Antimony-stabilized alkylation

Antimony pentachloride is a reactive Lewis acid that can be used for Friedel-Crafts reactions and some other Lewis-acid-catalyzed reactions. The HF-SbF5 system is known as magic acid, and carbocations are stabilized in this medium.353 By using the HF-SbF5 system, alkylation of acetophenone (a relatively unreactive aromatic compound) has been achieved (Scheme 87). 

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). 

Penta-alkyls and aryls. The penta-alkyls and -aryls R5M are of interest both structurally and in connection with the relative stabilities of the H-S oxidation state. Only antimony appears to form a pentamethyl derivative, MesSb (a liquid bp 126-127°, from MeLi + Me3Sb or Me4SbBr), which is surprisingly thermally stable, and unlike trimethylstibine it does not inflame in the air, though it oxidizes quickly and is decomposed by water. Its vibrational spectra are consistent with a trigonal bipyramidal structure. With an excess of methyl-lithium it forms the salt Li SbMe4. ... 

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