2- Triethylsilyl-l,3-butadiene

Polymerization of 2-triethylsilyl-l, 3-butadiene initiated by n-butyl-lithium in hexane yielded (E)-l, 4-poly(2-triethylsilyl-l, 3-butadiene). The molecular weight distribution (as determined by gel permeation chromatography) of the polymers depended on the ratio of monomer to initiator concentrations. Polymers of low polydispersity (Mu [weight-average molecular weight]/Mn [number-average molecular weight] = 1.3-1.6) and with up to 110,000 w re obtained. The... 

Anionic polymerization of 2-triethylsilyl-1,3-butadiene (I) in hexane at room temperature initiated by n-, sec-, or rf-butyllithium gave high yields of ( )-l,4-poly(2-triethylsilyl-l,3-butadiene) ( -11). Neither (Z)-1,4-poly(2-tri-ethylsiIyl-1,3-butadiene) (Z-II) nor 1,2 or 3,4 units were found. The reaction is both regio- and stereospecific. 

Triethylsilyl-l,3-butadiene, 502 Triflic acid, 504 Trifluoroacetic acid, 1, 503 Trifluoroacetic anhydride-Pyridine, 504 Trifluoroacetic anhydride-Sodium iodide,... 

The microstructure of anionic polymerization of other poly(l,3-diene)s with lithium as counterion in hydrocarbon media is also predominantly 1,4 (115). However, higher amounts of cis-1,4 microstructures are obtained with more sterically hindered diene monomers. Thus, using conditions which provide polyisoprene with 70% cis-1,4, 22% trans-l,A, and 7% 3,4 microstructure, 2-j-propyl-l,3-butadiene and 2- -propyl-l,3-butadiene provide 86% and 91% cfs-1,4 enchainment, respectively. Both 2-phenyl-l,3-butadiene (92% cis-1,4) and 2-(triethylsilyl)-l,3-butadiene (100% cis-1,4) also exhibit high cis-1,4 enchainment. 

Sterically hindered, 2-alkyl-substituted dienes form high 1,4 microstructure in polar media as well as in hydrocarbon media (115). Butyllithium-initiated polymerization of 2-isopropyl-l,3-butadiene in diethyl ether produces a polymer with 81% cis-1,4 and 19% trans-1,4 microstructure. Similarly, >90% 1,4 microstructure is observed in THF for butyllithium-initiated polymerization of 2-triethylsilyl-l,3-butadiene, 2-trimethoxysilyl-l,3-butadiene, l-phenyl-l,3-butadiene,l-pyridyl-l,3-butadiene, and 2-phenyl-l,3-butadiene. 

Moreover, the formation of enoxy-silanes via silylation of ketones127 by means of N-methyl-N-TMS-acetamide (1 72) in presence of sodium trimethylsilanolate (173) was reported in 1969 and since then, the use of silylating reagents in presence of a catalyst has found wide appreciation and growing utilization as shown in recent papers128-132 (Scheme 27). Diacetyl (181) can be converted by trifluoromethylsul-fonic acid-TMS-ester (182) into 2,3-bis(trimethylsiloxy)-l, 3-butadiene (7treatment with ethyl TMS acetate (7 5)/tetrakis(n-butyl)amine fluoride l-trimethylsiloxy-2-methyl-styrene (i<56)130. Cyclohexanone reacts with the combination dimethyl-TMS-amine (18 7)/p-toluenesulfonic acid to 1-trimethylsiloxy-l-cyclohexene (iSS)131. Similarly, acetylacetone plus phenyl-triethylsilyl-sulfide (189) afford 2-triethylsiloxy-2-pentene-4-one (790)132. ... 

Double silylation of 1,3-butadienes with chlorosilanes was found to proceed by the same procedure. Treatment of a mixture of isoprene, chlorotriethylsilane, and titanocene dichloride with "BuMgCI provided 2-methyl-l,4-bis(triethylsilyl)-2-bu-tene in 91% yield E/Z = 91/9) (Scheme 3.149). 

Organosilicon compounds are largely produced by the hydrosilylation of unsaturated organic substrates [47]. Various transition metal catalysts have been used to obtain alkyl-SiR products from the reaction of H-SiRj with an alkene. Alkene insertion into an M-Si bond is recognized as a fairly common process which plays a key role in catalytic hydrosilylation processes. The reaction of 1,3-butadiene (3-6) with triethylsilane in the presence of [Cr(CO)g] under photochemical condition yields exclusively the ds-1,4-adduct, ds-l-(triethylsilyl)-2-butene (7) (Scheme 10.7) [48]. In all cases, 1-4 addition products form in major, however, in some cases 1-2 addition product (9) also forms in minor yield. Formation of product 12 can be rationalized in terms of double bond migration subsequent to the initial hydrosilylation (Scheme 10.7). 

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