A Potent Halogen‐Bonding Donor Motif for Anion Recognition and Anion Template Mechanical Bond Synthesis

Abstract

The covalent attachment of electron deficient perfluoroaryl substituents to ab is-iodotriazole pyridinium group produces ar emarkably potent halogen bonding donor motif for anion recognition in aqueous media. Sucham otif also establishes halogen bonding anion templation as ahighly efficient method for constructing am echanically interlocked molecule in unprecedented near quantitative yield. The resulting bis-perfluoroaryl substituted iodotriazole pyridinium axle containing halogen bonding [2]rotaxane host exhibits exceptionally strong halide binding affinities in competitive 50 % water containing aqueous media, by af actor of at least three orders of magnitude greater in comparison to ah ydrogen bonding rotaxane host analogue.T hese observations further champion and advance halogen bonding as apowerfultool for recognizing anions in aqueous media.

Anti‐Hofmeister Anion Selectivity via a Mechanical Bond Effect in Neutral Halogen‐Bonding [2]Rotaxanes

“…Given reports that XB donor potency is highly sensitive to local electronic environments and is dramatically influenced by proximal electron‐deficient functional groups, [17, 27] we sought to explore a new 1,3‐bis‐iodotriazole motif wherein the central aromatic scaffold is further decorated with strongly electron‐withdrawing groups. Taking into account the nitro (−NO 2 ) substituent possesses one of the largest positive Hammett substituent constants for a neutral functional group (σ p =+0.778), a new 4,6‐dinitro‐1,3‐bis‐iodotriazole system was targeted, the synthesis of which is shown Scheme 1a.…”

“…To address this challenge, our group has sought to exploit potent, neutral, sigma (σ)‐hole‐based interactions such as halogen (XB), chalcogen (ChB) and pnictogen (PnB) bonding for the purposes of molecular ion recognition [10–18] . XB in particular has emerged as a powerful addition to the arsenal of non‐covalent interactions to achieve anion binding, [19–25] frequently exhibiting dramatically enhanced affinities relative to HB analogues, even in competitive aqueous media [26–29] . However, extensive anion solvation in aqueous media almost invariably confers so‐called “Hofmeister bias”, [30–32] wherein anion binding selectivity profiles are dictated by hydration enthalpies, i.e.…”

Solution Studies of a Water-Stable, Trivalent Antimony Pnictogen Bonding Anion Receptor with High Binding Affinities for CN–, OCN–, and OAc–

“…Up to three of these sites can be induced. The stabilizing interaction that results from an electron donor interacting with this site has been termed a pnictogen bond (PnB), in analogy to the closely related halogen (XB) and chalcogen (ChB) bonds − which have been employed in the design of anion receptors. ,− ,− An important feature of these supramolecular interactions that distinguishes them from formal Lewis acids such as BX 3 , AlX 3 , or PnX 5 (Pn = pnictogen, X = halogen) is that they form with minimal geometric reorganization which results in reversible PnB, ChB, or XB formation without an activation barrier. , These receptors have been applied to form supramolecular capsules to mimic biological molecules, as cross-membrane anion transporting agents, ,,, and as catalysts in substitution reactions. , …”

Dynamic Metalloporphyrin‐Based [2]Rotaxane Molecular Shuttles Stimulated by Neutral Lewis Base and Anion Coordination

“…Recent years have witnessed the exploitation of mechanically interlocked molecules (MIMs) in a diverse range of applications including molecular recognition, [1–6] sensing [7–10] and catalysis, [11–14] wherein the unique microenvironment or topology of the mechanical bond underpins the functional behaviour of the system [15–18] . The exquisite topological control afforded by the mechanical bond in MIMs frequently affords enhanced host‐guest binding behaviour, with increased selectivity and binding affinities over their non‐interlocked analogues [19] …”