Pathway-Dependent Post-assembly Modification of an Anthracene-Edged M^II₄L₆ Tetrahedron

FeII4L6 tetrahedral cage 1 undergoes post-assembly modification (PAM) via a Diels–Alder cycloaddition of the anthracene panels of the cage with tetracyanoethylene (TCNE). The modified cage 2 possesses an enclosed cavity suitable for encapsulation of the fullerene C60, whereas original cage 1 forms a unique covalent adduct through a Diels–Alder cycloaddition of three of its anthracene ligands with C60. This adduct undergoes further PAM via reaction of the remaining three ligands with TCNE, enabling the isolation of two distinct products depending on the order of addition of C60 and TCNE. Modified cage 2 was also able to bind an anionic guest, [Co­(C2B9H11)2]−, which was not encapsulated by the original cage, demonstrating the potential of PAM for tuning the binding properties of supramolecular hosts

Pathway-Dependent Post-assembly Modification of an Anthracene-Edged M^II₄L₆ Tetrahedron

FeII4L6 tetrahedral cage 1 undergoes post-assembly modification (PAM) via a Diels–Alder cycloaddition of the anthracene panels of the cage with tetracyanoethylene (TCNE). The modified cage 2 possesses an enclosed cavity suitable for encapsulation of the fullerene C60, whereas original cage 1 forms a unique covalent adduct through a Diels–Alder cycloaddition of three of its anthracene ligands with C60. This adduct undergoes further PAM via reaction of the remaining three ligands with TCNE, enabling the isolation of two distinct products depending on the order of addition of C60 and TCNE. Modified cage 2 was also able to bind an anionic guest, [Co­(C2B9H11)2]−, which was not encapsulated by the original cage, demonstrating the potential of PAM for tuning the binding properties of supramolecular hosts

Pathway-Dependent Post-assembly Modification of an Anthracene-Edged M^II₄L₆ Tetrahedron

Fe^II₄L₆ tetrahedral cage <b>1</b> undergoes post-assembly modification (PAM) via a Diels–Alder cycloaddition of the anthracene panels of the cage with tetracyanoethylene (TCNE). The modified cage <b>2</b> possesses an enclosed cavity suitable for encapsulation of the fullerene C₆₀, whereas original cage <b>1</b> forms a unique covalent adduct through a Diels–Alder cycloaddition of three of its anthracene ligands with C₆₀. This adduct undergoes further PAM via reaction of the remaining three ligands with TCNE, enabling the isolation of two distinct products depending on the order of addition of C₆₀ and TCNE. Modified cage <b>2</b> was also able to bind an anionic guest, [Co­(C₂B₉H₁₁)₂]⁻, which was not encapsulated by the original cage, demonstrating the potential of PAM for tuning the binding properties of supramolecular hosts

Covalent Post-assembly Modification Triggers Multiple Structural Transformations of a Tetrazine-Edged Fe₄L₆ Tetrahedron

Covalent post-assembly modification (PAM) reactions are useful synthetic tools for functionalizing and stabilizing self-assembled metal–organic complexes. Recently, PAM reactions have also been explored as stimuli for triggering supramolecular structural transformations. Herein we demonstrate the use of inverse electron-demand Diels–Alder (IEDDA) PAM reactions to induce supramolecular structural transformations starting from a tetrazine-edged Fe^II₄L₆ tetrahedral precursor. Following PAM, this tetrahedron rearranged to form three different architectures depending on the addition of other stimuli: an electron-rich aniline or a templating anion. By tracing the stimulus-response relationships within the system, we deciphered a network of transformations that mapped different combinations of stimuli onto specific transformation products. Given the many functions being developed for self-assembled three-dimensional architectures, this newly established ability to control the interconversion between structures using combinations of different stimulus types may serve as the basis for switching the functions expressed within a system

Covalent Post-assembly Modification Triggers Multiple Structural Transformations of a Tetrazine-Edged Fe₄L₆ Tetrahedron

Covalent post-assembly modification (PAM) reactions are useful synthetic tools for functionalizing and stabilizing self-assembled metal–organic complexes. Recently, PAM reactions have also been explored as stimuli for triggering supramolecular structural transformations. Herein we demonstrate the use of inverse electron-demand Diels–Alder (IEDDA) PAM reactions to induce supramolecular structural transformations starting from a tetrazine-edged Fe^II₄L₆ tetrahedral precursor. Following PAM, this tetrahedron rearranged to form three different architectures depending on the addition of other stimuli: an electron-rich aniline or a templating anion. By tracing the stimulus-response relationships within the system, we deciphered a network of transformations that mapped different combinations of stimuli onto specific transformation products. Given the many functions being developed for self-assembled three-dimensional architectures, this newly established ability to control the interconversion between structures using combinations of different stimulus types may serve as the basis for switching the functions expressed within a system

Modular Isoquinoline Synthesis Using Catalytic Enolate Arylation and <i>in Situ</i> Functionalization

A methyl ketone, an aryl bromide, an electrophile, and ammonium chloride were combined in a four-component, three-step, and one-pot coupling procedure to furnish substituted isoquinolines in overall yields of up to 80%. This protocol utilizes the palladium catalyzed α-arylation reaction of an enolate, followed by <i>in situ</i> trapping with an electrophile, and aromatization with ammonium chloride. <i>tert</i>-Butyl cyanoacetate participated in a similar protocol; after functionalization and decarboxylation, 3-amino-4-alkyl isoquinolines were prepared in high yield

Post-assembly Modification of Tetrazine-Edged Fe^II₄L₆ Tetrahedra

Post-assembly modification (PAM) is a powerful tool for the modular functionalization of self-assembled structures. We report a new family of tetrazine-edged Fe^II₄L₆ tetrahedral cages, prepared using different aniline subcomponents, which undergo rapid and efficient PAM by inverse electron-demand Diels–Alder (IEDDA) reactions. Remarkably, the electron-donating or -withdrawing ability of the <i>para</i>-substituent on the aniline moiety influences the IEDDA reactivity of the tetrazine ring 11 bonds away. This effect manifests as a linear free energy relationship, quantified using the Hammett equation, between σ_<i>para</i> and the rate of the IEDDA reaction. The rate of PAM can thus be adjusted by varying the aniline subcomponent

Post-assembly Modification of Tetrazine-Edged Fe^II₄L₆ Tetrahedra

Post-assembly modification (PAM) is a powerful tool for the modular functionalization of self-assembled structures. We report a new family of tetrazine-edged Fe^II₄L₆ tetrahedral cages, prepared using different aniline subcomponents, which undergo rapid and efficient PAM by inverse electron-demand Diels–Alder (IEDDA) reactions. Remarkably, the electron-donating or -withdrawing ability of the <i>para</i>-substituent on the aniline moiety influences the IEDDA reactivity of the tetrazine ring 11 bonds away. This effect manifests as a linear free energy relationship, quantified using the Hammett equation, between σ_<i>para</i> and the rate of the IEDDA reaction. The rate of PAM can thus be adjusted by varying the aniline subcomponent

Perfluorinated Ligands Induce Meridional Metal Stereochemistry to Generate M₈L₁₂, M₁₀L₁₅, and M₁₂L₁₈ Prisms

Meridional (<i>mer</i>) coordination promotes the generation of larger and lower-symmetry prismatic metallosupramolecular structures, in contrast with the facial (<i>fac</i>) coordination common to smaller and higher-symmetry polyhedra. Here, we describe a general route to the selective formation of large metallosupramolecular prisms that contain exclusively <i>mer</i>-coordinated metal vertices. The use of 2-formylpyridine subcomponents that contain perfluorophenylene substituents at their 5-positions resulted in stereoselective formation of the iron­(II) complexes from these subcomponents. Only <i>mer</i> vertices were observed, as opposed to the statistical <i>fac</i>/<i>mer</i> mixture otherwise generated. This <i>mer</i>-selective self-assembly could be used to prepare tetragonal (M₈L₁₂), pentagonal (M₁₀L₁₅), and hexagonal (M₁₂L₁₈) prisms by taking advantage of the subtle selectivities imposed by the different anilines and counterions employed. The equilibrium between the tetragonal and pentagonal prism followed a linear free-energy relationship, with the ratio between structures correlating with the Hammett σ_p⁺ parameter of the incorporated aniline. The contrasting preferences of the fluorinated and nonfluorinated ligands to generate prisms and tetrahedra, respectively, were quantified energetically, with the destabilization increasing linearly for each “incorrect ligand” incorporated into either structure

Perfluorinated Ligands Induce Meridional Metal Stereochemistry to Generate M₈L₁₂, M₁₀L₁₅, and M₁₂L₁₈ Prisms

Meridional (<i>mer</i>) coordination promotes the generation of larger and lower-symmetry prismatic metallosupramolecular structures, in contrast with the facial (<i>fac</i>) coordination common to smaller and higher-symmetry polyhedra. Here, we describe a general route to the selective formation of large metallosupramolecular prisms that contain exclusively <i>mer</i>-coordinated metal vertices. The use of 2-formylpyridine subcomponents that contain perfluorophenylene substituents at their 5-positions resulted in stereoselective formation of the iron­(II) complexes from these subcomponents. Only <i>mer</i> vertices were observed, as opposed to the statistical <i>fac</i>/<i>mer</i> mixture otherwise generated. This <i>mer</i>-selective self-assembly could be used to prepare tetragonal (M₈L₁₂), pentagonal (M₁₀L₁₅), and hexagonal (M₁₂L₁₈) prisms by taking advantage of the subtle selectivities imposed by the different anilines and counterions employed. The equilibrium between the tetragonal and pentagonal prism followed a linear free-energy relationship, with the ratio between structures correlating with the Hammett σ_p⁺ parameter of the incorporated aniline. The contrasting preferences of the fluorinated and nonfluorinated ligands to generate prisms and tetrahedra, respectively, were quantified energetically, with the destabilization increasing linearly for each “incorrect ligand” incorporated into either structure