Catecholase activity of a series of dicopper(II) complexes with variable Cu-OH(phenol) moieties

The catecholase activity of a series of dicopper(II) complexes containing different numbers of phenol groups coordinated to the metal centers was studied to identify functional as well as structural models for the type III copper enzymes tyrosinase and catechol oxidase. The syntheses and characterization of complexes [Cu(2)(H(2)bbppnol)(mu-OAc)(H(2)O)(2)]Cl(2).2H(2)O (1) and [Cu(2)(Hbtppnol)(mu-OAc)](ClO(4))(2) (2) were previously reported by us (Inorg. Chim. Acta 1998, 281, 111-115; Inorg. Chem. Commun. 1999, 2, 334-337), and complex [Cu(2)(P1-O(-))(OAc(-))](ClO(4))(2) (3) was previously reported by Karlin et al. (J. Am. Chem. Soc. 1997, 119, 2156-2162). The catalytic activity of the complexes 1-3 on the oxidation of 3,5-di-tert-butylcatechol was determined spectrophotometrically by monitoring the increase of the 3,5-di-tert-butyl-o-benzoquinone characteristic absorption band at about 400 nm over time in methanol saturated with O(2)/aqueous buffer pH 8 solutions at 25 degrees C. The complexes were able to oxidize 3,5-di-tert-butylcatechol to the corresponding o-quinone with distinct catalytic activity. A kinetic treatment of the data based on the Michaelis-Mentèn approach was applied. The [Cu(2)(H(2)bbppnol)(mu-OAc)(H(2)O)(2)]Cl(2) small middle dot2H(2)O complex showed the highest catalytic activity of the three complexes as a result of a high turnover rate (k(cat) = 28 h(-1)) combined with a moderate substrate-catalyst binding constant (K(ass) = 1.3 x 10(3) M(-1)). A mechanism for the oxidation reaction is proposed, and reactivity differences, k(cat)/K(M) of the complexes, were found to be dependent on (DeltaE)(1,2), the difference in the driving force for the reduction reactions Cu(II)(2)/Cu(II)Cu(I) and Cu(II)Cu(I)/Cu(I)(2).     

Synthesis, solid state and solution structures of two isomeric dicopper(II) complexes with functionalized azetidine ligands

Reported are the crystal and solution structures (determined by X-ray crystallography and EPR spectroscopy/simulation of the EPR spectra, respectively) of two dinuclear Cu^II complexes, coordinated to isomeric dinucleating azetidine-based ligands, whose N₃ cavities (pyridine/azetidine/secondary amine) are bridged by para- or meta-substituted phenyl groups. The Cu^II sites in the two dinuclear systems are similar to each other and as expected from the known structure of the corresponding mononuclear complex. The significant differences between the crystal structures of the mono- and the two dinuclear complexes and between the crystal and the solution structures are due to the elasticity of the Cu^II coordination sphere, the flexibility of the dinucleating ligands and subtle changes related to weak interactions (crystal lattice, solvation, anion coordination/ion pairing).     

Diaza-crown-N,N-dialkanoic acids copper(II) and dicopper(II) complexes

Twelve-, fifteen-, and eighteen-membered diaza-crown-N, N-′dialkanoic acids LH₂ and their inner salt copper(II) complexes CuL and dicopper complex [CuL(3). CuCl₂. CH₃OH_n were obtained. The complexes of 15- and 18-membered ligands contain Cu²⁺ ion inside the ring.     

Synthesis,characterization,structures and magnetic property of chiral oxalate-bridged dicopper(Ⅱ) complexes

The oxalato-bridged dicopper(II) complexes [Cu2(μ-ox)(LRR)2(H2O)2(ClO4)2] (1),[Cu2(μ-ox)(LRR)2(CH3COCH3)2(ClO4)2](1a),[Cu2(μ-ox)(LSS)2(H2O)2(ClO4)2] (2) and [Cu2(μ-ox)(LRR)(LSS)2(CH3COCH3)2(ClO4)2] (3) [LRR = (8R,10R)-(-)-[4,5]-pineno2,2′-bipyridine,LSS = (8S,10S)-(+)-[4,5]-pineno-2,2′-bipyridine;ox2= oxalate] were first prepared.A possible mechanism for the formation of the chial dicopper(II) complexes was proposed.Based on elemental analysis,conductance measurement,UV-Vis spectra,CD spectra and X-ray single-crystal diffraction,the oxalato-bridged structures of 1 and 2 were deduced to adopt two Cu(II) ions and the bridged oxalate lying in the nearly same plane.The crystal structures of 1a and 3 reveal that the coordination geometry around each Cu(II) ion is an elongated and distorted octahedron and two axial solvent molecules and two perchlorate ions are anti to each other respectively in both binuclear molecules.The solution CD spectra of 1 and 2 in the visible d-d range show very weak Cotton effects with peaks at 588 and 779 nm,which are approximately of mirror image,suggesting the optical activities may be derived from the vicinal effects of the chiragenic centers at the pinene group of LRR and LSS,respectively.Complex 1 has been characterized by variable-temperature magnetic susceptibility and the data was least-square fitted to the Blenaey-Bowers equation.The exchange integral J was found to be -338.41(4) cm-1,indicating a strong antiferromagnetic interaction between two copper(II) ions.     

Synthesis of new dinuclear dicopper(II) and dinickel(II) complexes. The kinetics of catechol oxidase and electrochemistry of a dicopper(II) complex

A new dinuclear ligand L, ethylene[OO-bis-salicylidene--diketone] bearing two symmetrical coordination sites was synthesized by the condensation of salicylaldehyde and acetylacetone, L, with 1,2-dibromoethane under reflux. The ligand L in a 1:1 ratio was treated with CuCl₂ and NiCl₂ to yield the complexes, tetrachloro bis[OO-bis- salicylidene--diketone copper(II)] and bis[OO-bis-salicylidene--diketone nickel(II)] chloride. The complexes were subsequently characterized by spectroscopic techniques, elemental analysis, i.r., ¹H-n.m.r., ¹³C-n.m.r., u.v.–vis., e.p.r. spectroscopy, and conductance measurements. The conductance measurements in DMF reveal that the Cu^II complex is covalent while the Ni^II complex is ionic and the spectral data support the Cu^II complex to be distorted octahedral whereas the Ni^II complex has square-planar geometry. The dioxygen binding was studied spectrophotometrically by the oxidation of tetrachloro bis[OO-bis-salicylidene--diketone copper(II)] with pyrocatechol in the presence of oxygen. The kinetic experiments were performed with the copper complex in DMF by monitoring the increase in absorbance over time at pH 8.0 in the presence of pyrocatechol at 25 °C. The kinetic parameters V_max and K_M were determined on the Michaelis–Menten Approach. Redox behavior of the dinuclear copper(II) complex was investigated by cyclic voltammetry in the presence of O₂ with the pyrocatechol (substrate) and also without the substrate. The large difference in potentials E⁰ is indicative of reversible oxygen binding of the complex and distinct catalytic activity.     

Modelling tyrosinase monooxygenase activity. Activation of dioxygen by dicopper(I) complexes and characterisation of dicopper(II) complexes

Activation of dioxygen on dicopper(I) centres was systematically investigated using a group of open-chain and a macrocyclicm-xylyl-based dinucleating ligand from a bioinorganic viewpoint. Even though intermediate peroxodicopper(II) species was not detected (even at −80°C for the open-chain system), the putative intermediate reacted with C–H groups in ligands giving oxygenated products (C–OH groups). Absorption, spectroscopic and magnetic properties of the final dicopper(II) complexes have been investigated.     

Interconversion between bis(mu-thiolato)dicopper(II) and disulfide-bridged dicopper(I) complexes mediated by chloride ion

An unprecedented clean interconversion between a novel bis(mu-thiolato)dicopper(II) complex (1) and a disulfide-bridged dicopper(I) complex (3) through a disulfide-bridged (mu-chloro)dicopper(I) complex (2) mediated by chloride ion has been established for the first time, providing a new redox chemistry of the transition metal-sulfur complexes. Crystal structures of 1 and 3 as well as spectroscopic features of the compounds are reported.     

Organic-acid effect on the structures of a series of lead(II) complexes

An investigation into the dependence of coordination polymer architectures on organic-acid ligands is reported on the basis of the reaction of Pb(NO3)2 and eight structurally related organic-acid ligands in the presence or absence of N-donor chelating ligands. Eight novel lead(II)-organic architectures, [Pb(adip)(dpdp)]2 1, [Pb(glu)(dpdp)] 2, [Pb(suc)(dpdp)] 3, [Pb(fum)(dpdp)] . H2O 4, [Pb2(oba)(dpdp)2] . 2(dpdp).2(NO3).2H2O 5, [Pb2(1,4-bdc)2(dpdp)2] . H2O 6, [Pb(dpdc)(dpdp)] 7, and [Pb(1,3-bdc)(dpdp)] . H2O 8, where dpdp = dipyrido[3,2-a:2',3'-c]-phenazine, H2adip = adipic acid, H2glu = glutaric acid, H2suc = succinic acid, H2fum = fumaric acid, H2oba = 4,4'-oxybis(benzoic acid), 1,4-H2bdc = benzene-1,4-dicarboxylic acid, H2dpdc = 2,2'-diphenyldicarboxylic acid, and 1,3-H2bdc = benzene-1,3-dicarboxylic acid, were successfully synthesized under hydrothermal conditions through varying the organic-acid linkers and structurally characterized by X-ray crystallography. Compounds 1-8 crystallize in the presence of organic-acid linkers as well as secondary N-donor chelating ligands. Diverse structures were observed for these complexes. 1 and 5 have dinuclear structures, which are further stacked via strong pi-pi interactions to form 2D layers. 2-3 and 6-8 feature chain structures, which are connected by strong pi-pi interactions to result in 2D and 3D supramolecular architectures. Compound 4 contains 2D layers, which are further extended to a 3D structure by pi-pi interactions. A systematic structural comparison of these 8 complexes indicates that the organic-acid structures have essential roles in the framework formation of the Pb(II) complexes.     

Syntheses, crystal structures and magnetic properties of two dicopper(II) complexes and a zigzag 1-D Cu(II) complex of a bidentate pyridyl-pyrazole ligand

Two new dinuclear copper compounds, [Cu₂(pypz)₂(N₃)₂(NO₃)₂] (1) and [Cu₂(pypz)₂(OH)₂(NO₃)₂] (2), and one 1-D polymeric Cu(II) complex, [Cu(pypz)(dca)₃]_n (3) [‘pypz’ = (3,5dimethyl-1-(2′-pyridyl)pyrazole) and dca = (dicyanamide)], have been synthesized and characterized crystallographically and spectroscopically. Complex 1 is pseudo-octahedral, adjacent Cu atoms are connected by a pair of μ(1,1) azido groups and the structure is stabilized by π-π interactions between two pyridyl moieties from two different neighboring complex molecules. Complexes 2 and 3 are square pyramidal. The hydroxo bridged complex 2 is further stabilized through H-bonding. The 1-D polymeric chain of 3 is bridged by an end-to-end dicyanamide bridge and it propagates along the crystallographic b axis, whilst the polymer chains are stacked one upon another along the crystallographic c axis. Low temperature magnetic measurement shows that complexes 1 and 2 are ferromagnetic (J values are 30.81 and 14.79 cm⁻¹, respectively), whereas due to larger Cu-Cu distances, complex 3 shows weak ferromagnetism.     

Dioxygen-binding kinetics and thermodynamics of a series of dicopper(I) complexes with bis[2-(2-pyridyl)ethyl]amine tridendate chelators forming side-on peroxo-bridged dicopper(II) adducts

Copper-dioxygen interactions are of interest due to their importance in biological systems as reversible O2- carriers, oxygenases, or oxidases and also because of their role in industrial and laboratory oxidation processes. Here we report on the kinetics (stopped-flow, -90 to 10 degrees C) of O2-binding to a series of dicopper(I) complexes, [Cu2(Nn)(MeCN)2]2+ (1Nn) (-(CH2)n- (n = 3-5) linked bis[(2-(2-pyridyl)ethyl]amine, PY2) and their close mononuclear analogue, [(MePY2)Cu(MeCN)]+ (3), which form mu-eta 2:eta 2-peroxodicopper(II) complexes [Cu2(Nn)-(O2)]2+ (2Nn) and [(MePY2)Cu]2(O2)]2+ (4), respectively. The overall kinetic mechanism involves initial reversible (k+,open/k-,open) formation of a nondetectable intermediate O2-adduct [Cu2(Nn)(O2)]2+ (open), suggested to be a CuI...CuII-O2- species, followed by its reversible closure (k+,closed/k-,closed) to form 2Nn. At higher temperatures (253 to 283 K), the first equilibrium lies far to the left and the observed rate law involves a simple reversible binding equilibrium process (kon,high = (k+,open/k-,open)(k+,closed)). From 213 to 233 K, the slow step in the oxygenation is the first reaction (kon,low = k+,open), and first-order behavior (in 1Nn and O2) is observed. For either temperature regime, the delta H++ for formation of 2Nn are low (delta H++ = -11 to 10 kJ/mol; kon,low = 1.1 x 10(3) to 4.1 x 10(3) M-1 s-1, kon,high = 2.2 x 10(3) to 2.8 x 10(4) M-1 s-1), reflecting the likely occurrence of preequilibria. The delta H degree ranges between -81 and -84 kJ mol-1 for the formation of 2Nn, and the corresponding equilibrium constant (K1) increases (3 x 10(8) to 5 x 10(10) M-1; 183 K) going from n = 3 to 5. Below 213 K, the half-life for formation of 2Nn increases with, rather than being independent of, the concentration of 1Nn, probably due to the oligomerization of 1Nn at these temperatures. The O2 reaction chemistry of 3 in CH2Cl2 is complicated, including the presence of induction periods, and could not be fully analyzed. However, qualitative comparisons show the expected slower intermolecular reaction of 3 with O2 compared to the intramolecular first-order reactions of 1Nn. Due to the likelihood of the partial dimerization of 3 in solution, the t1/2 for the formation of 4 remains constant with increasing complex concentration rather than decreasing. Acetonitrile significantly influences the kinetics of the O2 reactions with 1Nn and 3. For 1N4, the presence of MeCN inhibits the formation of a previously (Jung et al, J. Am. Chem. Soc. 1996, 118, 3763-3764) observed intermediate. Small amounts of added MeCN considerably slow the oxygenation rates of 3, inhibit its full formation to 4, and increase the length of the induction period. The results for 1Nn and their mononuclear analogue 3 are presented, and they are compared with each other as well as with other dinucleating dicopper(I) systems.     

Synthesis and characterization of several dicopper(I) complexes and a spin-delocalized dicopper(I,II) mixed-valence complex using a 1,8-naphthyridine-based dinucleating ligand

The synthesis of dicopper(I) complexes [Cu2(BBAN)(MeCN)2](OTf)2 (1), [Cu2(BBAN)(py)2](OTf)2 (2), [Cu2(BBAN)(1-Me-BzIm)2](OTf)2 (3), [Cu2(BBAN)(1-Me-Im)2](OTf)2 (4), and [Cu2(BBAN)(mu-O2CCPh3)](OTf) (5), where BBAN = 2,7-bis((dibenzylamino)methyl)-1,8-naphthyridine, py = pyridine, 1-Me-Im = 1-methylimidazole, and 1-Me-BzIm = 1-methylbenzimidazole, are described. Short copper-copper distances ranging from 2.6151(6) to 2.7325(5) A were observed in the solid-state structures of these complexes depending on the terminal ligands used. The cyclic voltammogram of compound 5 dissolved in THF exhibited a reversible redox wave at E1/2 = -25 mV vs Cp2Fe+/Cp2Fe. When complex 5 was treated with 1 equiv of silver(I) triflate, a mixed-valence dicopper(I,II) complex [Cu2(BBAN)(mu-O2CCPh3)(OTf)](OTf) (6) was prepared. A short copper-copper distance of 2.4493(14) A observed from the solid-state structure indicates the presence of a copper-copper interaction. Variable-temperature EPR studies showed that complex 6 has a fully delocalized electronic structure in frozen 2-methyltetrahydrofuran solution down to liquid helium temperature. The presence of anionic ligands seems to be an important factor to stabilize the mixed-valence dicopper(I,II) state. Compounds 1-4 with neutral nitrogen-donor terminal ligands cannot be oxidized to the mixed-valence analogues either chemically or electrochemically.     

Ferromagnetic exchange in two dicopper(II) complexes using a mu-alkoxo-mu-7-azaindolate bridge

Syntheses, structures, and magnetic properties of two heterobridged mu-alkoxo-mu-7-azaindolate dicopper(II) complexes, [Cu(II)2(L-F)(mu-C7H5N2)] (1) and [Cu(II)2(L-H)(mu-C7H5N2)].CH3OH (2) (H3L-F = 1,3-bis(3-fluorosalicylideneamino)-2-propanol; H3L-H = 1,3-bis(salicylideneamino)-2-propanol) have been reported. Aside from being a new type of heterobridged complex, 1 and 2 exhibit ferromagnetic interaction (2J = 52 cm(-1) for 1 and 33.4 cm(-1) for 2) despite orbital complementarity (7-azaindolate HOMO is antisymmetric).     

Heptacopper(II) and dicopper(II)-adenine complexes: synthesis,structural characterization,and magnetic properties

The syntheses, crystal structures, and magnetic properties of two new copper(II) complexes with molecular formulas [Cu₇(μ₂-OH₂)₆(μ₃-O)₆(adenine)₆](NO₃)₂·6H₂O (1) and [Cu₂(μ₂-H₂O)₂(adenine)₂(H₂O)₄](NO₃)₄·2H₂O (2) are reported. The heptanuclear compound is composed of a central octahedral CuO₆ core sharing edges with six adjacent copper octahedra. In 2, the copper octahedra shares one equatorial edge. In both compounds, these basic copper cluster units are further linked by water bridges and bridging adenine ligands through N3 and N9 donors. All copper(II) centers exhibit Jahn–Teller distorted octahedral coordination characteristic of a d⁹ center. The study of the magnetic properties of the heptacopper complex revealed a dominant ferromagnetic intra-cluster interaction, while the dicopper complex exhibits antiferromagnetic intra-dimer interactions with weakly ferromagnetic inter-dimer interaction.     

Diverse structures and adsorption properties of quasi-Werner-type copper(II) complexes with flexible and polar axial bonds

The quasi-Werner-type copper(II) complex, [Cu(PF(6))(2)(4-mepy)(4)] (1), in which 4-mepy is the 4-methylpyridine ligand, has flexible and polar axial bonds of Cu-PF(6). Flexibility of the Cu-PF(6) bonds induces diverse and unprecedented guest-inclusion structures, such as {[Cu(PF(6))(2)(4-mepy)(4)][Cu(PF(6))(4-mepy)(4)(acetone)]·PF(6)·4acetone} (γ-1?2.5acetone), {[Cu(PF(6))(2)(4-mepy)(4)][Cu(PF(6))(4-mepy)(4)(2-butanone)]·PF(6)·3.5(2-butanone)} (γ-1?2.25(2-butanone)), {[Cu(PF(6))(2)(4-mepy)(4)][Cu(PF(6))(4-mepy)(4)(H(2)O)]·PF(6)·4benzene} (γ-1?0.5H(2)O·2benzene), and {[Cu(PF(6))(2)(4-mepy)(4)]·2benzene} (γ-1?2benzene). Exposure of the dense form, α-1, to benzene vapor affords the benzene-inclusion complex {[Cu(PF(6))(2)(4-mepy)(4)]·2benzene} (γ-1?2benzene), all benzene guests of which are easily removed by vacuum drying, reforming guest-free, dense α-1' with smaller sized crystals than α-1. In contrast to α-1, which shows almost no CO(2) adsorption, α-1' adsorbs CO(2) gas with structural transformations, this being the first example that exhibits adsorption of gas in a dense Werner-type complex and a drastic change in adsorption properties depending on the size of the crystals.     

An expanded cavity hexaamine cage for copper(II)

The crystal structure of the bicyclic hexaamine complex [Cu(fac-Me5-tricosane-N6)](ClO4)2.H2O (fac-Me5-tricosane-N6 = facial-1,5,9,13,20-pentamethyl-3,7,11,15,18,22-hexaazabicyclo[7.7.7]tricosane) at 100 K defines an apparently tetragonally compressed octahedral geometry, which is attributed to a combination of dynamic interconversion and static disorder between two tetragonally elongated structures sharing a common short axis. This structure is fluxional at 60 K and above as shown by EPR spectroscopy. Aqueous cyclic voltammetry reveals that a remarkably stable Cu(I) form of the complex is stabilised by the encapsulating nature of the expanded cage ligand.     

Synthesis and structures of cadmium(II) complexes of a series of multinucleating N/S donor ligands

The coordination chemistry of a series of bis-bidentate ligands with cadmium(II) ions has been investigated. The ligands, containing two N,S-donor chelating (pyrazolyl/thioether) fragments, have afforded complexes of a variety of structural types (dinuclear M₂L₂ ‘mesocate’ complexes, a one-dimensional chain coordination polymer and a simple mononuclear complex) according to whether the bis-bidentate ligands act as bridges spanning two metal ions, or a tetradentate chelate to a single metal ion. The p-phenylene and m-biphenyl spaced ligands L¹ and L³ form dinuclear M₂L₂ complexes where the ligands are arranged in a ‘side-by-side’ fashion. In contrast the m-phenylene spaced ligand L² forms a one-dimensional coordination polymer where the ligands adopt a highly folded conformation. The 1,8-naphthalene spaced ligand L⁴ adopts a tetradendate chelating mode and affords a simple mononuclear complex.     

Crystal structures and luminescence of a series of cadmium(II) complexes based on isophorone derivative containing imidazolyl

Three new complexes, [CdL₂(CH₃COO)₂(H₂O)₂] (I), CdL₂Br₂ (II), CdL₂I₂ (III), have been successfully synthesized by self-assembly of corresponding metal salts with (E)-2-(3-(4-(1H-imidazole-1-yl)styryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile (L). The structures of the complexes were determined by single crystal X-ray diffraction analysis (CIF file CCDC nos. 957831 (I), 957792 (II), 957832 (III)). In complex I, central metal is six-coordinated and the crystal packing shows a 3D supramolecular framework. Complexes II and III display the similar 2D supramolecular structures in which the central metals are four-coordination. The luminescent properties were investigated.     

Determination of the solution structures of melamine-based bis- and tris-macrocyclic ligand copper(II) complexes

A combination of molecular mechanics (MM), electron paramagnetic resonance spectroscopy (EPR), and spectra simulation (MM-EPR) has been used to determine the solution structures of di- and trinuclear copper(II) complexes of melamine-based oligomacrocyclic ligands. The spin Hamiltonian parameters of the mononuclear, melamine-appended macrocyclic ligand copper(II) complex have been determined by EPR spectroscopy and were also studied with DFT methods. These spin Hamiltonian parameters, together with the structural parameters obtained from models optimized with MM, have been used for the simulation of the EPR spectra of the di- and trinuclear complexes. For the dinuclear complex, the syn isomer is preferred over the anti, for which an X-ray structure exists; for the trinuclear complex, the syn,syn isomer is preferred over the syn,anti form. Additional support for these assignments comes from DFT calculations, and this demonstrates that the MM-DFT-EPR method is a reliable approach for the determination of solution structures and for the analysis of spin Hamiltonian parameters of dipolar, coupled transition metal complexes (g and A tensors and J values).     

Rhodium-hydrido-benzylamine-triphenylphosphine complexes: solid-state and solution structures and implications in catalyzed imine hydrogenation

The complexes cis,trans,cis-[Rh(H)(2)(PPh(3))(2)(NH(2)CH(2)Ph)(2)]PF(6) (1) and cis-[Rh(PPh(3))(2)(NH(2)CH(2)Ph)(2)]PF(6) (2) are characterized by X-ray crystallography; the structures are maintained in CH(2)Cl(2) where the species are in equilibrium under H(2). In MeOH and in acetone, loss of amine and/or H(2) can occur. Traces of 1 and 2 are present after a Rh-catalyzed H(2)-hydrogenation of PhCH=NCH(2)Ph in MeOH, where the amine is generated by hydrolysis of the imine substrate through adventitious water. The findings are relevant to catalyst poisoning in the catalytic process.