3 levels. The reaction mechanisms were revealed through ab initio molecular orbital theory. On the basis of the MP2(full)/6-31G(d) optimized geometries, harmonic vibrational frequencies of various stationary points were calculated. The reaction paths were investigated and confirmed by intrinsic reaction coordinate (IRC) calculations. The results show that the thermal rearrangements of H3SiCH(OH)CH=CH2 happen in two ways. One is via the Brook rearrangement reactions (reaction A), and the silyl group migrates from carbon atom to oxygen atom passing through a double three-membered ring transition state, forming allyloxysilane CH2=CHCH2OSiH3. In the other, the reactant undergoes a dyotropic rearrangement; the hydroxyl group migrates from carbon atom to silicon atom coupled with a simultaneous migration of a hydrogen atom from silicon atom to carbon atom, forming allylsilanol CH2=CHCH2SiH2OH (reaction B). The barriers for reactions A and B were computed to be 343.5 and 203.7 kJ/mol, respectively, at the G3 level. The changes of the thermodynamic functions, entropy (DeltaS), entropy (DeltaS(doubledagger)) for the transition state, enthalpy (DeltaH), and free energy (DeltaG) were calculated by using the MP2(full)/6-31G(d) optimized geometries, and harmonic vibrational frequencies of reactants, transition states, and products with statistical mechanical methods, and equilibrium constant K(T) and reaction rate constant k(T) in canonical variational transition-state theory (CVT) with centrifugal-dominant small-curvature tunneling approximation (SCT) were calculated over a temperature range 400-1300 K. The conventional transition-state theory (TST) rate constants were also calculated for the purposes of comparison. The influences of the vinyl group attached to the center carbon of the alpha-silyl alcohols on reactions were discussed.     

热解/红外光谱联用技术用于热解反应的快速检测

详细介绍了快速热解装置CDS2000／红外联用仪(Py／FTIR)的特点。带有样品的热解探头插入并固定在接口装置上，接口装置可直接置于FTIR的光路中，对热解产物进行直接、快速检测，并且可分析重质热解产物。CDS2000热丝裂解器具有极快的升温速度，升温速度从0．01℃／min到20000℃／s，可以有效避免热解过程中的二次反应，有助于推断结构和热解机理；另外，本文对CDS2000／FTIR热解／红外联用仪使用过程中的有关参数进行了分析，如分辨率的选择。本文应用CDS2000／FTIR联用仪对PVC、生物质和模型化合物进行了热解实验，取得了满意的结果。     

Theoretical study on H2 elimination pathways of silylenoid H2SiLiF with CH4, NH3, H2O, HF, SiH4, PH3, H2S, and HCl

Ab initio molecular orbital calculations have been performed to explore the reaction potential energy surfaces of silylenoid H₂SiLiF with XH _n hydrides, where XH _n = CH₄, NH₃, H₂O, HF, SiH₄, PH₃, H₂S, and HCl. We have identified a previously unreported reaction pathway on each reaction surface, H₂SiLiF + H-XH _{n − 1} → H _n XSiLiF + H₂, which involves H₂ elimination following the initial formation of an association complex via a four-membered ring transition state to form the substituted three-membered ring silylenoid H _n XSiLiF and a H₂ molecule. This theoretical calculations suggest that (i) for H₂ eliminations there is a very clear trend toward lower activation barriers and more exothermic interactions on going from left to right along a given row in periodic table, and (ii) for the second-row hydrides, the H₂ elimination reactions are less exothermic than for the first-row hydrides and the reaction barriers are lower for X–S and Cl. Compared to the insertions of H₂SiLiF into XH _n , the H₂ elimination pathways should be unfavorable with higher barrier and lower exothermic.     

Synthesis and characterization of bis(methoxyl hydroxyl)-functionalized disiloxane and polysiloxane oligomers derivatives therefrom

With purpose to prepare waterborne polyurethane with improved performance, bis(methyoxyl hydroxyl)-functionalized polysiloxanes with different dimethylsiloxane segment length were prepared. The preparation includes three steps, the first is synthesis of 1,3-bis(glycidoxypropyl)tetramethyldisiloxane (compound I) via hydrosilylation of allylglycidyl ether with tetramethyldisiloxane, followed by a subsequent methoxylation of the resultant compound from the hydrosilylation to give 1,3-bis(3-(1-methoxy-2-hydroxypropoxy)propyl)tetramethyldisiloxane (compound II). Using this compound II and octamethylcyclotetrasiloxane (D₄), an equilibrium reaction was carried out to obtain the target Product III, i.e. bis(methoxyl hydroxyl)-functionalized polysiloxanes. The ratio of D₄/compound II was varied in order to prepare product III with different segment length consisting of dimethylsiloxane units. At each step, the outcome compounds were characterized through Infrared, ¹H NMR, ¹³C NMR as well as H-H and H-C Correlated Spectroscopy (COSY). The results showed that each step was successfully carried out and objective products were achieved. It was estimated that compound II was not exclusive in the methoxylation step. Characterizations of the compound II enabled us to give a reliable quantitative amount for the by-products for the first time. In addition, the molecular weights of the final product III with varying dimethylsiloxane length were estimated by hydroxyl group analysis, ¹H NMR and GPC, which showed a good agreement between the theoretical molecular weights and those from these tests.     

Adsorption and Aggregation Behavior in Aqueous Solution of Tetrasiloxane-based Carboxylate Surfactants via “Thiol-ene” Photochemical Reaction

Anionic silicone surfactants have long been a neglected field. In this paper three anionic silicone surfactants were synthesized first time from dichloromethylvinylsilane through hydrolysis-condensation, “thiol-ene” photo- chemical and then salting reaction. The critical aggregate concentration (CAC), surface tension, minimum surface area per surfactant molecule and surface pressure at CAC were studied by both surface tension and electrical conductivity. The results showed that they had significant surface activity at the gas/liquid interface and were capable to reduce the surface tension of water to approximately 20 mN m⁻¹. The results of transmission electron microscopy showed that the three silicone surfactants self-assembled into spherical aggregates of uniform size in aqueous solution above the CAC. The dynamic light scattering results demonstrated that the size of the aggregates was determined to be in the range from 60 to 300 nm at 0.05 mol L⁻¹ and the order of the size of the aggregates is (Me₃SiO)₃SiCO₂Li<(Me₃SiO)₃SiCO₂Na<(Me₃SiO)₃SiCO₂K.     

CoIIIcorrole: versatile synthetic methods and wide range of applications

Journal of Inclusion Phenomena and Macrocyclic Chemistry - This review introduces the synthesis, properties and applications of CoIIIcorroles. The synthesis methods are containing A2B type, A3...     

A DFT study on the thermal decomposition of 2-chloroethylsilane

Structural Chemistry - The thermal decomposition of 2-chloroethylsilane (H3SiCH2CH2Cl) was investigated by density functional theory (DFT) method at the B3LYP/6-311G(d,p) level. The structures of...     

Theoretical study on a new kind of thienyl-functionalized polysilane

A series of theoretical calculations were performed on thienyl-functionalized polysilanes in order to understand their geometries, excited state spectra, energy band structures, and adsorption stability onto Au (111) surfaces. The thienyl functionalization causes a significant red-shift of the electronic spectra of the oligosilanes, which is due to the maximum absorption energy resulting from σ → π* transition in oligo(methylthienylsilane) much lower than that from σ → σ* transition, and a great decrease of the σ → σ* transition energy in thienyl end-functionalized oligo(dimethylsilane). The thienyl substitution exerts a small effect on the band gap of the polysilane, and yet disturbs slightly the σ electronic delocalization. There exists a stable adsorption between thienyl-functionalized polysilanes and Au (111) surfaces through non-bonding interaction of thiophenes with Au.     

Ring‐Closing Metathesis on an Allyl‐Terminated Carbosilane Dendrimer

Grubbs' catalyst was used to prepare a series of carbosilane dendrimers with silacyclopentene peripheral groups, suitable for further elaboration to functional dendrimers. The efficiency of the ring closing metathesis reaction was found to be strongly dependent on the reaction temperature and the amount of catalyst used, as shown by ¹H NMR monitoring.     

A Self‐Supporting Strategy for Gas‐Phase and Slurry‐Phase Ethylene Polymerization using Late‐Transition‐Metal Catalysts

The polyolefin industry is dominated by gas‐phase and slurry‐phase polymerization using heterogeneous catalysts. In contrast, academic research is focused on homogeneous systems, especially for late‐transition‐metal catalysts. The heterogenization of homogeneous catalysts is a general strategy to provide catalyst solutions for existing industrial polyolefin synthesis. Herein, we report an alternative, potentially general strategy for using homogeneous late‐transition‐metal catalysts in gas‐phase and slurry‐phase polymerization. In this self‐supporting strategy, catalysts with moderate chain‐walking capabilities produced porous polymer supports during gas‐phase ethylene polymerization. Chain walking, in which the metal center can move up and down the polymer chain during polymerization, ensures that the metal center can travel along the polymer chain to find suitable sites for ethylene enchainment. This strategy enables simple heterogenization of catalysts on solid supports for slurry‐phase polymerization. Most importantly, various branched ultra‐high‐molecular‐weight polyethylenes can be prepared under various polymerization conditions with proper catalyst selection.