Copper Coordination Chemistry Research Articles

Fascinating novel coordination chemistry of copper(II) bound to d(CGCGCG) and explored by single-crystal X-ray analysis

Fascinating novel coordination chemistry of copper(II) bound to d(CGCGCG) and explored by single-crystal X-ray analysis

Anion influences on the solid state coordination chemistry of copper–bispyrazole materials

The reactions of the p-xylene-bridged and methylene-bridged bipyrazolyl ligands 1,4-bis[(3′,5′-dimethyl-1H-pyrazole-4′-yl)methylene]benzene (xdpH2) and bis[(3′,5′-dimethyl-1H-pyrazole-4′-yl)]methane (mdpH2) with the appropriate copper salt have provided eight unique members of the Cu/bipyrazole/X system with X=Cl−, Br−, I− and SO42−. The anionic component of [Cu(xdpH2)(H2O)]Cl·H2O (1·H2O) acts as a simple charge-compensating counterion. In contrast, the anionic units of [Cu(xdpH2)Cl2]·2DMF (2·2DMF), [Cu(xdpH2)Cl2(DMF)]·DMF (3·DMF), [Cu2(xdpH2)2Br2] (4), [Cu(mdpH2)Br2] (5), [Cu4(xdpH2)4I4] (6), [Cu2(xdpH2)2(SO4)]·H2O (7·H2O) and [Cu2(xdpH2)2(SO4)]·2H2O (8·2H2O) are involved in bonding to the copper sites. Compounds 1, 4, and 6–8 contain Cu(I) sites while compounds 2, 3, and 5 are polymers of Cu(II). Compounds 1–5 and 7 are one-dimensional, while 8 is two-dimensional and 6 is three-dimensional. Considering the {Cu4I4} clusters of 6 as nodes, the structure is a fivefold interpenetrated framework with individual networks adopting the common {33.123} topology in Schlafli notation.

ChemInform Abstract: DFT/TDDFT Insights into the Chemistry, Biochemistry and Photophysics of Copper Coordination Compounds

AbstractReview: 188 refs.

SAPP modulates iron efflux from brain microvascular endothelial cells by stabilizing the ferrous iron exporter ferroportin.

A sequence within the E2 domain of soluble amyloid precursor protein (sAPP) stimulates iron efflux. This activity has been attributed to a ferroxidase activity suggested for this motif. We demonstrate that the stimulation of efflux supported by this peptide and by sAPPα is due to their stabilization of the ferrous iron exporter, ferroportin (Fpn), in the plasma membrane of human brain microvascular endothelial cells (hBMVEC). The peptide does not bind ferric iron explaining why it does not and thermodynamically cannot promote ferrous iron autoxidation. This peptide specifically pulls Fpn down from the plasma membrane of hBMVEC; based on these results, FTP, for ferroportin-targeting peptide, correctly identifies the function of this peptide. The data suggest that in stabilizing Fpn via the targeting due to the FTP sequence, sAPP will increase the flux of iron into the cerebral interstitium. This inference correlates with the observation of significant iron deposition in the amyloid plaques characteristic of Alzheimer's disease.

Evaluation of [12C/11C]Carbon Monoxide Binding to Copper(I) Tris(pyrazolyl)borate Complexes

AbstractThe copper(I) coordination chemistry of tris(3‐R‐5‐R′‐pyrazolyl)borate ligands (TpR,R′) bearing substituent groups attached to the pyrazole rings has been investigated under nitrogen and carbon monoxide atmospheres [1 (TpPh,SMe) R = Ph, R′ = SCH3; 2 (TpPy) R = 2‐pyridyl, R′ = H; 3 (TpPhos,Me) R = 2‐(diphenylphosphinyl)phenyl, R′ = CH3]. The reactivity is strongly dependent on the coordinating potential of the substituent groups; in the absence of CO, 1 formed an insoluble complex [Cu(TpPh,SMe)]n (1b), 2 formed a multinuclear species [Cu(TpPy)]n (2a; tetrameric in solution, dimeric in the solid state) and 3 formed a discrete complex [Cu(TpPhos,Me)] (3a). Under a CO atmosphere, 1 displayed irreversible CO binding to form the complex [Cu(TpPh,SMe)CO] (1c), 2 showed reversible CO binding between 2a and the mononuclear species [Cu(TpPy)CO] (2b), and 3 did not bind to CO, but instead formed 3a. The reactivity of the copper complexes of 1 and 2 with [11C]carbon monoxide has been examined in the radiochemistry laboratory to investigate the reversibility of 11CO binding. The solid‐state structures of [Tl(TpPh,SMe)] (1a), 1c and 2a were elucidated by X‐ray crystallography.

DFT/TDDFT insights into the chemistry, biochemistry and photophysics of copper coordination compounds

Highlighting the recent progress in DFT/TDDFT application to coordination chemistry of copper.

ChemInform Abstract: Structure and Bonding in Copper(I) Carbonyl and Cyanide Complexes

AbstractReview: 285 refs.

Structure and Bonding in Copper(I) Carbonyl and Cyanide Complexes

The coordination chemistry of copper(I) carbonyls and cyano complexes is reviewed. Primary attention is focused on structural chemistry, including coordination behavior, bridging modes, network formation, flexible coordination number, and reversible ligand binding. Additional coverage of infrared spectroscopy and orbital interactions in carbonyl and cyanide bonding and the photophysical behavior of metal cyano complexes is also included.

Solid state coordination chemistry of copper with pyridyltetrazoles: Structural consequences of incorporation of coordinating anions

The hydrothermal reactions of various Cu(II) salts with 3- and 4-pyridinetetrazole and pyrazinetetrazole were exploited in the preparation of a series of Cu(II) and Cu(I) azolate materials. The parent copper/pyridyltetrazole compositions are observed in the two-dimensional [Cu(3-pyrtet)2] (1), the reduced three-dimensional [Cu(4-pyrtet)] (2) and reduced two-dimensional [Cu(4-pyrtet)]·0.5DMF (3·0.5DMF) (Hpyrtet=pyridyltetrazole). The consequences of introducing coordinating anions are revealed in the structures of the one-dimensional [CuCl2(4-Hpyrtet)]·0.5H2O (4·0.5H2O) and the two-dimensional [Cu2I2(4-Hpyrtet)] (5) and [Cu(acac)(4-pyrtet)] (7) (acac=acetylacetonate; H2en=ethylenediammonium cation). The pyrazinetetrazolate derivative [H2en]0.5[CuCl2(prztet)] (Hprztet=pyrazinetetrazole) (6) is one-dimensional, but structurally distinct from the chain observed for 4.

Copper

This chapter reviews the literature reported during 2011 on the chemistry of copper. In a departure from recent contributions published in Annual Reports that have preferentially selected examples of the biological and biomedical aspects of copper chemistry, this chapter focuses on key developments concerning the inorganic and coordination chemistry of copper. Selected areas describing the applications of copper containing compounds have been included.

Systematic coordination chemistry and cytotoxicity of copper(II) complexes with methyl substituted 4-nitropyridine N-oxides

Three new nitrato copper(II) complexes of dimethyl substituted 4-nitropyridine N-oxide were synthesized and characterized by elemental analysis, magnetic, spectroscopic, thermal and X-ray methods, respectively. They were isolated as trans isomers, mononuclear (μ = 1.70–1.88 BM), five ( 1– 2) and four (3) coordinate species of general formula [Cu(NO 3) 2(H 2O)L 2] where L = 2,3-dimethyl-, 2,5-dimethyl-4-nitropyridine N-oxide and [Cu (NO 3) 2L 2], L = 3,5-dimethyl-4-nitropyridine N-oxide, respectively. The X-ray crystal structure of ( 1) (L = 2,3-dimethyl-4-nitropyridine N-oxide) was determined. The organic ligands, the complexes and copper hexaqua ion as a reference were tested in vitro on the cytotoxic activity against human cancer cell lines: MCF-7 (breast), SW-707 (colon) and P-388 (murine leukemia). The complexes are relatively strong cytotoxic agents towards P-388 cell line. Comparative analysis was performed for all known copper(II) complexes containing methyl derivatives of the 4-nitropyridine N-oxide on the basis of their composition, structure and cytotoxic activities. To obtain the typical structure for these species (i.e., 4-coordinate mononuclear of the type trans-[Cu(inorganic anion) 2L 2]), two methyl groups must be situated on both sides of nitrogen atom(s) (i.e., NO and NO 2) in the ligand. The biological activity was found to be strongly dependent upon the number of the methyl groups and the type of cell line. The best cytotoxic results were found for the complexes without substituents or with one methyl group. Generally, for all cell lines, the complexation increased cytotoxicity when compared with the free ligands.

Dinuclear Copper Complexes Based on Parallel β-Diiminato Binding Sites and their Reactions with O2: Evidence for a Cu−O−Cu Entity

Investigations concerning the system β-diketiminato-Cu(I)/O(2) have revealed valuable insights that may be discussed in terms of the behavior of mononuclear oxygenases containing copper. On the other hand nature also employs dinuclear Cu enzymes for the activation of O(2). With this background the ligand system [(Me(2))(C(6)H(3))Xanthdim](2-) containing two parallel β-diiminato binding sites linked by a xanthene backbone with 2,3-dimethylphenyl residues at the diiminato units was investigated with respect to its copper coordination chemistry. The diimine [(Me(2))(C(6)H(3))Xanthdim]H(2) was treated with CuOtBu in the presence of acetonitrile, PPh(3), and PMe(3) to yield the corresponding complexes [(Me(2))(C(6)H(3))Xanthdim](Cu(L))(2) (L = CH(3)CN, 1, PPh(3), 2, and PMe(3), 3) that proved to be stable and were fully characterized. Single crystal X-ray diffraction analyses performed for the three complexes showed that considerable steric crowding within the binding pockets of 2 leads to a very long Cu-Cu distance while the structures of 1 and 3 are relaxed. Compounds 2 and 3 are relatively robust toward air, whereas 1 is very sensitive and quantitatively reacts with O(2) at room temperature (r.t.) within less than 2 min to give intractable compounds. At low temperatures the formation of a green intermediate was observed that was identified as a Cu(II)-O-Cu(II) species spectroscopically and chemically. This finding is of relevance also in the context of the results obtained testing 1 as a catalyst for phenol oxidation using O(2): 1 efficiently catalyzes phenol coupling, while there was no evidence for any oxygenation reactions occurring.

(Guanidine)copper complexes: structural variety and application in bioinorganic chemistry and catalysis

In this paper, guanidine copper compounds are reviewed with an emphasis on structural characteristics and their application in bioinorganic chemistry and catalysis. The literature survey includes the copper coordination chemistry of biological guanidine derivatives, peralkylated guanidines including bicyclic ones and of further nitrogen-rich guanidine-type systems such as azoimidazoles, triazolopyrimidines and triaminoguanidines. From a sporadic interest dating back to the 1960s, research on this ligand class and its use in copper coordination chemistry has gained new impetus since 2000. With the synthesis of examples with sophisticated substitution at the characteristic CN 3 framework, complex problems can be addressed in several fields of chemistry. This paper analyses the different types of guanidines for their special donor properties and highlights the specific advantages of guanidines as neutral donor ligands in copper coordination chemistry where a great variety of coordination modes was found. These compounds offer the ability to distribute the formal positive charge of the metal throughout the guanidine unit and represent more than simple σ-donating ligands.

Tripodal bis(imidazole)-based ligands and their chelation to copper(ii)

Three new copper(II) compounds are described containing chelating bis(imidazole)-based ligands. Compound 1, [Cu2(L1)2(H2O)2][SiF6]2·10H2O, was obtained by reaction of [bis-(1H-imidazol-2-yl)-methyl]-pyridin-2-ylmethyl-amine (L1) with Cu(BF4)2·6H2O in a glass vessel for a few weeks. The single-crystal X-ray structure of 1 consists of dinuclear copper(II) units, formed through ligand sharing. The starting BF4− anion was replaced by the SiF62− in the crystal structure of 1. In the crystal lattice, a discrete (H2O)8 cluster forms an eight-membered ring and is linked through four shared water molecules with the other (H2O)8 cluster. Both water clusters show hydrogen-bonding interactions with the neighbouring SiF62− anion. To investigate the effect of the presence of a bridging ligand such as oxalate on the coordination chemistry of L1 and copper(II) ion, compound 2, [Cu2(L1)(H2O)2][Cu(C2O4)2(ClO4)2]·2H2O, was prepared by reaction of L1 and Cu(ClO4)2·6H2O in the presence of oxalic acid; the crystal structure is built from 4+ and 4− ions in the crystal lattice. Compound 3, [Cu(ClO4)(C2O4)(HL2)H2O]·2H2O, was formed from the reaction of ligand [bis-(1H-imidazol-2-yl)-methyl]-isopropyl-amine (L2) and Cu(ClO4)2·6H2O in the presence of oxalic acid. The isopropylamine group is not coordinated to the copper in this case, but protonated. In compound 3, a mononuclear copper(II) unit is present, built from a bidentate L2, a bidentate oxalate, a monodentate perchlorate and a water. Two copper coordination entities are doubly bridged through hydrogen bonds with twice the pathway [Cu–OC2O4–(Owater)–Cu] to form a dimeric-like species. Low-temperature magnetic susceptibility studies showed no interaction between copper(II) ions.

Copper(II) coordination chemistry of 2-methyl-2-(2-pyridyl)-1,3-propan-diol: Syntheses and structures of mono-, di-, and tricopper complexes

Six copper(II) complexes with N,O-donor ligand 2-methyl-2-(2-pyridyl)-1,3-propan-diol (H 2ppdo) were synthesized and characterized. Treatment of CuCl 2 or Cu(OTf) 2 with H 2ppdo led to the formation of bis(H 2ppdo) monomers [Cu(H 2ppdo) 2][CuCl 4] ( 1) and [Cu(H 2ppdo) 2](OTf) 2 ( 2), respectively. Both 1 and 2 are comprised of the copper atom coordinated by two ligands in an axially-compressed tetragonal geometry with the pyridyl N atoms in the axial positions and the alcohol O atoms in the equatorial plane. The treatment of 1 or 2 with Et 3N produced copper(II) complexes of varying nuclearity. Treatment of 1 with excess Et 3N generated two binuclear Cu(II) clusters [Cu 2(Hppdo) 2Cl 2] ( 3) and [Cu 2(Hppdo) 2Cl 2(CH 3OH) 2] ( 4), where only one alcohol OH group per ligand has been deprotonated, while similar treatment of 2 with excess Et 3N afforded the trimeric copper(II) species [Cu 3(Hppdo) 4](OTf) 2 ( 5). The structures of 3 and 4 are similar, with alkoxo-O ligand atoms bridging between two square pyramidal copper atoms, and the alcohol-O ligand atoms either coordinating in the axial position in 3, or uncoordinated in 4. Treatment of CuCl 2 with H 2ppdo and Et 3N afforded the trinuclear Cu(II) complex, [Cu 3(Hppdo) 4]Cl 2 ( 6). Complexes 5 and 6 are made up of one square-planar copper sandwiched between two tetragonally distorted six-coordinate Cu(Hppdo) 2 moieties, where the bridging alkoxo-O atoms link the copper atoms.

Redox addressable ligands in copper(i) coordination chemistry: thione and oligosulfide-bridged 6-methyl-2,2′-bipyridines

The ligands 6-(6-methylpyridin-2-yl)pyridine-2(1H)-thione (1) and 1,2-bis(6′-methyl-2,2′-bipyridin-6-yl)disulfane (2) have been prepared and structurally characterized. Compound 2 is synthesized by the oxidative coupling of 1 using I2 or H2O2, but it also occurs spontaneously in solution in the absence of dithiothreitol. Under some conditions, oligosulfide bridges with three or four sulfur atoms (ligands 3 and 4, respectively) are produced in addition to 2. In the presence of dithiothreitol, 1 binds copper(I), functioning as a monodentate S-donor; the four ligands in [Cu(1)4]+ encapsulate the copper ion so that the sulfur atoms exhibit S⋯S contacts. The presence of the NH⋯N hydrogen bonded unit in the bpy domain in 1 prevents it acting as an N,N′-chelate. In the absence of dithiothreitol, copper(I) reacts with 1 to give [(1)2Cu(µ-2)Cu(1)2]2+ in addition to [Cu(1)4]+. While the thione ligand functions as an S-donor, the disulfide ligand 2, freed of the NH⋯N hydrogen bond, acts as a bis(bpy) chelate. Ligand 2 itself reacts with [Cu(NCMe)4]+ to give an orange solid, 5, tentatively proposed to be {[Cu(2)][PF6]}n. When 5 is treated with concentrated aqueous HCl, the insoluble [H22][CuCl4]·H2O is formed. By using a mixture of ligands 2, 3 and 4 with [Cu(NCMe)4]+, it is possible to isolate an example of a dinuclear copper(I) complex containing bridging 1,2-bis(6′-methyl-2,2′-bipyridin-6-yl)trisulfane (3) ligands. The complex [Cu2(3)2][PF6]2 features double helical P- and M-[Cu2(3)2]2+ cations. The role of face-to-face π-interactions, and the effect of the length and helical twist in the backbone of the oligosulfide-bridged bpy ligands in each of the structures have been evaluated.

Luminescent Copper(I) Halide Butterfly Dimers Coordinated to [Au(CH3imCH2py)2]BF4and [Au(CH3imCH2quin)2]BF4

The coordination chemistry of copper(I) halides to the homoleptic, N-heterocyclic carbene Au(I) complexes [Au(CH(3)imCH(2)quin)(2)]BF(4) and Au(CH(3)imCH(2)py)(2)]BF(4) was explored. The reaction of CuX (X = Cl, Br, I) with either [Au(CH(3)imCH(2)quin)(2)]BF(4) or [Au(CH(3)imCH(2)py)(2)]BF(4) produces trimetallic complexes containing Cu(2)X(2)-butterfly copper clusters coordinated to the two imine moieties. The triangular arrangement of the metals places the gold(I) center in close proximity (approximately 2.5-2.6 A) to the centroid of the Cu-Cu vector. The Cu-Cu separations vary as a function of bridging halide with the shortest Cu-Cu separations of approximately 2.5 A found in the iodo-complexes and the longest separations of 2.9 A found in the bridging chloride complexes. In all six complexes the Au-Cu separations range from approximately 2.8 to 3.0 A. In the absence of halides, the dimetallic complex [AuCu(CH(3)imCH(2)py)(2)(NCCH(3))(2)](BF(4))(2), containing a long Au-Cu distance of approximately 4.72 A is formed. Additionally, as the byproduct of the reaction of CuBr with [Au(CH(3)imCH(2)quin)(2)]BF(4) the deep-red, dimetallic compound, AuCuBr(2)(CH(3)imCH(2)quin)(2), was isolated in very low yield. All of these complexes were studied by NMR spectroscopy, mass spectrometry, and the copper containing species were additionally characterized by X-ray crystallography. In solution the copper centers dissociate from the gold complexes, but as shown by XANES and EXAFS spectroscopy, at low temperature the Cu-Cu linkage is broken, and the individual copper(I) halides reposition themselves to opposite sides of the gold complex while remaining coordinated to one imine moiety. In the solid state all of the complexes are photoluminescent, though the nature of the excited state was not determined.

Multicopper oxidases: a workshop on copper coordination chemistry, electron transfer, and metallophysiology

Multicopper oxidases (MCOs) are unique among copper proteins in that they contain at least one each of the three types of biologic copper sites, type 1, type 2, and the binuclear type 3. MCOs are descended from the family of small blue copper proteins (cupredoxins) that likely arose as a complement to the heme-iron-based cytochromes involved in electron transport; this event corresponded to the aerobiosis of the biosphere that resulted in the conversion of Fe(II) to Fe(III) as the predominant redox state of this essential metal and the solubilization of copper from Cu(2)S to Cu(H(2)O)( n ) (2+). MCOs are encoded in genomes in all three kingdoms and play essential roles in the physiology of essentially all aerobes. With four redox-active copper centers, MCOs share with terminal copper-heme oxidases the ability to catalyze the four-electron reduction of O(2) to two molecules of water. The electron transfers associated with this reaction are both outer and inner sphere in nature and their mechanisms have been fairly well established. A subset of MCO proteins exhibit specificity for Fe(2+), Cu(+), and/or Mn(2+) as reducing substrates and have been designated as metallooxidases. These enzymes, in particular the ferroxidases found in all fungi and metazoans, play critical roles in the metal metabolism of the expressing organism.

Molecular Oxygen and Sulfur Reactivity of a Cyclotriveratrylene Derived Trinuclear Copper(I) Complex

Our continuing efforts into developing copper coordination chemistry relevant to dioxygen-processing copper proteins has led us to design and synthesize a cyclotriveratrylene (CTV)-based trinucleating ligand, CTV-TMPA, which employs tetradentate tris(2-pyridylmethyl)-amine chelates (TMPA) for their copper ion binding sites. Binding of three copper ions per CTV-TMPA unit was established by various chemical and spectroscopic methods such as UV-vis and resonance Raman (rR) spectroscopies. The following complexes were observed: A tricopper(I) complex [(CTV-TMPA)Cu(I)(3)](3+) (1), a CO adduct [(CTV-TMPA)Cu(I)(3)(CO)(3)](3+) (1-CO; nu(C=O) = 2094 cm(-1)), a triphenylphosphine adduct [(CTV-TMPA)Cu(I)(3)(PPh(3))(3)](3+) (1-PPh(3)), a tricopper(II) complex [(CTV-TMPA)Cu(II)(3)](3+) (1-Ox), and its tris-monochloride or tris-monobromide adducts. Also, introduction of dioxygen to the -80 degrees C solutions of 1 leads to O(2)-adducts, the first example of a synthetic copper complex which can stabilize a mononuclear Cu(II)-superoxo and dinuclear peroxo species simultaneously within one complex {[Cu] = 1.53 mM in THF: (mu-1,2-peroxo complex, lambda(max) = 543 (epsilon 9650) nm): nu(O-O) = 825 ((Delta(18)O(2)) = -47) cm(-1); nu(Cu-O) = 506 ((Delta(18)O(2)) = -26) cm(-1): (superoxo complex, lambda(max) = 427 (epsilon 3150) nm): nu(O-O) = 1129 ((Delta(18)O(2)) = -60) cm(-1); nu(Cu-O) = 463 ((Delta(18)O(2)) = -27) cm(-1)}. Elemental sulfur reacts reversibly with 1 leading to a (proposed) hexanuclear species [{(CTV-TMPA)Cu(II)(3)}(2)(mu-1,2-S(2)(2-))(3)](6+) (1-S) {lambda(max) = 544 (epsilon 7270) nm}, possessing one dicopper(II)-disulfide structural type: {THF solvent) nu(S-S) = 489 ((Delta(34)S) = -10) cm(-1); nu(Cu-S) = 307 ((Delta(34)S) = -5) cm(-1)}. Derivation of spectroscopic, structural, and chemical conclusions were aided by the study of a close mononuclear analogue with one pyridyl group of the TMPA parent possessing a 6-CH(2)OCH(3) substituent, this being part of the CTV-TMPA architecture.

Copper-64 radiopharmaceuticals for PET imaging of cancer: advances in preclinical and clinical research.

Copper-64 (T(1/2) = 12.7 hours; beta(+), 0.653 MeV [17.8 %]; beta(-), 0.579 MeV [38.4 %]) has decay characteristics that allow for positron emission tomography (PET) imaging and targeted radiotherapy of cancer. The well-established coordination chemistry of copper allows for its reaction with a wide variety of chelator systems that can potentially be linked to peptides and other biologically relevant small molecules, antibodies, proteins, and nanoparticles. The 12.7-hours half-life of 64Cu provides the flexibility to image both smaller molecules and larger, slower clearing proteins and nanoparticles. In a practical sense, the radionuclide or the 64Cu-radiopharmaceuticals can be easily shipped for PET imaging studies at sites remote to the production facility. Due to the versatility of 64Cu, there has been an abundance of novel research in this area over the past 20 years, primarily in the area of PET imaging, but also for the targeted radiotherapy of cancer. The biologic activity of the hypoxia imaging agent, 60/64Cu-ATSM, has been described in great detail in animal models and in clinical PET studies. An investigational new drug application for 64Cu-ATSM was recently approved by the U.S. Food and Drug Administration (FDA) in the United States, paving the way for a multicenter trial to validate the utility of this agent, with the hopeful result being FDA approval for routine clinical use. This article discusses state-of-the-art cancer imaging with 64Cu radiopharmaceuticals, including 64Cu-ATSM for imaging hypoxia, 64Cu-labeled peptides for tumor-receptor targeting, (64)Cu-labeled monoclonal antibodies for targeting tumor antigens, and 64Cu-labeled nanoparticles for cancer targeting. The emphasis of this article will be on the new scientific discoveries involving (64)Cu radiopharmaceuticals, as well as the translation of these into human studies.