Antimony Ylides and Pentaalkylstiboranes

It is obvious from the literature summarized in recent reviews (11, 26) that very little information is available on ylidic compounds of antimony. Moreover, the few compounds synthesized were all taken from the aryl series, whereas those of the alkyl series appear to be completely unknown. Even the aryl antimony ylides were of very limited thermal stability and could only be isolated in special cases (11). 

therefore, to be expected that a compound such as trimethyl-methylene stiborane, (CHs SbCtE, should be relatively unstable and attempts to synthesize this species would have to be carried out at low temperature. Another difficulty arises from the experimental fact (104) that all conventional methods of synthesis for stibonium ylides lead to pentaalkylstiboranes instead of ylides (see Introduction). Thus mcthyl-ation of (CH3)4SbX or (CHY) sHbX2 halides by organometallic reagents of lithium, magnesium, aluminum, or zinc invariably yield (CHY) 5Sb as the sole product. 

In a search for other possible routes to trimethylmethylene stiborane 

This section is not complete without mentioning the hydrogen-deuterium exchange experiment by Doehring and Hoffmann (12), which indicated an enhanced acidity of the hydrogens in a tetramethylstibonium salt. In the corresponding equilibrium, stibonium ylides play the role of strong bases  

As would be expected, the proton exchange is much slower than in tetra-methylphosphonium and -arsonium salts (12). 

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