Binuclear Complexes Research Articles

Exo- or endo-1H-pyrazole metal coordination modulated by the polyamine chain length in [1 + 1] condensation azamacrocycles. Binuclear complexes with remarkable SOD activity.

The Cu2+ complexes of three [1 + 1] azacyclophane macrocycles having the 1H-pyrazole ring as the spacer and the pentaamine 1,5,8,11,15-pentaazadecane (L1) or hexaamines 1,5,8,12,15,19-hexaazanonadecane (L2) and 1,5,9,13,17,21-hexaazaheneicosane (L3) as bridges show endo- coordination of the pyrazolate bridge giving rise to discrete monomeric species. Previously reported pyrazolacyclophanes evidenced, however, exo-coordination with the formation of dimeric species of 2 : 2, 3 : 2 or even 4 : 2 Cu2+ : L stoichiometry. The complexes have been characterized in solution using potentiometric studies, UV-Vis spectroscopy, paramagnetic NMR, cyclic voltammetry and mass spectrometry. The measurements show that all three ligands have as many protonation steps in water as secondary amines are in the bridge, while they are able to form both mono- and binuclear Cu2+ species. The crystal structures of the complexes [Cu(HL1)Br]Br(1+x)(ClO4)(1-x)·yH2O (1) and [Cu2(H-1L2)Cl(ClO4)](ClO4)·H2O·C2H5OH (2) have been solved by X-ray diffraction studies. In 1 the metal ion lies at one side of the macrocyclic cavity being coordinated by one nitrogen of the pyrazolate moiety and the three consecutive nitrogen atoms of the polyamine bridge. The other nitrogen of the pyrazole ring is hydrogen-bonded to an amine group. In 2 the two metal ions are interconnected by a pyrazolate bis(monodentate) moiety and complete their coordination spheres with three amines and either a bromide or a perchlorate anion, which occupy the axial positions of distorted square pyramid geometries. Paramagnetic NMR studies of the binuclear complexes confirm the coordination pattern observed in the crystal structures. Cyclic voltamperommetry data show potentials within the adequate range to exhibit superoxide dismutase (SOD) activity. The IC50 values calculated by McCord-Fridovich enzymatic assays show that the binuclear Cu2+ complexes of L2 and L3 have SOD activities that rank amongst the highest ones reported so far.

Intrinsically chiral paddlewheel diruthenium complexes

This work presents an axially chiral platform based on ruthenium units, evaluates the crystal structures, configurational stability and electronic structure tunability, and proposes a general nomenclature system for binuclear paddlewheel complexes.

Tuning spin dynamics of binuclear Dy complexes using different nitroxide biradical derivatives.

By employing nitronyl/imino nitroxide biradicals, three Ln-Zn complexes, namely, [Ln2Zn2(hfac)10(ImPhPyobis)2] (LnIII = Gd 1, Dy 2; hfac = hexafluoroacetylacetonate; ImPhPyobis = 5-(4-oxypyridinium-1-yl)-1,3-bis(1'-oxyl-4',4',5',5'-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene) and [Dy2Zn2(hfac)10(NITPhPyobis)2] 3 (NITPhPyobis = 5-(4-oxypyridinium-1-yl)-1,3-bis(1'-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene), have been successfully prepared. The three complexes possess {Ln2O2} cores bridged by the oxygen atoms of the 4-oxypyridinium rings of the biradical ligands and one of the imino/nitronyl nitroxide groups of the biradical is coordinated to a ZnII ion, then producing a centrosymmetric tetranuclear six-spin structure. The studies of spin dynamics indicate that complexes 2 and 3 exhibit distinct magnetic relaxation behaviors at zero dc field: complex 2 presents single relaxation with an effective energy barrier (Ueff) of 69.8 K, while complex 3 exhibits double relaxation processes with Ueff values for the fast and slow relaxation being 15.8 K and 50.9 K, respectively. The observed different magnetic relaxation behaviors for the two Dy complexes could be mainly ascribed to the influence of the distinct nitroxide biradical derivatives.

Redox-neutral depolymerization of lignin-derived aryl ethers catalyzed by Rh(III)-complexes: a mechanistic insight.

Density functional theory (DFT) calculations at the TPSSh-D3(BJ)/def2-TZVP (SMD, water) level of theory were performed to understand the mechanism of redox-neutral depolymerization of four types of lignin-derived aryl ether dimers catalyzed by rhodium-terpyridine ([Rh]) and a binuclear Rh complex ([2Rh]). The cleavage of the Cβ-O bond in the β-O-4 model compound was initiated by the dehydrogenation of the alcohol moiety into a ketone intermediate, followed by the reductive cleavage of the ether bond, producing phenol and aromatic ketone products. The [Rh]-OH intermediate, generated by the interaction between the Rh-complex and NaOH, facilitated the transformation of the alcohol group to a CO group in the lignin model compound and subsequent H-transfer, selectively forming rhodium-H active species and the ketone intermediate. The [2Rh]-H complex exhibited high reactivity, with energy barriers for a rate-determining Cβ-O bond breakage of 35.3 kcal mol-1. In contrast to 1-phenylethan-1-ol and H2, lignin itself acted as a good hydrogen source to generate [Rh]-H species. The transformation of β-O-4 model compounds with the γ-OH group occurred via the elimination of the γ-OH group, reduction of the CC bond, and Cβ-O bond cleavage steps. However, since lignin itself was unable to supply enough hydrogen to form [Rh]-H species, the aromatic products were obtained in low yields, as observed in the experiment.

Nonheme binuclear transition metal complexes with hydrosulfide and polychalcogenides.

The intriguing chemistry of chalcogen (S, Se)-containing ligands and their capability to bridge multiple metal centres have resulted in a plethora of reports on transition metal complexes featuring hydrosulfide (HS-) and polychalcogenides (En2-, E = S, Se). While a large number of such molecules are strictly organometallic complexes, examples of non-organometallic complexes featuring HS- and En2- with N-/O-donor ligands are relatively rare. The general synthetic procedure for the transition metal-hydrosulfido complexes involves the reaction of the corresponding metal salts with HS-/H2S and this is prone to generate sulfido bridged oligomers in the absence of sterically demanding ligands. On the other hand, the synthetic methods for the preparation of transition metal-polychalcogenido complexes include the reaction of the corresponding metal salts with En2- or the two electron oxidation of low-valent metals with elemental chalcogen, often at an elevated temperature and/or for a long time. Recently, we have developed new synthetic methods for the preparation of two new classes of binuclear transition metal complexes featuring either HS-, or Sn2- and Sen2- ligands. The new method for the synthesis of transition metal-hydrosulfido complexes involved transition metal-mediated hydrolysis of thiolates at room temperature (RT), while the method for the synthesis of transition metal-polychalcogenido complexes involved redox reaction of coordinated thiolates and exogenous elemental chalcogens at RT. An overview of the synthetic aspects, structural properties and intriguing reactivity of these two new classes of transition metal complexes is presented.

Kinetic isotope effect offers selectivity in CO2 reduction.

A binuclear Ni complex with N,O donors catalyzes CO2 reduction via its Ni(I) state. The product distribution when H2O is used as a proton source shows similar yields for CO, HCOOH and H2. However, when D2O is used, the product distribution shows a ∼65% selectivity for HCOOH. In situ FTIR indicates that the reaction involves a Ni-COO* and a Ni-CO intermediate. Differences in H/D KIEs on different protonation pathways determine the selectivity of CO2 reduction.

Binuclear cyclometalated Ir(III) complexes with bis-bidentate butterfly-shaped ligands: synthesis, characterization, and application in efficient yellow-orange light-emitting electrochemical cells.

Two yellow-to-orange-emitting binuclear iridium complexes of the form [Ir2(ppy)4(N^N)](ClO4)2 (namely IrL1 and IrL2) were designed and synthesized, using phenylpyridine (ppy) as a cyclometalating ligand (C^N) and phenanthroimidazole-based bridging compounds as ancillary ligands (N^N), to explore the effect of sterically hindered bulky bridging ligands and their substituents on the electronic and emission properties of the related ionic transition metal complexes (iTMCs) and the performance of iTMC-based light-emitting electrochemical cells (iTMC-LECs). In CH2Cl2 solution, complexes IrL1 and IrL2 afford yellow-to-orange emission centered at 570 and 582 nm with PLQYs of 27% and 36%, respectively. The reversible and quasi-reversible redox behaviors of both complexes are shown to reveal the excellent stability of the emitters in solution. The electrochemical and photophysical data indicate that the substitution at the C2 position of the imidazole moiety does not significantly affect the electronic properties of the complexes. IrL1 and IrL2-based LECs show yellow-to-orange electroluminescence centered at 586 and 598 nm, with a maximum luminance (Lmax) of 430 and 570 cd m-2 and current efficiencies of 3.45 and 4.50 cd A-1, respectively. However, compared with their corresponding archetypecomplex, IrL1, and IrL2-based LECs exhibit several fold higher Lmax, which highlights the role of these ligands in the design of emitters.

Visible-light-responsive hybrid photocatalysts for quantitative conversion of CO2 to highly concentrated formate solutions.

Photocatalysts can use visible light to convert CO2 into useful products. However, to date photocatalysts for CO2 conversion are limited by insufficient long-term stability and low CO2 conversion rates. Here we report hybrid photocatalysts consisting of conjugated polymers and a ruthenium(ii)-ruthenium(ii) supramolecular photocatalyst which overcome these challenges. The use of conjugated polymers allows for easy fine-tuning of structural and optoelectronic properties through the choice of monomers, and after loading with silver nanoparticles and the ruthenium-based binuclear metal complex, the resulting hybrid systems displayed remarkably enhanced activity for visible light-driven CO2 conversion to formate. In particular, the hybrid photocatalyst system based on poly(dibenzo[b,d]thiophene sulfone) drove the very active, durable and selective photocatalytic CO2 conversion to formate under visible light irradiation. The turnover number was found to be very high (TON = 349 000) with a similarly high turnover frequency (TOF) of 6.5 s-1, exceeding the CO2 fixation activity of ribulose-1,5-bisphosphate carboxylase/oxygenase in natural photosynthesis (TOF = 3.3 s-1), and an apparent quantum yield of 11.2% at 440 nm. Remarkably, quantitative conversion of CO2 (737 μmol, 16.5 mL) to formate was achieved using only 8 mg of the hybrid photocatalyst containing 80 nmol of the supramolecular photocatalyst at standard temperature and pressure. The system sustained photocatalytic activity even after further replenishment of CO2, yielding a very high concentration of formate in the reaction solution up to 0.40 M without significant photocatalyst degradation within the timeframe studied. A range of experiments together with density functional theory calculations allowed us to understand the activity in more detail.

A novel copper(II) complex with a salicylidene carbohydrazide ligand that promotes oxidative stress and apoptosis in triple negative breast cancer cells.

We report the synthesis, characterization, anti-cancer activity and mechanism of action of a novel water-soluble Cu(II) complex with salicylidene carbohydrazide as the ligand and o-phenanthroline as the co-ligand. The synthesized complex (1) was characterized by FT-IR, EPR, and electronic spectroscopy, as well as single crystal X-ray diffraction. This compound was found to be paramagnetic from EPR spectra and X-ray crystallography revealed that the molecule crystallized in an orthorhombic crystal system. The crystal lattice was asymmetric containing two distinct binuclear copper complexes containing the Schiff base as the major ligand, o-phenanthroline as a co-ligand, two nitrate anions, and two water molecules. The Cu(II) in the first site coordinated with the enolised ligand comprising enolate O-, phenolate O-, and the imine N and N,N from o-phen. The major part of this complex exists as Cu(II) coordinated with two H2O molecules at the second site with nitrate acting as the counter anion. However, a smaller portion of the complex exists where Cu(II) is coordinated with NO3- and H2O, and the remaining water molecule acts as lattice water. It was tested for DNA binding and cleavage properties which revealed that it binds in an intercalative mode to CT-DNA with Kb value of 1.25 × 104 M-1. Furthermore, cleavage studies reveal that the complex has potential for efficient DNA cleavage under both oxidative and hydrolytic conditions. It was able to enhance the rate of cleavage by 2.8 × 108 times. The complex shows good cytotoxicity to breast cancer monolayer (2D) as well as spheroid (3D) systems. The IC50 values for MDA-MB-231 and MCF-7 monolayer culture was calculated as 1.86 ± 0.17 μM and 2.22 ± 0.08 μM, respectively, and in (3D) spheroids of MDA-MB-231 cells, the IC50 value was calculated to be 1.51 ± 0.29 μM. It was observed that the complex outperformed cisplatin in both breast cancer cell lines. The cells treated with complex 1 underwent severe DNA damage, increased oxidative stress and cell cycle arrest which finally led to programmed cell death or apoptosis in triple negative breast cancer cells through an intrinsic pathway.

Voltage-induced modulation of the magnetic exchange in binuclear Fe(III) complex deposited on Au(111) surface.

We present a complete computational study devoted to the deposition of a magnetic binuclear complex on a metallic surface, aimed to obtain insight into the interaction of magnetically coupled complexes with their supporting substrates, as well as their response to external electrical stimuli applied through a surface-molecule-STM molecular junction-like architecture. Our results not only show that the deposition is favorable in two of the four studied orientations, but also, that the magnetic coupling is only slightly perturbed once the complex is adsorbed. We observe that the effects of the applied bias voltage on the magnetic coupling strongly depend on the molecule orientation with respect to the surface and the voltage polarity. Further analysis shows that this behavior is attributable to the stabilization/destabilization of the d-type singly occupied orbitals of the iron centers, reinforced by the strong local electric fields and induced charge densities only present in certain orientations of the deposited molecule and applied voltage polarity.

Copper(I) complexes bearing pyrrole-bridged S,N and N-donor ligands as catalysts for tandem hydroamination-alkynylation: effect of anions on product formation.

In this study, the reaction between 2-(3,5-dimethylpyrazolylmethyl)-5-(dimethylaminomethyl)pyrrole and thiophenol under heating conditions afforded the new ligand 2-(3,5-dimethylpyrazolylmethyl)-5-(phenylthiomethyl)pyrrole 2. The reaction of 2 with meta-chloroperbenzoic acid provided sulfoxide 3 and sulfone 4 group-containing ligands. The reaction of 2 with copper(I) halides provided the binuclear complexes [Cu(μ-X){μ-C4H3N-2-(CH2Me2pz)-5-(CH2SPh)-κ2-S,N}]2 (X = Cl, Br and I, 5-7) in high yields. Conversely, the analogous reaction of 4 with copper(I) halides yielded two types of complexes, three coordinate bi- and mononuclear of the type [Cu(μ-Cl){C4H3N-2-(CH2Me2pz)-5-(CH2SO2Ph)-κ1-N}]28 and [CuX{C4H3N-2-(CH2Me2pz)-5-(CH2SO2Ph)-κ1-N}2], X = Br, 9 and I, 10. When the reaction was carried out in the presence of KPF6, the two-coordinate complex [Cu{C4H3N-2-(CH2Me2pz)-5-(CH2SO2Ph)-κ1-N}2]PF6-11a was isolated, whereas its BF4- analogue 11b was synthesized by the reaction of 8 with AgBF4. The structures of these complexes were determined using single-crystal X-ray crystallography. These copper complexes catalyzed the hydroamination-alkynylation reaction between several secondary amines and alkyl and aryl terminal alkynes. Using 1 mol% of complexes 5-10 as catalysts, both tri- and tetra-substituted propargylamines were isolated. Alternatively, phenylacetylene and different secondary amines afforded the corresponding trisubstituted propargylamines as the major products and alkyl terminal alkynes gave the tetrasubstituted products in excellent yields. In addition, the role of counter anions such as TfO-, PF6-, BF4-, PO43- and Ph4B- on the product selectivity was studied. When fluorinated anions such as TfO-, PF6-, and BF4- were present with the copper complexes, the hydroamination-hydrovinylation product 1-aminodiene 23 was observed, which was not formed with PO43-, Ph4B- or halide ions. Specifically, TfO- and PF6- favored the formation of 23, while BF4- favored the tetrasubstituted product as the major product. This was further supported by the isolated copper(I) complexes containing PF6- and BF4- and by other specific reactions. The peaks for enamines and [LCu]+ species in the HRMS spectra of the reaction mixtures and the isolation of the morpholinium copper(I) salt support the proposed mechanism.

Elucidating the catalytic mechanisms of O2 generation by [Mn2(μ-O)2(terpy)2(OH2)2]3+ using DFT calculations: a focus on ClO- as oxidant.

The experimentally reported Mn(IV)Mn(III) complex [Mn2(μ-O)2(terpy)2(OH2)2]3+ has been observed catalyzing O2 generation with oxidants like ClO- and HSO5-. Previous mechanistic studies primarily focused on O2 generation with HSO5-, concluding that Mn(IV)Mn(III) acts as a catalyst, generating a Mn(IV)Mn(IV)-oxyl species as a key intermediate responsible for O-O bond formation. This computational study employs DFT calculations to investigate whether the catalytic generation of O2 using ClO- follows the same mechanism previously identified with HSO5- as the oxidant, or if it proceeds through an alternate pathway. To this end, we explored multiple pathways using ClO- as the oxidant. Interestingly, our findings confirm that in the case of ClO- as the oxidant, similar to what was observed with HSO5-, the Mn(IV)Mn(IV)-oxyl species indeed plays a crucial role in driving the catalytic evolution of O2 with the potential formation of the binuclear complexes Mn(IV)Mn(IV)-oxy and Mn(IV)Mn(IV)-OH during the reaction. These complexes are reactive in producing O2, with activation free energies of 15.9 and 14.3 kcal mol-1, respectively. However, our calculations revealed that the Mn(IV)Mn(IV)-oxyl complex is significantly more reactive in producing O2 than Mn(IV)Mn(IV)-oxy and Mn(IV)Mn(IV)-OH, with a lower free energy barrier of 8.1 kcal mol-1. Consequently, even though Mn(IV)Mn(IV)-oxyl is predicted to be present in much lower concentrations than Mn(IV)Mn(IV)-oxy and Mn(IV)Mn(IV)-OH, it emerges as the species acting as the active catalyst for catalytic O2 generation. This study enhances our knowledge of high oxidation state (+3 and +4) manganese chemistry, highlighting its key role in catalysis and paving the way for more efficient Mn-based catalysts with broad applications.

Synthesis, structure and spectroelectrochemistry of hybrid metal(iv)phthalocyaninato-capped 3d-metal pyrazoloximates as prospective precursors of stimuli-induced (responsive) single-molecule magnets, logic gates and qubits

Hybrid binuclear complexes and their ZrIVMIIIMIIMIIZrIV-pentanuclear analogs were prepared using the template reactions of 3-acetylpyrazoloxime with metal(iv) phthalocyaninate on the metal ion as a matrix.

Correction: Magnetic response of photonic crystals based on nucleating agents of binuclear complexes

Correction for ‘Magnetic response of photonic crystals based on nucleating agents of binuclear complexes’ by Mengdong Tu et al., J. Mater. Chem. C, 2023, 11, 16922–16927, https://doi.org/10.1039/D3TC02786D.

Binuclear nitrosyl iron complex with 4-acetamidothiophenolyl: Synthesis and study of its decomposition in a system with glutathione and albumin

In this work, we synthesized a new binuclear nitrosyl iron complex of the family of Roussin's red salt ester [Fe2(C8H8NOS)2(NO)4] (complex 1) with 4-acetamidothiophenol (a structural analog of acetaminophen), which generates NO during hydrolysis and is promising for treatment socially significant diseases. It has been established that solvents have a significant effect on the process of its decomposition: in a buffer solution, complex 1 retains its binuclear structure, while in DMSO it forms mononuclear iron-nitrosyl products. Reduced glutathione does not replace 4-acetamidothiophenol ligands in the structure of complex 1. In addition, complex 1 and its products are not coordinated with the known binding sites of bovine serum albumin, including Cys34. It was found that the studied complex 1 is adsorbed on the protein surface due to weak intermolecular interactions, which leads to a decrease in the rate of decomposition, and, as a result, to a longer generation of NO.Thus, it has been shown for the first time that compound 1 and its decay products do not form coordination complexes with the biosubstrates studied in this work. It can be assumed that glutathione will not participate in the transformation of complex 1 in vivo, while albumin, due to the effective stabilization of the complex on the surface, can act as its carrier to therapeutic targets.

Antimicrobial activity study of some binuclear complexes with Schiff bases derived from an aromatic dialdehyde and some amino acids

Many metal complexes with amino acid derived Schiff bases have been synthesized and tested for their biological activity. Thus, the aim of the present study was to evaluate the antimicrobial activity of some binuclear complexes with Schiff bases derived from an aromatic dialdehyde and some amino acids by studying the influence of the tested compounds on the development of microbial biofilms on an inert substrate. The biofilms developed on inert substrate by Klebsiella pneumoniae ESBL+, Citrobacter freundii 1748, Bacillus sp., Serratia marcescens 0804, Staphylococcus aureus ATCC 25923 and Escherichia coli 1576 strains were inhibited at concentrations of the tested compounds between 250 μg∙mL-1 and 500 μg∙mL-1. The results of determining the influence of the tested compounds on the development of microbial biofilms showed that they have an inhibitory effect on microbial adhesion.

Quantum-Chemical Approaches to Creation of Mesogenic Binuclear Europium(III) Complexes with Intensive Luminescence

This article contains data on the application of quantum-chemical methods for simulation of mesogenic binuclear complexes of europium(III) (Eu(III)) with substituted β-diketones and Lewis bases along with the possibility of prediction of their liquid crystalline (LC) properties. The relationships between geometric parameters of the complexes' molecules, the structural features of their coordination polyhedra and the probability of mesophase behavior were considered. According to the calculated parameters of Voronoi-Dirichlet polyhedra, the structural features of the first coordination sphere of Eu(III) complexes were studied and compared with the data for mononuclear complexes. Using the calculated energies of the ligands' excited states, the luminescence efficiency of the complexes was estimated. The results of quantum-chemical simulations provide recommendations for selection of ligand environment for the synthesis of LC binuclear Eu(III) complexes.

Synthesis, Crystal Structure, Hirshfeld Surface Analysis, and DFT Calculations of the Novel Binuclear Copper(I) Complex Containing 2-Benzimidazolethiole and Triphenylphosphine Ligands.

The reaction of 2-benzimidazolethiole (2-BIT) with copper dichloride in the presence of two equivalents of triphenylphosphine led to a binuclear complex of the type [Cu(µ-S-2-BIT)2(Ph3P)2Cl2]: dichloridobis(μ-1,3-dihydro-2H-benzimidazole-2-thione)bis(triphenylphosphi ne)-di-copper. The Cu(I) compound has been fully identified by elemental analysis, molar conductivity, FT-IR, UV/Vis, and single-crystal X-ray diffraction (XRD). The XRD study reveals that the complex has distorted tetrahedral geometry around the Cu(I)center, which contains two bridge sulfur atoms. The Hirshfeld surface mappedover dnorm, shape index, and curvature revealed important H...H, H... C/C...H, and H... Cl/Cl...H intermolecular interactions as the main contributors to crystal packing. The natural bond orbital (NBO) was applied to understand the strength of nucleophilic and electrophilic attack between ligands and Cu(I)ions. Furthermore, density functional theory (DFT) was employed to demonstrate the molecular reactivity and stability of the ligands and coppercomplex.

Low-dimensional compounds containing bioactive ligands. Part XXIII: A comprehensive study of the preparation and cytotoxic activities of zirconium(IV) complexes with 8-hydroxyquinoline and its derivatives

Nine zirconium(IV) complexes, [Zr(8-HQ)4]·DMF·H2O (1), [Zr(dClQ)4]·EtOH (2), [Zr(ClNQ)4]·EtOH (3a), [Zr(ClNQ)4]·DMF (3b), [Zr(BrQ)4] (4), [Zr(dBrQ)4]·DME (5), [Zr(2-MedBrQ)4]·2DMF (6), [Zr2Cl2(CQ)4µ2-O(DMF)2]·0.33DMF (7), and [Zr2Cl2(ClBrQ)4µ2-O(DMF)2]·DMF (8) (DME = 1,2-dimethoxyethane, H8-HQ = 8-hydroxyquinoline, HdClQ = 5,7-dichloro-8-hydroxyquinoline, HClNQ = 5-chloro-7-nitro-8-hydroxyquinoline, HBrQ = 7-bromo-8-hydroxyquinoline, HdBrQ = 5,7-dibromo-8-hydroxyquinoline, H2-MedBrQ = 2-methyl-5,7-dibromo-8-hydroxyquinoline, HCQ = 5-chloro-7-iodo-8-hydroxyquinoline, HClBrQ = 5-chloro-7-bromo-8-hydroxyquinoline), have been prepared and characterized by elemental, single crystal X-ray structure analysis and IR spectroscopy. Complexes 1 – 6 are mononuclear complexes with Zr(IV) atoms octacoordinated by four bidentate quinoline ligands. Complexes 7 and 8 are binuclear complexes in which two Zr(IV) atoms are coordinated by two bidentate quinoline, one DMF and one chloro ligands, and the seventh coordination place occupies an oxygen atom bridging both complex species. The stability of complexes soluble in a DMSO was verified by NMR spectroscopy. In vitro cytotoxic properties of complexes 1, 2, 4, 5, and 6, and corresponding ligands were studied against 8 cancer cell lines, and their selectivity was verified on BJ-5ta non-cancerous cell line. The most potent complexes are 1 and 4 with the smallest quinoline ligands.

Convenient access to amidines by mesoionic singlet palladium carbene catalyzed hydrazone-isocyanide-amine (HIA) coupling: Scope and mechanistic insights

Facile synthesis of amidines 5(a-j), 6(a-g) and 7(a-j) by the tandem three-component coupling of N-tosylhydrazones, isocyanides and amines catalysed by the molecular binuclear Pd mesoionic singlet carbene complexes namely, [(R)-1,1′-(C10H6)2–2,2′-(OCH2(1-CH2Ph-3-R-1,2,3-triazol-5-ylidene))2]Pd2I4(NC5H5)2 [R = Me (4a) and Et (4b)] was achieved in good to excellent yields of ca. 51–97% at a low catalyst loading of 0.5 mol% in 6 h of the reaction time. A large opportunity for the utility of this coupling reaction was evident from its broader substrate scope arising from the use of a wide range of N-tosyl hydrazones, amines, and aromatic as well as aliphatic isocyanides. Combined experimental and computational studies performed on the representative substrates namely, PhCHNNHTs, 2,6-Me2C6H3NC, and morpholine indicated that the catalysis proceeded via the formation of palladium (0) active species [(R)-1,1′-(C10H6)2–2,2′-(OCH2(1-CH2Ph-3-R-1,2,3-triazol-5-ylidene))2]Pd2(2,6-Me2C6H3NC)2 [R = Me (B1), Et (B2)] alongside the generation of a ketenimine intermediate 2,6-Me2C6H3NCCHPh in the tricomponent coupling reaction. The dinitrogen elimination from the metal-coordinated diazo intermediate represents the rate-determining step of the reaction. The mechanistic revelations brought forth in this study hold promising potential for enriching our understanding of multi-component reactions leading to amidines enabled by transition metal catalysts.