Antimony complexes double bonds

Antimony(III) chloride forms colored 7t-complexes with double bond systems (e.g. vitamin A). 

Antimony(V) chloride forms colored x-complexes with double bond systems. 45 — 50) and menihofuran (hR( 80— 85) yielded grey to brown chrumalugiam zones on a pale background, they fluoresced yellow under long-wavelength UV... 

The carbon cation which forms cannot initiate a cationic polymerization of excess alkene molecules that are present in the reaction mixture, due to steric hindrance. The less hindered alkenes, however, like isobutylene, polymerize rapidly under the same conditions with antimony pentafluoride. It was therefore suggested that initiation involves an opening of a previously formed n complex of SbFs with the double bond, through halide participation. The a,y -haloalkylantimony tetrafluoride ionizes with excess Lewis acid to the related carbon cation that is capable of initiating cationic chain growth ... 

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