558-37-2Relevant articles and documents
Reactions of alkenylruthenium(II) complexes with hydrosilane: C-Si vs C-H bond formation
Maruyama, Yooichiroh,Yamamura, Kunihiro,Ozawa, Fumiyuki
, p. 905 - 906 (1998)
Alkenylruthenium complexes, Ru{C(R1)=CH(R2)}Cl(CO)-(PPh3)2 (R1 = H, R2 = Ph; R1 = H, R2 = t-Bu; R1 = Ph, R2 = Ph; R1 = CH=CH(SiMe3), R2 = SiMe2Ph), react with HSiMe2Ph via two reaction courses (path A and path B), leading to C-Si and C-H bond formation, respectively. Relative ratio of the two courses is strongly dependent upon steric bulkiness of substituent(s) on the alkenyl ligands.
Intermolecular chemistry of a cyclopropylcarbene and its mechanistic implications
Huang, Haiyong,Platz, Matthew S.
, p. 8337 - 8340 (1996)
Trans-3-(2-tert-butylcyclopropyl)-3H-diazirine was decomposed both thermally (100°C) and photochemically (350 nm, -25 to 25°C) to give the anticipated ring-expanded 3-tert-butylcyclobutene product (50% photochemical, 64% thermal), along with azine and products of trapping by solvent. In the presence of tetramethylethylene (TME), a bicyclopropyl adduct was formed in yields as high as 37% (thermal) or 32% (photochemical). The yield of 3-tert-butylcyclobutene product, however, is only very slightly (0-7%) decreased upon increasing the concentratin of TME. Similar results were obtained with propylamine as the carbene trapping agent. The response of the product mixture to changes in the concentration of the trapping agent shows that there are two product-forming pathways. The mechanistic implications of these observations are discussed.
The Application of 1,2-Oxazinanes as Chiral Cyclic Weinreb Amide-Type Auxiliaries Leading to a Three-Component, One-Pot Reaction
F?hrmann, Jan,Hermann, Ludmila,Hilt, Gerhard
, (2021/12/17)
1,2-Oxazines were synthesised via a copper-catalysed aerobic acyl nitroso Diels-Alder reaction from 1,4-disubstituted 1,3-dienes and N-Boc-hydroxylamine. From this, 1,2-oxazinanes were obtained in a novel follow-up reaction path. The stability of several 1,2-oxazines and 1,2-oxazinanes towards organometallic compounds was tested to rate their operability as cyclic chiral Weinreb amide auxiliaries. 3,6-Di-tertbutyl-1,2-oxazinane gave the best results and was introduced as a chiral Weinreb amide-type auxiliary to yield chiral α-substituted ketones in a diastereomeric ratio of up to 98:2. The removal of the auxiliary can be performed with BuLi to form unsymmetrical α-chiral ketones. Thereafter, the chiral auxiliary can be re-isolated and purified by sublimation under vacuum.
Deoxygenation of Epoxides with Carbon Monoxide
Maulbetsch, Theo,Jürgens, Eva,Kunz, Doris
, p. 10634 - 10640 (2020/07/30)
The use of carbon monoxide as a direct reducing agent for the deoxygenation of terminal and internal epoxides to the respective olefins is presented. This reaction is homogeneously catalyzed by a carbonyl pincer-iridium(I) complex in combination with a Lewis acid co-catalyst to achieve a pre-activation of the epoxide substrate, as well as the elimination of CO2 from a γ-2-iridabutyrolactone intermediate. Especially terminal alkyl epoxides react smoothly and without significant isomerization to the internal olefins under CO atmosphere in benzene or toluene at 80–120 °C. Detailed investigations reveal a substrate-dependent change in the mechanism for the epoxide C?O bond activation between an oxidative addition under retention of the configuration and an SN2 reaction that leads to an inversion of the configuration.
Carboxylate-Assisted β-(Z) Stereoselective Hydrosilylation of Terminal Alkynes Catalyzed by a Zwitterionic Bis-NHC Rhodium(III) Complex
Puerta-Oteo, Raquel,Munarriz, Julen,Polo, Víctor,Jiménez, M. Victoria,Pérez-Torrente, Jesús J.
, p. 7367 - 7380 (2020/07/21)
The zwitterionic compound [Cp*RhCl{(MeIm)2CHCOO}] is an efficient catalyst for the hydrosilylation of terminal alkynes with excellent regio- and stereoselectivity toward the less thermodynamically stable β-(Z)-vinylsilane isomer under mild reaction conditions. A broad range of linear 1-alkynes, cycloalkyl acetylenes, and aromatic alkynes undergo the hydrosilylation with HSiMe2Ph to afford the corresponding β-(Z)-vinylsilanes in quantitative yields in short reaction times. The reaction of aliphatic alkynes with HSiEt3 is slower, resulting in a slight decrease of selectivity toward the β-(Z)-vinylsilane product, which is still greater than 90%. However, a significant selectivity decrease is observed in the hydrosilylation of aromatic alkynes because of the β-(Z) → β-(E) vinylsilane isomerization. Moreover, the hydrosilylation of bulky alkynes, such as t-Bu-CCH or Et3SiCCH, is unselective. Experimental evidence suggests that the carboxylate function plays a key role in the reaction mechanism, which has been validated by means of density functional theory calculations, as well as by mass spectrometry and labeling studies. On the basis of previous results, we propose an ionic outer-sphere mechanism pathway in which the carboxylate fragment acts as a silyl carrier. Namely, the hydrosilylation mechanism entails the heterolytic activation of the hydrosilane assisted by the carboxylate function to give the hydrido intermediate [Cp*RhH{(MeIm)2CHCOO-SiR3}]+. The transference of the silylium moiety from the carboxylate to the alkyne results in the formation of a flat β-silyl carbocation intermediate that undergoes a hydride transfer from the Rh(III) center to generate the vinylsilane product. The outstanding β-(Z) selectivity results from the minimization of the steric interaction between the silyl moiety and the ligand system in the hydride transfer transition state.
A smarter approach to catalysts by design: Combining surface organometallic chemistry on oxide and metal gives selective catalysts for dehydrogenation of 2,3-dimethylbutane
Rouge, Pascal,Garron, Anthony,Norsic, Sébastien,Larabi, Cherif,Merle, Nicolas,Delevoye, Laurent,Gauvin, Regis M.,Szeto, Kai C.,Taoufik, Mostafa
, p. 21 - 26 (2019/04/25)
2,3-dimethylbutane is selectively converted into 2,3-dimethylbutenes at 500 °C under hydrogen or at 390 °C under nitrogen in the presence of bimetallic catalysts Pt-Sn/Li-Al2O3. The high stability of the catalyst along the reaction is obtained by selective modification of the Pt/Li-Al2O3 catalyst using Surface Organometallic Chemistry (SOMC).
Stereoselectivity in a series of 7-alkylbicyclo[3.2.0]hept-2-enes: Experimental and computational perspectives
Leber, Phyllis,Kidder, Katherine,Viray, Don,Dietrich-Peterson, Eric,Fang, Yuan,Davis, Alexander
, (2018/08/03)
Rate constants for overall decomposition (kd) for a series of exo-7-alkylbicyclo[3.2.0]hept-2-enes are relatively invariant. For the alkyl substituents ethyl, propyl, butyl, isopropyl, and t-butyl, the ratio of the rate constant for [1,3] sigmatropic rearrangement to the rate constant for fragmentation, k13/kf, is significantly lower than k13/kf?=?150 observed for exo-7-methylbicyclo[3.2.0]hept-2-ene. Regardless of the size and mass of the alkyl group, the stereoselectivity of the [1,3] carbon migration appears to be quite stable at 80% to 89% suprafacial inversion (si), an observation consistent with conservation of angular momentum but not conservation of orbital symmetry. This global result comports with the phenomenon of “dynamic matching” espoused by Carpenter and collaborators for [1,3] sigmatropic rearrangements in general.
Bifunctional Catalysts Based on Tungsten Hydrides Supported on Silicated Alumina for the Direct Production of 2,3-Dimethylbutenes and Neohexene from Isobutene
Larabi, Cherif,Garron, Anthony,Rouge, Pascal,Szeto, Kai C.,Norsic, Sébastien,De Mallmann, Aimery,Merle, Nicolas,Taoufik, Mostafa
, p. 2160 - 2166 (2017/06/27)
Well-defined bifunctional supported catalysts that comprise tungsten hydride moieties and Br?nsted acid sites were prepared successfully. The catalysts showed outstanding activities and selectivities toward the formation of high-value-added products, 2,3-dimethylbutenes and 3,3-dimethylbutene, through a combination of the metathesis and dimerization of isobutene. The relationship between the physicochemical properties of the catalysts and their activities and selectivities indicated that isobutene conversion increased from 4 to 95 % as a function of the silica content of the silicated alumina (obtained from Sasol). Nevertheless, the selectivity toward branched hexenes showed a volcano-shaped curve that presented a maximum for the catalyst with 5 wt % silica. Therefore, the control of the support acidity by the silica loading on alumina resulted in an increase of the selectivity toward neohexene.
Hydrosilylation of Terminal Alkynes Catalyzed by a ONO-Pincer Iridium(III) Hydride Compound: Mechanistic Insights into the Hydrosilylation and Dehydrogenative Silylation Catalysis
Pérez-Torrente, Jesús J.,Nguyen, Duc Hanh,Jiménez, M. Victoria,Modrego, F. Javier,Puerta-Oteo, Raquel,Gómez-Bautista, Daniel,Iglesias, Manuel,Oro, Luis A.
, p. 2410 - 2422 (2016/08/02)
The catalytic activity in the hydrosilylation of terminal alkynes by the unsaturated hydrido iridium(III) compound [IrH(κ3-hqca)(coe)] (1), which contains the rigid asymmetrical dianionic ONO pincer ligand 8-oxidoquinoline-2-carboxylate, has been studied. A range of aliphatic and aromatic 1-alkynes has been efficiently reduced using various hydrosilanes. Hydrosilylation of the linear 1-alkynes hex-1-yne and oct-1-yne gives a good selectivity toward the β-(Z)-vinylsilane product, while for the bulkier t-Bu-C≡CH a reverse selectivity toward the β-(E)-vinylsilane and significant amounts of alkene, from a competitive dehydrogenative silylation, has been observed. Compound 1, unreactive toward silanes, reacts with a range of terminal alkynes RC≡CH, affording the unsaturated η1-alkenyl complexes [Ir(κ3-hqca)(E-CH=CHR)(coe)] in good yield. These species are able to coordinate monodentate neutral ligands such as PPh3 and pyridine, or CO in a reversible way, to yield octahedral derivatives. Further mechanistic aspects of the hydrosilylation process have been studied by DFT calculations. The catalytic cycle passes through Ir(III) species with an iridacyclopropene (η2-vinylsilane) complex as the key intermediate. It has been found that this species may lead both to the dehydrogenative silylation products, via a β-elimination process, and to a hydrosilylation cycle. The β-elimination path has a higher activation energy than hydrosilylation. On the other hand, the selectivity to the vinylsilane hydrosilylation products can be accounted for by the different activation energies involved in the attack of a silane molecule at two different faces of the iridacyclopropene ring to give η1-vinylsilane complexes with either an E or Z configuration. Finally, proton transfer from a η2-silane to a η1-vinylsilane ligand results in the formation of the corresponding β-(Z)- and β-(E)-vinylsilane isomers, respectively.
Selective Oligomerization and [2 + 2 + 2] Cycloaddition of Terminal Alkynes from Simple Actinide Precatalysts
Batrice, Rami J.,McKinven, Jamie,Arnold, Polly L.,Eisen, Moris S.
, p. 4039 - 4050 (2015/09/01)
A catalyzed conversion of terminal alkynes into dimers, trimers, and trisubstituted benzenes has been developed using the actinide amides U[N(SiMe3)2]3 (1) and [(Me3Si)2N]2An[κ2-(N,C)-CH2Si(CH3)N(SiMe3)] (An = U (2), Th (3)) as precatalysts. These complexes allow for preferential product formation according to the identity of the metal and the catalyst loading. While these complexes are known as valuable precursors for the preparation of various actinide complexes, this is the first demonstration of their use as catalysts for C-C bond forming reactions. At high uranium catalyst loading, the cycloaddition of the terminal alkyne is generally preferred, whereas at low loadings, linear oligomerization to form enynes is favored. The thorium metallacycle produces only organic enynes, suggesting the importance of the ability of uranium to form stabilizing interactions with arenes and related π-electron-containing intermediates. Kinetic, spectroscopic, and mechanistic data that inform the nature of the activation and catalytic cycle of these reactions are presented. (Chemical Equation Presented).
