1066-40-6Relevant articles and documents
High-speed living polymerization of polar vinyl monomers by self-healing silylium catalysts
Zhang, Yuetao,Lay, Frank,Garcia-Garcia, Pilar,List, Benjamin,Chen, Eugene Y.-X.
, p. 10462 - 10473 (2010)
This contribution describes the development and demonstration of the ambient-temperature, high-speed living polymerization of polar vinyl monomers (M) with a low silylium catalyst loading (≤ 0.05 mol % relative to M). The catalyst is generated in situ by protonation of a trialkylsilyl ketene acetal (RSKA) initiator (I) with a strong Bryonsted acid. The living character of the polymerization system has been demonstrated by several key lines of evidence, including the observed linear growth of the chain length as a function of monomer conversion at a given [M]/[I] ratio, near-precise polymer number-average molecular weight (Mn, controlled by the [M]/[I] ratio) with narrow molecular weight distributions (MWD), absence of an induction period and chain-termination reactions (as revealed by kinetics), readily achievable chain extension, and the successful synthesis of well-defined block copolymers. Fundamental steps of activation, initiation, propagation, and catalyst self-repair involved in this living polymerization system have been elucidated, chiefly featuring a propagation catalysis cycle consisting of a rate-limiting C-C bond formation step and fast release of the silylium catalyst to the incoming monomer. Effects of acid activator, catalyst and monomer structure, and reaction temperature on polymerization characteristics have also been examined. Among the three strong acids incorporating a weakly coordinating borate or a chiral disulfonimide anion, the oxonium acid [H(Et2O)2] + [B(C 6F5)4]- is the most effective activator, which spontaneously delivers the most active R3Si +, reaching a high catalyst turn-over frequency (TOF) of 6.0 x 103 h-1 for methyl methacrylate polymerization by Me 3Si+ or an exceptionally high TOF of 2.4 x 105 h-1 for n-butyl acrylate polymerization by iBu3Si +, in addition to its high (>90%) to quantitative efficiencies and a high degree of control over Mn, and MWD (1.07-1.12). An intriguing catalyst self-repair feature has also been demonstrated for the current living polymerization system.
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Sommer,Pietrusza,Whitmore
, p. 2282 Anm.10 (1946)
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CONDENSATION REACTIONS OF α-AMINO-ZINCENAMINES WITH ALDEHYDES; APPLICATION TO INDOLIZINES
Wissing, Elmo,Havenith, Remco W. A.,Boersma, Jaap,Koten, Gerard van
, p. 7933 - 7936 (1992)
The zinc-enamine 1 is easy accessible via the reaction of Et2Zn with t-BuN=CHCH=Nt-Bu and is reactive towards aldehydes.The condensation reaction of 1 with 2-pyridine-carboxaldehyde results in the thermally instable zinc-aldolate 2b that subsequently rearranges to the indolizine 4.
Reaction of O(3P) with Trimethylsilane
Hoffmeyer, H.,Horie, O.,Potzinger, P.,Reimann, B.
, p. 2901 - 2905 (1985)
The title reaction has been investigated at room temperature in a discharge flow system as well as by stationary Hg(3P1) sensitized N2O photolysis experiments.O(3P) atoms abstract hydrogen from the silicon center with a rate constant of k(1) = (2.6 +/= 0.3)E-12 cm3s-1.Hydroxyl radicals formed in the primary step react in a second abstraction reaction to yield H2O with a rate constant larger than k(1) by a factor of about 20.The fate of trimethylsilyl radical, the other primary product, depends on the experimental conditions.In the flow system they combine with O and OH; the combination products decompose unimolecularly, yielding CH3 and CH4, respectively, and the common product (CH3)2SiO.In stationary photolyses they mainly abstract O from N2O to ultimately form (CH3)3SiOSi(CH3)3.In a separate static experiment a ratio of k(14)/k1/2(7) = 2.5E-12 cm3/2s-1/2 has been determined for oxygen abstraction of trimethylsilyl radicals from N2O vs. combination of two trimethylsilyl radicals.The rate constant of N(4S) with trimethylsilane has been measured in the flow system to be k(2) = (2.6 +/= 0.8)E-14 cm3s-1.
Enzyme mediated silicon-oxygen bond formation; The use of Rhizopus oryzae lipase, lysozyme and phytase under mild conditions
Abbate, Vincenzo,Bassindale, Alan R.,Brandstadt, Kurt F.,Lawson, Rachel,Taylor, Peter G.
, p. 9361 - 9368 (2010)
The potential for expanding the variety of enzymic methods for siloxane bond formation is explored. Three enzymes, Rhizopus oryzae lipase (ROL), lysozyme and phytase are reported to catalyse the condensation of the model compound, trimethylsilanol, formed in situ from trimethylethoxysilane, to produce hexamethyldisiloxane in aqueous media at 25 °C and pH 7. Thermal denaturation and reactant inhibition experiments were conducted to better understand the catalytic role of these enzyme candidates. It was found that enzyme activities were significantly reduced following thermal treatment, suggesting a potential key-role of the enzyme active sites in the catalysis. Similarly, residue-specific modification of the key-amino acids believed to participate in the ROL catalysis also had a significant effect on the silicon bio-catalysis, indicating that the catalytic triad of the lipase may be involved during the enzyme-mediated formation of the silicon-oxygen bond. E. coli phytase was found to be particularly effective at catalysing the condensation of trimethylsilanol in a predominantly organic medium consisting of 95% acetonitrile and 5% water. Whereas the use of enzymes in silicon chemistry is still very much a developing and frontier activity, the results presented herein give some grounds for optimism that the variety of enzyme mediated reactions will continue to increase and may one day become a routine element in the portfolio of the synthetic silicon chemist. The Royal Society of Chemistry.
A Quantitative Scale for the Structural Effect on Reactivity toward Nucleophilic Displacement at Silicon
Shimizu, Nobujiro,Takesue, Naohide,Yamamoto, Akiko,Tsutsumi, Toru,Yasuhara, Sigefumi,Tsuno, Yuho
, p. 1263 - 1266 (1992)
The rates of solvolysis for forty different triorganochlorosilanes have been measured in 89 molpercent aqueous dioxane at 25 deg C; the logarithmic rates relative to that for trimethylchlorosilane, log krel = log 1R2R3SiCl)/k(Me3SiCl)>, provide a quantitative scale for the structural effect of various silyl groups on the reactivity toward nucleophilic displacement at silicon, ranging from 1.99 for HSiMe2 to -6.89 for t-BuSiPh2 groups.
Synthesis of methyl(1-aminophosphonate)siloxane oligomers
Khairova,Milenin,Cherkaev,Stoikov,Muzafarov
, p. 1285 - 1288 (2016)
A synthesis of 1-aminophosphonate derivative of methylsiloxane oligomer was developed. A methodology of the introduction of 1-aminophosphonate fragment not only into the stable siloxane structures, but also into hydrolytically unstable alkoxyfunctional organosilicon compounds was suggested.
Eisch,Husk
, p. 254 (1964)
Spontaneous reduction and dispersion of graphene nano-platelets with in situ synthesized hydrazine assisted by hexamethyldisilazane
Han, Joong Tark,Jang, Jeong In,Jeong, Bo Hwa,Kim, Beom Joon,Jeong, Seung Yol,Jeong, Hee Jin,Cho, Jeong Ho,Lee, Geon-Woong
, p. 20477 - 20481 (2012)
The environmentally friendly reduction and a solution processability of chemically modified graphene nanosheets are most important for their applications. Here we report for the first time that in situ synthesis of hydrazine and spontaneous reduction of g
The low temperature crystal structure of trimethylsilanol
Minkwitz, Rolf,Schneider, Stefan
, p. 426 - 429 (1998)
A preparation of trimethylsilanol by hydrolysis of bis(trimethylsilyl)carbonate in diethylether at -20 °C is reported. At -80 °C, the crystals are monoclinic, space group P21/c, Z = 12 with cell dimensions a = 996.0(2) pm, b = 1730.2(3) pm, c = 1122.9(2) pm, β = 96,61(3)°. There are three independent Me3SiOH units with a slightly distorted tetrahedral C3SiO core structure.
Dihydrotrimethylsiloxyaluminum
Roberts, Charles B.,Toner, Darell D.
, p. 2361 - 2362 (1970)
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Disproportionation of oligodimethylsiloxanols in the presence of a protic acid in dioxane
Cypryk, M.,Rubinsztajn, S.,Chojnowski, J.
, p. 91 - 97 (1993)
The kinetics of the acid-catalyzed disproportionation of α,ω-dihydroxyoligodimethylsiloxanes HOnH, n = 2, 5, and their analogues having one hydroxyl function replaced by methyl MenH, n = 2, 5, were studied in dioxane in the presence of water.The formation of the primary disproportionation products was monitored by gas-liquid chromatography.The reaction in dioxane solution can compete with the condensation process only in the presence of water.It is of first order with respect to the substrate, catalyst, and water.The results are interpreted in terms of a stepwise mechanism involving rate determining cleavage of the terminal siloxane unit by water, followed by condensation of transiently-formed dimethylsilanediol with the substrate.The unzipping mechansim involving the dimethylsilanediol intermediate is suggested to operate in hydrolytic cleavage of polydimethylsiloxane exposed to water or water vapour.
Atmospheric degradation of volatile methyl-silicon compounds
Tuazon, Ernesto C.,Aschmann, Sara M.,Atkinson, Roger
, p. 1970 - 1976 (2000)
The current widespread use of poly(dimethylsiloxane)s (PDMS) in a broad range of applications leads to their release into soil environments where they degrade to monomeric products, primarily dimethylsilanediol, most of which enter the atmosphere by volatilization. The major degradation pathway of volatile organosilicon compounds in the atmosphere is expected to be a reaction with hydroxyl (OH) radicals. In this work, the kinetics of the gas- phase reactions of dimethylsilanediol, trimethylsilanol, and tetramethylsilane with the OH radical were measured using a relative rate method which employed the N2H4 + O3 reaction as a nonphotolytic source of OH radicals, with analysis by Fourier transform infrared (FT-IR) spectroscopy in a 5870 L chamber. The measured values of the OH radical reaction rate constants (cm3 molecule-1 s-1) at 298 ± 2 K are as follows: dimethylsilanediol, (8.1 ± 1.0) x 10-13; trimethylsilanol, (7.2 ± 0.8) x 10-13; and tetramethylsilane, (8.5 ± 0.9) x 10-13. These values lead to an estimate of tropospheric lifetimes with respect to reaction with the OH radical of ca. 15 days for these organosilicon compounds. FT-IR spectroscopy and atmospheric pressure ionization mass spectrometry (API-MS) were employed to analyze the products of OH radical- and Cl atom-initiated photooxidations of dimethylsilanediol and trimethylsilanol. Infrared signatures of the probable formate ester intermediate products from both silanols were detected. API-MS analyses indicated the formation of methylsilanetriol from dimethylsilanediol, of both dimethylsilanediol and methylsilanetriol from trimethylsilanol, and of the corresponding intermediate formate esters. Possible reaction mechanisms are discussed. The current widespread use of poly(dimethylsiloxane)s (PDMS) in a broad range of applications leads to their release into soil environments where they degrade to monomeric products, primarily dimethylsilanediol, most of which enter the atmosphere by volatilization. The major degradation pathway of volatile organosilicon compounds in the atmosphere is expected to be a reaction with hydroxyl (OH) radicals. In this work, the kinetics of the gas-phase reactions of dimethylsilanediol, trimethylsilanol, and tetramethylsilane with the OH radical were measured using a relative rate method which employed the N2H4 + O3 reaction as a nonphotolytic source of OH radicals, with analysis by Fourier transform infrared (FT-IR) spectroscopy in a 5870 L chamber. The measured values of the OH radical reaction rate constants (cm3 molecule-1 s-1) at 298 ± 2 K are as follows: dimethylsilanediol, (8.1 ± 1.0) × 10-13; trimethylsilanol, (7.2 ± 0.8) × 1013; and tetramethylsilane, (8.5 ± 0.9) × 10-13. These values lead to an estimate of tropospheric lifetimes with respect to reaction with the OH radical of ca. 15 days for these organosilicon compounds. FT-IR spectroscopy and atmospheric pressure ionization mass spectrometry (API-MS) were employed to analyze the products of OH radical- and Cl atom-initiated photooxidations of dimethylsilanediol and trimethylsilanol. Infrared signatures of the probable formate ester intermediate products from both silanols were detected. API-MS analyses indicated the formation of methylsilanetriol from dimethylsilanediol, of both dimethylsilanediol and methylsilanetriol from trimethylsilanol, and of the corresponding intermediate formate esters. Possible reaction mechanisms are discussed.
Proton-Coupled Electron Transfer Enables Tandem Radical Relay for Asymmetric Copper-Catalyzed Phosphinoylcyanation of Styrenes
Zhang, Guoyu,Fu, Liang,Chen, Pinhong,Zou, Jianping,Liu, Guosheng
, p. 5015 - 5020 (2019)
A tandem radical relay strategy was realized for the first Cu(I)-catalyzed enantioselective phosphinocyanation of styrenes. In this reaction, tBuOOSiMe3 generated in situ from tBuOOH serves as a radical initiator to trigger t-butoxy radical production upon oxidization of L?Cu(I) species via proton-coupled-electron transfer (PCET) pathway, which leads to sequential phosphinoyl radical and benzyl radical formations. The resultant β-cyanodiarylphosphine oxides could be easily converted to a series of chiral ?-amino phosphine ligands.
Influence of macroscopic factors on the composition of the products of cohydrolysis of triorganochlorosilanes
Ivanov,Mlakhovskaya,Chernyshev,Kostikova,Mozzhukhin,Buzyreva
, p. 719 - 725 (1997)
The composition of the products of heterogeneous cohydrolysis of trimethyl- and dimethylphenylchlorosilanes by excess aqueous ammonia (4-5% solution) is determined by the regime of heterofunctional condensation of the initial chlorosilanes with the products of their hydrolysis, triorganosilanols. In a diffusion regime, hexaorganodisiloxanes are formed because of the limited possibility of removing silanols from the reaction zone, while silanols are predominantly formed in a kinetic regime. The influence of the nature of the solvent and surfactant and the intensity of stirring of the reaction mixture on the composition of the final products of hydrolytic cocondensation of triorganochlorosilanes is considered.
Direct growth of crystalline triazine-based graphdiyne using surface-assisted deprotection-polymerisation
Amsalem, Patrick,Bojdys, Michael J.,Burmeister, David,Huang, Jieyang,Kass, Dustin,Koch, Norbert,Kulkarni, Ranjit,Müller, Johannes,Martin, Andréa,Trunk, Matthias
, p. 12661 - 12666 (2021/10/19)
Graphdiyne polymers have interesting electronic properties due to their π-conjugated structure and modular composition. Most of the known synthetic pathways for graphdiyne polymers yield amorphous solids because the irreversible formation of carbon-carbon bonds proceeds under kinetic control and because of defects introduced by the inherent chemical lability of terminal alkyne bonds in the monomers. Here, we present a one-pot surface-assisted deprotection/polymerisation protocol for the synthesis of crystalline graphdiynes over a copper surface starting with stable trimethylsilylated alkyne monomers. In comparison to conventional polymerisation protocols, our method yields large-area crystalline thin graphdiyne films and, at the same time, minimises detrimental effects on the monomers like oxidation or cyclotrimerisation side reactions typically associated with terminal alkynes. A detailed study of the reaction mechanism reveals that the deprotection and polymerisation of the monomer is promoted by Cu(ii) oxide/hydroxide species on the as-received copper surface. These findings pave the way for the scalable synthesis of crystalline graphdiyne-based materials as cohesive thin films.
