Ancillary Ligand-Controlled Dinitrogen Cleavage and Transformation at Titanium Centers

The activation and transformation of dinitrogen (N₂) represents a significant scientific challenge. In particular, while metal nitrides are pivotal intermediates, achieving N─N bond cleavage with 3d metals such as titanium remains scarce. Here we report unprecedented ancillary ligand control over the N₂ activation pathway in PCP-ligated (PCP = 2,6-(^tBu₂PCH₂)₂-C₆H₃) titanium complexes upon reduction, wherein aryloxide or diarylamide groups facilitate complete N─N bond scission to dititanium bis(μ-nitrido) complexes, whereas the phenyl analogue leads to C─P bond activation of the pincer. Computational studies suggest that heteroatom-mediated interactions with K⁺ ions in the secondary coordination sphere facilitate isomerization of the N₂ bridge from end-on to side-on, thereby promoting N─N bond rupture. Moreover, these complexes catalyze the silylation of N₂, producing up to 22.0 equiv. of N(SiMe₃)₃, representing the highest turnover number (TON) for Group IV metal systems to date. These findings highlight the role of ligand environment in N₂ activation and provide new insights into the design of efficient early-metal catalysts for nitrogen fixation.