Testing the Push–Pull Hypothesis: Lewis Acid Augmented N₂ Activation at Iron

Abstract

We present a systematic investigation of the structural and electronic changes that occur in an Fe(0)-N₂ unit (Fe(depe)₂(N₂); depe = 1,2-bis(diethylphosphino)ethane) upon the addition of exogenous Lewis acids. Addition of neutral boranes, alkali metal cations, and an Fe²⁺ complex increases the N-N bond activation (Δ ν_NN up to 172 cm^-1), decreases the Fe(0)-N₂ redox potential, polarizes the N-N bond, and enables -N protonation at uncommonly anodic potentials. These effects were rationalized using combined experimental and theoretical studies.