文摘
Hydrazine reacts with silica-supported tantalum-hydrides [(鈮iO)2TaHx] (x = 1, 3), 1, under mild conditions (100 掳C). The IR in situ monitoring of the reaction with N2H4 or 15N2H4, and the solid-state MAS NMR spectra of the fully 15N labeled compounds (CP 15N, 1H鈥?sup>15N HETCOR, 1H鈥?sup>1H double-quantum, and 1H鈥?sup>1H triple-quantum spectra) were used to identify stable intermediates and products. DFT calculations were used for determining the reaction pathway and calculating the 15N and 1H NMR chemical shifts. Combining the experimental and computational studies led to the following results. At room temperature, only hydrazine adducts, 1-N2H4, are formed. Upon heating at 100 掳C, the hydrazine adducts are converted to several species among which [(鈮iO)2Ta(鈺怤H)(NH2)], 2, [(鈮iO)2TaH(NH2)2], 3, and [(鈮iO)2TaH2(NH鈥擭H2)], 4, were identified. The final product 2 is also formed in the reaction of N2 with the same silica-supported tantalum-hydride complexes, and the species identified as 3 and 4 had been previously suggested by DFT studies as intermediates on the reaction pathway for N鈥揘 cleavage in N2. The present computational studies (cluster models with M06 functional complemented by selected calculations with periodic calculations) show that 2 is formed via 3 and 4, with either N2 or N2H4. This strengthens the previous proposal of the existence of 3 and 4 as intermediates in the reaction of N2 with the tantalum-hydrides. However, the reaction of N2 does not imply the formation of N2H4 or its hydrazido monoanionic or dianionic ligand as an intermediate. For this reason, this study informs both on the similarities and differences of the reaction pathways involving N2 and N2H4 with tantalum-hydrides.