Dinitrogen Fixation by Vanadium Complexes with a Triamidoamine Ligand.

Area of Science:

• Inorganic Chemistry
• Organometallic Chemistry
• Catalysis

Background:

• Dinitrogen-divanadium complexes are of interest for nitrogen fixation research.
• Understanding the structure and reactivity of these complexes is crucial for developing new catalytic systems.

Purpose of the Study:

• To synthesize and characterize novel dinitrogen-divanadium complexes with triamidoamine ligands.
• To investigate the structural integrity and electronic properties of these complexes in solution.
• To explore the potential of these complexes in the reduction of dinitrogen to ammonia.

Main Methods:

• Synthesis of dinitrogen-divanadium complexes (1-3) using triamidoamine ligands.
• Characterization using resonance Raman, UV-vis, NMR spectroscopy, elemental analysis, and X-ray crystallography.
• Density Functional Theory (DFT) calculations to support structural and electronic properties of complex 1.
• Reactivity studies involving reduction with alkali metals and protonation with various acids.

Main Results:

• X-ray crystallography confirmed a dimeric structure with a bridging μ-N2 ligand for all three complexes.
• Spectroscopic studies (Resonance Raman, NMR) indicated structural stability in benzene and toluene solutions.
• Complexes 1 and 3 showed characteristic 15N NMR signals for μ-N2 ligands, while complex 2 did not under identical conditions.
• 51V NMR spectra revealed vanadium ion signals at higher magnetic fields compared to previously reported complexes.
• All complexes successfully converted dinitrogen to ammonia in the presence of reducing agents and proton sources, without forming hydrazine.
• Complex 1 reacted with Na[C10H8] and HOTf under N2 to yield ammonia with an impressive 151% yield (per V atom).

Conclusions:

• Novel dinitrogen-divanadium complexes with triamidoamine ligands have been successfully synthesized and characterized.
• These complexes exhibit structural stability in solution and unique electronic properties.
• The complexes demonstrate significant potential for the catalytic reduction of dinitrogen to ammonia, achieving high yields.