Testing the Push-Pull Hypothesis: Lewis Acid Augmented N 2 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.