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

The activation and functionalization of dinitrogen (N ₂ ) with carbon dioxide (CO ₂ ) are of great interest and importance but highly challenging. We report here for the first time the reaction of N ₂ with CO ₂ 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 {[( ^acri PNP)Ti] ₂ ( μ ₂ - η ¹ : η ² -N ₂ )( μ ₂ -H) ₂ } ( 1 ) ( ^acri PNP = 4,5-bis(diisopropylphosphino)-2,7,9,9-tetramethyl-9H-acridin-10-ide) to a CO ₂ atmosphere at room temperature rapidly yielded a nitrido/ N , N -dicarboxylamido complex {[( ^acri PNP)Ti] ₂ ( μ ₂ -N)[ μ ₂ -N(CO ₂ ) ₂ ]} ( 2 , 28%) and a diisocyanato/dioxo complex {[( ^acri PNP)Ti] ₂ (NCO) ₂ ( μ ₂ -O) ₂ } ( 3 , 52%) with release of H ₂ . When the reaction of 1 with CO ₂ (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 CO ₂ for 30 min afforded 3 in 67% yield. When 1 was allowed to react with 1.5 equiv of CO ₂ at room temperature, an isocyanato/nitrido/oxo complex {[( ^acri PNP)Ti] ₂ (NCO)( μ ₂ -N)( μ ₂ -O)} ( 4 ) was exclusively formed in 89% yield within 5 min. The reaction of 4 with CO ₂ at room temperature almost quantitatively yielded the dioxo/diisocyanato complex 3 within 5 min. The mechanistic details were clarified by the ¹⁵ N- and ¹³ C-labeled experiments and density functional theory (DFT) calculations, providing unprecedented insights into the reaction of N ₂ with CO ₂ . A titanium-mediated cycle for the synthesis of trimethylsilyl isocyanate Me ₃ SiNCO from N ₂ , CO ₂ , and Me ₃ SiCl using H ₂ as a reducing agent was also established.