Inner-sphere two-electron reduction leads to cleavage and functionalization of coordinated dinitrogen

Area of Science:

• Organometallic Chemistry
• Inorganic Chemistry
• Catalysis

Background:

• Activation of molecular nitrogen (N2) by transition metal complexes is crucial for synthesizing organonitrogen compounds.
• Previous studies focused on adding hydride reagents to dinitrogen complexes, but reactions with zirconocene reagents were unexplored.

Purpose of the Study:

• To investigate the reaction of a ditantalum dinitrogen complex with zirconocene chlorohydride.
• To elucidate the mechanism of N-N bond cleavage and product formation.
• To explore the role of different zirconium hydride species in the reaction.

Main Methods:

• Reaction of ([NPN]Ta)2(mu-H)2(mu-eta1:eta2-N2) with [Cp2Zr(Cl)H]x and subsequent X-ray crystallography.
• Utilized zirconocene dihydride dimer ([Cp2ZrH2]2) for improved yield and 1H NMR spectroscopy to observe H2 evolution.
• Employed dideuterated dinitrogen complex (d2-1) and zirconocene dihydride to study hydrogen scrambling.

Main Results:

• Reaction with zirconocene chlorohydride yielded a phosphinimide and triply bridging nitride product in 35% yield.
• Using zirconocene dihydride dimer increased the yield to 76% and produced H2.
• Deuterium labeling confirmed no scrambling between the tantalum and zirconium hydride/deuteride sources.

Conclusions:

• The reaction proceeds via initial adduct formation and inner-sphere electron transfer, cleaving the N-N bond.
• A novel pathway to phosphinimide and bridging nitride species from coordinated dinitrogen was established.
• Zirconocene dihydride is more effective than zirconocene chlorohydride for this transformation.