Complexes 2e Research Articles

Selective Oxidative Scission of Olefins to Aldehydes Enabled by Ruthenium Complexes Containing Salicylaldimine Ligands

ABSTRACTTreatment of Ru3(CO)12 with salicylaldimine ligands [ArNCH(3‐tBuC6H3OH) [ArC6H5 (L1H); 4‐OMeC6H4 (L2H); 4‐MeC6H4 (L3H); 2,4,6‐Me3C6H2 (L4H); 4‐ClC6H4 (L5H); 4‐BrC6H4 (L6H)] in refluxing toluene afforded six bis‐ligand mononuclear ruthenium carbonyl complexes [ArNCH(3‐tBuC6H3O)]2Ru(CO)2 1a–1f in good yields. All of the Ru(II) complexes were characterized using IR, NMR, and elemental analysis. The molecular structures of complexes 1a, 1b, 1e, and 1f were further confirmed through X‐ray diffraction analysis. Additionally, the catalytic performance of these complexes was investigated in the oxidation of olefins to aldehydes, using TBHP as the oxidant in refluxing trichloromethane. With 1.0 mol% catalyst loading, these ruthenium complexes displayed high reactivity and good functional‐group compatibility, selectivity providing the corresponding oxidation product aldehydes in 73%–94% yields.

Synthesis, DFT calculations, and investigation of catalytic and biological activities of back‐bond functionalized re‐NHC‐Cu complexes

Five copper complexes (3a–e) stabilized by ring‐expanded back‐bond functionalized N‐heterocyclic carbene ligands (re‐NHCs) were produced in the glovebox by reacting free re‐NHC with CuI precursor. The potential of these re‐NHC‐Cu complexes as catalysts on the synthesis of mono‐ and di‐(1,4‐disubstituted‐1,2,3‐triazoles) by Cu‐catalyzed azide–alkyne cycloaddition (CuAAC) reactions was investigated. Various spectroscopic approaches were utilized to completely characterize the structures of the re‐Cu‐NHC complexes. Furthermore, density functional theory (DFT) calculations were carried out to get further insights into their molecular geometry and CuAAC reaction mechanism. The re‐NHC‐Cu complexes showed high activity on the CuAAC reaction in an open‐air atmosphere at rt. The Gibbs free energies as well as the optimized geometries of the intermediates and the transition states of the determining step of the reactions catalyzed by 3a, 3e, and 3b complexes were computed. Complex 3e was found to be the most efficient catalyst among these re‐NHC‐Cu complexes. Additionally, re‐Cu‐NHC complexes were investigated for their biological activities, including antiproliferative, antioxidant, AChE and TyrE inhibition, and antiparasitic activity. The results showed that the 3b, 3d, and 3e complexes possessed strong antiproliferative activity against human colon carcinoma (HCT‐116) and moderate cytotoxic activity against hepatocellular carcinoma (HepG‐2) cell lines. In addition, effective selective antileishmanial effects were observed for the 3e compound against both promastigotes and amastigotes stages of L. major with an IC50 value of 0.027 and 0.39 μM mL−1, respectively. These results demonstrate that these compounds are promising candidates for the treatment of colorectal cancer and leishmaniasis.

Synthesis, in vitro, and in silico studies of morpholine-based thiosemicarbazones as ectonucleotide pyrophosphatase/phosphodiesterase-1 and -3 inhibitors

An extensive range of new biologically active morpholine based thiosemicarbazones derivatives 3a-r were synthesized, characterized by spectral techniques and evaluated as inhibitors of ENPP isozymes. Most of the novel thiosemicarbazones exhibit potent inhibition towards NPP1 and NPP3 isozymes. Compound 3 h was potent inhibitor of NPP1 with IC50 value of 0.55 ± 0.02. However, the most powerful inhibitor of NPP3 was 3e with an IC50 value of 0.24 ± 0.02. Furthermore, Lineweaver-Burk plot for compound 3 h against NPP1 and for compound 3e against NPP3 was devised through enzymes kinetics studies. Molecular docking and in silico studies was also done for analysis of interaction pattern of all newly synthesized compounds. The results were further validated by molecular dynamic (MD) simulation where the stability of conformational transformation of the best protein-ligand complex (3e) were justified on the basis of RMSD and RMSF analysis.

Comparative Analysis of Nickel-Phosphine Complexes with Cumulated Double Bond Ligands: Structural Insights and Electronic Interactions via ETS-NOCV and QTAIM Approaches.

This study presents a comprehensive analysis of nickel-phosphine complexes, specifically Ni(PH3)2(OCCH2), Ni(PH3)2(H2CCO), Ni(PH3)2(H2CCCH2), Ni(PH3)2(NNCH2), and Ni(PH3)2(η1-H2CNN). Utilizing ETS-NOCV analysis, we explored orbital energy decomposition and the Hirshfeld charges of the ligands, providing insights into the electronic structures and donor-acceptor interactions within these complexes. The interactions in the ketene and allene complexes exhibit similar deformation densities and NOCV orbital shapes to those calculated for Ni(PH3)2(NNCH2), indicating consistent interaction characteristics across these complexes. The total interaction energy for all η2 complexes is observed to be over 60 kcal/mol, slightly exceeding that of the analogous carbon dioxide complex reported earlier. Furthermore, the study highlights the stronger back-donation as compared to donor interactions across all η2 complexes. This is further corroborated by Hirshfeld analysis, revealing the charge distribution dynamics within the ligand fragments. The research offers new perspectives on the electron distribution and interaction energies in nickel-phosphine complexes, contributing to a deeper understanding of their catalytic and reactive behaviors.

Unsaturated chiral-only-at-metal rhodium(III) complexes bearing SiN-type ligands.

Enantiopure chiral-at-metal rhodium(III) unsaturated 16e complexes have been obtained from racemic [Rh(SiN)2Cl] (SiN= 8-(dimethylsilyl)quinoline) using a readily accessible chiral spiroborate as chiral resolution agent. This strategy allows an easy access to enantiopure neutral Δ/Λ-Rh(SiN)2Cl and cationic Δ/Λ-Rh(SiN)2[BAr4F] unsaturated complexes, wherein rhodium(III) is coordinated to two inert silylquinoline ligands in a propeller-like arrangement.

Addressing Resistance to Therapy in Colorectal Cancer

Addressing Resistance to Therapy in Colorectal Cancer

New copper(I) complexes of bulky 5-substituted-2-iminopyrrolyl ligands as catalysts for azide-alkyne cycloaddition.

Five dinuclear copper(I) complexes of the type [Cu{κN,κN'-5-R-NC4H2-2-C(H)N(2,6-iPr2C6H3)}]2 (1a-e; R = 2,4,6-iPr3C6H2 (a), R = 2,6-Me2C6H3 (b), R = 3,5-(CF3)2C6H3 (c), R = 2,6-(OMe)2C6H2 (d), R = CPh3 (e)) were prepared by the reaction of the respective 5-R-2-iminopyrrolyl potassium salts KLa-e and [Cu(NCMe)4]BF4 in moderate yields. These new copper(I) complexes were characterized by NMR spectroscopy, elemental analysis and, in selected cases, by single crystal X-ray diffraction and their structural and electronic features further analyzed by DFT calculations and cyclic voltammetry, respectively. X-ray diffraction studies reveal dimeric Cu structures assembled by 2-iminopyrrolyl bridging ligands adopting a transoid conformation (complexes 1a and 1d), while complexes 1c and 1e displayed a cisoid conformation of those moieties, with respect to the Cu(I) centers. Additionally, VT-1H NMR and 1H-1H NOESY NMR experiments on complexes 1a-e exhibited complex fluxional processes in solution, assigned to a conformational inversion of the respective Cu2N4C4 metallacycles in all complexes but 1c, accompanied by a cisoid-transoid isomerization in the cases of complexes 1d,e. The Cu(I) complexes were also analyzed by cyclic voltammetry, where all complexes exhibit two oxidation processes, where the first oxidation is reversible, with the exception of 1b and 1c, which also show the highest oxidation potentials. The oxidation potentials follow clear trends related to the structural parameters of the complexes, in particular the Cu⋯Cu distance and the Cu2N4C4 macrocycles torsion angles. All new 5-substituted-2-iminopyrrolyl Cu(I) complexes 1a-e served as catalysts for azide-alkyne cycloaddition (CuAAC) reactions, being able to generate the respective 1,2,3-triazole products in yields as high as 82% and turnover frequencies (TOFs) as high as 859 h-1, after optimizing the conditions. The activity, as measured by the TOF, is in accordance with the oxidation potential of the corresponding complexes, the easier the oxidation, the higher the TOF value. Complex 1-H, where R = H, proved to be a poor catalyst for the same reactions, indicating that the 5-substitution in the ligand framework is crucial in stabilizing any potential catalytic species.

Synthesis, structure, and mechanism of the isomers of ruthenium complexes based on HC≡CC(OH)(CH3)2 and ortho-Carborane dithiolate ligands

Treatment of 16-electron complex ( p -cymene)Ru(S 2 C 2 B 10 H 10 ) ( 1 ) with HC≡CC(OH)(CH 3 ) 2 in chloroform at −10 °C leads to two isomers ( p -cymene)Ru(S 2 C 2 B 10 H 9 )(CH 2 CC(OH)(CH 3 ) 2 ) ( 2 and 3 ), which are converted to the corresponding complexes ( p -cymene)Ru(S 2 C 2 B 10 H 9 )(CH 2 CC(CH 3 )CH 2 ) ( 4 and 5 ) by loss of a water molecule at 62 °C, respectively. These complexes were characterized by elemental analysis, mass, IR and NMR spectroscopy. X-ray structural analysis were performed on 4 and 5 . The formation mechanisms for the title complexes were also studied. • ● In chloroform, treatment of 16e complex ( p -cymene)Ru(S 2 C 2 B 10 H 10 ) with HC≡CC(OH)(CH 3 ) 2 at − 10 °C leads to two isomers ( p -cymene)Ru(S 2 C 2 B 10 H 9 )(CH 2 CC(OH)(CH 3 ) 2 ), which are converted to the corresponding complexes ( p -cymene)Ru(S 2 C 2 B 10 H 9 )(CH 2 CC(CH 3 )CH 2 ) by loss of a water molecule at 62 °C, respectively. • ● Both isomers ( p -cymene)Ru(S 2 C 2 B 10 H 9 )(CH 2 CC(CH 3 )CH 2 ) have been characterized by IR, NMR, MS, elemental analysis and single-crystal X-ray diffraction. • ● The formation mechanisms for the title complexes were studied. Treatment of 16-electron complex ( p -cymene)Ru(S 2 C 2 B 10 H 10 ) ( 1 ) with HC≡CC(OH)(CH 3 ) 2 in chloroform at − 10 °C leads to two isomers ( p -cymene)Ru(S 2 C 2 B 10 H 9 )(CH 2 CC(OH)(CH 3 ) 2 ) ( 2 and 3 ), which are converted readily to the corresponding complexes ( p -cymene)Ru(S 2 C 2 B 10 H 9 )(CH 2 CC(CH 3 )CH 2 ) ( 4 and 5 ) by loss of a water molecule at 62 °C. These complexes were characterized by elemental analysis, mass, IR and NMR spectroscopy. X-ray structural analysis were performed on 4 and 5 . The formation mechanisms for the title complexes were also studied. The complex 4 crystallizes in monoclinic system, space group P 2 1 /n with a = 11.082(2), b = 14.529(3), c = 15.230(3) Å , α = 90, β = 101.022(2), γ = 90°, C 17 H 30 B 10 RuS 2 , Mr = 507.70, V = 2407.1(9) Å 3 , Dc = 1.401 g/cm 3 , Z = 4, F (0 0 0) = 1032, µ (Mo Kα ) = 0.828 mm −1 , R = 0.0424 and ωR = 0.1089 for 4470 observed reflections ( I > 2 σ ( I )). The complex 5 crystallizes in monoclinic system, space group P 2 1 /c with a = 16.0543(16), b = 10.5758(11), c = 14.0954(14) Å , α = 90, β = 99.0430(10), γ = 90°, C 17 H 30 B 10 RuS 2 , Mr = 507.70, V = 2363.5(4) Å 3 , Dc = 1.427 g/cm 3 , Z = 4, F (0 0 0) = 1032, µ (Mo Kα ) = 0.844 mm −1 , R = 0.0444 and ωR = 0.1076 for 3745 observed reflections ( I > 2 σ ( I )).

Pd(II)-Schiff base complexes: Synthesis, characterization, Suzuki–Miyaura and Mizoroki–Heck cross-coupling reactions, enzyme inhibition and antioxidant activities

In this study, new coordination complexes (1a-1e) of Pd(II) with Schiff base ligands were synthesized and characterized by elemental analysis, magnetic susceptibility, molar conductivity, FT-IR, 1H–13C NMR spectroscopy, UV–vis spectroscopy, and mass spectrometry techniques. The ligands formed only 1:2 complexes with the Pd(II) except for the complex 1e. The thermal analysis of the complexes was performed by the TGA technique. The antioxidant potential, enzyme inhibition activity, and catalytic properties of the complexes were investigated as well. The Pd(II) complexes 1b and 1c indicated the best catalytic activity with 62.63% and 61.05% selectivity in the conversions of 82.61% and 87.84%. The in vitro antioxidant activity showed that the Pd(II) complexes, particularly 1a and 1e have effective antioxidant activities. According to the enzyme activity analyses, complex 1b (IC50 value 69.3 ± 5.2 μM) showed the most effective pancreatic lipase inhibition, whereas complex 1e (IC50 value 25.7 ± 3.2 μM) had the most effective tyrosinase inhibition among the synthesized compounds. Overall, the present paper discusses the synthesis, characterization and catalytic activities of various novel Pd(II)-Schiff base complexes with their antioxidant potentials, pancreatic lipase and tyrosinase inhibitory activities.

Theoretical Approach for the Luminescent Properties of Ir(III) Complexes to Produce Red-Green-Blue LEC Devices.

With an appropriate mixture of cyclometalating and ancillary ligands, based on simple structures (commercial or easily synthesized), it has been possible to design a family of eight new Ir(III) complexes (1A, 1B, 2B, 2C, 3B, 3C, 3D and 3E) useful as luminescent materials in LEC devices. These complexes involved the use of phenylpyridines or fluorophenylpyridines as cyclometalating ligands and bipyridine or phenanthroline-type structures as ancillary ligands. The emitting properties have been evaluated from a theoretical approach through Density Functional Theory and Time-Dependent Density Functional Theory calculations, determining geometric parameters, frontier orbital energies, absorption and emission energies, injection and transport parameters of holes and electrons, and parameters associated with the radiative and non-radiative decays. With these complexes it was possible to obtain a wide range of emission colours, from deep red to blue (701–440 nm). Considering all the calculated parameters between all the complexes, it was identified that 1B was the best red, 2B was the best green, and 3D was the best blue emitter. Thus, with the mixture of these complexes, a dual host–guest system with 3D-1B and an RGB (red–green–blue) system with 3D-2B-1B are proposed, to produce white LECs.

Activity of Benzimidazole Derivatives and their N-Heterocyclic Carbene Silver Complexes Against Leishmania major Promastigotes and Amastigotes

Little progress was conducted concerning discovering new efficient antileishmanial drugs for many years. Hence, the disease has become a global health problem meanwhile. Benzimidazole derivatives and heavy metal complexes have shown potent antiparasitic activities. The present work is intended to evaluate fourteen synthetic benzimidazolium salts and N-heterocyclic silver carbene complexes against Leishmania major. Promastigotes and amastigotes of L. major were cultured in vitro to evaluate compound-induced inhibitory effects, and isolated mouse macrophages were used for cytotoxicity evaluation. Reactive oxygen species (ROS) formation was detected for all compounds as a possible mode of action. The silver complexes 3d and 3e revealed significant activity against L. major promastigotes with IC50 values of 6.4 and 5.5 µg mL-1, and SI of 1.77 and 2.02, respectively. Both complexes showed higher ROS production in promastigotes than in macrophages. Further in vivo and enzyme inhibition studies are recommended to evaluate the potential of these compounds as new antileishmanial.

Iron(0) tricarbonyl η4-1-azadiene complexes and their catalytic performance in the hydroboration of ketones, aldehydes and aldiminesviaa non-iron hydride pathway

Six iron(0) tricarbonyl complexes (1a-f) with a η4-1-azadiene moiety were prepared and their performance in the hydroboration of unsaturated organic compounds was investigated. All the complexes exhibit catalytic activity towards hydroboration of ketones, aldehydes and aldimines with pinacolborane (HBpin) as a hydride source to lead to secondary alcohols, primary alcohols, and secondary amines, respectively, after hydrolysis of the hydroboration products. Of the iron(0) tricarbonyl complexes, complex 1e is the most robust one and was employed throughout the catalytic investigation. Its preference towards the three types of substrates is as follows: aldimines > aldehydes ≫ ketones. In total, 24 substrates were examined for the catalytic hydroboration reactivity and generally, isolation yields ranging from 40% to 95% were achieved. Mechanistic investigation suggests that the catalytic hydroboration of the substrates proceeds via intramolecular hydride transfer without going through an Fe-H intermediate. As indicated by 1H NMR spectroscopic monitoring, the substrates and the borane agent bind to the iron centre and the imine N atom, respectively, which facilitates the hydride transfer by activating the B-H bond and polarizing the double bond of the substrates.

Half-sandwich chromium(III) complexes containing salicylbenzoxazole and salicylbenzothiazole ligands for ethylene polymerization

Half-sandwich chromium(III) complexes bearing salicylbenzoxazole ligands 2a-2f [L = R-2-(benzo[d]xazol-2-yl)-phenol (R = H (2a), R = 6-CH3 (2b), R = 6-tBu (2c), R = 4-OCH3 (2d), R = 4-Cl (2e), R = 4-NO2 (2f)] and salicylbenzothiazole ligands 3a-3f [L = R-2-(benzo[d]xazol-2-yl)-phenol (R = H (3a), R = 6-CH3 (3b), R = 6-tBu (3c), R = 4-OCH3 (3d), R = 4-Cl (3e), R = 4-NO2 (3f)] were synthesized by the salt-elimination reaction of CpCrCl2(THF) and the sodium salt of the corresponding ligands in THF at −78 °C. The molecular structures of complexes 3a and 3e are confirmed by single-crystal X-ray crystallographic analysis. Upon the activation of a small amount of AlEt3, all the half-sandwich chromium(III) complexes showed moderate to high catalytic activities for ethylene polymerization and afforded high molecular weight polyethylene (PE).

Dimerization and Cycloaddition Reactions of Transient Tri-tert-butylphosphacyclobutadiene Generated by Lewis Acid Induced Isomerization of Tri-tert-butylphosphatetrahedrane

Tri-tert-butylphosphatetrahedrane (1) is shown here to act as a synthon of isomeric tri-tert-butylphosphacyclobutadiene in the presence of a Lewis acid or transition-metal complex. When it is combined with a substoichiometric amount of triphenylborane, compound 1 forms a ladderane-type dimer of tri-tert-butylphosphacyclobutadiene in 72% isolated yield. Trapping of a generated intermediate was achieved by repeating the experiment in the presence of excess styrene (20 equiv) or ethylene (1 atm), and the corresponding [4 + 2] cycloadducts of tri-tert-butylphosphacyclobutadiene were isolated in 88% and 74% yields, respectively. The platinum complex (Ph3P)2Pt(C2H4) also reacts with 1 to form an orange η2 complex of tri-tert-butylphosphacyclobutadiene in 80% isolated yield. Additionally, we report a novel method for generating a phosphinidenoid species via fluoride-induced trimethylsilyl fluoride elimination, leading to an improved preparative procedure for 1 (182 mg, 33% isolated yield).

Synthesis, characterization, antimicrobial, BSA binding, DFT calculation, molecular docking and cytotoxicity of Ni(II) complexes with Schiff base ligands

A series of a tetradentate N2O2 Schiff base ligands (1a-e), [N,N′-(X)bis(salicylidene)1,2-phenylenediamine], salphens {where X = H (1a), Cl (1b), Br (1c), CH3 (1d), OCH3(1e)} were synthesized from condensation of substituted salicylaldehydes with 1,2-phenylenediamine and nickel(II) complexes(2a-e) from corresponding Schiff base ligands(1a-e). The stoichiometric ratios of the prepared ligands (1a-e) and their Ni(II)-salphen complexes (2a-e) were structurally characterized by various analytical and spectroscopic techniques such as 1H NMR, FT-IR, mass, UV‐–visible, PXRD, magnetic moments and molar conductivity measurements. These results suggest that Ni(II)-salphen complexes (2a-e) have square planar geometry. The molar conductivity measurements indicate that all complexes (2a-e) are non-electrolytes. Density Functional Theory (DFT) calculations have been used to investigate the optimized structure and chemical reactivity of these Ni(II) complexes(2a-e) from their Frontier Molecular Orbitals (FMO). The binding capabilities of the Ni(II) Schiff base complexes (2a-e) with Bovine Serum Albumin (BSA) have been studied through electronic absorption, fluorescence and cyclic voltammetric methods. Further the nature of interaction of Ni(II) complexes (2a-e) towards BSA were confirmed using molecular docking analyses. All these results demonstrated that the Ni(II) complexes 2d and 2e have better binding affinity towards BSA among all the Ni(II) complexes. The antimicrobial studies reveal that the Ni(II)-salphen complexes (2a-e) have higher inhibitory effect than ligands (1a-e) against the selected pathogenic microorganisms. Furthermore, in vitro cytotoxicity of ligands (1a-e) and Ni(II) complexes(2a-e) were evaluated by MTT assay against MCF-7. The observed IC50 values against MCF-7 cell lines suggest that Ni(II) complexes(2a-e) show more significant anticancer activity than their corresponding ligands(1a-e). It is explored that complexes 2d and 2e bearing electron donating groups have greater anticancer potency. Comparison of our results with cisplatin, Zn(II)-salphen and V(IV)-salphen complexes indicated that Ni(II)-salphen complexes can be considered as the potential candidates for use as effective anticancer agent in future.

Chromium(III) complexes based on phenoxy-imine ligands with pendant N- and O-donor groups as precatalysts for ethylene oligomerization: synthesis, characterization, and DFT studies

Chromium complexes of general formula [Cr{ZNO}(THF)Cl2] [2a, ZNO = C9H6N-8-(N=CH)-2,4-tert-butyl-2-(OC6H2); 2b, ZNO = Ph(NH)-C2H4-(N=CH)-2,4-tert-butyl-2-(OC6H2); 2c, ZNO = 2-MeO-Ph-CH2-(N=CH)-2,4-tert-butyl-2-(OC6H2); 2d, ZNO = 2-PhO-Ph-(N=CH)-2,4-tert-butyl-2-(OC6H2); 2e, ZNO = PhO-C2H4-(N=CH)-2,4-tert-butyl-2-(OC6H2)] and the bis(ligand) complex [Cr{C9H6N-8-NH2}2Cl2]Cl (4) were synthetized and characterized by elemental analysis, IR spectroscopy, and by X-ray crystallography for 4. In the solid state, 4 is monomeric with two 8-amino-quinoline acting as bidentate ligands and two chloride ligands in cis position. The DFT calculations showed slightly higher HOMO energy for 2d. In addition, the energy levels of the LUMO are slightly influenced by pendant O- and N-donor group. Particularly, the LUMOs for complexes 2a and 2d show a small contribution from Cr and Cl atoms as compared to other chromium complexes (2b, 2c and 2e), and the orbitals are almost entirely delocalized over the phenoxy-imine unit. Upon activation with methylaluminoxane (MAO), chromium precatalysts 2a-2e showed good activity in ethylene oligomerization (TOF = 22.0 – 52.7 × 103 (mol ethylene)(mol Cr)−1⋅h−1 at 80°C) with Schultz-Flory distribution of oligomers (KC4-C10 ≈ 0.92), and production of polymer varying from 2.9 to 22.3 wt.%. The catalytic performance is mainly controlled by electronic effects at the phenoxy-imine ligands. The bis(ligand) chromium complex 4 showed good activity in ethylene oligomerization (TOF = 39,400 (mol ethylene)(mol Cr)−1 h−1), producing mostly oligomers (95.2 wt% of total products) with high selectivity for α-olefins. The highest activity among the six precatalysts screened was reached with 2c (TOF = 52,700 mol(ethylene)•mol(Cr)−1•h−1).

Effect of Pendant Distal Residues on the Rate and Selectivity of Electrochemical Oxygen Reduction Reaction Catalyzed by Iron Porphyrin Complexes

Oxygen reduction reaction (ORR) is a complex 4e–/4H+ multistep process, and factors that determine the rate and selectivity of this reaction are a matter of contemporary interest. Synthetic iron po...

η2-Arene Binding at High-Spin Fe(I) Enabled by a Sterically Accommodating Tris(pyrazolyl)hydroborate Ligand

Transition-metal arene complexes are important species in catalysis and arene functionalization. Certain electron-rich metal fragments are capable of binding arenes across two adjacent carbon atoms, inducing significant dearomatization through strong back-bonding interactions. Such complexes generally adopt low-spin, closed-shell configurations with electronic and coordinative saturation. Herein, we report an asymmetric tris­(pyrazolyl)­hydroborate (Tp) ligand and its Fe­(I) fragment, which forms η2 complexes with a range of arenes and heteroarenes, including benzene, trifluoromethylbenzene, naphthalene, anthracene, and furan. X-band EPR and solution magnetometry definitively establish these complexes as high spin (S = 3/2), owing to the relatively weak ligand field provided by Tp. These compounds expand a small but growing family of complexes that feature strongly back-bonding metal fragments in high-spin configurations.

Synthesis, crystal structure and magnetic properties of new trinuclear Copper(II) complexes with Biphenol−Based dinucleating ligands

Treatment of (3,3′-bis-((2,6-dimethylphenyl)-imino)methyl)-(1,1′)-biphenyl-2,2′-diol) (H2L2) and (3,3′-bis-((2-methoxyphenyl))imino)methyl)-(1,1′)-biphenyl-2,2′-diol) (H2L3) with excess [Cu2(OAc)4(H2O)2] in the presence of triethylamine afforded new trinuclear complexes [Cu(3,3′-bis-((R)-iminomethyl)-(1,1′)-biphenyl-2,2′-dioxo)]3 [R = 2,6-Me2C6H3 (3e) and R = 2- OMeC6H3(4e)] respectively. The resulting complexes were characterized by elemental analysis, magnetic susceptibility, EPR, UV–Vis, IR, CV and Single crystal X-ray diffraction analysis. The magnetic susceptibility study of 3e and 4e was performed in the 5–300 K and revealed the existence of antiferromagnetic interaction in both complexes. The experimental data could be satisfactorily reproduced using an isotropic exchange model, H = -J (S1S2 + S2S3 + S1S3), yielding as best fit parameters: J = −15 cm−1, g = 1.99 for 3e and J = −18 cm−1, g = 1.99 for 4e. Both complexes have an angular C2/c-symmetric trinuclear core and each Cu(II) ion is in similar environments coordinated to two (O, N) donor sets as revealed from single-crystal X-ray diffraction studies. The coordination geometry can best be described as distorted square planar which could be judged using the τ4 index, τ4 = 360 – (α + β)/141°, where α and β are the two largest angles subtended by the ligand donor atoms in the four-coordinate complex. The average indexes for 3e and 4e were found to be 0.42 and 0.43 respectively, signifying a considerable distortion from an idealized square planar, D4h geometry (τ4 = 0.0) or idealized tetrahedral, Td geometry (τ4 = 1.0). The average Cu⋯Cu distance between closest copper(II) ions in the complex 3e is 4.48 Å. On the other hand, the single crystal X-ray analysis showed that each of the three Cu(II) centers in complex 4e is strongly tetracoordinated to two N and two O atoms & weakly to two O atoms of the methoxy groups of the ligand, N,N′,O,O′-3, 3′-bis ((2-methoxyphenyl)-iminomethyl)-[1, 1′-biphenyl]-2, 2′-diol (H2L3). Generally, Cu−N & Cu−O bond lengths are (1.983–1.994) & (1.882–1.893) respectively, comparable to similar systems.

Copper(II) complex with oxazoline ligand: Synthesis, structures and catalytic activity for nitro compounds reduction

The Cu(II) complexes bearing bisoxazolines, tridentate pincer pybox and terpyridine ligands have been synthesized and fully characterized. The molecular structures of copper complexes 1a and 1c were confirmed by single-crystal X-ray diffraction methods. These copper complexes highly catalyzed nitro compounds reduction to aniline and its derivatives in the presence of NaBH4 reducing agent in water solvent. The complex 1e was an efficient catalyst toward nitro compounds reduction with wide functional group substrate scope and aliphatic nitro compounds.