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

Dinitrogen (N 2 ), carbon monoxide (CO), and carbon dioxide (CO 2 ) are all abundant and readily available chemical feedstocks. The functionalization of N 2 with CO and CO 2 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 N 2, CO, CO 2, and alkynes within a dititanium framework. Sequential reactions of N 2, CO, alkynes (R 1 C≡CR 2 ), and CO 2 with a dititanium tetrahydride complex at room temperature selectively afforded the corresponding four-component coupling products, [O 2 CN 2 CH 2 C(R 2 )CR 1 ] 4– (R 1 = H, R 2 = Ph, Cy, or COOMe; R 1 = R 2 = Me). Combined experimental and computational studies reveal that coordination of an alkyne to one Ti center of a dititanium dinitrogen/oxymethylene complex, formed via N 2 and CO activation, induces N–C bond formation between the dinitrogen and oxymethylene moieties with simultaneous deoxygenation, leading to the formation of diazomethane species [NNCH 2 ] 2– at the other Ti center. Subsequent CO 2 incorporation at the terminal nitrogen of the diazomethane unit triggers the addition of the CH 2 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 N 2, CO, and CO 2, offering a new strategy for the valorization of small inert molecules at the molecular level.