Supramolecular Synthesis with Carboxyl-Substituted Secondary Dialkylammonium Salts and Macrocyclic Polyethers

Abstract

Self-assembly [1] — the spontaneous generation of ordered supramolecular aggregates or arrays using intermolecular bonds — has of late become the noncovalent craftsman’s primary tool for the supramolecular synthesis of organised, functioning superstructures. A recent report [2] from our laboratories has detailed an elementary self-assembling system in which secondary dialkylammonium ions — such as the dibenzylammonium ion 1-H+ — thread through the cavities of macrocyclic polyethers to afford pseudorotaxanes of varying stoichiometries (Scheme 1). These complexes are assembled using primarily [N+-H⋯O] hydrogen bonds, though occasional supplementary stabilisation may be provided by [C-H⋯O] hydrogen bonds in conjunction with aromatic edge-toface and face-to-face interactions. The monotopic crown ether dibenzo[24]crown-8 (DB24C8) can thread only one cationic strand through its macrocyclic cavity, while its ditopic counterpart bis-p-phenylene[34]crown-10 (BPP34C10) — possessing two disassociated arcs of oxygen atoms in order to interact with the ammonium sites — allows two secondary dialkylammonium ions to be inserted through its macrocyclic interior to form a double stranded [3] pseudorotaxane.