A new oxamido-bridged dinuclear copper(II) complex with large antiferromagnetic exchange interactions

A new oxamido-bridged dinuclear compound [Cu₂(µ-pmox)(DMF)₄]?·?2ClO₄ (1) (H₂pmox?=?N,N′-bis-(2-methylpyridyl)oxalamide, DMF?=?dimethylformamide) was synthesized and structurally characterized. The five-coordinate Cu(II) is bridged by oxamido groups and further cross-linked by C–H···O hydrogen bonds between the uncoordinated oxygen of perchlorate and methyl of DMF. The complex was also characterized by infrared spectroscopy and magnetic measurement. The copper complex exhibits strong antiferromagnetic interactions via the trans oxamido bridge with J of ?414?cm^?1, where J is the exchange parameter in the isotropic Hamiltonian H?=??JS₁S₂.     

Highly efficient phosphodiester hydrolysis promoted by a dinuclear copper(II) complex

The interaction of Cu(II) with the ligand tdci (1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol) was studied both in the solid state and in solution. The complexes that were formed were also tested for phosphoesterase activity. The pentanuclear complex [Cu(5)(tdciH(-2))(tdci)(2)(OH)(2)(NO(3))(2)](NO(3))(4).6H(2)O consists of two dinuclear units and one trinuclear unit, having two shared copper(II) ions. The metal centers within the pentanuclear structure have three distinct coordination environments. All five copper(II) ions are linked by hydroxo/alkoxo bridges forming a Cu(5)O(6) cage. The Cu-Cu separations of the bridged centers are between 2.916 and 3.782 A, while those of the nonbridged metal ions are 5.455-5.712 A. The solution equilibria in the Cu(II)-tdci system proved to be extremely complicated. Depending on the pH and metal-to-ligand ratio, several differently deprotonated mono-, di-, and trinuclear complexes are formed. Their presence in solution was supported by mass, CW, and pulse EPR spectroscopic study, too. In these complexes, the metal ions are presumed to occupy tridentate [O(ax),N(eq),O(ax)] coordination sites and the O-donors of tdci may serve as bridging units between two metal ions. Additionally, deprotonation of the metal-bound water molecules may occur. The dinuclear Cu(2)LH(-3) species, formed around pH 8.5, provides outstanding rate acceleration for the hydrolysis of the activated phosphodiester bis(4-nitrophenyl)phosphate (BNPP). The second-order rate constant of BNPP hydrolysis promoted by the dinuclear complex (T = 298 K) is 0.95 M(-1) s(-1), which is ca. 47600-fold higher than that of the hydroxide ion catalyzed hydrolysis (k(OH)). Its activity is selective for the phosphodiester, and the hydrolysis was proved to be catalytic. The proposed bifunctional mechanism of the hydrolysis includes double Lewis acid activation and intramolecular nucleophilic catalysis.     

Synthesis and structure of a dinuclear copper complex of a bis(bidentate)triazenide ligand

The synthesis and characterization of a dinuclear copper(II) complex with a bis(bidentate) ligand is reported. The ligand is a functionalized 1,3-diaryl triazene substituted with carboxymethyl groups at the ortho positions of the aryl rings. Reaction of this ligand with Cu₂(OAc)₄·2H₂O resulted in the formation of the Cu₂(OAc)₃(triazenide) where the triazenide binds to each copper through one of the triazenide nitrogens and the carbonyl oxygen of the pendant esters. The structures of this dinuclear complex and of the ligand are reported.     

Stacking interaction in crystals of a dinuclear rhodium complex with a bridging phenylborole ligand

Russian Chemical Bulletin -     

Synthesis and magnetism of a binuclear copper(II)–manganese(II) complex with N,N-bis(N-hydroxyethylaminoethyl)oxamido as a bridging ligand

The heterobinuclear complex, [CuMn(L)(phen)2](ClO4)2· H2O, [L = N,N-bis(N-hydroxyethyleneamine)oxamido, phen=1,10-phenanthroline], has been synthesized with N,N-bis(N-hydroxyethylaminoethyl)oxamido as the bridging ligand. The electronic reflectance spectrum indicates the presence of exchange-coupling interaction between bridging MnII and CuII ions. The variable-temperature magnetic susceptibility of the complex was measured over the 4–300K range. The magnetic coupling parameter is consistent with an antiferromagnetic exchange between the MnII ion and CuII ion and fits the data for a heterobinuclear CuII–MnII magnetic exchange model based on the Hamiltonian operator (H= –2JS1S2, S1=1/2, S2=5/2), giving the antiferromagnetic coupling parameter of 2J=–74.0cm–1.     

Influence of the bridging azine ligand on the rate of ligand substitution in a series of dinuclear platinum(II) complexes

A series of azine‐bridged dinuclear platinum(II) complexes of the type [{trans‐Pt(NH₃)₂(OH₂)}₂(μ‐azn)](ClO₄)₄ (where azn = pyrazine (pzn, Pt1 ), 2,3‐dimethylpyrazine (2,3‐pzn, Pt2 ), and 2,5‐dimethylpyrazine (2,5‐pzn, Pt3 )) were synthesized to investigate the influence of the bridging azine ligand on the reactivity of the platinum(II) centers. The pK_a values of the complexes were determined via acid–base titration, and the rate of substitution of the aqua moiety by a series of neutral nucleophiles, viz. thiourea (TU), 1,3‐dimethyl‐2‐thiourea (DMTU), and 1,1,3,3‐tetramethyl‐2‐thiourea (TMTU), was determined under pseudo‐first‐order conditions as a function of concentration and temperature using standard spectrophotometric techniques. The introduction of the methyl groups to the bridging azine linker in Pt2 and Pt3 leads to a moderate increase in the pK_a values obtained for the first and second deprotonation steps, respectively, as a result of the increased σ‐donor capacity of the bridging azine ligand trans to the aqua moiety. A comparison of the rate constants, k₁ and k₂, at 298 K, obtained for the substitution of the aqua moieties from Pt1 , Pt2 , and Pt3 by TU, shows that the introduction of the σ‐donating methyl groups on the bridging azine ligand in Pt2 and Pt3 results in a corresponding decrease in the reactivity, by ca. five times for the first substitution step and ca. 10 times for the second substitution step. Density functional theory calculations at the B3LYP/LACVP** level of theory for the complexes demonstrate that the introduction of electron‐donating methyl groups results in (i) increased steric hindrance over the metal centers and (ii) decreased the positive charge on the metal center and increases energy separation of the frontier molecular orbitals (E_HOMO – E_LUMO) of the ground‐state platinum(II) complexes, leading to a less‐reactive metal center. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 161–174, 2011     

Potent and selective inhibition of T-cell protein tyrosine phosphatase (TCPTP) by a dinuclear copper(II) complex

A dinuclear Cu(II) complex, [Cu(2)(μ-IDA)(phen)(3)(NO(3))]NO(3)·4H(2)O (phen = 1,10-phenanthroline, H(2)IDA = iminodiacetic acid), was found to potently and selectively inhibit T-cell protein tyrosine phosphatase, and lead to the anti-proliferation and apoptosis of C6 glioma cells.     

Synthesis,crystal structure and magnetic behavior of a two-dimensional copper(II) complex with mellitic anion as bridging ligand

A two-dimensional complex Cu₃[C₆(COO)₆](H₂O)₁₀ · 2H₂O has been prepared and its crystal structure determined by X-ray crystallography. In the complex each mellitic anion provides four carboxylate groups as coordinate groups and, according to the coordination, the four carboxylate groups are classified as two types according to its coordinate modes. The first is that a carboxylate group coordinates a copper(II) ion via its one oxygen atom, and the second one is that a carboxylate group, as a two-dentate ligand, coordinates to two copper(II) ions. The copper(II) ions also are classified as being of two types according to their coordinate modes. The configuration around each copper(II) ion is a distorted pyramid. The variable-temperature magnetic susceptibility of the complex was measured in the 4–300 K range and the magnetic data indicate that the magnetic interaction between bridging copper(II) ions displays an antiferromagnetic coupling below 42 K, while above 42 K a ferromagnetic interaction appears.     

Synthesis and reactivity of a (mu-1,1-hydroperoxo)(mu-hydroxo)dicopper(II) complex: ligand hydroxylation by a bridging hydroperoxo ligand

A new tetradentate tripodal ligand (L3) containing sterically bulky imidazolyl groups was synthesized, where L3 is tris(1-methyl-2-phenyl-4-imidazolylmethyl)amine. Reaction of a bis(mu-hydroxo)dicopper(II) complex, [Cu2(L3)2(OH)2]2+ (1), with H2O2 in acetonitrile at -40 degrees C generated a (mu-1,1-hydroperoxo)dicopper(II) complex [Cu2(L3)2(OOH)(OH)]2+ (2), which was characterized by various physicochemical measurements including X-ray crystallography. The crystal structure of 2 revealed that the complex cation has a Cu2(mu-1,1-OOH)(mu-OH) core and each copper has a square pyramidal structure having an N3O2 donor set with a weak ligation of a tertiary amine nitrogen in the apex. Consequently, one pendant arm of L3 in 2 is free from coordination, which produces a hydrophobic cavity around the Cu2(mu-1,1-OOH)(mu-OH) core. The hydrophobic cavity is preserved by hydrogen bondings between the hydroperoxide and the imidazole nitrogen of an uncoordinated pendant arm in one side and the hydroxide and the imidazole nitrogen of an uncoordinated pendant arm in the other side. The hydrophobic cavity significantly suppresses the H/D and 16O/18O exchange reactions in 2 compared to that in 1 and stabilizes the Cu2(mu-1,1-OOH)(mu-OH) core against decomposition. Decomposition of 2 in acetonitrile at 0 degrees C proceeded mainly via disproportionation of the hydroperoxo ligand and reduction of 2 to [Cu(L3)]+ by hydroperoxo ligand. In contrast, decomposition of a solid sample of 2 at 60 degrees C gave a complex having a hydroxylated ligand [Cu2(L3)(L3-OH)(OH)2]2+ (2-(L3-OH)) as a main product, where L3-OH is an oxidized ligand in which one of the methylene groups of the pendant arms is hydroxylated. ESI-TOF/MS measurement showed that complex 2-(L3-OH) is stable in acetonitrile at -40 degrees C, whereas warming 2-(L3-OH) at room temperature resulted in the N-dealkylation from L3-OH to give an N-dealkylated ligand, bis(1-methyl-2-phenyl-4-imidazolylmethyl)amine (L2) in approximately 80% yield based on 2, and 1-methyl-2-phenyl-4-formylimidazole (Phim-CHO). Isotope labeling experiments confirmed that the oxygen atom in both L3-OH and Phim-CHO come from OOH. This aliphatic hydroxylation performed by 2 is in marked contrast to the arene hydroxylation reported for some (mu-1,1-hydroperoxo)dicopper(II) complexes with a xylyl linker.     

High-pressure spin-crossover in a dinuclear Fe(II) complex

The effect of pressure on the dinuclear spin crossover material [{Fe(bpp)(NCS)(2)}(2)(4,4'-bipy)]·2MeOH (where bpp = 2,6-bis(pyrazol-3-yl)pyridine and 4,4'-bipy = 4,4'-bipyridine, 1) has been investigated with single crystal X-ray diffraction and Raman spectroscopy using diamond anvil cell techniques. The very gradual pressure-induced spin crossover occurs between 7 and 25 kbar, and shows no evidence of crystallographic phase transitions. The pressure-induced spin transition leads to a complete LS state which is not thermally accessible. This structural evolution under pressure is in stark contrast to the previously reported thermal spin crossover behaviour, in which a symmetry-breaking, purely structural phase transition results in only partial conversion to the low spin state. This observation is attributed to the symmetry-breaking phase transition becoming unfavourable under pressure.     

Homogeneous isotope exchange between copper(II) and bis(resacetophenone oxime)copper(II) complex

Isotope exchange behavior of bis(resacetophenone oxime)copper(II) complex with copper(II) in tri-n-butyl-phosphate and methanol medium has been studied. The studies were carried out at different temperatures varying the concentration of both metal ion and complex. The results show that the complex is labile in the kinetic sense. Increase in temperature increases the isotope exchange rate. The increase in concentration also results in enhancement of the rate of reaction.     

Aerobic oxidation of primary alcohols under mild aqueous conditions promoted by a dinuclear copper(II) complex

A sugar-discriminating dinuclear copper(II) complex was investigated for its ability to promote aerobic oxidation of primary benzylic alcohols in the presence of TEMPO and base. The transformation of benzyl alcohol to benzaldehyde was chosen as exploratory model reaction. The constitution of the catalytically active species was deducted from isothermal titration calorimetry and kinetic experiments, and the catalytic reaction was characterized both in aqueous organic and aqueous solution. The dinuclear complex is found to selectively oxidize primary over secondary alcohols in aqueous solution at ambient temperature with a turnover rate of 9 h⁻¹. A mechanism for the catalytic cycle is proposed.     

Alkyne–azide cycloaddition catalyzed by a dinuclear copper(I) complex

A novel dinuclear copper complex Cu^I₂(pip)₂ was used as a catalyst for alkyne–azide cycloaddition (CuAAC) reaction. High yields (95–99%) were obtained for various substrates at a low loading of 0.2 mol %. The unique structure, high stability of the dinuclear structure in solution, and easy preparation make this complex not only a high-efficiency catalyst but also a model for understanding the mechanism of the CuAAC reaction.     

Polynuclear complexes of chromium(III), copper(II) or nickel(II) with thiocyanate as a bridging ligand

Novel complexes of the type [CuL2]3[Cr(NCS)6]2·xH2O (L = 2,2-bipyridine (bpy), x = 0; L = o-phenanthroline (phen), x = 1), [Cu(dien)]3[Cr(NCS)6]2·3H2O (dien=diethylenetriamine) or [Ni(phen)2]3[Cr(NCS)6]2· 2H2O have been prepared and studied by elemental analyses, i.r. spectra and magnetic measurements. Some of the complexes have been characterized by temperature-dependent magnetic susceptibilities, and weak antiferromagnetic exchange interaction was found for [Cu-(phen)2]3[Cr(NCS)6]2·H2O and [Ni(phen)2]3[Cr(NCS)6]2· 2H2O. Physico-chemical studies account for the polymeric structure, with thiocyanate bridges between Cu or octahedral Ni and octahedral Cr (chromophore CrN6).     

Photochemical and thermal ligand exchange in a ruthenium(II) complex based on a scorpionate terpyridine ligand

A ruthenium(II) complex containing a 1,10-phenanthroline unit and a terpyridine fragment covalently linked to a benzonitrile group has been synthesised; coordination and decoordination of the benzonitrile group can be induced thermally and photochemically respectively, in an acetone-water mixture.     

Highly efficient DNA compaction mediated by an in vivo antitumor-active tetrazolato-bridged dinuclear platinum(II) complex

We investigated the effects of antitumor-active tetrazolato-bridged dinuclear platinum(II) complexes [{cis-Pt(NH(3))(2)}(2)(μ-OH)(μ-tetrazolato-N(1),N(2))](2+) (1) and [{cis-Pt(NH(3))(2)}(2)(μ-OH)(μ-tetrazolato-N(2),N(3))](2+) (2) on the higher-order structure of a large DNA molecule (T4 phage DNA, 166 kbp) in aqueous solution through single-molecule observation by fluorescence microscopy. Complexes 1 and 2 cause irreversible compaction of DNA through an intermediate state in which coil and compact parts coexist in a single DNA molecule. The potency of compaction is in the order 2 > 1 ? cisplatin. Transmission electron microscopic observation showed that both complexes collapsed DNA into an irregularly packed structure. Circular dichroism measurements revealed that the dinuclear platinum(II) complexes change the secondary structure of DNA from the B to C form. These characteristics of platinum(II) complexes are markedly different from those of the usual condensing agents such as spermidine(3+) and [Co(III)(NH(3))(6)](3+). The ability to cause DNA compaction by the platinum(II) complexes is discussed in relation to their potent antitumor activity.     

C-C bond cleavage of acetonitrile by a dinuclear copper(II) cryptate

The dinuclear copper(II) cryptate [Cu2L](ClO4)4 (1) cleaves the C-C bond of acetonitrile at room temperature to produce a cyanide bridged complex of [Cu2L(CN)](ClO4)3.2CH3CN.4H2O (2). The cleavage mechanism is presented on the basis of the results of the crystal structure of 2, electronic absorption spectra, ESI-MS spectroscopy, and GC spectra of 1, respectively.