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

The activation and functionalization of dinitrogen (N-2) with carbon dioxide (CO2) are of great interest and importance but highly challenging. We report here for the first time the reaction of N-2 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 {[((PNP)-P-acri)Ti](2)(mu(2)-eta(1):eta(2)-N-2)(mu(2)-H)(2)} (1) ((PNP)-P-acri = 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 {[((PNP)-P-acri)Ti](2)(mu(2)-N)[mu(2)-N(CO2)(2)]} (2, 28%) and a diisocyanato/dioxo complex {[((PNP)-P-acri)Ti](2)(NCO)(2)(mu(2)-O)(2)} (3, 52%) with release of H-2. When the reaction of 1 with CO2 (1 atm) was carried out at -50 degrees C, complex 2 was selectively formed in 82% yield within 5 min. Heating 2 at 80 degrees 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 {[((PNP)-P-acri)Ti](2)(NCO)(mu(2)-N)(mu(2)-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 N-15- and C-13-labeled experiments and density functional theory (DFT) calculations, providing unprecedented insights into the reaction of N-2 with CO2. A titanium-mediated cycle for the synthesis of trimethylsilyl isocyanate Me3SiNCO from N-2, CO2, and Me3SiCl using H-2 as a reducing agent was also established.