U. Herzog

METHYLCHLOROOLIGOSILANES AS PRODUCTS OF THE BASECATALYSED DISPROPORTIONATION OF VARIOUS METHYLCHLORODISILANES

Abstract The methylchlorodisilanes SiCl 2 MeSiCl 2 Me ( 1 ), SiCl 2 MeSiClMe 2 ( 2 ) and SiClMe 2 SiClMe 2 ( 3 ) disproportionate in the presence of a basic catalyst into methylchloromonosilanes and various methylchlorooligosilanes. Oligosilanes involving up to seven silicon atoms were identified by means of 29 Si-, 13 C- 1 H-NMR and GC-MS measurements. Formation of methylchlorooligosilanes is thoughtto take place via silylene intermediates.

Silicon Carbide — A Survey of Synthetic Approaches, Properties and Applications

The challenge to develop tailor-made precursor molecules for silicon carbide has significantly intensified the progress in synthesis of organosilicon polymers. A critical overview is presented regarding useful synthesis routes towards such molecules with appropriate chemical composition as well as controllable architecture (metal condensation of halogenosilanes or silahalogenocarbons, disproportionation of disilanes, dehydrocoupling of hydrosilanes, hydrosilylation of olefins).

Five- and six-membered ring Group 14 chalcogenides of the types (Me2ME)3 (M=Si, Ge, Sn), E(Si2Me4)2E, Me4Si2(E)2MRx (MRx=C(CH2)5, SiMe2, GeMe2, SnMe2, SnPh2, BPh) and [Me4Si2(E)2SiMe]2 (E=S, Se, Te)

Abstract The reactions of Me 2 MCl 2 (M=Si, Ge, Sn) with either H 2 S/NEt 3 or Li 2 E (E=Se, Te) yielded the six-membered-ring compounds (Me 2 ME) 3 . Similarly the treatment of ClMe 2 SiSiMe 2 Cl ( 1 ) with H 2 S/NEt 3 or Li 2 E resulted in the formation of E(Si 2 Me 4 ) 2 E. Mixed species E(Si 2 Me 4 ) 2 E′ could be obtained by reaction with mixtures of Li 2 E and Li 2 E′ or in the presence of traces of moisture (E′=O). Reactions of 1:1 mixtures of Me 2 MCl 2 and 1 with Li 2 E resulted in exclusive or at least preferred formation of five-membered rings Me 4 Si 2 (E) 2 MMe 2 . A carbon analogue, Me 4 Si 2 (S) 2 C(CH 2 ) 5 , was obtained from 1 and (HS) 2 C(CH 2 ) 5 . Boron could also be introduced in these ring systems, starting from PhBCl 2 and 1 the compounds PhB(E) 2 Si 2 Me 4 (E=S, Se) could be synthesized. Mixtures of 1 and Cl 2 MeSiSiMeCl 2 yielded, on treatment either with H 2 S/NEt 3 or Li 2 E (E=Se, Te), the bis(cyclopentyl) compounds [Me 4 Si 2 (E) 2 SiMe] 2 . All products have been characterized by multinuclear NMR ( 1 H, 11 B, 13 C, 29 Si, 77 Se, 119 Sn, 125 Te) measurements including coupling constants. Trends of chemical shifts and coupling constants are discussed. The crystal structures of E(Si 2 Me 4 ) 2 E (E=S, Se) and [Me 4 Si 2 (S) 2 SiMe] 2 are reported.

New chalcogen derivatives of silicon possessing adamantane and noradamantane structures

Abstract The reaction of Si 2 Cl 4 Me 2 ( 1 ) with Li 2 Se in THF yields exclusively the noradamantane (MeSi) 4 Se 5 ( 4 ). The sulfur analogue (MeSi) 4 S 5 ( 3 ) could be obtained from 1 , MeSiCl 3 , H 2 S and NEt 3 . Reactions of the disilylmethane CH 2 (SiMeCl 2 ) 2 ( 5c ) with either H 2 S/NEt 3 or Li 2 E (E=Se, Te) produced the new adamantanes (MeSi) 4 (CH 2 ) 2 E 4 (E=S ( 6 ), Se ( 7 ) and Te ( 8 )). Similar reactions of mixtures of 1 and 5c resulted in the formation of the noradamantanes (MeSi) 4 (CH 2 )E 4 (E=S ( 9 ), Se ( 10 )). All compounds were characterized by multinuclear NMR spectroscopy. The crystal structures of 3 , 6 , 7 , 8 ·CDCl 3 and 9 are reported.

Preparation of oligosilanes containing perhalogenated silyl groups and their hydrogenation by stannanes

Abstract Starting from methylphenylsubstituted oligosilanes the disilanes SiX 3 -SiX i Me 3− i ( i = 0, 1, 2; X = Cl, Br), trisilanes SiX 2 (SiX i Me 3− i ) ( i = 0, 1) and branched tetrasilanes SiX(SiXMe 2 ) 3 were synthesized and their behavior towards the Lewis-base catalyzed hydrogenation by stannanes was investigated. In the case of methylchlorodisilanes SiCl 3 -SiCl i Me 3− i Si-Si bond cleavage competes with the hydrogenation reaction.

Formation and characterization of cyclic and polycyclic silthianes containing Si Si bonds

Abstract The reactions of several organochlorosilanes and -oligosilanes with H2S and NEt3 have been investigated. Different bicyclic silthianes with bis-cyclopentyl, bicyclo-[3,3,0]-octane, bicyclo-[2,2,1]-heptane (norbornane), bicyclo-[3,2,1]-octane, bicyclo-[2,2,2]-octane and bicyclo-[3,2,1]-nonane skeletons were formed and have been characterized by MS and 1H-, 13C- and 29Si-NMR. The reaction of 1,1,2,2-tetrachlorodimethyldisilane with H2S and NEt3 yields 1,3,5,7,9,11-hexamethyl-1,3,5,7,9,11-hexasila-2,4,6,8,10,12-hexathiatetracyclo-[5,5,03,11,05,9]-dodecane (4c) containing three disilane units. Density functional theory calculations proved the general observation that compounds with Si3S2 five-membered rings are preferred. The crystal structures of 4c, 1,3,3,5,7,7-hexamethyl-1,3,5,7-tetrasila-2,4,6,8-tetrathiabicyclo-[3,3,0]-octane (6) and 1,2,2,4,4,5,6,6,8,8-decamethyl-1,2,4,5,6,8-hexasila-3,7-dithiabicyclo-[3,3,0]-octane (9) have been determined.

Bis(oligosilanyl)chalcogenides [(Me3Si)xMe3−xSi]2E, alkalimetal oligosilanylchalcogenolates (Me3Si)xMe3−xSiEMI and oligosilanylchalcogenols (Me3Si)xMe3−xSiEH (E=S, Se, Te): Syntheses and NMR study

Abstract Bis(oligosilanyl)chalcogenides [(Me 3 Si) x Me 3− x Si] 2 E, alkalimetal oligosilanylchalcogenolates (Me 3 Si) x Me 3− x SiEM I and oligosilanylchalcogenols (Me 3 Si) x Me 3− x SiEH ( x =1–3; E=S, Se, Te) were synthesized and characterized by 1 H-, 13 C-, 29 Si-, 77 Se- and 125 Te-NMR spectroscopy. Trends of NMR parameters (chemical shifts, coupling constants) are discussed.

Interactions of chloromethyldisilanes with tetrakis(dimethylamino)ethylene (TDAE), formation of [TDAE]+ [Si3Me2Cl7]−

Abstract The chlorodisilanes SiClMe2SiClMe2 (1), SiCl2MeSiCl2Me (2), SiCl3SiCl3 (3) and a 9:1 mixture of 2 and SiCl3SiCl2Me (4) were reacted with the electron-rich alkene tetrakis-(dimethylamino)-ethylene (TDAE) in n-hexane as well as in polar solvents. While 1 gave no reaction at all, 3 underwent a disproportionation reaction into SiCl4 and Si(SiCl3)4. Also 2 and mixtures of 2 and 4 were disproportionated into MeSiCl3 (2a) and methylchlorooligosilanes. Additionally a crystalline mixture of Si3Me3Cl6·TDAE (5a) plus Si3Me2Cl7·TDAE (5b) was obtained by reaction of a 9:1 mixture of 2 and 4 with TDAE in n-hexane as well as in 1,2-dimethoxyethane. The reaction of 2 with TDAE in acetonitrile (MeCN) led to a crystalline precipitation of [TDAE]Cl2·MeCN (6·MeCN) in addition to MeSiCl3 and methylchlorooligosilanes. The structures of 5b and 6·MeCN were determined by X-ray crystallography beside their NMR and IR spectroscopic characterization. Compound 5b crystallizes in the monoclinic space group P2/c (Z=4), 6·MeCN in the orthorhombic space group Pna21 (Z=4). The structure of 5b reveals a [TDAE] + radical cation and a 1,2-Me2Si3Cl7− anion with a pentacoordinated central silicon atom.

Group 14 chalcogenides featuring a bicyclo[3.3.0]octane skeleton

Abstract Reactions of mixtures of Cl2MeSiSiMeCl2 (1) and Me2MCl2 (M=Si, Ge, Sn) with either H2S/NEt3 or Li2E (E=Se, Te) yielded the bicyclo[3.3.0]octanes Me2M(E)2Si2Me2(E)2MMe2. A carbon containing analog, (CH2)5C(S)2Si2Me2(S)2C(CH2)5, was prepared from 1 and (CH2)5C(SH)2. Crystal structures of three of these compounds were determined and the observed conformations of the bicyclo[3.3.0]octane skeletons compared with results of density functional theory calculations. Another class of silchalcogenides featuring a bicyclo[3.3.0]octane skeleton, E(Me2Si)2Si2Me2(SiMe2)2E, was formed from the doubly branched hexasilane (ClMe2Si)2Si2Me2(SiMe2Cl)2 and H2S/NEt3 or Li2E. All products were characterized by multinuclear NMR (1H, 13C, 29Si, 77Se, 119Sn, and 125Te).

Reaction of the SiCl bond with trialkyl orthoformates preparation of alkoxy-substituted silanes

Abstract Trialkyl orthoformates in the presence of aluminium chloride represent quite useful reagents to generate silicon alkoxides from chlorosilanes. 3-Cyanopropyltrichlorosilane and 2-[(2-trichlorosily)ethyl]-pyridine give the triethoxy compounds 3-cyanopropyltriethoxysilane and 2-[(2-triethoxysilyl)ethyl]-pyridine respectively. Via this route, in methylchlorooligosilanes a partial or complete exchange of the chlorine substituents for alkoxy groups occurs depending on the starting molar ratio of silane:HC(OR)3 (R  Me, Et). SiCl2Me groups react to SiClMe(OR) first before SiMe(OR)2 groups are formed. (Si)2 SiClMe units are not affected by HC(OR)3.