EPR interpretation and electrocatalytic H2 evolution study of bis(3,5-di-methylpyrazol-1-yl)acetate anchored Cu(II) and Mn(II) complexes

Magnetic study and DFT analysis of a doubly carboxylato-bridged Co(II) derivative anchored with a 'scorpionate' precursor as a potential electrocatalyst for heterogeneous H2 evolution

A new doubly carboxylato-bridged Co(II) dinuclear complex, [Co(bdtbpza)(NCS)]2 (1), was obtained in a satisfactory yield by employing a 'scorpionate'-type precursor, bdtbpza {bis-(3,5-di-tert-butylpyrazol-1-yl)acetate}, and was then structurally characterized. Single-crystal X-ray diffraction analysis revealed that, in 1, each Co(II) is penta-coordinated, leading to a distorted trigonal-bipyramidal geometry within the coordination environment of N3O2. Weak antiferromagnetic coupling within the Co(II) ions in 1 was found based on the isotropic spin Hamiltonian H = -J(S1·S2) for the Si = 3/2 system. For evaluating the spin density distribution and the mechanism for the magnetic exchange coupling, DFT analysis was performed, with the calculated result agreeing the experimental magnetic data. A study into electrochemical H2 evolution, involving cyclic voltammetry (CV), controlled potential electrolysis (CPE), and gas chromatographic (GC) analyses of the graphite electrode modified with the cobalt complex in a neutral aqueous solution revealed the high catalytic activity of the complex with a low overpotential toward H2O reduction. The faradaic efficiency of the catalyst was found to be 83.7% and the di-cobalt catalyst-modified electrode displayed quite an interesting H2-evolution activity compared with that of bare electrodes. These results are encouraging for the future potential application of 1 in water splitting.

Electrocatalytic CO2 Reduction and H2 Evolution by a Copper (II) Complex with Redox-Active Ligand

The process of electrocatalytic CO2 reduction and H2 evolution from water, regarding renewable energy, has become one of the global solutions to problems related to energy consumption and environmental degradation. In order to promote the electrocatalytic reactivity, the study of the role of ligands in catalysis has attracted more and more attention. Herein, we have developed a copper (II) complex with redox-active ligand [Cu(L1)2NO3]NO3 (1, L1 = 2-(6-methoxypyridin-2-yl)-6-nitro-1h-benzo [D] imidazole). X-ray crystallography reveals that the Cu ion in cation of complex 1 is coordinated by two redox ligands L1 and one labile nitrate ligand, which could assist the metal center for catalysis. The longer Cu-O bond between the metal center and the labile nitrate ligand would break to provide an open coordination site for the binding of the substrate during the catalytic process. The electrocatalytic investigation combined with DFT calculations demonstrate that the copper (II) complex could homogeneously catalyze CO2 reduction towards CO and H2 evolution, and this could occur with great performance due to the cooperative effect between the central Cu (II) ion and the redox- active ligand L1. Further, we discovered that the added proton source H2O and TsOH·H2O (p-Toluenesulfonic acid) could greatly enhance its electrocatalytic activity for CO2 reduction and H2 evolution, respectively.

A New Dimeric Copper(II) Complex of Hexyl Bis(pyrazolyl)acetate Ligand as an Efficient Catalyst for Allylic Oxidations

A new dimeric copper(II) bromide complex, [Cu(L^OHex)Br(μ-Br)]₂ (1), was prepared by a reaction of CuBr₂ with the hexyl bis(pyrazol-1-yl)acetate ligand (L^OHex) in acetonitrile solution and fully characterized in the solid state and in solution. The crystal structure of 1 was also determined: the complex is interlinked by two bridging bromide ligands and possesses terminal bromide ligands on each copper atom. The two pyrazolyl ligands in 1 coordinate with the nitrogen atoms to complete the Cu coordination sphere, resulting in a five-coordinated geometry—away from idealized trigonal bipyramidal and square pyramidal geometries—which can better be described as distorted square pyramidal, as measured by the τ and χ structural parameters. The pendant hexyloxy chain is disordered over two arrangements, with final site occupancies refined to 0.705 and 0.295. The newly synthesized complex was evaluated as a catalyst in copper-catalyzed C–H oxidation for allylic functionalization through a Kharasch–Sosnovsky reaction without any external reducing agent. Using 0.5 mol% of this catalyst, and tert-butyl peroxybenzoate (Luperox) as an oxidant, allylic benzoates were obtained with up to 90% yield. The general reaction time was only slightly decreased to 24 h but a very significant decrease in the alkene:Luperox ratio to 3:1 was achieved. These factors show relevant improvements with respect to classical Kharasch–Sosnovsky reactions in terms of rate and amount of reagents. The present study highlights the potential of copper(II) complexes containing functionalized bis(pyrazol-1-yl)acetate ligands as efficient catalysts for allylic oxidations.

Development of new and efficient copper(II) complexes of hexyl bis(pyrazolyl)acetate ligands as catalysts for allylic oxidation

In this study, two new hexyl bis(pyrazol-1-yl)acetate ligands and related copper(ii) complexes were prepared and fully characterized in the solid state and in solution. Their electronic and molecular structures were investigated by X-ray photoelectron spectroscopy and near edge X-ray absorption; their ligand molecular structural stability upon coordination to copper was also investigated. The Cu(ii) complexes were studied as new catalysts in copper-catalyzed C-H oxidation for allylic functionalization (the Kharasch-Sosnovsky reaction) avoiding the use of any external reducing agents. Using 5 mol% of these catalysts and tert-butylperoxybenzoate as the oxidant, allylic benzoates were obtained in up to 90% yield: the general reaction time was decreased to 6 h and a 5 to 1 ratio of the alkene and tert-butylperoxybenzoate was used to overcome the two most important limitations on their use in chemistry.

Charge-assisted hydrogen bond and nitrile⋯nitrile interaction directed supramolecular associations in Cu(ii) and Mn(ii) coordination complexes: anticancer, hematotoxicity and theoretical studies

Charge-assisted H-bonds and nitrile⋯nitrile interactions directed assemblies in Cu(ii) and Mn(ii) complexes have been analyzed by MEP surface and NCI plot index. Anticancer activities and hematotoxictiy have been investigated.

Syntheses and Biological Studies of Cu(II) Complexes Bearing Bis(pyrazol-1-yl)- and Bis(triazol-1-yl)-acetato Heteroscorpionate Ligands

Copper(II) complexes of bis(pyrazol-1-yl)- and bis(triazol-1-yl)-acetate heteroscorpionate ligands have been synthesized. The copper(II) complexes [HC(COOH)(pz^Me2)₂]Cu[HC(COO)(pz^Me2)₂]·ClO₄, [HC(COOH)(pz)₂]₂Cu(ClO₄)₂ (pz^Me2 = 3,5-dimethylpyrazole; pz = pyrazole) were prepared by the reaction of Cu(ClO₄)₂·6H₂O with bis(3,5-dimethylpyrazol-1-yl)acetic acid (HC(COOH)(pz^Me2)₂) and bis(pyrazol-1-yl)acetic acid (HC(COOH)(pz)₂) ligands in ethanol solution. The copper(II) complex [HC(COOH)(tz)₂]₂Cu(ClO₄)₂·CH₃OH (tz = 1,2,4-triazole) was prepared by the reaction of Cu(ClO₄)₂·6H₂O with bis(1,2,4-triazol-1-yl)acetic acid (HC(COOH)(tz)₂) ligand in methanol solution. The synthesized Cu(II) complexes, as well as the corresponding uncoordinated ligands, were evaluated for their cytotoxic activity in monolayer and 3D spheroid cancer cell cultures with different Pt(II)-sensitivity. The results showed that [HC(COOH)(pz^Me2)₂]Cu[HC(COO)(pz^Me2)₂]·ClO₄ was active against cancer cell lines derived from solid tumors at low IC₅₀ and this effect was retained in the spheroid model. Structure and ultra-structure changes of treated cancer cells analyzed by Transmission Electron Microscopy (TEM) highlighted the induction of a cytoplasmic vacuolization, thus suggesting paraptotic-like cancer cell death triggering.