Silicon synthetic routes

The major synthetic routes to transition metal silyls fall into four main classes (1) salt elimination, (2) the mercurial route, a modification of (1), (3) elimination of a covalent molecule (Hj, HHal, or RjNH), and (4) oxidative addition or elimination. Additionally, (5) there are syntheses from Si—M precursors. Reactions (1), (2), and (4), but not (3), have precedence in C—M chemistry. Insertion reactions of Si(II) species (silylenes) have not yet been used to form Si—M bonds, although work may be stimulated by recent reports of MejSi 147) and FjSi (185). A new development has been the use of a strained silicon heterocycle as starting material (Section II,E,4). 

In addition to the telluration of a silylene, another unique synthetic route has been developed for the silicon-tellurium double bond system. Recently, it has been reported that the exhaustive reduction of an overcrowded dibromosilane Tbt(Dip)SiBr2 (61) with an excess amount (more than 4 equiv.) of lithium... 

We found a new route for preparing larger amounts of these disilanes. The stepwise substitution of the phenyl groups at the silicon atoms with triflic acid and the additional conversion to Si-H and Si-C1 functions at low temperatures leads to pure chloro-hydrogen disilanes. The synthetic routes to 1,1,1-trichlorodisilane 2 and 1,1-dichlorodisilane 3 [7] are shown in Eq.(4). 

Scheme 2.5-1. Synthetic routes to the silicon or germanium clusters 1 si and lcei some reactions of 1 si [16a, 16b],...

There are only few synthetic routes to oligosilsesquioxanes available with retention of the silicon-oxygen framework. These routes also involve halogenation and nitration. 

In order to incorporate the metal alkyl or aryl in a ring system of nitrogen and silicon atoms, we have used, over the past 10 years, the well-known amines 25 (58) and 26 (59), or have developed synthetic routes to oxoamines 27 (60)... 

The synthetic route (c) was recently utilized to prepare unsaturated monomers containing the hexacoordinate silicon unit, followed by polymerization to form novel polymers with hexacoordinate silicon in the polymer chain (equation 49)214. The29Si chemical shift measured in the polymer solution (ca —60 ppm) is very similar to that of the monomer (—63.8 ppm), and is evidence for hexacoordination in the polymer solution. 

A short time ago numerous triorganyl-cyclotriphosphanes have become accessible as pure substances on various synthetic routes (2). Moreover, three-membered phosphorus heterocycles with carbon, silicon, germanium, arsenic, boron, and sulfur as hetero ring atoms could be synthesized (2). Recently, we have found that such compounds with elements of the fifth periodtare als stable enough fop existence. Through the reaction of K(Bu )P-P(Bu )K with Bu S C1 or Bu -SnC at -78°C, the diphosphastib rane ... 

The most important synthetic routes continue to be (1) the elimination of an alkali halide between the salt of a transition-metal anion and a silicon halide, and (2) oxidative addition and addition-elimination reactions. The present position regarding the scope and limitations of these and other routes is outlined in this section. 

The effects of silicon substitution on the luminescence properties are of interest in the field of polymer LEDs. Poly(2-dimethyloctylsilyl-l,4-phenylenevi-nylene) (DMOS-PPV) is completely soluble in common organic solvents. Hwang et al. reported synthesis and LED properties of DMOS-PPV [85]. Scheme 12 shows the synthetic route to DMOS-PPV by dehydrohalogenation. 

Silicon-silicon multiple bonds with a bond order greater than two are still unknown. According to theoretical calculations, voluminous and concomitantly electropositive substituents are the most promising candidates with the potential to stabilize disilynes having a formal Si Si triple bond. When and by what synthetic route this challenge for experimental chemistry will be realized is a question that only time can answer. 

The sodium condensation reaction of a,co-bis(chlorosilyl)-substituted compounds and the coupling reaction of dilithio derivatives of compounds bearing 7t-electron systems with dichlorosilanes offer a convenient route to various silicon containing polymers. However, the polymers prepared by these methods always contain a small proportion of siloxy units in the polymer backbone, which would interrapt the electron delocalisation. Therefore, new synthetic routes to organosilicon polymers have been developed in which no alkali metal halide condensations are involved [6, 7]. We report syntheses of organosilicon... 

The reaction between halosilanes and ammonia or primary or secondary amines is the most widely used synthetic route to compounds containing 8i-N bonds. 8uch reactions are greatly controlled by steric effects if large groups are present on either the silicon or the amine, then less than full substitution may occur. For example, ammonia reacts with chlorosilanes to give a variety of products depending on the size of the chlorosilane (equation 32). 

Atomic Structure. The control of atomic structure is fundamental to any system, and an incomplete understanding of atomic structure can limit advancement. For example, our understanding of preceramic polymers, up through the formation of networks, is improving but the full exploitation of this chemistry is still limited by the lack of detailed knowledge of the structure of the resulting ceramic at the atomic level. Even with more familiar silicone polymer systems, synthetic barriers are encountered as polymers other than poly(dimethylsiloxane) are used. Stereochemical control is inadequate in the polymerization of unsymmetrical cyclic siloxanes to yield novel linear materials. Reliable synthetic routes to model ladder systems are insufficient. 

As was previously mentioned, alternative synthetic routes to polycarbosi-lanes are metathesis reactions of carbo anions and silicon halides. For example, Wurtz-Uke condensation of dichlorosilanes and dibromoethane with sodium metal yields [SiH2CH2] . 3... 

Figure 6.13 Synthetic route of siliconates to polysiloxanes (a) reaction of siliconate with acid to give a methyl silanol, followed by further decomposition in the presence of atmospheric carbon dioxide to methyl silicic acid and alkali carbonate (b) formation of polysiloxanes from methyl silicic acid via intermolecular condensation. X = Na, K...

Summary Our research on a-metalated organosilanes currently focuses on (aminomethyl)silanes containii a defined stereogenic center next to the silicon center. A synthetic route based on the preparation of 2-silyl-substituted pyrrolidines was developed. The racemic product could be synthesized by metalation of JV-Boc-pyrrolidine in the presence of TMEDA and conversion with the corresponding chlorosilane, whereas the enantioenriched form was achieved by metalation in the presence of the chiral amine (-)-sparteine. Subsequent metalation and transformation reactions yielded the formation of the corresponding (aminomethyl)(lithiomethyl)silane. 

Unaware of the above mentioned work we explored, almost at the same time, the similar theme and encountered some very interesting and novel findings about the synthesis and structure of (lithiomethyl)(aminomethyl)silanes. We are presenting new synthetic routes to (aminomethyl)silanes and (lithiomethyl)(aminomethyl)silanes and we want to give experimental information on two questions concerning (lithiomethyl)silanes (i) aggregation of (lithiomethyl)(aminomethyl)silanes in the solid state (ii) stabilizing effects of silicon in (lithiomethyl)silanes. 

Following the successful X-ray structure analysis of 1 and 2 the same synthetic route was applied to the synthesis of a compound with a longer silicon chain. A solution of Br(SiMe2)6Br in pentane was added dropwise to a THF solution of Na[(ii -C5Me4Et)Fe(CO)2] at -78°C. The reaction mixture was stirred at this temperature for 15 min and then brought to room temperature and stirred for 1 h The solvent was removed, the orange residue was extracted with pentane, and the mixture was filtered. Recrystallization from pentane gave compound 3 (Eq. 3). 

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