Are Redox‐Active Centers Bridged by Saturated Flexible Linkers Systematically Electrochemically Independent?

• Published in: Angewandte Chemie International Edition Vol. 63; no. 31; pp. e202406299 - n/a
• Main Authors: Vaněčková, Eva, Dahmane, Mustapha, Forté, Jérémy, Cherraben, Sawsen, Pham, Xuan‐Qui, Sokolová, Romana, Brémond, Éric, Hromadová, Magdaléna, Lainé, Philippe P.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 29.07.2024; Wiley-VCH Verlag
• Edition: International ed. in English
• Subjects: Cations; Chemical bonds; Chemical Sciences; computational chemistry; Covalent bonds; Current carriers; Electrochemistry; Electron spin; Electron transfer; Injection; London dispersion forces; molecular electrochemistry; Molecular orbitals; Potential energy; Pyridinium; Radicals; Redox properties; structure–activity relationship; London dispersion forces; Structure-activity relationship; Pyridinium; Computational Chemistry; molecular electrochemistry; computational chemistry; computational chemistry London dispersion forces molecular electrochemistry pyridinium structure-activity relationship; structure-activity relationship; pyridinium
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.202406299

The extent to which electrophores covalently bridged by a saturated linker are electrochemically independent was investigated considering the charge/spin duality of the electron and functionality of the electrophore as a spin carrier upon reduction. By combining computational modeling with electrochemical experiments, we investigated the mechanism by which tethered electrophores react together within 4,4′‐oligo[n]methylene‐bipyridinium assemblies (with n=2 to 5). We show that native dicationic electrophores (redox state Z=+2) are folded prior to electron injection into the system, allowing the emergence of supra‐molecular orbitals (supra‐MOs) likely to support the process of the reductive σ bond formation giving cyclomers. Indeed, for Z=+2, London Dispersion (LD) forces contribute to flatten the potential energy surface such that all‐trans and folded conformers are approximately isoenergetic. Then, upon one‐electron injection, for radical cations (Z=+1), LD forces significantly stabilize the folded conformers, except for the ethylene derivative deprived of supra‐MOs. For radical cations equipped with supra‐MOs, the unpaired electron is delocalized over both heterocycles through space. Cyclomer completion (Z=0) upon the second electron transfer occurs according to the inversion of redox potentials. This mechanism explains why intramolecular reactivity is favored and why pyridinium electrophores are not independent. Electrochemistry textbooks teach that the behavior of charged redox centers bound by saturated linkers is essentially governed by electrostatics. We show that for short alkanes and pyridiniums, as Coulombic and through‐bond interactions become ineffective, reductive cyclomer formation is governed by London dispersion and σ‐type overlap of 2pz atomic orbitals of the Cγ atoms of electrophoric ends rather than by electron spin‐spin interaction.