Rhodium-catalysed hydrosilylation: the direct production of alkenyl(triethyl)silanes from alk-1-enes and triethylsilane (original) (raw)
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The reaction of tris(trimethylsilyl)silane with acid chlorides
Tetrahedron Letters, 1992
Tris(trimethylsilyl)silane, in contrast with tributyltin hydride, reduces acid chlorides to the corresponding decarboxylated hydrocarbons via a free radical mechanism. This methodology could be a viable alternative to Barton's decarboxylation reaction.
Base-induced reactions of .alpha.-methylene-.beta.-hydroxysilanes. Formation of allenes
Organometallics, 1993
B-hydroxysilanes react with NaH in octane to give predominantly allenes resulting from @-elimination: The corresponding reactions in more polar solvents or with KHgive mixtures of products from 8-elimination and desilylation, with desilylation predominant in the more polar systems. Although simple (saturated) 8-hydroxysilanes readily undergo base-induced &elimination reactions to give olefins? &hydroxysilanes which are also vinylsilanes (aalkylidene-&hydroxyeilanes) are relatively unreactive to some of these conditions.3 Treatment of such compounds with fluoride has led to allylic alcohols4 from desilylation,6 and treatment with metal hydrides has led to allylic alcoholsuJ*6b or the corresponding silyl ethers.4d@afcvd Compared to the saturated systems, the 8-elimination reactions in the unsaturated systems are disfavored, presumably because they would lead to relatively strained allenes, and the desilylation reactions are favored by the greater stability of vinyl anions over the analogous alkyl anions. The base-induced @-elimination reactions of the saturated 8-hydroxysilanes are typically carried out with KH in an ethereal solvent such as ether or tetrahydrofuran (THF), or with NaH in a more polar solvent such as dimethylformamide.2 We have previously shown that simple (saturated) @-hydroxysilanes react with bases such
Journal of Organometallic Chemistry, 1985
Torr and 300-320°C yields products derived from the reactions of short-lived intermediates, such as silyl and silylmethyl radicals, silylenes, and sila-alkenes. In addition, small-ring silacycles of low stability are formed as the intermediates in some of the dehalogenation reactions. Combination and H-atom abstraction are the main reactions of silyl and silylmethyl radicals. These radicals are not prone to decomposition reactions when C-H, CC , or Si-C bonds are at the P-position to the radical centre. The pentamethyldisilanylmethyl radical decomposes at the p(Si-Si) bond with the formation of Me, Si=CH, and the trimethylsilyl radical. The generation of alkylmethylsilylenes is accompanied by their decomposition, with the formation of 1-alkene and methylsilane. A mechanism has been proposed for the decomposition process, which involves intramolecular j3 (C-H) insertion of alkylmethylsilylenes and [3-+ 2 + l]-thermocyclodecomposition of intermediate silacyclopropanes. The contribution of S(C-H) and e(C-H) insertion reactions is much less pronounced, and in the case of Me,Si(CH,),SiMe (x = 2 or 3), these insertion reactions result in the formation of five-or six-membered silacycles. We did not succeed in obtaining monosilacyclobutanes, as the intramolecular y(C-H)
Organometallics, 2005
The coupling reaction of silyl hydrides with alkoxysilanes to produce siloxanes and hydrocarbons catalyzed by tris(pentafluorophenyl)borane was studied by gas chromatography and UV spectroscopy using model reagent systems: Ph 2 MeSiH + Ph 2 MeSiOn-Oct (I) and Ph 2 MeSiH + Me 3 SiOn-Oct (II). Detailed kinetic studies performed for system I showed that the reaction is first order in both substrates and the rate is proportional to the catalyst concentration. A highly negative apparent entropy of activation points to a crowded transition state structure, leading to a significant dependence of the rate on steric effects. Studies of system II demonstrated that the exchange of the Si-H and Si-OR functionality accompanies the coupling process and in many cases is the dominating reaction in this system. Ultraviolet spectra recorded during the reaction show a distinct strong absorption band with λ max ) 303-306 nm, which is due to an allowed electronic transition in the uncomplexed B(C 6 F 5 ) 3 molecule. This absorption also gives rise to intense fluorescence with a maximum of the emission band at 460 nm. When the borane is complexed by oxygen nucleophiles, such as water, alcohol, or silanol and is not active as a catalyst, it does not show the absorption in the 303-306 nm region. This absorption may serve as a measure of the concentration of the active uncomplexed catalyst in the reaction system. Since complexes of B(C 6 F 5 ) 3 with the alkoxysilane substrates and the disiloxane products are relatively weak, the catalyst appears in the reaction system mostly as an uncomplexed species and its concentration is not significantly changed during the reaction. The mechanism proposed includes the transient formation of a complex between hydrosilane, borane, and alkoxysilane in which His transferred from silicon to boron and an oxonium ion moiety is generated by interaction of alkoxysilane with positive silicon. The decomposition of the complex occurs by the Htransfer to one of the three electrophilic centers of the oxonium structure, which explains the competition between the siloxane formation and the Si-H/Si-OR exchange. In the case of alkoxysilanes derived from primary alcohols, His preferably transferred to silicon. However, for alkoxysilanes derived from a secondary alcohol, such as isopropyl alcohol, the secondary carbon is more readily attacked than silicon by H -, which leads to a high yield of mixed disiloxane.
Catalytic activation of remote alkenes through silyl-rhodium(iii) complexes
Dalton Transactions, 2023
The tandem isomerization-hydrosilylation reaction is a highly valuable process able to transform mixtures of internal olefins into linear silanes. Unsaturated and cationic hydrido-silyl-Rh(III) complexes have proven to be effective catalysts for this reaction. Herein, three silicon-based bidentate ligands, 8-(dimethylsilyl) quinoline (L1), 8-(dimethylsilyl)-2-methylquinoline (L2) and 4-(dimethylsilyl)-9-phenylacridine (L3), have been used to synthesize three neutral [RhCl(H)(L)PPh 3 ] (1-L1, 1-L2 and 1-L3) and three cationic [Rh(H)(L) (PPh 3) 2 ][BAr F 4 ] (2-L1, 2-L2 and 2-L3) Rh(III) complexes. Among the neutral compounds, 1-L2 could be characterized in the solid state by X-ray diffraction showing a distorted trigonal bipyramidal structure. Neutral complexes (1-L1, 1-L2 and 1-L3) failed to catalyze the hydrosilylation of olefins. On the other hand, the cationic compound 2-L2 was also characterized by X-ray diffraction showing a square pyramidal structure. The unsaturated and cationic Rh(III) complexes 2-L1, 2-L2 and 2-L3 showed significant catalytic activity in the hydrosilylation of remote alkenes, with the most sterically hindered (2-L2) being the most active one. † Electronic supplementary information (ESI) available: Spectroscopic characterization and crystallography studies. CCDC 2219493 and 2219494. For ESI and crystallographic data in CIF or other electronic format see
Journal of Organometallic Chemistry, 2000
The nickel equivalent of Karstedt catalyst CHSiMe 2 ) 2 O} 2 {m-(h-CH 2 CHSiMe 2 ) 2 O}] (1) appeared to be a very efficient catalyst for dehydrogenative coupling of vinyl derivatives (styrene, vinylsilanes, vinylsiloxanes) with trisubstituted silanes HSi(OEt) 3 , HSiMe 2 Ph. The reaction occurs via three pathways of dehydrogenative coupling, involving formation of an unsaturated compound as the main product as well as a hydrogenated olefin (DS-1) pathway, hydrogenated dimeric olefin (DS-2) and dihydrogen (DC), respectively. The reaction is accompanied by side hydrosilylation. Stoichiometric reactions of 1 with styrene and triethoxysilane, in particular synthesis of the bis(triethoxysilyl) (divinyltetramethyldisiloxane) nickel complex 3 and the first documented insertion of olefin (styrene) into Ni Si bond of complex 3, as well as all catalytic data have allowed us to propose a scheme of catalysis of this complex reaction by 1.
Chemistry – A European Journal, 2013
The β-(Z)-selectivity in hydrosilylation of terminal alkynes has been hitherto explained by introduction of isomerisation steps in classical mechanisms. DFT calculations and experimental observations on the system [M(I)2{κ-C,C,O,O-bis(NHC)}]BF4 (M = Ir (3a), Rh (3b) bis-NHC = methylenebis(N-2-methoxyethyl)imidazole-2-ylidene)) support a new mechanism, alternative to classical postulations, based on an outer-sphere model. Heterolytic splitting of the silane molecule by the metal centre and acetone (solvent) affords a metal hydride and the oxocarbenium ion ([R3Si-O(CH3)2]+), which reacts with the corresponding alkyne in solution to give the silylation product ([R3Si-CH=C-R]+), thus acetone acts as a silane shuttle transferring the silyl moiety from the silane to the alkyne. Finally, nucleophilic attack of the hydrido ligand over [R3Si-CH=C-R]+ affords selectively the β-(Z)-vinylsilane. The β-(Z)selectivity has been explained on the grounds of the steric interaction between the silyl moiety and the ligand system resulting from the geometry of the approach that leads to β-(E)vinylsilanes.