Energetic bicyclic azolium salts

Bicyclic azoles, 2-methyl-5-(imidazol-1-yl)-2H-tetrazole (1), 2-methyl-5-(1,2,4-triazol-1-yl)-2H-tetrazole (4), 1-methyl-5-(imidazol-1-yl)-1H-tetrazole (7), 1-methyl-5-(1,2,4-triazol-1-yl)-1H-tetrazole (10), 1-methyl-4-nitro-2-(imidazol-1-yl)-1H-imidazole (13), and 1-methyl-4-nitro-2-(1,2,4-triazol-1-yl)-1H-imidazole (16) were prepared. Their thermally stable azolium salts, 3, 6, 9, 12, 15, and 18-21, with densities ranging between 1.519-1.674 g cm-3, were synthesized by quaternization with nitric or perchloric acid or with iodomethane followed by metathesis reactions with silver nitrate and silver perchlorate. The structures of 12 b and 21 b were confirmed by single-crystal X-ray analysis. The standard enthalpies of formation for some of the new salts were calculated by using the computationally feasible DFT(B3LYP) and MP2 methods in conjunction with an empirical approach based on densities of salts. The calculated values range from DeltaHdegreef=209.9 (21 a) to 412.3 (12 b) kJ mol-1 in which the experimental densities are >1.515 g cm-3.     

Mesomeric betaines of azolium azolate: Synthesis and properties

A facile entry into the almost unknown azolium azolate inner salts is described, and the structure of these highly dipolar compounds is well reflected by their spectroscopic properties and reactivity towards electrophiles (MeI) and dipolarophiles (DMAD) under mild conditions.     

Energetic salts from N-aminoazoles

New energetic salts (2, 3, 5, 6, 13, 14, 21, 22) were synthesized via the quaternization of derivatives of N-aminoazoles with nitric or perchloric acid or with iodomethane followed by metathesis reaction with silver nitrate or silver perchlorate. The structure of 2-amino-4,5-dimethyltetrazolium nitrate (21) was confirmed by single-crystal X-ray analysis. Most of the salts exhibit good thermal stabilities and low melting points. By using experimentally determined constant volume combustion energies, the standard molar enthalpies of formation were derived on the basis of designed Hess thermochemical cycles.     

Tuning azolium azolate ionic liquids to promote surface interactions with titanium nanoparticles leading to increased passivation and colloidal stability

The passivation and stability of suspensions of titanium nanoparticles in azolium azolate ionic liquids can be tuned by introducing metal specific binding sites in the azolate anion.     

Energetic nitrogen-rich salts and ionic liquids

Energetic salts offer many advantages over conventional energetic molecular compounds. The use of nitrogen containing anions and cations contributes to high heats of formations and high densities. Their low carbon and hydrogen content gives rise to a good oxygen balance. The decomposition of these compounds is predominantly through the generation of dinitrogen which makes them very promising candidates for highly energetic materials for industrial or military applications.     

Thermal analysis study of imidazolinium and some benzimid azolium salts by TG

The imidazolinium and benzimidazolium bromide salts with pentafluor substituents on N atom were synthesized. The structures of imidazolinium and benzimidazolium bromide salts obtained were conformed by ¹H and ¹³C NMR, ¹⁹F NMR and elemental analysis. It was found that pyrolytic decomposition occurs with melting in salts. The imidazolinium and benzimidazolium bromide salts were studied by TG-DTG and DTA from ambient temperature to 1000°C in nitrogen atmosphere. The decomposition occurred mainly in one stage and the values of activation energy E, frequency factor A, reaction order n, enthalpy change ΔH ^#, entropy change ΔS ^# and Gibbs free energy ΔG ^#, of the thermal decomposition were calculated by means of Coats-Redfern (CR), MacCallum-Tanner (MC) and van Krevelen (vK) methods. The activation energy value obtained by CR and MC methods were in good agreement with each other while those obtained by vK were found to be 10–12 kJ mol⁻¹ larger.     

An efficient procedure for the synthesis of phenacyl and benzyl azolium salts using fluorous alcohols

An efficient procedure for the synthesis of phenacyl and benzyl azolium salts in 2,2,2-trifluoroethanol and 1,1,1,3,3,3-hexafluoroisopropanol as fluorous alcohols have been developed. This synthetic methodology has some advantages with the respect to yield, atom efficiency, solvent and reagents used and wastes generated when compared to the currently in use methods. Using this procedure, a range of phenacyl and benzyl azolium salts can be synthesized with good to excellent yields. The pure salts are separated from the reaction mixture by simple filtration and washing with dry ether.     

Theoretical studies of the oxidative addition of azolium salts to a model Wilkinson's catalyst

The oxidative addition of 1,3-dimethylimidazolium to a model Wilkinson's catalyst (RhCl(PH(3))(3)) has been studied with density functional calculations (B3LYP). According to our free energy calculations, the octahedral rhodium carbene hydride product forms from initial predissociation of a phosphine molecule to subsequently form a 5 ligand intermediate; however, results indicate that a six ligand, associative route with a concerted three-centred transition structure may also be competitive. Exchange of the phosphine molecule on the metal centre with trimethylphosphine had a significant effect in lowering the barrier to oxidative addition and decreasing the endothermicity of the reaction. Solvation was found to have a moderate effect on the overall reaction. Bulk solvent calculations reflected a relative stabilisation of reactants for both pathways, resulting in an endothermic overall reaction. A study of alternative azolium salts revealed the saturated 1,3-dimethyl-4,5-dihydroimidazolium resulted in little change to the reaction geometries or energies, while the use of 3-methylthiazolium salt significantly reduced the barrier to addition and increased the exothermicity of the reaction considerably.     

Oxidative addition of 2-substituted azolium salts to Group-10 metal zero complexes--a DFT study

Generation of N-heterocyclic carbene (NHC) complexes [(dmpe)M(azol-2-ylidene)R] via the oxidative addition of a series of 2-substituted azolium salts to Group-10 zerovalent metal complexes has been investigated using density functional theory (2-R = H, Me, Ph; Azole = imidazole, thiazole, oxazole; M = Ni, Pd, Pt). Overall, platinum-based pathways result in the greatest enthalpies of reaction, but due to the reactive nature of Group-10 metals bearing the 1,2-bis(dimethylphosphino)ethane (dmpe) chelate, nickel and palladium species also have little trouble proceeding to stable products in the absence of a significant barrier. Imidazolium salts were found to be the most vulnerable to oxidative addition due to their low stabilisation energies when compared to the oxazolium and thiazolium species. Activation barriers show the general trend of phenyl > methyl > hydrido with regard to the azole 2-substituent, with no observed barrier for all but one of the 2-hydrido cases. Minimal barriers were found to exist in a number of cases for activation of a C(2)-CH3 bond suggesting that synthesis of alkyl-carbene complexes may be possible via this route under certain conditions, and therefore ionic liquids based on these substituted azolium salts may be active participants in catalytic reactions.     

Energetic salts based on dipicrylamine and its amino derivative

Energetic salts based on dipicrylamine and its amino derivative were synthesized. All salts were fully characterized by multinuclear NMR spectroscopy ((1)H, (13)C), vibrational spectroscopy (IR), and elemental analysis. Ethylenediammonium di-DPA (DPA=dipicrylamine) and 1,3-diaminoguanidinium DPA were further confirmed by single-crystal X-ray diffraction. These salts exhibit reasonable physical properties, such as high densities (1.71-1.81 g cm(-3)), good thermal stabilities (T(d) =155-285 °C), and low solubilities in water. The impact sensitivity of 1-methyl-3,4,5-triamino-1,2,4-triazolium DPA is lower than that of 2,4,6-trinitrotoluene (TNT), and for some other energetic salts their impact sensitivities are comparable to that of TNT. Based on experimental densities and theoretical calculations carried out by using the Gaussian 03 suite of programs, all the salts have calculated detonation pressures (22.5-27.8 GPa) and velocities (7226-7917 m s(-1)) that exceed those of conventional TNT. The toxicities of these salts measured by luminescent bacteria toxicity tests are much lower than that of TNT, and two binary eutectic mixtures with melting points that fall between 70 and 100 °C were identified.     

Energetic quaternary salts containing bi(1,2,4-triazoles)

New energetic salts (2, 3, 9, 10, and 11) were synthesized via the protonation of 4,4'-bi(1,2,4-triazole) or N-4-(1,2,4-triazole)-N-3-(4-methyl-1,2,4-triazole)amine with nitric acid or perchloric acid or 5-nitro-tetrazole. The structures of 4,4'-bi(1,2,4-triazolium) nitrate (2), N,N-dimethyl-N'-(5-methyl-tetrazole)methanimidamide (8), and N-4-(1,2,4-triazole)-N-3-(4-methyl-1,2,4-triazolium)amine perchlorate (10) were confirmed by a single-crystal X-ray analysis. The physical properties and heats of combustion of the new ionic salts were measured, and the heats of formation were also determined.     

An efficient route to unsymmetrical bis(azolium) salts: CCC-NHC pincer ligand complex precursors

The coupling of N-heterocyclic azoles (imidazoles, benzimidazoles, triazoles) to bromobenzenes (1,2-; 1,3-; or 1,4) in a step-wise, sequential manner was accomplished by manipulation of reaction time and stoichiometry, which provided straight-forward access to unsymmetrical bis(azolium) salts in only three isolation steps from commercially-available starting materials. Eight mono(azole) substituted bromobenzenes, four mono(azolium)bromobenzene salts, twelve unsymmetrical bis(azole)benzenes, and fourteen unsymmetrical bis(azolium) salts, which are precursors for pincer ligand complexes, are reported.     

Unexpected ring transformation to pyrrolo[3.2-b]pyridine derivatives. Fused azolium salts. 22

2-Arylsulfanyl and 2-benzylsulfanylpyridinium N-arylimides (2) easily prepared from 3-aryltetrazolopyridinium salts (1) with aryl and benzylthiolates, respectively, reacted with various dipolarophiles yielding cycloadducts that underwent transformation to give tetrahydropyrrolo[3,2-b]pyridines (5, 6, and 8) in good yields. A similar rearrangement (formation of 15) was also observed in the case of parent derivatives being unsubstituted in position 2 (12). The abscence of any significant solvent effect, comparison of the sulfur and non-sulfur analogues, as well as the stereoselective nature of the observed ring transformation seem to support a sigmatropic mechanism. Structure elucidation of the products has been carried out by single-crystal X-ray diffraction and (1)H NMR experiments.     

Hydroxy-amide functionalized azolium salts for Cu-catalyzed asymmetric conjugate addition: stereocontrol based on ligand structure and copper precatalyst

A series of hydroxy-amide functionalized azolium salts have been designed and synthesized for Cu-catalyzed asymmetric conjugate addition reaction. The (CH(2))(2)-bridged hydroxy-amide functionalized azolium ligand precursors 2, in addition to the previously reported CH(2)-bridged azolium salts 1, have been prepared from readily available enantiopure β-amino alcohols. The combination of a Cu species with 1 or 2 efficiently promoted the 1,4-addition reaction of cyclic enones with dialkylzincs. For example, the reaction of 2-cyclohepten-1-one (17) with Bu(2)Zn in the presence of catalytic amounts of Cu(OTf)(2) and 1 gave (S)-3-butylcycloheptanone (20) in 99% yield and 96% ee. On the other hand, when the reaction was carried out under the influence of Cu(OTf)(2) combined with 2, (R)-20 in preference to (S)-20 was obtained in 98% yield and 80% ee. In this manner, the enantioselecvity was switched by controlling the structure of chiral ligand. Additionally, the reversal of enantioselectivity was also achieved by changing the Cu precatalyst from Cu(OTf)(2) to Cu(acac)(2) with the same ligand. The combination of Cu(acac)(2) with CH(2)-bridged azolium salt 1 in the reaction of 17 with Bu(2)Zn led to formation of (R)-20 as a major product in 55% yield and 80% ee. This result was in contrast to the Cu(OTf)(2)/1 catalytic system, where the 1,4-adduct with opposite configuration was obtained. Moreover, use of the Cu(acac)(2)/2 catalytic system produced (S)-20, while (R)-20 was formed by the Cu(OTf)(2)/2 catalytic system. Thus, it was found that either varying the linker of the chiral ligands or changing the counterion of Cu species between a OTf and acac ligand initially on the metal led to dual enantioselective control in the 1,4-addition reaction.     

In search of ionic liquids incorporating azolate anions

Twenty-eight novel salts with tetramethyl-, tetraethyl-, and tetrabutylammonium and 1-butyl-3-methylimidazolium cations paired with 3,5-dinitro-1,2,4-triazolate, 4-nitro-1,2,3-triazolate, 2,4-dinitroimidazolate, 4,5-dinitroimidazolate, 4,5-dicyanoimidazolate, 4-nitroimidazolate, and tetrazolate anions have been prepared and characterized by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and single-crystal X-ray crystallography. The effects of cation and anion type and structure on the physicochemical properties of the resulting salts, including several ionic liquids, have been examined and discussed. Ionic liquids (defined as having m.p.<100 degrees C) were obtained with all combinations of the 1-butyl-3-methylimidazolium cation ([C(4)mim](+)) and the heterocyclic azolate anions studied, and with several combinations of tetraethyl or tetrabutylammonium cations and the azolate anions. The [C(4)mim](+) azolates were liquid at room temperature exhibiting large liquid ranges and forming glasses on cooling with glass-transition temperatures in the range of -53 to -82 degrees C (except for the 3,5-dinitro-1,2,4-triazolate salt with m.p. 33 degrees C). Six crystal structures of the corresponding tetraalkylammonium salts were determined and the effects of changes to the cations and anions on the packing of the structure have been investigated.     

New thiocarbonyl iridium and rhodium complexes with azolate type ligands

Transition Metal Chemistry -     

含能盐和含能离子液体

近年来含能盐和含能离子液体由于其独特的性质而受到广泛关注。本文综述了多种含能盐和含能离子液体（阳离子包括三唑、四唑、双环唑、六次甲基四胺等;阴离子包括硝酸根、高氯酸根、硝基唑、叠氮根、四硝基铝、多腈基化合物、二硝基尿素等）的合成;结合其表征结果分析了阳离子上的取代基以及阴阳离子对它们的性能如熔点、生成焓、密度等的影响。对含能盐和含能离子液体在炸药和推进剂方面的应用进行了展望。     

Energetic Materials Based on the 5‐Azido‐3‐nitro‐1, 2,4‐tri­azolate Anion

This study presents the preparation of 5‐azido‐3‐nitro‐1H‐1, 2,4‐triazole ( 1 ) in both good yield and high purity, starting from commercially available chemicals in a three step synthesis. Furthermore, several metal and nitrogen‐rich salts with sodium ( 3 ), potassium ( 4 ), cesium ( 5 ), silver ( 6 ), lead ( 7 ), ammonium ( 8 ), guanidinium ( 9 ), and aminoguanidinium ( 10 ) were prepared by simple acid‐base reactions. All compounds were well characterized by various means, including vibrational (IR, Raman) and multinuclear (¹H, ¹³C, ¹⁴N, ¹⁵N) NMR spectroscopy, mass spectrometry, and DSC. Additionally the structure of 7 was determined by single‐crystal X‐ray diffraction. The sensitivities towards various outer stimuli (impact, friction, electrostatic discharge) were determined according to BAM standards. The metal salts were tested as potential primary explosives utilizing various preliminary tests.     

Energetic polymer salts from 1‐vinyl‐1,2,4‐triazole derivatives

Energetic polymers salts from 1‐vinyl‐1,2,4‐triazole derivatives have been synthesized via free radical polymerization of 1‐vinyl‐1,2,4‐triazolium monomer salts or by protonation of poly(1‐vinyl‐1,2,4‐triazole) with inorganic or organic acids. Standard enthalpies of formation of the new monomer salts were calculated using the computationally feasible DFT(B3LYP) and MP2 methods in conjunction with an empirical approach based on densities of salts. Compared with the monomer salts, the polymer salts have good thermal properties with high densities > 1.5 g cm^?3. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2414–2421, 2008     

Energetic salts of azotetrazolate, iminobis(5-tetrazolate) and 5, 5'-bis(tetrazolate)

Energetic ionic salts of azotetrazolate (AT), iminobis(5-tetrazolate) (IBT) and 5, 5'-bis(tetrazole) (BT) were synthesized; 1-methyl-4-aminotriazolium azotetrazolate has a layered structure and exhibits a heat of formation of +4360 kJ kg(-1).