The Intramolecular Assembly of Polynitrobiazoles and Ether-Bridge: A Facile Strategy to Access High-Energy and Thermostable Polynitro-Functionalized Diazole-1,3,6-Oxadiazepines

Abstract

Recently, the construction of novel fused-ring frameworks has become one of the most significant innovative approaches to access high-energy and thermostable energetic molecules. In this work, the ether-bridge was utilized as a building block to construct energetic fused-ring skeletons for the first time. Two new [5,7,5]-tricyclic N -heterocycle-based backbones, ditriazole-1,3,6-oxadiazepine and pyrazole-triazole-1,3,6-oxadiazepine, were synthesized via straightforward one-step synthetic route and the energetic performances of their derivatives were further evaluated. With containing an additional oxygen atom and the high-density pyrazole-triazole asymmetric backbone, asymmetric molecule 2,10,11-trinitro-5 H ,7 H -pyrazolo[1,5-c][1,2,4]triazolo[5,1-e][1,3,6]oxadiazepine ( NOB-3 ) features with a high crystal density of 1.825 g cm -3 , much higher than those of symmetrical analogues 2,10-dinitro-5 H ,7 H -bis([1,2,4]triazolo)[1,5-c:5',1'-e][1,3,6]oxadiazepine ( NOB-4 , d = 1.758 g cm -3 ) and 2,10-dinitro-6,7-dihydro-5 H -bis([1,2,4]triazolo)[1,5-a:5',1'-c][1,4]diazepine ( D , d = 1.634 g cm -3 ). Meanwhile, compounds NOB-3 and NOB-4 exhibit better thermal stability than parent molecule DNBT ( T d = 251 °C), and their decomposition temperatures reach up to 294 °C and 303 °C, respectively. The remarkable overall performance of NOB-3 and NOB-4 strongly suggests them as appropriate candidates for heat-resistant explosives. Our study may give new insights into the close correlation of structure-properties of energetic fused-ring frameworks, and the universality of asymmetric heterocycles combination strategy for designing advanced HEDMs was emphasized again.

Keywords: Novel fused-ring frameworks, Ditriazole-1, 3, 6-oxadiazepine, Pyrazole-triazole-1, 3, 6-oxadiazepine, Asymmetric combination, Heat-resistant explosive