Potentiometric and antimicrobial studies on the asymmetric Schiff bases and their binuclear Ni(II) and Fe(III) complexes; synthesis and characterization of the complexes

The protonation constants of two nitro-Schiff bases SB¹, SB² and three asymmetric tetradentate diimines H₂L¹, H₂L² and H₂L³ and the stability constants of their ML type binuclear Ni(II) and Fe(III) complexes have been determined potentiometrically. The asymmetric diimines are (2OH) RCHNC₆H₄CHNR′ (2OH) type compounds [where R = R′ = phenyl for H₂L¹; R = naphthyl, R′ = phenyl for H₂L² and R = R′ = naphthyl for H₂L³]. The effect of tautomeric forms on the acid-base properties of the diimines has been investigated and discussed. In addition, dimeric and binuclear Ni(II) and Fe(III) complexes of the diimines have been synthesized and characterized by physical and spectroscopic techniques. Also, in vitro antimicrobial activities of the diimines and the complexes have been evaluated against three bacteria: Micrococcus luteus (NRLL B-4375), Bacillus cereus (RSKK 863), Escherichia coli (ATCC 11230) and the fungus: Candida albicans (ATCC 10239).     

Reduction of aromatic ketones with the (dpp-BIAN)AlI(Et2O) complex

Reduction of benzophenone and 4,4′-bis(methoxy)benzophenone with the aluminum complex (dpp-BIAN)AlI(Et₂O) (1) containing the dianionic dpp-BIAN ligand (dpp-BIAN is 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) affords the pinacolate complexes [(dpp-BIAN)AlI]₂[μ-O₂C₂Ph₄] (2) and [(dpp-BIAN)AlI]₂[μ-O₂C₂(C₆H₄OMe)₄] (3), respectively, which undergo the pinacolone rearrangement upon prolonged storage in diethyl ether to form [(dpp-BIAN)AlI]₂O (4). The reaction of 1 with fluoren-9-one produces stable pinacolate (dpp-BIAN)Al[μ-O₂(C₁₃H₈)₂] (7) and the (dpp-BIAN)AlI₂ complex (8). Compounds 2—4, 7, and 8 were characterized by ESR spectroscopy. Hydrolysis products of compounds 2 and 3 were characterized by ¹H NMR spectroscopy. The structures of complexes 4 and 7 were established by X-ray diffraction. dpp-BIAN is 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1134–1140, July, 2006.     

Synthesis,characterization and anticancer activity of new palladacycles derived from chiral α‐diimines

Optically pure α‐diimines quantitatively obtained in solvent‐free conditions starting from 2,3‐butanedione and (S)‐(?)‐1‐phenylethylamine and (S)‐(?)‐1‐(4‐methylphenyl)ethylamine, respectively, yielded the new chiral mono‐Pd complexes 2a–b, which have been partly characterized by IR, ¹H‐ and ¹³C‐NMR spectroscopies along with MS‐FAB⁺ spectrometry. The crystal and molecular structure for palladacycle 2a has been fully confirmed by single‐crystal X‐ray studies. Studies in vitro of 2a–b have displayed growth inhibition against different classes of cancer: leukemia (K‐562 CML), colon cancer (HCT‐15), breast cancer (MCF‐7), central nervous system (U‐251 Glio) and prostate cancer (PC‐3) cell lines. Copyright © 2009 John Wiley & Sons, Ltd.     

A Series of Diamagnetic Pyridine Monoimine Rhenium Complexes with Different Degrees of Metal‐to‐Ligand Charge Transfer: Correlating 13C NMR Chemical Shifts with Bond Lengths in Redox‐Active Ligands

A set of pyridine monoimine (PMI) rhenium(I) tricarbonyl chlorido complexes with substituents of different steric and electronic properties was synthesized and fully characterized. Spectroscopic (NMR and IR) and single‐crystal X‐ray diffraction analyses of these complexes showed that the redox‐active PMI ligands are neutral and that the overall electronic structure is little affected by the choices of the substituent at the ligand backbone. One‐ and two‐electron reduction products were prepared from selected starting compounds and could also be characterized by multiple spectroscopic methods and X‐ray diffraction. The final product of a one‐electron reduction in THF is a diamagnetic metal–metal‐bonded dimer after loss of the chlorido ligand. Bond lengths in and NMR chemical shifts of the PMI ligand backbone indicate partial electron transfer to the ligand. Two‐electron reduction in THF also leads to the loss of the chlorido ligand and a pentacoordinate complex is obtained. The comparison with reported bond lengths and ¹³C NMR chemical shifts of doubly reduced free pyridine monoaldimine ligands indicates that both redox equivalents in the doubly reduced rhenium complex investigated here are located in the PMI ligand. With diamagnetic complexes varying over three formal reduction stages at the PMI ligand we were, for the first time, able to establish correlations of the ¹³C NMR chemical shifts with the relevant bond lengths in redox‐active ligands over a full redox series.     

Diiminic Schiff Bases: An Intriguing Class of Compounds for a Copper‐Nanoparticle‐Induced Fluorescence Study

The condensation products of salicylaldehyde and different diamines constitute an important class of diiminic Schiff bases (DSBs). This class of compounds has been rediscovered as reducing as well as capping agents under UV irradiation. UV irradiation of alkaline DSB solutions in the presence of water‐soluble copper salts has been employed to produce copper nanoparticles (CuNPs). Intriguing CuNP‐stimulated fluorescence behavior of the solution has been observed. Depending upon the nature of the spacer in between two iminic bonds, fluorescence enhancement or quenching is observed. Such surprising fluorescence contrast has been ascribed to far‐field radiation and lossy surface waves.     

Ethylene polymerization with imine and phosphine nickel complexes containing isothiocyanate

Three isothiocyanate complexes of nickel(II) containing diimine [ArN?C(Me)? C(Me)?NAr]Ni‐ (NCS)₂ (1), iminophosphine [Ph₂PC₆H₄CH?NAr]Ni(NCS)₂ (2), or diphosphine (dppe)Ni(NCS)₂ (3), [Ar = 2, 6‐ⁱPr‐C₆H₃; dppe = 1, 2‐bis(diphenylphosphine)ethane] were synthesized and examined for ethylene polymerization activated by methylaluminoxane (MAO). Their behavior was compared with those of the corresponding halide analogues [ArN?C(Me)? C(Me)?NAr]NiBr₂ (4), [Ph₂PC₆H₄CH?NAr]NiBr₂ (5), and (dppe)NiCl₂ (6). The diimines showed the highest polymerization activity. Replacement of the halide for the NCS pseudo halide affected the activity and decreased the molecular weight of the polymer formed. The highest molecular weights were obtained with the diimine complexes. Highly branched polyethylenes were obtained with the bulkier complexes 1 and 4. Replacement of the halide for NCS in the diimine complexes also caused an increase in the branching content, whereas the opposite occurs for the iminophosphine complexes. The different activities and behavior of the catalyst systems with halide versus NCS in the polymerization of ethylene and the characteristics of the final products suggest a modification in the active species caused by the non‐chelating ligand. Polymer molecular weight and branching content is dependent on the MAO/Ni molar ratio and on the working temperature. Copyright © 2004 John Wiley & Sons, Ltd.     

TETRAETHYLPHYROPHOSPHITE AS A BRIDGING LIGAND IN A BIMETALLIC RUTHENIUM(II) - RUTHENIUM(II) COMPLEX

Abstract

The complex μ-TEPP-trans-bis[P(OEt)₃Ru(NH₃)₄]₂(PF₆)₄ has been prepared and characterized by microanalysis, vibrational and electronic spectroscopy (λ_max=299 nm, ?=6.4 × 10² M^?1 cm^?1; λ_max=262 nm, ?=8.6 × 10² M^?1 cm^?1), and cyclic voltammetry (E°'=+0.64 V versus S.C.E., 25°, μ=0.10 M NaCf₃COO, C_H+=1 × 10^?3 M). In aqueous solutions, ([H⁺] > 1 × 10^?4 M), the binuclear species undergoes hydrolysis yielding the mononuclear species trans-(Ru(NH₃)₄P(OEt)₃(H₂O)]²⁺ with a specific rate constant of 2.4 × 10^?5 sec^?1 at 25° δH^#=84.5 kJ mol^?1; δS^#=?49.4 J mol^?1 K^?1.     

New acenaphthene-1,2-diimine and its reduction to the tetraanion. Molecular structures of 1,2-bis[(trimethylsilyl)imino]acenaphthene and its lithium derivatives

1,2-Bis[(trimethylsilyl)imino]acenaphthene (1) was synthesized by the reaction of acenaphthenequinone with (Me₃Si)₂NLi in toluene followed by treatment of the reaction product with trimethylchlorosilane. The dianionic derivative [(tms-BIAN)Li₂]₂ (3) was obtained as the final product by reduction of compound 1 with lithium in toluene, whereas reduction in diethyl ether afforded the tetraanion [(tms-BIAN)Li₄(Et₂O)₃]₂ (5). The formation of the paramagnetic mono-and trianions in solution was confirmed by ESR spectroscopy. Compounds 3 and 5 were isolated in the crystalline state and characterized by elemental analysis, IR spectroscopy, and NMR spectroscopy. The crystal structures of 1, 3, and 5 were established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 697–705, April, 2006.     

Synthesis,Characterisation and Photophysical Study of Alkynylrhenium(I) Tricarbonyl Diimine Complexes and Their Metal‐Ion Coordination‐Assisted Metallogelation Properties

A series of alkynylrhenium(I) tricarbonyl diimine complexes has been synthesized and characterized. A blue shift of the intense low‐energy MLCT absorption band in the visible region was observed upon coordination of Cu^I or Ag^I. This class of complexes has been found to show rich thermotropic gelation behaviour upon Cu^I or Ag^I coordination with their morphology characterized by SEM. Their variable‐temperature UV/Vis absorption and emission properties have also been studied. A blue shift in the MLCT absorption band and the switching on of luminescence were observed upon sol–gel transition.