Design and self-assembly of wide and robust coordination cages

Abstract

The self-assembly of a new class of coordination cages formed from two tetrapyridyl-substituted cavitands connected through four square-planar palladium or platinum complexes is reported. The shape of the internal cavity resembles an ellipsoid with a calculated volume of 840 Å 3 . The four lateral portals have a diameter of about 6 Å, large enough to allow the fast entrance͞ egress of counterions in solution. The platinum cages 3a,e cannot be disassembled using triethylamine as competitive ligand and they are kinetically stable at room temperature, whereas the palladium cages 3b-d, 3f-h are disassembled and kinetically labile under the same conditions. The different solubility properties of the cage components have allowed the extension of this selfassembly protocol to the liquid-liquid interface. cavitands M etal-directed self-assembly has been widely used to construct three-dimensional structures presenting internal cavities of molecular dimensions, capable of trapping ions and neutral molecules (1, 2). The ability of such container molecules to confine (3) and stabilize (4) their guests makes them particularly attractive for many potential applications ranging from catalysis (5, 6) to nanotechnology (for self-assembly in nanotechnology, see ref. 7; ref. 8). Specifically, surface-controlled self-assembly is rapidly emerging as a valuable tool for the generation of complex structures directly on solid supports (9-11). Unlike the covalent approach used for carcerands synthesis (12), the thermodynamic control of the process conveys interesting features, among which reversibility (13), selection (14), and self-repairing properties are the most interesting.Cavitand-based coordination cages are receiving increasing attention because of the versatility of cavitand platforms in terms of preorganization and synthetic modularity (15)(16)(17)(18)(19)(20). Strong metal-ligand interactions are necessary to operate cage selfassembly (CSA) in a wide range of solvents, to extend further these self-assembly protocols to solid-liquid and liquid-liquid interfaces.For this purpose we designed and synthesized new cavitands bearing pyridines (for references on cages derived from multidentate pyridine ligands, see ref. 21; refs. 22 and 23) instead of nitriles (24) at the upper rim as ligands for the coordination to the metal centers. CSA requires a cavitand with four pyridines preorganized in a diverging spatial orientation, pointing outward (o) the cavity, being designated the oooo isomer (for in͞out isomerism in cavitands, see ref. 25). Materials and MethodsGeneral. All commercial reagents were ACS reagent grade and used as received. All solvents were dried over 3-and 4-Å molecular sieves. Resorcinarenes 1a,b were prepared according to the literature (26). Metal precursors were prepared from the corresponding dichlorobis derivatives following established procedures (27-29). 1 H NMR were recorded on Bruker (Billerica, MA) AC300 (300 MHz) and AMX400 (400 MHz) spectrometers and all chemical shifts (␦) were reported in parts per milli...

Solvent‐Dependent Self‐Assembly Behaviour and Speciation Control of Pd6L8 Metallo‐supramolecular Cages

“…This is contrasting behaviour to that reported by Dalcanale and co-workers on similar types of cavitand-based metallocage systems. [24] They mixed two distinct homoleptic Pt 4 L 2 cages where the L ligands were pyridyl-derived calix [4]resorcinarene cavitands with different lower rim groups, and observed formation of heteroleptic cages in solution on heating and standing. Zheng and Stang have likewise shown that combinations of homoleptic Pt-based supramolecular polygons undergo dynamic ligand exchange to form mixtures of heteroleptic polygons.…”

Binding Mechanisms in Supramolecular Complexes

“…[588] These can be made water soluble through the introduction of ionic groups (such as in 50), [589] and bind, for example, nucleotides, besides through ion-pair bridges, largely through hydrophobic interactions, with enthalpic contributions dominant. [595] [591] Similar complexes are accessible by using phosphorylated calixarenes.…”

Mesoscopic self-organization of a self-assembled supramolecular rectangle on highly oriented pyrolytic graphite and Au(111) surfaces

“…Metal-containing macrocycles with high symmetry and precise architecture are a new class of promising supramolecules for future application in nanotechnology because of their exact shape and size, as well as magnetic, photophysical, and electrostatic properties (14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27). In this article, we describe scanning tunneling microscopy (STM) studies of the self-assembled supramolecular metallacyclic rectangle, cyclobis[(1,8-bis(transPt(PEt 3 ) 2 )anthracene)(1,4Ј-bis(4-ethynylpyridyl)benzene](PF 6 ) 4 , (Fig.…”