Identifying the Rate-Limiting Elementary Steps of Nitrogen Fixation with Single-Site Fe Model Complexes

Abstract

on single-site iron complexes with EPPP tetradentate ligands (E = B, Si). We examine all possible mechanisms and identify the dominant pathways and the critical elementary steps that can be rate-determining in the catalytic cycle of nitrogen fixation. We find that the catalytic mechanism depends on the applied ligand and that the distal pathway observed with E = B is the most favorable route regarding the catalytic performance. Our calculations also reveal the lack of thermodynamic driving force in the last steps of the catalytic cycle that can be responsible for the low catalytic activity of the studied biomimetic catalysts. Our results can serve as a starting point for the rational design of biomimetic complexes, which should focus on establishing a steadily decreasing Gibbs free energy profile, as suggested by the Sabatier principle.