Reductive N₂ Cleavage and Nitride Insertion Reactivity at Molybdenum Complexes Supported by a Rigid PNP Pincer

Area of Science:

• Inorganic Chemistry
• Organometallic Chemistry
• Nitrogen Fixation

Background:

• Metal-nitride species are crucial intermediates in nitrogen (N₂) reduction and functionalization.
• Understanding nitride transfer reactivity is key to developing new N₂ fixation catalysts.

Purpose of the Study:

• To synthesize and characterize novel molybdenum-nitride complexes.
• To investigate the structural and electronic properties of these complexes.
• To explore the reactivity of Mo-nitride species in N₂ functionalization.

Main Methods:

• Synthesis of Mo-nitride complexes supported by a diphosphino-acridane pincer ligand.
• Stepwise reduction of a Mo(IV) chloride complex under N₂ atmosphere.
• Characterization using extensive ¹⁵N-labeling studies.
• Structural analysis of the dinuclear Mo-nitride species.
• Computational studies to elucidate reaction mechanisms.

Main Results:

• Isolation of a bridging diazenido intermediate and a dinuclear Mo-nitride species with a bridging N₂ moiety.
• First example of a Mo(IV) nitride-N₂ species, featuring orthogonal π-backbonding interactions.
• Synthesis of PMe₃, CO, and CNᵗBu substituted analogues.
• Formation of Mo(II)-isocyanate and -carbodiimide species from reactions with CO and isocyanide.
• Computational evidence for an associative nitride insertion pathway in carbonylation.

Conclusions:

• The rigid diphosphino-acridane pincer ligand stabilizes unique Mo-nitride and Mo-nitride-N₂ species.
• The Mo(IV) nitride fragment effectively engages in π-backbonding with N₂, enabling isolation of novel intermediates.
• Reactivity studies demonstrate the potential for functionalization of the nitride moiety, leading to valuable products.
• Findings encourage further research into direct N₂ fixation for producing value-added chemicals.