RESUMEN
A series of novel Cp*Ir complexes with nitrogen-rich NÌN bidentate ligands were developed for the catalytic dehydrogenation of formic acid in water under base-free conditions. These complexes were synthesized by using pyridyl 1,2,4-triazole, methylated species, or pyridyl 1,2,3-triazole as a N-site regulation ligand and were fully characterized. Complex 1-H2O bearing 1,2,4-triazole achieved a high turnover frequency of 14192 h-1 at 90 °C in 4 M FA aqueous solution. The terminal and bridged Ir-H intermediates of 1-H2O were successfully detected by 1H NMR and mass spectrometry measurements. Kinetic isotope effect experiments and density functional theory (DFT) calculations were performed; then a plausible mechanism was proposed involving the ß-hydride elimination and formation of H2. Water-assisted H2 release was proven to be the rate-determining step of the reaction. The distribution of Mulliken charges on N atoms of triazole ligand internally revealed that the ortho site N2 of 1-H2O with a higher electron density was conducive to efficient proton transfer. Additionally, the advantage of water-assisted short-range bridge of 1,2,4-triazole moieties led to a higher catalytic activity of 1-H2O. This study demonstrated the effectiveness of nitrogen-rich ligands on FA dehydrogenation and revealed a good strategy for N site regulation in the development of new homogeneous catalysts.
RESUMEN
Heat-resistant explosives play an irreplaceable role in specialized applications. Two energetic metal-organic frameworks (EMOFs), potassium 4,4'-oxybis[3,3'-(5-tetrazol)]furazan and potassium (1,2,4-triazol-3-yl)tetrazole, featuring a three-dimensional metal-organic framework structure, were first synthesized and characterized by chemical (1H NMR, 13C NMR, MS, IR spectroscopy, and single-crystal XRD) and physicochemical analyses (sensitivity toward friction, impact, electrostatic, and DSC-TGA test). The new 3D EMOFs were found to show high thermostability, highly positive heat of formation, and suitable sensitivities. The Hirshfeld surface was further analyzed in order to explore the effect on sensitivities. Their detonation properties (detonation velocity, detonation pressure, etc.) were calculated by the EXPLO5 program. K2NTT exhibits extremely high decomposition temperatures of up to 361 °C; meanwhile, its detonation performance is comparable to that of TATB and other energetic potassium salts, which makes it a promising heat-resistant explosive.
RESUMEN
The demand for high energy density materials (HEDMs) remains a major challenge. Density functional theory (DFT) methods were employed to design a new family of bridged 1,2,4-triazole N-oxides by the manipulation of the linkage and oxygen-containing groups. The optimized geometry, electronic properties, energetic properties and sensitivities of new 40 molecules in this study were extensively evaluated. These designed compounds exhibit high densities (1.87-1.98 g cm-3), condensed-phase heat of formation values (457.31-986.40 kJ mol-1), impressive values for detonation velocity (9.28-9.49 km s-1) and detonation pressure (21.22-41.31 GPa). Their sensitivities (impact, electrostatic, and shock) were calculated and compared with 1,3,5-triamino-2,4,6-trinitrobenzene (TABT) and 4,6-dinitrobenzofuroxan (DNBF). Some new compounds 4,4'-trinitro-5,5'-bridged-bis-1,2,4-triazole-2,2'-diol (TN1-TN8) and 4,4'-dinitro-5,5'-ammonia-bis-1,2,4-triazole-2,2'-diol (DN3) were distinguished from this system, making them promising candidates for HEDMs. In addition, we found that the gas-relative parameters (detonation heat, oxygen balance, φ) were as important as the density, which were highly correlated to the detonation properties (P, D). Their comprehensive correlations should also be considered in the design of new energetic molecules.