Coordination-driven self-assembly of functionalized supramolecular metallacycles

Abstract

Coordination-driven self-assembly that combines rigid ditopic Pt(II) metal acceptors and bis-pyridyl organic donors provides a facile means of synthesizing well-defined metallacycles of predetermined size and geometry. Functionalization of the component acceptor or donor building blocks allows for the preparation of multifunctional supramolecular materials wherein the stoichiometry and position of individual functional moieties can be precisely controlled. The design, self-assembly, and applications of polyfunctional supramolecules incorporating functional moieties with host-guest, photonic, materials, and self-organizational properties is discussed.

Figure 1

Representative examples of edge and corner functionalization of 2D metallacycles: (A) an edge functionalized diaza-crown ether supramolecular rhomboid, (B) an edge functionalized phenanthroline rectangle, (C) a corner functionalized cavitand triangle, and (D) a corner functionalized carborane hexagon.

Figure 2

Representation of endo-functionalized coordination cage assemblies prepared by Fujita and coworkers. The gold coloured spheres projecting inward to the centre of the cage represent functional groups such as oligo(ethylene oxide) chains, perfluoroalkanes, azobenzene units, or polymerizable methyl methacrylate moieties.

Figure 3

Chemical structures and schematic representation of [G0]-[G3] dendritic 120° bispyridyl donors.

Figure 4

Chemical structures and schematic representations of a crown ether functionalized donor (11) and acceptor (12)

Scheme 1

Representation of the coordination-driven self-assembly approach to the construction of 2D metallacycles from rigid, pre-designed di-Pt(II) acceptors (blue) and ditopic organic donors (red).

Scheme 2

Functional moieties may be incorporated into metal-organic coordination compounds through the use of functionalized edge or corner building blocks or covalent attachment of functional groups endo- or exo-to the metallacycles or metallacages.

Scheme 3

The self-assembly of [2+2] rhomboid, [3+3] hexagonal, and [6+6] hexagonal dendritic metallacycles.

Scheme 4

The self-assembly of metallacyclic rhomboids exo-functionalized with pendent DB24C8 macrocycles.

Scheme 5

The self-assembly of [3+3] and [6+6] hexagonal metallacycles bearing 2 and 3 DB24C8 host functionalities, respectively, that are covalently linked to both donor (18-20) and acceptor (20-22) building blocks.

Scheme 6

Demonstration of the abilities of multi-crown ether metallacycles to act as hosts for dibenzylammonium cations (inset). (A) The formation of poly[2]pseudorotaxanes is thermodynamically favoured when DB24C8 macrocycles are linked to donor building blocks. (B) Poly[2]psedorotaxane formation is less favoured when the electron rich macrocycles are covalently linked to electron poor di-Pt(II) building blocks. (C) Example of the orthogonality of the self-assembly approach wherein 9 individual subunits are spontaneously brought together in one step.

Scheme 7

Chemical structures and schematic representation of ferrocene functionalized 120° donor (23) and acceptor (24) units (inset) along with their self-assembly into exo-functionalized ferrocenyl rhomboids and hexagons of varying size and ferrocene stoichiometry.

Scheme 8

Chemical structures and schematic representations of hydrophobic (30a-c) and hydrophilic (31a-c) functionalized 180° donors and their self-assembly into hydrophobic and hydrophilic supramolecular rectangles of varying size.