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

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 νNN 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.