Evaluating the Effectiveness of Tethered Bis(urazolyl) Diradicals as Molecular Building Blocks for Dynamic Covalent Chemistry

• Type of Material: Article
• Authors: Gary W Breton, Berry College, Mount Berry; Kenneth L Martin, Berry College, Mount Berry; James Alexander Bowron, Berry College, Mount Berry; John Bacsa, Emory University
• Language: English
• Date: 2023-07-07
• Publisher: American Chemical Society
• Publication Version: Final Published Version
• Copyright Statement: © 2023 The Authors.
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1021/acs.joc.3c00732
• Title of Journal or Parent Work: Journal of Organic Chemistry
• Volume: 88
• Issue: 13
• Start Page: 9157
• End Page: 9166
• Grant/Funding Information: G.W.B. and K.L.M. thank Berry College for providing generous financial support for this project
• Keywords: Dynamic covalent chemistry; Bis(urazolyl) Diradical; urazolyl radicals; diurazole
• Research Categories: Chemistry, Organic; Engineering, Materials Science

Abstract

Dynamic covalent chemistry (DCvC) is a powerful means by which to rapidly prepare complex structures from simple molecular building blocks. Effective DCvC behavior is contingent upon the reversibility of covalent bond formation. Stabilized radical species, therefore, have been effectively used for these applications. In earlier work we demonstrated that properly substituted 1-arylurazolyl radicals showed promise as oxygen-insensitive heterocyclic N-centered radicals with a propensity for reversible bond formation. In this work we have synthesized several tethered bis(urazolyl) diradicals, varying by the type and length of connectivity between the urazole rings, and tested them for DCvC behavior. We have found that when the two aryl rings to which the urazolyl radical sites are attached are tethered by a chain of five or more carbons, equilibrium mixtures of monomeric and dimeric species are formed by N-N bond formation between two radical sites. DCvC behavior is observed that is sensitive to changes in temperature, concentration, and (to a lesser extent) solvent. In general, the dimer species is favored at lower temperatures and higher concentrations.