- Ruthenium-catalyzed C-H bond activation of Michael acceptors: An unusual reactivity leading to allylsilanes
-
We report here an improved catalyst for the functionalization of Michael acceptors, involving C-C bond formation via C-H bond activation, using an in situ generated ruthenium active species. Moreover, on some particular substrates, the C-H functionalizati
- Simon, Marc-Olivier,Martinez, Remi,Genet, Jean-Pierre,Darses, Sylvain
-
supporting information; experimental part
p. 153 - 157
(2009/09/25)
-
- Alkenylsilane structure effects on mononuclear and binuclear organotitanium-mediated ethylene polymerization: Scope and mechanism of simultaneous polyolefin branch and functional group introduction
-
Alkenylsilanes of varying chain lengths are investigated as simultaneous chain-transfer agents and comonomers in organotitanium-mediated olefin polymerization processes. Ethylene polymerizations were carried out with activated CGCTiMe2 and EBICGCTi2Me4 (CGC = Me2Si(Me4C5)(NtBu); EBICGC = (μ-CH2CH2-3,3′){(η5-indenyl)[1- Me2Si(tBuN)]}2) precatalysts in the presence of allylsilane, 3-butenylsilane, 5-hexenylsilane, and 7-octenylsilane. In the presence of these alkenylsilanes, high polymerization activities (up to 10 7 g of polymer/(mol of Ti-atm ethylene·h)), narrow product copolymer polydispersities, and substantial amounts of long-chain branching are observed. Regardless of Ti nuclearity, alkenylsilane incorporation levels follow the trend C8H15SiH3 6H 11SiH3 ≈ C4H7SiH3 3H5SiH3. Alkenylsilane comonomer incorporation levels are consistently higher for CGCTiMe2-mediated copolymerizations (up to 54%) in comparison with EBICGCTi2Me 4-mediated copolymerizations (up to 32%). The long-chain branching levels as compared to the total branch content follow the trend C 3H5SiH3 4H7SiH 3 ≈ C6H11SiH3 ≈ C 8H15SiH3, with gel permeation chromatography-multi-angle laser light scattering-derived branching ratios (gM) approaching 1.0 for C8H15SiH3. Time-dependent experiments indicate a linear increase of copolymer Mw with increasing polymerization reaction time. This process for producing long-chain branched polyolefins by coupling of an α-olefin with a chain-transfer agent in one comonomer is unprecedented. Under the conditions investigated, alkenylsilanes ranging from C3 to C8 are all efficient chain-transfer agents. Ti nuclearity significantly influences silanolytic chain-transfer processes, with the binuclear system exhibiting a sublinear relationship between Mn and [alkenylsilane]-1 for allylsilane and 3-butenylsilane, and a superlinear relationship between Mn and [alkenylsilane]-1 for 5-hexenylsilane and 7-octenylsilane. For the mononuclear Ti system, alkenylsilanes up to C 6 exhibit a linear relationship between Mn and [alkenylsilane]-1, consistent with a simple silanolytic chain termination mechanism.
- Amin, Smruti B.,Marks, Tobin J.
-
p. 2938 - 2953
(2007/10/03)
-
- Transition metal oxo complexes as catalysts of synthetic processes involving alkyne reactants
-
A method is provided for synthesizing substituted alkynes from an alkyne reactant and a nucleophile using rhenium (V) oxo complex as a catalyst. The alkyne reactant is substituted at the propargylic position with a leaving group susceptible to displacement by the nucleophile in a nucleophilic substitution reaction. The method involves contacting the alkyne reactant with a nucleophilic reactant in the presence of a catalytically effective amount of the rhenium (V) oxo complex. The method does not require activation of the leaving group or ionization of the nucleophilic reactant, and may be carried out in the presence of air and moisture. The invention is useful in synthesizing propargyl ethers, propargyl amines, and the like.
- -
-
-
- Reaction of Hydrogen Peroxide with Organosilanes under Chemical Vapour Deposition Conditions
-
When a stream of vapour at low pressure which contained a mixture of H2O2 with an organosilane, RSiH3 (R = alkyl or alkenyl), impinged on a silicon wafer, deposition of oxide films of nominal composition RxSiO(2-0.5x), where x 3 or higher alkenyl groups. or higher alkenylgroups. Possible mechanism for the Si-C bond cleavage reaction are discussed, with energetic rearrangement of radical intermediates of type Si(H)(R)(OOH)' being favoured.
- Moore, Darren L.,Taylor, Mark P.,Timms, Peter L.
-
p. 2673 - 2678
(2007/10/03)
-
- Preparation of vinylsilane from monosilane and vinyl chloride
-
Vinylsilane (CH2=CH-SiH3) was prepared by the dehydrochlorination reaction between SiH4 and vinyl chloride. The reactions were carried out in the gas phase at 450-500°C using a tube reactor, and the maximum yield of vinylsilane was 21% when the conversion of SiH4 was 32%. A small amount of CCl4 and CH3NO2 accelerated the reaction. A reaction mechanism involving :SiH2, which was generated by the thermal decomposition of SiH4, was proposed.
- Itoh, Masayoshi,Iwata, Kenji,Kobayashi, Mineo
-
-
- Synthesis and Characterization of Simple α-Sila- and α,ω-Disilaalkanes: Precursors for the CVD Production of Amorphous Silicon a-SiC:H
-
Preparative methods have been explored for the synthesis of small, volatile polysilaalkanes, which could serve as starting materials for the production of amorphous silicon a-SiC:H.High yield pathways have been developed for H3SiCH2CH2SiH3 and H3SiCH2CH2CH2SiH3.These compounds can be converted into symmetrically halogen-functional derivatives through the reactions with SnCl4 or Br2.The homologous H3SiCH2CH2SiH2CH3 has also been prepared and halogenated, starting from the corresponding vinylsilane via the hydrosilylation route.Allylsilanes were the source of the synthesis of H3SiCH2CH=CH2, CH3SiH2CH2CH=CH2, SiH2(CH2CH=CH2)2, SiH2(CH2CH2CH2SiH3)2, or HSi(CH2CH2CH2SiH3)3.Methylated derivatives are also available. - Some physical and spectroscopic properties of the new compounds have been investigated.In particular, NMR data were collected and used for an assessment of structure and isomerism. - Key words: Disilaalkanes, Silanes, Amorphous Silicon, Hydrosilylation
- Schmidbaur, Hubert,Doerzbach, Cornelia
-
p. 1088 - 1096
(2007/10/02)
-
- Fluorinated allylic compounds and a process for preparing these compounds
-
There are described fluorinated allylic compounds as expressed by the following general formula STR1 wherein Rf is a fluorinated aliphatic group and R is a group expressed by a general formula STR2 wherein R1 is an aliphatic or aromatic hydrocarbon group and R2 and R3 are the same group or different groups as selected among hydrogen atom, aliphatic and aromatic hydrocarbon groups, and heterocyclic groups. Further, a process of preparing fluorinated allylic compounds is described which includes a process step wherein a silane metal halide as expressed by a general formula wherein R1 is either an aliphatic or aromatic hydrocarbon group, M is an element that belongs to the group IIa, IIIb, or VIIb of the periodic table, and X is a halogen atom, is reacted with a fluorinated carboxylic acid ester as expressed by a general formula wherein Rf is a fluorinated aliphatic group and R' is either an aliphatic or aromatic hydrocarbon group, to form a fluorinated carbinol as expressed by a general formula STR3 wherein R1 and Rf are as defined above, and further a molecule of (R1)3 SiOH, where R1 is as defined above, is eliminated from this carbinol to produce a fluorinated allylsilane as expressed by a general formula STR4 wherein R1 and Rf are as defined above.
- -
-
-
- MAGNITUDE AND ORIGIN OF THE beta -SILICON EFFECT ON CARBENIUM IONS.
-
Ab initio molecular orbital calculations have been carried out on alpha - and beta -substituted methyl and vinyl cations to obtain a quantitative measure of the substituent effect of a silyl group relative to a methyl group and hydrogen. Geometries optimized with the 3-21G **(***) basis set were used in calculations at the MP3/6-31G* level. The stabilization energies due to various substituents were determined by means of isodesmic reactions involving the parent methyl and classical vinyl cations. alpha -Methyl substitution of the methyl cation leads to a stabilization energy of 34. 0 kcal/mol compared to 17. 8 kcal/mol obtained through alpha -silyl substitution. The stabilization due to alpha -methyl and alpha -silyl groups is comparable for the vinyl cation (27. 2 and 24. 1 kcal/mol), suggesting that the inductive effect of silicon is more effective in this case.
- Wierschke,Chandrasekhar,Jorgensen
-
p. 1496 - 1500
(2007/10/02)
-