Single-molecule resolution of an organometallic intermediate in a surface-supported Ullmann coupling reaction

We have studied the organometallic intermediate of a surface-supported Ullmann coupling reaction from 4, 4″-dibromo-p-terphenyl to poly(para-phenylene) by scanning tunneling microscopy/spectroscopy and density functional theory calculations. Our study reveals at a single-molecular level that the intermediate consists of biradical terphenyl (ph)(3) units that are connected by single Cu atoms through C-Cu-C bridges. Upon further increasing the temperature, the neighboring biradical (ph)(3) units are coupled by C-C bonds forming poly(para-phenylene) oligomers while the Cu atoms are released.     

A novel entry to xanthones by an intramolecular Diels-Alder reaction involving 2-(1,2-dichlorovinyloxy) aryl dienones

A wide array of synthetic methods are described in the literature for the preparation of xanthones—a prominent class of tricyclic molecules that occur widely in nature. Majority of these reported methods involve linking the two aromatic rings and forming the central pyrone ring using a variety of classical and non-classical cyclization strategies. In a conceptually different approach, we describe here a new xanthone synthesis wherein both the pyrone and the second aromatic rings were forged in a single step by an intramolecular cycloaddition reaction involving 2-(1,2-dichlorovinyloxy) aryldienones.     

Thermally reversible photochromic behaviour of new naphthopyrans involving an intramolecular [2+2] cyclization reaction

New 4-(2,2-diphenylethenyl)naphthopyrans were synthesized and their photochromic behaviour in solution were studied under continuous UV light irradiation conditions. Although only one coloured photoproduct was expected to be formed, due to the naphthopyran substitution pattern, NMR analysis on degassed UV irradiated solutions, performed at low temperature, showed the formation of different compounds. Among them, the main product is formed through an intramolecular [2+2] cyclization reaction and show thermally reversible photochromic properties.     

Reaction of a copper(II)-nitrosyl complex with hydrogen peroxide: putative formation of a copper(I)-peroxynitrite intermediate

The reaction of a Cu(II)-nitrosyl complex (1) with hydrogen peroxide at -20 °C in acetonitrile results in the formation of the corresponding Cu(I)-peroxynitrite intermediate. The reduction of the Cu(II) center was monitored by UV-visible spectroscopic studies. Formation of the peroxynitrite intermediate has been confirmed by its characteristic phenol ring nitration reaction as well as isolation of corresponding Cu(I)-nitrate (2). On air oxidation, 2 resulted in the corresponding Cu(II)-nitrate (3). Thus, these results demonstrate a possible decomposition pathway for H(2)O(2) and NO through the formation of a peroxynitrite intermediate in biological systems.     

Electron transfer. 123. Competitive redox reactions involving a Cobalt(I) intermediate

he hypophosphito derivative of Co^III, (NH₃)₅CoO₂PH₂ ²⁺, decomposes in basic media, yielding Co(II) quantitatively, along with a 1:1 mixture of hypophosphite and phosphite. Earlier studies point to a cobalt (I) intermediate, which rapidly reduces a second molecule of Co(III) reactant to Co(II). In the presence of an external cobalt (III) oxidant (Co³X), the latter competes with the hypophosphito complex for Co(I), lowering the yield of free hypophosphite. From the ratio of phosphorus products (P³/P¹), evaluated by proton decoupled ³¹P NMR, the relative reactivities (k_t/k_c) of the external Co(III) “traps” and the hypophosphito complex may be determined. A log-log plot comparing values of k_t/k_c with rates for reductions of the same series of Co(III) oxidants with Ru(NH₃)₆ ²⁺ (k_Ru values) is badly scattered with a slope of only 0.23, well below the value of unity stipulated by the Marcus model, indicating that an outer-sphere mechanism cannot operate for all of the Co(III)-Co(I) reactions and may not operate for any, except for that with Co(NH₃)₅(py)₃₊. Among the carboxylato-substituted oxidants, there are no rate enhancements by neighbouring pyridine, -SR,-OH, -CHO, or -SO₃H functions, in contrast to the accelerations previously observed for reductions by Cr(II), Eu(II) and Ti(III), which are attributed to intermediacy of chelate-stabilized precursor complexes. It is suggested that the Co(III)-Co(I) reactions, which determine the ratio of phosphorus products, are much more rapid than the ligand substitution at the Co(I) center which must precede chelate formation, and that the latter therefore does not intervene significantly in the redox processes.     

The reaction of copper(I) sulphide with a product of its oxidation copper(II) sulphate

The course of the reaction between copper(I) sulphide and copper(II) sulphate in SO₂ at 710–785 K was studied by the TG method under isothermal and non-isothermal conditions, as well as by the DTA method, X-ray analysis and scanning electron microscopy. It was established that the reaction is essentially dependent upon the initial composition of the substrate mixture, Cu₂SO₂ and Cu₂SO₂ being the chief intermediates in the reaction. Copper(I) oxide appears as the permanent final product of the reaction of interest. The reaction network, with the intermediate stages depending on the initial compositions in the temperature range studied, has been demonstrated.

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Zusammenfassung Der Verlauf der Reaktion von Kupfer(I)-sulfid mit Kupfer(II)-sulfat wurde in SO₂ bei 710–785 K durch isotherme und nichtisotherme Thermogravimetrie sowie DTA, Röntgenanalyse und Scanning-Elektronenmikroskopie untersucht. Es wurde festgestellt, daß die Reaktion wesentlich von der Ausgangszusammensetzung des Substratgemisches abhängt, wobei Cu₂SO₂ und Cu₂SO₄ die vorherrschenden intermediären Produkte der Reaktion sind. Kupfer(I)-oxid tritt als Endprodukt auf. Der die intermediären, im untersuchten Temperaturbereich von der Ausgangszusammensetzung abhängigen Reaktionsschritte in sich einschließende Reaktionsverlauf wird dargelegt.

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710–785 , , . , . Cu₂SO₂ Cu₂SO₄, . , .

     

Solid-state (63)Cu and (65)Cu NMR spectroscopy of inorganic and organometallic copper(I) complexes

Solid-state 63Cu and 65Cu NMR experiments have been conducted on a series of inorganic and organometallic copper(I) complexes possessing a variety of spherically asymmetric two-, three-, and four-coordinate Cu coordination environments. Variations in structure and symmetry, and corresponding changes in the electric field gradient (EFG) tensors, yield 63/65Cu quadrupolar coupling constants (CQ) ranging from 22.0 to 71.0 MHz for spherically asymmetric Cu sites. These large quadrupolar interactions result in spectra featuring quadrupolar-dominated central transition patterns with breadths ranging from 760 kHz to 6.7 MHz. Accordingly, Hahn-echo and/or QCPMG pulse sequences were applied in a frequency-stepped manner to rapidly acquire high S/N powder patterns. Significant copper chemical shielding anisotropies (CSAs) are also observed in some cases, ranging from 1000 to 1500 ppm. 31P CP/MAS NMR spectra for complexes featuring 63/65Cu-31P spin pairs exhibit residual dipolar coupling and are simulated to determine both the sign of CQ and the EFG tensor orientations relative to the Cu-P bond axes. X-ray crystallographic data and theoretical (Hartree-Fock and density functional theory) calculations of 63/65Cu EFG and CS tensors are utilized to examine the relationships between NMR interaction tensor parameters, the magnitudes and orientations of the principal components, and molecular structure and symmetry.     

Studies of the reaction mechanism between copper(I) sulphide and excess copper(II) sulphate

The reaction between copper(I) sulphide and excess copper(II) sulphate in the temperature range 600–750 K was investigated by methods of thermal analysis as well as by measuring the phase composition as a function of the fractional conversions. The reaction proceeds in four stages. The transient products are Cu₂S, a Cu₂SO₂ phase and CU₂SO₄, and the final product is CU₂O with the non-defect structure. The initial composition of the substrate mixture strongly influence the reaction kinetics.

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Zusammenfassung Die Reaktion zwischen Kupfer(I)-sulfid und überschüssigem Kupfer(II)-sulfat im Temperaturbereich von 600–750 K wurde mittels thermoanalytischer Methoden und durch Ermittlung der Phasenzusammensetzung in AbhÄngigkeit von der Konversion untersucht. Die Reaktion verlÄuft in vier Schritten. Als Zwischenprodukte treten CU₂S, eine Cu₂SO₂-Phase und Cu₃SO₄ auf, Endprodukt ist ein Cu₂O mit ungestörter Struktur. Die Reaktionskinetik wird stark von der Ausgangszusammensetzung des Substratgemisches beeinflu\t.

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600–750 K , . . Cu₂S, Cu₂SO₂ + Cu₂SO₄ — Cu₂O . .

     

Studies of the reaction mechanism between copper(II) sulphate and excess copper(I) sulphide

The reaction process between CuSO₄ and excess Cu₂S in the temperature range 650–750 K was investigated by methods of thermal analysis and by studying the phase contentss of the products as a function of the fractional conversion. The reaction proceeds in three steps, with Cu₂S and a new phase described by the formula Cu₂SO₂ as intermediates. This new phase is liquid under the conditions of the reaction. The final product of the reaction is a defective crystalline Cu₂O.

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Zusammenfassung Der Verlauf der Reaktion zwischen CuSO₄ und überschüssigem Cu₂S im Temperaturbereich von 650–750 K wurde mittels thermoanalytischer Methoden und durch Ermittlung der Phasenzusammensetzung in AbhÄngigkeit von der Konversion untersucht. Die Reaktion verlÄuft in drei Schritten mit Cu₂S und einer neuen Phase der Zusammensetzung Cu₂SO₂ als Zwischenproduke. Die neue Phase ist unter den Reaktionsbedingungen eine Flüssigkeit. Endprodukt der Reaktion ist nicht völlig kristallines Cu₂O.

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CuSO₄ Cu₂S 650–750 K . Cu₂S , Cu₂SO₂ . Cu₂O .

     

Unprecedented copper(I)-catalyzed in situ double cycloaddition reaction based on 2-cyanopyrimidine

The solvothermal in situ double cycloaddition reaction of 2-cyanopyrimidine, Cu(2)O and NaN(3) with aqueous ammonia additive generated a two dimensional copper(I) coordination polymer with 5-pyrimidyl-tetrazolate, 3,5-bispyrimidyl-1,2,4-triazolate and the cyano group as the ligands. This reaction can be tuned to yield two dimensional coordination polymers solely based on tetrazolate or 1,2,4-triazolate ligands.     

The directional reaction of hydrazine with silver complexes. Part 3. Synthesis and characterization of a copper(I)-hydrazine intermediate complex,Na(N2H4)CuCl2

On the basis of previous work on the directional reaction of hydrazine with silver complexes, the Na(N₂H₄)CuCl₂ complex was prepared in NaOH solution and its structure determined by elemental analysis, electronic, e.s.r., i.r. spectra and by d.t.a. analysis. The i.r. spectrum indicated the presence of bridging hydrazine and chloride. The complex may be polymeric, i.e. an axially elongated (4 + 2) octahedron, with a layer structure connected by hydrazine and chloride ions. Na⁺ ions are also present in the layers. The addition of the Na(N₂H₄)CuCl₂ complex to N₂H₄ plus the Ag(NH₃)₂ ⁺ cation not only enhances the oxidation rate, but also increases the N₂(%) formed by four-electron reduction of hydrazine by the silver complex.     

Synthesis of the first examples of stable heterometallic isopropoxides of an organometallic RSn(IV) moiety

Five-, six-, and seven-coordinate volatile butyltin(IV) heterobimetallic derivatives, respectively of the types, [BuSn{(μ-OPrⁱ)₂Al(OPrⁱ)₂}Cl₂] (1), [BuSn{(μ-OPrⁱ)₂Al(OPrⁱ)₂}₂Cl] (2), and BuSn{(μ-OPrⁱ)₂M(OPrⁱ)_x − 2}₃ (3:M = Al (x = 4); 4:M = Ga (x = 4); 5:M = Nb (x = 6)) have been synthesized by the reactions of BuSnCl₃ with potassium tetraisopropoxoaluminate in 1:1, 1:2, and 1:3 molar ratios. Replacement reactions of chloride in (1) and (2) with appropriate alkoxometallate (tetraisopropoxoaluminate, tetraisopropoxogallate, or hexaisopropoxoniobate) ligands result in the formation of novel BuSn(IV) heterotri- and tetra-metallic derivatives. All of these derivatives have been characterized by elemental analyses, molecular weight measurements, and spectroscopic (IR, ¹H, ²⁷Al, and ¹¹⁹Sn NMR) studies. Based on these studies, plausible structures for the new derivatives involving bidentate ligation of the alkoxometallate ligands have been suggested.     

Perturbation of the Electronic Structure of a Copper(II) ion by a Cu(I)Cl Moiety in a Class I Mixed Valence Copper Complex, Cu(II)(Me(5)dien)Cl(2)(Cu(I)Cl)

A new mixed valence copper complex Cu(II)(Me(5)dien)Cl(2)(Cu(I)Cl) (2) was obtained from the reaction of CuCl with Cu(II)(Me(5)dien)Cl(2) (1) in acetonitrile. The structures of 1 and 2 have been determined by single-crystal X-ray diffraction analyses. Compound 1 crystallizes in the monoclinic space group P2(1)/n with a = 8.374(5) ?, b = 17.155(3) ?, c = 23.806(5) ?, beta = 94.40(4) degrees, Z = 8, and V = 3398(1) ?(3) while compound 2 crystallizes in orthorhombic space group Pbcn with a = 14.71(1) ?, b = 16.06(2) ?, c = 13.38(1) ?, Z = 8, and V = 3159(5) ?. The Cu(II)(Me(5)dien)Cl(2) unit in both compounds has a similar distorted square-pyramidal geometry. The Cu(I)Cl moiety in 2 is attached to the Cu(II) unit via two bridging chlorine atoms and has a distorted trigonal planar geometry. UV-vis and EPR spectroscopic studies and molecular orbital calculations established the presence of significant perturbation of the Cu(I)Cl unit to the electronic structure of the Cu(II) ion in compound 2.     

Stereoselective synthesis of an advanced taxusin intermediate: an application of the type 2 intramolecular Diels–Alder reaction

Stereoselective synthesis of an advanced taxusin intermediate is described. The key step is the successful application of the type 2 intramolecular Diels–Alder (IMDA) reaction for the assembly of the tricyclic core of this natural product.     

Tris-(2-aminoethyl) amine as a novel and efficient tripod ligand for a copper(I)-catalyzed C-O coupling reaction

We have introduced a novel, efficient, commercially available and economically attractive N-donor tripod ligand, tris-(2-aminoethyl)amine for copper-catalyzed Ullmann diaryl ether synthesis. This catalyst system is highly active for both aryl iodides and aryl bromides. Variously substituted diaryl ethers have been synthesized in good to excellent yields.