Azido Complexes Research Articles

Thiocyanato-metal(II) and azido-cobalt(III) complexes with hydroxymethylpyridines

A dimeric [Cu(μ-4-HOMP)(4-HOMP)(NCS)2]2 (1) and three discrete monomeric complexes [Ni(3-HOMP)2(NCS)2(H2O)2] (2), [Co(3-HOMP)3(N3)3]·H2O (3) and [Zn(4-HOMP)2(NCS)2] (4), (3-HOMP = 3-hydroxymethylpyridine, 4-HOMP = 4-hydroxymethylpyridine) have been isolated and structurally characterized by IR, UV–Vis spectroscopy, XRPD, single crystal X-ray crystallography and Hirshfeld surface analysis as well as thermogravimetric analyses for complexes 1, 2 and 4. In dimeric complex 1 each penta-coordinated Cu2+ center is bridged through N,O-4-HOMP ligands, whereas metal ions in 2 and 3 are located in distorted octahedral geometry with mer-configuration in the azido complex 3. Distorted tetrahedral geometry is observed around Zn2+ in complex 4. The variable temperature magnetic susceptibility measurements of 1 showed very weak antiferromagnetic interaction.

A visible-light photoactivatable di-nuclear PtIV triazolato azido complex.

A novel PtIV triazolato azido complex [3]-[N1,N3] has been synthesised via a strain-promoted double-click reaction (SPDC) between a PtIV azido complex (1) and the Sondheimer diyne (2). Photoactivation of [3]-[N1,N3] with visible light (452 nm) in the presence of 5'-guanosine monophosphate (5'-GMP) produced both PtIV and PtII 5'-GMP species; EPR spectroscopy confirmed the production of both azidyl and hydroxyl radicals. Spin-trapping of photogenerated radicals - particularly hydroxyl radicals - was significantly reduced in the presence of 5'-GMP.

A novel Pt(iv) mono azido mono triazolato complex evolves azidyl radicals following irradiation with visible light.

The platinum(iv) azido complex trans,trans,trans-[PtIV(N3)2(OH)2(py)2] (1) undergoes cycloaddition with 1,4-diphenyl-2-butyne-1,4-dione (2) under mild, catalyst-free conditions, affording a number of mono and bis click products. The major mono click product (3) exists in MeCN as an equilibrium mixture between two species; 3a and 3b rapidly interconvert through nucleophilic attack of the axial Pt-OH group at the adjacent Ph-CO group. The kinetic and thermodynamic parameters for this interconversion have been measured by selective saturation-transfer NMR spectroscopic experiments and are consistent with cyclisation at the Pt centre. Complex 3b was also characterised by X-ray crystallography. Visible light irradiation (440-480 nm) of 3 in d3-MeCN produces azidyl radicals (N3˙), as demonstrated by EPR spin-trapping with DMPO; no generation of hydroxyl radicals was observed. 1H-195Pt HMBC NMR confirmed that the photoproducts were PtIV rather than PtII species, and HPLC was consistent with these being [3-N3]+ species; no facile photoejection of the triazolato ligand was observed, consistent with MS/MS fragmentation of 3. When 3 was irradiated in the presence of 5'-GMP, no 5'-GMP photoproducts were observed, suggesting that complex 3 is likely to exhibit significantly simplified biological activity (release of azidyl radicals but not DNA binding) compared with complex 1.

Synthesis, characterization and chemosensitivity studies of half-sandwich ruthenium, rhodium and iridium complexes containing к1(S) and к2(N,S) aroylthiourea ligands

The reaction of [(p-cymene)RuCl2]2 and [Cp*MCl2]2 (M = Rh/Ir) metal precursors with aroylthiourea ligands (L1-L3) yielded a series of neutral mono-dentate complexes 1–9. The neutral mono-dentate coordination of aroylthiourea with metals via S atom was confirmed by single crystal X-ray diffraction study. Further reaction of mono-dentate complexes 1–9 with excess NaN3 in polar solvent resulted in the formation of highly strained four member ring к2(N,S) azido complexes 10–18. Further these complexes were treated with activated alkynes to isolate triazole complexes, but unfortunately the reaction was unsuccessful. All these complexes were fully characterized by various spectroscopic techniques. The molecular structures of the representative complexes have been determined by single crystal X-ray diffraction studies. The molecular structures of the complexes revealed typical piano stool geometry around the metal center. The chemosensitivity activities of the complexes 1–9 evaluated against the cancer cell line HCT-116 (human colorectal carcinoma) and ARPE-19 (human retinal epithelial cells) cell line. Of these, complex 3 was the most potent and whilst its potency was less than cisplatin, its selectivity for cancer as opposed to non-cancer cell lines in vitro was comparable to cisplatin.

Application of POCOP Pincer Nickel Complexes to the Catalytic Hydroboration of Carbon Dioxide

The reduction of CO2 is of great importance. In this paper, different types of bis(phosphinite) (POCOP) pincer nickel complexes, [2,6-(R2PO)2C6H3]NiX (R = tBu, iPr, Ph; X = SH, N3, NCS), were applied to the catalytic hydroboration of CO2 with catecholborane (HBcat). It was found that pincer complexes with tBu2P or iPr2P phosphine arms are active catalysts for this reaction in which CO2 was successfully reduced to a methanol derivative (CH3OBcat) with a maximum turnover frequency of 1908 h−1 at room temperature under an atmospheric pressure of CO2. However, complexes with phenyl-substituted phosphine arms failed to catalyze this reaction—the catalysts decomposed under the catalytic conditions. Complexes with iPr2P phosphine arms are more active catalysts compared with the corresponding complexes with tBu2P phosphine arms. For complexes with the same phosphine arms, the catalytic activity follows the series of mercapto complex (X = SH) ≈ azido complex (X = N3) >> isothiocyanato complex (X = NCS). It is believed that all of these catalytic active complexes are catalyst precursors which generate the nickel hydride complex [2,6-(R2PO)2C6H3]NiH in situ, and the nickel hydride complex is the active species to catalyze this reaction.

Enhanced pseudo-halide promoted corrosion inhibition by biologically active zinc(II) Schiff base complexes

Four novel biologically significant Zn (II) Schiff base complexes ([Zn(L1)2](ClO4)2(1), [Zn(μ-fumarate)(L1)]n(2), [ZnL1(N3)2] (3) and [ZnL2(N3)2] (4) were synthesized from two ligands L1 [N1,N1-dimethyl-N2-(1-(pyridine-2-yl)ethylidene)ethane-1,2-diamine] and L2 [N1,N1-diethyl-N2-(1-(pyridine-2-yl)ethylidene)ethane-1,2-diamine]. Detailed electrochemical polarization and impedance studies prove that corrosion inhibition activity of newly synthesized zinc complexes in 15% HCl on mild steel gets enhanced significantly due to the incorporation of psudo-halide azide as co-ligand. Different microscopic images (FE-SEM and AFM) depicted that metal surface is protected by Zn(II) complexes. Antibacterial activity of these Zn (II) azido Schiff base complexes against Gram-positive Staphylococcus aureus was studied and reported. Further, antiproliferative activities of these azido complexes were studied against breast cancer cell line MCF 7.

Domino N2-Extrusion-Cyclization of Alkynylarylketone Derivatives for the Synthesis of Indoloquinolines and Carbocycle-Fused Quinolines.

New synthetic approaches for the synthesis of indoloquinolines and carbocycle-fused quinolines have been developed employing alkynylketone substrates. These synthetic transformations involved the application of N2-extrusion of azido complexes as a key step to generate carbodiimidium ion and nitrilium ion in situ, which further cyclized intramolecularly with alkyne via a domino process to provide indoloquinolines and carbocycle-fused quinolines, respectively, in moderate to good yields.

Synthesis of strained complexes of arene d6 metals with benzoylthiourea and their spectral studies

Halide bridged arene d6 platinum group metal precursors on treatment with thiourea derivatives (L1 and L2) yielded a series of neutral mono-dentate complexes (1–8). In general complexes have been formulated as [(arene)M(L)к1(S)Cl2] where L = L1, M = Ru, arene = p-cymene 1; benzene 2; arene = Cp*, M = Rh 3 and Ir 4; L = L2, M = Ru, p-cymene 5; benzene 6; arene = Cp*, M = Rh 7 and Ir 8. Structural studies revealed that thiourea ligand coordinate to the metal in a mono-dentate fashion via S atom. Further treatment of mono-dentate complexes 1 and 5 with NaN3 in polar solvent resulted in the formation of highly strained к2(N,S) azido complexes 9 and 10 whereas reaction of complex 7 yielded a six membered ring к2(S,O) azido complex 11. Reaction of complex 9 with dimethylacetylene dicarboxylate (DMAD) and diethylacetylene dicarboxylate (DEAD) leads to the formation of nitrogen (N2) bound triazolato complexes 12 and 13 whereas reaction of complex 11 with the same yielded nitrogen (N1) bound triazolato complexes 14 and 15. However reaction of complex 10 with both DMAD and DEAD leads to decomposition of the products. All these complexes have been characterized by various spectroscopic techniques. The molecular structures of the representative complexes 1, 2, 3, 6, 7, 9, 11 and 12 have been determined by single crystal X-ray diffraction study.

3+2] Cycloaddition of ruthenium azido complex with ethyl propiolate and related reactions

The [3+2] cycloaddition reaction of ethyl propiolate with ruthenium azido complex [Ru]−N3 (1, [Ru] = (η5-C5H5)(dppe)Ru, dppe = Ph2PCH2CH2PPh2) has been investigated. The metal-bound heterocyclic complex produced is N(2)-bound triazolate [Ru]N3CHCO2Et (2). A regiospecific alkylation happens by treatment of 2 with organic halides and gives a series of cationic N(1)-bound N(3)-alkylated-4-ethoxycarbonyl triazolato complexes {[Ru]N3(R)C2HCO2Et}[X] (3a, R = CH3, X = I; 3b, R = CH2Ph, X = Br; 3c, R = CH2C6F5, X = Br; 3d, R = CH2CN, X = I; 3e, CH2CO2CH3, X = Br) and the following cleavage of the Ru-N bond of 3a and 3b gives ruthenium halides and N(1)-alkylated five-membered-ring organic triazoles N3(R)C2HCO2Et (4a, R = CH3; 4b, R = CH2Ph). The structures of 2 and 3c have been determined by single-crystal X-ray diffraction analysis.

Platinum(iv) azido complexes undergo copper-free click reactions with alkynes.

We report our investigations into the first examples of copper-free 1,3-dipolar cycloaddition (click) reactions of electrophiles with a PtIV azido complex. The Pt-IV azido complex trans, trans, trans-[PtIV(py)2(N3)2(OH)2] (1) was reactive towards dimethyl acetylenedicarboxylate (DMAD) (2), diethyl acetylenedicarboxylate DEACD (3), N-[(1R,8S,9s)-bicyclo[6.1.0]non-4-yn-9-ylmethyloxycarbonyl]-1,8-diamino-3,6-dioxaoctane (BCN) (11) and dibenzocyclooctyne-amine (DBCO) (12) resulting in formation of the corresponding mono (a) and bis-substituted (b) complexes. Complexes of 2 undergo further reactions between the Pt centre and the carbonyl group to form 2a' and 2b'. This is not seen for the products of the corresponding PtII azido complex trans-[Pt(py)2(N3)2] with acetylene 2. Novel complexes 2a', 2b', 11a and 11b have been characterised by multinuclear NMR, IR and UV-vis spectroscopy and ESI-MS. These reactions represent new synthetic routes to novel Pt(iv) complexes.

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.

Synthesis, structural characterization, photo-physical and magnetic properties of cobalt salphen pseudo halide complexes showing meta-magnetic ordering

The solvo-thermal syntheses of [(CoSalphen)2Co (SCN)2]n (1), CoSalphen(NH3)(N3)(2), Na[CoIIIsalphen(N3)2](3), Na[CoIIIsalen(N3)2](4) and CoIIIsalen(NH3)(N3) (5) {salphen = N,N’-o-phenylene-bis(salicylideneimine)} are reported. The structural studies using X-ray diffraction measurements revealed that 1 crystalizes in a monoclinic C2/c space group. Two cobalt (II) metal centers in penta-coordinated and octahedral local coordination environments are bridged via alternating O and μ1,3 SCN bridges resulting in a novel 2D layered coordination polymer. Compound 2 is a trivalent mononuclear cobalt azido complex with an octahedral coordination environment. The magnetic investigations of 1 revealed ferromagnetic coupling (J = +49.1 cm−1) and meta-magnetic ordering. Time resolved photoluminescence studies of the complexes showed excited state lifetimes of (τ1 = 0.4675 ns, τ2 = 5.23 ns) for 1 and (τ1 = 0.5078 ns, τ2 = 6.79 ns) for 2.

Crystal structures, magnetic properties and DFT study of cobalt(II) azido complexes with the condensation product of 2-quinolinecarboxaldehyde and Girard’s T reagent

A tridentate NNO condensation product of 2-quinolinecarboxaldehyde and Girard’s T reagent (HLCl) in the presence of azide ions coordinates with cobalt(II) giving mononuclear azido Co(II) complex [CoHL(N3)3] (1) as a main product and dinuclear end-on azido bridged Co(II) complex [Co2L2(μ-1,1-N3)2(N3)2] (2) in traces. Crystal structures of both complexes were determined. Variable temperature magnetic susceptibility measurement studies of complex 1 showed that Co(II) cation is in the low-spin state with t2g6eg1 (S = 1/2) configuration. DFT-BS calculations for complex 2 anticipated ferromagnetic type interaction between paramagnetic centers (J = 53 cm−1).

Electrocatalytic Azide Oxidation Mediated by a Rh(PNP) Pincer Complex.

One‐electron oxidation of the rhodium(I) azido complex [Rh(N3)(PNP)] (5), bearing the neutral, pyridine‐based PNP ligand 2,6‐bis(di‐tert‐butylphosphinomethyl)pyridine, leads to instantaneous and selective formation of the mononuclear rhodium(I) dinitrogen complex [Rh(N2)(PNP)]+ (9 +). Interestingly, complex 5 also acts as a catalyst for electrochemical N3 − oxidation (E p≈−0.23 V vs. Fc+/0) in the presence of excess azide. This is of potential relevance for the design of azide‐based and direct ammonia fuel cells, expelling only harmless dinitrogen as an exhaust gas.

N-donor ligands-directed coordination of Zn- azido complexes

Two zinc (II) pseudo-halide complexes [Zn(L1)(N3)2]n (1L1: 1,2-diaminocyclohexane) and Zn(L2)2(N3)2 (2L2: 4,5-dimethy-2-(pyridine-2-yl) imidazole) have been synthesized and characterized. Single-crystal X-ray structural analysis revealed that the central ZnII atoms in 1 displays distorted trigonal bipyramidal arrangement with a 1D chain structure bridged by N3− anions, while in 2, the central ZnII atoms incorporating with two bidentate L2 ligands, and adopts an octahedral geometry and shows a “butterfly” coordination framework. Structural analysis demonstrated that the organic ligands play an important role in determining the resultant structure. In addition, both complexes were further characterized by thermal stability properties and Hirshfeld surface analysis.

Synthesis, Crystal Structure and Magnetic Properties of [Mn((1R, 2R)‐Salcy)N3/NCS] Complexes: Solvent Dependent Crystallization of Monomers, Chains and Dimers.

AbstractFive new chiral MnIII complexes [Mn((1R, 2R)‐Salcy)N3]∞⋅CH3CN (1), [Mn((R,R)‐Salcy)N3]∞ (2), [Mn((R,R)‐Salcy)N3] (4), [Mn((R,R)‐Salcy)(H2O)N3]⋅C4H8O (5) and [Mn((R,R)‐Salcy)NCS] (6) have been synthesized and characterized by X‐ray structural analysis and magnetic measurements (Salcy=N,N′‐bis(salicylidene)‐1,2‐diaminocyclohexane}. The four azido complexes have been obtained from the previously known [Mn((R,R)‐Salcy)(CH3OH)N3] (3) by crystallization from various solvents. Compounds 1 and 2 are trans‐μ‐1,3‐azide bridged coordination polymers. While 1 forms helical chains, the chain in 2 is formed via translation of a dimeric helicate repeat unit. Compound 3 is a methanol coordinated mononuclear azido complex which forms a 2D‐network through H‐bonding. Compounds 4 and 6 are phenoxo‐bridged dimers without inversion center. Compound 5 is an aqua coordinated mononuclear azido complex, which forms a 1D‐chain through O−H⋅⋅⋅N hydrogen bonding involving axial ligands. In all six compounds MnIII exhibits a characteristic Jahn−Teller elongation. The magnetic coupling in 1 and 2 leads to antiferromagnetic interaction along the chain (2 J=−11.6 cm−1 for 1 and –11.9 cm−1 for 2) through the μ‐1,3‐azide bridge. Compound 3 is weakly antiferromagnetic due to hydrogen bonding interactions in the lattice. The phenoxo dimers (4 and 6) do not have measurable exchange interaction, the low temperature susceptibility being influenced mainly by zero‐field splitting.

1,3-Dipolar Cycloadditions of Rhodium(III) Azido Complexes with Alkynes and Nitriles

Spanish Ministerio de Ciencia e Innovacion [CTQ2011-28641]; Spanish Ministerio de Educacion, Cultura y Deporte

Synthesis, crystal structure and antibacterial activity of azido complexes of cobalt(III) containing heteroaromatic Schiff bases

Three new Schiff base complexes of cobalt(III) viz. [Co(L1)(N3)]2 (1), [Co(L2)2(N3)2]NO3 (2) and [Co(L3)2(N3)2]ClO4 (3), where H2L1=N,N′-propane-1,3-diylbis[1-(pyrrol-2-yl)methanimine], L2=1-[(thiophen-2-ylmethylidene)amino]propan-2-amine and L3=1-[(3-methylthiophen-2-ylmethylidene)amino]propan-2-amine, have been prepared and characterized. The syntheses have been achieved by the reaction of cobalt(II) nitrate or perchlorate with the tetradentate Schiff base (H2L1) or the bidentate ligands L2 and L3 in presence of azide. All the complexes 1–3 have been characterized by microanalytical, spectroscopic, single crystal X-ray diffraction and other physicochemical studies. Structural studies reveal that all the complexes contain CoN6 chromophore in which the central Co(III) ions adopt distorted octahedral geometry. While 1 is a binuclear end-on bis(μ-azido) complex, both of 2 and 3 are mononuclear with two terminal azide ions disposed in cis positions. Structural studies reveal that weak intermolecular H-bonding or π…π interactions are operative to bind the complex units or the anions in the solid state. The antibacterial activity of all the complexes and their constituent Schiff base ligands has been tested against some Gram(+) and Gram(−) bacteria.

Control of Complex Formation through Peripheral Substituents in Click-Tripodal Ligands: Structural Diversity in Homo- and Heterodinuclear Cobalt-Azido Complexes.

The azide anion is widely used as a ligand in coordination chemistry. Despite its ubiquitous presence, controlled synthesis of azido complexes remains a challenging task. Making use of click-derived tripodal ligands, we present here various coordination motifs of the azido ligands, the formation of which appears to be controlled by the peripheral substituents on the tripodal ligands with otherwise identical structure of the coordination moieties. Thus, the flexible benzyl substituents on the tripodal ligand TBTA led to the formation of the first example of an unsupported and solely μ1,1-azido-bridged dicobalt(II) complex. The more rigid phenyl substituents on the TPTA ligand deliver an unsupported and solely μ1,3-azido-bridged dicobalt(II) complex. Bulky diisopropylphenyl substituents on the TDTA ligand deliver a doubly μ1,1-azido-bridged dicobalt(II) complex. Intriguingly, the mononuclear copper(II) complex [Cu(TBTA)N3]+ is an excellent synthon for generating mixed dinuclear complexes of the form [(TBTA)Co(μ1,1-N3)Cu(TBTA)]3+ or [(TBTA)Cu(μ1,1-N3)Cu(TPTA)]3+, both of which contain a single unsupported μ1,1-N3 as a bridge. To the best of our knowledge, these are also the first examples of mixed dinuclear complexes with a μ1,1-N3 monoazido bridge. All complexes were crystallographically characterized, and selected examples were probed via magnetometry and high-field EPR spectroscopy to elucidate the electronic structures of these complexes and the nature of magnetic coupling in the various azido-bridged complexes. These results thus prove the power of click-tripodal ligands in generating hitherto unknown chemical structures and properties.

Is Nanostructuring Sufficient To Get Catalytically Active Au?

Gold nanoparticles on transition-metal oxides were synthesized by two different methods: precipitation and photoinduced decomposition of an intermediate gold–azido complex. Only samples prepared by the precipitation method showed significant CO conversion at low temperature. XPS shows the formation of two Au species (Au0 and Auδ+) on the surface of active Au/TiO2 and Au/Fe2O3 samples. The energy shift of the Auδ+ peak depends on the support and is 0.6 and 0.9 eV for Au/TiO2 and Au/Fe2O3, respectively. TEM images indicate the formation of overlayer on Au particles. These results prove Au activation via a strong metal–support interaction, on the basis of the strong influence of the support on the electronic structure of the gold through charge transfer and stabilization of low-coordinated Au atoms.