Dinitrogen Cleavage and Functionalization with Carbon Dioxide in a Dititanium Dihydride Framework

The activation and functionalization of dinitrogen (N₂) with carbon dioxide (CO₂) are of great interest and importance but highly challenging. We report here for the first time the reaction of N₂ with CO₂ in a dititanium dihydride framework, which leads to N-C bond formation and N-N and C-O bond cleavage. Exposure of a dinitrogen dititanium hydride complex {[(^acriPNP)Ti]₂(μ₂-η¹:η²-N₂)(μ₂-H)₂} (1) (^acriPNP = 4,5-bis(diisopropylphosphino)-2,7,9,9-tetramethyl-9H-acridin-10-ide) to a CO₂ atmosphere at room temperature rapidly yielded a nitrido/N,N-dicarboxylamido complex {[(^acriPNP)Ti]₂(μ₂-N)[μ₂-N(CO₂)₂]} (2, 28%) and a diisocyanato/dioxo complex {[(^acriPNP)Ti]₂(NCO)₂(μ₂-O)₂} (3, 52%) with release of H₂. When the reaction of 1 with CO₂ (1 atm) was carried out at -50 °C, complex 2 was selectively formed in 82% yield within 5 min. Heating 2 at 80 °C under 1 atm CO₂ for 30 min afforded 3 in 67% yield. When 1 was allowed to react with 1.5 equiv of CO₂ at room temperature, an isocyanato/nitrido/oxo complex {[(^acriPNP)Ti]₂(NCO)(μ₂-N)(μ₂-O)} (4) was exclusively formed in 89% yield within 5 min. The reaction of 4 with CO₂ at room temperature almost quantitatively yielded the dioxo/diisocyanato complex 3 within 5 min. The mechanistic details were clarified by the ¹⁵N- and ¹³C-labeled experiments and density functional theory (DFT) calculations, providing unprecedented insights into the reaction of N₂ with CO₂. A titanium-mediated cycle for the synthesis of trimethylsilyl isocyanate Me₃SiNCO from N₂, CO₂, and Me₃SiCl using H₂ as a reducing agent was also established.