Aminations of Aryl Halides Using Nitroaromatics as Coupling Partners: Overcoming the Hydrodehalogenation Pathway under a Hydrogen Atmosphere in Water

While overcoming hydrodehalogenation in a reductive environment, a catalytic aqueous micellar technology has been developed for the C-N cross-coupling of nitroarenes with aryl halides. The bimetallic palladium-copper (Pd-Cu) nanocatalyst configuration in aqueous micelles selectively facilitates the highly selective amination pathway, possibly through in situ formation of Cu-hydride species as supported by the nuclear magnetic resonance (NMR) spectroscopy. These species prevent Pd-hydride-mediated hydrodehalogenation even under a molecular hydrogen atmosphere. The nanocatalyst has been thoroughly characterized by using various spectroscopic and imaging tools, including P-31 and H-1 NMR, X-ray absorption spectroscopy (XAS), and high-resolution transmission electron microscopy. The oxidation states of Cu and Pd needed for the desired selectivity have been verified using X-ray photoelectron spectroscopy, while metal-metal and metal-ligand interactions have been characterized by XAS. Control experiments have been performed to determine the significance of each constituent of the nanocatalyst on the desired reaction pathway. As revealed by control mass spectrometry, the reaction pathway does not involve azo- or nitroso-type intermediates. The catalytic methodology can be applied to numerous substrates with a broad functional and protecting group tolerance.