CuII Complexes Research Articles

Oxa‐TriQuinoline: A New Entry to Aza‐Oxa‐Crown Architectures**

AbstractA new 15‐membered‐macrocyclic molecular entity, oxa‐TriQuinoline (o‐TQ), was designed and synthesized. In o‐TQ, three oxygen atoms were joined onto three quinoline units at the 2‐ and 8‐positions in a head‐to‐tail fashion by three‐fold SNAr reactions, giving rise to the characteristic N3O3 aza‐oxa‐crown architecture. o‐TQ can serve as a new tridentate nitrogen ligand to capture a CuI cation and adopt a bowl shape, before supramolecular complexation with corannulene and [12]cycloparaphenylene (CPP) occurs through π–π and CH–π interactions. In the presence of the CuI cation, the non‐emissive o‐TQ becomes a highly emissive material in the solid state, whereby the emission wavelengths depend on the ancillary ligand on the CuI cation. The o‐TQ/CuI complex is able to promote carbene catalysis to provide a range of enamines with a gem‐difluorinated terminus.

Two New Compounds Based on Bi-Capped Keggin Polyoxoanions and Cu-Bpy Cations Contain Both CuII and CuI Complexes: Synthesis, Characterization and Properties.

Two inorganic-organic hybrid complexes based on bi-capped Keggin-type cluster, {([CuII(2,2'-bpy)2]2[PMoVI8VV2VIV2O40(VIVO)2])[CuI(2,2'-bpy)]}∙2H2O (1) and {[CuII(2,2'-bpy)2]2[SiMoVI8.5MoV2.5VIVO40(VIVO)2]}[CuI0.5(2,2'-bpy)(H2O)0.5] (2) (bpy = bipyridine), had been hydrothermally synthesized and structurally characterized by elemental analysis, FT-IR, TGA, PXRD and X-ray single-crystal diffraction analysis. Compound 1 consists of a novel 1-D chain structure constructed from [CuI(2,2'-bpy)]+ unit linking bi-supported POMs anion {[CuII(2,2'-bpy)2]2[PMoVI8VV2VIV2O40(VIVO)2]}-. Compound 2 is a bi-capped Keggin cluster bi-supported Cu-bpy complex. The main highlights of the two compounds are that Cu-bpy cations contain both CuI and CuII complexes. Furthermore, the fluorescence properties, the catalytic properties, and the photocatalytic performance of compounds 1 and 2 have been assessed, and the results show that both compounds are active for styrene epoxidation and degradation and adsorption of Methylene blue (MB), Rhodamine B (RhB) and mixed aqueous solutions.

Spin Frustrated Pyrazolato Triangular CuII Complex: Structure and Magnetic Properties, an Overview

The synthesis and structural characterization of a new triangular Cu3–μ3OH pyrazolato complex of formula, [Cu3(μ3−OH)(pz)3(Hpz)3][BF4]2 (1−Cu3), Hpz = pyrazole, is presented. The triangular unit forms a quasi-isosceles triangle with Cu–Cu distances of 3.3739(9), 3.3571(9), and 3.370(1) Å. This complex is isostructural to the hexanuclear complex [Cu3(μ3−OH)(pz)3(Hpz)3](ClO4)2]2 (QOPJIP). A comparative structural analysis with other reported triangular Cu3–μ3OH pyrazolato complexes has been carried out, showing that, depending on the pyrazolato derivative, an auxiliary ligand or counter-anion can affect the nuclearity and/or the dimensionality of the system. The magnetic properties of 1−Cu3 are analyzed using experimental data and DFT calculation. A detailed analysis was performed on the magnetic properties, comparing experimental and theoretical data of other molecular triangular Cu3–μ3OH complexes, showing that the displacement of the μ3−OH− from the Cu3 plane, together with the type of organic ligands, influences the nature of the magnetic exchange interaction between the spin-carrier centers, since it affects the overlap of the magnetic orbitals involved in the exchange pathways. Finally, a detailed comparison of the magnetic properties of 1−Cu3 and QOPJIP was carried out, which allowed us to understand the differences in their magnetic properties.

Aqua-{μ-1,4-bis-[(1,4,7,10-tetra-aza-cyclo-dodecan-1-yl)meth-yl]benzene}(nitrato-κO)dicopper(II) tris-(nitrate) trihydrate.

In the title dinuclear CuII complex, [Cu2(NO3)(C24H46N8)(H2O)](NO3)3·3H2O, the two CuII mol-ecules both have a square-pyramidal geometry, but the ligands in the axial positions are different: a water mol-ecule and a nitrate ion. All nitrate ions, water mol-ecules, and N-H groups are involved in an inter-molecular hydrogen-bond network.

Synthesis and Transition Metal Complexes of ((Phenylphosphanediyl) bis(ethyne‐2,1‐diyl))bis(diphenyl‐phosphane), [PhP{C≡CPPh2}2

AbstractThis paper describes the synthesis of a new acetylene‐bridged triphosphine, ((phenylphosphanediyl)bis‐(ethyne‐2,1‐diyl))bis(diphenylphosphane) [PhP{C≡CPPh2}2] (2) and its coordination complexes of RuII, RhIII, CuI, PdII and PtII. The reaction of diethynylphenylphosphine [PhP{C≡CH}2] (1) with two equivalents of LiHMDS followed by the addition of PPh2Cl resulted in 2. Treatment of 2 with [Ru(η6‐p‐cymene)Cl2]2 and [RhCp*Cl2]2 in 1 : 1.5 molar ratios produced trinuclear complexes [{Ru(η6‐p‐cymene)Cl2}3{μ3‐PPh(C≡CPPh2)2}] (3) and [(RhCp*Cl2)3{μ3‐PPh(C≡CPPh2)2}] (4). The molecular structure of 3 was confirmed by single crystal X‐ray analysis. Treatment of 2 with M(COD)Cl2 (M=Pd, Pt) in 2 : 3 ratio afforded open book type complexes [(MCl2)3{μ3‐PPh(C≡CPPh2)}2] (5 M=Pd, 6 M=Pt). The reaction of 2 with CuI in 1 : 2 ratio afforded 1‐D coordination polymer [{Cu2(μ2‐I)2(CH3CN)}{PPh(C≡CPPh2)2}3{CuI}2] (7) containing [(CuI)2{μ2‐(P−C≡C−P)3}] cylindrical units.

Self-Assembled Macrocyclic Copper Complex Enables Homogeneous Catalysis for High-Loading Lithium-Sulfur Batteries.

The practical viability of high energy density lithium-sulfur (Li-S) batteries stipulates the use of a high-loading cathode and lean electrolyte. However, under such harsh conditions, the liquid-solid sulfur redox reaction is much-retarded due to the poor sulfur and polysulfides utilization, leading to low capacity and fast fading. Herein, a self-assembled macrocyclic Cu(II) complex (CuL) is designed as an effective catalyst to homogenize and maximize the liquid-involved reaction. The four-N atoms coordinated Cu(II) ion features a planar dsp 2 hybridization, showing a strong bonding affinity towards lithium polysulfides (LiPSs) along the dz 2 orbital via steric effect. Such a structure not only lowers the energy barrier of the liquid-solid conversion (Li2 S4 to Li2 S2 ) but also guides a 3D deposition of Li2 S2 /Li2 S. As such, with a 1 wt% electrolyte additive of CuL, a high initial capacity of 925 mAh g-1 and areal capacity of 9.62 mAh cm-2 with a low decay of 0.3%/cycle can be achieved under a high sulfur loading of 10.4mg cm-2 and low electrolyte/sulfur ratio of 6μL mgs -1 . This work is expected to inspire the design of homogenous catalysts and accelerate the uptake of high-energy-density Li-S batteries. This article is protected by copyright. All rights reserved.

A polynuclear CuIIBiIII complex with antipyrine‐derived Schiff‐base: Preparation, characterization, and biological evaluations

Schiff base {(E)‐4‐((2‐hydroxy‐3‐methoxybenzylidene)amino)‐1,5‐dimethyl‐2‐phenyl‐1,2‐dihydro‐3H‐pyrazol‐3‐one} was prepared by the condensation reaction between 2‐hydroxy‐3‐methoxybenzaldehyde and 4‐aminoantipyrine. In the process of forming the title complex, Schiff base was first coordinated with CuII ions to form the mononuclear CuII complex (abbreviated as the complex (I)). Next, Schiff base in the complex (I) removed a phenyl group and then changed from the amide to the iminol. The tautomer further formed the complex through the iminol oxygen, and the phenolic oxygen coordinated with metal ions (CuII and BiIII). The structure of the polynuclear CuIIBiIII complex (abbreviated as the complex (II)) was identified as [Bi2Cu6 L6O3] (L = C13H13N3O3) by elemental analysis, FT‐IR spectra, and single‐crystal X‐ray diffraction analysis. The antibacterial effect of Schiff base and its complex (II) were assessed on four bacterial strains involving gram‐positive strains (S. aureus and B. subtilis) and gram‐negative strains (E. coli and P. aeruginosa). The complex (II) exhibited stronger antibacterial activity than Schiff base. Assessment of cytotoxic activity against SNU‐16 cells (Human gastric cancer) has demonstrated that the complex (II) was more active than Schiff base, and their IC50 values were 0.29 and 1.83 μM, respectively.

Quantitative Electromerism of a Well-defined Mononuclear Copper Complex Through Reversible Intramolecular Metal-Ligand Electron Transfer.

Copper amine oxidases are enzymes that exhibit in their active site a mononuclear copper complex and a 2,4,5-trihydroxyphenylalanine quinone (TPQ) cofactor; in the oxidative half of the catalytic cycle, the enzymes regulate their activity by a temperature-dependent electron transfer equilibrium between the CuII complex with the reduced, aminoquinol form of the cofactor and the reactive CuI complex with the corresponding oxidized, semiquinone form of the cofactor. Here, we report the first mononuclear copper complex with redox-active ligands showing quantitative, reversible electromerism between a CuII eletromer with reduced, neutral ligand and a CuI electromer with an oxidized, radical monocationic ligand. The CuII form, being exclusively present at low temperature, exhibits a lower enthalpy (like the enzymes), but the CuI complex exhibits a higher entropy and is exclusively present at room temperature in CH2Cl2 solution. Further analysis, based on six different copper complexes, discloses a large solvent effect on electromerism.

Complexes of NiII, CoII, ZnII, and CuII with Promising Anti-Tuberculosis Drug: Solid-State Structures and DFT Calculations

Four new NiII, CoII, ZnII, and CuII complexes with the promising anti-tuberculosis drug (E/Z)-N′-((5-Hydroxy-3,4-bis(hydroxymethyl)-6-methylpyridin-2-yl)methylene)-isonicotino-hydrazide (LH) were synthesized and characterized by structural methods: single-crystal X-ray diffraction, vibrational spectroscopy, and mass spectrometry. The NiII, CoII, and ZnII metal ions form only amorphous phases with various morphologies according to mass spectrometry and IR spectroscopy. The CuII forms a crystalline 1D coordination polymer with the relative formula {[CuLCl]·0.5H2O}∞1. Even though the LH ligand in the crystalline state includes a mixture of E-/Z-isomers, only the tautomeric iminol E-/Z-form is coordinated by CuII in the crystal. The copper(II) complex crystallizes in the monoclinic P21/n space group with the corresponding cell parameters a = 16.3539(11) Å, b = 12.2647(6) Å, and c = 17.4916(10) Å; α = 90°, β = 108.431(7)°, and γ = 90°. DFT calculations showed that the Z-isomer of the LH ligand in solution has the lowest formation energy due to intramolecular hydrogen bonds. According to the quantum chemical calculations, the coordination environment of the CuII atom during the transfer of the molecule into the solution remains the same as in the crystal, except for the polymeric bond, namely, distorted trigonal bipyramidal. Some of the complexes investigated can be used as effective sensors in biosystems.

DNA interactions, docking and in vitro cytotoxicity studies of [M(Hvalmea)2] complexes (M = CuII, CoIII)

Two new Schiff base mononuclear CuII and CoIII complexes were synthesized by the condensation of monoethanolamine and o-vanillin precursors. The X-ray crystallography of the complexes were reported. Both complexes had same ligands in their structures with different environment around transition metal ions. Different experimental such as absorption studies, cyclic voltammetry, ethidium bromide displacement studies and viscosity measurement besides of docking method were used to study the binding of the complexes to DNA. Based on these studies, intercalation was proposed to be the main mode of binding for both complexes and CuII complex was a better intercalator in interaction with DNA than CoIII complex. Also, CuII complex triggered double strand break in presence of oxidized agent, H2O2. The MTT and Apoptosis/necrosis analysis were revealed that CuII complex induced apoptosis as compared with anticancer agent, Cisplatin.

Room-Temperature Cu-Catalyzed Amination of Aryl Bromides Enabled by DFT-Guided Ligand Design.

Ullmann-type C-N coupling reactions represent an important alternative to well-established Pd-catalyzed approaches due to the differing reactivity and the lower cost of Cu. While the design of anionic Cu ligands, particularly those by Ma, has enabled the coupling of various classes of aryl halides and alkyl amines, most methods require conditions that can limit their utility on complex substrates. Herein, we disclose the development of anionic N1,N2-diarylbenzene-1,2-diamine ligands that promote the Cu-catalyzed amination of aryl bromides under mild conditions. Guided by DFT calculations, these ligands were designed to (1) increase the electron density on Cu, thereby increasing the rate of oxidative addition of aryl bromides, and (2) stabilize the active anionic CuI complex via a π-interaction. Under optimized conditions, structurally diverse aryl and heteroaryl bromides and a broad range of alkyl amine nucleophiles, including pharmaceuticals bearing multiple functional groups, were efficiently coupled at room temperature. Combined computational and experimental studies support a mechanism of C-N bond formation that follows a catalytic cycle akin to the well-explored Pd-catalyzed variants. Modification of the ligand structure to include a naphthyl residue resulted in a lower energy barrier to oxidative addition, providing a 30-fold rate increase relative to what is seen with other ligands. Collectively, these results establish a new class of anionic ligands for Cu-catalyzed C-N couplings, which we anticipate may be extended to other Cu-catalyzed C-heteroatom and C-C bond-forming reactions.

Metal complexes of 1,4-bis(2-hydroxyethyl) piperazine: Thermodynamic and theoretical approach.

In the present study, the acid-base equilibria of 1,4-bis(2-hydroxyethyl)piperazine (BHEB) and the formation equilibria of complexes with the metal ions Cu(II), Ni(II), Co(II) and Zn(II) are investigated using the potentiometric technique. The acid-dissociation constants of BHEP in the protonated form and the formation constants of the complexes are determined using the Miniquad-75 program in the temperature range (15oC - 35oC). The thermodynamic parameters were determined and discussed. The concentration distribution diagrams of the complexes are evaluated. The effect of metal ion properties such as atomic number, ionic radius, electronegativity, and ionization potential are investigated. The complexes were synthesized and characterized by elemental analysis and mass spectra. Density Functional Theory (DFT) calculations have been performed to study the equilibrium geometry of 1,4-bis(2-hydroxyethyl)piperazine and its complexes. The optimization of the structure of the complexes reveals that CuII and CoII complexes have distorted octahedral geometry. NiII complex has a distorted square planar geometry. ZnII complex has a distorted tetrahedral geometry. The calculated total energies, energies of highest occupied molecular orbital (HOMO), energies of lowest unoccupied molecular orbital (LUMO) and dipole moments are reported. The N---N distance for uncoordinated 1,4-bis(2-hydroxyethyl)piperazine is calculated to be 2.870 Å and decreased to 2.588 Å, 2.491 Å, 2.502 Å, 2.479 Å, and 2.552 Å for Cu(II), Co(II), Ni(II) and Zn(II) complexes respectively. Also, bonds connected to N atoms are elongated upon complex formation. The interactions with the receptors as breast cancer oxidoreductase were feasible as evidenced by Docking analysis.

Dual Role of Glutathione as a Reducing Agent and Cu-Ligand Governs the ROS Production by Anticancer Cu-Thiosemicarbazone Complexes.

α-Pyridyl thiosemicarbazones (TSC) such as Triapine (3AP) and Dp44mT are a promising class of anticancer agents. Contrary to Triapine, Dp44mT showed a pronounced synergism with CuII, which may be due to the generation of reactive oxygen species (ROS) by Dp44mT-bound CuII ions. However, in the intracellular environment, CuII complexes have to cope with glutathione (GSH), a relevant CuII reductant and CuI-chelator. Here, aiming at rationalizing the different biological activity of Triapine and Dp44mT, we first evaluated the ROS production by their CuII-complexes in the presence of GSH, showing that CuII-Dp44mT is a better catalyst than CuII-3AP. Furthermore, we performed density functional theory (DFT) calculations, which suggest that a different hard/soft character of the complexes could account for their different reactivity with GSH.

Carbon dots as green photocatalysts for atom transfer radical polymerization of methacrylates

We herein report the use of carbon dots (CDs) in photoinduced atom transfer radical polymerizations (ATRP) as green metal-free sensitizers. In particular, the production of a polymethacrylate (poly-METAC, METAC = 2-(methacryloyloxy)ethyl]trimethylammonium chloride) by using cheap and easily affordable CDs made from citric acid and diethylenetriamine, under both ultraviolet (UV, λ = 365 nm) and visible light was studied. Different solvent systems have been tested and a CuII complex was used as catalyst. Under the best conditions a polymer in 89% conversion and with a narrow dispersity (1.4) was obtained. The first order kinetics and the “on-off” experiments gave further evidence of the constant concentration of radicals and of the controlled mechanism of the polymerization.

A Rigid Linker for Site-Selective Coordination of Transition Metal Cations: Combining an Acetylacetone with a Caged Phosphine

The combination of a soft phosphorus and a hard oxygen donor in the new ligand HacacTRIP leads to excellent site selectivity for the coordination of two different metal cations of matching Pearson character. The deprotonation step required for coordinating the acetylacetone oxygen donor further increases the selectivity. In contrast to most phosphines, the use of the caged phosphatriptycene motif enables a rigid and directional orientation of the phosphorus binding site which is required to form stable coordination network structures. In addition to the synthesis of HacacTRIP, we present its selective coordination. The deprotonated acetylacetone was selectively bound to CuII and FeIII. The solid state structure of the former displays a rare axial coordination of chloroform molecules. The phosphorus donor was selectively coordinated to the monovalent coinage metal cations CuI, AgI, and AuI. The CuI and AgI complexes represent the first examples in which a phosphatriptycene is bound to these metal cations. Heterometallic coordination compounds were characterized with combinations of these two groups. They comprise an oligonuclear CuI/CuII mixed-valence compound in which iodide binds to both CuI and CuII cations and a complex in which acacTRIP- bridges CuII and AuI. In addition to these discrete aggregates, the ligand has been used to link FeIII and AgI into a 2D coordination polymer with unprecedented trigonal planar coordination of three bulky phosphatriptycenes to a cation and resulting honeycomb topology. Its almost regular hexagons underline the desired rigidity of the ditopic acacTRIP- ligand.

Cationic surfactant influence on ternary complexes of CoII, NiII, CuII and ZnII ions with aspartic and citric acids

A potentiometric titration study has been undertaken to determine the cationic surfactant influence on mixed ligand complexes in ternary systems consisting of cobalt (II), nickel (II), copper (II), and zinc (II) with aspartic and citric acids at various concentrations (0.0–2.5% w/v) of the CTAB (Cetyltrimethyl ammonium bromide)-surfactant solution while maintaining an ionic strength of 0.16 mol L-1 (NaCl) at 30 °C. Titrations were performed in the presence of different ratios (M:L:X = 1:2:2, 1:4:2, and 1:2:4) of metal (M) and aspartic acid (L) to citric acid (X) using sodium hydroxide. Model systems were developed based on statistical parameters and residual analysis. For Co(II), Ni(II), Cu(II), and Zn(II), the species detected were MLXH2, MLX2H5, and MLX3. The electrostatic relationship of the ligands' side chains, charge neutralization, chelate effect, stacking interactions, and hydrogen bonding are used to explain the trend in the variation of logarithm of stability constants (log β) values with changing dielectric constant and mole fraction of the surfactant. The variation in species distribution as a function of pH and surfactant composition is also presented and discussed, as are plausible equilibria for the formation of the species and structures of the ternary complexes are also presented and discussed.

Impact of human serum albumin on CuII and ZnII complexation by ATSM (diacetyl-bis(N4-methylthiosemicarbazone)) and a water soluble analogue.

The chelator diacetyl-bis(N4-methylthiosemicarbazone) (ATSM) and its complexes with CuII and ZnII are becoming increasingly investigated for medical applications such as PET imaging for anti-tumour therapy and the treatment of amyotrophic lateral sclerosis. However, the solubility in water of both the ligand and the complexes presents certain limitations for in vitro studies. Moreover, the stability of the CuII and ZnII complexes and their metal exchange reaction against the potential biological competitor human serum albumin (HSA) has not been studied in depth. In this work it was observed that the ATSM with an added carboxylic group into the structure increases its solubility in aqueous solutions without altering the coordination mode and the conjugated system of the ligand. The poorly water-soluble CuII- and ZnII-ATSM complexes were prevented from precipitating due to the binding to HSA. Both HSA and ATSM show a similar thermodynamic affinity for ZnII. Finally, the CuII-competition experiments with EDTA and the water-soluble ATSM ligands yielded an apparent log Kd at pH 7.4 of about -19. When ATSM was added to CuII- and ZnII-loaded HSA, withdrawing of ZnII was kinetically favoured, but this metal is slowly substituted by the CuII afterwards taken from HSA so that this protein could be considered as a source of CuII for ATSM.

Elucidating the reaction mechanism of SO2 with Cu-CHA catalysts for NH3-SCR by X-ray absorption spectroscopy.

The application of Cu-CHA catalysts for the selective catalytic reduction of NOx by ammonia (NH3-SCR) in exhaust systems of diesel vehicles requires the use of fuel with low sulfur content, because the Cu-CHA catalysts are poisoned by higher concentrations of SO2. Understanding the mechanism of the interaction between the Cu-CHA catalyst and SO2 is crucial for elucidating the SO2 poisoning and development of efficient catalysts for SCR reactions. Earlier we have shown that SO2 reacts with the [Cu2II(NH3)4O2]2+ complex that is formed in the pores of Cu-CHA upon activation of O2 in the NH3-SCR cycle. In order to determine the products of this reaction, we use X-ray absorption spectroscopy (XAS) at the Cu K-edge and S K-edge, and X-ray emission spectroscopy (XES) for Cu-CHA catalysts with 0.8 wt% Cu and 3.2 wt% Cu loadings. We find that the mechanism for SO2 uptake is similar for catalysts with low and high Cu content. We show that the SO2 uptake proceeds via an oxidation of SO2 by the [Cu2II(NH3)4O2]2+ complex, resulting in the formation of different CuI species, which do not react with SO2, and a sulfated CuII complex that is accumulated in the pores of the zeolite. The increase of the SO2 uptake upon addition of oxygen to the SO2-containing feed, evidenced by X-ray adsorbate quantification (XAQ) and temperature-programmed desorption of SO2, is explained by the re-oxidation of the CuI species into the [Cu2II(NH3)4O2]2+ complexes, which makes them available for reaction with SO2.

Nitrene transfer from a sterically confined copper nitrenoid dipyrrin complex.

Despite the myriad Cu-catalyzed nitrene transfer methodologies to form new C-N bonds (e.g., amination, aziridination), the critical reaction intermediates have largely eluded direct characterization due to their inherent reactivity. Herein, we report the synthesis of dipyrrin-supported Cu nitrenoid adducts, investigate their spectroscopic features, and probe their nitrene transfer chemistry through detailed mechanistic analyses. Treatment of the dipyrrin CuI complexes with substituted organoazides affords terminally ligated organoazide adducts with minimal activation of the azide unit as evidenced by vibrational spectroscopy and single crystal X-ray diffraction. The Cu nitrenoid, with an electronic structure most consistent with a triplet nitrene adduct of CuI, is accessed following geometric rearrangement of the azide adduct from κ1-N terminal ligation to κ1-N internal ligation with subsequent expulsion of N2. For perfluorinated arylazides, stoichiometric and catalytic C-H amination and aziridination was observed. Mechanistic analysis employing substrate competition reveals an enthalpically-controlled, electrophilic nitrene transfer for primary and secondary C-H bonds. Kinetic analyses for catalytic amination using tetrahydrofuran as a model substrate reveal pseudo-first order kinetics under relevant amination conditions with a first-order dependence on both Cu and organoazide. Activation parameters determined from Eyring analysis (ΔH‡ = 9.2(2) kcal mol-1, ΔS‡ = -42(2) cal mol-1 K-1, ΔG‡298K = 21.7(2) kcal mol-1) and parallel kinetic isotope effect measurements (1.10(2)) are consistent with rate-limiting Cu nitrenoid formation, followed by a proposed stepwise hydrogen-atom abstraction and rapid radical recombination to furnish the resulting C-N bond. The proposed mechanism and experimental analysis are further corroborated by density functional theory calculations. Multiconfigurational calculations provide insight into the electronic structure of the catalytically relevant Cu nitrene intermediates. The findings presented herein will assist in the development of future methodology for Cu-mediated C-N bond forming catalysis.

Syn-Selective Chlorosulfonylation of Alkynes via a Copper-Powder-Initiated Atom Transfer Radical Addition Reaction and Mechanistic Studies.

Copper-powder-catalyzed syn-selective chlorosulfonylation of readily available alkynes by an atom transfer radical addition (ATAR) process has been developed, providing straightforward access to a broad range of (Z)-β-chlorovinylsulfones in good yields under mild conditions. In addition, this method is ligand-free and features excellent stereoselectivity and high atom economy. Moreover, the product was obtained without an apparent loss of yield when the reaction was performed on the gram scale at a low catalyst loading. In this reaction, the copper powder not only acts as a sulfone radical initiator but also produces the catalytically active CuCl species. Mechanistic investigations and DFT calculation studies revealed that the stereoselectivity is controlled by the thermodynamic stabilities of the in situ-generated cyclic alkenyl CuII complex intermediate, which can serve as a chlorine atom transfer agent.