Rational syntheses of trisubstituted sulfur-bearing closoboranes are presented. In the development of these syntheses unusual cationic closo-boranes [1,7,9-(Me2S)(3)-B12H9] (3) and [1,2,10-(Me2S)(3)-B10H7](+) (4) have been identified. These were initially recognized to be intermediates in the formation of the neutral trisubstituted species 1,7-(Me2S)(2)-9-(MeS)-B12H9 (1) and 1,10-(Me2S)(2)-2-(MeS)-B10H7 (2), respectively. Stable tetrafluoroborate salts were prepared and isolated, and their structures are presented. They are believed to represent the first structural determinations of cationic borane clusters of any type.