Ancillary Ligand-Controlled Dinitrogen Cleavage and Transformation at Titanium Centers

Area of Science:

• Inorganic Chemistry
• Organometallic Chemistry
• Catalysis

Background:

• Nitrogen (N₂) activation and transformation is a significant scientific challenge.
• Cleaving the strong N─N bond, especially with 3d metals like titanium, is particularly difficult.
• Metal nitrides are key intermediates in nitrogen fixation.

Purpose of the Study:

• To investigate ancillary ligand control over N₂ activation in titanium complexes.
• To achieve N─N bond cleavage using PCP-ligated titanium complexes.
• To develop efficient catalysts for nitrogen fixation.

Main Methods:

• Synthesis of PCP-ligated titanium complexes with varying ancillary ligands (aryloxide, diarylamide, phenyl).
• Reductive activation of N₂.
• Computational studies (DFT) to elucidate reaction mechanisms.
• Catalytic testing for N₂ silylation.

Main Results:

• Aryloxide and diarylamide ligands facilitated N─N bond scission to form dititanium bis(μ-nitrido) complexes.
• The phenyl analogue induced pincer ligand C─P bond activation.
• Computational studies revealed K⁺ ion interactions promoting N₂ isomerization and cleavage.
• Catalytic N₂ silylation yielded up to 22.0 equiv. of N(SiMe₃)₃, a record TON for Group IV metals.

Conclusions:

• Ancillary ligand choice critically controls the N₂ activation pathway in titanium complexes.
• Heteroatom interactions in the secondary coordination sphere are vital for N─N bond rupture.
• These findings provide insights for designing novel early-metal catalysts for nitrogen fixation.