title: 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-1. 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.
authors.affiliation: Department of Chemistry, Indiana University , 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States.
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Benson
authors.affiliation: Department of Chemistry, Indiana University , 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States.
authors.forename: Elisabeth M
authors.initials: EM
authors.lastname: Fatila
authors.affiliation: The Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
authors.forename: Semin
authors.initials: S
authors.lastname: Lee
authors.affiliation: Department of Chemistry, Indiana University , 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States.
authors.forename: Matthew G
authors.initials: MG
authors.lastname: Marzo
authors.affiliation: Department of Chemistry, Indiana University , 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States.
authors.forename: Maren
authors.initials: M
authors.lastname: Pink
authors.affiliation: Department of Chemistry, University of Guelph , Guelph, Ontario N1G 2W1, Canada.
authors.forename: Michelle B
authors.initials: MB
authors.lastname: Mills
authors.affiliation: Department of Chemistry, University of Guelph , Guelph, Ontario N1G 2W1, Canada.
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Preuss
authors.affiliation: Department of Chemistry, Indiana University , 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States.
authors.forename: Amar H
authors.initials: AH
authors.lastname: Flood