Catalytic N-N oxidative coupling reactions can yield useful synthetic products as well as release energy stored in N-H bonds, e.g. in an ammonia fuel cell. Mechanistic analysis of electrocatalytic and stoichiometric reactions shows that the Cu+2/Cu+1 redox couple is capable of mediating several N-N coupling reactions. One such class of N-H substrates is imines, which are interesting as NH3 surrogates. The resulting azine N-N coupling product is in turn a masked hydrazine equivalent. An electrocatalytic process for this reaction has been realized that gives insight into previously reported aerobic reactions. Thermodynamic analysis of this reaction in turn gives insights into strategies to achieve low-overpotential NH3 oxidation. Specifically, the imine N-H bond is activated compared to that of NH3. Imine substituents have a minimal effect on the imine N-H bond strength, presumably due to their divergent influence on the requisite electron and proton transfers. Coordination of the imine modulates the reduction potential of the copper to be lower, but still high enough to drive the reaction.

Transition metal-mediated N-N coupling reactions and implications for organocatalytic ammonia oxidation at low overpotential

ACS Spring Meeting 2021

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