Efficient Aminations of Aryl Halides by a Cu(II) Catalyst

Abstract

Aminations of aryl halides catalyzed by copper complexes with ancillary ligands have become valuable for the formation of anilines, and the mechanisms for these reactions have been shown to occur by a Cu(I)/(III) cycle. We show that the coupling of aryl and heteroaryl bromides with a range of nitrogen nucleophiles, including hydrazine hydrate and complex amines, occurs with copper and a simple dianionic, dimethylpyrrole-based oxalohydrazido ligand by a cycle in which Cu(II) complexes of this ligand are the resting state and an active, low-valent, catalytic intermediate. These couplings involving Cu(II) occur in many cases with just 0.1–0.2 mol % catalyst and take place under air, due to the absence of Cu(I) that is less stable to disproportionation and to air. Kinetic profiles and EPR spectroscopy of reactions initiated with Cu(I) and Cu(II) precursors provide strong evidence that both systems react through an active Cu(II) complex, thereby indicating that a recently uncovered mechanistic manifold for copper-catalyzed couplings of phenoxides with oxalamide ligands is also followed for the coupling of nitrogen nucleophiles catalyzed by copper complexes of oxalohydrazido ligands.