Aryl-silicon halides

Silicon tetraalkyl and tetraaryl derivatives (R4Si), as well as alkyl or aryl silicon halides (R SiCl4 , n = 1-3) can be prepared by reaction types 18.38-18.42. Note that variation in stoichiometry provides flexibility in synthesis, although the product specificity may be influenced by steric requirements of the organic substituents. Reaction 18.38 is used industrially (the Rochow process). 

Alkyl- and Aryl-silicon Halides.77 These compounds are of special importance because of their hydrolytic reactions. They may be obtained by normal Grignard procedures from SiCl4, or, in the case of the methyl derivatives, by the Rochow process in which methyl chloride is passed over a heated, copper-activated silicon ... 

If an alkyl- or aryl-silicon halide is used in place of the silicon tetrahalide, unsymmetrical organosilicon compounds can be synthesized in this way.314... 

Aminolysis of the corresponding halides is the preferred method for the synthesis of dialkylamino derivatives of boron,1 silicon,2 germanium,3 phosphorus,4 arsenic,5 and sulfur.6 (Dialkylamino) chlorosilanes are prepared stepwise by the reaction of silicon tetrachloride with dialkylamines. This method may be utilized equally well for the conversion of alkyl- or aryl-substituted halides [e.g., (CH3) SiCl4. ] or of oxide and sulfide halides (e.g., POCl3 or PSC13) to the corresponding dialkylamino compounds. 

Aryloxytitanium halides, 25 83 2-Arylpyridines, 27 111 Aryl phosphate esters, 79 51 Aryl phosphates, 7 7 493 Aryl phosphonates, 79 37 Arylphosphorus compounds, 79 28 Aryls, palladium, 79 652 Aryl-silicon compounds, 22 553, 554 Arylsulfinic acids, 27 248-249 Arylsulfonylated gelatin, 72 444 Aryltin trihalides, 24 810-811 Arylyl amines, 70 396-399 Asahi Chemical Industries EHD processes, 9 676-677 sebacic acid production, 9 679-680 ASAM (alkaline-sulfite-AQ-methanol) process, 27 30... 

Hydrolysis of the alkyl and aryl substituted silicon halides produces silicones (Kipping, 1937). The halogen derivatives themselves are made by passing an alkyl or aryl halide over a copper-silicon alloy at about 300°. Hurd and Rochow (1945) found evidence for the mechanism ... 

Aryl silicon compounds can be prepared by metal-catalysed reaction of halides with silanes, as in the rhodium-catalysed reaction below. The mechanistic details of this reaction (probably) differ from the palladium-catalysed borane reaction. (NOTE triethoxy silane is extremely toxic )... 

The sagging pattern which is so characteristic of sequential halogen substitution in alkyl and aryl silanes is not observed in the simple mixed silicon halides (Y4 SiX ). The sagging pattern apparently arises as a result of a substantial electronegativity difference between X and Y which is not present in the mixed halides. The chemical shift trends for the mixed halosilanes are shown in Figure ll69,70. 

Analogously, starting from appropriate silicon halides or alkoxides and introducing various alkyl, aryl, or alkenyl groups stepwise leads to racemic organosilicon compounds such as methyl-(l-naphthyl)(phenyl)silane297 and methoxy-(l-naphthyl)(phenyl)(vinyl)silane298 which can be separated into their enantiomers. 

In the processes described above a silicon halide, ethoxide, or hydride is brought into reaction always with an organic derivative of another metal however, a Si-C bond can also be formed by treating a silylmetal compound, e.g., (triphenylsilyl)-potassium308 or -lithium309 with an aryl or alkyl halide, thus ... 

Alkyl and Aryl Derivatives.—The cleavage of silicon-nitrogen bonds in A-silylphosphazenes by reactions with phosphorus and silicon halides has been studied in some detail. For example, with phosphorus trichloride a novel tri(phosphazenyl)phosphine is obtained ... 

The reaction is carried out by first reacting the alkyl or aryl halide with magnesium shavings in an ether suspension and then treating with silicon tetrachloride (prepared by passing chlorine over heated silicon). With methyl chloride the following sequence of reactions occur ... 

The palladium-catalyzed cross-coupling of alkenylsilanols has been extensively studied with respect to the structure of both the silicon component and the acceptor halide. The preferred catalyst for coupling of aryl iodides is Pd(dba)2 and for aryl bromides it is [allylPdCl]2. The most effective promoter is tetrabutylammonium fluoride used as a 1.0M solution in THF. In general the coupling reactions occur under mild conditions (room temperature, in 10 min to 12 hr) and some are even exothermic. 

Isomerically pure 1 is obtained when HMes2SiSiPh2SiPh2SiMes2H (Mes = mesityl) 5 is used as a starting material, because bonds between silicon and methyl substituted aryl groups like p-tolyl or mesityl are cleaved much faster by hydrogen halides than Si-Ph bonds [3], Further reaction of I with HCl or HBr leads to the formation of the corresponding halo-derivatives 2 and 3 ... 

Several reports have been made of a successful catalyzed addition/ substitution reaction resulting in direct attachment of phosphorus to aromatic rings. The preparation of mixed triarylphosphines has been accomplished by the reaction of tin- or silicon-substituted diphe-nylphosphines with aryl halides catalyzed by palladium reagents.74 A similar transformation has also been reported using nickel catalysis.75 The addition/substitution of diphenylphosphine to triflate functionalized phenolic linkages has been of use for the preparation of substances as analogues of tyrosine-related amino acid derivatives, accomplished with catalysis by palladium acetate (Equation 4.29).76... 

The alkyl- or aryl-halogenosilanes are prepared commercially by passing the vapour of an alkyl or an aryl halide over a heated intimate mixture of powdered silicon and either copper or silver. 

The reaction of heterocyclic lithium derivatives with organic halides to form a C-C bond has been discussed in Section 3.3.3.8.2. This cannot, however, be extended to aryl, alkenyl or heteroaryl halides in which the halogen is attached to an sp2 carbon. Such cross-coupling can be successfully achieved by nickel or palladium-catalyzed reaction of the unsaturated organohalide with a suitable heterocyclic metal derivative. The metal is usually zinc, magnesium, boron or tin occasionally lithium, mercury, copper, and silicon derivatives of thiophene have also found application in such reactions. In addition to this type, the Pd-catalyzed reaction of halogenated heterocycles with suitable alkenes and alkynes, usually referred to as the Heck reaction, is also discussed in this section. 

SILICONK RESINS. The chemistry of the silicones is based on the hydrides, or silanes, the halides, the esters, and the alkyls or aryls. The silicon oxides are composed of networks of alternate atoms of silicon and oxygen so arranged that each silicon atom is surrounded by four oxygen atoms and each oxygen atom is attached to two independent silicon atoms ... 

The reaction of MeLi in Et20 with alkyl- and aryl-substituted branched tetrasilanes proceeds by cleavage of one Si—Si bond, thus affording various trisilanes, which are lithiated at the central silicon atom (equation 26)62. The outcome of these reactions apparently is insensitive as to whether halide-free MeLi or the MeLi-LiBr complex is used62. The decrease in the reaction rate in the order R = Tip > Mes > Ph has been suggested by Fink and coworkers to reflect the relief of steric strain on converting the tetrasilane into the metalated silane626. 

Since a carbon-halogen bond is more easily reduced than a silicon-halogen bond, cathodic reduction of organic halides such as allyl, benzyl, aryl and vinyl halides in the... 

Polysilanes have also been modified by removal of aryl groups under acidic conditions, to give Si-functional polymers. Phenyl or other aryl groups on silicon can be selectively replaced by halogens, upon treatment with a hydrogen halide and a Lewis acid. 

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