Hypervalent Iodine(III) versus Sulfonium Salts as Electrophilic Group-Transfer Reagents: A Comparative Review of Stability, Reactivity, Safety and Sustainability

Many modern methods install a group by reversing its usual polarity: a trifluoromethyl, alkynyl, cyano, aryl or vinyl unit is handed to a nucleophile as if it were a cation. Two reagent families carry most of this chemistry, hypervalent iodine(III) compounds (λ3-iodanes) and sulfonium salts. In both, the group sits on a heavy main-group atom that leaves in reduced form, as an iodoarene or a neutral sulfide. The two families are rarely judged side by side, and this review does so on four practical axes. For stability, we contrast the three-centre, four-electron bond of iodine(III) with the octet sulfonium cation. For reactivity, we follow polar, single-electron and metal-catalysed pathways and collect the few studies that tested both classes on the same bond. The available calorimetric and impact data are collected for safety. Several benziodoxol(on)e reagents are energetic decompositions but at least one alkynyl sulfonium salt is also high-energy. Data on sulfonium salts is scant. For sustainability, we combine element supply estimates with a mass partition of fifteen reagents estimated from their formulae. 7 to 42% of the mass of each reagent ends up in the result, hence the waste balance depends on the recovery of the carrier. We read the evidence straightforwardly. Iodine(III) reagents are still the top choice for quick polar transfers on a small scale, but sulfonium salts become desirable when thermal margins, site-selective arene activation or recycling of the carrier matter more. We end with data gaps that nevertheless prevent a fair, quantitative choice.