Synthesis and Reactivity of Tricoordinate Organoberyllium Azides

A series of terminal mono- and disubstituted beryllium azides of the form [(CAAC)Be(N3)R] (R=CAACH, Dur; CAACH/CAAC=1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-yl/idene, Dur=2,3,5,6-tetramethylphenyl) and [L2Be(N3)2] (L=CAACNH=1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-imine, IiPrMe=1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene), respectively, were synthesized and characterized by NMR spectroscopy and X-ray crystallography. Thermolysis and photolysis products of these first examples of tricoordinate azidoberyllium complexes evidence extensive ligand scrambling and the formal insertion of nitrenes into the CAAC-Be bond, generating cyclic alkyl(amino)imine (CAAI) ligands. Furthermore, the reaction with a small N-heterocyclic carbene (NHC) leads to unexpected CAAC-NHC ligand exchange, while the reaction with pentaphenylborole yields the first γ-azide adduct of a borole, long postulated to be the first step in the synthesis of 1,2-azaborinines from boroles and azides.

Azido-mediated intermolecular interactions of transition metal complexes

The coordinated azido ligand has a variety of ways to establish intermolecular contacts whose nature is computationally analysed in this work on dimers of the [N3-Hg(CF3)] complex with different interactions involving only N⋯N contacts, or with an additional Hg⋯N contact. The applied tools include the molecular electrostatic map of the monomer, an energy decomposition analysis (EDA), a topological AIM analysis of the electron density and the study of NCI (non-covalent interactions) isosurfaces. The interactions between two azido ligands are found to be weakly stabilizing (by 0.2 to 2.7 kcal mol-1), topology-dependent and require dispersion forces to complement orbital and electrostatic stabilization. Those interactions are supplemented by the formation of simultaneous Hg⋯N secondary interactions by about -1 kcal mol-1, and by the ability of the monomer to simultaneously interact with several neighbours in the crystal structure.

Jellyfish-type Dinuclear Hafnium Azido Complexes: Synthesis and Reactivity

Di- and multinuclear hafnium complexes bridged by ligands have been rarely reported. In this article, a novel 3,5-disubstituted pyrazolate-bridged ligand LH5 with two [N2 N]2- -type chelating side arms was designed and synthesized, which supported a series of dinuclear hafnium complexes. Dinuclear hafnium azides [LHf2 (μ-1,1-N3 )2 (N3 )2 ][Na(THF)4 ] 3 and [LHf2 (μ-1,1-N3 )2 (N3 )2 ][Na(2,2,2-Kryptofix)] 4 were further synthesized and structurally characterized, featuring two sets of terminal and bridging azido ligands like jellyfishes. The reactivity of 3 under reduction conditions was conducted, leading to a formation of a tetranuclear hafnium imido complex [L1 Hf2 (μ1 -NH)(N3 ){μ2 -K}]2 5. DFT calculations revealed that the mixed imido azide 5 was generated via an intramolecular C-H insertion from a putative dinuclear HfIV -nitridyl intermediate.

The First Alkaline-Earth Azidoaurate(III), Ba[Au(N3 )4 ]2 ⋅ 4 H2 O

Transparent, dark orange Ba[Au(N₃ )₄ ]₂  ⋅ 4 H₂ O was synthesized by reaction of Ba(N₃ )₂ and AuCl₃ or HAuCl₄ in aqueous solution. The novel barium tetraazidoaurate(III) tetrahydrate crystallizes in the monoclinic space group Cc (no. 9) with a=1813.68(17) pm, b=1737.95(11) pm, c=682.04(8) pm and β=108.849(4)°. The predominant structural features of Ba[Au(N₃ )₄ ]₂  ⋅ 4 H₂ O are two crystallographically independent discrete anions [Au(N₃ )₄ ]^- with gold in a tetragonal planar coordination by nitrogen. Vibrational spectra show good agreement with those of other azidoaurates(III). Upon drying, this salt was shown to be a highly explosive material.

Synthesis and Characterization of Hypercoordinated Silicon Anions: Catching Intermediates of Lewis Base Catalysis

Anionic hypercoordinated silicates with weak donors were proposed as key intermediates in numerous silicon-based reactions. However, their short-lived nature rendered even spectroscopic observations highly challenging. Here, we characterize hypercoordinated silicon anions, including the first bromido-, iodido-, formato-, acetato-, triflato- and sulfato-silicates. This is enabled by a new, donor-free polymeric form of Lewis superacidic bis(perchlorocatecholato)silane 1. Spectroscopic, structural, and computational insights allow a reassessment of Gutmann's empirical rules for the role of silicon hypercoordination in synthesis and catalysis. The electronic perturbations of 1 exerted on the bound anions indicate pronounced substrate activation.

Platinum(IV)-azido monocarboxylato complexes are photocytotoxic under irradiation with visible light

Complexes trans,trans,trans-[Pt(N3)2(OH)(OCOR)(py)2] where py = pyridine and where OCOR = succinate (1); 4-oxo-4-propoxybutanoate (2) and N-methylisatoate (3) have been synthesized by derivation of trans,trans,trans-[Pt(OH)2(N3)2(py)2] (4) and characterised by NMR and EPR spectroscopy, ESI-MS and X-ray crystallography. Irradiation of 1-3 with green (517 nm) light initiated photoreduction to Pt(ii) and release of the axial ligands at a 3-fold faster rate than for 4. TD-DFT calculations showed dissociative transitions at longer wavelengths for 1 compared to 4. Complexes 1 and 2 showed greater photocytotoxicity than 4 when irradiated with 420 nm light (A2780 cell line IC50 values: 2.7 and 3.7 μM) and complex 2 was particularly active towards the cisplatin-resistant cell line A2780cis (IC50 3.7 μM). Unlike 4, complexes 1-3 were phototoxic under green light irradiation (517 nm), with minimal toxicity in the dark. A pKa(H2O) of 5.13 for the free carboxylate group was determined for 1, corresponding to an overall negative charge during biological experiments, which crucially, did not appear to impede cellular accumulation and photocytotoxicity.

Automated Crystal Structure Determination Has its Pitfalls: Correction to the Crystal Structures of Iodine Azide

Previously published crystal structure determinations of two modifications of iodine azide (IN3 ) are corrected. In the original determinations, the very weak X-ray reflections with odd k Miller indices had been discarded, resulting in too small unit cells and models with misordered, partly occupied atomic positions. Using the original diffraction data, refinements with the correct unit cells yield structures of polymeric (-I-N3 -)n chains that are interlocked to layers. A skilled look at the primary X-ray data is always recommended to overcome the lack of crystallographic expertise of computers at automated structure determinations.

A metastable RuIII azido complex with metallo-Staudinger reactivity

The metastable purple [(Py5Me2)RuIII(N3)]2+ ion reacts with PPh3 at room temperature to form the phosphinimine complex [(Py5Me2)RuII(N(H)PPh3)]2+ and free [H2NPPh3]+ in a combined 23% conversion. Mechanistic studies suggest that this is the first metallo-Staudinger reaction of a late transition metal that bypasses the nitrido mechanism and instead utilizes a Ru-N[double bond, length as m-dash]N[double bond, length as m-dash]N-PPh3 phosphazide intermediate.

Properties and Promise of Catenated Nitrogen Systems As High-Energy-Density Materials

The properties of catenated nitrogen molecules, molecules containing internal chains of bonded nitrogen atoms, is of fundamental scientific interest in chemical structure and bonding, as nitrogen is uniquely situated in the periodic table to form kinetically stable compounds often with chemically stable N-N bonds but which are thermodynamically unstable in that the formation of stable multiply bonded N₂ is usually thermodynamically preferable. This unique placement in the periodic table makes catenated nitrogen compounds of interest for development of high-energy-density materials, including explosives for defense and construction purposes, as well as propellants for missile propulsion and for space exploration. This review, designed for a chemical audience, describes foundational subjects, methods, and metrics relevant to the energetic materials community and provides an overview of important classes of catenated nitrogen compounds ranging from theoretical investigation of hypothetical molecules to the practical application of real-world energetic materials. The review is intended to provide detailed chemical insight into the synthesis and decomposition of such materials as well as foundational knowledge of energetic science new to most chemists.

Borane Adducts of Hydrazoic Acid and Organic Azides: Intermediates for the Formation of Aminoboranes

The reaction of HN₃ with the strong Lewis acid B(C₆ F₅ )₃ led to the formation of a very labile HN₃ ⋅B(C₆ F₅ )₃ adduct, which decomposed to an aminoborane, H(C₆ F₅ )NB(C₆ F₅ )₂ , above -20 °C with release of molecular nitrogen and simultaneous migration of a C₆ F₅ group from boron to the nitrogen atom. The intermediary formation of azide-borane adducts with B(C₆ F₅ )₃ was also demonstrated for a series of organic azides, RN₃ (R=Me₃ Si, Ph, 3,5-(CF₃ )₂ C₆ H₃ ), which also underwent Staudinger-like decomposition along with C₆ F₅ group migration. In accord with experiment, computations revealed rather small barriers towards nitrogen release for these highly labile azide adducts for all organic substituents except R=Me₃ Si (m.p. 120 °C, T_dec =189 °C). Hydrolysis of the aminoboranes provided C₆ F₅ -substituted amines, HN(R)(C₆ F₅ ), in good yields.

Recent developments in the chemistry of metal oxopolyazides

The recent acomplished syntheses of novel metal oxopolyazides VO(N3)3, NbO(N3)3, NbO(N3)3·2CH3CN, MoO(N3)3, MoO(N3)3·2CH3CN, WO(N3)4, WO(N3)4·CH3CN, MoO2(N3)2, MoO2(N3)2·2CH3CN, WO2(N3)2, WO2(N3)2·2CH3CN and UO2(N3)2·CH3CN by the author is reviewed. The conversion of the compounds into 2,2'-bipyridine donor adducts and oxaazido metallates is discribed. The properties and X-ray crystal structures of the metal oxopolyazides are compared and discussed.

Structural versatility of the quasi-aromatic Möbius type zinc(ii)-pseudohalide complexes – experimental and theoretical investigations

In this contribution we report for the first time fabrication, isolation, structural and theoretical characterization of the quasi-aromatic Möbius complexes [Zn(NCS)₂L^I] (1), [Zn₂(μ_1,1-N₃)₂(L^I)₂][ZnCl₃(MeOH)]₂·6MeOH (2) and [Zn(NCS)L^II]₂[Zn(NCS)₄]·MeOH (3), constructed from 1,2-diphenyl-1,2-bis((phenyl(pyridin-2-yl)methylene)hydrazono)ethane (L^I) or benzilbis(acetylpyridin-2-yl)methylidenehydrazone (L^II), respectively, and ZnCl₂ mixed with NH₄NCS or NaN₃. Structures 1–3 are dictated by both the bulkiness of the organic ligand and the nature of the inorganic counter ion. As evidenced from single crystal X-ray diffraction data species 1 has a neutral discrete heteroleptic mononuclear structure, whereas, complexes 2 and 3 exhibit a salt-like structure. Each structure contains a Zn^II atom chelated by one tetradentate twisted ligand L^I creating the unusual Möbius type topology. Theoretical investigations based on the EDDB method allowed us to determine that it constitutes the quasi-aromatic Möbius motif where a metal only induces the π-delocalization solely within the ligand part: 2.44|e| in 3, 3.14|e| in 2 and 3.44|e| in 1. It is found, that the degree of quasi-aromatic π-delocalization in the case of zinc species is significantly weaker (by ∼50%) than the corresponding estimations for cadmium systems – it is associated with the Zn–N bonds being more polar than the related Cd–N connections. The ETS-NOCV showed, that the monomers in 1 are bonded primarily through London dispersion forces, whereas long-range electrostatic stabilization is crucial in 2 and 3. A number of non-covalent interactions are additionally identified in the lattices of 1–3.

Interplay between various types of non-covalent interactions allowed for isolation of rare examples of Zn(ii) based quasi-aromatic Möbius type species.

A carbon-free inorganic-metal complex consisting of an all-nitrogen pentazole anion, a Zn(ii) cation and H2O

A carbon-free inorganic-metal complex [Zn(H₂O)₄(N₅)₂]·4H₂O was synthesized by the ion metathesis of [Na(H₂O)(N₅)]·2H₂O solution with Zn(NO₃)₂·6H₂O. The complex was well characterized by IR and Raman spectroscopy, elemental analysis (EA), powder X-ray diffraction (PXRD), and differential scanning calorimetry (DSC). The structure of the complex was confirmed by single-crystal X-ray crystallography and a Zn(ii) ion is coordinated in a quadrilateral bipyramid environment in which the axial position is formed by two nitrogen atoms (N1) from two pentazolate rings (cyclo-N₅^-) and the equatorial plane is formed by four oxygen atoms (O1) from four coordinated water molecules. The thermal analysis of [Zn(H₂O)₄(N₅)₂]·4H₂O reveals that although water plays an important role in stabilizing cyclo-N₅^-, dehydration does not cause immediate decomposition of the anion. However, cyclo-N₅^- decomposed into N₃^- and N₂ gas at 107.9 °C (onset). Based on its chemical compatibility and stability, the complex exhibits promising potential as a modern environmentally-friendly energetic material.

Labile Low-Valent Tin Azides: Syntheses, Structural Characterization, and Thermal Properties

The first two examples of the class of tetracoordinate low-valent, mixed-ligand tin azido complexes, Sn(N₃)₂(L)₂, are shown to form upon reaction of SnCl₂ with NaN₃ and SnF₂ with Me₃SiN₃ in either pyridine or 4-picoline (2, L = py; 3, L = pic). These adducts of Sn(N₃)₂ are shock- and friction-insensitive and stable at r.t. under an atmosphere of pyridine or picoline, respectively. A new, fast, and efficient method for the preparation of Sn(N₃)₂ (1) directly from SnF₂, and by the stepwise de-coordination of py from 2 at r.t., is reported that yields 1 in microcrystalline form, permitting powder X-ray diffraction studies. Reaction of 1 with a nonbulky cationic H-bond donor forms the salt-like compound {C(NH₂)₃}Sn(N₃)₃ (4) which is comparably stable despite its high nitrogen content (55%) and the absence of bulky weakly coordinating cations that are conventionally deemed essential in related systems of homoleptic azido metallates. The spectroscopic and crystallographic characterization of the polyazides 1-4 provides insight into azide-based H-bonded networks and unravels the previously unknown structure of 1 as an important lighter binary azide homologue of Pb(N₃)₂. The atomic coordinates for 1 and 2-4 were derived from powder and single crystal XRD data, respectively; those for 1 are consistent with predictions made by DFT-D calculations under periodic boundary conditions.

A series of energetic metal pentazolate hydrates

Singly or doubly bonded polynitrogen compounds can decompose to dinitrogen (N₂) with an extremely large energy release. This makes them attractive as potential explosives or propellants, but also challenging to produce in a stable form. Polynitrogen materials containing nitrogen as the only element exist in the form of high-pressure polymeric phases, but under ambient conditions even metastability is realized only in the presence of other elements that provide stabilization. An early example is the molecule phenylpentazole, with a five-membered all-nitrogen ring, which was first reported in the 1900s and characterized in the 1950s. Salts containing the azide anion (N₃^-) or pentazenium cation (N₅⁺) are also known, with compounds containing the pentazole anion, cyclo-N₅^-, a more recent addition. Very recently, a bulk material containing this species was reported and then used to prepare the first example of a solid-state metal-N₅ complex. Here we report the synthesis and characterization of five metal pentazolate hydrate complexes [Na(H₂O)(N₅)]·2H₂O, [M(H₂O)₄(N₅)₂]·4H₂O (M = Mn, Fe and Co) and [Mg(H₂O)₆(N₅)₂]·4H₂O that, with the exception of the Co complex, exhibit good thermal stability with onset decomposition temperatures greater than 100 °C. For this series we find that the N₅^- ion can coordinate to the metal cation through either ionic or covalent interactions, and is stabilized through hydrogen-bonding interactions with water. Given their energetic properties and stability, pentazole-metal complexes might potentially serve as a new class of high-energy density materials or enable the development of such materials containing only nitrogen. We also anticipate that the adaptability of the N₅^- ion in terms of its bonding interactions will enable the exploration of inorganic nitrogen analogues of metallocenes and other unusual polynitrogen complexes.

The Uranium(VI) Oxoazides [UO2 (N3 )2 ⋅CH3 CN], [(bipy)2 (UO2 )2 (N3 )4 ], [(bipy)UO2 (N3 )3 ]- , [UO2 (N3 )4 ]2- , and [(UO2 )2 (N3 )8 ]4

The reaction between [UO₂ F₂ ] and an excess of Me₃ SiN₃ in acetonitrile solution results in fluoride-azide exchange and the uranium(VI) dioxodiazide adduct [UO₂ (N₃ )₂ ⋅CH₃ CN] was isolated in quantitative yield. The subsequent reaction of [UO₂ (N₃ )₂ ⋅CH₃ CN] with 2,2'-bipyridine (bipy) resulted in the formation of the azido-bridged binuclear complex [(bipy)₂ (UO₂ )₂ (N₃ )₄ ]. The triazido anion [(bipy)UO₂ (N₃ )₃ ]^- was obtained by the reaction of [UO₂ (N₃ )₂ ⋅CH₃ CN] with stoichiometric amounts of bipy and the ionic azide [PPh₄ ][N₃ ]. The reaction of [UO₂ (N₃ )₂ ] with two equivalents of the [PPh₄ ][N₃ ] resulted in the formation of the mononuclear tetraazido anion [UO₂ (N₃ )₄ ]^2- as well as the azido-bridged binuclear anion [(UO₂ )₂ (N₃ )₈ ]^4- . The novel uranium oxoazides were characterized by their vibrational spectra and in the case of [(bipy)₂ (UO₂ )₂ (N₃ )₄ ]⋅CH₃ CN, [PPh₄ ][(bipy)UO₂ (N₃ )₃ ], [PPh₄ ]₂ [UO₂ (N₃ )₄ ], [PPh₄ ]₂ [UO₂ (N₃ )₄ ]⋅2CH₃ CN, and [PPh₄ ]₄ [(UO₂ )₂ (N₃ )₈ ]⋅4CH₃ CN by their X-ray crystal structures.

SMM behaviour and magnetocaloric effect in heterometallic 3d–4f coordination clusters with high azide : metal ratios

We present the synthesis and characterization of heterometallic compounds with a very large azide to metal ratio and fascinating magnetic properties.

Solvent-driven azide-induced mononuclear discreteversusone-dimensional polymeric aromatic Möbius cadmium(ii) complexes of an N6tetradentate helical ligand

We report on a solvent-driven formation of discrete[Cd(N₃)₂(L)(MeOH)]·MeOHand a one-dimensional coordination polymer[Cd3(N3)6(L)]n.

Synthesis of six-coordinate mono-, bis-, and tris(tetrazolato) complexes via [3 + 2] cycloadditions of nitriles to silicon-bound azido ligands

A convenient synthetic route to poly(tetrazolato) silicon complexes is described based on the four reactive centres of the N-rich, highly endothermic tetraazides of the type Si(N₃)₄(L₂). Hypercoordinate azido(tetrazolato) silicon complexes Si(N₃)₂(N₄C-R)₂(L₂), R = CH₃, C₆H₅, 4-C₆H₄CH₃ (4a, 5, 6, 7) and Si(N₃)₂(N₄C-L)₂ (9, L = 2-C₅H₄N), L₂ = 2,2'-bipyridine, 1,10-phenanthroline, with SiN₆ skeletons were synthesised via multiple [3 + 2] dipolar cycloaddition reactions starting from Si(N₃)₄(L₂) and a nitrile. The isolated new complexes were characterised by standard analytical methods, single crystal X-ray diffraction and differential scanning calorimetry (4a,b). Tetrazolato ligand linkage isomerism was observed for complex 4a. The crystallographically characterised methyl tetrazolato complexes and plausible configurational and linkage isomers were evaluated by DFT calculations at the B3LYP/6-311G(d,p) level.

The niobium oxoazides [NbO(N3)3], [NbO(N3)3·2CH3CN], [(bipy)NbO(N3)3], Cs2[NbO(N3)5] and [PPh4]2[NbO(N3)5]

Niobium oxotriazide, [NbO(N3)3], was prepared in a fluoride-azide exchange reaction between [NbOF3] and an excess of Me3SiN3 in SO2 solution. In acetonitrile solution, the fluoride-azide exchange resulted in the isolation of the adduct [NbO(N3)3·2CH3CN]. The subsequent reaction of [NbO(N3)3] with 2,2'-bipyridine (bipy) resulted in the isolation of the bipyridine adduct [(bipy)NbO(N3)3]. The pentaazido anion [NbO(N3)5](2-) was obtained by the reaction of [NbO(N3)3] with two equivalents of ionic azide. The novel niobium oxoazides were fully characterized by their vibrational spectra, impact, friction and thermal sensitivity data and, in the case of [(bipy)NbO(N3)3], Cs2[NbO(N3)5], and [PPh4]2[NbO2(N3)5] by their X-ray crystal structures.

New Twists and Turns for Actinide Chemistry: Organometallic Infinite Coordination Polymers of Thorium Diazide

Two organometallic 1D infinite coordination polymers and two organometallic monometallic complexes of thorium diazide have been synthesized and characterized. Steric control of these self-assembled arrays, which are dense in thorium and nitrogen, has also been demonstrated: infinite chains can be circumvented by using steric bulk either at the metallocene or with a donor ligand in the wedge.

From single-point to three-point halogen bonding between zinc(ii) tetrathiocyanate and tetrabromomethane

The strengths of three- and two-point halogen bonding in CBr₄·[Zn(NCS)₄]²⁻dyads are close to that of single-point CBr₄·NCS⁻interaction.

Structural snapshots in the copper(ii) induced azide–nitrile cycloaddition: effects of peripheral ligand substituents on the formation of unsupported μ1,1-azido vs. μ1,4-tetrazolato bridged complexes

Peripheral substituents on click-derived tripodal ligands dictate the reactivity of their copper(ii) azido complexes.

A straightforward and versatile protocol for the direct conversion of benzylic azides to ketones and aldehydes

We report that the benzyl azido group is directly converted to carbonyls in good yields through a rapid hydrolysis (basic conditions) of benzylideneamides generated readily/efficiently in situ under a very simple procedure involving conventional reagents.

Taming Tin(IV) Polyazides

The first charge-neutral Lewis base adducts of tin(IV) tetraazide, [Sn(N3)4(bpy)], [Sn(N3)4(phen)] and [Sn(N3)4(py)2], and the salt bis{bis(triphenylphosphine)iminium} hexa(azido)stannate [(PPN)2Sn(N3)6] (bpy = 2,2'-bipyridine; phen = 1,10-phenanthroline; py = pyridine; PPN = N(PPh3)2) have been prepared using covalent or ionic azide-transfer reagents and ligand-exchange reactions. The azides were isolated on the 0.3 to 1 g scale and characterized by IR and NMR spectroscopies, microanalytical and thermal methods and their molecular structures determined by single-crystal XRD. All complexes have a distorted octahedral Sn[N]6 coordination geometry and possess greater thermal stability than their Si and Ge homologues. The nitrogen content of the adducts of up to 44% exceed any Sn(IV) compound known hitherto.

The First Molybdenum(VI) and Tungsten(VI) Oxoazides MO2(N3)2, MO2(N3)2⋅2 CH3CN, (bipy)MO2(N3)2, and [MO2(N3)4](2-) (M=Mo, W)

Molybdenum(VI) and tungsten(VI) dioxodiazide, MO2(N3)2 (M=Mo, W), were prepared through fluoride-azide exchange reactions between MO2F2 and Me3SiN3 in SO2 solution. In acetonitrile solution, the fluoride-azide exchange resulted in the isolation of the adducts MO2(N3)2⋅2 CH3CN. The subsequent reaction of MO2(N3)2 with 2,2'-bipyridine (bipy) gave the bipyridine adducts (bipy)MO2(N3)2. The hydrolysis of (bipy)MoO2(N3)2 resulted in the formation and isolation of [(bipy)MoO2N3]2O. The tetraazido anions [MO2(N3)4](2-) were obtained by the reaction of MO2(N3)2 with two equivalents of ionic azide. Most molybdenum(VI) and tungsten(VI) dioxoazides were fully characterized by their vibrational spectra, impact, friction, and thermal sensitivity data and, in the case of (bipy)MoO2(N3)2, (bipy)WO2(N3)2, [PPh4]2[MoO2(N3)4], [PPh4]2[WO2(N3)4], and [(bipy)MoO2N3]2O by their X-ray crystal structures.