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The industry‐scale production of methylchloromonosilanes in the Müller–Rochow Direct Process is accompanied by the formation of a residue, the direct process residue (DPR), comprised of disilanes MenSi2Cl6‐n (n=1–6). Great research efforts have been devoted to the recycling of these disilanes into monosilanes to allow reintroduction into the siloxane production chain. In this work, disilane cleavage by using alkali and alkaline earth metal salts is reported. The reaction with metal hydrides, in particular lithium hydride (LiH), leads to efficient reduction of chlorine containing disilanes but also induces disproportionation into mono‐ and oligosilanes. Alkali and alkaline earth chlorides, formed in the course of the reduction, specifically induce disproportionation of highly chlorinated disilanes, whereas highly methylated disilanes (n>3) remain unreacted. Nearly quantitative DPR conversion into monosilanes was achieved by using concentrated HCl/ether solutions in the presence of lithium chloride., Too valuable for disposal or incineration: Simple recycling of the Müller–Rochow Direct Process residue with LiH yields monosilanes suitable for the reintroduction into the silicone production chain.

A preparatively facile, highly selective synthesis of bifunctional monosilanes R2 SiHCl, RSiHCl2 and RSiH2 Cl is reported. By chlorination of R2 SiH2 and RSiH3 with concentrated HCl/ether solutions, the stepwise introduction of Si-Cl bonds is readily controlled by temperature and reaction time for a broad range of substrates. In a combined experimental and computational study, we establish a new mode of Si-H bond activation assisted by Lewis bases such as ethers, amines, phosphines, and chloride ions. Elucidation of the underlying reaction mechanisms shows that alcohol assistance through hydrogen-bond networks is equally efficient and selective. Remarkably, formation of alkoxysilanes or siloxanes is not observed under moderate reaction conditions.

The industrial production of monosilanes Men SiCl4-n (n=1-3) through the Muller-Rochow Direct Process generates disilanes Men Si2 Cl6-n (n=2-6) as unwanted byproducts ("Direct Process Residue", DPR) by the thousands of tons annually, large quantities of which are usually disposed of by incineration. Herein we report a surprisingly facile and highly effective protocol for conversion of the DPR: hydrogenation with complex metal hydrides followed by Si-Si bond cleavage with HCl/ether solutions gives (mostly bifunctional) monosilanes in excellent yields. Competing side reactions are efficiently suppressed by the appropriate choice of reaction conditions.

The Muller-Rochow direct process (DP) for the large-scale production of methylchlorosilanes Men SiCl4-n (n=1-3) generates a disilane residue (Men Si2 Cl6-n , n=1-6, DPR) in thousands of tons annually. This report is on methylchlorodisilane cleavage reactions with use of phosphonium chlorides as the cleavage catalysts and reaction partners to preferably obtain bifunctional monosilanes Mex SiHy Clz (x=2, y=z=1; x,y=1, z=2; x=z=1, y=2). Product formation is controlled by the reaction temperature, the amount of phosphonium chloride employed, the choice of substituents at the phosphorus atom, and optionally by the presence of hydrogen chloride, dissolved in ethers, in the reaction mixture. Replacement of chloro by hydrido substituents at the disilane backbone strongly increases the overall efficiency of disilane cleavage, which allows nearly quantitative silane monomer formation under comparably moderate conditions. This efficient workup of the DPR thus not only increases the economic value of the DP, but also minimizes environmental pollution.

A combined experimental and theoretical study of the high-temperature reaction of SiCl4 and elemental silicon is presented. The nature and reactivity of the product formed upon rapid cooling of the gaseous reaction mixture is investigated by comparison with defined model compounds, i.e. cyclo-Si5Cl10, n-Si5Cl12 and n-Si4Cl10. A DFT assessment provides mechanistic insight into the oligosilane formation. Experimental 29Si NMR investigations, supported by quantum-chemical 29Si NMR calculations, consistently show that the reaction product is composed of discrete molecular perchlorinated oligosilanes. Low-temperature chlorination is an unexpectedly selective means for the transformation of cyclosilanes to acyclic species by endocyclic Si-Si bond cleavage, and we provide a mechanistic rationalization for this observation. In contrast to the raw material, the product obtained after low-temperature chlorination represents an efficient source of neo-Si5Cl12 or the amine-stabilized disilene EtMe2N*SiCl2Si(SiCl3)2 through reaction with aliphatic amines.

A series of crystalline sodium and potassium organo substituted cyclotrisiloxanolates (I–IV) has been synthesized from the corresponding organotrialkoxysilanes and alkali bases in aqueous alcohol solvent media. Sodium ethyl- and n-propylcyclotrisiloxanolates (I, II) are obtained in high yields in a wide range of reaction conditions, while for the reaction of methyl- and vinyltrialkoxysilanes the use of potassium hydroxide under strictly controlled conditions for the formation of crystalline products (III, IV) is required. The four differently substituted alkali metal cation based cyclotrisiloxanolates were characterized by single crystal X-ray analyses that proved the six-membered siloxanolate cycles to adopt a distorted sofa or boat conformation, most probably resulting from intermolecular interactions. Regarding the crystal packing the corresponding cations and coordinated water molecules form layers that are coated with organotrisiloxanolate anions and ethanol molecules. This supramolecular organization is best described by hydrophilic layers with hydrophobic coatings regardless the nature of alkali metal cations. Relevant quantum chemical calculations show that the contribution of O–H⋯O bonding for the stabilization of the hydrophilic layers is predominant over that of the coordination K–O and Na–O bonds. The analysis of the bonding situation between the hydrophobic parts of the organotrisiloxanolate anions proves that the sum of energies of the H⋯H and C⋯H interactions might be characteristic for bonding within the interlayer space and this is much less for sodium cyclotrisiloxanolates compared to their potassium cation analogs (6.89/7.32 kcal mol−1 vs. 10.1/12.7 kcal mol−1). From these calculations important insight into the energies of non-covalent interactions, which play a crucial role for the stabilization of the molecular structures of sodium and potassium organocyclotrisiloxanolates, is obtained.

The well-established Muller–Rochow Direct Process for the chloromethylsilane synthesis produces a disilane residue (DPR) consisting of compounds MenSi2Cl6−n (n=1–6) in thousands of tons annually. Technologically, much effort is made to retransfer the disilanes into monosilanes suitable for introduction into the siloxane production chain for increase in economic value. Here, we report on a single step reaction to directly form cyclic, linear, and cage-like siloxanes upon treatment of the DPR with a 5 m HCl in Et2O solution at about 120 °C for 60 h. For simplification of the Si−Si bond cleavage and aiming on product selectivity the grade of methylation at the silicon backbone is increased to n≥4. Moreover, the HCl/Et2O reagent is also suitable to produce siloxanes from the corresponding monosilanes under comparable conditions.

A series of six 2,3-diphenyl-4-neopentyl-1-silacyclobut-2-enes with different 1,1-substituents has been prepared and characterized by single-crystal X-ray crystallography. These compounds possess a cis-stilbene-like chromophore involving also the four-membered ring, and exhibit a photophysical behavior similar to that of previously reported 1,2-diphenyl-cycloalkenes. This chromophore system is confirmed by a theoretical investigation of the electronic structure and excitation spectra. The absorption and photoluminescence of selected derivatives were studied in solution, as solid powder samples, and in doped-polymer thin films. In well-dissolved solution, the silacyclobutenes show only very weak fluorescence emission (quantum yield approximately 0.1%), due to competition with photochemical and non-radiative photophysical relaxation. When the solubility is degraded in a poor (aqueous) solvent, the formation of nanoscale aggregates leads to a significant enhancement factor in the emission intensity, due to the suppression of the photoreactivity in the more rigid molecular environment, although the quantum yield still remains below a few percent. In the solid-state, however, photoreactivity is completely suppressed leading to fluorescence quantum efficiencies of 8-23% depending on the 1,1-substituents, which demonstrates these compounds' potential as chromophores for condensed-phase luminescence applications. Two dominant competing photochemical reactions have been identified in solution (for excitation in the lowest-energy absorption band, >260 nm), which are analogous to related (sila-)cyclobutenes and stilbenoids. The first involves ring-opening due to cleavage of the 1,4-Si-C bond to form metastable silabutadienes, which was confirmed by isolating the stereospecifically formed allylsilane which results from a secondary reaction with trapping agents such as methanol or water. The second photochemical reaction involves ring closure of the 2,3-diphenyl substructure to form a dihydrophenanthrene analogue, which was confirmed by isolating the phenanthrene derivative that results following subsequent hydrogen abstraction in the presence of oxygen. Measurements of the silacyclobutenes in doped-polymer thin films reveal a spectroscopic behavior ranging from that in solution to the nano-aggregate case as the silacyclobutene dopant concentration is increased.

Seven silicon based model compounds that contain stilbene, butadiene or styrene subunits with different molecular structures were synthesized and characterized by NMR spectroscopy and single crystal X-ray crystallography. The UV–Vis absorption and photoluminescence spectra were measured in THF solution as well as in the solid state. The interpretation of the spectra reveals that the absorption and emission properties of the compounds originate from the stilbene or butadiene molecular subunits. This investigation provides basic information about the influence of silicon groups, molecular structures and substituents at silicon to absorption and emission properties in organic compounds. Furthermore, due to the functionality of the phenylethynyl substituents at silicon, these compounds may serve as optical active tools and precursors for the introduction of interesting physical properties into new materials for different applications.

Starting from a silicon dichloro substituted silole and a silacyclobutene, a series of new organosilicon-based spiro compounds was synthesized by using standard organometallic reaction procedures. The spiro compounds that combine two organic photoactive subunits at one silicon center were fully characterized by the usual analytical and spectroscopic methods, which include molecular structure determination by single-crystal X-ray analysis. Photoluminescence spectra of the compounds were recorded in the solid state and also as dilute solutions in THF. Interpretation of the spectra revealed that photoluminescence in this series of compounds originated from the stilbene or its vinylogue subunits. Different linkages of these groups to the silicon atoms (cyclic or open structures, four- or five-membered cycles) strongly affected both the excitation and the emission spectra, which show different emission maxima depending on the state of the sample (solid state or in solution) and the wavelength of light used for excitation. Thus, owing to their optoelectronic properties these compounds might be useful tools for the design of sensitive sensor materials and of optical switches.

Crystalline phenylsilanetriol, PhSi(OH)3 (1) was obtained by smooth hydrolysis of phenyltrimethoxysilane and characterised by different analytical methods (wide angle X-ray powder diffraction, NMR, IR, thermogravimetric analysis). The title-compound is surprisingly stable in the solid state but slowly condenses in acetone solution. Reaction of 1 with Me3SiCl and Me2(CH2Cl)SiCl gave the corresponding tris-triorganylsiloxy substituted derivatives in high yields.

A metal-free catalytic intramolecular hydrosilylation reaction is reported. The key intermediates in the catalytic cycle are silyl cationic species. The reaction is used to produce 2-silanorbornanes 2 from 3-cyclopentenemethylsilanes 1 under mild conditions and in high isolated yields.Key words: hydrosilylation, catalysis, silaheterocycles, silyl cations.

Reaction of bis(cyclopentenemethyl)diethylplumbane (2) with trityl cation leads to the formation of the plumbyl cation bis(cyclopentenemethyl)plumbylium (1), in which the positively charged lead atom interacts with the two C=C double bonds of the cyclopentene ligands. The plumbyl cation 1 is characterized by NMR spectroscopy (delta((207)Pb)=807 ppm, delta((13)C(C=C))= 136.1 ppm, (1)J(Pb,C=C)=14.4 Hz) and X-ray crystallography. The structure of 1 reveals a distorted trigonal-bipyramidal coordination sphere for the lead atom with a unique coordination of two C=C double bonds in apical positions. According to quantum-mechanical calculations (MP2/6-311G(d,p) (C, H), SDD (Pb)//MP2/6-31G(d), SDD (Pb)) this interaction stabilizes 1 by 28.3 kcal mol(-1) relative to the tricoordinated plumbylium ion 10. An "atoms in molecules" (AIM) analysis indicates a pi-type interaction between the lead atom and the C=C double bonds, reminiscent of that in the 2-norbornyl cation.

The X-ray crystal structures of four 1-(halodimethylsilylmethyl)-2-quinolinones have been measured and used to model the reaction profile for nucleophilic substitution at silicon. Similar structural correlations have been performed in solution, the percentage SiO bond formation being obtained from the 13 C chemical shifts of the quinolinone carbons and the extent of pentacoordination from the 29 Si chemical shift of the silicon. Excellent agreement is obtained between the two methods confirming the validity of the NMR technique for structural correlation in solution.

We have measured the photoelectron (PE) spectra of two new silenes: the kinetically stable long-lived silene t-BuMe2Si(Me3Si)SiAd (3) and a transient silene which was generated in the gas phase by...

Low-pressure pyrolysis of 2,5-bis(1,1-dimethyl-1-silacyclobut-1-yl)-p-xylene (1) results in the formation of 1,2,4,5-tetrahydro-1,1,4,4-tetramethyl-1,4-disiladicyclobuta[a,d]benzene (2), here named as the butterfly compound and representing the first silacyclobutene diannelated [a,d]benzene. Both compounds, 1 and 2, were characterized by NMR, IR, and MS methods; furthermore, the molecular structures were determined by single-crystal X-ray diffraction analysis. Density functional and ab initio calculations prove that the difference in the benzene carbon−carbon bond lengths in 2 results primarily from substituent effects and is not caused by ring strain effects. Forming strongly bent silicon−carbon bonds, silicon decreases the amount of strain in the model compounds, in the 1-silacyclobut-2-ene 10 by 8.3 kcal/mol and in the 1,4-disiladicyclobuta[a,d]benzene 15 by 19.0 kcal mol-1, compared to the analogous hydrocarbons. The total strain energy is additive, depending on the number of annelated rings. The phot...

Amorphous silicon is synthesized by treating the tetrahalosilanes SiX4 (X=Cl, F) with molten sodium in high boiling polar and non-polar solvents such as diglyme or nonane to give a brown or a black solid showing different reactivities towards suitable reagents. With regards to their technical relevance, their stability towards oxygen, air, moisture, chlorine-containing reaction partners RCl (R=H, Cl, Me) and alcohols is investigated. In particular, reactions with methanol are a versatile tool to deliver important products. Besides tetramethoxysilane formation, methanolysis of silicon releases hydrogen gas under ambient conditions and is thus suitable for a decentralized hydrogen production; competitive insertion into the MeO-H versus the Me-OH bond either yields H- and/or methyl-substituted methoxy functional silanes. Moreover, compounds, such as Men Si(OMe)4-n (n=0-3) are simply accessible in more than 75 % yield from thermolysis of, for example, tetramethoxysilane over molten sodium. Based on our systematic investigations we identified reaction conditions to produce the methoxysilanes Men Si(OMe)4-n in excellent (n=0:100 %) to acceptable yields (n=1:51 %; n=2:27 %); the yield of HSi(OMe)3 is about 85 %. Thus, the methoxysilanes formed might possibly open the door for future routes to silicon-based products.

A series of differently substituted alkeneinylhalogensilanes R 2 Si(X)–CC–C(Me)CH 2 (X=Cl: R=Me ( 2 ), Cl ( 3 ), Ph ( 4 ); X=F: R=Me ( 5 ), Mes ( 6 ), Tip ( 7 )) is reacted with t -BuLi in solvents of different polarity to give mainly E / Z -isomeric 2,4-bispentenylidene-1,3-disilacyclobutanes ( 11 , 23 and 31 ) and E / Z -isomeric 2,4,6-trispentenylidene-1,3,5-trisilacyclohexanes ( 12 and 24 ) competitively. Obviously the four- and six-membered silacycles are formed stepwise by intermolecular coupling reactions of the lithiated precursors R 2 Si(X)C(Li)CC(Me)– t -Bu which preliminary result from the 1,4-addition of the lithium organyle to the alkeneinylhalogensilanes. Alternatively, silacumulene formation (R 2 SiCCC(Me)CH 2 – t -Bu) might be discussed, but the isolation of Cl 3 Si–C(CC(Me)CH 2 – t -Bu)–CC–C(Me)CH 2 ( 22 ) as coupling product starting from trichlorosilane 3 and t -BuLi and high molecular multistep coupling products starting from the fluorinated precursors 5 and 7 strongly favour the the coupling reactions over silacumulene formation. Consequently, all attempts to isolate a stable silacumulene from the silicon sterically overcrowded starting compounds 6 and 7 failed.

Equimolar amounts of trichlorovinylsilane (9), lithium-tert-butyl, and 1,3-enynes were reacted to yield the corresponding isomeric silacyclobutanes and silacyclobutenes competitively. As reaction pathway the mixture 9/tBuLi is discussed to give a silene equivalent, Cl2Si=CHCH2tBu (10), yielding the four-membered ring silacycles by formal [2 + 2] cycloaddition reactions of 10 with the C=C double or the C=C triple bond of the 1,3-enyne. The relative ratio of the products formed depends on the polarity of the multiple bonds in the enyne, which is mainly determined by the substituent pattern. Thus, from the organosubstituted 1,3-enynes R1 C=C-C(R2)=CR3R4 (R1 = Me, Et, SiMe3, Ph; R2 = H, Me, Ph; R3=Me, OMe, Ph; R4=H; and R1C=C-R' (R' = 1-cyclohexenyl, cyclohexanevinylidyne)) and 9/tBuLi the silacyclobutanes 12, 13, and 15 and the silacyclobutenes 14,16-24, and 27 (from 10 and 3-hexyne) are prepared in a one-step synthesis and isolated from the reaction mixtures. The silacyclobutanes and -butenes are thermally stable and can be distilled under vacuo up to temperatures of about 150°C without decomposition. The experimental results are confirmed qualitatively by semiempiric calculations at the AM-1 level and their analysis using FMO theory. The solid state structure of the silacyclobutene 19 (C17H30Cl2Si2) has been determined by single crystal X-ray diffractometry. 19 is orthorhombic, space group P212121, a = 1030.94(2) pm, b = 1244.6(2) pm, c = 1605.5(3) pm, Z = 4.Key words: neopentylsilene, dichloroneopentylsilene, silacyclobutenes, silacyclobutanes, 1,3-enynes.

The silenes H2SiCH2 (2), MeHSiCH2 (7), and Me2SiCH2 (8) have been prepared by low-pressure flow pyrolysis from the corresponding siletanes (1), (5), and (6). 2, 7, and 8 were identified by residual gas analysis of the pyrolysis stream and by low-temperature NMR spectroscopy of their complexes 2·O(CD3)2 (16), 7·O(CD3)2 (17), and 8·O(CD3)2 (18). The complexes 16−18 are stable to temperatures between −140 and −100 °C. Above these temperatures rapid polymerization occurs. The complexation with dimethyl ether obviously stabilizes the silenes and allows their spectroscopic investigation. The 29Si chemical shifts of the complexes are −25.2 (16), −1.8 (17) and 16.8 ppm (18). The experimental results are supported by ab initio and density functional calculations of geometries and magnetic properties of the silenes 2, 7, and 8 and the dimethyl ether complexes 16−18. The calculations predict a relatively short Si−O separation of about 1.7 A in the corresponding silene−ether adducts. Natural bond analysis of the dono...

Equimolar mixtures of trichlorovinylsilane and t-BuLi (1) were reacted with different vinyl ethers, CH2CH−OR (R = Et, n-Pr, n-Bu, i-Bu, t-Bu), to yield the silacyclobutanes 2−6. NMR spectroscopic investigations showed the addition of the formal silene unit Cl2SiCHCH2t-Bu to the vinyl group of the vinyl ethers to be stereo- and regiospecific, forming products of E-configuration. In contrast, in the presence of bisvinyl [CH2CH−O−(CH2)n−O−CHCH2 (n = 2, 4, 6)] or cyclic vinyl ethers, such as 2,3-dihydrofuran and 3,4-dihydro-2H-pyran, the formation of silacylobutanes was suppressed and the formation of addition and SiCl/CHLi coupling products, such as Cl2(R)SiCH2CH2t-Bu (RCl, 7; t-Bu, 8) and the tetrachloro-1,3-disilacyclobutane, (Cl2SiCHCH2t-Bu)2 (10), was favored. Compounds 8 and 10 were characterized by single-crystal X-ray diffraction studies.

Two different synthetic routes for the formation of sodium phenylsiloxanolate (SPS) have been developed: (i) the cleavage of oligo(phenylsilsesquioxane), OPSSO, by NaOH in n-butyl alcohol and (ii) the reaction of phenyltri-n-butoxysilane, PhSi(n-BuO)3, and NaOH in n-butyl alcohol in the presence of water. From both reactions, (i) and (ii), crystalline sym-cis-{(Na+)4[PhSi(O)O-]4}·8n-BuOH (A) was the product isolated and characterized by X-ray diffraction. Reaction of SPS with Me3SiCl resulted in the formation of the corresponding sym-cis-tetraphenyltetrakis(trimethylsiloxy)cyclotetrasiloxane, [PhSi(O)OSiMe3]4. Under anhydrous conditions, PhSi(n-BuO)3 and NaOH reacted to give sodium phenyldi-n-butoxysilanolate, PhSi(ONa)(n-BuO)2. Subsequent treatment with Me3SiCl led to the formation of phenyl(trimethylsiloxy)di-n-butoxysilane, PhSi(n-BuO)2(OSiMe3).

Catalytic hydrogenation of olefins containing functionalized silicon groups affords the saturated products in good yields. Chloro and alkoxy substituents at the silicon atom remain unaffected and, in the case of heterocyclic compounds, the cyclic or bicyclic moieties remain intact. The 2-silanorbornanes 4, 5, and 6 were synthesized from the corresponding 2-silanorbornenes 1, 2, and 3, and organosilanes 13 and 14 possessing the cyclopentyl group, were prepared from the cyclopentenyl-substituted precursors 10 and 12. The 3-vinyl-substituted silacyclobutanes 15, 17, and 18 were also hydrogenated in a simple apparatus with diethyl ether or THF as solvent, and Pd/C as a recoverable catalyst system. A basic organosilicon compound, trichloro(vinyl)silane, is hydrogenated in a nearly quantitative yield to form the saturated trichloro(ethyl)silane; this emphasizes the general applicability of this method.

3-(Cyclohexylamino)propylmethoxydimethylsilane 1 is readily hydrolized to give the silanol 3-(cyclohexyl-amino)propyldimethylsilanol 2, which forms hydrogen bonded chains in the solid state.

The synthesis of carbon substituted 1, 1-dichloro- and l, l-bis(diethylamino)silacyclobutanes and butenes and their polycondensation reactions with bisphenol A, 1,2-ethanediol and 1,6-hexanediol is described. The monomer silacycles and the organosiloxane polymers are characterized by NMR (1H-, 13C-, 29Si-), GPC, DSC and elemental analysis.

Reactions of 1.1-dichloro-2-neopentyl-3-vinyl-l-silacyclobutane ( 1a, b ) with carbonyl metallates [{M(CO) n } m ] 2- (M = Fe, m = 1, n = 4; M = Cr, m = 1, n = 5; M = W, m = 2, n = 5) in THF/HMPA lead to novel compounds [(CO) n MSiC 10 H 18 ] · HMPA (M = Fe, n = 4; M = Cr, W, n = 5). 1 H, 13 C and 29 Si NMR spectroscopic studies in solution support the formation of four diastereomeric pairs of enantiomers. The X-ray structure analyses of the crystals show folded 1-metallated 1-silacyclobutane units in which the HMPA ligand increases the coordination number of Si to 3 + 1. Crystals of [(CO) 5 CrSiC 10 H 18 ] · HMPA ( 2 ) and of [(CO) 5 WSiC 10 H 18 ] · HMPA ( 3 ) (corresponding values in brackets) are isotypic: P 2 1 / n (No. 14); a = 1084(1)/[1099(1)], b = 1927(1)/[1937(1)], c = 1342.1(8)/[1342(1)] pm, β = 97.11(7)/[97.18(7)]°, Z = 4. In both crystals enantiomeric [1 S ,2 S ,3 S ]/[1 R ,2 R ,3 R ] pairs are present. In orthorhombic crystals of [(CO) 4 FeSiC 10 H 18 ]. · HMPA ( 4 ) ( P 2 1 2 1 2 1 (No. 19), a = 896.4(5), b = 1693(1), c = 1753(1) pm, Z = 4) only the [1 S ,2 S ,3 S ]-isomer is detected.

Organosilicon Chemistry: From Molecules to Materials The transition from basic to applied organosilicon chemistry is described for the research fields that are studied by the author's group: silaethene chemistry, organosilicon polymer chemistry with silacycles and the chemistry of higher coordinated silicon species. Early investigations started with the study of the pyrolysis of silacyclobutanes that yielded silaethenes in the gas phase. However, these investigations are tedious and are of little use for a widespread study of silaethene chemistry. Therefore the generation of silaethenes in solution (from vinylchlorosilanes and tert-butyllithium) is the preferred method. Numerous differently substituted silaethenes have been generated in situ and their reactivity, especially in cycloaddition reactions, has been studied. Silaethenes that have two chlorine substituents at the silicon atom (especially Cl2SiCHCH2But) show an unusual cycloaddition reactivity and yield unexpected products with dienes and trienes (e. g. from [2+2] and [6+2] reactions); some of the silenes with donorfunctional groups at the α-C-atom undergo interesting intramolecular rearrangements. The cycloadducts of Si-dichlorofunctional silenes also show rearrangements when thermolyzed (e. g. [2+2] [4+2] adducts). The reactivity of these silaethenes and their cyclo-adducts is due to the two chlorine atoms at the silicon atom and their influence can be explained by theoretical models. Silacycles synthesized from silaethenes have been incorporated or have been transformed into silicon containing polymers. Model compounds for nucleophilic substitution reactions at silicon centers and for the hydrolysis of chlorosilanes are higher coordinated silicon species up to coordination number „seven”. Some structures that describe such reactions have been characterized by X-ray crystallography.

Structural characterization of a polymethylsilsesquioxane (PMSQ) and a DT-type methyl silicone resin (MeDT) has been carried out by various instrumental analyses including GPC, NMR, gas chromatography, and gas chromatography-mass spectrometry. Although the PMSQ had aMwaround 5000, the resin contained a significant amount of low molecular weight species consisting of T2[MeSi(OH)O2/2] and T3[MeSiO3/2] units, ranging from to including many isomers. One isomer of was isolated of which structure was determined as a cage structure. The species are supposed to consist mainly of cyclotetra- and cyclopentasiloxanes, but presence of strained rings such as cyclotrisiloxane rings also was suggested. In MeDT, species in which the T2units in the molecules from PMSQ is replaced with D2[Me2SiO2/2] were found, for example, , suggesting that general silicone resins consist of similar structures as silsesquioxanes. The Mark-Houwink exponent for these methyl resins was~0.3, indicating the molecular shape to be compact. Investigation on the formation chemistry of the cubic octamers indicates that siloxane bond rearrangement is an important mechanism in the molecule build-up process.

Generation by two different methods of silylenes stabilized by o -amino(aryl) groups is reported. The halodemetallation of difluoro or dichloro-silanes with Li metal or lithium-naphthalene gave the same product, a stabilized sila-ylide (hypercoordinated silylene). Intramolecular Lewis base stabilization is not sufficient to isolate a monomeric species. The silylenes, however, have been trapped with 2,3-dimethylbutadiene. An unexpected intramolecular rearrangement to silaacenaphthene has been observed in the case of a six-membered ring amino(aryl) coordinated silylene. Photolysis of o -1-[( N , N -dimethylamino)inethyl]-2-[tris(trimethylsilyl)silyl]benzene produced, among other products, Me 3 SiSiMe 3 and the sila-ylide, which has been trapped with Et 3 SiH and dimethylbutadiene. Our mechanistic interpretation is supported by spectral observation of the photochemically generated reaction intermediates in a 3-methylpentane glass at low temperature.

Silicon compounds substituted by 2-(dimethylaminomethyl)phenyl groups [C6H4CH2N(CH3)2]nSiX4-n (X  Cl, H, organo group, n = 1–4) are available by the reaction of the appropriate chlorosilanes with 2-(dimethylaminomethyl)phenyllithium. A comparison of the 29Si NMR spectroscopic shifts δ with the values obtained for corresponding phenyl silanes shows that there is higher coordination of the silicon atom by N → Si contacts, except for the silanes 11 (X  Cl; n = 3) and 12 (n = 4). X-ray crystal structure analysis confirms pentacoordination of the silicon atom in the dichlorosilanes 4 (X  Cl; n = 2) and 5. For [C6H4CH2N(CH3)2]3SiH (10) heptacoordination of the silicon atom is found in the crystalline state [d(N → Si) ≈ 301 pm]. The tetrasubstituted derivative [C6H 4CH2N(CH3)2]4Si (12) has no N → Si contacts in solution and in the solid state: st eric congestion does not allow higher coordination. 10: colourless prisms, monoclinic, space group P 21/n; lattice constants: a = 889.0(3), b = 1677.5(8), c = 3471(1) pm; β = 90.35(3)°. 12: colourless prisms, pseudo tetragonal, space group I41/a; lattice constants: a = b = 1699.7(4), c = 3398.9(17) pm.

Quantum-mechanical calculations suggest that silenes are probably not involved as intermediates in the reaction of the trichlorovinylsilane/t-BuLi reagent with alkynes. Instead, the product 7 is ob...

1,4-Diaza-8,8,8-trimethoxy-8-silaoctane (1) loses methanol upon heating and gives an eight-membered silatrane-like silaheterocyle, 1,6-diaza-2,2-dimethoxy-2-silacyclooctane (2).