Chlorosilanes, exchange reactions

Metal-exchange reactions were also observed, as in the reaction of phenyl-chlorosilanes and phenyl-silylhydrides, when products in addition to the expected Siy 4 were formed195). This may be due to the formation of metal-silyl compounds during the reaction. It is known that organometallic compounds are easily formed with phenyl-substituted silane derivatives and with the Si—H bond. 

The fluoro compounds could be obtained by halogen exchange reactions from the corresponding chloro compounds with zinc fluoride in diethylether The acetylene-bridged compound 17 was prepared by reaction of di(/er/-butyl)chlorosilane with sodium acetylide in THF (Eq 2). Remarkably, during such reactions gaseous acetylene was formed, so that the acetylene bridged compounds arose in a one-step synthesis. 

Since chlorosilanes are unstable and readily hydrolyzed when subjected to aqueous conditions an isotopic exchange reaction using nanomolar quantities of di-tert-butyl-phenyl- F-fluorosilane as precursor was tested and evaluated to result at room temperature within 15 min... 

The chlorosilanes are available from classical synthetic routes [108]. In most cases the products can be obtained from SiCl4 and the lithium salts of the introduced substituents with sufficient selectivity and in high yield. This is particularly true for the alcoholates and the thiolates. The exchange problems R vs. Cl which arise with the t-butylthiochlorosilanes will not be discussed in detail here. These problems are overcome by an appropriate choice of the reaction conditions. 

The silanization reaction in liquid phase (usually in dry toluene) is technologically more convenient, although it is practically impossible to ensure the complete absence of water in a reaction mixture that leads to hydrolysis of chlorosilanes. Using deuterium exchange, Roumeliotis and Unger [55] analyzed surface silanol concentration before and after the modification with different reagents (Table 3-2). 

Competing reactions forming chlorosilanes occur also. Alkysilanes exchange similarly, although C—Si bond cleavage also occurs. 

Reaction of Silyllithium with Chlorosilane Halogen-metal exchange and Si-Si Bond Cleavage Reaction... 

AllykUanes. Replacement of one of the seleno substituents by a silyl group is achieved by reaction with BuLi and a chlorosilane. A second Se/Li exchange on the remaining MeSe group provides reactive nucleophilic reagents. 

The anions (67c)-((i7e) are prepared by the low temperature transmetallation reactions of n-butylli-thium with the corresponding allylic tin or lead compounds. The addition of (67d) to aldehydes and ketones proceeds with C—C bond formation at either terminus. Dialkyl ketones give the a-products, while benzaldehydes and benzophenone afford the y-products. Aliphatic aldehydes, acetophenone and substituted acetophenones give both types of products. The anion (67e) is not stable in solution even at -95 °C and cannot be preformed prior to its reaction with the desired substrate (67e) may be generated by Li-Br exchange between n-butyllithium and 3,3-difluoro-3-bromopropene at -95 C. ) en this preparation is performed in the presence of chlorosilanes, aldehydes, ketones, and esters, the a-products are obtained, often in good yields (Scheme 46). Reactions of (67c) with TMS-Cl and benzaldehyde afford y-adducts, whereas those with methyl iodide, acetophenone and pentanal produce a-adducts predomi-nantly. ° Anions (67a) and (67b) give a-alkylation products wiA aliphatic halides and TMS-Cl, but afford y-adducts with iminium salts. ... 

Next to ion exchange resins, the polymeric supports most likely to be used for catalysts are other cross-linked polystyrenes or silica gels. Both are inexpensive, easy to functionalize, and void of other reactive functional groups. Their limitations are the thermal and physical stability of polystyrene and the solubility of silica in alkali. Polystyrene can be derivatized by almost every known reaction of mononuclear aromatic hydrocarbons, and the conditions for those reactions on polymers have been published and reviewed (2D- The surface of silica gel can be covered with a wide range of organic materials by reaction of its hydroxyl groups with silyl esters and chlorosilanes f381. 

---