Controlling the Recognition and Reactivity of Alkyl Ammonium Guests Using an Anion Coordination-Based Tetrahedral Cage

Abstract

Caged structures have found wide application in a variety of areas, including guest encapsulation and catalysis. Although metal-based cages have dominated the field, anion-coordination-based cages are emerging as a new type of supramolecular ensemble with interesting host-guest properties. In the current work, we report a C-symmetric tris-bis(urea) ligand based on the 2,4,6-triphenyl-1,3,5-triazine spacer, which assembles with phosphate anions to form an AL-type (A = anion, L = ligand) tetrahedral cage, 3, with unusually high packing coefficients (up to 99.5% for the best substrate). Cage 3 is able to adjust its size and shape (from 136 to 216 Å) by bending of the triphenyltriazine plane. This allows it to accommodate relatively large guests. In the case of DABCO, inclusion within the cage allows the degree of methylation to be controlled and the monomethylated product to be isolated cleanly under conditions where mixtures of the mono- and dimethylated adduct are obtained in the absence of cage 3.

Catalysis of an Aldol Condensation Using a Coordination Cage

“…The combined volume of two ID guests (74%) significantly exceeded the value of 55 ± 9% of the host cavity volume (409 Å 3 ), which Rebek showed a while ago afforded optimal guest binding in solution [50,51]. However, a crystalline sponge experiment was performed under highly forcing and non-equilibrium conditions using a large excess of the guest; we [48] and others [52][53][54] have observed packing coefficients for guests inside supramolecular host cavities of >80% when favourable interactions such as π-stacking between multiple guests and favourable interactions between guests and the cage interior surface result in a particularly compact guest array. In dilute solution-the conditions under which guest binding is normally evaluated-we can imagine that for this reason, the second binding constant K 2 would be substantially smaller than the first binding constant K 1 , in which case, the single-guest binding would dominate the solution speciation behaviour [48].…”

Acid‐Tolerant Sulfate Tetrahedral Cages from Anion‐Coordination‐Driven Assembly

“…Various methods, including the well‐established metal‐coordination‐driven assembly, have been applied to construct polyhedral cages [2] . As an alternative approach for such assemblies, anion‐coordination‐driven assembly (ACDA) [3] has emerged in recent years and shown its power in the construction of well‐defined “anionic” architectures, including tetrahedral cages [3e,f] . Such metal‐free, multiple hydrogen‐bonded systems can be readily assembled and disassembled under mild conditions and be directly monitored by NMR spectroscopy.…”

Urea Derivatives as Functional Molecules: Supramolecular Capsules, Supramolecular Polymers, Supramolecular Gels, Artificial Hosts, and Catalysts

“…[135] Wu et al realized the construction of at etrahedral cage with at hree-dimensional cavity capable of guest encapsulationb yt he interaction of tripodal hexakis-urea 32 ( Figure 21) and aphosphate anion. [136] One application of an artificial anion receptor is at ransmembrane anion transporter that mimics biological ionc hannels. [137,138] Decalin bis-urea 33 efficiently recognizes anions, and functions as at ransmembrane transport of those anions ( Figure 22).…”

“…Wu et al. realized the construction of a tetrahedral cage with a three‐dimensional cavity capable of guest encapsulation by the interaction of tripodal hexakis‐urea 32 (Figure 21) and a phosphate anion [136] …”