- CO Displacement in an Oxidative Addition of Primary Silanes to Rhodium(I)
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The rhodium dicarbonyl {PhB(Ox Me2)2ImMes}Rh(CO)2 (1) and primary silanes react by oxidative addition of a nonpolar Si-H bond and, uniquely, a thermal dissociation of CO. These reactions are reversible, and kinetic measurements model the approach to equilibrium. Thus, 1 and RSiH3 react by oxidative addition at room temperature in the dark, even in CO-Saturated solutions. The oxidative addition reaction is first-Order in both 1 and RSiH3, with rate constants for oxidative addition of PhSiH3 and PhSiD3 revealing kH/kD a 1. The reverse reaction, reductive elimination of Si-H from {PhB(Ox Me2)2ImMes}RhH(SiH2R)CO (2), is also first-Order in [2] and depends on [CO]. The equilibrium concentrations, determined over a 30 °C temperature range, provide ?"H° = a'5.5 ± 0.2 kcal/mol and ?"S° = a'16 ± 1 cal·mol-1K-1 (for 1 a?., 2). The rate laws and activation parameters for oxidative addition (?"Ha§§ = 11 ± 1 kcal·mol-1 and ?"Sa§§ = a'26 ± 3 cal·mol-1·K-1) and reductive elimination (?"Ha§§ = 17 ± 1 kcal·mol-1 and ?"Sa§§ = a'10 ± 3 cal·mol-1K-1), particularly the negative activation entropy for both forward and reverse reactions, suggest the transition state of the rate-Determining step contains {PhB(Ox Me2)2ImMes}Rh(CO)2 and RSiH3. Comparison of a series of primary silanes reveals that oxidative addition of arylsilanes is ca. 5× faster than alkylsilanes, whereas reductive elimination of Rh-Si/Rh-H from alkylsilyl and arylsilyl rhodium(III) occurs with similar rate constants. Thus, the equilibrium constant Ke for oxidative addition of arylsilanes is >1, whereas reductive elimination is favored for alkylsilanes.
- Biswas, Abhranil,Ellern, Arkady,Sadow, Aaron D.
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- Carbon-Silicon Bond Formation in the Synthesis of Benzylic Silanes
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Sterically encumbered organosilanes can be difficult to synthesize with conventional, strongly basic reagents; the harsh reaction conditions are often low yielding and not suitable for many functional groups. As an alternative to the typical anionic strat
- Visco, Michael D.,Wieting, Joshua M.,Mattson, Anita E.
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p. 2883 - 2885
(2016/07/06)
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- One-pot synthesis and structural characterization of poly(alkoxysilane)s catalyzed by silver-gold complexes
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Combinative one-pot Si-Si/Si-O dehydrocoupling of hydrosilanes with alcohols (1:1.5 mole ratio), mediated by a mixture of AgNO3-AuCl 3 (100/1 mole ratio) rapidly produced poly(alkoxysilane)s in reasonably high yield. The addition of small amount of gold complex to the reaction mixture effectively accelerated the coupling reaction compared to the reaction rate with AgNO3 alone. The hydrosilanes include p-X-C 6H4SiH3 (X = H, CH3, OCH 3, F), PhCH2SiH3, and (PhSiH2) 2. The alcohols include MeOH, EtOH, iPrOH, PhOH, and CF 3(CF2)2CH2OH. The weight average molecular weight and polydispersity of the poly(alkoxysilane)s were in the range of 1,600~8,000 Dalton and 1.4~3.5, respectively. The dehydrocoupling reactions of phenylsilane with ethanol (1:3 mole ratio) in the presence of the Ag-Au complexes gave only triethoxyphenylsilane. Copyright
- Cheong, Hyeonsook,Roh, Sung-Hee,Cho, Myong-Shik,Kim, Myoung-Hee,Woo, Hee-Gweon,Yang, Kap-Seung,Kim, Bo-Hye,Jun, Jin,Sohn, Honglae
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p. 702 - 705
(2013/06/26)
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- One-pot synthesis of poly(alkoxysilane)s by Si-Si/Si-O dehydrocoupling of silanes with alcohols using Group IV and VIII metallocene complexes
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Si-Si/Si-O dehydrocoupling reactions of silanes with alcohols (1:1.5 mole ratio), catalyzed by Cp2MCl2/Red-Al (M=Ti, Zr) and Cp2M′ (M′=Co, Ni), produced poly(alkoxysilane)s in one-pot in high yield. The silanes included p-X-C6H4SiH3 (X=H, CH3, OCH3, F), PhCH2SiH3, and (PhSiH2)2. The alcohols were MeOH, EtOH, iPrOH, PhOH, and CF3(CF2) 2CH2OH. The weight average molecular weight of the poly(alkoxysilane)s ranged from 600 to 8000. The dehydrocoupling reactions of phenylsilane with ethanol (1:1.5 mole ratio) using Cp2HfCl2/Red-Al and phenylsilane with ethanol (1:3 mole ratio) using Cp2TiCl2/Red-Al gave only triethoxyphenylsilane as product.
- Kim, Bo-Hye,Cho, Myong-Shik,Kim, Mi-Ae,Woo, Gee-Gweon
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- Synthesis, structure and photoluminescence of 1,2-disila-acenaphthene Si2C10H10 and 1,2-diaryldisilane reference compounds
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For the synthesis of the diaryldisilanes Ar-SiH2SiH2-Ar (la, Ar = phenyl; Ib, Ar = p-tolyl; le, Ar = mesityl; Id, Ar = p-anisyl) two convenient preparative routes are reported. The crystal structures of le and Id have been determined in Xray diffraction studies; the disilanes have a staggered transconformation with a crystallographically imposed center of inversion. For la-d no photoluminescence phenomena can be observed. 1,2-Disila-acenaphthene (2) is synthesized in acceptable yield by treatment of 1,8-dilithionaphthalene with 1 equivalent of l,2-bis[((trifluoromethyl)sulfonyl)oxy]disilane Tf-SiH2SiH2-Tf. The crystal structure of 2 has also been determined by X-ray diffraction. The molecule has no crystallographically imposed symmetry but closely follows the symmetry elements of point group C2v. Solutions of 2 exhibit intense fluorescence in the near UV region at room temperature. The fluorescence spectra are discussed in comparison with data on acenaphthene and naphthalene. WILEY-VCH Verlag GmbH 1997.
- Soeldner, Marcus,Sandor, Mario,Schier, Annette,Schmidbaur, Hubert
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p. 1671 - 1676
(2007/10/03)
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- CARBON-SILICON BOND CLEAVAGE OF ORGANOTRIALKOXYSILANES AND ORGANOSILATRANES WITH m-CHLOROPERBENZOIC ACID AND N-BROMOSUCCINIMIDE. NEW ROUTE TO PHENOLS, PRIMARY ALCOHOLS AND BROMIDES
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Alkyl- and aryltriethoxysilanes undergo oxidative carbon-silicon bond cleavage smoothly with m-chloroperbenzoic acid (MCPBA) to afford the corresponding alcohols.Silatranes similarly gave alcohols and bromides with MCPBA and N-bromosuccinimide, respectively.
- Hosomi, Akira,Iijima, Susumu,Sakurai, Hideki
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p. 243 - 246
(2007/10/02)
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