Unexpected Self-Sorting Self-Assembly Formation of a [4:4] Sulfate:Ligand Cage from a Preorganized Tripodal Urea Ligand

• Published in: Angewandte Chemie (International ed.) Vol. 54; no. 15; pp. 4566 - 4570
• Main Authors: Pandurangan, Komala, Kitchen, Jonathan A., Blasco, Salvador, Boyle, Elaine M., Fitzpatrick, Bella, Feeney, Martin, Kruger, Paul E., Gunnlaugsson, Thorfinnur
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 07.04.2015; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: anion recognition; Anions; Benzamides - chemistry; Binding Sites; Chemistry; Chemistry, Multidisciplinary; Crystal structure; Encapsulation; Holes; Hydrogen Bonding; Ligands; Methylation; Models, Molecular; Phosphates - chemistry; Physical Sciences; Platforms; Science & Technology; Self assembly; self-sorting; Stoichiometry; Sulfates - chemistry; supramolecular chemistry; tripodal ligands; Urea - analogs & derivatives; Ureas; anion recognition; CRYSTALLINE CAPSULES; AQUEOUS-MEDIA; SELECTIVE RECOGNITION; self-sorting; CYCLIC-PEPTIDES; self-assembly; ANION RECEPTORS; TRANSPORT; LUMINESCENT; CHEMISTRY; SEPARATION; supramolecular chemistry; BINDING; tripodal ligands
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201411857

The design and synthesis of tripodal ligands 1–3 based upon the N‐methyl‐1,3,5‐benzenetricarboxamide platform appended with three aryl urea arms is reported. This ligand platform gives rise to highly preorganized structures and is ideally suited for binding SO42− and H2PO4− ions through multiple hydrogen‐bonding interactions. The solid‐state crystal structures of 1–3 with SO42− show the encapsulation of a single anion within a cage structure, whereas the crystal structure of 1 with H2PO4− showed that two anions are encapsulated. We further demonstrate that ligand 4, based on the same platform but consisting of two bis‐urea moieties and a single ammonium moiety, also recognizes SO42− to form a self‐assembled capsule with [4:4] SO42−:4 stoichiometry in which the anions are clustered within a cavity formed by the four ligands. This is the first example of a self‐sorting self‐assembled capsule where four tetrahedrally arranged SO42− ions are embedded within a hydrophobic cavity. All wrapped up: A tripodal ligand based on the N‐methyl‐1,3,5‐benzenetricarboxamide platform having two bis‐urea arms and an ammonium moiety undergoes self‐assembly with SO42− ions to form a capsule with [4:4] SO42−:ligand stoichiometry. In this self‐sorted self‐assembled structure, the four tetrahedrally arranged anions (see picture; anions given in space‐filling mode) are clustered within a hydrophobic cavity formed by four ligands.