Aza-m-Xylylene Diradical with Increased Steric Protection of the Aminyl Radicals

Aminyl diradical 3, a derivative of aza-m-xylylene, is expected to be more stable than diradical 1, due to increased steric protection of the radicals by additional methyl groups in the pendant group. Here we report synthesis and characterization of diradical 3. The structure of diamine precursor 6 is characterized by high-field (1)H NMR spectroscopy in which the two diastereomers (meso and ± pair) are distinguishable. In addition, correlation between the DFT-calculated and experimental (1)H and (13)C NMR chemical shifts provides evidence in support of the diamine structure. Electrochemistry of the diamine is carried out to explore redox properties and stability of the corresponding aminium diradical dications. The ground state and ΔEST for 3 are established by statistical analyses of mean χT determined by EPR spectroscopy. Decay kinetics of aminyl diradical 3 indicates that the decay of 3 is faster than that of 1, possibly due to intramolecular hydrogen atom abstraction from benzylic methyl groups in 3, followed by intermolecular hydrogen atom abstraction from 2-MeTHF solvent.