New Hydrazinium Azide Compounds

The synthesis and characterization of several azide salts of organic hydrazinium derivatives is reported. The crystal structures of N‐amino‐1‐azoniacycloheptane azide, morpholinium azide, N,N‐dibenzylhydrazine and phenylhydrazinium azide phenylhydrazinate were determined. The thermal, shock and friction sensitivity of these compounds was investigated. For several compounds the products formed in the explosive decomposition were determined.     

Vitamin B12 Phosphate Conjugation and Its Effect on Binding to the Human B12‐Binding Proteins Intrinsic Factor and Haptocorrin

The binding of vitamin B₁₂ derivatives to human B₁₂ transporter proteins is strongly influenced by the type and site of modification of the cobalamin original structure. We have prepared the first cobalamin derivative modified at the phosphate moiety. The reaction conditions were fully optimized and its limitations examined. The resulting derivatives, particularly those bearing terminal alkyne and azide groups, were isolated and used in copper‐catalyzed alkyne–azide cycloaddition reactions (CuAAC). Their sensitivity towards light revealed their potential as photocleavable molecules. The binding abilities of selected derivatives were examined and compared with cyanocobalamin. The interaction of the alkylated derivatives with haptocorrin was less affected than the interaction with intrinsic factor. Furthermore, the configuration of the phosphate moiety was irrelevant to the binding process.     

New Energetic Copper(II) Complexes With Pyrazolyl Type Ligands

Nine Cu^II complexes ( I – IX ) containing the azide ion and bis‐2,6‐(pyrazol‐1‐yl)pyridine (pp), bis‐2,6‐(pyrazol‐1‐yl)pyridine (dmpp), and 2‐(pyrazol‐1‐yl)‐6‐(3,5‐dimethylpyrazol‐1‐yl)pyridine (mpp), which are derivatives of pyrazolylpyridine, were prepared in nonaqueous medium. These complexes were characterized by elemental analyses and IR spectroscopy. Crystals of one of these complexes [CumppClN₃ ( VII )] were prepared in suitable size, and a molecular structure of this complex was obtained with X‐ray diffraction method. Complexes were examined by thermogravimetry and differential scanning calorimetry methods. Thermal decomposition was observed in complexes including two azide groups similar to that seen in explosives. In the complexes containing one azide group, formation of the Cu^I complexes was observed after thermal decomposition of the azide group.     

Increasing the hydrophilicity of star‐shaped amphiphilic co‐networks by using of PEG and dendritic s‐PCL cross‐linkers

New hyperbranched hydrophobic cross‐linkers with peripheral azide groups were synthesized as follows: First, star‐shaped polycaprolactones (sPCL) were synthesized by ring‐opening polymerization of caprolactone in the presence of pentaerythritol and tin (II) octoate. In the next step, sequential acrylation, Micheal addition, tosylation, and azidation by acryloyl chloride, diethanol amine, tosyl chloride, and sodium azide were respectively exploited to synthesize azide‐functionalized hyperbranched star‐shaped polycaprolactones which were named sPCL‐acrylate‐diethanolamine‐azide (sPCL‐AC‐DEA‐N₃) and sPCL‐acrylate‐diethanolamine‐acrylate‐diethanolamine‐azide (sPCL‐AC‐DEA‐AC‐N₃). All steps were thoroughly characterized by FT‐IR and ¹H NMR spectroscopy. The GPC analysis showed that the molecular weight of sPCL increased after two azide functionalizations. Amphiphilic hydrogels based on sPCL‐AC‐DEA‐N₃ (M_n = 8130 g/mol) and sPCL‐AC‐DEA‐AC‐N₃ (M_n = 10112 g/mol) with linear alkyne‐terminated polyethylene glycols (PEG) (M_n = 2000, 4000, and 6000 g/mol) were synthesized through click coupling between azide and alkyne groups. In both hydrogels, the swelling ratio increased by increasing the molecular weight of PEG. The obtained results showed that the branching of the cross‐linker, significantly affected the swelling ratio of hydrogels. For instance, the swelling ratio of sPCL‐AC‐DEA‐AC‐N₃ and PEG‐6000 (Q = 900) was higher than sPCL‐AC‐DEA‐N₃ and PEG‐6000 (Q = 600). Despite the high cross‐linking density of sPCL‐AC‐DEA‐AC‐DEA‐N₃–based hydrogels, the amount of released theophylline was higher than sPCL‐AC‐DEA‐N₃–based hydrogels, due to the high content of PEG in these hydrogels.     

(2‐Hydroxy­ethyl)­hydrazinium(2+) dichloride

The crystal structure of the title compound, C₂H₁₀N₂O²⁺·2Cl⁻, is built up from one 2‐hydroxy­ethyl­hydrazinium(2+) cation and two Cl⁻ anions. The mol­ecular structure is stabilized by O—H⋯Cl and N—H⋯Cl hydrogen bonds. The crystal structure is stabilized by one N—H⋯O and three N—H⋯Cl inter­actions, and the three‐dimensional network of hydrogen bonds stabilizes the crystal packing. All five hydrazinium H atoms are involved in hydrogen bonds to Cl⁻ anions. The Cl⋯H contact distances range from 2.122 (15) to 2.809 (14) Å.     

Synthesis of 5‐Aminotetrazole‐1 N‐oxide and Its Azo Derivative: A Key Step in the Development of New Energetic Materials

1‐Hydroxy‐5‐aminotetrazole ( 1 ), which is a long‐desired starting material for the synthesis of hundreds of new energetic materials, was synthesized for the first time by the reaction of aqueous hydroxylamine with cyanogen azide. The use of this unique precursor was demonstrated by the preparation of several energetic compounds with equal or higher performance than that of commonly used explosives, such as hexogen (RDX). The prepared compounds, including energetic salts of 1‐hydroxy‐5‐aminotetrazole (hydroxylammonium ( 2 , two polymorphs) and ammonium ( 3 )), azo‐coupled derivatives (potassium ( 5 ), hydroxylammonium ( 6 ), ammonium ( 7 ), and hydrazinium 5,5′‐azo‐bis(1‐N‐oxidotetrazolate ( 8 , two polymorphs)), as well as neutral compounds 5,5′‐azo‐bis(1‐oxidotetrazole) ( 4 ) and 5,5′‐bis(1‐oxidotetrazole)hydrazine ( 9 ), were intensively characterized by low‐temperature X‐ray diffraction, IR, Raman, and multinuclear NMR spectroscopy, elemental analysis, and DSC. The calculated energetic performance, by using the EXPLO5 code, based on the calculated (CBS‐4M) heats of formation and X‐ray densities confirm the high energetic performance of tetrazole‐N‐oxides as energetic materials. Last but not least, their sensitivity towards impact, friction, and electrostatic discharge were explored. 5,5′‐Azo‐bis(1‐N‐oxidotetrazole) deflagrates close to the DDT (deflagration‐to‐detonation transition) faster than all compounds that have been investigated in our research group to date.     

Synthesis and spectral characterization of N‐[2‐(4‐halophenoxy)‐3‐(3‐chlorophenyl)‐3, 4‐dihydro‐2H‐1,3,2‐λ5‐benzoxazaphosphinin‐2‐yliden]‐N‐substituted amines by the Staudinger reaction

The synthesis of the title compounds was accomplished in four steps. The synthetic route involves the preparation of Schiff's base by reacting salicylaldehyde with m‐chloroaniline in EtOH. The Schiff's base was then reduced with NaBH₄/MeOH. In the second step, PCl₃ was reacted with p‐chlorophenol/p‐bromophenol in THF in the presence of Et₃N to obtain P(III) dichloride derivatives. The reduced Schiff's base and dichloride derivatives were reacted in equimolar quantities in the presence of Et₃N in THF to get the cyclized product. Alkyl azides were prepared by reacting alkyl bromides with sodium azide, and then alkyl azides were treated with the cyclized product to obtain the title compounds. The structure of these novel compounds was elucidated by elemental analysis, IR, ¹H, ¹³C, ³¹P NMR, and mass spectroscopy. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:499–504, 2010; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20639     

Postsynthetic Metal and Ligand Exchange in MFU‐4l: A Screening Approach toward Functional Metal–Organic Frameworks Comprising Single‐Site Active Centers

The isomorphous partial substitution of Zn²⁺ ions in the secondary building unit (SBU) of MFU‐4l leads to frameworks with the general formula [M_xZn_(5–x)Cl₄(BTDD)₃], in which x≈2, M=Mn^II, Fe^II, Co^II, Ni^II, or Cu^II, and BTDD=bis(1,2,3‐triazolato‐[4,5‐b],[4′,5′‐i])dibenzo‐[1,4]‐dioxin. Subsequent exchange of chloride ligands by nitrite, nitrate, triflate, azide, isocyanate, formate, acetate, or fluoride leads to a variety of MFU‐4l derivatives, which have been characterized by using XRPD, EDX, IR, UV/Vis‐NIR, TGA, and gas sorption measurements. Several MFU‐4l derivatives show high catalytic activity in a liquid‐phase oxidation of ethylbenzene to acetophenone with air under mild conditions, among which Co‐ and Cu derivatives with chloride side‐ligands are the most active catalysts. Upon thermal treatment, several side‐ligands can be transformed selectively into reactive intermediates without destroying the framework. Thus, at 300 °C, Co^II‐azide units in the SBU of Co‐MFU‐4l are converted into Co^II‐isocyanate under continuous CO gas flow, involving the formation of a nitrene intermediate. The reaction of Cu^II‐fluoride units with H₂ at 240 °C leads to Cu^I and proceeds through the heterolytic cleavage of the H₂ molecule.     

A Cation‐Exchange Approach for the Fabrication of Efficient Methylammonium Tin Iodide Perovskite Solar Cells

Tin‐based halide perovskite materials have been successfully employed in lead‐free perovskite solar cells, but the overall power conversion efficiencies (PCEs) have been limited by the high carrier concentration from the facile oxidation of Sn²⁺ to Sn⁴⁺. Now a chemical route is developed for fabrication of high‐quality methylammonium tin iodide perovskite (MASnI₃) films: hydrazinium tin iodide (HASnI₃) perovskite film is first solution‐deposited using presursors hydrazinium iodide (HAI) and tin iodide (SnI₂), and then transformed into MASnI₃ via a cation displacement approach. With the two‐step process, a dense and uniform MASnI₃ film is obtained with large grain sizes and high crystallization. Detrimental oxidation is suppressed by the hydrazine released from the film during the transformation. With the MASnI₃ as light harvester, mesoporous perovskite solar cells were prepared, and a maximum power conversion efficiency (PCE) of 7.13 % is delivered with good reproducibility.     

Energetic 2,2‐Dimethyltriazanium Salts: A New Family of Nitrogen‐Rich Hydrazine Derivatives

Amination of 1,1‐dimethylhydrazine with NH₂Cl or hydroxylamine‐O‐sulfonic acid yields 2,2‐dimethyltriazanium (DMTZ) chloride ( 3 ) and sulphate ( 4 ), respectively. The DMTZ cation was paired with the nitrogen‐rich anions 5‐aminotetrazolate ( 5 ), 5‐nitrotetrazolate ( 6 ), 5,5′‐azobistetrazolate ( 7 ), and azide ( 8 ), yielding a new family of energetic salts. The synthesis was carried out by metathesis reactions of salts 3 or 4 and a suitable silver or barium salt. To minimize the risks involved when using heavy metal salts, we used electrodialysis for the synthesis of azide 8 , which avoids the use of highly sensitive species. The DMTZ derivatives were characterized by IR and multinuclear NMR spectroscopy, elemental analysis, and X‐ray diffraction. Thermal stabilities were measured using DSC analysis and their sensitivities towards classical stimuli were determined using standard tests. Lastly, the relationship between hydrogen bonding in the solid state and sensitivity is discussed.     

Strain‐Promoted Azide–Alkyne Cycloaddition with Ruthenium(II)–Azido Complexes

The reactivity of an exemplary ruthenium(II)–azido complex towards non‐activated, electron‐deficient, and towards strain‐activated alkynes at room temperature and low millimolar azide and alkyne concentrations has been investigated. Non‐activated terminal and internal alkynes failed to react under such conditions, even under copper(I) catalysis conditions. In contrast, as expected, rapid cycloaddition was observed with electron‐deficient dimethyl acetylenedicarboxylate (DMAD) as the dipolarophile. Since DMAD and related propargylic esters are excellent Michael acceptors and thus unsuitable for biological applications, we investigated the reactivity of the azido complex towards cycloaddition with derivatives of cyclooctyne (OCT), bicyclo[6.1.0]non‐4‐yne (BCN), and azadibenzocyclooctyne (ADIBO). While no reaction could be observed in the case of the less strained cyclooctyne OCT, the highly strained cyclooctynes BCN and ADIBO readily reacted with the azido complex, providing the corresponding stable triazolato complexes, which were amenable to purification by conventional silica gel column chromatography. An X‐ray crystal structure of an ADIBO cycloadduct was obtained and verified that the formed 1,2,3‐triazolato ligand coordinates the metal center through the central N2 atom. Importantly, the determined second‐order rate constant for the ADIBO cycloaddition with the azido complex (k₂=6.9 × 10^?2 M ^?1 s^?1) is comparable to the rate determined for the ADIBO cycloaddition with organic benzyl azide (k₂=4.0 × 10^?1 M ^?1 s^?1). Our results demonstrate that it is possible to transfer the concept of strain‐promoted azide–alkyne cycloaddition (SPAAC) from purely organic azides to metal‐coordinated azido ligands. The favorable reaction kinetics for the ADIBO‐azido‐ligand cycloaddition and the well‐proven bioorthogonality of strain‐activated alkynes should pave the way for applications in living biological systems.     

Synthesis and Characterization of a Novel Class of PPV Derivatives Covalently Linked to C60

Poly(phenylenevinylene) (PPV) derivatives covalently linked to fullerene C₆₀ (PPV‐1‐C₆₀ and PPV‐2‐C₆₀) were synthesized by cycloaddition reaction between C₆₀ and azide group‐containing PPV derivatives. By tuning the initial feed ratio of the azido monomer, the content of C₆₀ in the copolymers was controlled. The copolymers were partially soluble in common organic solvents and were characterized by means of ¹H NMR, FT‐IR, UV‐Vis and fluorescence spectroscopy, as well as by GPC, TGA and cyclic voltammetry techniques.     

Synthesis of well‐defined azide‐terminated poly(vinyl alcohol) and their subsequent modification via click chemistry

A new azide‐functionalized xanthate, S‐(4‐azidomethylbenzyl) O‐(2‐methoxyethyl) xanthate, was synthesized and used to mediate the reversible addition fragmentation chain transfer polymerization of vinyl acetate. The polymerization was demonstrated to be controlled, and well‐defined PVAc with α‐azide, ω‐xanthate groups were obtained, the xanthate groups of which were further removed by radical‐induced reduction with lauroyl peroxide in the presence of excess 2‐propanol. Hydrolysis of α‐azide‐terminated PVAc (N₃‐PVAc) led to the formation of the corresponding α‐azide‐terminated PVA (N₃‐PVA). Finally, end‐modification of N₃‐PVA by click chemistry with alkyne‐end‐capped poly(caprolactone) (A‐PCL), alkynyl‐mannose, and alkynyl‐pyrene was carried out to obtain a new block copolymer PCL‐b‐PVA, and two PVA with mannose or pyrene as the end functional groups. The polymers were characterized by gel permeation chromatography, ¹H NMR spectroscopy, and FTIR. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4494–4504, 2009     

catena‐Poly[[{4‐bromo‐2‐[2‐(dimethyl­amino)ethyl­imino­methyl]­phenol­ato}­copper(II)]‐μ‐azido]

The title complex, [Cu(C₁₁H₁₄BrN₂O)(N₃)]_n, is an inter­esting azide‐bridged polynuclear copper(II) compound. The Cu^II atom is five‐coordinated in a square‐pyramidal configuration, with one O and two N atoms of one Schiff base and one terminal N atom of a bridging azide ligand defining the basal plane, and another terminal N atom of another bridging azide ligand occupying the axial position. The {4‐bromo‐2‐[2‐(dimethyl­amino)ethyl­imino­meth­yl]phenolato}copper(II) moieties are linked by the bridging azide ligands, forming polymeric chains running along the b axis. Adjacent chains are further linked by weak Br⋯Br inter­actions into a sheet.     

Visible‐Light‐Accelerated Copper(II)‐Catalyzed Regio‐ and Chemoselective Oxo‐Azidation of Vinyl Arenes

The visible‐light‐accelerated oxo‐azidation of vinyl arenes with trimethylsilylazide and molecular oxygen as stoichiometric oxidant was achieved. In contrast to photocatalysts based on iridium, ruthenium, or organic dyes, [Cu(dap)₂]Cl or [Cu(dap)Cl₂] were found to be unique for this transformation, which is attributed to their ability to interact with the substrates through ligand exchange and rebound mechanisms. Cu^II is proposed as the catalytically active species, which upon coordinating azide will undergo light‐accelerated homolysis to form Cu^I and azide radicals. This activation principle (Cu^II‐X→Cu^I+X^.) opens up new avenues for copper‐based photocatalysis.     

Ligand‐Based Control of Single‐Site vs. Multi‐Site Reactivity by a Trichromium Cluster

The trichromium cluster (^tbsL)Cr₃(thf) ([^tbsL]^6?=[1,3,5‐C₆H₉(NC₆H₄‐o‐NSi^tBuMe₂)₃]^6?) exhibits steric‐ and solvation‐controlled reactivity with organic azides to form three distinct products: reaction of (^tbsL)Cr₃(thf) with benzyl azide forms a symmetrized bridging imido complex (^tbsL)Cr₃(μ³‐NBn); reaction with mesityl azide in benzene affords a terminally bound imido complex (^tbsL)Cr₃(μ¹‐NMes); whereas the reaction with mesityl azide in THF leads to terminal N‐atom excision from the azide to yield the nitride complex (^tbsL)Cr₃(μ³‐N). The reactivity of this complex demonstrates the ability of the cluster‐templating ligand to produce a well‐defined polynuclear transition metal cluster that can access distinct single‐site and cooperative reactivity controlled by either substrate steric demands or reaction media.     

Potassium 1,1′‐Dinitramino‐5,5′‐bistetrazolate: A Primary Explosive with Fast Detonation and High Initiation Power

Adequate primary explosives such as lead azide mostly contain toxic ingredients, which have to be replaced. A new candidate that shows high potential, potassium 1,1′‐dinitramino‐5,5′‐bistetrazolate (K₂DNABT), was synthesized by a sophisticated synthetic procedure based on dimethylcarbonate and glyoxal. It was intensively characterized for its chemical (X‐ray diffraction, EA, NMR and vibrational spectroscopy) and physico‐chemical properties (sensitivity towards impact, friction, and electrostatic, DSC). The obtained primary explosive combines good thermal stability with the desired mechanical stability. Owing to its high heat of formation (326 kJ mol^?1) and density (2.11 g cm^?3), impressive values for its detonation velocity (8330 m s^?1) and pressure (311 kbar) were computed. Its superior calculated performance output was successfully confirmed and demonstrated by different convenient energetic test methods.     

The Photochemistry of [FeIIIN3(cyclam‐ac)]PF6 at 266 nm

The photochemistry of iron azido complexes is quite challenging and poorly understood. For example, the photochemical decomposition of [Fe^IIIN₃(cyclam‐ac)]PF₆ ([ 1 ]PF₆), where cyclam‐ac represents the 1,4,8,11‐tetraazacyclotetradecane‐1‐acetate ligand, has been shown to be wavelength‐dependent, leading either to the rare high‐valent iron(V) nitrido complex [Fe^VN(cyclam‐ac)]PF₆ ([ 3 ]PF₆) after cleavage of the azide N_α? N_β bond, or to a photoreduced Fe^II species after Fe? N_azide bond homolysis. The mechanistic details of this intriguing reactivity have never been studied in detail. Here, the photochemistry of 1 in acetonitrile solution at room temperature has been investigated using step‐scan and rapid‐scan time‐resolved Fourier transform infrared (FTIR) spectroscopy following a 266 nm, 10 ns pulsed laser excitation. Using carbon monoxide as a quencher for the primary iron‐containing photochemical product, it is shown that 266 nm excitation of 1 results exclusively in the cleavage of the Fe? N_azide bond, as was suspected from earlier steady‐state irradiation studies. In argon‐purged solutions of [ 1 ]PF₆, the solvent‐stabilized complex cation [Fe^II(CH₃CN)(cyclam‐ac)]⁺ ( 2 red ) together with the azide radical (N₃^.) is formed with a relative yield of 80 %, as evidenced by the appearance of their characteristic vibrational resonances. Strikingly, step‐scan experiments with a higher time resolution reveal the formation of azide anions (N₃^?) during the first 500 ns after photolysis, with a yield of 20 %. These azide ions can subsequently react thermally with 2 red to form [Fe^IIN₃(cyclam‐ac)] ( 1 red ) as a secondary product of the photochemical decomposition of 1 . Molecular oxygen was further used to quench 1 red and 2 red to form what seems to be the elusive complex [Fe(O₂)(cyclam‐ac)]⁺ ( 6 ).     

Reactions of Rare‐Earth Metal Based Lewis Pairs with Azides†

The reactivity of homoleptic rare‐earth metal aryloxide based Lewis pairs toward organic azide substrates has been investigated herein. Treatment of RE(OAr)₃ (RE = La, Sm, Y, and Sc, Ar = 2,6‐^tBu₂‐C₆H₃), PEt₃ and Me₃SiN₃ in 2 : 1 : 1 molar ratio resulted in formation of separated ion pair complexes [Me₃Si‐PEt₃]⁺[(ArO)₃RE‐N=N=N‐RE(OAr)₃]^– under mild conditions. Replacement of phosphine with the nitrogen‐containing Lewis base 1,4‐diazabicyclo[2.2.2]octane (DABCO) produced analogous rare‐earth azide complexes with [Me₃Si‐DABCO]⁺ counterions. In contrast, reaction of the La(OAr)₃/PEt₃ Lewis pair with 1‐adamantyl azide (AdN₃) afforded the typical frustrated Lewis pair‐type 1,1‐addition product. A tetrahydrofuran ring‐opening reaction was also observed for the resulting rare‐earth azide complex with the [Me₃Si‐PEt₃]⁺ cation, with cleavage of the C—O bond by Si/P cooperation.     

Selective Detection of Hg2+ Ions with Boron Dipyrromethene‐Based Fluorescent Probes Appended with a Bis(1,2,3‐triazole)amino Receptor

By using a copper‐promoted alkyne–azide cycloaddition reaction, two boron dipyrromethene (BODIPY) derivatives bearing a bis(1,2,3‐triazole)amino receptor at the meso position were prepared and characterized. For the analogue with two terminal triethylene glycol chains, the fluorescence emission at 509 nm responded selectively toward Hg²⁺ ions, which greatly increased the fluorescence quantum yield from 0.003 to 0.25 as a result of inhibition of the photoinduced electron transfer (PET) process. By introducing two additional rhodamine moieties at the termini, the resulting conjugate could also detect Hg²⁺ ions in a highly selective manner. Upon excitation at the BODIPY core, the fluorescence emission of rhodamine at 580 nm was observed and the intensity increased substantially upon addition of Hg²⁺ ions due to inhibition of the PET process followed by highly efficient fluorescence resonance energy transfer (FRET) from the BODIPY core to the rhodamine moieties. The Hg²⁺‐responsive fluorescence change of these two probes could be easily seen with the naked eye. The binding stoichiometry between the probes and Hg²⁺ ions in CH₃CN was determined to be 1:2 by Job′s plot analysis and ¹H NMR titration, and the binding constants were found to be (1.2±0.1)×10¹¹ m ^?2 and (1.3±0.3)×10¹⁰ m ^?2, respectively. The overall results suggest that these two BODIPY derivatives can serve as highly selective fluorescent probes for Hg²⁺ ions. The rhodamine derivative makes use of a combined PET‐FRET sensing mechanism which can greatly increase the sensitivity of detection.