Regiospecific C-H bond activation: reversible H/D exchange promoted by CuI complexes with triazamacrocyclic ligands.

Selective C H bond activation by metals under mild conditions is a major subject of research targeting the final functionalization of organic substrates. The characterization of the usually unstable intermediates of the C H bond activation prior to functionalization is crucial for the mechanistic comprehension of the reaction. Different mechanisms, such as oxidative addition, electrophilic metalation, or agostic bonding, have been proposed in extensive work published on the C H activation of aromatic or aliphatic compounds catalyzed by secondand third-row transition metals (TMs; i.e., Pd and Pt, and Ru, Rh, and Ir). However, much less work is found with first row TMs (i.e., Ni, Co, Fe, and Mn) and even less for the biologically relevant metal copper. We have already reported an example of intramolecular aromatic C H activation by Cu in a disproportionation reaction and characterized an aryl copper(iii) species as a reaction product. Herein, we report on the reactivity of five triazamacrocyclic ligands with Cu and the study of these reactions by H and H NMR spectroscopy, ESI mass spectrometry, and density functional computations. The reaction of the ligands H-H33m, pMe-H33m, and pNO2-H33m (Scheme 1) with one equivalent of [Cu (CH3CN)4]PF6 in CD3CN under N2 afforded the correspond-