Relating N–H Bond Strengths to the Overpotential for Catalytic Nitrogen Fixation
Matthew J. Chalkley, Jonas C. Peters
Abstract
Nitrogen (N 2 ) fixation to produce bio‐available ammonia (NH 3 ) is essential to all life but is a challenging transformation to catalyze owing to the chemical inertness of N 2 . Transition metals can, however, bind N 2 and activate it for functionalization. Significant opportunities remain in developing robust and efficient transition metal catalysts for the N 2 reduction reaction (N 2 RR). One opportunity to target in catalyst design concerns the stabilization of transition metal diazenido species (M‐NNH) that result from the first N 2 functionalization step. Well‐characterized M‐NNH species remain very rare, likely a consequence of their low N–H bond dissociation free energies (BDFEs). In this essay, we discuss the relationship between the BDFE N–H of a given M‐NNH species to the observed overpotential and selectivity for N 2 RR catalysis with that catalyst system. We note that developing strategies to either increase the N–H BDFEs of M‐NNH species, or to avoid M‐NNH intermediates altogether, are potential routes to improved N 2 RR efficiency.