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.