<div><p>The life-sustaining reduction of N<sub>2</sub> to NH<sub>3</sub> is thermoneutral yet kinetically challenged by high energy intermediates such as N<sub>2</sub>H<sub>2</sub>. Exploring intramolecular H-bonding as a potential strategy to stabilize diazene intermediates, we employ a series of [<sup>xHet</sup>TpCu]<sub>2</sub>(𝜇-N<sub>2</sub>H<sub>2</sub>) complexes that exhibit H-bonding between pendant aromatic N-heterocycles (<sup>X</sup>Het) such as pyridine and a bridging <i>trans</i>-N<sub>2</sub>H<sub>2</sub> ligand at copper(I) centers. X-ray crystallography and IR spectroscopy clearly reveal H-bonding in [<sup>pyMe</sup>TpCu]<sub>2</sub>(𝜇-N<sub>2</sub>H<sub>2</sub>) while low temperature <sup>1</sup>H NMR studies coupled with DFT analysis reveals a dynamic equilibrium between two closely related, symmetric H-bonded structural motifs. Importantly, the <sup>x</sup>Het pendant negligibly influences the electronic structure of <sup>xHet</sup>TpCu<sup>I</sup> centers in <sup>xHet</sup>TpCu(CNAr<sup>2,6-Me2</sup>) complexes that lack H-bonding as judged by nearly indistinguishable n(CN) frequencies (2113 - 2117 cm<sup>-1</sup>). Nonetheless, H-bonding in the corresponding [<sup>xHet</sup>TpCu]<sub>2</sub>(𝜇-N<sub>2</sub>H<sub>2</sub>) complexes results in marked changes in n(NN) (1398 - 1419 cm<sup>-1</sup>) revealed through rRaman studies. Due to the closely matched N-H BDE’s of N<sub>2</sub>H<sub>2</sub> and the neutral pyH<sup>0</sup> cation radical, the aromatic N-heterocylic pendants may encourage partial H-atom transfer (HAT) from N<sub>2</sub>H<sub>2</sub> to <sup>x</sup>Het through redox non-innocent H-bonding in [<sup>xHet</sup>TpCu]<sub>2</sub>(𝜇-N<sub>2</sub>H<sub>2</sub>). DFT studies reveal modest thermodynamic barriers for concerted transfer of both H-atoms of coordinated N<sub>2</sub>H<sub>2</sub> to the <sup>x</sup>Het pendants to generate tautomeric [<sup>xHetH</sup>TpCu]<sub>2</sub>(𝜇-N<sub>2</sub>) complexes, identifying concerted dual HAT as a thermodynamically favorable pathway for N<sub>2</sub> / N<sub>2</sub>H<sub>2</sub> interconversion.</p></div>
Synthesis [1-(4-acetylphenyl)-3-(2-methylphenyl)]triazene: NMR, Vibrational, X-ray Crystallography Characterization with HF/DFT Studies