- Conformational stability, ab initio calculations and vibrational assignment for 1,1-difluoro- and 1,1-dichloro-1-silacyclopentane
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The infrared spectrum (3200-400 cm-1) of the gas and the Raman spectrum (3200-50 cm-1) of liquid and solid 1,1-difluoro-1- silacyclopentane and 1,1-dichloro-1-silacyclopentane have been recorded. In all of these physical states only the twisted (C2) conformer was detected. The conformational energies have been calculated with the Moller-Plesset perturbation method to the second order; MP2(Full) as well as the density functional theory by the B3LYP method utilizing a variety of basis sets up to 6-311 + G(2df,2pd). All the calculations predict only the twisted form as the stable conformer of 1,1-difluoro-1-silacyclopentane with the average barrier to planarity of 2548 cm-1 (30.49 kJ/mol) from the MP2 calculations and a significantly lower value of 1422 cm-1 (17.01 kJ/mol) from the density functional calculations. Neither calculation was significantly affected by the inclusion of diffuse functions. The Cs conformer has a lower energy of 1703 cm-1 (MP2) and 1334 cm -1 (B3LYP) than the planar form. Thus the path between the two identical C2 conformers is by pseudorotational motion rather than through the planar form. Similar results obtain for 1,1-dichloro-1- silacyclopentane. The optimized geometry calculated with the 6-311 + G(2df,2pd) basis is given together with a complete vibrational assignment for the twisted (C2) conformer. These assignments are supported by normal coordinate calculations with scaled force constants from MP2(Full)/6-31G(d) calculations. The results of these spectroscopic and theoretical studies are discussed and compared to the corresponding results for silacyclopentane.
- Bell, Stephen,Stidham, Howard D.,LaPlante, Arthur J.,Zheng, Ya Ying,Guirgis, Gamil A.
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- Pure rotational spectrum and structural determination of 1,1-difluoro-1-silacyclopentane
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The ground state, pure rotational spectrum of 1,1-difluoro-1-silacyclopentane has been studied using chirped-pulse, Fourier transform microwave (CP-FTMW) spectroscopy and observed in the 6-20.3 GHz region of the electromagnetic spectrum. This spectrum was acquired leveraging the deep averaging capability of the technique. The parent species, 13C, 29Si, and 30Si singly substituted isotopologues were observed in natural abundance and are reported. Only one conformer, the C2 conformer (half-chair), was observed. This is confirmed with a determined CCCC dihedral angle of -48.1(11)°. The spectrum is comprised of entirely a-type transitions in accordance with quantum chemical calculations. Multiple split transitions are present in the spectrum which have been attributed to a ring-twisting of the carbon atoms attached to the silicon atom in the ring. This motion has the carbons crossing the a-axis in the bc-plane leading to an inversion potential. Potential energy surfaces for the ring-twisting motion were undertaken and the experimentally determined energy level difference observed in comparison to these surfaces is reasonable. A Kraitchman analysis of the experimentally determined, singly substituted isotopologues is in agreement with the optimized, twisted (nonplanar) equilibrium structure. This structure has been compared to other similar silicon-containing ring molecules using second moment arguments and these comparisons are discussed.
- Grubbs, Garry S.,Guirgis, Gamil A.,Laane, Jaan,Marshall, Frank E.,McFadden, Thomas M. C.,Moon, Nicole T.,Ocola, Esther J.
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- 3-Silaazetidine: An Unexplored yet Versatile Organosilane Species for Ring Expansion toward Silaazacycles
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Small-ring silacycles are important organosilane species in main-group chemistry and have found numerous applications in organic synthesis. 3-Silaazetidine, a unique small silacycle bearing silicon and nitrogen atoms, has not been adequately explored due to the lack of a general synthetic scheme and its sensitivity to air. Here, we describe that 3-silaazetidine can be easily prepared in situ from diverse air-stable precursors (RSO2NHCH2SiR12CH2Cl). 3-Silaazetidine shows excellent functional group tolerance in a palladium-catalyzed ring expansion reaction with terminal alkynes, giving 3-silatetrahydropyridines and diverse silaazacycle derivatives, which are promising ring frameworks for the discovery of Si-containing functional molecules.
- Dong, Xue,Gao, Lu,He, Yuanhang,Li, Linjie,Song, Zhenlei,Wang, Qiantao,Wang, Wanshu,Zhou, Song
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supporting information
p. 11141 - 11151
(2021/08/03)
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- METHOD FOR PREPARING OF NOVEL LIGAND COMPOUND AND TRANSITON METAL COMPOUND
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The present invention relates to a ligand compound and to a method for preparing a transition metal compound, wherein the ligand compound and the transition metal compound containing the ligand compound exhibits excellent copolymerization properties, thereby being able to be used for preparing olefin-based polymers, particularly, olefin-based polymers with high molecular weight and low density.COPYRIGHT KIPO 2019
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Paragraph 0123-0129
(2019/02/16)
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- NOVEL LIGAND COMPOUND AND TRANSITION METAL COMPOUND COMPRISING THE SAME
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The present invention relates to a novel ligand compound and a transition metal compound. The ligand compound and the transition metal compound comprising the same exhibit excellent copolymerization and can be used for manufacturing olefinic polymers, particularly, olefinic polymers of high molecular weight and low density.COPYRIGHT KIPO 2019
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Paragraph 0120-0126
(2019/03/22)
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- A kind of preparation method of the midbody of entecavir, and intermediate
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The invention discloses Entecavir intermediates and a preparation method thereof. The preparation method of an Entecavir intermediate represented by a formula IV or IV' shown in descriptions comprises the following step of enabling a compound V to be subjected to amino protecting group and hydroxyl protecting group removal reaction in the presence of protonic acid in a solvent. The preparation method disclosed by the invention has the advantages that raw materials are cheap and are easily obtained, reaction conditions are mild, side reactions are few, the yield is high, the pollution to the environment is little, and the intermediates are easily purified and separated, so that the preparation method is applicable to industrial production.
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Paragraph 0386; 0395; 0403
(2017/08/02)
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- Entecavir intermediate and its preparation method
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The invention discloses an entecavir intermediate and a preparation method thereof. A provided preparation method for an entecavir intermediate compound 10 comprises the following steps: performing reducing reaction on an ester compound 11 in an organic solvent under the effect of a reducing agent, so as to obtain the compound 10. A provided preparation method for an entecavir intermediate compound 11 comprises the following steps: reacting a compound 12 with a hydroxyl protection reagent in an organic solvent in the presence of an acid to add a hydroxyl protection group, so as to obtain the compound 11. The preparation methods are cheap and easily available in raw materials, mild in reaction conditions, relatively high in product yield, good in atom economy, friendly to environment, and suitable for industrialized production.
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Paragraph 0380; 0385-0387; 395; 0397
(2017/12/28)
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- 9-Silafluorenyl Dichlorides as Chemically Ligating Coupling Agents and Their Application in Peptide Synthesis
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A fundamentally simple, mild, and practical procedure for peptide bond formation is reported that employs a stoichiometric amount of easy-to-access 9-silafluorenyl dichlorides as the coupling agent. Without initial preactivation or elaboration of the carboxylic acid or amine termini of the amino acids, the developed reagent is proposed to act through an unprecedented chemical ligation mechanism, bringing the two coupling partners together before being subsequently eliminated. The desired amides or peptide bonds are thus furnished in good yields and with low to no epimerization.
- Aspin, Samuel J.,Taillemaud, Sylvain,Cyr, Patrick,Charette, André B.
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supporting information
p. 13833 - 13837
(2016/10/26)
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- Hexacoordinate silacyclobutane dichelate complexes: Structure, properties, and ligand crossover
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Hexacoordinate dichelate silacyclobutane complexes have been synthesized from dichlorosilacyclobutane and O-trimethylsilylated hydrazides by transsilylation. Like previously reported hexacoordinate silicon complexes, they readily and quantitatively undergo ligand exchange with other silicon compounds (XSiCl3 and differently substituted O-trimethylsilylated hydrazides), evidence that ionic dissociation does not play a significant role in the exchange mechanism. Germanium tetrachloride causes central-element exchange and formation of analogous hexacoordinate germanium complexes. Likewise, silicon tetrachloride replaces germanium from its hexacoordinate complexes, obeying certain selectivity constraints. When silicon complexes have strongly electron-withdrawing chelate-ring substituents (CF3 or CH2CN), GeCl4 causes, in addition to central-element exchange, also oxidative opening of the four-membered ring and addition of two chlorine atoms. Both chelate exchange and central-element exchange are shown to be dominated by monodentate ligand priorities.
- Yakubovich, Shiri,Gostevskii, Boris,Kalikhman, Inna,Botoshansky, Mark,Gusel'Nikov, Leonid E.,Pestunovich, Vadim A.,Kost, Daniel
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scheme or table
p. 405 - 413
(2011/03/21)
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- 1,1-Diethynylsilacycloalkanes and propellanes based thereon
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Previously unknown 1,1-diethylnylsilacycloalkanes (CH2)nSi(C=CH)2 (n = 3, 4) were prepared by the reaction of HC=CMgBr with 1,1-dichlorosilacycloalkanes (CH2)nSiCl2 (n = 3, 4). The reaction of (CH2)4Si(C=CMgBr)2 with (CH2)4SiCl2 in THF under conditions of high dilution gives cyclo(tetramethylene)-silethynes [(CH2)4SiC=C]4 with an admixture of cyclodi(tetramethylene)silethyne [(CH2)4SiC=C]2. The reaction of Me2Si(C=CSiMe2C=CMgBr)2 with (CH2)4SiCl2 was used to prepare 1,1,4,4,7,7-hexamelhyl-10,10-tetramethylene-1,4,4,10-tetrasilacyclododeca-2,5,8, 11-tetrayne.
- Voronkov,Zhilitskaya,Yarosh,Burnashova,Albanov,Klyba
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p. 537 - 539
(2007/10/03)
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- Macrocyclic polyether compounds
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Macrocyclic polyether "crown" compounds of the formula EQU1 WHEREIN T is a C2 -C3 alkylene, A is EQU2 R being H or C1 -C18 alkyl, R2 and R3 being independently C1 -C18 alkyl, C2 -C4 alkenyl, or C6 -C14 aryl; Q and Z are independently 1,2-arylene (or saturated derivatives thereof) or substituted 1,2-arylene (or saturated derivatives thereof); a is 0, 1, 2, or 3; b is an integer from 3 to 20; y is 1 or zero; x1, x2, x3, and x4 are integers independently selected to give a 15-60 atom ring. Such crown compounds are generally useful in the formation of complexes with ionic metal compounds, thus making it possible to use certain chemical reagents in media wherein they are normally insoluble.
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