- Platinum Complexes with a Phosphino-Oxime/Oximate Ligand
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The platinum(II) complex [PtCl2(COD)] (2; COD = 1,5-cyclooctadiene) reacted with 1 and 2 equiv. of 2-(diphenylphosphanyl)benzaldehyde oxime (1) to generate [PtCl2{κ2-(P,N)-2-Ph2PC6H4CH=NOH}] (3) and [Pt{κ2-(P,N)-2-Ph2PC6H4CH=NOH}2][Cl]2 (4), respectively. Deprotonation of the oxime hydroxyl group of 3 with Na2CO3 led to the selective formation of the dinuclear species (μ-O)-[PtCl{κ2-(P,N)-2-Ph2PC6H4CH=NO}]2 (5), while the related methylated derivative (μ-O)-[PtMe{κ2-(P,N)-2-Ph2PC6H4CH=NO}]2 (7) could be obtained from the direct reaction of [PtMe2(COD)] (6) with the phosphino-oxime ligand 1. In the case of 4, its treatment with Na2CO3 yielded complex [Pt({κ2-(P,N)-2-Ph2PC6H4CH=NO}2H)][Cl] (8), as a result of the deprotonation of only one of the OH groups of 4. On the other hand, contrary to what was observed with 6, no deprotonation of the oxime occurred in the reaction of [PtMe3I]4 (9) with 1, from which the mononuclear PtIV derivative fac-[PtIMe3{κ2-(P,N)-2-Ph2PC6H4CH=NOH}] (10) was isolated. The solid-state structures of compounds 3, 4, 7 and 10 were determined by X-ray crystallography. In addition, the potential of all the synthesized complexes as catalysts for the dehydrogenative coupling of hydrosilanes with alcohols is also briefly discussed.
- Francos, Javier,Borge, Javier,Conejero, Salvador,Cadierno, Victorio
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- Aryldisilane photochemistry. A kinetic and product study of the mechanism of alcohol additions to transient silenes
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Steady state and nanosecond laser flash photolysis techniques have been employed to investigate the mechanism of the reaction of transient silenes with alcohols in polar solvents. The photolysis of a homologous series of three aryldisilanes PhRR′SiSiMesu
- Leigh, William J.,Sluggett, Gregory W.
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- Dehydrogenative coupling of silanes with alcohols catalyzed by Cu3(BTC)2
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Cu3(BTC)2 is an efficient and reusable heterogeneous catalyst for the dehydrogenative coupling of silanes with alcohols. Activity data and CO adsorption suggest that Cu(ii) and in situ generated Cu(i) are the active species. Other MOFs such as Fe(BTC), MIL-101(Cr) and UiO-66(Zr) are unable to promote this cross-coupling.
- Dhakshinamoorthy, Amarajothi,Concepcion, Patricia,Garcia, Hermenegildo
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- Carbon Dioxide Reduction to Silyl-Protected Methanol Catalyzed by an Oxorhenium Pincer PNN Complex
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Reaction of the rhenium pincer PNN complex [(PNN)Re(O)2][OTf] (2) with Me2PhSiH results in addition of Si-H across the ReO bond and a complex capable of reducing CO2 under mild conditions (ambient temperature and 100 psig) to silyl formate in 95% yield. Reaction of 2 with PhSiH3 yields a more reactive complex that catalytically reduces silyl formate to silyl formal (85% yield) and over longer times to silyl methanol (53% yield) with extrusion of siloxane. This system represents the unusual case of a high-valent metal oxo complex capable of reducing CO2 in a two-step, one-pot reaction to methanol.
- Mazzotta,Xiong, Manxi,Abu-Omar, Mahdi M.
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- Benzoimidazole-Pyridylamido Zirconium and Hafnium Alkyl Complexes as Homogeneous Catalysts for Tandem Carbon Dioxide Hydrosilylation to Methane
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Neutral ZrIV and HfIV alkyl/amido complexes stabilized by a tridentate N ligand that contains a “rolling” heterodentate benzoimidazole fragment have been prepared and characterized. The ultimate nature of the ligand denticity, the electronic properties of the ligand binding pocket and the metal coordination environment are controlled by the protection/deprotection of the benzoimidazole NH group. The metal precursor used [MIV(Bn)4 or MIV(NMe2)4] also has an influence on the final coordination sphere of the complex; indeed, a permanent central pyridine dearomatization occurs in the presence of dimethylamido ancillary groups. DFT calculations on the real system have been used to elucidate the mechanism. Selected alkyl species from this series have been scrutinized for the tandem hydrosilylation of CO2 to CH4 in combination with the strong Lewis acid B(C6F5)3 using a variety of hydrosilanes. A positive effect of the hardness modification of the ligand donor atom set is observed in the catalytic outcomes. Indeed, κ3{N?,N,N?}ZrIV(Bn)2 catalyzes the process to methane selectively with a turnover frequency as high as 272 h?1 (at 96 % substrate conversion) almost twice as much as that claimed for the benchmark κ3{O?,O,O?}ZrIV(Bn)2 complex under similar experimental conditions.
- Luconi, Lapo,Rossin, Andrea,Tuci, Giulia,Gafurov, Zufar,Lyubov, Dmitrii M.,Trifonov, Alexander A.,Cicchi, Stefano,Ba, Housseinou,Pham-Huu, Cuong,Yakhvarov, Dmitry,Giambastiani, Giuliano
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- Nanoporous palladium catalyzed silicon-based one-pot cross-coupling reaction of aryl iodides with organosilanes
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One-pot cross-coupling of aryl iodides with organosilanes is realized in excellent yield by utilizing dealloyed nanoporous palladium as a sustainable and heterogeneous catalyst. The reaction is completed under mild conditions and the catalyst can be reused several times without evident loss of its catalytic activity. This journal is the Partner Organisations 2014.
- Li, Zhiwen,Lin, Sha,Ji, Lisha,Zhang, Zhonghua,Zhang, Xiaomei,Ding, Yi
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- Hydrolysis and Methanolysis of Silanes Catalyzed by Iridium(III) Bis-N-Heterocyclic Carbene Complexes: Influence of the Wingtip Groups
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New [Ir(CH3CN)2(I)2{κC,C′-bis(NHC)}]BF4 complexes featuring bis-NHC ligands with a methylene bridge and different N substitution (-CH2CH2CH2CH3 and -CH2CH2OPh) were synthesized. NMR studies and X-ray diffraction structures evidenced that the wingtip group -CH2CH2OPh presents a hemilabile behavior in solution, with the oxygen atom coordinating and dissociating at room temperature, which contrasts with the strong coordination of the ether functions in the complex [Ir(I)2{κC,C′,O,O′-bis(NHCOMe)}]BF4 (bis(NHCOMe) = methylenebis(N,N′-bis(2-methoxyethyl)imidazol-2-ylidene)), previously reported by us. These complexes proved to be efficient catalysts for the hydrolysis and methanolysis of silanes, affording molecular hydrogen and silyl alcohols or silyl ethers as the main reaction products in excellent yields. The hydrogen generation rates were very much dependent on the nature of the hydrosilane and the coordination ability of the wingtip group. The latter also played a key role in the recyclability of the catalytic system. (Chemical Equation Presented).
- Aliaga-Lavrijsen, Mélanie,Iglesias, Manuel,Cebollada, Andrea,Garcés, Karin,García, Nestor,Sanz Miguel, Pablo J.,Fernández-Alvarez, Francisco J.,Pérez-Torrente, Jesús J.,Oro, Luis A.
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- Cobalt single atoms anchored on nitrogen-doped porous carbon as an efficient catalyst for oxidation of silanes
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The oxidation reactions of organic compounds are important transformations for the fine and bulk chemical industry. However, they usually involve the use of noble metal catalysts and suffer from toxic or environmental issues. Here, an efficient, environmentally friendly, and atomically dispersed Co catalyst (Co-N-C) was preparedviaa simple, porous MgO template and etching method using 1,10-phenanthroline as C and N sources, and CoCl2·6H2O as the metal source. The obtained Co-N-C catalyst exhibits excellent catalytic performance for the oxidation of silanes with 97% isolated yield of organosilanol under mild conditions (room temperature, H2O as an oxidant, 1.8 h), and good stability with 95% isolated yield after nine consecutive reactions. The turnover frequency (TOF) is as high as 381 h?1, exceeding those of most non-noble metal catalysts and some noble metal catalysts. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), extended X-ray absorption fine structure (EXAFS), and wavelet transform (WT) spectroscopy corroborate the existence of atomically dispersed Co. The coordination numbers of Co affected by the pyrolysis temperature in Co-N-C-700, Co-N-C-800, and Co-N-C-900 are 4.1, 3.6, and 2.2, respectively. Owing to a higher Co-N3content, Co-N-C-800 shows more outstanding catalytic performance than Co-N-C-700 and Co-N-C-800. Moreover, density functional theory (DFT) calculations reveal that the Co-N3structure exhibits more activity compared with Co-N4and Co-N2, which is because the Co atom in Co-N3was bound with both H atom and Si atom, and it induced the longest Si-H bond.
- Yang, Fan,Liu, Zhihui,Liu, Xiaodong,Feng, Andong,Zhang, Bing,Yang, Wang,Li, Yongfeng
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p. 1026 - 1035
(2021/02/09)
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- Charge Modified Porous Organic Polymer Stabilized Ultrasmall Platinum Nanoparticles for the Catalytic Dehydrogenative Coupling of Silanes with Alcohols
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Developing an ideal stabilizer to prevent the aggregation of nanoparticles is still a big challenge for the practical application of noble metal nanocatalysts. Herein, we develop a charge (NTf2?) modified porous organic polymer (POP-NTf2) to stabilize ultrasmall platinum nanoparticles. The catalyst is characterized and applied in the catalytic dehydrogenative coupling of silanes with alcohols. The catalyst exhibits excellent catalytic performance with highly dispersed ultrasmall platinum nanoparticles (ca. 2.22?nm). Moreover, the catalyst can be reused at least five times without any performance significant loss and Pt NPs aggregation. Graphic Abstract: [Figure not available: see fulltext.]
- Chen, Chao,Cheng, Dan,Ding, Shunmin,Liang, Sanqi,Liu, Senqun,Ma, Xiaohua,Su, Tongtong,Wu, Shaohua,Zeng, Rong
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- Self-Assembled Open Porous Nanoparticle Superstructures
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Imparting porosity to inorganic nanoparticle assemblies to build up self-assembled open porous nanoparticle superstructures represents one of the most challenging issues and will reshape the property and application scope of traditional inorganic nanoparticle solids. Herein, we discovered how to engineer open pores into diverse ordered nanoparticle superstructures via their inclusion-induced assembly within 1D nanotubes, akin to the molecular host-guest complexation. The open porous structure of self-assembled composites is generated from nonclose-packing of nanoparticles in 1D confined space. Tuning the size ratios of the tube-to-nanoparticle enables the structural modulation of these porous nanoparticle superstructures, with symmetries such as C1, zigzag, C2, C4, and C5. Moreover, when the internal surface of the nanotubes is blocked by molecular additives, the nanoparticles would switch their assembly pathway and self-assemble on the external surface of the nanotubes without the formation of porous nanoparticle assemblies. We also show that the open porous nanoparticle superstructures can be ideal candidate for catalysis with accelerated reaction rates.
- Liu, Rongjuan,Wei, Jingjing,Wei, Yanze,Yang, Zhijie,Zhang, Fenghua
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supporting information
(2021/08/20)
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- Swollen-induced in-situ encapsulation of chiral silver catalysts in cross-linked polysiloxane elastomers: Homogeneous reaction and heterogeneous separation
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The immobilization of molecular catalysts to fabricate heterogeneous catalysts for catalytic asymmetric transformations is extremely important and has attracted great attentions. Herein we developed a simple and new strategy for the heterogenization of ho
- Yin, Guan-Wu,Wu, Shi-Lu,Yan, Jun-Hao,Zhang, Peng-Fei,Yang, Meng-Meng,Li, Li,Xu, Zheng,Yang, Ke-Fang,Xu, Li-Wen
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- Catalytic Disproportionation of Formic Acid to Methanol by using Recyclable Silylformates
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A novel strategy to prepare methanol from formic acid without an external reductant is presented. The overall process described herein consists of the disproportionation of silyl formates to methoxysilanes, catalyzed by ruthenium complexes, and the production of methanol by simple hydrolysis. Aqueous solutions of MeOH (>1 mL, >70 percent yield) were prepared in this manner. The sustainability of the reaction has been established by recycling of the silicon-containing by-products with inexpensive, readily available, and environmentally benign reagents.
- Cantat, Thibault,Chauvier, Clément,Imberdis, Arnaud,Thuéry, Pierre
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supporting information
p. 14019 - 14023
(2020/06/09)
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- Half-sandwich ruthenium(ii) complexes with tethered arene-phosphinite ligands: Synthesis, structure and application in catalytic cross dehydrogenative coupling reactions of silanes and alcohols
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The preparation of the tethered arene-ruthenium(ii) complexes [RuCl2{η6:κ1(P)-C6H5(CH2)nOPR2}] (R = Ph, n = 1 (9a), 2 (9b), 3 (9c); R = iPr, n = 1 (10a), 2 (10b), 3 (10c)) from the corresponding phosphinite ligands R2PO(CH2)nPh (R = Ph, n = 1 (1a), 2 (1b), 3 (1c); R = iPr, n = 1 (2a), 2 (2b), 3 (2c)) is presented. Thus, in a first step, the treatment at room temperature of tetrahydrofuran solutions of dimers [{RuCl(μ-Cl)(η6-arene)}2] (arene = p-cymene (3), benzene (4)) with 1-2a-c led to the clean formation of the corresponding mononuclear derivatives [RuCl2(η6-p-cymene){R2PO(CH2)nPh}] (5-6a-c) and [RuCl2(η6-benzene){R2PO(CH2)nPh}] (7-8a-c), which were isolated in 66-99% yield. The subsequent heating of 1,2-dichloroethane solutions of these compounds at 120 °C allowed the exchange of the coordinated arene. The substitution process proceeded faster with the benzene derivatives 7-8a-c, from which complexes 9-10a-c were generated in 61-82% yield after 0.5-10 h of heating. The molecular structures of [RuCl2(η6-p-cymene){iPr2PO(CH2)3Ph}] (6c) and [RuCl2{η6:κ1(P)-C6H5(CH2)nOPiPr2}] (n = 1 (10a), 2 (10b), 3 (10c)) were unequivocally confirmed by X-ray diffraction methods. In addition, complexes [RuCl2{η6:κ1(P)-C6H5(CH2)nOPR2}] (9-10a-c) proved to be active catalysts for the dehydrogenative coupling of hydrosilanes and alcohols under mild conditions (r.t.). The best results were obtained with [RuCl2{η6:κ1(P)-C6H5(CH2)3OPiPr2}] (10c), which reached TOF and TON values up to 117 600 h-1 and 57 000, respectively.
- González-Fernández, Rebeca,Crochet, Pascale,Cadierno, Victorio
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p. 210 - 222
(2019/12/28)
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- Coexistence of Cu(ii) and Cu(i) in Cu ion-doped zeolitic imidazolate frameworks (ZIF-8) for the dehydrogenative coupling of silanes with alcohols
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Recently, metal-ion-doped zeolitic imidazolate frameworks have gained considerable attention for their structure tailorability and potential catalytic applications. Herein, Cu ion-doped ZIF-8 nanocrystals were successfully prepared by the mechanical grind
- Dai, Yan,Xing, Peng,Cui, Xiaoqin,Li, Zhihong,Zhang, Xianming
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p. 16562 - 16568
(2019/11/19)
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- High Production of Hydrogen on Demand from Silanes Catalyzed by Iridium Complexes as a Versatile Hydrogen Storage System
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The catalytic dehydrogenative coupling of silanes and alcohols represents a convenient process to produce hydrogen on demand. The catalyst, an iridium complex of the formula [IrCp?(Cl)2(NHC)] containing an N-heterocyclic carbene (NHC) ligand functionalized with a pyrene tag, catalyzes efficiently the reaction at room temperature producing H2 quantitatively within a few minutes. As a result, the dehydrogenative coupling of 1,4-disilabutane and methanol enables an effective hydrogen storage capacity of 4.3 wt % that is as high as the hydrogen contained in the dehydrogenation of formic acid, positioning the silane/alcohol pair as a potential liquid organic hydrogen carrier for energy storage. In addition, the heterogenization of the iridium complex on graphene presents a recyclable catalyst that retains its activity for at least 10 additional runs. The homogeneous distribution of catalytic active sites on the basal plane of graphene prevents diffusion problems, and the reaction kinetics are maintained after immobilization.
- Ventura-Espinosa, David,Sabater, Sara,Carretero-Cerdán, Alba,Baya, Miguel,Mata, Jose A.
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p. 2558 - 2566
(2018/03/13)
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- Ruthenium-catalyzed alkoxylation of a hydrodisilane without Si[sbnd]Si bond cleavage
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Transition metal-catalyzed synthesis of alkoxydisilanes via dehydrogenative coupling of a hydrodisilane with alcohols is reported. During the reaction, the Si[sbnd]Si bond is preserved effectively when [RuCl2(p-cymene)]2is used as a catalyst. Various alcohols can be used in this alkoxylation.
- Kanno, Ken-ichiro,Aikawa, Yumi,Kyushin, Soichiro
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supporting information
p. 9 - 12
(2016/12/23)
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- Catalytic Dehydrogenative Coupling of Hydrosilanes with Alcohols for the Production of Hydrogen On-demand: Application of a Silane/Alcohol Pair as a Liquid Organic Hydrogen Carrier
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The compound [Ru(p-cym)(Cl)2(NHC)] is an effective catalyst for the room-temperature coupling of silanes and alcohols with the concomitant formation of molecular hydrogen. High catalyst activity is observed for a variety of substrates affording quantitative yields in minutes at room temperature and with a catalyst loading as low as 0.1 mol %. The coupling reaction is thermodynamically and, in the presence of a Ru complex, kinetically favourable and allows rapid molecular hydrogen generation on-demand at room temperature, under air, and without any additive. The pair silane/alcohol is a potential liquid organic hydrogen carrier (LOHC) for energy storage over long periods in a safe and secure way. Silanes and alcohols are non-toxic compounds and do not require special handling precautions such as high pressure or an inert atmosphere. These properties enhance the practical applications of the pair silane/alcohol as a good LOHC in the automotive industry. The variety and availability of silanes and alcohols permits a pair combination that fulfils the requirements for developing an efficient LOHC.
- Ventura-Espinosa, David,Carretero-Cerdán, Alba,Baya, Miguel,García, Hermenegildo,Mata, Jose A.
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supporting information
p. 10815 - 10821
(2017/08/18)
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- Synthesis of nitrogen and sulfur co-doped hierarchical porous carbons and metal-free oxidative coupling of silanes with alcohols
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Hierarchically porous N and S co-doped carbon was prepared by using 2,5-dihydroxy-1,4-benzoquinone as the carbon source, thiourea as the N and S source, and SiO2 particles as the template. Using the material as the catalyst, oxidative coupling of silanes with alcohols was conducted for the first time under metal-free conditions.
- Chen, Bingfeng,Li, Fengbo,Mei, Qingqing,Yang, Youdi,Liu, Huizhen,Yuan, Guoqing,Han, Buxing
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supporting information
p. 13019 - 13022
(2017/12/15)
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- Silica-supported ultra small gold nanoparticles as nanoreactors for the etherification of silanes
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Ultra small gold nanoparticles supported by porous silica (Au-SiO2) were successfully synthesized. Due to enrichment of reactants by silica, the Au-SiO2 particles functioned as nanoreactors for catalytic etherification of silanes wit
- Wang, Cui,Lin, Xijie,Ge, Yuzhen,Shah, Zameer Hussain,Lu, Rongwen,Zhang, Shufen
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p. 102102 - 102108
(2016/11/09)
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- Highly selective oxidation of organosilanes with a reusable nanoporous silver catalyst
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Room temperature highly selective oxidation of organosilanes to organosilanols and organosilyl ethers is achieved in liquid-phase with dealloyed nanoporous silver catalysts. In both cases, aromatic and aliphatic silanes can be effectively converted into the corresponding silanols and silyl ethers by using water and alcohols as oxidant, respectively. Moreover, hydrogen gas is the only by-product and the catalyst can be recycled for several times without evident loss of activity and selectivity.
- Li, Zhiwen,Zhang, Congcong,Tian, Jing,Zhang, Zhonghua,Zhang, Xiaomei,Ding, Yi
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- Copper nanoparticles supported on doped graphenes as catalyst for the dehydrogenative coupling of silanes and alcohols
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Copper nanoparticles (NPs) supported on a series of undoped and doped graphene materials (Gs) have been obtained by pyrolysis of alginate or chitosan biopolymers, modified or not with boric acid, containing Cu2+ ions at 900 °C under inert atmosphere. The resulting Cu-G materials containing about 17 wt% Cu NPs (from 10 to 200 nm) exhibit high catalytic activity for the dehydrogenative coupling of silanes with alcohols. The optimal material consisting on Cu-(B)G is more efficient than Cu NPs on other carbon supports.
- Blez, Juan F.,Primo, Ana,Asiri, Abdullah M.,lvaro, Mercedes,Garc, Hermenegildo
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supporting information
p. 12581 - 12586
(2015/04/16)
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- Highly efficient etherification of silanes by using a gold nanoparticle catalyst: Remarkable effect of O2
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O2 is acting! A nanosized hydroxylapatite-supported Au nanoparticle (NP) catalyst exhibited high activity under aerobic conditions, and various silyl ethers could be obtained from diverse combinations of silanes with alcohols. Moreover, O2 was found to act not as a stoichiometric oxidizing reagent, but as a non-consumed promoter, significantly boosting the catalytic activity of AuNPs (see figure). Copyright
- Mitsudome, Takato,Yamamoto, Yuya,Noujima, Akifumi,Mizugaki, Tomoo,Jitsukawa, Koichiro,Kaneda, Kiyotomi
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p. 14398 - 14402
(2013/11/06)
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- Using the nonaqueous electrolytic solution and secondary battery
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PROBLEM TO BE SOLVED: To provide nonaqueous electrolyte solution capable of improving at least either large-current charge/discharge characteristics or charge/discharge capacity, and a nonaqueous electrolyte solution secondary battery using it. SOLUTION: Electrolyte solution that is liquid electrolyte is immersed in a separator 23. The electrolyte solution contains a liquid solvent, for instance, a nonaqueous solvent such as an organic solvent, and electrolyte salt dissolved in the nonaqueous solvent. Further, as additives, it contains at least one type selected from tris (penta-fluorophenyl) borane (TPFPB) and tris-borate (2H-hexafluoro isopropyl) (THFPB), and at least one type selected from vinylene carbonate (VC) and vinyl ethylene carbonate (VEC). COPYRIGHT: (C)2008,JPO&INPIT
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- An efficient solvent-free route to silyl esters and silyl ethers
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Dinuclear metal complexes, especially (p-cymene)ruthenium dichloride dimer {[RuCl2(p-cymene)]2}, have been found to exhibit high catalytic performance for the dehydrosilylation of various kinds of carboxylic acids and alcohols. The dehydrosilylation with [RuCl2(p-cymene)] 2 proceeded efficiently with only one equivalent of silane with respect to substrate (carboxylic acids or alcohols) under solvent-free conditions to give the corresponding silyl esters and ethers in excellent yields with a high turnover number (TON) and frequency (TOF). The 1H NMR spectrum of a toluene-d8 solution of [RuCl2(p-cymene)] 2 and a silane showed a signal assignable to the ruthenium hydride species. In contrast, no new signals were detected in the 1H NMR spectrum of a toluene-d8 solution of [RuCl2(p-cymene)] 2 and a carboxylic acid or an alcohol. There-fore, the ruthenium metal in [RuCl2(p-cymene)]2 activates a silane to afford the hydride intermediate, possibly a silylmetal hydride species. Then, the nucleophilic attack of a substrate (carboxylic acid or alcohol) to the hydride intermediate proceeds to give the corresponding silylated product. The present dehydrosilylation with an optically active silane proceeded exclusively under inversion of stereochemistry at the chiral silicon center, suggesting that the nucleophilic attack of a substrate to the hydride intermediate occurs from the backside of the ruthenium-silicon bond.
- Ojima, Yuko,Yamaguchi, Kazuya,Mizuno, Noritaka
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scheme or table
p. 1405 - 1411
(2009/12/07)
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- Electrochemical synthesis of symmetrical difunctional disilanes as precursors for organofunctional silanes
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Difunctional disilanes of the general type XR2SiSiR2X (1-5) (X = OMe, H; R = Me, Ph, H) have been synthesized by electrolysis of the appropriate chlorosilanes XR2SiCl in an undivided cell with a constant current supply and in the absence of any complexing agent. Reduction potentials of the chlorosilane starting materials derived from cyclic voltammetry measurements were used to rationalize the results of preparative electrolyses. Organofunctional silanes of the general formula MeO(Me 2)SiC6H4Y (6a-c, 7) were subsequently obtained by the reaction of sym-dimethoxytetramethyldisilane (1) with NaOMe in the presence of p-functional aryl bromides BrC6H4Y (Y = OMe, NEt2, NH2).
- Grogger, Christa,Loidl, Bernhard,Stueger, Harald,Kammel, Thomas,Pachaly, Bernd
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p. 105 - 110
(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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- Steady state and time-resolved spectroscopic studies of the photochemistry of 1-arylsilacyclobutanes and the chemistry of 1-arylsilenes
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Direct photolysis of 1-phenylsilacyclobutane and 1-phenyl-, 1-(2-phenylethynyl)-, and 1-(4'-biphenylyl)-1-methylsilacyclobutane in hexane solution leads to the formation of ethylene and the corresponding 1-arylsilenes, which have been trapped by photolysis in the presence of methanol. Quantum yields for photolysis of the three methyl-substituted compounds have been determined to be 0.04, 0.26, and 0.29, respectively, using the photolysis of 1,1-diphenylsilacyclobutane (Φ(silene) = 0.21) as the actinometer. The corresponding silenes have been detected by laser flash photolysis; they have lifetimes of several microseconds, exhibit UV absorption maxima ranging from 315 to 330 nm, and react with methanol with rate constants on the order of (2-5) x 109 M-1 s-1 in hexane. Absolute rate constants for reaction of 1-phenylsilene and 1-methyl-1-phenylsilene with water, methanol, tert-butanol, and acetic acid in acetonitrile solution have been determined, and are compared to those of 1,1-diphenylsilene under the same conditions. With the phenylethynyl- and biphenyl-substituted methylsilacyclobutanes, the triplet states can also be detected by laser flash photolysis, and are shown to not be involved in silene formation on the basis of triplet sensitization and (or) quenching experiments. Fluorescence emission spectra and singlet lifetimes have been determined for the three 1-aryl-1-methylsilacyclobutanes, 1,1-diphenylsilacyclobutane, and a series of acyclic arylmethylsilane model compounds. These data, along with the reaction quantum yields, allow estimates to be made of the rate constants for the excited singlet state reaction responsible for silene formation. 1-Methyl-1-phenylsilacyclobutane undergoes reaction from its lowest excited singlet state with a rate constant 10-80 times lower than those of the other three derivatives. The results are consistent with a stepwise mechanism for silene formation, involving a 1,4-biradicaloid intermediate that partitions between product and starting material.
- Leigh,Boukherroub,Bradaric,Cserti,Schmeisser
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p. 1136 - 1147
(2007/10/03)
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- An Efficient Catalyst for the Conversion of Hydrosilanes to Alkoxysilanes
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The copper(I) hydride 6 is an efficient catalyst for the alcoholysis of primary and secondary silanes.The reactions proceed at room temperature within a few hours and give the alkoxysilanes in high yields.Only with bulky alcohols or silanes are longer reaction times and/or increased temperatures required.The presence of air accelarates the reactions and gives rise to higher yields of alkoxysilanes, particularly with bulky alcohols.Diols react with PhRSiH2 (R = Me, Ph) to afford 1,3-dioxo-2-silacycloalkanes and with tertiary silanes to furnish the bissilylated diols.When unsaturated alcohols (2-propen-1-ol or 2-propyn-1-ol) are employed, the double or triple bond is retained. - Keywords: Catalytic silane alcoholysis; Alkoxysilanes
- Lorenz, Catrin,Schubert, Ulrich
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p. 1267 - 1270
(2007/10/03)
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- RHODACARBORANE-CATALYZED ALCOHOLYSIS OF SILICON HYDRIDES TO GIVE SILYL ETHERS
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Rhodacarboranes, closo-3,3-(η4-cycloocta-1,5-diene)-1-isopropylidene-3,1,2-dicarbollylrhodium and closo-3-(η3-cyclooctenyl)-1-(1-methylethenyl)-3,1,2-dicarbollylrhodium, catalyze alcoholysis of silicon hydrides to give silyl ethers, but they are inactive in reactions of silicon hydrides with amines or thiols.
- Zhigareva, G. G.,Podvisotskaya, L. S.
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p. 564 - 565
(2007/10/02)
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- Photochemical protodesilylation of 2-R3Si-1,3-dimethoxybenzenes. Direct observation of β-silyl-substituted cyclohexadienyl cations
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Irradiation (254 nm) of the title compounds 5 (R3Si = Me3Si, Ph2MeSi, and 4-XC6H4Me2Si with X = 4-MeO, 4-Me, H, 4-F, and 4-Cl) in 1,1,1,3,3,3-hexafluoroisopropyl alcohol (HFIP) results in q
- Lew, Calvin S. Q.,McClelland, Robert A.
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p. 11516 - 11520
(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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- Silicon-oxygen bond-forming reactions upon addition of silanes and silyl halides to the 16-electron alkoxyiridium complexes trans-ROIr(CO)[P(p-tol)3]2 (R = Me or Ph; p-tol = p-Tolyl). Crystal and molecular structure of H2Ir(CO)(SiMe2Ph)[P(p-tol)3]2
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The reactions of silanes and silyl halides with the 16-electron alkoxyiridium complexes trans-ROIr(CO)[P(p-tol)3]2 (R = Me or Ph; p-tol = p-tolyl) are reported. The silanes add oxidatively to the alkoxyiridium complex; the resulting complex undergoes reductive elimination of an alkoxysilane with ultimate formation of H2Ir(CO)(SiR3)[P(p-tol)3]2. Reactions of silyl halides with the alkoxy complex results in formation of silicon-oxygen bonds. The dihydride H2Ir(CO)(SiMe2Ph)[P(p-tol)3]2, which is an active hydrogenation catalyst, was subjected to structural analysis. It crystallizes in the centrosymmetric triclinic space group P1 with a = 10.692 (1) ?, b = 11.199 (2) ?, c = 20.557 (4) ?, α = 75.991 (14)°, β = 84.505 (14)°, γ = 77.503 (11)°, V = 2329 (1) ?3, and Z = 2. Diffraction data (Mo Kα, 2θ = 4.5-45.0°) were collected with a Syntex P21 automated diffractometer; the structure was solved and refined to RF = 4.9% for all 6119 reflections (RF = 3.6% for those 5094 data with |Fo| > 6σ(|Fo|)). The non-hydride ligands occupy expanded sites in an octahedral iridium(III) complex with Ir-P(1) = Ir-P(2) = 2.366 (2) ?, Ir-Si = 2.414 (2) ?, and Ir-CO = 1.900 (8) ?. The SiMe2Ph ligand is trans to a P(p-tol)3 ligand (P(1)-Ir-Si = 146.39 (7)°). The hydride ligands were located and refined; their positions are of limited accuracy, but they lie in mutually cis sites, trans to a P(p-tol)3 ligand (P(2)-Ir-H(1) = 169.2 (21)°) and to the CO ligand (C-(1)-Ir-H(2) = 169.4 (22)°).
- Rappoli, Brian J.,Janik, Thomas S.,Churchill, Melvyn Rowen,Thompson, Jeffrey S.,Atwood, Jim D.
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p. 1939 - 1944
(2008/10/08)
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- On the Thermal Behaviour of Some (Methylphenylsilyl)methyl Carbonate Derivatives
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The synthesis and the thermal behaviour of the (methylphenylsilyl)methyl carbonates CH3(C6H5)Si(H)CH2OC(O)X (6: X = OCH3; 7: X = Cl; 8: X = N(CH3)2) is described. 8 rearranges in toluene solution at 100 deg C quantitatively to give the carbamoyloxysilane C6H5(CH3)2SiOC(O)N(CH3)2 (11), whereas neat 6 and 7 at 135 deg C undergo quantitative formation of C6H5(CH3)2SiOCH3 (12) and C6H5(CH3)2SiCl (13), respectively.The formation of 12 and 13 is explained by a rearrangement reaction (by analogy to the rearrangement of 8), followed by a decarboxylation.The thermally induced transformations 6-->12, 7-->13, and 8-->11 were found to be first-order reactions with half-lifes of ca. 2.6 h (135 deg C, neat), ca. 4.5 h (135 deg C, neat), and ca. 3.7 h (100 deg C, in toluene), respectively. - Keywords: (Methylphenylsilyl)methyl Carbonates, Rearrangement, Dimethylphenylsilyl Carbonates, Decarboxylation
- Tacke, Reinhold,Link, Matthias,Bentlage-Felten, Anke,Zilch, Harald
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p. 942 - 947
(2007/10/02)
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- MARKED MEDIUM EFFECTS ON THE SUBSTITUTION AND THE ADDITION-REARRANGEMENT-EJECTION REACTIONS OF (HALOMETHYL)SILANES WITH METHOXIDES
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Reactions of methoxides with (halomethyl)silanes at silicon are facilitated by aprotic solvents and cation separation.
- Kreeger, R. L.,Menard, P. R.,Sans, E. A.,Shechter, H.
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p. 1115 - 1118
(2007/10/02)
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- Thermally Induced Rearrangement of (Acyloxymethyl)diorganylsilanes
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The (acyloxymethyl)diorganylsilanes R1R2Si(H)CH2OC(O)R3 (2a-d) rearrange to the corresponding acyloxy(methyl)diorganylsilanes R1R2Si(CH3)OC(O)R3 (3a-d).This reaction is formally equivalent to an exchange of the hydrogen bound to silicon and acyloxy group bound to carbon.The 1,2-hydrogen shift could be shown experimentally to be an intramolecular process.
- Tacke, Reinhold,Lange, Hartwig
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p. 3685 - 3691
(2007/10/02)
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