Thiophenol-Catalyzed Visible-Light Photoredox Decarboxylative Couplings of <i>N</i>‑(Acetoxy)­phthalimides

We have developed visible-light photoredox decarboxylative couplings of <i>N</i>-(acetoxy)­phthalimides without an added photocatalyst in which simple and commercially available thiophenols are used as the effective organocatalysts, and 4-(trifluoromethyl)­thiophenol shows optimal catalytic activity. Three representative decarboxylative examples were chosen including one amination and two C–C bond couplings to confirm efficacy of the visible-light photoredox reactions, and the results exhibited that they performed very well at room temperature. The interesting discovery should provide a novel and environmentally friendly strategy for visible-light photoredox transformation of organic molecules

Designing Difunctional Promoters for Hypergolic Ignitions of Green Bipropellants Combining Ionic Liquids with H₂O₂

The emergence of tetrahydroborate (BH4–)/cyanoborohydride (BH3CN–) anion-based ionic liquid fuels in combination with high test peroxide (>90%H2O2, HTP) oxidizers has accelerated the greening of bipropellants. However, most BH4– and BH3CN– anion-based ionic liquids are sensitive to water, making it difficult to store them. Here, novel difunctional promoters are designed for hypergolic ignition of BH4–/BH3CN– anion-free ionic liquids with 90%H2O2. The transition metal in anions of promoters is expected to catalyze the exothermic decomposition of H2O2, and the substituted borohydride in cations of promoters acts as the ignition source. These novel difunctional promoters show good solubility in commercially available 1-allyl-3-methylimidazolium dicyanamide and 1-butyl-3-methylimidazolium dicyanamide ionic liquid fuels, and the composite fuels exhibit high density, acceptable viscosity, and high thermostability. The addition of difunctional promoters ensures the smooth hypergolic ignition of BH4–/BH3CN– anion-free ionic liquid fuels with a minimum ignition delay time of 34.0 ms, and no apparent microexplosion and secondary combustion are observed during the ignition process. With the increase in the amount of the promoter, density specific impulses of the composite fuels improve gradually. This work provides a platform strategy for designing promoters by synergy of cations and anions and makes efforts to seek green bipropellants

Theoretical Study on Hydrolytic Stability of Borohydride-Rich Hypergolic Ionic Liquids

Hypergolic ionic liquids (HILs) are a new kind of green rocket fuels, which are used as potential replacements for toxic hydrazine derivatives in liquid bipropellants. These functional HILs can react with oxidizers and release a large amount of heat in a very short time, finally leading to ignition of the propellant system. Among them, most borohydride-rich HILs were very sensitive to water, but a few special examples displayed good hydrophobicity and remained very stable in air even after a month or more. However, the reasons behind their hydrolytic stability are unclear. In this study, several calculation methods including electrostatic potentials (ESPs), molecular orbital energy gaps, and interaction energy were used to explore the water stability of eight typical borohydride-rich HILs. The obtained results demonstrated that negatively charged anions with high absolute ESP values usually reacted more easily with positively charged water. The large molecular orbital energy gap with BPB–, BCNBCN–, CTB–, and BTB– indicates the high degree of difficulty of interactions between anions and water, leading to a better hydrolytic stability of borohydride-rich anions. During the analyses of interaction energy, the relatively water-sensitive borohydride-rich anions (BH4–, BH3CN–, etc.) generally had lower interaction energy with water than stable anions such as BPB– and BCNBCN–. Studies on their stepwise hydrolysis mechanism demonstrate that, in the case of all the reactions, the first step is the rate-determining step and high energy barrier values of anions correspond to good hydrophobicity. This study will help us understand the hydrolysis of borohydride-rich HILs and provide a guide for the development of new HILs with promising properties

Copper-Catalyzed Aerobic Oxidative Intramolecular C–H Amination Leading to Imidazobenzimidazole Derivatives

A highly efficient copper-catalyzed aerobic oxidative intramolecular C–H amination has been developed using substituted 2-(1<i>H</i>-imidazol-1-yl)-<i>N</i>-alkylbenzenamines as the starting materials, and the corresponding imidazobenzimidazole derivatives were obtained in excellent yields. This is an economical and practical method for the construction of <i>N</i>-heterocycles

Photocatalyst-Free Visible-Light Photoredox Dearomatization of Phenol Derivatives Containing Ketoximes: An Easy Access to Spiropyrrolines

A novel and simple visible-light photoredox intramolecular dearomatization of phenol derivatives containing ketoximes leading to spiropyrrolines has been developed. The protocol uses readily available 1,8-diazabicyclo[5.4.0]­undec-7-ene (DBU) as the base and electron-donor, visible light as the light source, and the reaction was performed well at room temperature without need of a photocatalyst. Therefore, the present method should provide a useful strategy for synthesis of spiropyrrolines

Synthesis of Thermally Stable and Insensitive Energetic Materials by Incorporating the Tetrazole Functionality into a Fused-Ring 3,6-Dinitropyrazolo-[4,3‑<i>c</i>]Pyrazole Framework

A series of fused-ring energetic materials, i.e., 3,6-dinitro-1,4-di­(1H-tetrazol-5-yl)-pyrazolo­[4,3-c]­pyrazole (DNTPP, compound 2) and its ionic derivatives (compounds 3–8), were designed and synthesized in this study. The molecular structures of compounds 2, 3, 6, 7·2H2O, and 8 were confirmed using single-crystal X-ray diffraction. Their physicochemical and energetic properties, such as density, thermal stability, heat of formation, sensitivity, and detonation properties (e.g., detonation velocity and detonation pressure), were also evaluated. The results indicate that DNTPP and most of its ionic derivatives are extremely thermally stable and insensitive toward mechanical stimuli. In particular, the thermal decomposition temperature of compound 3 is up to 329 °C, while compounds 7 and 8 are very insensitive (impact sensitivity: >20 J; friction sensitivity: >360 N). Compounds 2, 3, and 6 possess good comprehensive properties, including excellent thermal stability, remarkable low sensitivities, and favorable detonation performance. These features show that DNTPP and its ionic derivatives have considerable promise as thermally stable and insensitive energetic materials

Synthesis of Thermally Stable and Insensitive Energetic Materials by Incorporating the Tetrazole Functionality into a Fused-Ring 3,6-Dinitropyrazolo-[4,3‑<i>c</i>]Pyrazole Framework

A series of fused-ring energetic materials, i.e., 3,6-dinitro-1,4-di­(1H-tetrazol-5-yl)-pyrazolo­[4,3-c]­pyrazole (DNTPP, compound 2) and its ionic derivatives (compounds 3–8), were designed and synthesized in this study. The molecular structures of compounds 2, 3, 6, 7·2H2O, and 8 were confirmed using single-crystal X-ray diffraction. Their physicochemical and energetic properties, such as density, thermal stability, heat of formation, sensitivity, and detonation properties (e.g., detonation velocity and detonation pressure), were also evaluated. The results indicate that DNTPP and most of its ionic derivatives are extremely thermally stable and insensitive toward mechanical stimuli. In particular, the thermal decomposition temperature of compound 3 is up to 329 °C, while compounds 7 and 8 are very insensitive (impact sensitivity: >20 J; friction sensitivity: >360 N). Compounds 2, 3, and 6 possess good comprehensive properties, including excellent thermal stability, remarkable low sensitivities, and favorable detonation performance. These features show that DNTPP and its ionic derivatives have considerable promise as thermally stable and insensitive energetic materials

Heterometallic Hybrid Open Frameworks: Synthesis and Application for Selective Detection of Nitro Explosives

Three inorganic–organic hybrid open frameworks based on heterometallic cluster building blocks, formulated as Cd₂Cs₃­(NDC)₃­(OAc)­(DMA)₂­(H₂O) (<b>1</b>), [NH₂­(CH₃)₂]₂·​Cd₂Mg­(NDC)₄·​G_<i>x</i> (<b>2</b>), and [NH₂­(CH₃)₂]₃·​Cd₂K­(NDC)₄·​G_<i>x</i> (<b>3</b>) (H₂NDC = 2,6-naph­thalene­dicarbox­ylic acid, G = guest solvent molecule), were synthesized under solvothermal conditions. Compound <b>1</b> has a pillared layered structure featuring inorganic hcb-type layers with 14-ring windows and simultaneously exhibits a 3D open framework constructed from two types of heterometallic clusters, i.e., {Cd₂Cs₂­O₁₈} and {CdCs₄­O₁₈}, and the NDC^2– ligand. Compounds <b>2</b> and <b>3</b> are constructed from linear trinuclear {Cd₂M} (M = Mg and K) building blocks and the NDC^2– ligand, featuring 1D square channels with rld-z topology. Of the three heterometallic hybrid open frameworks, compounds <b>1</b> and <b>2</b> exhibited strong blue-light emission due to the presence of fluorescent organic ligands in the anionic frameworks, and more importantly, their strong fluorescence could be selectively quenched toward the nitro explosive picric acid (PA). Mechanism study has demonstrated that the high fluorescence quenching selectivity of both hybrid materials toward PA might be due to resonance energy transfer and photoinduced electron transfer processes

Construction of a Thermally Stable and Highly Energetic Metal–Organic Framework as Lead-Free Primary Explosives

Two energetic compounds, 4,8-dinitraminodifurazano­[3,4-<i>b</i>,<i>e</i>]­pyrazine (<b>1</b>) and its potassium-based energetic metal–organic framework (E-MOF) (<b>2</b>), were prepared, and their crystal structures were confirmed by single-crystal X-ray diffraction analysis. Compound <b>1</b> cocrystallizes with water molecules and shows a three-dimensional (3D) sandwich-like supramolecular structure, which is rare in the known energetic organic compounds. Compound <b>2</b> has a pillared layered structure with a pcu topology. The layered structure in the 3D framework featuring sql topology was constructed from inorganic chains {K₂O} and nitroamine groups. The crystal density of <b>2</b> is up to 2.114 g cm^–3. This potassium-based E-MOF shows high thermal stability, high detonation velocity, and high impact and friction sensitivities, which make it a potential high-performing primary explosive

Synthesis of Thermally Stable and Insensitive Energetic Materials by Incorporating the Tetrazole Functionality into a Fused-Ring 3,6-Dinitropyrazolo-[4,3‑<i>c</i>]Pyrazole Framework

A series of fused-ring energetic materials, i.e., 3,6-dinitro-1,4-di­(1H-tetrazol-5-yl)-pyrazolo­[4,3-c]­pyrazole (DNTPP, compound 2) and its ionic derivatives (compounds 3–8), were designed and synthesized in this study. The molecular structures of compounds 2, 3, 6, 7·2H2O, and 8 were confirmed using single-crystal X-ray diffraction. Their physicochemical and energetic properties, such as density, thermal stability, heat of formation, sensitivity, and detonation properties (e.g., detonation velocity and detonation pressure), were also evaluated. The results indicate that DNTPP and most of its ionic derivatives are extremely thermally stable and insensitive toward mechanical stimuli. In particular, the thermal decomposition temperature of compound 3 is up to 329 °C, while compounds 7 and 8 are very insensitive (impact sensitivity: >20 J; friction sensitivity: >360 N). Compounds 2, 3, and 6 possess good comprehensive properties, including excellent thermal stability, remarkable low sensitivities, and favorable detonation performance. These features show that DNTPP and its ionic derivatives have considerable promise as thermally stable and insensitive energetic materials