To Split or Not to Split: [AsCCAs]-Coordinated Mo, W, and Re Complexes and Their Reactivity toward Molecular...

Area of Science:

• Organometallic Chemistry
• Inorganic Synthesis
• Nitrogen Fixation Research

Background:

• Dinitrogen (N₂) activation by transition metals is crucial for synthesizing nitrogen-containing compounds.
• The development of ligands that facilitate N₂ cleavage and stabilize reactive metal-nitrogen species is an ongoing challenge.
• Previous studies have explored various metal halides for N₂ reduction, but efficient routes to stable nitrides remain limited.

Purpose of the Study:

• To synthesize and characterize novel molybdenum, tungsten, and rhenium halides and their corresponding nitrides and dinitrogen complexes.
• To investigate the reductive cleavage of dinitrogen (N₂) using a 2,2'-(bis(2-arsenosophenyl)acetylene) ligand ([AsCCAs]).
• To explore the stability and electronic properties of the resulting metal-dinitrogen and metal-nitride compounds.

Main Methods:

• Synthesis of molybdenum, tungsten, and rhenium halide precursors bearing the [AsCCAs] ligand.
• Reductive cleavage of dinitrogen (N₂) under an inert atmosphere using these precursors.
• Isolation and characterization of metal-nitride complexes ([AsCCAs]Mo≡N(I), [AsCCAs]Re≡N(Cl)₂, and a tungsten nitride precursor) and dinuclear dinitrogen-bridged dimers ({[AsCCAs]WCl₂}₂(N₂), {[AsCCAs]ReCl₂}₂(N₂)).
• Spectroscopic and structural analyses to confirm the composition and electronic configurations of the synthesized compounds.

Main Results:

• Successful synthesis of molybdenum, tungsten, and rhenium complexes with the [AsCCAs] ligand.
• Reductive N₂ splitting achieved for molybdenum and tungsten precursors, yielding metal nitrides and a dinuclear dinitrogen-bridged tungsten dimer.
• A dinuclear dinitrogen-bridged rhenium dimer was formed but decomposed, necessitating an alternative route to the rhenium nitride.
• Isolated metal nitrides ([AsCCAs]Mo≡N(I), [AsCCAs]Re≡N(Cl)₂, and tungsten nitride) demonstrated considerable robustness.
• The dinuclear dinitrogen-bridged dimers exhibited varying stabilities, attributed to differences in their metal-N₂-metal core electronic configurations (π⁸δ⁴ for W vs. π¹⁰δ⁴ for Re).

Conclusions:

• The [AsCCAs] ligand effectively facilitates the reductive cleavage of dinitrogen (N₂) with molybdenum, tungsten, and rhenium.
• Robust metal nitrides of molybdenum, tungsten, and rhenium were synthesized, showcasing the potential of this ligand system.
• The study highlights the influence of electronic structure on the stability of dinuclear dinitrogen-bridged metal complexes.