Ki-Whan Chi

Self-Organization in Coordination-Driven Self-Assembly

Self-assembly allows for the preparation of highly complex molecular and supramolecular systems from relatively simple starting materials. Typically, self-assembled supramolecules are constructed by combining complementary pairs of two highly symmetric molecular components, thus limiting the chances of forming unwanted side products. Combining asymmetric molecular components or multiple complementary sets of molecules in one complex mixture can produce myriad different ordered and disordered supramolecular assemblies. Alternatively, spontaneous self-organization phenomena can promote the formation of specific product(s) out of a collection of multiple possibilities. Self-organization processes are common throughout much of nature and are especially common in biological systems. Recently, researchers have studied self-organized self-assembly in purely synthetic systems. This Account describes our investigations of self-organization in the coordination-driven self-assembly of platinum(II)-based metallosupramolecules. The modularity of the coordination-driven approach to self-assembly has allowed us to systematically study a wide variety of different factors that can control the extent of supramolecular self-organization. In particular, we have evaluated the effects of the symmetry and polarity of ambidentate donor subunits, differences in geometrical parameters (e.g., the size, angularity, and dimensionality) of Pt(II)-based acceptors and organic donors, the influence of temperature and solvent, and the effects of intermolecular steric interactions and hydrophobic interactions on self-organization. Our studies have shown that the extent of self-organization in the coordination-driven self-assembly of both 2D polygons and 3D polyhedra ranges from no organization (a statistical mixture of multiple products) to amplified organization (wherein a particular product or products are favored over others) and all the way to the absolute self-organization of discrete supramolecular assemblies. In many cases, inputs such as dipolar interactions, steric interactions, and differences in the geometric parameters of subunits, used either alone or as multiple factors simultaneously, can achieve absolute self-organization of discrete supramolecules. We have also observed instances where self-organization is not absolute and varies in its deviation from statistical results. Steric interactions are particularly useful control factors for driving such amplified self-organization because they can be subtly tuned through small structural variations. Having the ability to fully understand and control the self-organization of complex mixtures into specific synthetic supramolecules can provide a better understanding of analogous processes in biological systems. Furthermore, self-organization may allow for the facile synthesis of complex multifunctional, multicomponent systems from simply mixing a collection of much simpler, judiciously designed individual molecular components.

Rhodium-Catalyzed Oxidative ortho-Acylation of Benzamides with Aldehydes: Direct Functionalization of the sp2 C–H Bond

A rhodium-catalyzed oxidative acylation of benzamides with aryl aldehydes via direct sp(2) C-H bond cleavage is described. In the presence of [Cp*RhCl(2)](2), AgSbF(6), and silver carbonate as an oxidant, N,N-diethyl benzamides can be effectively carbonylated to yield ortho-acyl benzamides.

Unusually Stable, Versatile, and Pure Arenediazonium Tosylates: Their Preparation, Structures, and Synthetic Applicability

A new, simple, and effective method for the diazotization of a wide range of arylamines has been developed by using a polymer-supported diazotization agent in the presence of p-toluenesulfonic acid. Various pure arenediazonium tosylates with unusual stabilities can be easily prepared by this method. As a result, these salts are useful and versatile substrates for subsequent transformations, such as halogenation and Heck-type reactions. The unusual stabilities of arenediazonium tosylates are also preliminarily discussed with their X-ray structures.

Pd-Catalyzed Decarboxylative Coupling of Propiolic Acids: One-Pot Synthesis of 1,4-Disubstituted 1,3-Diynes via Sonogashira−Homocoupling Sequence

One-pot synthesis of symmetric 1,4-disubstituted 1,3-diynes from iodoarenes and propiolic acid via Sonogashira reaction followed by Pd-catalyzed decarboxylative homocoupling is developed in high yields. Also, this system allows the one-pot synthesis of unsymmetric 1,4-disubstituted 1,3-diynes by cross-coupling of two different 3-substituted propiolic acids.

Self-selection in the self-assembly of isomeric supramolecular squares from unsymmetrical bis(4-pyridyl)acetylene ligands.

A new approach wherein steric interactions between substituents of unsymmetrical bis(4-pyridyl)acetylene ligands dictate the self-selection of single isomers of [4 + 4] self-assembled squares is presented. Each [4 + 4] self-assembly is characterized by multinuclear (31)P and (1)H NMR spectroscopies and electrospray ionization mass spectrometry. NMR spectroscopic studies are used to provide a means of evaluating the efficiency of bulky substituents at proximal or remote positions relative to the Pt-N bonding motif to direct self-selection. Molecular modeling using the MMFF force field is utilized to determine the relative energy of different isomers of each assembly, and modeling results reasonably explain the trend in self-selectivity with varying pyridyl substitution.

Selective Synthesis of Ruthenium(II) Metalla[2]Catenane via Solvent and Guest-Dependent Self-Assembly

The coordination-driven self-assembly of an anthracene-functionalized ditopic pyridyl donor and a tetracene-based dinuclear Ru(II) acceptor resulted in an interlocked metalla[2]catenane, [M2L2]2, in methanol and a corresponding monorectangle, [M2L2], in nitromethane. Subsequently, guest template, solvent, and concentration effects allowed the self-assembly to be reversibly fine-tuned among monorectangle and catenane structures.

Selective Synthesis of Molecular Borromean Rings: Engineering of Supramolecular Topology via Coordination-Driven Self-Assembly

Molecular Borromean rings (BRs) is one of the rare topology among interlocked molecules. Template-free synthesis of BRs via coordination-driven self-assembly of tetracene-based Ru(II) acceptor and ditopic pyridyl donors is reported. NMR and single-crystal XRD analysis observed sequential transformation of a fully characterized monomeric rectangle to molecular BRs and vice versa. Crystal structure of BRs revealed that the particular topology was enforced by the appropriate geometry of the metallacycle and multiple parallel-displaced π-π interactions between the donor and tetracene moiety of the acceptor. Computational studies based on density functional theory also supported the formation of BRs through dispersive intermolecular interactions in solution.

Reaction of 1,1,2-trifluoro-2-hexafluoro-2′-(heptafluoropropoxy)-propoxyethylene with amines or alcohols

Abstract Reaction between 1,1,2-trifluoro-2-hexafluoro-2′-(heptafluoropropoxy)-propoxyethylene and secondary amines (dimethylamine, diethylamine, dibutylamine, pyrrolidine, piperidine, morpholine) leads either to perfluoro-2-propoxy-3(1H′)-ethoxy-2″-alkoxypropanes — the addition products to the double bond — or to an N , N -dialkylamide of α-substituted fluoroacetic acid depending on the solvent used and the following work-up of the crude product. With primary amines (propylamine, butylamine, monoethanolamine), fluorine-containing imines or N -alkylamides of the α-substituted fluoroacetic acid (as a mixture of diastereomers) were obtained. The use of diethanolamine produces 2-{fluoro-2[hexafluoro-2′-(heptafluoropropoxy)-propoxy]-methyl}-4,5,7,8-tetrahydro-[1.6.3]dioxasozine. Reaction of 1,1,2-trifluoro-2′-hexafluoro-2′-(heptafluoropropoxy)-propoxyethylene with alcohols (methanol, ethanol, β,β,β-trifluoroethanol, 2-methoxyethanol, 2-ethoxyethanol, iso-propanol, butanol and pentafluorophenol) in the presence of KOH in tetrahydrofuran (sulfolane, DMSO, acetonitrile) or sodium alkoxide in an alcoholic medium yields only the corresponding ethers as a mixture of diastereomers. Treatment of ethyleneglycol, glycerine, pentaerythritol, triethanolamine, 2-(2-hydroxyethylsulphanyl) ethanol, 4-(2-hydroxyethyl) phenol with 1,1,2-trifluoro-2′-(heptafluoropropoxy)-2-hexafluoropropoxyethylene provides the addition products to all OH groups if the reaction is carried out in DMSO, sulfolane or acetonitrile. However, the use of THF as the solvent leads to the formation of α-substituted tetrahydrofuran together with the formation of ethers. The initial perfluoro(propoxypropoxy) olefin can be hydrolyzed in the alkaline media to give fluoro-[hexafluoro-2-(heptafluoropropoxy)propoxy]acetic acid.

Template-Free Synthesis of a Molecular Solomon Link by Two-Component Self-Assembly.

A molecular Solomon link was synthesized in high yield through the template-free, coordination-driven self-assembly of a carbazole-functionalized donor and a tetracene-based dinuclear ruthenium(II) acceptor. The doubly interlocked topology was realized by a strategically chosen ligand which was capable of participating in multiple CH⋅⋅⋅π and π-π interactions, as evidenced from single-crystal X-ray analysis and computational studies. This method is the first example of a two-component self-assembly of a molecular Solomon link using a directional bonding approach. The donor alone was not responsible for the construction of the Solomon link, and was confirmed by its noncatenane self-assemblies obtained with other similar ruthenium(II) acceptors.

Synthesis and characterization of self-assembled nanoscopic metallarectangles capable of binding fullerenes with size-selective responses.

Two new metallarectangles, 4 and 5, were obtained from the self-assembly of areneruthenium-based molecular clips 2 and 3 with a new dipyridyl donor ligand 1 containing a diamide core and ethynyl spacers. The metallarectangles were characterized by multinuclear NMR, electrospray ionization mass spectrometry, and UV-vis spectroscopy, and the molecular structure of 4 was unambiguously determined by single-crystal X-ray diffraction analysis. Because of the presence of an extended π-electron aromatic surface, the tetracene-containing molecular rectangle 5 was capable of binding C60 and C70 fullerenes as quantified by UV-vis, emission, and (1)H NMR experiments, providing an example of a supramolecular host capable of recognizing large guest molecules.