Coordination-driven self-assembly of cavity-cored multiple crown ether derivatives and poly[2]pseudorotaxanes

The synthesis of a new 120 degrees diplatinum(II) acceptor unit and the self-assembly of a series of two-dimensional metallacyclic polypseudorotaxanes that utilize both metal-ligand and crown ether-dialkyl-ammonium noncovalent interactions are described. Judiciously combining complementary diplatinum(II) acceptors with bispyridyl donor building blocks, with an acceptor and/or donor possessing a pendant dibenzo[24]crown78 (DB24C8) moiety, allows for the formation of three new rhomboidal bis-DB24C8, one new hexagonal tris-DB24C8, and four new hexakis-DB24C8 metallacyclic polygons in quantitative yields. The size and shape of each assembly, as well as the location and stoichiometry of the DB24C8 macrocycle, can be precisely controlled. Each polygon is able to complex two, three, or six dibenzylammonium ions without disrupting the underlying metallacyclic polygons, thus producing eight different poly[2]pseudorotaxanes and demonstrating the utility and scope of this orthogonal self-assembly technique. The assemblies are characterized with one-dimensional multinuclear (H-1 and P-31) and two-dimensional (H-1-H-1 COSY and NOESY) NMR spectroscopy as well as mass spectrometry (ESI-MS). Further analysis of the size and shape of each assembly is obtained through molecular force-field simulations. H-1 NMR titration experiments are used to establish thermodynamic binding constants and poly[2]pseudorotaxane/dibenzylammonium stoichionnetries. Factors influencing the efficiency of poly[2]pseudorotaxane formation are discussed.