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

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 C₃-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 A₄L₄-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 ų) 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.