Fluorosilanes

TiF is a colorless, very hygroscopic soHd and is classified as a soft fluorinating reagent (4), fluorinating chlorosilanes to fluorosilanes at 100°C. It also forms adducts, some of them quite stable, with ammonia, pyridine, and ethanol. TiF sublimes at 285.5°C, and melts at temperatures >400° C. It is soluble in water, alcohol, and pyridine, hydroly2ing in the former, and has a density of 2.79 g/mL. 

Lithium hydride is perhaps the most usehil of the other metal hydrides. The principal limitation is poor solubiUty, which essentially limits reaction media to such solvents as dioxane and dibutyl ether. Sodium hydride, which is too insoluble to function efficiently in solvents, is an effective reducing agent for the production of silane when dissolved in a LiCl—KCl eutectic at 348°C (63—65). Magnesium hydride has also been shown to be effective in the reduction of chloro- and fluorosilanes in solvent systems (66) and eutectic melts (67). 

Intereshngly it is also possible to form a stable silicon-fluonne bond by treatment of a methoxysilole with boron-tnfluonde etherate or of a silole with tntyl tetrafluoroborate [106] The resultant fluorosilane is also a buildmg block for further transformations of the silole (equation 84)... 

Microwave studies of equilibrium orientations of methyl groups show that the forces act like repulsions, i.e., the hydrogens are staggered with respect to the atoms at the other end, at least in ethyl chloride, methyl silane, methyl fluorosilane, and methyl germane. Where there are only two attached atoms at one end, one connected by a single, the other by a double bond, as in acetaldehyde, propylene, acetyl fluoride and chloride, one of the methyl hydrogens is opposite the double bond, i.e., eclipsed. 

Fluorosilanes are all more highly shielded than their carbon counterparts (Scheme 7.2). 

An attempt to prepare azidosilane by interaction of azidogermane and fluorosilane exploded. 

This common way of synthesis has to cope with the problem that the reaction is nearly uncontrollable because of polycondensation [1], Intermediates, e.g., chlorosilanols, cannot be proved or isolated. However, starting with the alkaline hydrolysis of fluorosilanes, halosilanols, silandiols, and aminosilanols can be prepared and stabilized by bulky groups. 

More illustrative is the structure of the fluorosilane which exhibits the same tricapped tetrahedron geometry. The three N-Si interactions take place in the frontal position towards the Si-F bond instead of the rear coordination observed in penta- and hexacoordinated structures. Furthermore, the benzylamino groups have the possibility not to be coordinated at silicon since these groups have the capability of free rotation around the carbon-nitrogen bond. 

The dilithium phosphandiide dimer 9 is complexed by two molecules of a fluorosilane. The complex crystallizes in the monoclinic space group P2i/n. The framework of the aggregate consists of a cen-... 

The constant potential electrolysis of tetraaikylsiianes in the presence of Et4NH3F4 at 2.3 V results in the cleavage of the C-Si bond and the formation of the corresponding fluorosilanes [21], Presumably, the first step involves the formation of the pentacoordinate anionic species (RR 3SiF ) which is oxidized... 

In contrast to alcohols, trimethyl- and triphenylsilanol react with TeF to form the corresponding fluorosilane and pentafluoroorthotelluric acid (71). The system TeF6-ROH has also been studied by reacting Te(OCH3)6 with anhydrous hydrogen fluoride [Eq. (12)]. 

These include the variations of sacrificial anode, sonication, and alternating polarity cell mentioned above, different solvent/co-solvent and electrolyte systems, monomer concentration, total current passed, and temperature. Best results appear to be obtained with THF and dimethyl ether (DME) as solvent and a perchlorate supporting electrolyte in some systems using fluorides, electrolyte decomposition occurred releasing fluoride anion which formed unreactive fluorosilanes.125... 

Oxidation of alkyl fluorosilanes to the corresponding alcohols. A variant of the Fleming-Kumada oxidation. 

Several mechanisms for the peroxide oxidation of organosilanes to alcohols are compared. Without doubt, the reaction proceeds via anionic, pentacoordinate silicate species, but a profound difference is found between in vacuo and solvated reaction profiles, as expected. In the solvents investigated (CH2CI2 and MeOH), the most favorable mechanism is addition of peroxide anion to a fluorosilane used as starting material or formed in situ, followed by a concerted migration and dissociation of hydroxide anion. In the gas phase, and possibly in very nonpolar solvents, concerted addition-migration of H2O2 to a pentacoordinate fluorosilicate is also plausible. ... 

Thiocarbonyl fluoride has also been prepared by reaction of bis(trifluoromethyl-thio)merkury and iodosilane (5i). The first product formed is trifluoromethyl-thiosilane, which spontaneously decomposes to thiocarbonyl fluoride and fluorosilane. 

---