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The Divergent Dimerization Behavior of N‐Substituted Dicyanomethyl Radicals: Dynamically Stabilized versus Stable Radicals
Author(s) -
Okino Kohei,
Hira Shota,
Inoue Yuki,
Sakamaki Daisuke,
Seki Shu
Publication year - 2017
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201710354
Subject(s) - radical , chemistry , photochemistry , organic chemistry
Herein, we demonstrate that the dimerization behavior of amine‐substituted dicyanomethyl radicals can be switched from σ‐ to π‐dimerization simply by varying the electron‐donating substituents. For dicyanomethyl radicals with a 4,4′‐ditolylamine ( DT . ) or a phenothiazine ( PT . ) substituent, the monomeric radical form and the corresponding dimer connected by a reversible C−C bond (σ‐dimer) are in equilibrium in solution. On the other hand, the radical with the julolidine skeleton ( JD . ) does not undergo σ‐dimerization and was isolated as a stable radical in spite of the absence of bulky protecting groups. X‐ray single‐crystal analysis revealed that JD . forms the π‐dimer in the crystalline state, and variable‐temperature spectroscopy showed that JD . is in equilibrium with the π‐dimer in toluene solution. DFT calculations point to the importance of electrostatic interactions as a driving force for the π‐dimerization of JD . because of its polarized structure.