Il Nam Jung

Aluminum chloride catalyzed stereo- and regiospecific allylsilylation of alkynes: a convenient route to silyldienes

Abstract Allyltrimethylsilane reacts with phenylalkynes in the presence of aluminium chloride catalyst under mild conditions to afford silylphenyldienes in moderate yield. In this allylsilylation reaction, the silyl group adds regioselectively to the terminal carbon and the allyl group to the inner carbon of the triple bond. The allylsilylation of phenylacetylene gives the allylsilylated product having the silyl and allyl groups in the cis -position, while diphenylacetylene gives the trans product. The allylic inversion was also observed in the allylsilylation with the stereohomogeneous ( Z )-crotyltrimethylsilane. These results are consistent with the initial formation of trimethylsilyl cation intermediate and a stepwise process of allylsilylation.

Pyrolysis of 1,1,2,2,2-tetramethyl-1,2-disila-3,6-dithiacyclohexane; Evidence for dimethylsilathione [(CH3)2SiS] intermediates

Abstract The pyrolysis of 1,1,2,2-tetramethyl-1,2-disila-3,6-dithiacyclohexane (I) yields 1,1-dimethyl-1-sila-2,5-dithiacyclopentane (II), 1,1,2,2,4,4-hexamethyl-1,2,4-trisila-3,5-dithiacyclopentane (III) and ethylene in equal amounts. While pyrolysis of a mixture of I and tetramethylcyclodisilthiane yields equal amounts of II, III and no ethylene. Finally, pyrolysis of a mixture of I and hexamethylcyclotrisilane yields 1,1,3,35,57,7-octamethyl-2,4,6-trioxo-1,3,5,7-tetrasila-8-thiacyclooctane. Possible mechanisms to explain these results are presented. In addition, the first example of insertion of dimethylsilylene into a siliconsulfur bond is reported.

Synthesis of Organosilicon Compounds by New Direct Reactions

Publisher Summary Todays silicone industry is based on direct reaction, which does not require a preformed organometallic reagent and a flammable solvent and does not generate large quantities of metal halide. This chapter discusses the recent developing trend of the direct reaction of elemental silicon with activated or unactivated alkyl chlorides, in particular, emphasizing direct reactions with a mixture of hydrogen chloride and activated alkyl chlorides, such as polychlorinated methanes, silylmethyl chlorides and dichlorides, and allyl chloride. About 90% of the starting materials for the silicone industry are prepared by the direct reaction and the other portion by hydrosilylation reactions. Furthermore, in the direct reaction of elemental silicon with activated alkyl chlorides and polychloromethanes, the decomposition of the reactants can be suppressed and the production of polymeric carbosilanes reduced by adding hydrogen chloride to the reactants. These reactions provide a variety of new organosilicon compounds containing Si–H and Si–Cl functionalities, which should find considerable application in the silicone industry.

EFFECTS OF HYDROGEN CHLORIDE ADDITION TO THE DIRECT REACTION OF METHYLENE CHLORIDE WITH ELEMENTAL SILICON

Abstract Direct synthesis of bis(chlorosily)methanes has been reinvestigated by reacting elemental silicon simultaneously with methylene chloride and hydrogen chloride in the presence of copper catalyst using a stirred reactor equipped with a spiral band agitator at a carefully controlled temperature between 260 and 340°C. Bis(dichlorosily)methane and (dichlorosily)(trichlorosily)methane were obtained as the major products and bis(trichlorosily)methane as a minor product along with trichlorosilabe and tetrachlorosilane derived from the reaction between elemental silicon and hydrogen chloride. The decomposition of methylene chloride was suppressed and the production of polymeric carbosilanes reduced by adding hydrogen chloride to the methylene chloride reactant. The optimum mixing ratio of methylene chloride and hydrogen chloride for the direct synthesis of bis(silyl)methanes was 1:4. The deactivation problem of elemental silicon owing to decomposition of methylene chloride and polycarbosilanes was eliminated. Cadmium was a good promoter for the reaction, while zinc was found to be an inhibitor for this particular reaction.

Friedel—Crafts polyalkylation of alkylbenzenes with dichloromethylvinylsilane

Abstract The Friedel—Crafts alkylation of alkylbenzenes such as toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, o-, m-, p-xylene, and mesitylene with dichloromethylvinylsilane in the presence of aluminum chloride catalyst has been studied under mild conditions. Alkylation with dichloromethylvinylsilane at room temperature gave peralkylated products in yields ranging from 25 to 63%, depending upon the number of substituents on the benzene ring. Less alkylated compounds were also obtained as minor products along with alkyl-reoriented products or transalkylated products. The alkylations of substituted benzenes such as chlorobenzene and anisole did not give the peralkylated products under the same conditions. The molecular structure of tris(dichloromethylsilylethyl)mesitylene has been determined by X-ray diffraction studies. The two chlorosilyl group containing substituents are arranged above the benzene plane and the other one below. Peralkylated compounds were methylated or reduced to the corresponding derivatives by reacting with methyl Grignard reagent and LiAlH4.

Effect of the substituents at the silicon of (ω-chloroalkyl)silanes on the alkylation to benzene

Abstract (ω-Chloroalkyl)silanes [Cl 3− m Me m Si(CH 2 ) n Cl: m =0–3, n =1–3] underwent Friedel–Crafts alkylation with benzene in the presence of aluminum chloride to give alkylated products. Such alkylation reactions took place at temperatures ranging from room temperature ( m =0–1, n =2, 3; m =3, n =1) to 80 ( m =1, 2; n =1) and 200°C ( m =0; n =1), depending on the substituent(s) of the silicon and the alkylene-chain spacer between the silicon and CCl bond of (ω-chloroalkyl)silanes. In the alkylation to benzene, the reactivities of (ω-chloroalkyl)silanes increase as the number ( m ) of methyl-group(s) at the silicon and the alkylene length between the silicon and CCl bond increases. While decomposition of alkylation products was observed at two more methyl groups substituted at silicon in the cases of (chloromethyl)silanes such as (chloromethyl)dimethylchlorosilane and (chloromethyl)trimethylsilane. The reaction with (chloromethyl)trimethylsilane occurred at room temperature to give trimethylchlorosilane, toluene and xylene via a decomposition reaction of the products. No (trimethylsilylmethyl)benzene was formed. In the alkylation to benzene, the reactivity of (ω-chloroalkyl)silanes decreases in the following order: m =3>2>1>0; n =3>2≫1. The results are consistent with the stability of the carbocation generated by the complexation of (ω-chloroalkyl)silanes with aluminum chloride.

Synthesis and biological evaluation of [1‐(1H‐1,2,4‐triazol‐1‐yl)alkyl]‐1‐silacyclopentanes

A series of 1-aryl-1-(1H-1,2,4-triazol-1-yl)alkyl-1-silacyclopentanes has been synthesized by four-step reactions starting from 1-chloroalkyltrichlorosilane and tested for fungicidal activities in vitro for ten fungi and in vivo for four fungi occurring in rice, cucumber, tomato etc. Biological activities of the title compounds are strongly dependent upon the p-substituent on the phenyl group in the following order: F > Cl > Ph > OEt > H. Especially, 1-p-fluorophenyl-1-[1-(1H-1,2,4-triazol-1-yl)alkyl]-1-silacyclopentanes (alkyl = methyl or ethyl) showed significant fungicidal activity with a broad spectrum comparable to flusilazole in in-vivo assay.

Green Light-Emitting Diodes (LED) Based on Diarylethene

A novel class of diarylethene derivatives, (diaryl = N-7-azaindolylpheny, naphthylphenylamine, m-tolylphenylamine, ethene = perfluorocyclopentene) were synthesized and experiments were performed their usage in organic light-emitting diodes (OLEDs). Compound 3 , 1,2-Bis{4-[(phenyl)(m-tolyl)amino]biphenyl}-3,3,4,4,5,5-hexafluorocyclopentene, exhibits a strong green emission in both a solution and a thin film at ∼540 nm. The device with 3 as an emitting material (structure: ITO/TPD/ 3 /Alq3 (q = tris-(8-hydroxyquinolinolate))/Al:Li) shows high quantum efficiency with 7677 cd/m2 at ∼13 V.

Friedel–Crafts alkylation of benzene with (polychloromethyl)silanes

Abstract (Polychloromethyl)silanes (Cl 3− m Me m SiCH 3− n Cl n : m =0–3; n =2, 3) reacted with excess benzene in the presence of aluminum chloride to give (polyphenylmethyl)silanes. Such reactions occurred at the temperatures ranging from room temperature ( m =2, 3; n =2) to 80°C ( m =0, 1; n =2, 3), indicating that the reactivity increases with increasing the number (m) of electron-donating methyl-group(s) at the silicon. In particular, (dichloromethyl)silanes with two or three methyl groups at the silicon ( m =2 or 3; n =2) underwent the alkylation and the decomposition of their products at room temperature. The reaction with (dichloromethyl)trimethylsilane occurred immediately at room temperature to give no (diphenylmethyl)trimethylsilane, but diphenylmethane and trimethylchlorosilane via the decomposition of alkylation product. (Trichloromethyl)silanes ( m =0, 1; n =3) reacted with excess benzene to give (triphenylmethyl)silanes as major products and the unusual (diphenylmethyl)silanes as minor. It was found that unusual (diphenylmethyl)silanes were formed by the decomposition of (triphenylmethyl)silanes under the reaction condition. In the alkylation to benzene, the reactivity of (polychloromethyl)silanes (Cl 3− m Me m SiCH 3− n Cl n : m =0–3; n =2, 3) decreases in the following order: m =3>2>1>0; n =3>2.

Friedel-Crafts alkylations with silicon compounds

Publisher Summary This chapter discusses the reactivities of organo-silicon compounds for the Frieda–Crafts alkylation of aromatic compounds in the presence of aluminum chloride catalyst and the mechanism of the alkylation reactions. The reactivities of alkenylsilanes in the presence of a Lewis acid vary depending upon the nature of substituents on silicon. The substituent effect of vinylsilanes is similar to that of allylsilanes. The reactivity of vinylsilanes increased as the number of chlorine atom on the silicon increased, but decreased as the number of methyl groups increased. The rearrangement of alkylating agent under Friedel–Crafts reaction conditions and chloride exchange between aluminum chloride and alkyl chloride are well known. These indicate that the alkylation proceeds via the transitory existence of carbocations resulting from complexation between the alkylating agent and Lewis acid catalyst. The alkylation of mono-substituted benzenes gives an isomeric mixture of ortho, meta, and para-products. The ratio of isomeric products varies depending upon the electronic nature and steric bulk of the substituents on the benzene.