Silicon anion stabilisation

The same disconnection but of the opposite polarity requires some acylating agent for synthon 9 this is no problem as we have various acid derivatives at our disposal. But the nucleophilic synthon 10, a d3 synthon or homoenolate, is another matter. There is no stabilisation of the anion as drawn but if it were to cyclise to the oxyanion 56, it would be rather more stable and there is evidence-trapping with silicon to give 57 for example-that this can occur. 

Reports of nucleophilic attack at atoms other than those above have also appeared. A kinetic study has compared the effectiveness of tertiary phosphines and phosphite esters in the catalysis of the cleavage of the silicon-silicon bond of methylchlorodisilanes, providing evidence for the involvement of a stabilised silylene intermediate. The anion of the y-phosphino-p-diketimine (197) has been shown to react with arsenic trichloride to give the phosphino-arsino-p-diketimine (198), in which there is a coordinative link from phosphorus to arsenic. ... 

Another way that allenes can be used to provide an acyl anion equivalent is by the Lewis acid catalysed addition of propargyl silanes to electrophiles 109 followed by oxidative cleavage of the allene. The intermediate vinyl cation 110 is stabilised by the silicon (3-effect (chapter 12) and loss of the Me3Si group gives the allene 111. Oxidative cleavage of the sensitive allene reveals that it has acted as a reagent for the formyl anion. 

Fig. 2.9 The stabilisation of an anion by adjacent sulfur, phosphoms and silicon groups...

Obey and Vincent carried out extensive H and Si NMR studies on the PDMS ( silicone oil) phase that formed. They showed that the product was predominantly the cyclic D4 species (where D is a -Me2SiO- repeat unit), although some short, linear homologues of the form 0-(Me2Si0)x-Me2Si0- are also formed (x < 6). Because of their anionic nature, these linear species would appear to accumulate at the silicone oil/water interface, and hence give rise to charge stabilisation of the droplets. The electrophoretic mobility of the (dialysed) droplets. 

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