ELECTROPHILE-PROMOTED CARBON-SULFUR BOND-CLEAVAGE IN ETA(2)-THIOPHENECOMPLEXES OF PENTAAMMINEOSMIUM(II)

Several S-alkylthiophenium complexes of the type [Os(NH3)(5)(4,5-eta(2 )-L)](OTf)(3) (where L = S-alkylthiophenium, S-methylbenzo[b]thiopheni um) are prepared by alkylation of the corresponding thiophene complexe s. The S-alkylthiophenium species are proposed to undergo rapid and re versible cleavage of the C5-S bond, forming highly electrophilic metal lacyclopropene intermediates. Although not directly observable, these vinyl cation intermediates may be trapped with both anionic and neutra l nucleophiles affording eta(2)-4-(alkylthio)-1,3-butadiene complexes. Treatment of selected 4-(alkylthio)-1,3-butadiene complexes with an o xidant (e.g., DDQ) affords the organic ligand in good yield.