Hydrazine N-N Bond Cleavage over Silica-Supported Tantalum-Hydrides

Hydrazine reacts with silica-supported tantalum-hydrides [( SiO)(2)TaHx] (x = 1, 3), 1, under mild conditions (100 degrees C). The IR in situ monitoring of the reaction with N2H4 or (N2H4)-N-15, and the solid-state MAS NMR spectra of the fully N-15 labeled compounds (CP N-15, H-1-N-15 HETCOR, double-quantum, and H-1-H-1 triple-quantum spectra) were used to identify stable intermediates and products. DFT calculations were used for determining the reaction pathway and calculating the N-15 and 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 degrees C, the hydrazine adducts are converted to several species among whit!). [( SiO)(2)Ta(=NH)(NH2)], 2, [(SiO)(2)TaH(NH2)2], 3, and [(SiO)(2)TaH2(NH-NH2)], 4, were identified. The final product 2 is also formed in the reaction of N-2 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-N cleavage in N-2. 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 N-2 or N2H4. This strengthens the previous proposal of the existence of 3 and 4 as intermediates in the reaction of N-2 with the tantalum-hydrides. However, the reaction of N-2 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 sitnilarities and differences of the reaction pathways involving N-2 and N2H4 with tantalum-hydrides.