Diruthenium (II, III) tetracarboxylates efficiently catalyze the oxygenation of organic sulfides by tert-butyl hydroperoxide (TBHP). The study of linear free-energy relationships revealed the electrophilic nature of the diruthenium-activated peroxo species. Organic solubility of Ru2 (esp) 2Cl enables catalytic reactions proceeding with high turnover frequency (TOF) and excellent selectivity under “solvent-free” conditions.