Chapter 2: Synthesis, Structure and Reactivity of Energetic Nitrobis(Pyrazolyl)Benzenes

Two new energetic nitroaromatic compounds, 1,4-bis(1H-pyrazol-4'-yl)-2,5-dinitrobenzene (H₂dpzb(NO₂)₂) and 1,4-bis(1H-3',5'-dinitropyrazol-4'-yl)-2,5-dinitrobenzene (H₂dpzb(NO₂)₆), were prepared by nitration of 1,4-bis(1H-pyrazol-4'-yl)benzene (H₂dpzb) with mixed acid. H₂dpzb(NO₂)_x were isolated as yellow powders in moderate yields. They are stable under ambient conditions, soluble in dimethylformamide and dimethylsulfoxide, but poorly soluble in weakly coordinating solvents, and deflagrate in the heat. Both compounds have been characterised by ¹H, ¹³C NMR and IR spectroscopies as well as by X-ray crystallography. H₂dpzb(NO₂)_x crystallise readily as impact-insensitive dmso or thf solvates. Due to steric crowding at the (pyrazolyl group)–(benzene) bonds, H₂dpzb(NO₂)_x adopt a twisted molecular geometry with extended (x = 2) or localised intermolecular hydrogen-bonding (x = 6) that involve the pyrazolyl H atoms and solvent of crystallisation. H₂dpzb(NO₂)₆ reacts with base to form crystalline [B-H]₂[dpzb(NO₂)₆], B = NEt₃, which possesses remarkably high density ([B-H]₂[dpzb(NO₂)₆]), or a powder consisting of Na₂dpzb(NO₂)₆ (B = NaHCO₃, crystallised as the coordination polymer Na(dmso)(dpzb(NO₂)₆). A mixture of H₂dpzb(NO₂)₆, Zn(NO₃)2, NEt₃, dmso and water afforded the coordination compound [Zn(κ(O)-dmso)₆]₂[dpzb(NO₂)₆.