Imine Nitrogen Atoms Research Articles

Synthesis and inner-sphere hydrophosphorylation of (η1-N)-N-benzyl-N-(1,3-dimethylbut-2-enylidene)amine-(dicarbonyl)(1,3,5-triorganyl-1,3,5-triazacyclohexane) molybdenum(0) and -tungsten(0)

Complexes of group VIb metals (Mo and W) has been prepared with N-benzyl-(3-methylbut-2-enylidene)amine, where the latter is coordinated with the dicarbonyl(1,3,5-triorganyl-1,3,5-triazacyclohexane)-metal(0) fragment exclusively through the lone electron pair of the imine nitrogen atom. The reactions of the synthesized metal complexes with diethyl phosphite in various conditions always involved the addition of the phosphite across the С=N bond to form, depending on the conditions, aminophosphonates or their inner-sphere rearrangement products amidophosphates. Both organophosphorus compounds remain in the coordination sphere of the transition metal complex.

Synthesis of polysubstituted 2-azetidinones via in situ generation of a vanillinyl ketene and electrocyclic reaction of the corresponding zwitterionic intermediate

Highly stereoselective synthesis of polyfunctionalized 2-azetidinones was achieved starting from vanillin as an available natural product. Our approach to these valuable heterocyclic scaffolds involves a formal [2π + 2π] cycloaddition between Schiff bases and the aryloxyketene as a novel ketene which was generated in situ in the key step. A zwitterionic intermediate formed from the attack of the nitrogen atom of imine to the carbonyl of ketene and the electrocyclic reaction of the mention zwitterionic intermediate caused to form trans- β-lactams as the only observed products.

Cis-1,4-Polymerization of Isoprene Catalyzed by 1,3-Bis(2-pyridylimino)isoindoline-Ligated Rare-Earth-Metal Dialkyl Complexes

The two rare-earth-metal dialkyl complexes 1 and 2 (1, Ln = Sc; 2, Ln = Lu) were obtained via the same acid–base reaction between 1,3-bis(2-pyridylimino)isoindoline (BPI) ligand and rare-earth-metal trialkyl complexes. These complexes 1 and 2 were structurally characterized by X-ray diffraction. Both in the solid state and in the solution state, the mononuclear Sc dialkyl complex 1, containing one monoanionic tridentate C2-symmetric pincer-type BPI ligand, adopts a distorted-trigonal-bipyramidal configuration. When the Sc center of complex 1 was replaced by the larger Lu center, the intramolecular proton transfer from the isoindoline nitrogen atom to one of the imine nitrogen atoms could be observed in the tautomeric BPI ligand, which served as a monoanionic tetradentate ligand bridging two Lu centers and finally afforded the binuclear Lu dialkyl complex 2 with a cage-like symmetrical structure in the solid state. However, this binuclear Lu complex 2 could dissociate into a mononuclear structure in the so...

New fluorescent [Ag(I)(Schiff base)] complexes derived from 9-anthracenecarboxaldehyde and their application in thin layers deposition

New Ag(I) complexes with Schiff bases derived from 9-anthracenecarboxaldehyde and 2-thiopheneethylamine thet(9-anthraceneca) (L1) or (1R,2R)(+)-diphenylethylenediamine (1R,2R)(+)-diphenen(9-anthraceneca) (L2) were obtained and characterized by 1H, 13C, 15N NMR, 1H differential Nuclear Overhauser Effect (NOE diff.) NMR technique, UV–Vis, CD and IR spectroscopy in solution and in the solid phase. X-ray crystal structure of [Ag(thet(9-anthraceneca))2]NO3] (1), revealed silver(I) linearly coordinated by the ligand imine nitrogen atoms. X-ray crystal structure detremination and DFT calculations for complexes and ligands, related confirming their geometry in solution and in the solid phase. 1H NMR NOE diff. spectra indicate that both Schiff bases adopt different conformation in solution and in the solid state. For Ag complexes with (L1) and (L2) the significant NOE enhacement between the imine hydrogen atoms and hydrogen of the aromatic rings was observed, indicating changes of the silver ion coordination sphere in solution. The highest quantum yield of the fluorescence was achieved for (2) with φ2=0.52 (λex=347nm). For all investigated compounds the fluorescence is related to the excitation HOMO→LUMO+1 or HOMO→LUMO in the anthracene moiety. The homogeneous layers of complexes uniformly covering the silicon substrate have been obtained with a spin- or dip-coating techniques and characterized by scanning electron microscopy (SEM/EDS) and atomic force microscopy (AFM). The complex [Ag2((1R,2R)(+)-diphenen(9-anthraceneca))(NO3)2] (2) was deposited on Si(111) covered with PMMA. Fluorescence spectra of [Ag(thet(9-anthraceneca))2]NO3] (1)/Si materials exhibit emission at 480nm from intra-ligand transitions (λex=360nm) and differ slightly from the spectra obtained for the solid complexes or their solutions. The highest fluorescence intensity was noted for the layers obtained by a multistage deposition at variable spin rates and deposition time 5s.

Synthesis, characterization, crystal structure and DNA, HSA-binding studies of four Schiff base complexes derived from salicylaldehyde and isopropylamine

Four new Schiff base complexes (NiL2, CoL2, CuL2 and ZnL2) (HL: ((E)-2-((isopropylamino) methyl) phenol) were synthesized and characterized by CHN elemental analysis, FT-IR and single crystal X-ray diffraction technique. The crystallographic data reveal that in all complexes the metal centers are four-coordinated by two phenolate oxygen and two imine nitrogen atoms of two moles of Schiff base ligand HL and geometry around the metal center in all of them is distorted tetrahedral. In addition, 1H and 13C NMR techniques were employed for characterization of diamagnetic ZnL2 complex. The binding affinity of complexes with DNA (fish sperm DNA, FS-DNA) and Human Serum Albumin (HSA) were investigated using fluorescence quenching, chemometrics, UV–Vis spectroscopy, viscosity measurements and molecular docking methods. The obtained results revealed that the DNA and HSA affinity for binding to complexes are in the following order: CuL2>ZnL2>CoL2>NiL2 and NiL2>ZnL2>CuL2>CoL2. The distance between complexes and HSA was obtained based on the Förster’s theory of non-radiative energy transfer. The computational molecular docking results showed that H-bond interactions, hydrophobic interactions, π-π stacking and π-cation interactions have dominant role in the stability of HSA-ML2 (M: Cu, Co, Ni and Zn). The computational docking and viscosity results suggest that all metal complexes interact with DNA presumably by the groove binding mechanism.

Crystal structure, DNA interaction and thermal analysis data of two new antimicrobial active binuclear cadmium and mercury complexes

Two new binuclear Schiff base complexes with the general formula [CdLBr(μ-Br)]2 (1) and [Hg2L(μ-I)2I2] (2) were prepared by the reaction of 2,2-dimethyl-N,N'- bis-(3-phenyl-allylidene)-propane-1,3-diamine (L), CdBr2 and HgI2. The crystal structure of two complexes was determined by X-ray crystallography. The common structures for four-coordinated compounds are square planar or the tetrahedral geometries, which is evaluated by the Houser angular index (τ4). In [CdLBr(μ-Br)]2 (1), each cadmium center is five-coordinated by two iminic nitrogen atoms from Schiff base ligand, two μ2-bridging bromide anions and one terminal coordinating bromide anion. The metal center in this centrosymmetric dimer has a distorted square-pyramidal geometry. [Hg2L(μ-I)2I2] (2) consists of two four-coordinated mercury centers with different coordination spheres (HgN2I2 for Hg1 and HgI4 for Hg2). The TG/DTG diagrams showed that both complexes were completely decomposed under a nitrogen atmosphere. Furthermore, antibacterial activities of compounds have been screened against various bacteria and fungi by Disk diffusion method. Mercury complex inhibited the growth of the microorganisms more efficient than cadmium complex. DNA cleavage potential of compounds was evaluated by agarose gel electrophoresis method. Finally, nano-structure cadmium complex was sono-chemically synthesized and applied as precursor for preparation of cadmium oxide nanoparticles.

Pyrazoles and C‐Imidoylaziridines through [4+1] Annulation and [2+1] Cycloaddition of 1‐Azabuta‐1,3‐dienes with a Synthetic Equivalent of Phthalimidonitrene

Oxidative addition of N‐aminophthalimide to 1,2,4‐triaryl‐1‐azabuta‐1,3‐dienes leads, in most cases, to the regiodefined formation of 1,3,5‐triarylpyrazoles in moderate to good yields through [4+1] annulation. This transformation is supposed to proceed by nitrenoid attack onto a lone pair of electrons of the imine nitrogen atom to give the vinylazomethine imine, followed by its 1,5‐electrocyclization into pyrazoline and further aromatization into pyrazole. Rare examples of 2‐imidoyl‐1‐phthalimidoaziridines that are formed by competitive [2+1] cycloaddition onto the C=C bond were isolated in low yields for 1‐azadienes with electron‐deficient aryl substituents at the imine nitrogen atom.

Ruthenium(II/III) complexes of redox non-innocent bis(thiosemicarbazone) ligands: Synthesis, X-ray crystal structures, electrochemical, DNA binding and DFT studies

Six tetradentate bis-thiosemicarbazone ligands formed by condensation of pyruvaldehyde with 4-(aryl) thiosmicarbazides and their Ru(II) complexes are reported. The complexes are of formula [Ru(PPh3)2(L)], where L is the dianionic form of the bis-thiosemicarbazone ligands. X-ray crystal structures of two of the complexes suggest that the thiosmicarbazone ligands act in a tetradentate fashion occupying the basal plane of the Ru(II) coordination octahedron and each of the two thiosemicarbazone moiety forms five membered chelate ring involving deprotonated thiolato sulfur and the imine nitrogen atoms; the two triphenylphosphine ligands are trans to each other. The complexes undergo Ru(II)/Ru(III) oxidation at a relatively low potential of 0.05–0.12V versus Ag/AgCl. One of the Ru(II) complex has been chemically oxidized to the corresponding Ru(III) complex [Ru(PPh3)2(L)]PF6 using ferrocenium hexafluorophosphate as an oxidizing agent. E.P.R. spectra of the Ru(III) complex and DFT calculations on the Ru(III) as well as two of the Ru(II) complexes suggest that there is extensive mixing between the ligand and metal valence orbitals. The DNA-binding properties of the Ru(II) complexes were studied by both UV–Vis spectroscopy and fluorescence quenching of ethidium bromide-DNA complex. The complexes showed strong DNA-binding ability with Kapp of the order of 106M−1.

Reaction of N-sulfonyl-1,4-benzoquinone imines with enamines

N-Sulfonyl derivatives of 1,4-benzoquinone imine reacted with enamines to give 1,4-addition products and products of their subsequent cyclization, substituted 5-aminobenzofurans and 5-aminoindoles, depending on the solvent nature, electron-withdrawing power of the substituent on the quinone imine nitrogen atom, and enamine structure. The presence of strong electron-withdrawing trifluoromethanesulfonyl group on the quinone imine nitrogen atom favors formation of 1,4-addition products and benzofuran derivatives.

Some divalent metal(II) complexes of novel potentially tetradentate Schiff base N,N′‐bis(2‐carboxyphenylimine)‐2,5‐thiophenedicarboxaldhyde: Synthesis, spectroscopic characterization and bioactivities

A novel tetradentate dianionic Schiff base ligand, N,N′‐bis(2‐carboxyphenylimine)‐2,5‐thiophenedicarboxaldhyde (H2L) and some first row d‐transition metal chelates (Co(II), Cu(II), Ni(II) and Zn(II)) were synthesized and characterized using various physicochemical and spectroscopic methods. The spectroscopic data suggested that the parent Schiff base ligand coordinates through both deprotonated carboxylic oxygen and imine nitrogen atoms. The free Schiff base and its metal chelates were screened for their antimicrobial activities for various pathogenic bacteria and fungi using the agar well diffusion method. The antibacterial and antifungal activities of all the newly synthesized compounds are significant compared to the standard drugs ciprofloxacin and nystatin. The antioxidant activities of the compounds were determined by reduction of 1,1‐diphenyl‐2‐picrylhydrazyl and compared with that of vitamin C as a standard. DNA binding ability of the novel Schiff base and its complexes was investigated using absorption spectroscopy, fluorescence spectroscopy, viscosity measurements and thermal denaturation. The obtained results clearly demonstrate that the binding affinity with calf thymus DNA follows the order: Cu(II) complex > Ni(II) complex > Zn(II) complex > Co(II) complex >H2L. Furthermore, the DNA cleavage activity of the newly synthesized ligand and its metal complexes was investigated using supercoiled plasmid DNA (pUC18) gel electrophoresis.

New tetrahedral zinc halide Schiff base complexes: Synthesis, crystal structure, theoretical, 3D Hirshfeld surface analyses, antimicrobial and thermal studies

A new bidentate Schiff base ligand named as N,N′-bis((E)-3-phenylallylidene)butane-1,4-diamine (L) and three its zinc halide complexes were synthesized and characterized by FT-IR, 1H NMR, 13C NMR and UV–Vis spectroscopy. The crystal structure of zinc bromide and iodide complexes were characterized using single crystal X-ray diffraction. The two structures are isomorphous, crystallizing in the monoclinic crystal system with space group C2/c with closely similar unit cell dimensions. In these complexes, the Zn(II) ion is in the center of a distorted tetrahedral environment completed by two iminic nitrogen atoms of Schiff base ligand and two halide anions. The analysis of crystal structures shows that intermolecular interactions such as CH⋯halogen, π⋯π and CH⋯π interactions have effective role in stabilization of complexes structure. Intermolecular interactions were more analyzed using 3D Hirshfeld surface analysis and corresponding 2D fingerprint plots. Furthermore, structural optimization by DFT calculations at the B3LYP/LANL2DZ level have been performed and then compared with the experimental data. Time-dependent density functional theory (TDDFT) has been also used to calculate the electronic transitions of molecules at B3LYP/LANL2DZ level using the optimized ground-state geometries. NBO analysis was applied for investigation of intra and inter-molecular bonding and conjugative interaction in molecular systems. Schiff base ligand and their zinc complexes have been screened for their antibacterial and antifungal activities by disc diffusion method. Thermal behaviors of all compounds were studied by TG/DTG analysis data. Also, nanostructures of zinc complexes were synthesized by sonochemical method and characterized by FT-IR spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). ZnO nanoparticles were simply prepared by calcination of zinc iodide complex as new precursor at 600°C.

Structural diversities and preliminary antimicrobial studies of 1-((E)-(pentylimino)methyl)naphthalen-2-ol and its metal complexes

Schiff bases and their metal complexes have a number of biological activities such as antidepressant, analgesic, antimicrobial, antiviral, and antitumor. In the present studies, the 1-((E)-(pentylimino)methyl)naphthalen-2-ol ligand is prepared by the reaction of 2-hydroxynaphthaldehyde with n-amyl amine. The ligand results in CoL3, NiL2 and CuL2 complexes when reacted with the cobalt acetate, nickel acetate, and copper acetate salts respectively. The complexes along with their ligand are fully characterized by X-ray diffraction studies and biologically screened. The ligand structure reveals that it is a zwitterion species where the iminic nitrogen atom is protonated and the C–O bond shows a high double bond character. The cobalt complex has an octahedral geometry around the metal center and each nitrogen atom is in the trans position to the oxygen donor site. On the other hand, the copper complex shows a centrosymmetric square planar coordination, and in this case, the nitrogen sites are trans to each other. The complexes and the ligand are found to be more potent than the standard drugs used against some microbes in their preliminary biological studies.

Binuclear zinc(II) complexes of N(4)-substituted bis(thiosemicarbazone) ligands incorporating hydroxyl group and their non-hydroxyl analogues

We have reported the synthesis and physical and chemical studies of the new zinc complexes of N(4)-substituted bis(thiosemicarbazones). The complexes characterized by spectroscopic methods. The crystal structures of the compounds [Zn2L2(CH3COO)]·EtOH and [Zn2L4(CH3COO)]·MeOH is determined. Bis(thiosemicarbazones) involving a pendant OH group having SNONS donor sequences can hold two metal ions in close proximity. The coordination sphere has been formed by the imine nitrogen and sulfur atom, and the remaining positions, in a square-based pyramid, has been occupied by three oxygen atoms derived of pendant OH, ether group and acetate ligand. Acetate ligand and alkoxide oxygen are bridged between two metal centers. Whereas, their non-hydroxyl analogues are dimer. In dimer complexes, two ligands are tetradentate coordinated via N2S2 donor atoms. The presence of bulky groups on the nitrogens of thiosemicarbazide enforce an s-trans conformation for the H2L1 and H2L3 ligands in [ZnL1]2·MeOH and [ZnL3]2·MeOH. Fluorescence studies suggest that the [ZnL1]2·MeOH complex can be utilized as a fluorescent imaging agent.

Self assembly of dialkoxo bridged dinuclear Fe(III) complex of pyridoxal Schiff base with C[sbnd]C bond formation – Structure, spectral and magnetic properties

The new dinuclear Fe(III) complex, [Fe2(µ-L)2]·3(H2O)·0.38(O), [L=(E)-2-(((5-(hydroxymethyl)-2-methyl-3-oxido-1κO-pyridin-4-yl)methylene)amino-1κN)-3-(3-(hydroxymethyl)-2-methyl-5-oxido-1κO-pyridin-1-ium-4-yl)-3-oxido-1:2κ2O-propanoato-2κO]∗ (∗The second ligand has swapped indices 1 and 2, denoting the individual Fe centers.), was synthesized by reaction of FeCl3·6H2O with potassium pyridoxylidenglycinate in ethanol-water solution. Pentadentate pyridoxal Schiff base ligand was generated in situ by aldol condensation of potassium pyridoxylidenglycinate and pyridoxal. A CC coupling was achieved at room temperature under metal template reaction. The complex was characterized by X-ray structural analysis at 100K, elemental analysis, spectral and magnetic measurements. The compound crystallizes in the monoclinic space group P 21/n, with unit cell parameters: a=9.7445(15)Å, b=19.489(3)Å, c=20.862(6)Å, β=92.595(17)°. Structural analysis of the complex showed that each Fe(III) center has a distorted octahedral FeNO5 core, which is sixfold coordinated through iminic nitrogen atom, two phenoxido oxygen atoms, alkoxo oxygen atom and carboxylato oxygen atom from two Schiff-base ligands forming a rhombic arrangement of metal ions and oxygen atoms. In the structure, two Fe(III) atoms are connected with two alkoxo-bridging ligands providing covalent superexchange pathway by linkage Fe1–O–Fe2 with the Fe1⋯Fe2 distance of 3.195Å. In the crystal lattice, the noncovalent interactions, hydrogen bonds, and π-π stacking interactions expand the mononuclear units to 3D supramolecular network. The temperature dependent magnetic susceptibility data (6.5–300K)indicate that the octahedral Fe(III) centers in this complex retain high-spin S=5/2 (6A1g) in the whole temperature range. The effects of zero-field splitting (D=7.67cm−1) and an antiferromagnetic coupling (J=−14.66cm−1) between the two alkoxo-oxygen bridged Fe(III) ions are discussed.

Tin(IV) Schiff base complexes derived from pyridoxal: Synthesis, spectroscopic properties and cytotoxicity

The synthesis of monomeric pentacoordinated diorganotin(IV) complexes derived from pyridoxal hydrochloride and 4‐ or 5‐R‐substituted ortho‐aminophenols is described. The complexes were characterized using UV–visible, infrared, mass, 1H NMR, 13C NMR and 119Sn NMR spectral techniques. The molecular structure of three complexes was established using X‐ray diffraction: 3b and 3d show a distorted trigonal bipyramidal geometry, in which the basal plane is defined by the butyl groups and the iminic nitrogen atom, whereas the oxygen atoms from the aromatic ring occupy axial positions; in contrast, complex 3e exhibits a square pyramidal geometry. The cytotoxic activity of all complexes against human cell lines U‐251 (glioblastoma), K‐562 (chronic myelogenous leukemia), HCT‐15 (human colorectal cancer), MCF‐7 (human breast cancer) and SKLU‐1 (non‐small‐cell lung cancer) was evaluated, and the inhibitory percentage values indicated higher activity than the reference standard, cisplatin. Acute toxicity studies were performed in vivo for the prepared complexes to determine the lethal medium dose (LD50) after intraperitoneal administration to mice.

Synthesis and Characterisation of Organosilicon and Organotin Complexes derived from DHA Ligand

Organosilicon(IV) and organotin(IV) complexes with dehydroacetic acid and amino ether Schiff base ligand have been described with the help of elemental analyses, electronic, infrared, multinuclear magnetic resonance spectroscopy. Analysis of data suggested that the Schiff base provides two bidentate NO domains and was coordinated to silicon and tin moiety through the imine nitrogen and hydroxyl oxygen atom forming penta coordinated and hexa coordinate complexes in 1: 2 and 1: 1 molar ratio. Thermal studies of the synthesized organotin compounds shows that they are stable and decomposition of the complexes occur in two steps with the formation of metal oxides as the end product.

Silver complexes of ligands derived from adamantylamines: Water-soluble silver-donating compounds with antibacterial properties

Two new silver(I) complexes, namely [Ag(qyAm)2](CF3SO3) (1) and [Ag(qyTAm)2](CF3SO3) (2), (qyAm=2-(quinonyl)iminoadamantane, qyTAm=2-(quinonyl)iminotriazaadamantane) have been synthesized and characterized by elemental analyses, 1H NMR, IR, electronic absorption spectroscopy, and X-ray diffraction. The coordination geometry of the silver center in both complexes is distorted tetrahedral where their respective qyAm and qyTAm ligand bind in a bidentate fashion using the imine and quinoline nitrogen atoms. Complex 2 is soluble in water and exhibits strong antimicrobial actions on both Gram-negative (E. coli, and P. aeruginosa) and Gram-positive (S. aureus) bacteria. The minimal inhibitory concentration (MIC) values for complex 2 (4, 4, and 8 μg for E. coli, P. aeruginosa, and S. aureus, respectively) are comparable to MIC values of silver nitrate and silver sulfadiazine.

Synthesis, characterization, and quantitative structure–activity relationship studies of bioactive dehydroacetic acid and amino ether Schiff base complexes

AbstractStructural aspects of organosilicon(IV) and organotin(IV) complexes with dehydroacetic acid and amino ether Schiff base ligand have been described with the help of elemental analyses, conductance measurements, UV–Vis, infrared, multinuclear magnetic resonance, mass spectroscopy as well as thermogravimetric analysis, and X‐ray diffraction studies. Analysis of data suggested that the Schiff base provides two bidentate NO domains and was coordinated to silicon and tin moiety through the imine nitrogen and hydroxyl oxygen atom. Complexes were found to be nonelectrolytic and monomeric in nature. The thermal decomposition for tin compounds occurred in two steps and resulted into the formation of pure SnO2 as end product. The in vitro biological effects of the synthesized compounds were tested against two Gram‐positive and two Gram‐negative bacteria. The results of biological activity showed that all the complexes have enhanced activity as compared with the corresponding ligand, and compounds 5, 9, 11, 12, 13, 15, 16, and 17 were more potent than the standard drug ciprofloxacin. Compound 17 exhibited best antibacterial activity with lowest minimum inhibitory concentration value and maximum zone of inhibition. Further, quantitative structure–activity relationship studies pointed out that more stable compound were more active as antibacterial agents.

Methoxy group containing bidentate Schiff base ligands and their transition metal complexes: Synthesis, structural characterisation, photoluminescence, antioxidant capacity and superoxide dismutase activity studies

Co(II), Ni(II) and Cu(II) complexes of the two new Schiff base ligands (HL1 and HL2 derived from 2-hydroxy-3-methoxybenzaldehyde and 2-hydroxy-1-naphtaldehyde with 2,4-dimethoxyaniline) have been prepared. The structures of the synthesized compounds were characterized by elemental analyses and spectral methods (IR, 1H NMR, 13C NMR, thermogravimetric analysis (TGA), magnetic susceptibility. IR spectra show that HL1 and HL2 coordinated to the metal ions in a neutral bidentate manner with ON donor sites of the phenolic oxygen and imine nitrogen atoms. The molecular structures of HL1 and HL2 ligands and complex [Cu(L1)2]H2O were also determined by single crystal X-ray diffraction studies. To determine the antioxidant properties of Schiff base ligands and transition metal complexes, the CUPRAC and DPPH methods of antioxidant assays were used. Superoxide dismutase activities (SOD) of the Schiff base complexes were investigated and results were discussed.

Copper(II) complexes with imino phenoxide ligands: synthesis, characterization, and their application as catalysts for the ring-opening polymerization of rac-lactide.

Four new copper complexes based on bidentate imino phenoxide ligands were synthesized and characterized by IR, UV–Vis spectroscopy, ESI mass spectrometry, single crystal X-ray diffraction, and electrochemistry. The crystal structures revealed that the copper(II) atoms are surrounded by phenolate oxygen and imine nitrogen atoms of two ligands in a distorted square-planar geometry. The existence of ligand-centered, as well as Cu(II)-centered quasi-reversible and reversible redox reactions are observed in the cyclic voltammetry experiments of all the complexes. All complexes are able to catalyze the ring-opening polymerization of rac-lactide yielding polymers with moderate molecular weights and moderately broad molecular weight distributions.Graphical abstract Electronic supplementary materialThe online version of this article (doi:10.1007/s00706-016-1830-7) contains supplementary material, which is available to authorized users.