Designing Multistep Transformations Using the Hammett Equation: Imine Exchange on a Copper(I) Template

Herein, we quantify how imine exchange may be used to selectively transform one metallo−organic structure into another. A series of imine exchange reactions were studied, involving a set of 4-substituted anilines, their 2-pyridylimines and 1,10-phenanthrolyl-2,9-diimines, as well as the copper complexes of these imine ligands. Electron-rich anilines were found to displace electron-poor anilines in all cases. Linear free energy relationships (LFERs) were discovered connecting the electron-donating or -withdrawing character of the 4-substituent of an aniline, as measured by the Hammett σpara parameter, to that aniline's ability to compete with unsubstituted aniline to form imines. The quality of these LFERs allowed for quantitative predictions:  to obtain the desired degree of selectivity in an imine exchange between anilines A and B, the required σpara differential could be predicted using a variant of the Hammett equation, log(KAB) = ρ(σA − σB). We validated this methodology by designing and executing a three-step transformation of a series of copper(I)-containing structures. Each step proceeded in predictably high yield, as calculated from σ differentials. At each step in the series of transformations, macrocyclic structures could be created or destroyed through the selection of mono- or di-amines as subcomponents. The same methodology could be used to predict the formation of a diverse dynamic library of helicates from a set of four aniline precursors, as well as the collapse of this library into one helicate upon the addition of a fifth aniline

Narcissistic, Integrative, and Kinetic Self-Sorting within a System of Coordination Cages

Many useful principles of self-assembly have been elucidated through studies of systems where multiple components combine to create a single structure. More complex systems, where multiple product structures self-assemble in parallel from a shared set of precursors, are also of great interest, as biological systems exhibit this behavior. The greater complexity of such systems leads to an increased likelihood that discrete species will not be formed, however. Here we show how the kinetics of self-assembly govern the formation of multiple metal–organic architectures from a mixture of five building blocks, preventing the formation of a discrete structure of intermediate size. By varying ligand symmetry, denticity, and orientation, we explore how five distinct polyhedraa tetrahedron, an octahedron, a cube, a cuboctahedron, and a triangular prismassemble in concert around CoII template ions. The underlying rules dictating the organization of assemblies into specific shapes are deciphered, explaining the formation of only three discrete entities when five could form in principle

Efficient, High-Yield Route to Long, Functionalized <i>p</i>-Phenylene Oligomers Containing Perfluorinated Segments, and Their Cyclodimerizations by Zirconocene Coupling

Linear oligophenylene diynes containing 6, 9, and 12 phenylene rings were synthesized in high yields using the nucleophilic aromatic substitution (SNAr) of perfluoroarenes by aryllithium reagents as the key carbon−carbon bond-forming reaction. This reaction was demonstrated to proceed readily at low temperatures with sterically hindered substrates and in the presence of base-sensitive silylalkynyl groups. Diynes synthesized by this methodology were readily zirconocene-coupled into large dimeric macrocycles using the zirconocene reagent Cp2Zr(py)(Me3SiC⋮CSiMe3)

Two Distinct Allosteric Active Sites Regulate Guest Binding Within a Fe₈Mo₁₂¹⁶⁺ Cubic Receptor

The binding of phosphine ligands to molybdenum sites on the faces of a supramolecular cube served to inhibit allosterically the encapsulation of a neutral or anionic guest. The edges of the cube also provided a distinct second allosteric site, where the binding of tetraphenylborate also allosterically inhibited anion binding in the cube’s cavity. The two allosteric sites were shown to regulate the binding of an anionic guest either independently or in concert. The use of a tertiary amine as an allosteric effector also enabled a phosphine guest to be ejected from the cube’s cavity into solution, to generate phosphine complexes with other metal ions

Directed Phase Transfer of an Fe^II₄L₄ Cage and Encapsulated Cargo

Supramolecular capsules can now be prepared with a wide range of volumes and geometries. Consequently, many of these capsules encapsulate guests selectively by size and shape, an important design feature for separations. To successfully address practical separations problems, however, a guest cannot simply be isolated from its environment; the molecular cargo must be removed to a separate physical space. Here we demonstrate that an Fe^II₄L₄ coordination cage <b>1</b> can transport a cargo spontaneously and quantitatively from water across a phase boundary and into an ionic liquid layer. This process is triggered by an anion exchange from <b>1</b>[SO₄] to <b>1</b>[BF₄]. Upon undergoing a second anion exchange, from <b>1</b>[BF₄] to <b>1</b>[SO₄], the cage, together with its encapsulated guest, can then be manipulated back into a water layer. Furthermore, we demonstrate the selective phase transfer of cationic cages to separate a mixture of two cages and their respective cargoes. We envisage that supramolecular technologies based upon these concepts could ultimately be employed to carry out separations of industrially relevant compounds

Separation and Selective Formation of Fullerene Adducts within an M^II₈L₆ Cage

The self-assembly of 4-fold-symmetric porphyrins with FeII or ZnII gave a new cubic MII8L6 cage framework with electron-deficient walls. This cage bound C60-indene or C60-anthracene bisadducts selectively, whereas unfunctionalized fullerenes and monoadducts were not encapsulated. The FeII8L6 cage also enabled the reaction of C60 and anthracene to yield the bisadducts selectively under conditions where no reaction was observed in the absence of the cage. These findings have relevance in the context of polymer solar cells, where C60 bisadducts have found use as electron acceptors, because these adducts currently require laborious and time-consuming syntheses and purification

Metal and Organic Templates Together Control the Size of Covalent Macrocycles and Cages

Covalent macrocycles and three-dimensional cages were prepared by the self-assembly of di- or tritopic anilines and 2,6-diformylpyridine subcomponents around palladium­(II) templates. The resulting 2,6-bis­(imino)­pyridyl-PdII motif contains a tridentate ligand, leaving a free coordination site on the PdII centers, which points inward. The binding of ligands to the free coordination sites in these assemblies was found to alter the product stability, and multitopic ligands could be used to control product size. Multitopic ligands also bridged metallomacrocycles to form higher-order supramolecular assemblies, which were characterized via NMR spectroscopy, mass spectrometry, and X-ray crystallography. An efficient method was developed to reduce the imine bonds to secondary amines, leading to fully organic covalent macrocycles and cages that were inaccessible through other means

Metal and Organic Templates Together Control the Size of Covalent Macrocycles and Cages

Covalent macrocycles and three-dimensional cages were prepared by the self-assembly of di- or tritopic anilines and 2,6-diformylpyridine subcomponents around palladium­(II) templates. The resulting 2,6-bis­(imino)­pyridyl-PdII motif contains a tridentate ligand, leaving a free coordination site on the PdII centers, which points inward. The binding of ligands to the free coordination sites in these assemblies was found to alter the product stability, and multitopic ligands could be used to control product size. Multitopic ligands also bridged metallomacrocycles to form higher-order supramolecular assemblies, which were characterized via NMR spectroscopy, mass spectrometry, and X-ray crystallography. An efficient method was developed to reduce the imine bonds to secondary amines, leading to fully organic covalent macrocycles and cages that were inaccessible through other means

Metal and Organic Templates Together Control the Size of Covalent Macrocycles and Cages

Covalent macrocycles and three-dimensional cages were prepared by the self-assembly of di- or tritopic anilines and 2,6-diformylpyridine subcomponents around palladium­(II) templates. The resulting 2,6-bis­(imino)­pyridyl-PdII motif contains a tridentate ligand, leaving a free coordination site on the PdII centers, which points inward. The binding of ligands to the free coordination sites in these assemblies was found to alter the product stability, and multitopic ligands could be used to control product size. Multitopic ligands also bridged metallomacrocycles to form higher-order supramolecular assemblies, which were characterized via NMR spectroscopy, mass spectrometry, and X-ray crystallography. An efficient method was developed to reduce the imine bonds to secondary amines, leading to fully organic covalent macrocycles and cages that were inaccessible through other means