Halide Effects in Reductive Splitting of Dinitrogen with Rhenium Pincer Complexes.

Area of Science:

• Inorganic Chemistry
• Electrochemistry
• Computational Chemistry

Background:

• Transition metal halide complexes are crucial precursors for reductive nitrogen (N₂) activation.
• Understanding halide effects on redox properties and yields in N₂ splitting is essential but not well-established.
• Rhenium complexes are investigated for their potential in N₂ reduction to nitride complexes.

Purpose of the Study:

• To electrochemically and computationally examine reductive N₂ splitting using rhenium(III) complexes with varying halides (Cl, Br, I).
• To elucidate the distinct halide effects on redox potentials, reaction mechanisms, and yields of N₂ splitting.
• To understand the role of dinuclear bridged intermediates in the N₂ splitting process.

Main Methods:

• Electrochemical reduction of rhenium(III) complexes [ReX₂(PNP)] (X = Cl, Br, I).
• Identification of reaction intermediates using spectroscopic and analytical techniques.
• Computational analysis including energy decomposition analysis (EDA) of redox couples.

Main Results:

• Heavier halides (Br, I) lead to rhenium(V) nitrides in good yields, similar to chloride, but at anodically shifted potentials.
• Dinuclear, end-on N₂-bridged rhenium complexes were identified as key intermediates for all halides.
• Chloride complex formation involves 2-electron reduction and Reᴵᴵᴵ/Reᴵ comproportionation, while iodide also utilizes a Reᴵᴵ/Reᴵᴵ dimerization pathway.

Conclusions:

• Halide identity profoundly influences the electrochemical potentials and reaction mechanisms of reductive N₂ splitting.
• The observed trends in potentials are primarily attributed to electrostatic Re-X bonding interactions.
• Distinct mechanistic pathways, including alternative dimerization, can operate depending on the halide and applied potential.