A series of new pyridyl‐ or 2‐pyridyloxide‐containing donor‐acceptor diarylnitroxides was obtained and characterized; high stability of the ortho‐2‐pyridyl‐containing diarylnitroxides was determined by kinetic measurements (τ1/2=1733 h in benzene). Comparative voltammetric study of new nitroxides and their analog in which the Py replaces the Ph group revealed both through‐bond and through‐space stabilization of the NO redox states with the pyridyl/ 2‐pyridyloxide moiety, providing reversibility of both oxidation and reduction processes. Adaptive conformational behavior of new pyridyl/pyridyloxide containing nitroxides upon one‐electron oxidation and reduction was confirmed by DFT calculations. Stimuli‐responsive conformational changes allow switching on/off dispersion and electrostatic interactions within the molecule and increase stability of the redox states. Spectroelectrochemical measurements provided experimental evidence for reversibility of the through‐space stabilization of the oxidized state of the nitroxides with the neighboring pyridine lone pair.
New pyridyl-containing diarylamines were obtained via Cu-assisted reductive amination of the ortho-2-pyridylarylboronic acids. Comparative analysis of the spectral and electrochemical data obtained for new diarylamines and their pyridyl-free counterparts revealed the intramolecular H-bond (IMHB) formation which significantly influences the properties of the amino group. The electron density at the N atom of the amino group is increased due to partial weakening of the N–H bond, although the BDE and activation energy for the H-atom abstraction is increased due to the chelating effect of two N atoms. The ortho-pyridyl-containing diarylamines are more prone to be oxidized as compared to their pyridyl-free counterparts; the shift in the oxidation potential values correlates with the strength of the intramolecular H-bonding which can be tuned by inserting substituents in the pyridyl or phenyl rings. The IMHB is reserved even in polar solvents having a significant H-acceptor ability (such as DMSO) but can be destroyed in methanol, testifying in favor of the dynamic nature of the H-bonding.
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