Trichlorosilane derivatives

Trichlorosilane derivatives of large dye molecules are difficult to purify and owing to moisture sensitivity are hard to handle. Their organic solutions tend to become turbid rather quickly owing to the formation of insoluble polymers. Thus, solutions must be replaced frequendy. An exception may be the combination of self-assembly and surface chemical reaction (186-189,202). On the other hand, co-substituted alkyltrichlorosilane derivatives are easy to synthesize the purify. These could be used for the engineering of surface free energy through the control of chemical functionalities in their SAMs, or as active layers for attachment of biomolecules in biosensors. 

Tillman, N., Ulman, A., Schildkraut, J. S., and Penner, T. L. Incorporation of phenoxy groups in self-assembled monolayers of trichlorosilane derivatives. Effects on films thickness, wettability, and molecular orientation./. Am. Chem. Soc. 110, 6136 (1998). 

Despite the fact that the uncatalyzed reactions are reported to be very rapid at -78 °C, Deiunark has demonstrated that the addition reaction is dramatically accelerated in the presence of a catalytic amounts of Lewis-basic phospho-ramides, such as hexamethylphosphoric triamide (HMPA). This remarkable observation coupled with mechanistic investigations has led to the successful development of chiral phosphoramides 248 to 250 as Lewis-base catalysts for enan-tioselective Mukaiyama aldol addition reactions. Initial investigations documented the superiority of phosphoramide 250 in delivering products of high optical purity for example, the addition reaction of enol trichlorosilane derived from methyl acetate with trimethylacetaldehyde at -78 °C affords the aldol adduct in 62% ee and 78% yield (Eq. 53). 

Summary The reactivity of some trichlorosilane-derived silazanes has been studied. Treatment of 2-amino-l,3-bis(trimethylsilyl)-l,3-diaza-2-silacyclopentane (2) with two equivalents of n-butyllithium results in the formation of its hexameric W,A-dilithium derivative 3, the structure skeleton of which is best described as a singly truncated but lithium-centered rhombic dodecahedron of eight lithium and five nitrogen atoms. Reduction of Si-Cl-containing silazanes with lithium alanate opens a straightforward access to aminoalanes. Bis[(tert-butylamino)chloroalane] (8), bis[(tert-butyl-amino)alane] (9), and l,3-di-/er/-butyl-lC7 , 3CT -diaza-2o , 60 -dialumina[2.1.1]bicyclo-hexane (10) have been synthesized and structurally characterized. 

The production of sihcon tetrachloride by these methods was abandoned worldwide in the early 1980s. Industrial tetrachlorosilane derives from two processes associated with trichlorosilane, the direct reaction of hydrogen chloride on sihcon primarily produced as an intermediate for fumed sihca production, and as a by-product in the disproportionation reaction of trichlorosilane to silane utilized in microelectronics. Substantial quantities of tetrachlorosilane are produced as a by-product in the production of zirconium tetrachloride, but this source has decreased in the 1990s owing to reduction in demand for zirconium in nuclear facihties (see Nuclearreactors). The price of tetrachlorosilane varies between l/kg and 25/kg, depending on grade and container. 

More recently, P-cored derivative (116) was prepared from a straightforward combination of a Heck coupling, to afford an intermediate functionalised stil-bene phosphine oxide (114),a Horner-Wittig reaction yielding the phosphine oxide (115), and finally trichlorosilane reduction (Scheme 31) [89]. Using similar strategies, both the valence isoelectronic N- (117) and C- (118) cored dendrimers have been prepared (Scheme 31). 

Substitution of P-substituents other than halogens has been reported for P-ethoxy-l,3,2-diazaphospholene and l,3,2-diazaphospholene-2-oxide which react with trichlorosilane to yield the corresponding P-chloro-substituted heterocycles [49,50]. This reaction reflects a typical behavior of phosphine derivatives undergoing halogen replacement similar to the previously discussed transformations. 

The asymmetric hydrosilylation that has been most extensively studied so far is the palladium-catalyzed hydrosilylation of styrene derivatives with trichlorosilane. This is mainly due to the easy manipulation of this reaction, which usually proceeds with perfect regioselectivity in giving benzylic silanes, 1-aryl-1-silylethanes. This regioselectivity is ascribed to the formation of stable 7t-benzylpalladium intermediates (Scheme 3).1,S Sa It is known that bisphosphine-palladium complexes are catalytically much less active than monophosphine-palladium complexes, and, hence, asymmetric synthesis has been attempted by use of chiral monodentate phosphine ligands. In the first report published in 1972, menthyldiphenylphosphine 4a and neomenthyldiphenylphosphine 4b have been used for the palladium-catalyzed reaction of styrene 1 with trichlorosilane. The reactions gave l-(trichlorosilyl)-l-phenylethane 2 with 34% and 22% ee, respectively (entries 1 and 2 in Table l).22 23... 

Linear 1,3-dienes have also been subjected to the palladium-catalyzed asymmetric hydrosilylation (Scheme 12, Table 5). Reaction of 1-phenyl-l,3-butadiene 46a with HSiClj catalyzed by palladium-(/ )-(A)-PPFA 5a gave a mixture of regioisomeric allysilanes 47, and 48 and 49, in a ratio of 94 to 6, the major isomer 47 and the minor isomer 48 being 64% ee (S) and 30% ee (R), respectively (entry l).60 7r-Allylpalladium intermediate 50 was proposed for this hydrosilylation. Use of phenyldifluorosilane in place of trichlorosilane slightly improved the enantioselectivity (entry 8).58,61 Similar level of enantioselectivity (71-72% ee) was reported for the reaction using Ar-MOP ligand 37f (entry 11) and its dioctylated derivative 37g (entry 12).57a... 

Table /. Results of the hydrosilylation of styrene and its derivatives with trichlorosilane with 1 as a catalyst precursor.

Hydrosilylation of o-allylstyrene (82) with trichlorosilane in the presence of 0.3mol% of a palladium catalyst bearing triphenylphosphine has been found to produce a mixture of indane (83) and the open-chain products (84) and (85) (Scheme 11). The reaction of styrene with trichlorosilane gave a quantitative yield of 1-phenyl-l-(trichlorosilyl)ethane whereas allylbenzene did not give silylation products under the same reaction conditions. These results show that the hydropalladation process is operative in the hydrosilylation of styrene derivatives with trichlorosilane catalysed by palladium-phosphine complexes." ... 

Direction b of Scheme 1.10. The mixture of trichlorosilane and tributylamine in benzene reduces organic derivatives of two-valence sulfur such as benzene sulfenates. However, nitrobenzene sulf-enates remain intact in this system (Todres and Avagyan 1978 Scheme 1.13). 

Next, a few examples of asymmetric reductions with trichlorosilane are presented. An asymmetric reduction of ketones and imines was reported by Matsumura and coworkers by using trichlorosilane as reductant and A-formyl pyrrolidine derivative 36 as ligand (Scheme 28) [101, 102]. 

The antimony(V) chloride catalyzed fluorination with antimony(III) fluoride has been used to prepare (2,2-difluoroethyl)trifluorosilane in 83 % yield from the corresponding trichlorosilyl derivative.88 Also, other trichlorosilanes containing electron-withdrawing fiuorinated alkyl groups (difluoromethyl, 1,1,2,2-tetrafluoroethyl, 1,1-difluoroethyl) arc converted into the corresponding trifluorosilanes in about 80% yield by treatment with the antimony(III) fluoride/ antimony(V) chloride system.89-90... 

Stereo specific generation and reactions of allylic alkali and alkaline earth metals have been reviewed121 and solvent-mediated allylation of carbonyl compounds with allylstannanes has been explored.122 Chiral phosphoramides derived from (5 )-proliiie have been used to catalyse asymmetric allylation of aromatic aldehydes by allylic trichlorosilanes.123... 

For the synthesis of hexasilaprismane, tetrachlorodisilane (RSiCl2—SiC R) and trichlorosilane (RSiCb) are utilized as the starting compounds. The Mg/MgBr2 reagent is quite useful also for the synthesis of hexasilaprismane. A hexasilaprismane derivative, hexakis(2,6-diisopropylphenyl)tetracyclo[2.2.0.02 6.03 5]hexasilane (12), was successfully... 

The dilithio derivatives of catechol and hexafluorocumyl alcohol react with organo-trichlorosilanes to give spirosilicates (equations 11 and 12)34,35. 

S)-Proline-derived phosphoramides catalyse enantioselective allylation of aromatic aldehydes with allylic trichlorosilanes.90 Chiral a-aminoaldehydes have been allylated diastereoselectively with various reagents.91... 

Formamides derived from L-pipecolinic acid act as Lewis base organocatalysts for reduction of A-arylimines with trichlorosilane, giving yields and ees in the high 90s for a wide range of imine substrates.54... 

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