- Synthesis and catalytic activity of N-heterocyclic silylene (NHSi) iron (II) hydride for hydrosilylation of aldehydes and ketones
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A novel silylene supported iron hydride [Si, C]FeH (PMe3)3 (1) was synthesized by C (sp3)-H bond activation with zero-valent iron complex Fe (PMe3)4. Complex 1 was fully characterized by spectroscopic methods and single crystal X-ray diffraction analysis. To the best of our knowledge, 1 is the first example of silylene-based hydrido chelate iron complex produced through activation of the C (sp3)?H bond. It was found that complex 1 exhibited excellent catalytic activity for hydrosilylation of aldehydes and ketones. The catalytic system showed good tolerance and catalytic activity for the substrates with different functional groups on the benzene ring. It is worth mentioning that, the experimental results showed that both ketones and aldehydes could be reduced in good to excellent yields under the same catalytic conditions. Based on the experiments and literature reports, a possible catalytic mechanism was proposed.
- Du, Xinyu,Qi, Xinghao,Li, Kai,Li, Xiaoyan,Sun, Hongjian,Fuhr, Olaf,Fenske, Dieter
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- Heavier Alkaline-Earth Catalyzed Dehydrocoupling of Silanes and Alcohols for the Synthesis of Metallo-Polysilylethers
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The dehydrocoupling of silanes and alcohols mediated by heavier alkaline-earth catalysts, [Ae{N(SiMe3)2}2?(THF)2] (I–III) and [Ae{CH(SiMe3)2}2?(THF)2], (IV–VI) (Ae=Ca, Sr, Ba) is described. Primary, secondary, and tertiary alcohols were coupled to phenylsilane or diphenylsilane, whereas tertiary silanes are less tolerant towards bulky substrates. Some control over reaction selectivity towards mono-, di-, or tri-substituted silylether products was achieved through alteration of reaction stoichiometry, conditions, and catalyst. The ferrocenyl silylether, FeCp(C5H4SiPh(OBn)2) (2), was prepared and fully characterized from the ferrocenylsilane, FeCp(C5H4SiPhH2) (1), and benzyl alcohol using barium catalysis. Stoichiometric experiments suggested a reaction manifold involving the formation of Ae–alkoxide and hydride species, and a series of dimeric Ae–alkoxides [(Ph3CO)Ae(μ2-OCPh3)Ae(THF)] (3 a–c, Ae=Ca, Sr, Ba) were isolated and fully characterized. Mechanistic experiments suggested a complex reaction mechanism involving dimeric or polynuclear active species, whose kinetics are highly dependent on variables such as the identity and concentration of the precatalyst, silane, and alcohol. Turnover frequencies increase on descending Group 2 of the periodic table, with the barium precatalyst III displaying an apparent first-order dependence in both silane and alcohol, and an optimum catalyst loading of 3 mol % Ba, above which activity decreases. With precatalyst III in THF, ferrocene-containing poly- and oligosilylethers with ferrocene pendent to- (P1–P4) or as a constituent (P5, P6) of the main polymer chain were prepared from 1 or Fe(C5H4SiPhH2)2 (4) with diols 1,4-(HOCH2)2-(C6H4) and 1,4-(CH(CH3)OH)2-(C6H4), respectively. The resultant materials were characterized by NMR spectroscopy, gel permeation chromatography (GPC) and DOSY NMR spectroscopy, with estimated molecular weights in excess of 20,000 Da for P1 and P4. The iron centers display reversible redox behavior and thermal analysis showed P1 and P5 to be promising precursors to magnetic ceramic materials.
- Hill, Michael S.,Mahon, Mary F.,Manners, Ian,Morris, Louis J.,S. McMenamy, Fred,Whittell, George R.
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supporting information
p. 2954 - 2966
(2020/03/04)
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- Nickel-Catalyzed Three-Component Coupling Reaction of Tetrafluoroethylene and Aldehydes with Silanes via Oxa-Nickelacycles
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The nickel-catalyzed synthesis of a variety of fluorine-containing silyl ethers from tetrafluoroethylene (TFE) and aldehydes with silanes in a selective manner is disclosed. Stoichiometric reactions revealed that the oxa-nickelacycle, which is generated u
- Shirataki, Hiroshi,Ohashi, Masato,Ogoshi, Sensuke
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supporting information
p. 1883 - 1887
(2019/01/05)
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- Mild synthesis of silyl ethers: Via potassium carbonate catalyzed reactions between alcohols and hydrosilanes
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A method has been developed for the silanolysis of alcohols using an abundant and non-corrosive base K2CO3 as a catalyst. Reactions between a variety of alcohols and hydrosilanes generate silyl ethers under mild conditions. The use of hydrosilanes leads to the formation of H2 as the only byproduct thus avoiding the formation of stoichiometric strong acids. The mild conditions lead to a wide scope of possible alcohol substrates and good functional group tolerance. Selective alcohol silanolysis is also observed in the presence of reactive C-H bonds, lending this method for extensive use in protection group chemistry.
- Delucia, Nicholas A.,Das, Nivedita,Vannucci, Aaron K.
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p. 3415 - 3418
(2018/05/23)
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- Cationic rhenium(iii) complexes: synthesis, characterization, and reactivity for hydrosilylation of aldehydes
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A series of novel cationic Re(iii) complexes [(DAAm)Re(CO)(NCCH3)2][X] [DAAm = N,N-bis(2-arylaminoethyl)methylamine; aryl = C6F5 (a), Mes (b)] [X = OTf (2), BArF4 [BArF4 = tetrakis[3,5-(trifluoromethyl)phenyl]borate] (3), BF4 (4), PF6 (5)], and their analogue [(DAmA)Re(CO)(Cl)2] [DAmA = N,N-bis(2-arylamineethyl)methylamino; aryl = C6F5] (6) were synthesized. The catalytic efficiency for the hydrosilylation reaction of aldehydes using 4a (0.03 mol%) has been demonstrated to be significantly more active than rhenium catalysts previously reported in the literature. The data suggest that electron-withdrawing substituents at the diamido amine ligand increase the catalytic efficiency of the complexes. Excellent yields were achieved at ambient temperature under neat conditions using dimethylphenylsilane. The reaction affords TONs of up to 9200 and a TOF of up to 126 h-1. Kinetic and mechanistic studies were performed, and the data suggest that the reaction is via a non-hydride ionic hydrosilylation mechanism.
- Pérez, Damaris E.,Smeltz, Jessica L.,Sommer, Roger D.,Boyle, Paul D.,Ison, Elon A.
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p. 4609 - 4616
(2017/04/11)
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- Exploring Multistep Continuous-Flow Hydrosilylation Reactions Catalyzed by Tris(pentafluorophenyl)borane
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Exploring the combination of continuous-flow processes with the boron Lewis acid catalyzed hydrosilylation of aldehydes and ketones has delivered a robust and generally applicable reaction protocol. Notably this approach permits ready access to high temperatures and pressures and thus allows improved reactivity of substrates that were previously recalcitrant under the traditional approach. Efforts to quench the output from the flow reactor with water showed surprising tolerance leading to the application of continuous-flow systems in multistep imine formation/hydrosilylation processes to generate the corresponding secondary amines from their aldehyde and aniline precursors. (Figure presented.).
- Wilkins, Lewis C.,Howard, Joseph L.,Burger, Stefan,Frentzel-Beyme, Louis,Browne, Duncan L.,Melen, Rebecca L.
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supporting information
p. 2580 - 2584
(2017/08/16)
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- Silanol Compound, Composition, and Method for Producing Silanol Compound
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The purpose of the present invention is to provide silanol compounds that can be used as raw materials of siloxane compounds and the like, and a composition of the silanol compounds, as well as to provide a production method that makes it possible to produce silanol compounds at excellent yield. A composition comprising 5 mass % to 100 mass % of a silanol compound represented by Formulas (A) to (C) can be prepared by devising to produce silanol compounds under water-free conditions, to produce silanol compounds in a solvent having the effect of suppressing the condensation of silanol compounds, and to perform other such processes, the composition being able to be used as a raw material or the like of siloxane compounds because the silanol compounds can be stably present in the resulting composition.
- -
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Paragraph 0163
(2017/07/14)
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- Dehydrogenative Coupling of Hydrosilanes and Alcohols by Alkali Metal Catalysts for Facile Synthesis of Silyl Ethers
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Cross-dehydrogenative coupling (CDC) of hydrosilanes with hydroxyl groups, using alkali metal hexamethyldisilazide as a single-component catalyst for the formation of Si-O bonds under mild condition, is reported. The potassium salt [KN(SiMe3)2] is highly efficient and chemoselective for a wide range of functionalized alcohols (99% conversion) under solvent-free conditions. The CDC reaction of alcohols with silanes exhibits first-order kinetics with respect to both catalyst and substrate concentrations. The most plausible mechanism for this reaction suggests that the initial step most likely involves the formation of an alkoxide followed by the formation of metal hydride as active species.
- Harinath, Adimulam,Bhattacharjee, Jayeeta,Anga, Srinivas,Panda, Tarun K.
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p. 724 - 730
(2017/05/31)
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- N-Methyl-Benzothiazolium Salts as Carbon Lewis Acids for Si?H σ-Bond Activation and Catalytic (De)hydrosilylation
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N?Me-Benzothiazolium salts are introduced as a new family of Lewis acids able to activate Si?H σ bonds. These carbon-centred Lewis acids were demonstrated to have comparable Lewis acidity towards hydride as found for the triarylboranes widely used in Si?H σ-bond activation. However, they display low Lewis acidity towards hard Lewis bases such as Et3PO and H2O in contrast to triarylboranes. The N?Me-benzothiazolium salts are effective catalysts for a range of hydrosilylation and dehydrosilylation reactions. Judicious selection of the C2 aryl substituent in these cations enables tuning of the steric and electronic environment around the electrophilic centre to generate more active catalysts. Finally, related benzoxazolium and benzimidazolium salts were found also to be active for Si?H bond activation and as catalysts for the hydrosilylation of imines.
- Fasano, Valerio,Radcliffe, James E.,Curless, Liam D.,Ingleson, Michael J.
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supporting information
p. 187 - 193
(2017/01/09)
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- Method for producing polyimidesiloxane
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PROBLEM TO BE SOLVED: To provide a method for synthesizing siloxanes at will in good yield while maintaining high structural controllability, which can be applied to substrates having various substituents.SOLUTION: The method comprises reacting benzyloxysilanes and silicon halides in the absence of hydrogen using a catalyst comprising a transition metal or a compound thereof, preferably a metal of group 9 or group 10 of the periodic table or a compound thereof. Thereby, corresponding siloxanes can be produced safely and simply in high yield under a mild reaction condition accompanied by elimination of a benzyl halide. Especially, by using an active carbon-supported catalyst as a heterogeneous catalyst, the target siloxanes can be separated easily.
- -
-
Paragraph 0033
(2018/10/16)
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- Dehydrogenative coupling of alcohols and carboxylic acids with hydrosilanes catalyzed by a salen-Mn(v) complex
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A Mn(v)-salen complex was found to be an effective catalyst for the dehydrogenative coupling of hydroxyl groups with hydrosilane. The reaction conditions were optimized with different silanes and efficient dehydrogenative coupling was achieved by using triethoxysilane and diphenylsilane. Various alcohols and phenols and a limited number of carboxylic acids were converted into the corresponding silyl ethers and silyl esters. A range of functional groups such as chloro, nitro, methoxy, carbonyl and carbon-carbon multiple bonds are tolerated in the reaction.
- Vijjamarri, Srikanth,Chidara, Vamshi K.,Rousova, Jana,Du, Guodong
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p. 3886 - 3892
(2016/06/14)
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- Ruthenium catalyzed selective hydrosilylation of aldehydes
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A chemoselective hydrosilylation method for aldehydes is developed using a ruthenium catalyst [(Ru(p-cymene)Cl2)2] and triethylsilane; a mono hydride bridged dinuclear complex [{(η6-p- cymene)RuCl}2(μ-H-μ-Cl)] a
- Chatterjee, Basujit,Gunanathan, Chidambaram
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supporting information
p. 888 - 890
(2014/01/06)
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- Nonhydrolytic synthesis of silanols by the hydrogenolysis of benzyloxysilanes
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The hydrogenolysis of benzyloxysilanes was smoothly catalyzed by Pd/C in THF to give corresponding silanols under nonhydrolytic conditions. The reaction proved to be applicable to various benzyloxysilanes giving silanemonools, diol, and triol.
- Igarashi, Masayasu,Matsumoto, Tomohiro,Sato, Kazuhiko,Ando, Wataru,Shimada, Shigeru
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supporting information
p. 429 - 431
(2014/04/17)
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- N-Methylacridinium Salts: Carbon Lewis Acids in Frustrated Lewis Pairs for σ-Bond Activation and Catalytic Reductions
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N-methylacridinium salts are Lewis acids with high hydride ion affinity but low oxophilicity. The cation forms a Lewis adduct with 4-(N,N-dimethylamino)pyridine but a frustrated Lewis pair (FLP) with the weaker base 2,6-lutidine which activates H2, even in the presence of H2O. Anion effects dominate reactivity, with both solubility and rate of H2 cleavage showing marked anion dependency. With the optimal anion, a N-methylacridinium salt catalyzes the reductive transfer hydrogenation and hydrosilylation of aldimines through amine-boranes and silanes, respectively. Furthermore, the same salt is active for the catalytic dehydrosilylation of alcohols (primary, secondary, tertiary, and ArOH) by silanes with no observable over-reduction to the alkanes.
- Clark, Ewan R.,Ingleson, Michael J.
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supporting information
p. 11306 - 11309
(2016/02/19)
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- Trioxorhena(VII)carborane anion and its methyl-substituted analogue: Synthesis, structure, DFT, and catalytic studies
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Synthesis and characterization of trioxorhena(VII)carborane [Bu 4N][(η1-C2B9H 11)ReO3] (1a) and its methyl-substituted analogue [Bu 4N][(7,8-Me2-η1-C2
- Pichaandi, Kothanda Rama,Fanwick, Phillip E.,Abu-Omar, Mahdi M.
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scheme or table
p. 1888 - 1896
(2012/04/23)
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- Catalytic hydrosilylation of carbonyls via Re(CO)5Cl photolysis
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The hydrosilylation reaction between silanes and various carbonyl substrates such as aldehyde, ketone, ester, and carbonate has been catalyzed by Re(CO)5Cl UV photolysis. Kinetic studies have shown that the reaction is favored for the least sterically hindered silanes with aldehydes followed by aliphatic ketones. The IR spectrum of the rhenium carbonyl dimer HRe 2(CO)9(SiR3) has been recorded in the reaction mixture. This complex is believed to be the resting state of the active catalyst Re(CO)4SiR3, which could be released upon photactivation. A catalytic mechanism involving this species has been proposed and shown to be thermodynamically feasible using computational studies. In addition, the relative hydrosilylation rates among the various carbonyl substrates can be explained using the same mechanism.
- Toh, Chun Keong,Sum, Yin Ngai,Fong, Wai Kit,Ang, Siau Gek,Fan, Wai Yip
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experimental part
p. 3880 - 3887
(2012/07/02)
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- Rhodium carbene complexes as versatile catalyst precursors for Si-H bond activation
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Rhodium(III) complexes comprising monoanionic C,C,C-tridentate dicarbene ligands activate Si-H bonds and catalyse the hydrolysis of hydrosilanes to form silanols and siloxanes with concomitant release of H2. In dry MeNO2, selective formation of siloxanes takes place, while changing conditions to wet THF produces silanols exclusively. Silyl ethers are formed when ROH is used as substrate, thus providing a mild route towards the protection of alcohols with H2 as the only by-product. With alkynes, comparably fast hydrosilylation takes place, while carbonyl groups are unaffected. Further expansion of the Si-H bond activation to dihydrosilanes afforded silicones and polysilyl ethers. Mechanistic investigations using deuterated silane revealed deuterium incorporation into the abnormal carbene ligand and thus suggests a ligand-assisted mechanism involving heterolytic Si-H bond cleavage. Ligand-assisted Si-H bond cleavage: Rhodium-catalysed Si-H bond activation provides a methodology for the silyl group to be transferred to oxygen centres, thus providing access to siloxanes and silanols (using H 2O), alkoxysilanes (using ROH) and to polysiloxanes, such as silicones, when using difunctional silanes. The process is pH neutral, avoids sensitive silylating agents and produces H2 as useful and exclusive side product. Copyright
- Krueger, Anneke,Albrecht, Martin
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scheme or table
p. 652 - 658
(2012/03/08)
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- Highly efficient and chemoselective ruthenium-catalyzed hydrosilylation of aldehydes
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The highly chemoselective hydrosilylation of aldehydes was achieved using a ruthenium catalyst activated by a household fluorescent light (30 W) at or below room temperature. The hydrosilylation was almost exclusive to aldehydes over ketones and olefins.
- Do, Youngshil,Han, Junghoon,Rhee, Young Ho,Park, Jaiwook
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experimental part
p. 3363 - 3366
(2012/02/01)
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- Unsuccessful attempts to add alcohols to transient 2-amino-2-siloxy- silenes-leading to a new benign route for base-free alcohol protection
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Thermolytic formation of transient 1,1-bis(trimethylsilyl)-2-dimethylamino- 2-trimethylsiloxysilene (2) from N,N-dimethyl(tris(trimethylsilyl)silyl) methaneamide (1) in presence of a series of alcohols was investigated. The products are, however, not the expected alcohol-silene addition adducts but silylethers formed in nearly quantitative yields. Thermolysis of 1 in the presence of both alcohols (MeOH or iPrOH) and 1,3-dienes (1,3-butadiene or 2,3-dimethyl-1,3-butadiene) gives alkyl-tris(trimethylsilyl)silylethers and the [4+2] cycloadducts between the silene and diene, which confirms the presence of 2 and that it is unreactive towards alcohols. The observed silylethers are substitution adducts where the amide group of the silylamide is replaced by an alkoxy group, and the reaction time is reflected in the steric bulk of the alcohol. Indeed, the formation of silylethers from the reaction of alcohols with silylamide represents a new base-free method for protection of alcohols. The protection reactions using 1 progresses at elevated temperatures, or alternatively, under acid catalysis at ambient temperature, and similar protections can be carried out with N-cyclohexyl(triphenylsilyl)methaneamide and N,N-dimethyl(trimethylsilyl)methaneamide. The latter silylamide can be used under neutral conditions at room temperature. The only by-products are formamides (N,N-dimethylformamide (DMF) or N-cyclohexylformamide), and the reactions can be performed without solvent. In addition to alcohols we also examined the method for protection of diols, thiols and carboxylic acids, and also these reactions proceeded in high yields and with good selectivities. The Royal Society of Chemistry.
- Guliashvili, Tamaz,Tibbelin, Julius,Ryu, Jiyeon,Ottosson, Henrik
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supporting information; experimental part
p. 9379 - 9385
(2011/01/07)
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- High oxidation state rhodium and iridium bis(silyl)dihydride complexes supported by a chelating pyridyl-pyrrolide ligand
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New rhodium and iridium complexes containing the bidentate ligand 3,5-diphenyl-2-(2-pyridyl)pyrrolide (PyPyr) were prepared. The bis(ethylene) complex (PyPyr)Rh(C2H4)2 (3) reacted with HSiEt 3, HSiPh3, and HSitBuPh2 to produce the 16-electron Rh(V) bis(silyl)dihydrides (PyPyr)Rh(H)2(SiEt 3)2 (8), (PyPyr)Rh-(H)2(SiPh3) 2 (9), and (PyPyr)Rh(H)2(SitBuPh 2)2 (10), respectively. The analogous Ir(V) bis(silyl)dihyride (PyPyr)Ir(H)2(SiPh3)2 (11) has also been synthesized. X-ray crystallography reveals that 9-11 adopt a coordination geometry best described as a bicapped tetrahedron. Silane elimination from 9 and 10 occurred in the presence of either HSiEt3 or PPh3. Mechanistic studies of the silane exchange process involving 10 and free HSiEt3 (to give 8) indicate that this process occurs by rate-limiting reductive elimination of HSitBuPh2 from 10 to generate a 14-electron Rh(III) intermediate of the type (PyPyr)Rh(H)(Si tBuPh2).
- McBee, Jennifer L.,Escalada, Jose,Tilley, T. Don
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scheme or table
p. 12703 - 12713
(2010/01/30)
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- Studies on the Mechanism of B(C6F5)3-Catalyzed Hydrosilation of Carbonyl Functions
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The strong organoborane Lewis acid B(C6F5)3 catalyzes the hydrosilation (using R3SiH) of aromatic and aliphatic carbonyl functions at convenient rates with loadings of 1-4%. For aldehydes and ketones, the product silyl ethers are isolated in 75-96% yield; for esters, the aldehydes produced upon workup of the silyl acetal products can be obtained in 45-70% yield. Extensive mechanistic studies point to an unusual silane activation mechanism rather than one involving borane activation of the carbonyl function. Quantitative kinetic studies show that the least basic substrates are hydrosilated at the fastest rates; furthermore, increased concentrations of substrate have an inhibitory effect on the observed reaction rate. Paradoxically, the most basic substrates are reduced selectively, albeit at a slower rate, in competition experiments. The borane thus must dissociate from the carbonyl to activate the silane via hydride abstraction; the incipient silylium species then coordinates the most basic function, which is selectively reduced by [HB(C6F5)3]-. In addition to the kinetic data, this mechanistic proposal is supported by a kinetic isotope effect of 1.4(5) for the hydrosilation of acetophenone, the observation that B(C6F5)3 catalyzes H/D and H/H scrambling in silanes in the absence of substrate, computational investigations, the synthesis of models for proposed intermediates, and other isotope labeling and crossover experiments.
- Parks, Daniel J.,Blackwell, James M.,Piers, Warren E.
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p. 3090 - 3098
(2007/10/03)
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- B(C6F5)3-Catalyzed Silation of Alcohols: A Mild, General Method for Synthesis of Silyl Ethers
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The commercially available borane tris(pentafluorophenyl)borane, B(C6F5)3, is an effective catalyst for the dehydrogenative silation of alcohols using a variety of silanes, R3SiH, R2SiH2, and R2R′SiH. Generally, the reactions occur in a convenient time frame at room temperature using 2 mol % of the borane and are clean and high yielding, with dihydrogen as the only byproduct. Primary aliphatic alcohols are silated cleanly but slowly, with reaction times ranging from 20 to 144 h. Faster reaction times can be achieved by increasing the catalyst loading to 8 mol % or by heating the reaction to ~60°C. Secondary and tertiary alcohols react more rapidly, with most reactions being complete in 0.5-2 h. The reaction is tolerant of many functional groups including C=C, C=C, -Br, aliphatic ketones, C(O)OR, lactones, furans, OBn, OMe, and NO2; examples of each are given. Using the phenolic substrate 2,4,6-trimethylphenol, a number of different silanes were tested. Only the most bulky silanes (Bn3SiH and Pri3SiH) were not reactive under these conditions. The selectivity of the silation reactions are roughly governed by the relative basicity of the alcohols (and other functions in the molecule) with more basic groups being selectively silated. These observations are rationalized on the basis of a mechanism that invokes borane activation of the silane by hydride abstraction. The resulting intermediate silylium/hydridoborate ion pair then reacts with alcohols to give the observed silyl ether and dihydrogen products.
- Blackwell, James M.,Foster, Katherine L.,Beck, Victoria H.,Piers, Warren E.
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p. 4887 - 4892
(2007/10/03)
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