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.

The Cluster Polyazide Complexes: Synthesis, Crystal Structures, and 14N NMR Studies of [{Re3(μ-X)3}(N3)9]3- (X = Br or I)

Azide cluster complexes [{Re₃(μ-Br)₃}(N₃)₉]^3- and [{Re₃(μ-I)₃}(N₃)₉]^3- were obtained by reaction of Re₃X₉ (X = Br or I, respectively) with sodium azide in methanol. The complexes were crystallized as cesium salts of the compositions Cs₃[{Re₃(μ-Br)₃}(N₃)₉]·H₂O (1) and Cs₃[{Re₃(μ-I)₃}(N₃)₉]·H₂O (2) and characterized by X-ray single-crystal diffraction and elemental analyses, mass spectrometry, ¹⁴N NMR spectroscopy, and DFT calculations. In the anions, each rhenium atom is coordinated by three azide ligands. To the best of our knowledge, these compounds represent the first case of metal cluster polyazide complexes (i.e., where each metal atom bears more than one azide ligand). Both complexes are stable in air but are very shock sensitive, and spontaneous explosive decomposition is also possible.

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.

Catalyst-free room-temperature iClick reaction of molybdenum(ii) and tungsten(ii) azide complexes with electron-poor alkynes: structural preferences and kinetic studies

Two isostructural and isoelectronic group VI azide complexes of the general formula [M(η³-allyl)(N₃)(bpy)(CO)₂] with M = Mo, W and bpy = 2,2'-bipyridine were prepared and fully characterized, including X-ray structure analysis. Both reacted smoothly with electron-poor alkynes such as dimethyl acetylenedicarboxylate (DMAD) and 4,4,4-trifluoro-2-butynoic acid ethyl ester in a catalyst-free room-temperature iClick [3 + 2] cycloaddition reaction. Reaction with phenyl(trifluoromethyl)acetylene, on the other hand, did not lead to any product formation. X-ray structures of the four triazolate complexes isolated showed the monodentate ligand to be N2-coordinated in all cases, which requires a 1,2-shift of the nitrogen from the terminal azide to the triazolate cycloaddition product. On the other hand, a ¹⁹F NMR spectroscopic study of the reaction of the fluorinated alkyne with the tungsten azide complex at 27 °C allowed detection of the N1-coordinated intermediate. With this method, the second-order rate constant was determined as (7.3 ± 0.1) × 10^-2 M^-1 s^-1, which compares favorably with that of first-generation compounds such as difluorocyclooctyne (DIFO) used in the strain-promoted azide-alkyne cycloaddition (SPAAC). In contrast, the reaction of the molybdenum analogue was too fast to be studied with NMR methods. Alternatively, solution IR studies revealed pseudo-first order rate constants of 0.4 to 6.5 × 10^-3 s^-1, which increased in the order of Mo > W and F₃C-C[triple bond, length as m-dash]C-COOEt > DMAD.

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.

Preparation and Characterization of Antimony and Arsenic Tricyanide and Their 2,2'-Bipyridine Adducts

The arsenic(III) and antimony(III) cyanides M(CN)3 (M=As, Sb) have been prepared in quantitative yields from the corresponding trifluorides through fluoride-cyanide exchange with Me3 SiCN in acetonitrile. When the reaction was carried out in the presence of one equivalent of 2,2'-bipyridine, the adducts [M(CN)3 ⋅(2,2'-bipy)] were obtained. The crystal structures of As(CN)3 , [As(CN)3 ⋅(2,2'-bipy)] and [Sb(CN)3 ⋅(2,2'-bipy)] were determined and are surprisingly different. As(CN)3 possesses a polymeric three-dimensional structure, [As(CN)3 ⋅(2,2'-bipy)] exhibits a two-dimensional sheet structure, and [Sb(CN)3 ⋅(2,2'-bipy)] has a chain structure, and none of the structures resembles those found for the corresponding arsenic and antimony triazides.