Redox-controlled chalcogen and pnictogen bonding: the case of a sulfonium/stibonium dication as a preanionophore for chloride anion transport

Abstract

Our interest in the chemistry of tunable chalcogen and pnictogen bond donors as Lewis acidic platforms for the complexation and transport of anions has led us to investigate examples of such compounds that can be activated by redox events. Here, we describe the synthesis of [o-MePhS(C₆H₄)SbPh₃]²⁺ ([3]²⁺) and [o-MePhS(C₆H₄)Sb(p-Tol)₃]²⁺ ([4]²⁺), two dicationic stibonium/sulfonium bifunctional Lewis acids which were obtained by methylation of the phenylthioether derivatives [o-PhS(C₆H₄)SbPh₃]⁺ ([1]⁺) and [o-PhS(C₆H₄)Sb(p-Tol)₃]⁺ ([2]⁺), respectively. An evaluation of the chloride anion transport properties of these derivatives using chloride-loaded POPC unilamellar vesicles shows that the activity of the monocations [1]⁺ and [2]⁺ greatly exceeds that of the dications [3]²⁺ and [4]²⁺, a phenomenon that we assign to the higher lipophilicity of the monocationic compounds. Harnessing this large transport activity differential, we show that [4]²⁺ can be used as a prechloridophore that is readily activated by reduction of the sulfonium moiety. Indeed, [4]²⁺ reacts with GSH to afford [2]⁺ as an active transporter. This activation, which has been monitored in aqueous solution, can also be carried out in situ, in the presence of the chloride-loaded POPC unilamellar vesicles.