ISSN:0008-4042    

DOI:10.1139/cjc7811pre

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The photolysis of tris(trimethylsilyl)silane (TTMSS) was studied in the absence and in the presence of added trapping agents such as alkenes and alcohols. It was found that, unlike the case with pyrolysis, silyl radicals rather than silylenes are produced. They may be efficiently trapped with alkenes, to give the hydrosilylation products, but not with alcohols. The major product from the photolysis of TTMSS in the absence of added trapping agent (or with alcohols as trapping agents) was tetrakis(trimethylsilyl)silane. Possible mechanisms to account for the photoproducts are presented.Key words: hydrosilane, photolysis, silylenes, silyl radical, sisyl hydride.

ISSN:0008-4042    

DOI:10.1139/v00-085

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Bis(trimethylsilyl)methylamine, BSMA, an original primary amine, was proven to be the source of a large variety ofN-bis(trimethylsilyl)methylamino derivatives that otherwise have to be prepared indirectly. Because of the bulkiness of the bissilylmethyl group, regio- and stereoselectivities resulted in appropriated examples. Apart from the potential biological properties associated with the Si-C-N framework, these derivatives were powerful synthetic intermediates. Special emphasis was given to the chemistry of corresponding imines. Cleavage of Si—C bonds or abstraction of the methine proton afforded &agr;-nitrogen carbanions in very mild conditions. Application of these results to the &bgr;-lactam chemistry allowed the introduction of new synthetic methodologies in this field. It results the (Me3Si)2CH- group could now be regarded as a Me3SiCH2- or a CH3- group or a proton equivalent.Key words: bis(silyl)methylamine, preparations, reactivity, nitrogen heterocycles, &agr;-nitrogen carbanions

ISSN:0008-4042    

DOI:10.1139/v00-090

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Treatment of Si(OMe)4with three molar equivalents of 1,2-C6H4(OH)2(= 1,2-dihydroxybenzene) and two molar equivalents of HO(CH2)nNMe2(n= 2, 3) in acetonitrile at room temperature yields the &lgr;6Si-silicates (HO(CH2)nNMe2H)2(SiL3) (5:n= 2;6:n= 3; L2–= 1,2-C6H4(O)22–(= benzene-1,2-diolato(2–))). The analogous &lgr;6Ge-germanates (HO(CH2)nNMe2H)2(GeL3) (7:n= 2;8:n= 3) were synthesized analogously starting from Ge(OMe)4. Compounds5·2CH3CN and6-8were structurally characterized by single-crystal X-ray diffraction. In addition, aqueous solutions of the Si/Ge analogs5/7and6/8were studied by NMR spectroscopy. The title compounds may be regarded as model systems for the transport and storage of silicon in biological systems and as tools to investigate biosilification.Key words: hexacoordinate silicon, hexacoordinate germanium, silicon biochemis

ISSN:0008-4042    

DOI:10.1139/v00-072

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The photobromination of 1,1,3,3,5,5-hexamethyl-1,3,5-trisilacyclohexane (1) almost exclusively attacks CH2groups and results in 2,2-dibromo-trisilacyclohexane (2) as well as 2,2,4,4-tetrabromo-trisilacyclohexane (3)in high yields. Starting from a mixture of C-brominated trisilacyclohexanes the isomeric 2,2,9-tribromo-1,3,3,5,5,8,8,10,10,13,13-undecamethyl-1,3,5,8,10,13-hexasilabicyclo[7.2.2]tridec-6-yne (6) had been obtained in very low yield in an attempt to establish a preparative route to adamantanes with a C4Si6skeleton, i.e., with C bridgeheads and SiR2bridges. By ICl-cleavage of a Si—methyl bond in2and subsequent substitution with Br3CLi, the trisilacyclohexane4with functional groups in opposite positions of the ring can be obtained. Linking the step-by-step synthesized Cl-Me2Si-C=C-SiMe2-CH2-SiMe2-Ph to the CBr3group of4results after HBr-cleavage of the Si—Ph bond in (ω-bromo-octynyl)-trisilacyclohexane (12). A ring closure of12would result in an isomeric hexasila bicyclo[7.2.2]tridec-6-yne. The compounds were characterized by1H,13C, and29Si NMR spectra. Additionally, the molecular structures of4and6were confirmed by X-ray single crystal investigations.Key words: 1,1,3,3,5,5-hexamethyl-1,3,5-trisilacyclohexane, bromination, 2,2,9-tribromo-1,3,3,5,5,8,8,10,10,13,13-undecamethyl-1,3,5,8,10,13-hexasilabicyclo[7.2.2]tridec-6-yne, carbosilane synthesis, NMR data, crystal structure investigatio

ISSN:0008-4042    

DOI:10.1139/v00-035

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A variety of &agr;,&bgr;-unsaturated esters and cyclic ketones underwent smooth reduction of the carbon–carbon double bond with a combination of inexpensive and readily available trichlorosilane and CoCl2. The reactions are performed under very mild conditions and products are obtained in high yields.Key words: reduction, carbonyl compounds, trichlorosilane, ketones, chemoselectivity

ISSN:0008-4042    

DOI:10.1139/v99-238

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Protodesilylation of diphenylsilane with trifluoromethanesulfonic acid and subsequent reaction of the obtained bis(trifluoromethanesulfonyloxy)silane with tris(trimethylsilyl)silyllithium (1) (molar ratio 1:2) afforded bis[tris(trimethylsilyl)silyl]silane (8). Methyl-bis[tris(trimethylsilyl)silyl]silane (3) and phenyl-bis[tris(trimethylsilyl)silyl]silane (10) were obtained by coupling reactions of1with MeHSiCl2or PhHSiCl2, respectively, (2:1). By treatment with HCBr3, the H-silanes3,8, and10were converted into the bromosilanes [(Me3Si)3Si]2SiR1R2(9: R1= R2= Br;11: R1= Me, R2= Br;12: R1= Ph, R2= Br). X-ray crystal structure analyses, performed for3,10and12, confirmed the expected distortions of the molecular skeletons of the compounds. Thus, e.g., in10, the spatial demand of the two extended hemispherical hypersilyl groups forces a widening of the Si-Si-Si angle at the central Si atom to a value of 128.3°.Key words: silanes, sterically congested, bis(hypersilyl)silanes, hypersilylsilanes, bis(hypersilyl)germanes, tris(trimethylsilyl)silylsilanes

ISSN:0008-4042    

DOI:10.1139/v00-136

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A new efficient laboratory method of preparation of chlorodimethylsilane (Cl(CH3)2SiH) has been elaborated, which is a modification of the Eaborn et al. method (34) and is based on atranssilylation reactionof substituted (amino)dimethylhydrosilanes, R2NSiMe2H(R2= Me2, Et2, (CH2)n, etc.) withdimethyldichlorosilane (Me2SiCl2). The reaction proceeds at reflux, at 70°C, preferably with an excess of Me2SiCl2. The most important feature of this novel method is a recovery of intermediate (amino)chlorodimethylsilanes (R2NSiMe2Cl), which can be again reduced to R2NSiMe2H.The transsilylation mechanismhas been proven by reaction of (diethylamino)methylphenylsilane with Me2SiCl2. The products of this latter reaction are HMePhSiCl and R2NSiMe2Cl, thus a disproportionation mechanism has been excluded. New substituted bis(amino)dimethylsilanes ((R2N)2SiMe2), (amino)dimethylchlorosilanes (R2NSiMe2Cl), and (amino)dimethylhydrosilanes (R2NSiMe2H) have been synthesized and characterized by NMR and IR.Key words: chlorodimethylsilane, (CH3)2SiHCl, synthesis, new laboratory method, transsilylation mechanism

ISSN:0008-4042    

DOI:10.1139/v00-025

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The [4 + 2] cycloadducts of Me2E=C(SiMe3)2(E = Si, Ge, Sn) and anthracene are prepared by reaction of an excess of anthracene in benzene with the [2 + 2] cycloadduct of Me2Si=C(SiMe3)2and Ph2C=NSiMe3at 130°C, with Me2Ge(OPh)-CLi(SiMe3)2at 100°C, and with Me2SnBr-CNa(SiMe3)2at 80°C, respectively. The mentioned adducts act as sources for the ethenes Me2E=C(SiMe3)2above 100°C, the intermediate formation of which has been demonstrated by trapping experiments with 2,3-dimethylbutadiene (formation of a [4 + 2] and an ene reaction product). The half life time of the anthracene adducts with E = Si, Ge, and Sn in the presence of DMB (= 2,3-dimethylbutadiene) in benzene on thermolysis at 130°C (first order reactions) is found to be 141, 12, and 0.3 h, respectively. In the absence of DMB, thermolysis of the cycloadducts leads in benzene as reaction medium exclusively to the dimers of the Me2E=C(SiMe3)2intermediates. In toluene as reaction medium ene products of Me2E=C(SiMe3)2are observed in addition to the dimers. The ene products are not isolable as such, but only after migration of the Me2E-CH(SiMe3)2substituents. The formed derivatives C6H5CH2EMe2CH(SiMe3)2of toluene in part give a second ene reaction with another Me2E=C(SiMe3)2molecule. X-ray structure analyses of the mentioned sources in fact prove the latter to be normal [4 + 2] cycloadducts of Me2E=C(SiMe3)2and anthracene.Key words: silaethene, germaethene, stannaethene, [4 + 2] anthracene adducts, [4 + 2] cycloadditions and reversions, ene reactions, X-ray structure anal

ISSN:0008-4042    

DOI:10.1139/v00-095

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The alkoxides ofo-silyl benzyl alcohols4undergo cleavage reactions under mild conditions allowing transfer of a benzyl or silyl group to an electrophile. Reactions3a8, and3cor4c11illustrate their potential as benzyl and silyl anion equivalents.Key words: silyl migration, benzyl anion equivalent, silyl anion equivalent, &bgr;-silyl ketone, &ggr;-hydroxysilane.

ISSN:0008-4042    

DOI:10.1139/v99-250

出版商:NRC Research Press    

年代:2000

数据来源: NRC