- Phosphines as Silylium Ion Carriers for Controlled C-O Deoxygenation: Catalyst Speciation and Turnover Mechanisms
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We report studies delineating the speciation, kinetics, and deoxygenation catalysis of phosphine-modified mixtures of B(C6F5)3 (BCF) and R3SiH. Combinations of BCF, a tertiary silane, and PAr3 generat
- Gudz, Anton,Payne, Philippa R.,Gagné, Michel R.
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- Light-Promoted Transfer of an Iridium Hydride in Alkyl Ether Cleavage
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A catalytic, light-promoted hydrosilylative cleavage reaction of alkyl ethers is reported. Initial studies are consistent with a mechanism involving heterolytic silane activation followed by delivery of a photohydride equivalent to a silyloxonium ion generated in situ. The catalyst resting state is a mixture of Cp*Ir(ppy)H (ppy = 2-phenylpyridine-κC,N) and a related hydride-bridged dimer. Trends in selectivity in substrate reduction are consistent with nonradical mechanisms for C-O bond scission. Irradiation of Cp*Ir(ppy)H with blue light is found to increase the rate of hydride delivery to an oxonium ion in a stoichiometric test. A comparable rate enhancement is found in carbonyl hydrosilylation catalysis, which operates through a related mechanism also involving Cp*Ir(ppy)H as the resting state.
- Fast, Caleb D.,Schley, Nathan D.
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supporting information
p. 3291 - 3297
(2021/10/12)
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- Metal-Free Catalytic Reductive Cleavage of Enol Ethers
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In contrast to the well-known reductive cleavage of the alkyl-O bond, the cleavage of the alkenyl-O bond is much more challenging especially using metal-free approaches. Unexpectedly, alkenyl-O bonds were reductively cleaved when enol ethers were reacted with Et3SiH and a catalytic amount of B(C6F5)3. Supposedly, this reaction is the result of a B(C6F5)3-catalyzed tandem hydrosilylation reaction and a silicon-assisted β-elimination. A mechanism for this cleavage reaction is proposed based on experiments and density functional theory (DFT) calculations.
- Chulsky, Karina,Dobrovetsky, Roman
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supporting information
p. 6804 - 6807
(2018/11/02)
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- Electrophilic phosphonium cations (EPCs) with perchlorinated-aryl substituents: Towards air-stable phosphorus-based Lewis acid catalysts
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A series of phosphines incorporating (C6Cl5) substituents, Ph2P(C6Cl5) 1, PhP(C6Cl5)22, P(C6Cl5)33 and (C6F5)P(C6Cl5)24 were prepared. In the case of 1, 2 and 4, these were converted to the corresponding aryl-difluorophosphoranes 5-7via reaction with XeF2, whereas reaction of 3 with XeF2 afforded only an inseparable mixture of products. The compounds 5-7 were converted to the fluorophosphonium cations 8-10, whereas the reaction of 3 with Selectfluor afforded (C6Cl5)2POF and (C6Cl5)2. The fluorophosphonium salts showed evidence of improved air stability as well as Lewis acid catalytic activity in hydrodefluorination, hydrosilylation, deoxygenation and dehydrocoupling chemistry.
- Postle, Shawn,Podgorny, Vitali,Stephan, Douglas W.
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p. 14651 - 14657
(2016/10/03)
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- Pyridinium-phosphonium dications: Highly electrophilic phosphorus-based Lewis acid catalysts
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Using commercially available 2-pyridyldiphenylphosphine (o-NC5H4)PPh2, a family of electrophilic phosphonium cations [(o-NC5H4)PFPh2]+ (2) and dications [(o-MeNC5H4)PRPh2]2+ (R = F (4); Me (5)) were prepared. The Lewis acidity of these pyridinium-phosphonium dications was probed in Friedel-Crafts dimerization, hydrodefluorination, hydrosilylation, dehydrocoupling and hydrodeoxygenation reactions. The influence of the counterion on the catalytic activity of the electrophilic phosphonium cations is also discussed.
- Bayne, Julia M.,Holthausen, Michael H.,Stephan, Douglas W.
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p. 5949 - 5957
(2016/04/26)
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- Room temperature organocatalyzed reductive depolymerization of waste polyethers, polyesters, and polycarbonates
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The reductive depolymerization of a variety of polymeric materials based on polyethers, polyesters, and polycarbonates is described using hydrosilanes as reductants and metal-free catalysts. This strategy enables the selective depolymerization of waste polymers as well as bio-based polyesters to functional chemicals such as alcohols and phenols at room temperature. Commercially available B(C6F5)3 and [Ph3C+,B(C6F5)4-] catalysts are active hydrosilylation catalysts in this procedure and they are compatible with the use of inexpensive and air-stable polymethylhydrosiloxane and tetramethyldisiloxane as reductants. A significant advantage of this recycling method is derived from its tolerance to the additives present in waste plastics and its ability to selectively depolymerize mixtures of polymers. Silanes pitted against waste: The reductive depolymerization of a variety of polymeric materials based on polyethers, polyesters, and polycarbonates is described, using hydrosilanes as reductants and metal-free catalysts. This strategy enables the selective depolymerization of waste polymers as well as bio-based polyesters to functional chemicals such as alcohols and phenols at room temperature.
- Feghali, Elias,Cantat, Thibault
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p. 980 - 984
(2015/03/30)
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- The synergistic effect of nanoporous AuPd alloy catalysts on highly chemoselective 1,4-hydrosilylation of conjugated cyclic enones
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The nanoporous AuPd (AuPdNPore) alloy catalyst showed superior chemoselectivity and high catalytic activity for the direct 1,4-hydrosilylation of the conjugated cyclic enones with hydrosilane in comparison with the monometallic nanoporous Au and Pd catalysts. The enhanced catalytic properties of AuPdNPore arise mainly from the nanoporous structure and the synergistic effect of the AuPd alloy. The Royal Society of Chemistry 2014.
- Chen, Qiang,Tanaka, Shinya,Fujita, Takeshi,Chen, Luyang,Minato, Taketoshi,Ishikawa, Yoshifumi,Chen, Mingwei,Asao, Naoki,Yamamoto, Yoshinori,Jin, Tienan
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p. 3344 - 3346
(2014/03/21)
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- Unprecedented organocatalytic reduction of lignin model compounds to phenols and primary alcohols using hydrosilanes
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The first metal-free reduction of lignin model compounds is described. Using inexpensive Et3SiH, PMHS and TMDS hydrosilanes as reductants, α-O-4 and β-O-4 linkages are reduced to primary alcohols and phenols under mild conditions using B(C6F5)3 as an efficient catalyst. The Royal Society of Chemistry.
- Feghali, Elias,Cantat, Thibault
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supporting information
p. 862 - 865
(2014/01/06)
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- Preparation of nano silica supported sodium hydrogen sulfate: As an efficient catalyst for the trimethyl, triethyl and t-butyldimethyl silylations of aliphatic and aromatic alcohols in solution and under solvent-free conditions
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Nano silica supported sodium hydrogen sulfate has been prepared by mixing NaHSO4 with activated Nano silicagel. We wish to report a new method for the synthesis of trimethyl (TMS), triethyl (TES) and t-butyldimethyl silyl (TBS) ethers from benzylic, allylic, propargylic alcohols, phenols, naphtholes and some of phenolic drugs in the solution and under solvent-free conditions.
- Abri, Abdolreza,Ranjdar, Somayeh
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p. 929 - 934
(2014/10/16)
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- A mild and highly efficient method for the preparation of silyl ethers using Fe(HSO4)3/Et3N by chlorosilanes
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Avery efficient and mild procedure for preparation of silyl ethers from benzylic, allylic, propargilic alcohols, phenols, naphtoles and some of phenolic drugs with trimethylsilylchloride (TMSCl), triethylsilylchloride (TESCl) and t-buthyldimethylsilyl chloride (TDSCl) ethers in the presence of Fe(HSO 4)3/Et3N in roomtemperature in excellent yields is reported. This procedure also allows the excellent selectivity for silylation of alcohols and phenols.
- Abri, Abdolreza,Assadi, Mohammad Galeh,Pourreza, Samira
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p. 1449 - 1454
(2013/03/13)
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- Scope and mechanism of the iridium-catalyzed cleavage of alkyl ethers with triethylsilane
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The cationic iridium pincer complex [(POCOP)lr(H)(acetone)] +[B(C6F5)4]- {1, POCOP = 2,6 [OP(tBu)2]2C6H3} was found to be a highly active catalyst for the room-temperature cleavage and reduction of a wide variety of unactivated alkyl ethers including primary, secondary, and tertiary alkyl ethers as well as aryl alkyl ethers by triethylsilane. Mechanistic studies have revealed the full details of the catalytic cycle with the catalyst resting state(s) depending on the basicity of the alkyl ether. During the catalytic reduction of diethyl ether, cationic iridium silane complex, [(POCOP)lr(H)(n1-Et3SiH)]+[B(C 6F5]- (3), andEt20 are in rapid equilibrium with neutral dihydride, (POCOP )lr(H)2 (5) and diethyl(triethylsilyl)oxonium ion, [Et3SiOEt2] +[B(C6F5)4]- (7), with 5 + 7 strongly favored. Species 7 has beenisolated from the reaction mixture and fully characterized. The turnove r-limiting step in this cycle is the reduction of 7 by the neutral dihydride 5. The relative rates of reduction of 7 by dihydride 5 and Et3SiH were determined to be ~30,000: 1. In the cleavage of the less basic ethers anisole and EtOSiEt3, the cationic iridium silane complex, 3, was found to be the catalyst resting state. The hydride reduction of the intermediate oxonium ion EtO(SiEt3) 2+, 9, occurs via attack by Et3SiH. In the case of anisole, the intermediate PhMeOSiEt3+, 10, is reduced by 5 and/or Et3SiH.
- Yang, Jian,White, Peter S.,Brookhart, Maurice
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experimental part
p. 17509 - 17518
(2009/09/08)
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- Cationic Au(I)- and Pt(II)-catalyzed silylation of alcohols using allylsilanes
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The silylation of alcohols using allylsilanes was catalyzed by cationic Au(I) and Pt(II) species, which were prepared in situ from the metal chlorides ([AuCl(PPh3)], PtCl2) and a silver salt. TBS-, TES-, and TIPS-protections of vario
- Shibata, Takanori,Kanda, Kazumasa,Ueno, Yasunori,Fujiwara, Ryo
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p. 1146 - 1147
(2007/10/03)
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- A Novel B(C6F5)3-Catalyzed Reduction of Alcohols and Cleavage of Aryl and Alkyl Ethers with Hydrosilanes
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The primary alcohols 1a-e and ethers 4a-d were effectively reduced to the corresponding hydrocarbons 2 by HSiEt3 in the presence of catalytic amounts of B(C6F5)3. To the best of our knowledge, this is the first example of catalytic use of Lewis acid in the reduction of alcohols and ethers with hydrosilanes. The secondary alkyl ethers 4j,k enabled cleavage and/or reduction under similar reaction conditions to produce either the silyl ethers 3m-n or the corresponding alcohol 5a upon subsequent deprotection with TBAF. It was found that the secondary alcohols 1g-i and tertiary alcohol 1j, as well as the tertiary alkyl ether 4l, did not react with HSiEt3/(B(C6F5)3 reducing reagent at all. The following relative reactivity order of substrates was found: primary ? secondary > tertiary. A plausible mechanism for this nontraditional Lewis acid catalyzed reaction is proposed.
- Gevorgyan, Vladimir,Rubin, Michael,Benson, Sharonda,Liu, Jian-Xiu,Yamamoto, Yoshinori
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p. 6179 - 6186
(2007/10/03)
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- One-step conversion of formate esters to O-silyl ethers by means of samarium diiodide in the presence of chlorosilane reagents
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One-step conversion of various types of formate esters into the corresponding O-silyl ethers under neutral reaction conditions was established by employing samarium diiodide in the presence of chlorosilane reagents.
- Honda, Toshio,Ishikawa, Fumihiro
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p. 3323 - 3328
(2007/10/03)
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- A novel reduction of alcohols and ethers with a HSiEt3/catalytic B(C6F5)3 system
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The primary alcohols 1a-d and ethers 4a-b were effectively reduced into the corresponding hydrocarbons 2 by HSiEt3 in the presence of catalytic amounts of B(C6F5)3. The secondary alkyl ethers 4g,h underwent cleavage and/or reduction under similar reaction conditions to produce either the silyl ether 3k or the corresponding alcohol 5b upon subsequent deprotection with TBAF. The secondary alcohols (1g,h) and tertiary alcohol 1i, as well as tertiary alkyl ether 4i, did not react with the HSiEt3/(B(C6F5)3 reducing reagent at all. The following relative reactivity order of substrates was found: primary>>secondary>tertiary. The methyl aryl ethers 4c-e and alkyl aryl ether 4f were smoothly deprotected to give the corresponding silyl ethers 3b,h-j in nearly quantitative isolated yields.
- Gevorgyan, Vladimir,Liu, Jian-Xiu,Rubin, Michael,Benson, Sharonda,Yamamoto, Yoshinori
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p. 8919 - 8922
(2007/10/03)
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- NMR spectra of phenoxysilanes with various silyl groups
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Ten phenoxysilanes with various organic groups on the silicon were prepared and their 1H and 13C NMR spectra recorded. The groups on the silicon had only a small effect on the proton and carbon chemical shifts.
- Hudrlik, Paul F.,Minus, Donald K.
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p. 157 - 162
(2007/10/03)
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