Aerobic Oxidative Homo- and Cross-Coupling of Amines Catalyzed by Phenazine Radical Cations

Phenazine
radical cations (PhRCs) were used for the first time
as efficient metal-free catalysts for the oxidative homo- and cross-coupling
of a variety of different amines. A series of functional PhRCs were
prepared, characterized with X-ray diffraction, and their radical
character was investigated with DFT calculations. They were tested
as catalysts under neat conditions with low oxygen pressure to prepare
homo- and cross-coupled aliphatic and aromatic imines in high yields.
Although all synthesized phenazines were catalytically active, the
highest reaction rates and the best selectivity were achieved using
the 5,10-dihydro-5,10-dimethylphenazine radical cation. By means of
fluorescence, UV–vis and EPR spectroscopy, a mechanism of the
oxidative amine coupling, catalyzed by PhRCs, is proposed.