Cascade Coupling of Dinitrogen, Carbon Monoxide, Carbon Dioxide, and Alkynes in a Dititanium Framework

Dinitrogen (N₂), carbon monoxide (CO), and carbon dioxide (CO₂) are all abundant and readily available chemical feedstocks. The functionalization of N₂ with CO and CO₂ is of considerable interest and importance, but remains a formidable challenge, owing to their high thermodynamic and kinetic stability. Here, we report an unprecedented cascade coupling of N₂, CO, CO₂, and alkynes within a dititanium framework. Sequential reactions of N₂, CO, alkynes (R¹C≡CR²), and CO₂ with a dititanium tetrahydride complex at room temperature selectively afforded the corresponding four-component coupling products, [O₂CN₂CH₂C(R²)CR¹]⁴⁻ (R¹ = H, R² = Ph, Cy, or COOMe; R¹ = R² = Me). Combined experimental and computational studies reveal that coordination of an alkyne to one Ti center of a dititanium dinitrogen/oxymethylene complex, formed via N₂ and CO activation, induces N-C bond formation between the dinitrogen and oxymethylene moieties with simultaneous deoxygenation, leading to the formation of diazomethane species [NNCH₂]²⁻ at the other Ti center. Subsequent CO₂ incorporation at the terminal nitrogen of the diazomethane unit triggers the addition of the CH₂ unit to the coordinated alkyne, thereby generating an allylhydrazinocarboxylate species as the final four-component coupling product. This work highlights the unique synergistic reactivity of multinuclear titanium complexes toward cooperative activation and incorporation of N₂, CO, and CO₂, offering a new strategy for the valorization of small inert molecules at the molecular level.