Article

The first organocopper tetrazole derivative: Synthesis and characterization

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Abstract

1-(5-Amino-3-azapentyl)tetrazole dihydrochloride (HL·2HCl) was prepared by heterocyclization of diethylenetriamine with triethyl orthoformate and sodium azide followed by treatment with potassium carbonate and hydrochloric acid. The reaction of CuCl2, HL·2HCl and triethylamine (NEt3) in a molar ratio of 1 : 1 : 3 in water was found to generate a novel organometallic tetrazole derivative Cu2L2Cl2. This compound is present as a binuclear centrosymmetric molecular complex, in which C-deprotonated tetrazole L acts as a chelating ligand via the two amino N and tetrazole ring C coordination sites and the two copper atoms are linked together through two tetrazole ring N(4)-C(5) bridges. This complex is the first organocopper tetrazole derivative. When the molar ratio of the reagents in the abovementioned reaction was changed to 1 : 2 : 2, the complex Cu(HL)2Cl2 was formed along with Cu2L2Cl2. Pure Cu(HL)2Cl2 was isolated after reaction of the reagents in a molar ratio of 1 : 3 : 6. The complex Cu(HL)2Cl2 is present as a mononuclear molecular complex, with a chelating coordination mode of HL via the two amino N atoms only. Both complexes as well as HL·2HCl were characterized by single-crystal X-ray analysis.

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Published data on the synthesis, structure, properties and applications of metal derivatives of tetrazoles are generalised and described systematically. Compounds based on the anionic and neutral tetrazole forms, C- and N-mono- and C,N-disubstituted tetrazoles are considered.
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The azido complexes [RhCp*(μ-N3)(N3)]2 (Cp*=η-C5Me5), trans-Rh(N3)(CO)(PPh3)2, Na2[Pd(N3)4], Na2[Pd2(μ-N3)2(N3)4] and Na[Au(N3)4], prepared in situ from metal halide precursors and a three- to ten-fold excess of NaN3 in water, react with aliphatic isocyanides to give a series of new metal–carbon bonded tetrazolato complexes. All azide ligands in the coordination sphere undergo this cycloaddition with isocyanides except on palladium(II) where only two tetrazol-5-ato groups are formed. In the neutral species HAu(CN4R)4 (R=tBu (2c), Cy (2d)) presumably one of the four tetrazol-5-ato groups has been protonated to afford a tetrazol-5-ylidene (carbene) ligand. The reactivities of the isocyanides decrease in the order CNtBu>CNCy>CN(CH2)4Cl>CN-allyl>CNCH2CO2Na; surprisingly, no reaction occurs with methylisocyanide. With tert-butyl isocyanide in the cold, [Ru(μ-N3)(N3)(η-C10H14)]2 (C10H14:4-isopropyltoluene) only reacts with cleavage of the azido bridges giving rise to [Ru(N3)2(η-C10H14)CNtBu] (5a), while heating of the same mixture affords a second azido-isocyanide complex, trans-[Ru(N3)2(CNtBu)4] (5b), of which an X-ray structure analysis has been carried out. In some cases the reactions proceed with N2 evolution, and rhodium complexes 6a–c are also formed probably containing cyanamido (N{R}CN) or carbodiimido (NCNR) ligands, respectively.
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The data are integrated and systematized on preparation procedures and application to the organic synthesis of organometallic tetrazole derivatives, including 5-metallated tetrazoles and tetrazoles with a metal-carbon bond in a substituent, and also organotin tetrazoles.
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Salt metathesis reaction of the dihalo-bis(carbene) complex trans-[NiBr2(NHC)(2)] (1, NHC = 1,3-diisopropylbenzimidazolin-2-ylidene) with NaN3 in DMF at elevated temperature afforded the diazidobis(carbene) complex trans-[Ni(N-3)(2)(NHC)(2)] (2) as a red crystalline solid in a yield of 78%. Complex 2 served as a metal-template for the 1,3-dipolar cycloaddition of 2,6-dimethylphenylisocyanide (CN-Xyl) to the azido ligands to yield the mixed tetrazolato-carbodiimido complex trans- [Ni(CN4-Xyl)(NCN-Xyl)(NHC)(2)] (3) at ambient temperature and the dicarbodiimido complex trans- [Ni(NCN-Xyl)2(NHC)(2)] (4) at 70 degrees C. Reaction of alkyl isocyanides with 2 at ambient temperature gave the ditetrazolato complexes trans-[Ni(CN4-R)(2)(NHC)(2)] (5, R = tert-butyl; 6, R = cyclohexyl) in good yields. The novel cationic "abnormal" tetrazolin-5-ylidene complex trans-[Ni(CN4-Bu-t,Me)(2)(NHC)(2)] (BF4)(2) (7, Bu-t = tert-butyl) was synthesized by direct methylation of 5 with [Me3O]BF4. All compounds have been fully characterized by multinuclear NMR spectroscopies and ESI mass spectrometry. The solid state molecular structures of complexes 2, 4, 5, and 7 center dot 2CH(2)O(2) have also been confirmed by X-ray diffraction studies.
Article
The diphenylphosphoryl-carbaporpholactone hybrid is a new aromatic porphyrinoid, which preserves the essential features of the carbaporpholactone frame and provides a suitable environment allowing stabilization of the organocopper(II) complex affording a peculiar side-on coordination of copper(II).
Article
The square-planar structure of a diamagnetic Cu(III) complex of tetrakis(pentafluorophenyl)-substituted N-confused porphyrin was elucidated by X-ray diffraction analysis. The facile interconversion between Cu(II) (1) and Cu(III) (2) complexes was achieved by chemical oxidation/reduction, and the Cu(III)/Cu(II) redox potential was controlled by adding anions through the hydrogen-bonding interaction to the peripheral NH.
Article
Incorporation of a nitrogen functionality into a tripodal N-heterocyclic carbene ligand system affords the first N-anchored tetradentate tris-carbene ligands TIMEN(R) (R = Me (5a), t-Bu (5b), Bz (5c)). Treatment of the methyl derivatized [H(3)TIMEN(Me)](PF(6))(3) imidazolium salt (H(3)5a) with silver oxide yields the silver complex [(TIMEN(Me))(2)Ag(3)](PF(6))(3) (9), which, in a ligand transfer reaction, reacts with copper(I) bromide to give the trinuclear copper(I) complex [(TIMEN(Me))(2)Cu(3)](PF(6))(3) (10). Deprotonation of the tert-butyl and benzyl derivatives [H(3)TIMEN(t-Bu)](PF(6))(3) and [H(3)TIMEN(Bz)](PF(6))(3) yields the free tris-carbenes TIMEN(t-Bu) (5b) and TIMEN(Bz) (5c), which react readily with copper(I) salts to give mononuclear complexes [(TIMEN(t-Bu))Cu](PF(6)) (11b) and [(TIMEN(Bz))Cu]Br (11c). The solid-state structures of 10, 11b, and 11c were determined by single-crystal X-ray diffraction. While the TIMEN(Me) ligand yields trinuclear complex 10, with both T-shaped three-coordinate and linear two-coordinate copper(I) centers, the TIMEN(t-Bu) and TIMEN(Bz) ligands induce mononuclear complexes 11b and 11c, rendering the cuprous ion in a trigonal planar ligand environment of three carbenoid carbon centers and an additional, weak axial nitrogen interaction. Complexes 11b and 11c exhibit reversible one-electron redox events at half-wave potentials of 110 and -100 mV vs Fc/Fc(+), respectively, indicating sufficient electronic and structural flexibility of both TIMEN(R) ligands (R = t-Bu, Bz) to stabilize copper(I) and copper(II) oxidation states. Accordingly, a copper(II) NHC complex, [(TIMEN(Bz))Cu](OTf)(2) (12), was synthesized. Paramagnetic complex 12 was characterized by elemental analysis, EPR spectroscopy, and SQUID magnetization measurements.
Article
Alles ändert sich: Der im Bild gezeigte stabile, diamagnetische, trigonal-bipyramidale CuIII-Komplex, der bei der Einelektronenoxidation eines CuII-Komplexes erhalten wird, lagert sich bei der Zugabe von Cl−-Ionen in einen paramagnetischen, oktaedrischen CuIII-Komplex um. Die Charakterisierung der Komplexe und Dichtefunktionalrechnungen sprechen dafür, dass die urspüngliche Einelektronenoxidation metall- und nicht ligandenzentriert ist.
Article
Fireworks are probably the application of chemistry which resonates best with the general public. However, fireworks and (civil and military) pyrotechnic applications cause environmental pollution and thus have given rise to the development of new, environmentally friendly pyrotechnic compounds and formulations. Nitrogen-rich energetic materials, such as the derivatives of tetrazoles and tetrazines, are about to revolutionize traditional pyrotechnic compositions. This Review summarizes the sources of pollution in current formulations and recent efforts toward "green" pyrotechnics.
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