Silicon halides amides

Si H M agostic interactions in silylamido complexes have been extensively studied to date. The earlier examples were prepared by halide displacement in the coordination sphere of a metal by a silylated amide, which puts severe limitations on the nature of the substituents at silicon (usually, robust methyl groups are used). More recently, a new route to p-agostic silylamides based on the direct coupling of silanes with imido ligands was discovered that allows one to trace the effect of substitution at silicon on the extent of the Si-H bond complexation (vide infra). 

This synthetic method is of great importance in the synthesis of silicon amides. Halides of the type R SiCL,. (x = 0, 1, 2, 3) react with ammonia or primary and secondary amines to give the corresponding amides.17"24 Again, with sterically demanding amines only partial halide displacement is possible (equations 6 and 7).22,23... 

Due to the presence of silicon which stabilizes the a-carbanion, strong bases such as butyllithium and sodium amide are able to give an ylid from silylmethylammonium halides. Fluoride ion-assisted desilylation of these salts represents another means to create an ylid. These ylids are prone to rearrange and the results differ upon the nature of... 

So far, no crystallographic evidence for adducts of silanes with aldehydes, ketones, esters, or acyl halides has been reported [81]. Dimethylformamide [86-88] and tetramethylurea [89], however, are known to enter the silicon coordination sphere (e.g., in 13 and 14, respectively). In a similar manner amine-M-oxides (e.g., in 15) [90], phosphine oxides (e.g., in 16 and 17) [90,91], and phosphoric amides [92-94] form hypercoordinated Si complexes. Although dimethyl sulfoxide (DMSO) increases the silicon coordination number (as shown Si NMR spectroscopy) [49], crystallographic evidence for a siUcmi complex with DMSO Ugand(s) is still lacking [81]. 

Oligosilanyl halides are also very abundant and their treatment as a separate compound class would thus be too exhaustive. Silyl halides are of major importance for the generation of numerous silicon species. By reaction with nucleophiles including lithium alkyls, silyl anions, amines, amides, alcohols, and alkoxides, Si-X bonds are easily formed. They also serve as starting materials for Si-Si bond formation by Wurtz coupling or for the generation of unsaturated compounds such as disilenes, disilynes, or silylenes. 

---