- Platinum Catalysed Regioselective ortho-Silylation of Benzylideneamines via Intramolecular C-H Activation
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The Pt-P(OCH2)3CEt complex catalyses the ortho-silylation of benzylideneamines with disilanes via intramolecular C-H activation; both mono- and bis-silylated products are obtained.
- Williams, Neil A.,Uchimaru, Yuko,Tanaka, Masato
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- Metal-free hydrogen evolution cross-coupling enabled by synergistic photoredox and polarity reversal catalysis
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A synergistic combination of photoredox and polarity reversal catalysis enabled a hydrogen evolution cross-coupling of silanes with H2O, alcohols, phenols, and silanols, which afforded the corresponding silanols, monosilyl ethers, and disilyl ethers, respectively, in moderate to excellent yields. The dehydrogenative cross-coupling of Si-H and O-H proceeded smoothly with broad substrate scope and good functional group compatibility in the presence of only an organophotocatalyst 4-CzIPN and a thiol HAT catalyst, without the requirement of any metals, external oxidants and proton reductants, which is distinct from the previously reported photocatalytic hydrogen evolution cross-coupling reactions where a proton reduction cocatalyst such as a cobalt complex is generally required. Mechanistically, a silyl cation intermediate is generated to facilitate the cross-coupling reaction, which therefore represents an unprecedented approach for the generation of silyl cationviavisible-light photoredox catalysis.
- Cao, Jilei,Lu, Kanghui,Ma, Lishuang,Yang, Xiaona,Zhou, Rong
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supporting information
p. 8988 - 8994
(2021/11/23)
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- Hydrogenolysis of Polysilanes Catalyzed by Low-Valent Nickel Complexes
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The dehydrogenation of organosilanes (RxSiH4?x) under the formation of Si?Si bonds is an intensively investigated process leading to oligo- or polysilanes. The reverse reaction is little studied. To date, the hydrogenolysis of Si?Si bonds requires very harsh conditions and is very unselective, leading to multiple side products. Herein, we describe a new catalytic hydrogenation of oligo- and polysilanes that is highly selective and proceeds under mild conditions. New low-valent nickel hydride complexes are used as catalysts and secondary silanes, RR′SiH2, are obtained as products in high purity.
- Comas-Vives, Aleix,Eiler, Frederik,Grützmacher, Hansj?rg,Pribanic, Bruno,Trincado, Monica,Vogt, Matthias
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supporting information
p. 15603 - 15609
(2020/04/29)
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- Synthesis of hydrosilanes: Via Lewis-base-catalysed reduction of alkoxy silanes with NaBH4
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Hydrosilanes were synthesized by reduction of alkoxy silanes with BH3 in the presence of hexamethylphosphoric triamide (HMPA) as a Lewis-base catalyst. The reaction was also achieved using an inexpensive and easily handled hydride source NaBH4, which reacted with EtBr as a sacrificial reagent to form BH3in situ.
- Aoyagi, Keiya,Ohmori, Yu,Inomata, Koya,Matsumoto, Kazuhiro,Shimada, Shigeru,Sato, Kazuhiko,Nakajima, Yumiko
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supporting information
p. 5859 - 5862
(2019/05/27)
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- Catalytic Reduction of Alkoxysilanes with Borane Using a Metallocene-Type Yttrium Complex
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The catalytic reduction of alkoxysilanes with the borane HBpin (pin = pinacolato) was achieved using a metallocene-type yttrium complex as a catalyst precursor. Mechanistic study supported the pivotal role of the rigid metallocene structure of the catalyst, which bears two bulky n5-C5Me4SiMe3 ligands, in suppressing the coordination of the side product MeOBpin that is generated during the reaction.
- Aoyagi, Keiya,Matsumoto, Kazuhiro,Shimada, Shigeru,Sato, Kazuhiko,Nakajima, Yumiko
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supporting information
p. 210 - 212
(2019/02/01)
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- PRODUCTION METHOD OF HYDROSILANE
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PROBLEM TO BE SOLVED: To provide a production method of hydrosilane capable of producing hydrosilane efficiently. SOLUTION: Silane having a structure shown by formula (a) is reacted with hydrogen in the presence of iridium complex shown by formula (I) and organic base, to thereby produce hydrosilane efficiently. SELECTED DRAWING: None COPYRIGHT: (C)2018,JPOandINPIT
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Paragraph 0030-0033; 0040-0043
(2018/10/03)
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- METHOD FOR PRODUCING HYDROSILANE
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PROBLEM TO BE SOLVED: To provide a method for producing hydrosilane capable of efficiently producing hydrosilane under mild conditions. SOLUTION: Provided is a method for producing hydrosilane where hydrosilane can be efficiently produced by reacting alkoxysilane having a structure represented by formula (a) with hydroborane and/or hydrogen under the presence of a complex with at least one kind of atom selected from the group consisting of a yttrium atom (Y), a zirconium atom (zr) and a hafnium atom (Hf) as a central metal(s)(in the formula (a), R denotes a 1 to 20C hydrocarbon group). SELECTED DRAWING: None COPYRIGHT: (C)2018,JPO&INPIT
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Paragraph 0024; 0027; 0028; 0029; 0030; 0031; 0032-0035
(2019/01/06)
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- A silicon hydrogenation for the preparation of compounds
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The invention relates to a method for preparing silicon hydrides. Under the protection of Ar gas, THF and/or HMPA are/is used as a solvent, chlorosilane or derivatives of chlorosilane reacts with magnesium metal to prepare the silicon hydrides. The method has the characteristics of being cheap in raw materials, easy to get the raw materials, easy to operate, mild in reaction conditions and low in cost.
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Paragraph 0026; 0027; 0028; 0029
(2018/03/09)
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- Hydrosilane synthesis via catalytic hydrogenolysis of halosilanes using a metal-ligand bifunctional iridium catalyst
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Hydrogenolysis of various halosilanes was catalysed by iridium amido complexes to produce hydrosilanes. Selective monohydrogenolysis of di- and trichlorosilanes similarly proceeded, resulting in the formation of chlorohydrosilanes (R2SiHCl or RSiHCl2) as synthetically important building blocks for various organosilicon compounds. A mechanistic study supported the in-situ formation of an iridium hydride species as a key intermediate, which could transfer the hydride to the silicon atom through a metal–ligand bifunctional mechanism. One-pot hydrotrimethylsilylation of olefins was achieved via successive hydrogenolysis and hydrosilylation reactions starting from Me3SiCl.
- Beppu, Teruo,Sakamoto, Kei,Nakajima, Yumiko,Matsumoto, Kazuhiro,Sato, Kazuhiko,Shimada, Shigeru
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- Rhodium-catalyzed carbonylative synthesis of silyl-substituted indenones
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A novel and efficient rhodium-catalyzed procedure for the preparation of silyl-substituted indenones has been developed. Using silanes and internal alkynes as the substrates, in the presence of CO, good to excellent yields of the desired indenones were isolated. A wide range of functional groups, encompassing esters, amines, nitriles and halides, is compatible in this system.
- Zhu, Fengxiang,Spannenberg, Anke,Wu, Xiao-Feng
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supporting information
p. 13149 - 13152
(2017/12/26)
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- Activation of Si-H bonds across the nickel carbene bond in electron rich nickel PCcarbeneP pincer complexes
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Silicon-hydrogen bonds are shown to add to a nickel carbon double bond to yield nickel α-silylalkyl hydrido complexes. Kinetic and isotope labeling studies suggest that a concerted 4-centred addition across the NiC bond is operative rather than a mechanism involving Si-H oxidative addition. This constitutes an example of Si-H bond activation via ligand cooperativity.
- LaPierre, Etienne A.,Piers, Warren E.,Spasyuk, Denis M.,Bi, David W.
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supporting information
p. 1361 - 1364
(2016/01/25)
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- Iridium Pincer Catalysts for Silane Dehydrocoupling: Ligand Effects on Selectivity and Activity
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Catalytic reactions of bisphosphinite pincer-ligated iridium compounds p-XR(POCOP)IrHCl (POCOP) [2,6-(R2PO)2C6H3, R = iPr, X = H (1); R = tBu, X = COOMe (2); = H (3); = NMe2 (4)] with primary and secondary silanes have been performed. Complex 1 is primarily a silane redistribution precatalyst, but dehydrocoupling catalysis is observed for sterically demanding silane substrates or with aggressive removal of H2. The bulkier compounds (2-4) are silane dehydrocoupling precatalysts that also undergo competitive redistribution with less hindered substrates. Products generated from reactions utilizing 2-4 include low molecular weight oligosilanes with varying degrees of redistribution present or disilanes when employing more sterically demanding silane substrates. Selectivity for redistribution versus dehydrocoupling depends on the steric and electronic environment of the metal but can also be affected by reaction conditions. (Chemical Equation Presented).
- Mucha, Neil T.,Waterman, Rory
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supporting information
p. 3865 - 3872
(2015/08/19)
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- Si-H bond activation at {(NHC)2Ni0} leading to hydrido silyl and bis(silyl) complexes: A versatile tool for catalytic Si-H/D exchange, acceptorless dehydrogenative coupling of hydrosilanes, and hydrogenation of disilanes to hydrosilanes
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The unique reactivity of the nickel(0) complex [Ni2(iPr 2Im)4(COD)] (1) (iPr2Im = 1,3-di-isopropyl- imidazolin-2-ylidene) towards hydrosilanes in stoichiometric and catalytic reactions is reported. A series of nickel hydrido silyl complexes cis-[Ni(iPr2Im)2(H)(SiHn-1R4-n)] (n = 1, 2) and nickel bis(silyl) complexes cis-[Ni(iPr2Im) 2(SiHn-1R4-n)2] (n = 1, 2, 3) were synthesized by stoichiometric reactions of 1 with hydrosilanes H nSiR4-n, and fully characterized by X-ray diffraction and spectroscopic methods. These hydrido silyl complexes are examples where the full oxidative addition step is hindered. They have, as a result of the remaining Si-H interactions, remarkably short Si-H distances and feature a unique dynamic behavior in solution. Cis-[Ni(iPr2Im)2(H)(SiMePh 2)] (cis-5) shows in solution at room temperature a dynamic site exchange of the NHC ligands, H-D exchange with C6D6 to give the deuteride complex cis-[Ni(iPr2Im)2(D)(SiMePh 2)] (cis-5-D), and at elevated temperatures an irreversible isomerization to trans-[Ni(iPr2Im)2(D)(SiMePh 2)] (trans-5-D). Reactions with sterically less demanding silanes give cis-configured bis(silyl) complexes accompanied by the release of dihydrogen. These complexes display, similarly to the hydrido silyl complexes, interestingly short Si-Si distances. Complex 1 reacts with 4 eq. HSi(OEt) 3, in contrast to all the other silanes used in this study, to give the trans-configured bis(silyl) complex trans-[Ni(iPr2Im) 2Ni(Si(OEt)3)2] (trans-12). The addition of two equivalents of Ph2SiH2 to 1 results, at elevated temperatures, in the formation of the dinuclear complex [{(iPr 2Im)Ni-μ2-(HSiPh2)}2] (6). This diamagnetic, formal Ni(i) complex exhibits a long Ni-Ni bond in the solid state, as established by X-ray diffraction. The capability of the electron rich {Ni(iPr2Im)2} complex fragment to activate Si-H bonds was applied catalytically in the deuteration of Et3Si-H to Et 3Si-D employing C6D6 as a convenient deuterium source. Furthermore, we show that 1 serves as a catalyst for the acceptorless dehydrogenative coupling of Ph2SiH2 to the corresponding disilane Ph2HSi-SiHPh2 and trisilane Ph 2HSi-Si(Ph)2-SiHPh2, and the coupling of PhSiH3 to give a mixture of cyclic and linear polysilanes with high polydispersity (Mw = 1119; Mn = 924; Mw/M n = 1.2). The capability of 1 to catalyze the formal reverse reaction as well is demonstrated by the hydrogenation of disilanes. The hydrogenation of the disilanes Ph2MeSi-SiMePh2 and PhMe 2Si-SiMe2Ph to the corresponding hydrosilanes Ph 2MeSi-H and PhMe2Si-H, respectively, proceeds effectively in the presence of 1 under very mild conditions (room temperature, 1.8 bar H2 pressure).
- Schmidt, David,Zell, Thomas,Schaub, Thomas,Radius, Udo
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supporting information
p. 10816 - 10827
(2014/07/08)
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- Gold nanoparticles-catalyzed activation of 1,2-disilanes: Hydrolysis, silyl protection of alcohols and reduction of tert-benzylic alcohols
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Gold nanoparticles supported on TiO2 catalyze under mild conditions the activation of a series of 1,2-disilanes towards hydrolysis and alcoholysis, with concomitant evolution of H2 gas. For the case of tert-benzyl alcohols, the main or only pathway is reduction to the corresponding alkanes.
- Gryparis, Charis,Stratakis, Manolis
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supporting information
p. 10751 - 10753,3
(2020/09/02)
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- Cooperative catalytic activation of Si-H bonds by a polar Ru-S bond: Regioselective low-temperature c-h silylation of indoles under neutral conditions by a Friedel-crafts mechanism
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Merging cooperative Si-H bond activation and electrophilic aromatic substitution paves the way for C-3-selective indole C-H functionalization under electronic and not conventional steric control. The Si-H bond is heterolytically split by the Ru-S bond of a coordinatively unsaturated cationic ruthenium(II) complex, forming a sulfur-stabilized silicon electrophile. The Wheland intermediate of the subsequent Friedel-Crafts-type process is assumed to be deprotonated by the sulfur atom, no added base required. The overall catalysis proceeds without solvent at low temperature, only liberating dihydrogen.
- Klare, Hendrik F. T.,Oestreich, Martin,Ito, Jun-Ichi,Nishiyama, Hisao,Ohki, Yasuhiro,Tatsumi, Kazuyuki
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supporting information; experimental part
p. 3312 - 3315
(2011/04/24)
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- Carbonyl reduction with CaH2 and R3SiCl catalyzed by ZnCl2
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Ketones and aldehydes were effectively reduced to the corresponding alcohols (or their silyl ethers) by the reaction with CaH2 and R3SiCl in the presence of a catalytic amount of ZnCl2. In the absence of the carbonyl substrate, the reagent reduced R3SiCl to the corresponding hydrosilane under mild reaction conditions.
- Tsuhako, Akiko,He, Jing-Qian,Mihara, Mariko,Saino, Naoko,Okamoto, Sentaro
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p. 9120 - 9123
(2008/09/17)
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- Analysis of an unprecedented mechanism for the catalytic hydrosilylation of carbonyl compounds
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This work details an in-depth evaluation of an unprecedented mechanism for the hydrosilylation of carbonyl compounds catalyzed by (PPh3) 2Re(O)2I. The proposed mechanism involves addition of a silane Si-H bond across one of the rhenium-oxo bonds to form siloxyrhenium hydride intermediate 2 that reacts with a carbonyl substrate to generate siloxyrhenium alkoxide 4, which, in turn, affords the silyl ether product. Compelling evidence for the operation of this pathway includes the following: (a) isolation and structural characterization by X-ray diffraction of siloxyrhenium hydride intermediate 2, (b) demonstration of the catalytic competence of intermediate 2 in the hydrosilylation reaction, (c) 1H and 31P{1H} NMR and ESI-MS evidence for single-turnover conversion of 2 into 1, (d) observation of intermediate 2 in the working catalyst system, and (e) kinetic analysis of the catalytic hydrosilylation of carbonyl compounds by 1.
- Nolin, Kristine A.,Krumper, Jennifer R.,Pluth, Michael D.,Bergman, Robert G.,Toste, F. Dean
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p. 14684 - 14696
(2008/09/20)
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- Palladium-catalyzed silylation of alcohols with hexamethyldisilane
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The combination of hexamethyldisilane and a catalytic amount of [PdCl(η3-C3H5)]2-PPh 3 was found to be effective for the trimethylsilylation of alcohols, where both of the two trimethylsilyl groups of hexamethyldisilane were transferred to alcohols without coproduction of any stoichiometric amount of byproduct but H2. The Royal Society of Chemistry 2006.
- Shirakawa, Eiji,Hironaka, Koji,Otsuka, Hidehito,Hayashi, Tamio
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p. 3927 - 3929
(2007/10/03)
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- Fluoride-Promoted Rearrangement of Organo Silicon Compounds: A New Synthesis of 2-(Arylmethyl)aldehydes from 1-Alkynes
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A new approach to 2-(arylmethyl)aldehydes 4 based upon a 1,2-anionotropic rearrangement of an aryl group is presented. The synthetic sequence begins with a silylformylation reaction of terminal acetylenes 5 with aryl and heteroaryl silanes 6, followed by treatment of the products (Z)-1 with TBAF. The optimization of the experimental conditions of the fluoride-promoted step is described, together with the synthetic potentialities of the process. A plausible mechanism of the rearrangement reaction is reported that suggests the addition of the fluoride ion to the arylsilicon moiety of β-silylalkenals (Z)-1 and the consequent migration of the aryl group to the adjacent carbon atom. Both aryl and heteroaryl substituents can rearrange without any loss of configuration. Bromofunctionalized substrates undergo an intramolecular reaction that affords exclusively carbacyclobenzyl aldehydes, further enhancing the high synthetic value of this method.
- Aronica, Laura Antonella,Raffa, Patrizio,Caporusso, Anna Maria,Salvadori, Piero
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p. 9292 - 9298
(2007/10/03)
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- Titanocene(III) catalyzed homogeneous hydrosilation-hydrogenation of pyridines
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The homogeneous catalytic hydrosilation-hydrogenation of pyridines is observed in the presence of Cp2TiMe2 (Cp = η5-C5H5) and CpCp*TiMe2 (Cp* = η5-C5Me5) as catalysts and using PhSiH3 or PhMeSiH2 as the source of Si-H. Under appropriate conditions, and with appropriate ring-substitution, good yields of the N-silyldihydropyridine or N-silyltetrahydropyridine products are be obtained. Although complete saturation is not achieved with organosilane alone, carrying out the reaction under moderate H2 pressures can give excellent yields of N-silylpiperidines. Under moderate pressures of H2, [Cp2TiH]2 catalyzes rapid H-D exchange between H2 and the 2- and 6-positions of C5D5N. Under the same conditions, only traces of hydrogenation are observed. This, together with the regioselectivity of 3-picoline hydrosilation-hydrogenation, leads to the conclusion that the key step in the reaction is probably addition of Ti-Si to C=N.
- Harrod,Shu,Woo,Samuel
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p. 1075 - 1085
(2007/10/03)
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- The one- and two-photon photochemistry of benzylsilacyclobutanes, acyclic benzylsilanes, and 1,1,2-triphenylsilacyclobutane
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The photochemistry of several ∝-silylbenzyl compounds has been investigated in hexane and in methanol solution. Direct photolysis of 1-benzyl-1-methylsilacyclobutane (1) in methanolic hexane solution produces 1-propyl-1methyl-2,3-benzosilacyclobutene (6) in quantitative yield, by a sequential two-photon process involving the photoactive isotoluene derivative 1-methylene-6-(1-methylsilacyclobutyl)-2,4-cyclohexadiene (13a), which has been identified on the basis of its 1H NMR and UV absorption spectra. In contrast, direct irradiation of 1-benzyl-1-phenylsilacyclobutane (2) under similar conditions results in the formation of a complex mixture of products consistent with the competing formation of 1-benzyl-1-phenylsilene and benzyl- and 1-phenylsilacyclobutyl radicals. The silene is a transient which has been detected directly by laser flash photolysis of 2 (λmax = 315 nm, τ ~ 4.5 μs). Free radical formation is shown to be due to secondary photolysis of a second primary product, 1-methylene-6-(1-phenylsilacyclobutyl)-2,4-cyclohexadiene (13b), which has also been detected and identified by static UV absorption (λmax = 335 nm) and 1H NMR spectroscopy. In a reaction with some analogy to the acid-catalyzed desilylation of allylsilanes, both 13a and 13b can be intercepted in neutral or acidic methanol solution to yield toluene and 1-methyl- or 1-phenyl-1-methoxysilacyclobutane, respectively. Direct photolysis of benzyldimethylphenylsilane (4) also leads to the formation of the corresponding isotoluene derivative, while benzyltrimethylsilane (3) exhibits negligible photoreactivity. The endocyclic benzylsilane 1,1,2-triphenylsilacyclobutane (5) is shown to undergo competing [2 + 2]-cycloreversion and [1,3]-silyl migration to yield a bicyclic isotoluene analogue, which reacts rapidly with methanol to yield the acyclic methoxysilane reported previously to be the main product of photolysis of this silacyclobutane in methanol solution. Relative quantum yields for isotoluene formation from photolysis of 1-4 and absolute rate constants for methanolysis of several of these compounds under neutral and acidic conditions have also been determined.
- Leigh,Owens
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p. 1459 - 1468
(2007/10/03)
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- Synthesis and reactivity of stannyloligosilanes, I. Stannyloligosilane chains containing SiMe2 moieties
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Stannyloligosilanes 1 and 2 with terminal organotin groups are available by reacting alkali metal tri-or diorganostannides with α,ω-dichloro-or difluorosilanes, or by treatment of organochlorostannanes with α,ω-difluorosilanes in the presence of magnesium. Attempts to functionalize the triorganotin derivatives 2 by halogenation reagents did not result in the halogen compounds 5; instead cleavage of silicon-tin bonds is observed. In contrast, reactions of the hydridotin derivatives 1 with CHX3 (X = Cl, Br) lead to the quantitative formation of the bis(chloro-or bromostannyl)oligosilanes 5. All compounds were characterized by NMR, IR, MS and elemental analysis. In addition, the triorganotin compound 2i and the hydridotin species 1b have been characterized by X-ray crystallography.
- Uhlig, Frank,Kayser, Christian,Klassen, Ralph,Hermann, Uwe,Brecker, Lothar,Schürmann, Markus,Ruhland-Senge, Karin,Englich, Ulrich
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p. 278 - 287
(2007/10/03)
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- The preparation and analysis of the phenyldimethylsilyllithium reagent and its reaction with silyl enol ethers
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Phenyldimethylsilyllithium is formed from lithium and phenyldimethylsilyl chloride by slow cleavage of the Si-Si bond of 1,1,2,2-tetramethyl-1,2-diphenyldisilane after the rapid formation of the disilane. 1,1,2,2-Tetramethyl-1,2-diphenyldisiloxane, produced from the silyl chloride by reaction with oxides and hydroxides on the lithium metal surface, is cleaved by dimethyl(phenyl)silyllithium to give lithium dimethyl(phenyl)silanoxide. Dimethyl(phenyl)silyllithium reacts with 1,2-dibromoethane to give dimethyl(phenyl)silyl bromide, which is so rapidly consumed by excess silyllithium reagent that it does not interfere with the double titration used to measure its concentration. Dimethyl(phenyl)silane, produced by protonation of the silyllithium reagent, is also consumed by the silyllithium reagent to give 1,1,2,2-tetramethyl-1,2-diphenyldisilane, which regenerates the silyllithium reagent, as long as lithium is still present. By-products in the preparation of dimethyl(phenyl)silyllithium include 1,3-diphenyl-1,1,2,2,3,3-hexamethyltrisilane, dimethyldiphenylsilane and 1,4-bis[dimethyl(phenyl)-silyl]benzene. Dimethyl(phenyl)silyllithium displaces the silyl group from the tert-butyldimethylsilyl enol ether of cyclohexanone to give the lithium enolate under relatively mild conditions.
- Fleming, Ian,Roberts, Richard S.,Smith, Stephen C.
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p. 1209 - 1214
(2007/10/03)
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- Polymeric organosilicon systems. XXIX. Thermal properties of poly[(disilanylene)oligophenylenes]
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Thermal properties of variously substituted poly[(disilanylene)oligophenylenes], [(SiR1R2SiR1R2)(p-C6H4)m]n (R1=R2=Me, R1=R2=Et, and R1=Ph, R2=Me, m=1-4) were investigated. The thermogravimetric analysis of the polymers in the range of 20-1000°C showed rapid weight loss starting from about 400°C. The total weight loss of the polymers at 1000°C was calculated to be 54.5-75.5% based on the initial weight of the polymers. GC-MS analysis of the volatile products obtained from the pyrolysis of the polymers with R1=R2=Me, m=2 and R1=R2=Et, m=1-4 at 500°C indicated the formation of silicon-containing oligomers arising from the Si-Si and Si-phenylene bond cleavage, mainly. The formation of oligophenylenes, H(C6H4)lH (l=1-4), was also observed in the pyrolysis of the polymers with m=3 and 4. A model reaction for the polymer degradation was also examined, using 1,2-diphenyltetramethyldisilane.
- Ohshita, Joji,Sugimoto, Kazunori,Watanabe, Tsuguo,Kunai, Atsutaka,Ishikawa, Mitsuo,Aoyama, Susumu
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- Kinetic Control in the Cleavage of Unsymmetrical Disilanes
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A series of 12 phenyl-substituted arylpentamethyldisilanes 1a-1 have been synthesized in order to examine the regioselectivity of their nucleophilic Si,Si bond cleavage reactions under Still's conditions (MeLi/HMPA/0°C). It has been found that the sensitivity of these reactions to the electronic effects of the substituents in the phenyl ring could be described by the Hammett-type equation log(kA/kB) = 0.4334 + 2.421(Σσ); (correlation coefficient R = 0.983). The kA/kB ratio represents the relative rate of attack at silicon atom A (linked to the aryl ring) or at silicon atom B (away from the aryl ring) of the unsymmetrical disilanes. Thus, the present investigation shows that the earlier belief according to which the nucleophilic cleavage of unsymmetrical disilanes always produces the more stable silyl anionic species (thermodynamic control) should be abandoned, or at least seriously amended: kinetic factors appear to exert a primary influence on the regioselectivity of such reactions. Since the two major kinetic factors (i.e., electrophilic character of and steric hindrance at a given silicon atom) have opposite effects on the orientation of the reaction, it may happen that kinetic and thermodynamic control lead to the same result. For some of the unsymmetrical disilanes studied, the major reaction path was not the Si,Si bond cleavage; instead, Si-aryl bond breaking occurred, producing the corresponding aryl anions.
- Hevesi, Laszlo,Dehon, Michael,Crutzen, Raphael,Lazarescu-Grigore, Adriana
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p. 2011 - 2017
(2007/10/03)
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- Silicon-carbon unsaturated compounds LIV: Nickel-catalyzed reactions of 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene with alkynes
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The nickel-catalyzed reactions of 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene (1) with disubstituted acetylenes have been investigated.Treatment of I with 3-hexyne and diphenylacetylene at 150 deg C gave two types of adducts: 5,6-benzo-1,4-disilacyclohexa- 2,5-dienes and 5,6-benzo-1,2-disilacyclohexa-3,5-dienes.With methylphenylacetylene,1 afforded a 5,6-benzo-1,4-disilacyclohexa-2,5-di- ene and 5,6-benzo-1,2-disilacyclohexa-3,5-diene, together with a small amount of the other isomer.The reaction of I with phenyl(trimethylsilyl)acetylene produced 5,6-benzo-1,1,4,4-tetraethyl-3-phenyl-2-trimethylsilyl-1,4-disilacyclohexa-2,5-diene and 4,5-benzo-1,1,3,3-tetraethyl-2--1,3-disilacyclopent-4-ene (IO).Similar reaction of 1 with 1-(trimethylsilyl)hexyne also afforded 5,6-benzo-3-butyl-1,1,4,4-tetraethyl-2-trimethylsilyl-1,4-disilacyclohexa-2,5-diene and 4,5-benzo-2--1,1,3,3-tetraethyl-1,3-disilacyclopent-4-ene (12).A vinylidene carbene-nickel complex is proposed for the formation of 10 and 12, as a key intermediate.Keywords: Silicon; Transition metals; o-Quinodisilane; Nickel
- Naka, Akinobu,Okazaki, Shougo,Hayashi, Masaki,Ishikawa, Mitsuo
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- Access to Stabilized Silyl Anions by Electroreduction of Chlorosilanes
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Using the sacrificial anode technique, the electroreduction of arylchlorosilanes into the corresponding arylhydrosilanes occurs via a silylaluminium intermediate characterized for the first time in such reactions.
- Duprat, C.,Biran, C.,Bordeau, M.,Constantieux, T.,Gerval, P.,Dunogues, J.
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p. 2107 - 2108
(2007/10/02)
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- Peculiarities in the cleavage by methyllithium of unsymmetrical disilanes
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The title reactions did not produce the more stable silyl anions from the disilanes studied, they either occurred by attack at the more electrophilic silicon atom, or led to unexpected products.
- Hevesi,Dehon
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p. 8031 - 8032
(2007/10/02)
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- Silicon-carbon unsaturated compounds XL. Photolysis of 1,4-bis(2-phenyltetramethyldisilanyl)-benzene
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The photolysis of 1,4-bis(2-phenyltetramethyldisilanyl)benzene (1) in the presence of isobutene in benzene gave 4-(isobutyldimethylsilyl)-1-(2-phenyltetramethyldisilanyl)-3-(dimethylphenylsilyl)benzene, 2-(isobutyldimethylsilyl)-1-silyl>benzene, and 1,4-bis(isobutyldimethylsilyl)-2,5-bis(dimethylphenylsilyl)benzene in 49, 4 and 12percent yields, respectively, along with small amounts of 1-(2-phenyltetramethyldisilanyl)-4-(dimethylphenylsilyl)benzene (6) dimethylphenylsilane (7) and dimethyldiphenyl-silane (8a).Irradiation of 1 in the absence of isobutene afforded 5a (2percent yield), 6 (less than 1percent yield), 7 (2percent yield)and 8a (3percent yield).Similar irradiation of 1 in deuteriobenzene produced a mixture of 5a and 4--1-(2-phenyltetramethyldisilanyl)benzene, in addition to 6, 7 and (pentadeuteriophenyl)dimethylphenylsilane.
- Ishikawa, Mitsuo,Watanabe, Koki,Sakamoto, Hiromu,Kunai, Atsutaka
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p. 249 - 256
(2007/10/02)
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- Cleavage of Si-C and Ge-C bonds in heterylsilanes and -germanes by organolithium reagents
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Organolithium reagents RLi can cleave Si-C and Ge-C bonds in heterylsilanes and -germanes substituting furyl, dihydrofuryl and dihydropyranyl groups for the organolithium residue R.
- Gevorgyan, Vladimir,Borisova, Larisa,Lukevics, Edmunds
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p. 381 - 387
(2007/10/02)
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- Convenient route to di- and triorganosilyl ethyl ethers and the corresponding di- and triorganosilanes
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Tetraethoxysilane was treated with alkyl- and aryllithium reagents for the reparation of organosilyl ethyl ethers of the type R3SiOEt, R2R'SiOEt, and R2Si(OEt)2, that can be reduced to the organosilanes R3SiH, R2R'SiH, and R2SiH2, respectively, Compounds of the type RR'R''SiOEt cannot be cleanly formed.The reduction procedure involves treatment of the silyl alkoxy ethers with diisobutylaluminium hydride (DIBALH) and hydrolysis of the remaining alkylaluminium compounds with Na2SO4*10H2O.This hydrolysis provides a convenient method for the isolation of R3SiH, R2R'SiH, and R2SiH2 compounds without hydrolysis of the Si-H moiety that often occurs in standard aqueous work-up procedures of unhindered silanes.
- Tour, James M.,John, Jens A.,Stephens, Eric B.
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p. 301 - 310
(2007/10/02)
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- Photochemical reactions of aryl-substituted catenates of group 4B elements, PhMe2E-E'Me3 (E, E' = Si and Ge). Formation of a radical pair
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Photochemical reactions of phenyl substituted catenates of group 4B elements, PhMe2E-E'Me3 (E, E' = Si and Ge) have been investigated by chemical trapping experiments and laser flash-photolysis.On irradiation, the phenylated group 4B catenate undergoes E-E' bond homolysis to give a pair of radicals (PhMe2E. and Me3E'.).In CCl4, these radicals are converted to the corresponding chlorides by abstraction of a chlorine atom.In a nonhalogenated solvent, the radical pair couples at the ipso-position of the phenyl group of the pairing radical (PhMe2E.) to yield the cor responding diradical.This undergoes either elimination of a divalent species (Me2E:) with concomitant formation of trimethylphenyl group 4B element PhMe3E') or intramolecular 1,2-group 4B element migration to yield group 4B metal-carbon double bonded species.The radical escapes from the solvent cage coupled to the metal atom of the radical to yield the dimetallic product.The reaction path observed is highly dependent on the nature of the group 4B element comprising the phenyl substituted catenate.
- Mochida, Kunio,Kikkawa, Haruhiko,Nakadaira, Yasuhiro
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- Photochemical 1,3-Silyl Migration in Allylsilanes Occurring with Inversion of Silyl Configuration
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In apparent disagreement with the prediction by the Woodward-Hoffmann rule, facile intramolecular 1,3-silyl migration of allyl- and propargylsilanes with aromatic substituents at the silicon atom took place reversibly in various solvents under irradiation with 254-nm light, accompanied by the inversion of the silyl configuration.
- Kira, Mitsuo,Taki, Takayuki,Sakurai, Hideki
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p. 5647 - 5648
(2007/10/02)
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- Reactivity of Hypervalent Species: Reactions of Anionic Penta-Coordinated Silicon Complexes towards Nucleophiles
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The reactivity of anionic penta-coordinated silicon complexes 4-O)2>-Na+ 1 with nucleophilic reagents has been studied. 1 can be reduced to organosilanes RSiH3 by metallic hydrides.Reactions with an excess of Grignard or organolithium reagents (R'MgX or R'Li) gave tetraorganosilanes RSiR'3.When only two molar equivalents of Grignard reagents (R'MgX) or lithium reagents (R'Li) are added to complexs 1 functional silanes RR'2SiX can be prepared.
- Boudin, Alain,Cerveau, Genevieve,Chuit, Claude,Corriu, Robert J. P.
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p. 101 - 106
(2007/10/02)
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- Pentacoordinate silicon complexes, the process for their preparation and their application to the preparation of organosilanes
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The present invention relates to new pentacoordinate silicon complexes, the process for their preparation and their application to the preparation of organosilanes. The pentacoordinate silicon complexes according to the invention correspond to the general formula I: STR1 in which: R denotes an alkyl, alkenyl, alkynyl, aryl, aralkyl, aralkenyl, aralkynyl or alkylaryl radical in which the aliphatic fragments are linear, branched or cyclic and contain from 1 to 20 carbon atoms, A represents an alkali metal or alkaline earth metal, with the proviso however that A represents neither sodium nor potassium when R is a phenyl radical, and n=1 or 2.
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- REDUCTION OF ALKOXYSILANES, HALO-SILANES AND -GERMANES WITH LITHIUM ALUMINIUM HYDRIDE UNDER PHASE-TRANSFER CONDITIONS
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In the presence of phase-transfer catalysts, silicon and germanium organohydrides were obtained in high yield by reduction of the corresponding halo and alkoxy derivatives with lithium aluminium hydride in the solid LiAlH4/hydrocarbon two-phase system.
- Gevorgyan, V. N.,Ignatovich, L. M.,Lukevics, E.
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p. C31 - C32
(2007/10/02)
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- INSERTION REACTIONS OF CALCIUM ATOM INTO Si-Cl AND Ge-Cl BONDS
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Calcium atom is inserted into Si-Cl and Ge-Cl bonds of organosilylchlorides and organogermylchlorides to give the corresponding organosilylcalcium chlorides and organogermylcalcium chlorides, respectively.
- Mochida, Kunio,Manishi, Masaharu
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p. 1077 - 1080
(2007/10/02)
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- Alkyl and Silyl Derivatives of Benzene Radical-cations formed by Radiolysis : an Electron Spin Resonance Study
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Exposure of dilute solutions of variuos alkyl- and silyl-benzenes in trichlorofluoromethane to 60CoSg-rays at 77 K gave species whose e.s.r. spectra are characteristic of substituted benzene cations.For the ethyl derivative large hyperfine coupling to the methyl protons establishes a preferred conformation in which the methyl group lies in the plane of the benzene ring.For the isopropyl derivative, and particularly for p-cymene cations, several conformes were detected, the sterically most favourable being the least stable.This is interpreted in terms of strong electron-donation from the C-H ?-orbitals into the ring ?-orbital with is greater than that from C-Me ?-orbitals so that ?-overlap with the C-H bonds is maximised.The energy difference is slightly greater than the steric energy differences.The SOMO for the silyl derivatives (SiH3, SiHMe2, and SiMe3) is also the a1 orbital (ΠSa) which places maximum spin-density on the position of the substituent.However, the degree of hyperconjugation involving Si-H ?-orbitals is reduced by a factor of ca. 2, as judged by the 1H hyperfine coupling constants.Nevertheless, it was not found necessary to invoke a mixture of the a1 and a2 orbitals (ΠSS and ΠSA) to explain the results.These results are compared wiyh those for the corresponding radical-anions and for the neutral cyclopentadienyl radicals.
- Ramakrishna Rao, D. N.,Chandra, Harish,Symons, Martyn C. R.
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p. 1201 - 1206
(2007/10/02)
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- SILYL-TITANATION OF ACETYLENES AND 1,3-DIENES
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A TiIII-Si active species, Cp2TiSiMe2Ph, is formed either by the reaction of Cp2TiCl2 with two equivalents of PhMe2SiLi or by the reaction of Cp2TiCl with one equivalent of PhMe2SiLi.Highly regio- and stereo-selective silyltitanation by this species has been observed with acetylenes and 1,3-dienes.
- Tamao, Kohei,Akita, Munetaka,Kanatani, Ryuichiro,Ishida, Neyoshi,Kumada, Makoto
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- Ylide Reactions of Benzyldimethylammonium Halides
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Deprotonation of benzyldimethylammonium halides (10) with sodium amide or n-butyllithium afforded silylated ylide intermediates 11, which were rearranged into N,N-dimethyl-2-benzylamines (13) accompanied by the formation of Sommelet-Hauser and Stevens rearrangement products (12 and 22).The ylide formation by the cleavage of carbon-silicon bonds also is discussed in the reaction of 10 with sodium amide and lithium aluminum hydride.
- Sato, Yoshiro,Yagi, Yoko,Koto, Masami
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p. 613 - 617
(2007/10/02)
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- Phosphorescence exhibiting materials for optically pumped lasers
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Chemical compounds resulting from the mixing of organosilanes and quinones in the presence of di-tert-butyl peroxide as a sensitizer, exhibit strong blue phosphorescence. These compounds are highly resistant to deterioration by heat and UV irradiation. The unique feature of enhanced phosphorescence quantum efficiency at high temperature makes these systems most suitable for solar pumped lasers which usually will operate at relatively high temperature.
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