CuII Complexes Research Articles

Copper Complexes with Diazoolefin Ligands and their Photochemical Conversion into Alkenylidene Complexes

AbstractHomometallic copper complexes with alkenylidene ligands are discussed as intermediates in catalysis but the isolation of such complexes has remained elusive. Herein, we report the structural characterization of copper complexes with bridging and terminal alkenylidene ligands. The compounds were obtained by irradiation of CuI complexes with N‐heterocyclic diazoolefin ligands. The complex with a terminal alkenylidene ligand required isolation in a crystalline matrix, and its structural characterization was enabled by in crystallo photolysis at low temperature.

Copper Complexes with Diazoolefin Ligands and their Photochemical Conversion into Alkenylidene Complexes.

Homometallic copper complexes with alkenylidene ligands are discussed as intermediates in catalysis but the isolation of such complexes has remained elusive. Herein, we report the structural characterization of copper complexes with bridging and terminal alkenylidene ligands. The compounds were obtained by irradiation of CuI complexes with N-heterocyclic diazoolefin ligands. The complex with a terminal alkenylidene ligand required isolation in a crystalline matrix, and its structural characterization was enabled by in crystallo photolysis at low temperature.

Syntheses, characterization, crystal structures and Jack bean urease inhibitory property of NiII, CdII, CuII and FeIII complexes with bis-Schiff bases

Four new nickel(II), cadmium(II), copper(II) and iron(III) complexes, [Ni3(L1)2(μ2-η1:η1-CH3COO)2] (1), [Cd2(L1)2(CH3OH)2] (2), [Cu(L2)] (3) and [Fe2(L3)2(μ2-OCH3)2] (4), where L1, L2 and L3 are the dianionic form of N,N'-bis(5-fluorosalicylidene)-1,3-propanediamine (H2L1), N,N'-bis(3,5-difluorosalicylidene)-1,3-propanediamine (H2L2) and N,N'-bis(4-fluorosalicylidene)-1,3-propanediamine (H2L3), respectively, were prepared. The compounds have been characterized by physico-chemical methods. The structures of the metal complexes were also confirmed by single crystal X-ray diffraction. The Ni atoms in complex 1 are in square pyramidal and octahedral coordination environments. The Cd atoms in complex 2 are in an octahedral coordination environment. The Cu atom in complex 3 is in a tetrahedrally distorted square planar coordination environment. The Fe atoms in complex 4 are in an octahedral coordination environment. The Jack bean urease inhibitory assay indicated that the copper complex displays good activity.

Cu‐Catalyzed Atom Transfer Radical Polymerization: The Effect of Cocatalysts

AbstractAtom transfer radical polymerization (ATRP) is one of the most powerful methods to prepare well‐defined (co)polymers. Cu‐catalyzed ATRP methods are most commonly used because of the excellent control and tunable catalytic activities via ligand functionalization. This minireview summarizes the development of Cu‐catalyzed ATRP in the presence of cocatalysts, which are used to regenerate CuI complex activators during polymerizations. Fundamentals of Cu‐based ATRP catalysts are first introduced, followed by the discussion of different types of cocatalysts in different Cu‐catalyzed ATRP methods. Recent developments of photochemical cocatalysts for oxygen‐tolerant ATRP and ATRP using long‐wavelength irradiation are highlighted, which significantly expand the applications of Cu‐catalyzed ATRP. Methods to study the properties of cocatalysts and their roles in Cu‐catalyzed ATRP are discussed, with an outlook for the future development of cocatalysts.

ROS scavenging of SOD/CAT mimics probed by EPR and reduction of lipid peroxidation in S. cerevisiae and mouse liver, under severe hydroxyl radical stress condition

The interaction between CuII, FeIII and MnII complexes, derived from the ligands 1-[bis(pyridine-2-ylmethyl)amino]-3-chloropropan-2-ol (hpclnol) and bis(pyridine-2-ylmethyl)amine (bpma), and the free radical 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl (DPPH) and reactive oxygen species (ROS), was investigated by colorimetric and EPR (Electron Paramagnetic Resonance) techniques. A comparison between these results and those reported to [Mn(salen)Cl] or EUK-8 was also addressed. EPR studies allowed us the identification of intermediates species such as superoxide‑copper(I) and superoxide‑copper(II), a mixed-valence FeIIIFeII species and a 16-line feature attributed to MnIII-oxo-MnIV species. The biomarker malondialdehyde (MDA) was determined by TBARS assay in S. cerevisiae cells, and the determination of the IC50 indicate that the antioxidant activity shown dependence on the metal center (CuII ≈ FeIII > MnII ≈ [Mn(salen)Cl]. The lipid peroxidation attenuation was also investigated in liver homogenates obtained from Swiss mice and the IC50 values were in the nanomolar concentrations. We demonstrated here that all the complexes interact with the free radical DPPH and with ROS (H2O2, O2•- and hydroxyl radical), enhancing the cellular protection against oxidative stress generated by hydroxyl radical, employing two experimental model systems, S. cerevisiae (in vivo) and mouse liver (ex vivo).

Experimental and Theoretical Evaluation of Four NLO‐Active Divalent Transition‐Metal Complexes Supported by an Enantiomerically Pure Tetradentate Schiff Base Ligand

AbstractThis paper reports on a series of five chiral Schiff base push‐pull compounds derived from enantiomerically pure (1R,2R)‐(−)‐1,2‐diaminocyclohexane. The NiII, CuII, ZnII and PdII complexes supported by a ferrocene‐containing unsymmetrically‐substituted N2O2 quadridentate Schiff base ligand were prepared via template reactions and isolated in 74–87 % yields. A combination of EA, IR, UV/vis and 1H/13C{1H} NMR spectroscopy, HRMS spectrometry, cyclic voltammetry and single‐crystal X‐ray analysis (for the proligand 2 and its NiII derivative 3), together with computational methods (DFT and TD‐DFT) was used to fully characterize and study the properties of all products. Both 2 and 3 crystallize in the orthorhombic non‐centrosymmetric space group P212121, with two (R,R)‐(−)‐chiral carbon atoms in their structure. Second‐order nonlinear polarizabilities β have been measured by using Harmonic Light Scattering at 1.91 μm, with the Pd(II) species showing the higher NLO response of 460×10−30 esu.

Photophysics of Anionic Bis(4H-imidazolato)CuI Complexes.

In this paper, the photophysical behavior of four panchromatically absorbing, homoleptic bis(4H-imidazolato)CuI complexes, with a systematic variation in the electron-withdrawing properties of the imidazolate ligand, were studied by wavelength-dependent time-resolved femtosecond transient absorption spectroscopy. Excitation at 400, 480, and 630 nm populates metal-to-ligand charge transfer, intraligand charge transfer, and mixed-character singlet states. The pump wavelength-dependent transient absorption data were analyzed by a recently established 2D correlation approach. Data analysis revealed that all excitation conditions yield similar excited-state dynamics. Key to the excited-state relaxation is fast, sub-picosecond pseudo-Jahn-Teller distortion, which is accompanied by the relocalization of electron density onto a single ligand from the initially delocalized state at Franck-Condon geometry. Subsequent intersystem crossing to the triplet manifold is followed by a sub-100 ps decay to the ground state. The fast, nonradiative decay is rationalized by the low triplet-state energy as found by DFT calculations, which suggest perspective treatment at the strong coupling limit of the energy gap law.

Single Crystal to Single Crystal Transformation of CuII Complexes Induced by Dehydrating and Hydrating of Ligands with Chroma Rewritable Behaviors.

In this work, the single crystal to single crystal (SCSC) transformations in three mononuclear copper complexes [CuL22]Cl2·2H2O (1), [CuL12Cl2] (2), and [CuL22]Cl2·4H2O (3) (L1 = di-2-pyridyl ketone, L2 = di(pyridin-2-yl)methanediol) are realized by the irreversible dehydration and hydration reaction of L1 and L2. Dark purple crystal 1 is obtained by self-assembly of L1 and CuCl2·2H2O in solvothermal reactions, in which the carbonyl group of L1 undergoes a hydration addition reaction to form L2. On heating, 1 transforms to 2 by dehydrating water accompanied by the change of the color and coordination octahedron of CuII ions. In a saturated water vapor environment, 2 can absorb six water molecules and transform to 3 with the same color and coordination environment with 1 but different lattice water. The SCSC process from 2 to 3 is reversible: 3 can transform back to 2 on heating like that of 1. Chroma rewritable behaviors in the structural transformation of the complexes make them visually identifiable temperature or water probes.

Heterogeneous catalytic oxidation of chromotrope 2B with H2O2 and metal complexes supported on aluminum oxide hydroxide as catalyst

AbstractThe heterogeneous catalytic oxidation of Chromotrope 2B (C2B) dye with H2O2 and the aluminum oxide hydroxide (AlOOH) modified with ammonia complexes of CuII, CoII, NiII, and CrIII (AlOOH/[Mn+(amm)m]) as catalysts were studied. The AlOOH/[CuII(amm)4] is the most efficient catalyst and therefore it was chosen as the potential catalyst for the oxidative degradation of C2B in an aqueous solution. The AlOOH/[CuII(amm)4] was characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy‐dispersive X‐ray (EDX), and transmission electron microscopy (TEM), techniques. The rate of reaction was dependent on the type of the metal complex supported on the AlOOH, initial concentration of the dye and H2O2, catalyst dose, pH, the concentration of NaCl, and temperature. The catalytic activity of the AlOOH/[Mn+(amm)m] according to the kind of metal ion decreased in the order: CuII > CoII > CrIII > NiII. Other catalysts consisting of the AlOOH supported with CuII complexed with ethylenediamine, ethanolamine, 1,3 propanediamine, and 1,4 butanediamine, (AlOOH/[CuII(amine)m]), were also investigated. The activity of the (AlOOH/[CuII(amine)m]) as catalyst according to the type of ligand followed the order: 1,4 butanediamine > 1,3 propanediamine > ethanolamine > ethylenediamine > ammonia. The reaction rate increased with increasing the catalyst dose, concentration of H2O2, C2B, and NaCl, pH, and temperature. Since the reusability results for the AlOOH/[CuII(amm)4] revealed good stability over seven cycles, it can thus be considered a promising and cost‐effective catalyst for the removal of harmful dyes from wastewater.

Zinc(II) Complexes with Triplet Charge-Transfer Excited States Enabling Energy-Transfer Catalysis, Photoinduced Electron Transfer, and Upconversion.

Many CuI complexes have luminescent triplet charge-transfer excited states with diverse applications in photophysics and photochemistry, but for isoelectronic ZnII compounds, this behavior is much less common, and they typically only show ligand-based fluorescence from singlet π–π* states. We report two closely related tetrahedral ZnII compounds, in which intersystem crossing occurs with appreciable quantum yields and leads to the population of triplet excited states with intraligand charge-transfer (ILCT) character. In addition to showing fluorescence from their initially excited 1ILCT states, these new compounds therefore undergo triplet–triplet energy transfer (TTET) from their 3ILCT states and consequently can act as sensitizers for photo-isomerization reactions and triplet–triplet annihilation upconversion from the blue to the ultraviolet spectral range. The photoactive 3ILCT state furthermore facilitates photoinduced electron transfer. Collectively, our findings demonstrate that mononuclear ZnII compounds with photophysical and photochemical properties reminiscent of well-known CuI complexes are accessible with suitable ligands and that they are potentially amenable to many different applications. Our insights seem relevant in the greater context of obtaining photoactive compounds based on abundant transition metals, complementing well-known precious-metal-based luminophores and photosensitizers.

Theoretical exploration on structures, bonding aspects and molecular docking of α-aminophosphonate ligated copper complexes against SARS-CoV-2 proteases.

Recent years have witnessed a growing interest in the biological activity of metal complexes of α-aminophosphonates. Here for the first time, a detailed DFT study on five α-aminophosphonate ligated mononuclear/dinuclear CuII complexes is reported using the dispersion corrected density functional (B3LYP-D2) method. The electronic structures spin densities, FMO analysis, energetic description of spin states, and theoretical reactivity behaviour using molecular electrostatic potential (MEP) maps of all five species are reported. All possible spin states of the dinuclear species were computed and their ground state S values were determined along with the computation of their magnetic coupling constants. NBO analysis was also performed to provide details on stabilization energies. A molecular docking study was performed for the five complexes against two SARS-CoV-2 coronavirus protein targets (PDB ID: 6LU7 and 7T9K). The docking results indicated that the mononuclear species had a higher binding affinity for the targets compared to the dinuclear species. Among the species investigated, species I showed the highest binding affinity with the SARS-CoV-2 Omicron protease. NPA charge analysis showed that the heteroatoms of model species III had a more nucleophilic nature. A comparative study was performed to observe any variations and/or correlations in properties among all species.

Molecular Docking, HOMO-LUMO, Quantum Chemical Computation and Bioactivity Analysis of vic-Dioxim Derivatives Bearing Hydrazone Group Ligand and Their NiII and CuII Complexes

Molecular docking process was performed to investigate the interactions between the synthesized compounds and human epidermal growth factor protein kinase domain EGFR (PDB ID:1M17) and cyclin-dependent kinase-2 CDK2 (PDB ID:3IG7) proteins. HOMO LUMO orbital energy analysis, quantum chemical calculations were made and the bioactivity parameters of the compounds were evaluated. NiII and CuII complexes of the L1H2 L2H2 and L3H2, ligands showed higher binding affinity to EGFR and CDK2. Especially, [Cu(L1H)2] and [Cu(L2H)2] complexes can be suggested as hit compounds against CDK2 and EGFR, respectively. These were supported by the inhibition constant values which were the lowest when compared to others. L1H2 L2H2 and L3H2, ligands had the lowest binding energy values when compared to metal complexes. Also, [Cu(L2H)2] complex had a high binding energy value against EGFR. [Ni(L2H)2] and [Cu(L2H)2] complexes with EGFR had the highest LE and FQ values and these were found to be in the recommended range. Furthermore, [Cu(L3H)2] had an acceptable FQ value however its LE value was out of range. Besides, [Cu(L2H)2] had a potent and sufficient electrophile ability (acceptor) among other compounds. In conclusion, these compounds may be suitable compounds for further analysis in anti-cancer drug development with low toxic and targeted properties.

Diversification of copper complexes with 2,2′-bipyridyl ligand bearing benzylthio groups due to the different gas atmosphere

The reaction of CuI with 5,5′-bis((benzylthio)methyl)-2,2′-bipyridine could produce two complexes under different gas atmosphere. Via SCXRD characterizations, the mixed-valence CuII/CuI complex could be obtained under ambient atmosphere, while CuII complex with oxalate could be produced via the reduction of CO2.

Coordination Chemistry, Antibacterial Screening, and In Silico ADME Study of Mononuclear NiII and CuII Complexes of Asymmetric Schiff Base of Streptomycin and Aniline

Two novel metal complexes, that is, Ni (StmAn)2(4) and Cu (StmAn)2(5), were synthesized from unsymmetrical Schiff base ligand StmAn (3). The ligand was prepared by refluxing streptomycin (2) and aniline (1). They were characterized by elemental microanalysis, conductivity measurements, and spectroscopic techniques such as 1H NMR, FT-IR, ESI-mass, and electronic absorption spectral study. Interestingly, the study revealed metal coordination through azomethine nitrogen and N-atom of NH-CH3 of N-methyl-L-glucosamine unit of streptomycin. The electronic absorption spectral study supported an octahedral geometry for complex 4 and a tetrahedral geometry for complex 5. Particle size calculation by Scherrer’s formula indicated their nanocrystalline nature. The geometry optimization of the complexes was achieved by running an MM2 job in Gaussian supported Cs-ChemOffice ultra-12.0.1 and ArgusLab 4.0.1 version software. Based on SwissADME predictions, a theoretical drug profile was generated by analyzing absorption, distribution, metabolism, excretion, and toxicity (ADMET) scores of the compounds. They were screened for in vitro antibacterial activity study against four clinical pathogens such as E. coli, S. pneumoniae, P. vulgaris, and S. aureus. Minimum inhibitory concentration (MIC) study demonstrated greater inhibitory potency of complex (4) (0.024 g/L) for S. aureus relative to ligand (3) and complex (5). Studies show that metal complexes are more toxic to bacteria.

Self‐Assembly of a Bis‐NHC Ligand and Coinage Metal Ions: Unprecedented Metal‐Driven Chemistry between the Tri‐ and Tetranuclear Species

AbstractThe discrete multinuclear AgI−NHC complexes [Agn(1)n)](X)n; (n=3 or 4, X=BF4, PF6), synthesized from a bis‐NHC ligand 1 and AgI ions via multiligand self‐assembly, were observed to be in equilibrium between two forms (tri‐ and tetranuclear) in solution on the NMR timescale, which is unprecedented in CNHC‐donor based chemistry. The existence of both the species was confirmed by various studies such as NMR (1H, VT, 2D‐DOSY) and ESI‐MS analysis along with concentration studies. Importantly, replacing AgI with other coinage metals (AuI and CuI) was found to alter the phenomenon entirely: a slow exchange from the tetra‐ to trinuclear species was noticed for the AuI complexes (4 a, b), whereas no such process was detected in case of the CuI complexes (5 a, b).

Coordinative diversity in mononuclear CuI and CuII complexes of O,N,S-ambidentate camphoriminoquinone ligands

The ligands N-phenylcamphoriminoquinone 1 and N-(2-thiomethylphenyl)camphoriminoquinone 2 were reacted with copper(I) and copper(II) precursors to yield structurally characterized compounds with N-, O,N-, N,S- and O,N,S-coordination: [CuI(1-κ2O,N)(dppf)](PF6) 3(PF6), [CuI(2- κ2N,S)(dppf)](PF6) 4(PF6), [CuII(1- κN)(NO3– κO)2] and [CuII(1-κ2O,N)(NO3-κO)2] 5, and [CuII(2-κ3O,N,S)(NO3-κO)2] 7 where dppf is 1,1′-bis(diphenylphosphino)ferrocene. Spectroelectrochemistry reveals that the cations 3+ and 4+ exhibit ferrocene-based oxidation and camphoriminoquinone-centered reduction. The copper(II) compounds 5 and 7 exhibit coordinative variety with monodentate and bidentate coordination of the ligand 1 for two different molecules in 5, and with O,N,S-tridentate coordination for 2 in 7.

Toward Improved Charge Separation through Conformational Control in Copper Coordination Complexes.

The continued development of solar energy as a renewable resource necessitates new approaches to sustaining photodriven charge separation (CS). We present a bioinspired approach in which photoinduced conformational rearrangements at a ligand are translated into changes in coordination geometry and environment about a bound metal ion. Taking advantage of the differential coordination properties of CuI and CuII, these dynamics aim to facilitate intramolecular electron transfer (ET) from CuI to the ligand to create a CS state. The synthesis and photophysical characterization of CuCl(dpaaR) (dpaa = dipicolylaminoacetophenone, with R = H and OMe) are presented. These ligands incorporate a fluorophore that gives rise to a twisted intramolecular charge transfer (TICT) excited state. Excited-state ligand twisting provides a tetragonal coordination geometry capable of capturing CuII when an internal ortho-OMe binding site is present. NMR, IR, electron paramagnetic resonance (EPR), and optical spectroscopies, X-ray diffraction, and electrochemical methods establish the ground-state properties of these CuI and CuII complexes. The photophysical dynamics of the CuI complexes are explored by time-resolved photoluminescence and optical transient absorption spectroscopies. Relative to control complexes lacking a TICT-active ligand, the lifetimes of CS states are enhanced ∼1000-fold. Further, the presence of the ortho-OMe substituent greatly enhances the lifetime of the TICT* state and biases the coordination environment toward CuII. The presence of CuI decreases photoinduced degradation from 14 to <2% but does not result in significant quenching via ET. Factors affecting CS in these systems are discussed, laying the groundwork for our strategy toward solar energy conversion.

Complexes of NOTA‐Monoamides with CuII Ions: Structural, Equilibrium, and Kinetic Study

AbstractNOTA monoamides are commonly and widely used chelators for the complexation of copper radioisotopes applied in molecular imaging and targeted nuclear therapy. However, information about their coordination behavior remains scarce. In this study, two NOTA‐monoamides, N‐ethyl (H2L1) and N,N‐diethyl (H2L2), were synthesized as model ligands and tested to probe differences in their coordination behavior between the secondary and tertiary amide pendant arms for potential applications as copper radioisotope carriers. Our results demonstrated that the solid [Cu(L1)] and [Cu(L2)] complex have a distorted octahedral arrangement, similar to structure of the [Cu(Hnota)] complex. As shown by equilibrium data, the ligands have a slightly lower basicity, and thus complexes with divalent metal ions and LiI have slightly lower stability constants than those of the parent ligand, H3nota. The dissociation constants of the CuII, ZnII and NiII complexes with H2L1 also indicate deprotonation and N‐coordination of the secondary amide group at pH&gt;9. Complexation of CuII ions with the title ligands is slower than that with H3nota but still very fast (quantitative binding in &lt;1 s, pH 2, millimolar concentrations), and CuII complexes of both monoamide ligands are more resistant to acid‐assisted decomplexation than the CuII‐H3nota complex. Therefore, our coordination data highlight that NOTA‐monoamides are suitable chelators for molecular imaging and nuclear medicine.

Investigating the antiproliferative activities of new CuII complexes with pyridine hydrazone derivatives of nalidixic acid

To further explore the structural features and potential antibacterial and antitumor activities of polynuclear CuII coordination compounds with nalidixic acid (nx) derivatives, new complexes bearing nx hydrazones with N-pyridinyl moieties substituted at positions 2 and 3 (h2py and h3py) were synthesized. Complexes [Cu3(C18H16N5O2)2(C18H17N5O2)2(H2O)]4BF4∙H2O (1), and [Cu3(C18H16N5O2)2(C18H17N5O2)2(H2O)3]4BF4∙3H2O (%) (2) were synthesized using h2py and h3py with Cu(BF4)2∙nH2O as precursor, whereas the [Cu(C18H17N5O2)Cl2]∙0.5H2O complex (3) was synthesized with h2py and CuCl2∙2H2O. Crystallographic studies of complex 1, showed that coordination of hydrazones to CuII occurs by tridentate modes of type κ3(O,N,N′) as well as bidentate modes of type κ2(O′,N″). Complexes 1, 2 and 3 had their antiproliferative activities evaluated in vitro against a panel of tumor cells by the determination of GI50 values. Complexes 1 and 2 were more active than complex 3, suggesting an effect of the complex charge on their activities. The interactions of such complexes towards bovine serum albumin (BSA) and DNA plasmid (pGEX-4 T1) were investigated using fluorescence spectroscopy and gel electrophoresis. All complexes were shown to interact with the DNA model as metallonucleases, but no interaction with BSA was observed. DNA molecular docking of complex 1 encompassing both its trinuclear (TN) form and a possible mononuclear (MN) derivative suggests that naphthyridyl ring performs π-stacking interactions with DNA. The TN species were also shown to be possible minor groove binders.

Synthesis, structural and electrochemical properties of a new family of amino-acid-based coordination complexes.

Metalloproteins involved in oxidation-reduction processes in metabolism are fundamental for the wellbeing of every organism. The use of amino-acid-based compounds as ligands for the construction of biomimetic coordination systems represents a promising alternative for the development of new catalysts. Herein is presented a new family of copper, zinc and nickel coordination compounds, which show four-, five- and six- coordination geometries, synthesized using Schiff base ligands obtained from the amino acids L-alanine and L-phenylalanine. Structural analysis and property studies were performed using single-crystal X-ray diffraction data, spectroscopic and electrochemical experiments and DFT calculations. The analysis of the molecular and supramolecular architectures showed that the non-covalent interactions developed in the systems, together with the identity of the metal and the amino acid backbone, are determinants for the formation of the complexes and the stabilization of the resultant geometries. The CuII complexes were tested as candidates for the electrochemical conversion reduction of nitrite to NO, finding that the five-coordinate L-phenylalanine complex is the most suitable. Finally, some insights into the rational design of ligands for the construction of biomimetic complexes are suggested.