Reactivity of Polynucleating Titanium Complexes toward Catalytic N 2 Silylation

Although multimetallic cooperativity is widely recognized as a key driving force in both enzymatic and industrial N2 fixation, systematic investigations of well-defined multimetallic catalysts for catalytic N2 transformation remain limited, particularly for early transition metals. In this study, a series of dititanium dichloride complexes supported by polynucleating N2N2−-derived ligands were designed, synthesized, and evaluated for catalytic N2 silylation. This series include phenoxide-bridged complex 1, benzyl-bridged complexes 2a−2b, and alkyl-bridged complexes 3a−3c, enabling a systematic investigation of how bridging motifs influence catalytic performance. To compare the catalytic behavior of mononuclear and dinuclear titanium species during N2 conversion, a set of mononuclear titanium dichloride complexes (4−6) bearing analogous ligand frameworks were prepared as reference compounds. Despite this rational design strategy, under identical reaction conditions, all dinuclear titanium precatalysts prepared in this work exhibited lower catalytic activity toward N2 silylation than their corresponding mononuclear titanium counterparts. Preliminary analysis suggests that the discrepancy may arise from the distinct Ti–N intermediates formed by these precatalysts under reductive conditions. These intermediates were highly susceptible to multiple factors, including the steric and electronic effects, ligand denticity, and the intramolecular Ti···Ti distance.