Theoretical and Experimental Studies: Cu(I)/Cu(II) Catalytic Cycle in CuI/Oxalamide-Promoted C–N Bond Formation

In
modern Ullmann–Goldberg reactions, cheaper aryl chlorides are
poor substrates. Recently, attention has been paid to facile CuI/oxalamide-promoted
arylation of heteroatoms (N, O, and S) using cheaper aryl chlorides.
However, the mechanism of the reaction and the role of oxalamides
have not yet been investigated. In the present investigation, theoretical
(density functional theory) and supporting in situ 1H NMR
spectroscopy, UV–vis spectroscopy, Fourier transform infrared
spectroscopy, and cyclic voltammetry studies have been performed to
provide insight into the various aspects of the mechanism. Five different
possible pathways have been investigated. [LCu­(NHNu)] is the active
copper catalytic species, in which L (oxalamide) coordinates Cu­(I)
through both −CO groups. Our studies show that the
reaction follows an outer-sphere single-electron transfer pathway.
Moreover, these studies also address the reason for the deactivation
of a copper catalyst.