Uncovering Redox Non-innocent Hydrogen-Bonding in Cu(I)-Diazene Complexes.

The life-sustaining reduction of N to NH is thermoneutral yet kinetically challenged by high-energy intermediates such as NH. Exploring intramolecular H-bonding as a potential strategy to stabilize diazene intermediates, we employ a series of [TpCu](μ-NH) complexes that exhibit H-bonding between pendant aromatic N-heterocycles (Het) such as pyridine and a bridging -NH ligand at copper(I) centers. X-ray crystallography and IR spectroscopy clearly reveal H-bonding in [TpCu](μ-NH) while low-temperature H NMR studies coupled with DFT analysis reveals a dynamic equilibrium between two closely related, symmetric H-bonded structural motifs.