Extreme Stabilization and Redox Switching of Organic Anions and Radical Anions by Large-Cavity, CH Hydrogen-Bonding Cyanostar Macrocycles

Abstract

Encapsulation of unstable guests is a powerful way to enhance their stability. The lifetimes of organic anions and their radicals produced by reduction are typically short on account of reactivity with oxygen while their larger sizes preclude use of traditional anion receptors. Here we demonstrate the encapsulation and noncovalent stabilization of organic radical anions by C-H hydrogen bonding in π-stacked pairs of cyanostar macrocycles having large cavities. Using electrogenerated tetrazine radical anions, we observe significant extension of their lifetimes, facile molecular switching, and extremely large stabilization energies. The guests form threaded pseudorotaxanes. Complexation extends the radical lifetimes from 2 h to over 20 days without altering its electronic structure. Electrochemical studies show tetrazines thread inside a pair of cyanostar macrocycles following voltage-driven reduction (+e) of the tetrazine at -1.00 V and that the complex disassembles after reoxidation (-e) at -0.05 V. This reoxidation is shifted 830 mV relative to the free tetrazine radical indicating it is stabilized by an unexpectedly large -80 kJ mol. The stabilization is general as shown using a dithiadiazolyl anion. This finding opens up a new approach to capturing and studying unstable anions and a radical anions when encapsulated by size-complementary anion receptors.

High‐Fidelity Multistate Switching with Anion–Anion and Acid–Anion Dimers of Organophosphates in Cyanostar Complexes

“…Phosphate switching is possible with acid–base addition yet opportunities to investigate this functionality have emerged only recently with the creation of receptors large enough for this anion. Complementary examples include Texas‐sized boxes with large pH‐switchable terephthalates, and cyanostar macrocycles with large redox‐switchable tetrazines . We present the first investigation of switchable phosphate complexes involving cyanostars ( CS , Figure ), their binding fidelity, and the discovery of a novel acid–anion heterodimer along one route in the switching pathway.…”

“…Second, local sterics may also negatively impact the 2:1 complex. The hydrogen atoms on the naphthyl rings likely prevent the phosphate moiety of NpHPO 4 − from being located in the exact center between the two macrocycles as is typical in sandwich complexes . Both factors turn off the stability of the competing complexes to enhance the fidelity of the 2:2 complex.…”

π‐Extended Dihydrophenazines with Three‐State NIR Electrochromism Involving Large Conformational Changes

“…[1] Among these molecules, redox-active compounds have received much attentiond ue to potential applications in nano-sized electronicd evices. [2][3][4] In order to read the stored information recorded by electrochemical stimuli, other physicalo utputs such as optical changes are required. Accordingly,e lectrochromic dyes have been developedf or this purpose.…”

Bridge‐Clamp Bis(tetrazine)s with [N]8 π‐Stacking Interactions and Azido‐s‐Aryl Tetrazines: Two Classes of Doubly Clickable Tetrazines

“…[1][2][3][4][5][6][7][8] Notably,t he preparation of tailored s-tetrazines allows their implementation, by pyridazine reductive formation, for bioconjugate chemistry (Tz click chemistry). [9][10][11][12][13][14][15] This field has experienced agrowing number applications in supramolecular chemistry and bioorthogonal chemistry. [16] Accordingly,t he development of synthetic routes to more diverse tetrazine structures has become very useful as it diversifies current applications and facilitates the emergence of new ones.…”

“…We further envisioned that the introduction of as econd clickable functionality on s-tetrazines,d ifferent and complementary to the tetrazine core used in the iEDDAc ycloaddition, would be highly valuable for the development of synthetic routes to more diverse tetrazine structures. [5,[9][10][11][12][13][14][15][16]31] In particular, the introduction of the versatile azide function would be advantageous for stepwise introduction of various…”