Silylations triethoxysilane

Tamao and Ito have reported a nickel-catalyzed protocol for the cyclization/hydrosilylation of 1,7-diynes to form (Z)-silylated dialkylidene cyclohexane derivatives.For example, reaction of 1,7-octadiyne with triethoxysilane catalyzed by a mixture of Ni(acac)2 (lmol%) and DIBAL-H (2mol%) in benzene at 50°G for 6h gave the corresponding silylated dialkylidene cyclohexane in 70% yield as a single isomer (Table 1). The reaction of 1,7-octadiyne was also realized with mono- and dialkoxysilanes, trialkylsilanes, and dialkylaminosilanes (Table 1). Diynes that possessed an internal alkyne also underwent nickel-catalyzed reaction, albeit with diminished efficiency (Table 1), while 1,6- and 1,8-diynes failed to undergo nickel-catalyzed cyclization/hydrosilylation. 

As we have already mentioned, ruthenium complexes predominantly catalyze the dehydrogenative silylation of alkenes but competitively with the hydrosilylation so the reaction usually gives a mixture of the dehydrogenative silylation and hydrosilylation products. Ru3(CO)12 appears to be a very active catalyst for the dehydrogenative silylation of styrene, para-substituted styrenes [ 19, 20],trifluoropropene and pentafluorostyrene [21] by trialkyl-, phenyldialkyl-silanes (but also triethoxysilane) (Eq. 10). 

Ethylene hydrosilylation with triethoxysilane has not yet been described in the literature. There are data concerning ethylene and propylene hydrosilylation in the presence of ihodium catalyst [RhCl(CO)2]2- However, it is known that a side reaction, dehydrogenating silylation, is typical for rhodium catalysts (Scheme 1). 

Summary Rhodium-siloxide dimer [ (diene)Rh(jr-OSiMe3) 2] (I) appeared to be an active catalyst (even at room temperature) of the hydrosilylation of allyl ethers, CH2=CHCH20R (R = CH2(I HCH20, C4H9, Ph, CH2Ph, (CH2CH20)7H) by triethoxysilane and methylbis(trimethylsiloxy)silane as well as of allyl esters of selected carboxylic acids, i.e. allyl acetate and allyl butyrate, to yield the usual hydrosilylation products accompanied (in the case of ethers) by traces of dehydrogenative silylation products. 

Hydrosilylation occnrs by the reaction of triethoxysilane with ketones or aldehyde in the presence of CaO or hydroxyapatite (115). Benzaldehyde reacts with (C2H5)3SiH and PhMe2SiH to afford the corresponding silyl benzyl ether in the presence of KF/AI2O3 in 93% and 99% yields, respectively, at 303 K (112). 

Direct alkyne insertion into a Rh—Si bond has been observed for the intermediate rhodium silyl complex (dtbpm) Rh[Si(OEt)3] (PMe3) [dtbpm = di(ferf-butyl)phosphino methane] in the hydrosilylation of 2-butyne with triethoxysilane catalyzed by the rhodium alkyl complex (dtbpm)RhMe(PMc3). The crystal structure of (dtbpm)Rh[Si(OEt)3j (PMes) shows that the coordination around the Rh metal is planar with a Rh—Si bond length [2.325(2) A] similar to that found for the complex (Me3P)3RhH(C6F5) Si(OEt)3 (Table ll) . The proposed mechanism for the hydrosilylation reaction of 2-butyne with HSi(OEt)3 yielding mainly the E-isomer of MeCH=C(Me)Si(OEt)3 is outlined in Scheme 36. 

In addition to the silylation of aryl halides, alkenyl iodides can also be silylated in the presence of a palladium(O) catalyst (eq 22). This silylation proceeds stereoselectively with retention of the carbon-carbon bond stereochemistry, with neither the a-nor (Z)-isomer being produced. The byproduct that arises from this reaction is the saturated /3-aryl triethoxysilane resulting from hydrosilylative reduction of the olefin (97 3 unsaturated saturated). Interesting to note is the increased observance of this saturated byproduct in the presence of other silanes, including dimethoxymethylsilane (93 7), triethylsilane (87 13), dimethylphenylsilane (87 13) and triphenylsilane (90 10), once again demonstrating the specific advantage of triethoxysilane. The alkenylsilanes produced in this reaction are versatile intermediates that have been used effectively in other synthetic transformations. ... 

Silylation of Aryl and Alkenyl Halides. Aryl halides can be successfully silylated in the presence of palladium and rhodium catalysts. The palladium(0)-catalyzed coupling reaction of triethoxysilane with aryl iodides and bromides was developed by Masuda and Murata (eq 21), and later improved on by DeShong. This is an efficient process in most cases, resulting in facile formation of arylsilanes. One limitation of this palladium(0)-catalyzed process is the decreased effectiveness in the presence of ort/zo-substituted and electron-deficient aryl halides. The successively developed rhodium(I)-catalyzed process by Murata and Masuda is broadly applicable to a wide range... 

Park, K.W., Jeong, S.Y., Kwon, O.Y. Interlamellar silylation of H-kenyaite with 3-aminopropyl-triethoxysilane. Appl. Clay Sci. 27, 21-27 (2004)... 

Silylation of borosilicate with APTS (Y-aminopropyl)triethoxysilane) was attempted as a tool to improve its incorporation in PI (polyimide) films (Vankelecom et al. 1996). This was achieved by a minimal coverage of zeolite crystals with APTS, as evidenced by the characterization of silylation through xylene sorptions, NMR spectroscopy, and measurements of the specific surface of the zeolites. Silylated zeolite was incorporated in PI films on which tensile strength, density, and xylene sorption were measured. Indeed, the density and tensile strength measurements on these composite PI membranes proved a better incorporation of borosilicates after silylation with APTS without changing xylene sorption. 

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