Enaminone Ligands Research Articles

Undirected C-H Bond Activation in Aluminium Hydrido Enaminonates.

Two new aluminium hydrido complexes were synthesized by reacting AlH3 with the enaminone ligand N-(4,4,4-trifluorobut-1-en-3-on)-6,6,6-trifluoroethylamine (HTFB-TFEA) in different molar ratios to obtain mono- and di-hydrido-aluminium enaminonates. Both air and moisture sensitive compounds could be purified via sublimation under reduced pressure. The spectroscopic analysis and structural motif of the monohydrido compound [H-Al(TFB-TBA)2] (3) showed a monomeric 5-coordinated Al(III) centre bearing two chelating enaminone units and a terminal hydride ligand. However, the dihydrido compound exhibited a rapid C-H bond activation and C-C bond formation in the resulting compound [(Al-TFB-TBA)-HCH2] (4a), which was confirmed by single crystal structural data. The intramolecular hydride shift involving the migration of a hydride ligand from aluminium centre to the alkenyl carbon of the enaminone ligand was probed and verified by multi-nuclear spectral studies (1H,1H NOESY, 13C, 19F, and 27Al NMR).

Polymeric REE coordination compounds based on novel enaminone derivative

A novel enaminone derivative, 2-{[(3-methoxyphenyl)amino]methylene}-5,5-dimethylcyclohexane-1,3-dione (HL) and its lanthanide(III) complexes [Ln(HL)2(NO3)3]n have been prepared. The composition and structure of products have been investigated using IR-spectroscopy, elemental and X-ray diffraction analysis (powder and single-crystal). HOMO/LUMO, as well as triplet state energy has been established by means of DFT calculations. According to the single-crystal X-ray diffraction analysis, the enaminone ligand exhibits bidentate-bridging coordination resulting in polymeric net. All obtained complexes are isomorphous to each other. Photoluminescence of free ligand in polycrystalline state is very low; the quantum yield is only 0.33%, most probably due enhancement of internal conversion in the singlet excited state by the presence of methoxy substituent. Energy transfer from the ligand to lanthanide ions is observed only for europium(III) and, in less extent, samarium(III) complexes.

2D polymeric lanthanide(III) compounds based on novel bright green emitting enaminone ligand

New enaminone derivative, 2-{[(4-methoxyphenyl)amino]methylene}-5,5-dimethyl-cyclohexane-1,3-dione (HL), and lanthanide(III) compounds based on it [Ln(HL)2(NO3)3]n, (where Ln3+=Eu (1Eu), Sm (2Sm), Tb(3 Tb) and Dy (4Dy)) have been synthesized. The complexes have been fully characterized by spectroscopic and analytical methods including single crystal X-ray structure. To establish closer intermolecular contacts and HOMO/LUMO energy, the Hirshfeld surface analysis, as well as DFT calculations has been carried out. According to single-crystal X-ray diffraction analysis ligand exhibits bidentate-bridging mode. This leads to the formation of polymeric structure as layer, arranged parallel to ab crystallographic plane. The lanthanide polyhedron is close to bicapped square antiprism. All obtained compounds are isomorphous to each other. The study of photoluminescence showed the presence of a bright green emission of the ligand with a quantum yield of 41 %. The weak sensitization occurs only in case of europium(III) complex leading to apparent luminescence quantum yield of 0.021 %, with ∼4 % sensitization efficiency. Emission spectra of other compounds are the same to the ligand one.

Syntheses, crystal structures, and electrochemistry of a series of ferrocene-containing ketoimines

Condensation of ferrocenoylacetone with arylamine or benzylamine in toluene at reflux afforded a series of N,O-bidentate ferrocenoyl enaminone ligands, Fc–C(O)CH = C(CH3)N(H)R1 (HL1: R1 = C6H5; HL2: R1 = 4-I-C6H4; HL3: R1 = 4-Cl-C6H4; HL4: R1 = 4-Me-C6H4; HL5: R1 = 4-OMe-C6H4; HL6: R1 = 2-Me-C6H4; HL7: R1 = 2-OMe-C6H4; HL8: R1 = 2-F-C6H4; HL9: R 1 = CH2C6H5; Fc = ferrocenyl). Reaction of Cu(CH3COO)2 with two equivalents of HL1, HL3, and HL5-HL8 in the presence of CH3ONa in ethanol gave six copper complexes, [Cu(L1)2] (1), [Cu(L3)2] (2), [Cu(L5)2] (3), [Cu(L6)2] (4), [Cu(L7)2] (5) and [Cu(L8)2] (6), respectively. All compounds were characterized by 1H NMR, FT-IR, and UV–vis spectroscopies along with their electrochemical properties. The molecular structures of HL1-HL3, HL5, HL6, and HL8, together with the copper complexes 2.0.6C2H5OH and 3.CH3OH have been established by single-crystal X-ray diffraction.

Thermal and spectroscopic studies of some metal complexes with a new enaminone ligand 3-chloro-4-((4-methoxyphenyl)amino)pent-3-en-2-one and their investigation as anti-urease and cytotoxic potential drugs

Complexes of transition metals [Co(II), Cd(II) and Mo(0)] with a new enaminone (PA) 3 -chloro-4-((4-methoxyphenyl)amino)pent-3-en-2-one were synthesized and afterwards characterized by 1 H NMR, 13 C NMR, FAB-MS, UV–Vis, ICP-OES, TGA and FTIR. The spectroscopic and conductance data suggested that the ligand (PA) is attached to the metal ions in bidentate, neutral form through the nitrogen atom of amino group and the oxygen of carbonyl group. Metal complexes displayed octahedral geometries. In vitro urease inhibition and cytotoxic activities of all the compounds were evaluated. Results revealed that Co(II) complex (PA-Co) was even more significant than the reference drug thiourea. Analysis of the cytotoxicity indicated that, the Co(II) complex has more cytotoxic effect than enaminone ligand and other complexes when assessed on the human cancer cell lines MCF-7.Molecular docking simulation was also performed to find out the putative binding mode within the target protein.

Syntheses, characterizations and structures of organometallic tri- and tetra-dentate ferrocenoyl enaminone ligands and their unsymmetrical Schiff base derivatives

Condensation of ferrocenoylacetone with alkyl or aryl diamine (1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminocyclohexane, 1,4-diaminobenzene) afforded three tridentate ferrocenoyl enaminone ligands (Fc–C(O)CHC(CH3)NHR1) (L1: R1 = CH2CH2NH2; L3: R1 = 4-C6H4NH2; L5: R1 = 4-C6H10NH2; Fc = ferrocenyl) and four symmetrical tetradentate ferrocenoyl enaminone ligands [(Fc–C(O)CHC(CH3)NH]2R (L2: R = CH2CH2; L4: R = 4-C6H4; L6: R = 4-C6H10; L8: R = CH2CH2CH2). Of which, L3 was further reacted with appropriate substituted salicylaldehydes to give unsymmetrical Schiff base ligands Fc–C(O)CHC(CH3)NH(4-C6H4)NCH(2-OHAr) (L9: Ar = C6H4; L10: Ar = 5-ClC6H3; L11: Ar = 5-NO2C6H3; L12: Ar = 3,5-Br2C6H2; L13: Ar = 3,5-tBu2C6H2). All new ligands L3∼L6, L8 and L9∼L13 were characterized by 1H NMR, 13C NMR, FT-IR, and UV–Vis spectroscopies along with their electrochemical properties. Moreover, molecular structures of ligands L2∼L4, L8 and L9 have been established by single-crystal X-ray crystallography.

Synthesis of 6,7-Dihydro-1H,5H-pyrazolo[1,2-a]pyrazoles by Azomethine Imine-Alkyne Cycloadditions Using Immobilized Cu(II)-Catalysts.

A series of 12 silica gel-bound enaminones and their Cu(II) complexes were prepared and tested for their suitability as heterogeneous catalysts in azomethine imine-alkyne cycloadditions (CuAIAC). Immobilized Cu(II)–enaminone complexes showed promising catalytic activity in the CuAIAC reaction, but these new catalysts suffered from poor reusability. This was not due to the decoordination of copper ions, as the use of enaminone ligands with additional complexation sites resulted in negligible improvement. On the other hand, reusability was improved by the use of 4-aminobenzoic acid linker, attached to 3-aminopropyl silica gel via an amide bond to the enaminone over the more hydrolytically stable N-arylenamine C-N bond. The study showed that silica gel-bound Cu(II)–enaminone complexes are readily available and suitable heterogeneous catalysts for the synthesis of 6,7-dihydro-1H,5H-pyrazolo[1,2-a]pyrazoles.

Unexpected structure of enaminone Pd(II) complex in comparison with Cu(II) complex: Synthesis, characterization, DNA binding and antitumor activity

Novel Pd(II) and Cu(II) complexes have been synthesized by the reaction of Na2PdCl4 and CuCl2·2H2O with fluorinated enaminone ligand leading to the formation of complexes having the formulae [Pd(enm)Cl2] and [Cu2(diCO)4]; where enm and diCO are enaminone and deprotonated dicarbonyl containing ligands, respectively. The structures and geometry of the two metal chelates have been elucidated by applying alternative spectral and analytical tools including elemental analysis, FT-IR spectra, 1H NMR spectra and UV–Vis spectra. The molecular structure of the Cu(II) complex has been determined by single crystal X-ray diffraction; the complex crystalizes in monoclinic P21/c space group. Square pyramidal geometry has been confirmed for Cu(II) complex where Pd(II) complex has the expected square planar geometry. The mechanism of the in-situ conversion of the enaminone to dicarbonyl ligand with CuCl2·2H2O was illustrated. The type of interaction between the two complexes and salmon sperm DNA (SS-DNA) has been studied applying absorption spectra and viscosity measurements. The binding constant values (kb) was calculated to be (1.17 ± 0.6) × 104 and (3.62 ± 0.4) × 104 M−1 for Pd(enm)Cl2 and Cu2(diCO)4, respectively, which confirmed the interaction of the two complexes with DNA via intercalative mode of interaction. Intercalative binding mode between the studied compounds and DNA was further confirmed by the results of viscosity measurements. The anticancer activity of the two metal complexes has been evaluated against breast cancer cell line (MCF-7) and the liver cancer cell line (HepG-2) in comparison with the well-known anticancer drug cis-DDP. Surprisingly, we found that Cu2(diCO)4 complex has activity (IC50 = 3.26 μg/mL) against a human liver cancer cell line (HepG2) exceeding the efficiency of the reference drug cis-DDP (IC50 = 3.67 μg/mL).

Synthesis, Characterization, Molecular Docking and Enzyme Inhibition Studies of Some Novel Enaminone Derivatives and Their Complexes with Cu(II), Cd(II) and Co(II) Ions

Two new enaminone ligands, 3-chloro-4-{(4-chlorophenyl)amino}pent-3-en-2-one (Ac-PCA), 4-(benzylamino)-3-chloropent-3-en-2-one (Ac-BA) and their metal complexes with transition metal ions [Cu(II), Cd(II) and Co(II)] were prepared and subsequently characterized by FTIR, ICP-AES, UV-Vis, TGA, 1H NMR, 13C NMR and FAB-MS. These newly synthesized compounds were further investigated for anti-acetylcholinesterase (AChE) and anti-urease activities. The (Ac-BA)Cu(II) complex exhibited good anti-AChE while (Ac-BA)2Co(II) complex was potent against anti-urease activities. Other ligands and complexes showed poor to no enzyme inhibitory activities. The synthesized compounds were docked inside acetylcholinesterase enzymes to determine their putative binding mode.

Synthesis, Characterization, Molecular Docking and Enzyme Inhibition Studies of Some Novel Enaminone Derivatives and Their Complexes with Cu(II), Cd(II) and Co(II) Ions

Two new enaminone ligands, 3-chloro-4-{(4-chlorophenyl)amino}pent-3-en-2-one (Ac-PCA), 4-(benzylamino)-3-chloropent-3-en-2-one (Ac-BA) and their metal complexes with transition metal ions were prepared and subsequently characterized by FTIR, ICP-AES, UV-Vis, TGA, 1H NMR, 13C NMR and FAB-MS. These newly synthesized compounds were further investigated for anti-acetylcholinesterase (AChE) and anti-urease activities. The (Ac-BA)Cu(II) complex exhibited good anti-AChE while (Ac-BA)2Co(II) complex was potent against anti-urease activities. Other ligands and complexes showed poor to no enzyme inhibitory activities. The synthesized compounds were docked inside acetylcholinesterase enzymes to determine their putative binding mode. Keywords: Antiureas activity, enaminone, metal complexes, acetylcholinesterase inhibition studies

Design of mononuclear, binuclear and polynuclear molybdenum(VI) complexes based on ONO benzoylacetone derived enaminones and their in vitro biological activity

Molybdenum(VI) complexes of different nuclearity, mononuclear, [MoO2(L1 or 2)(MeOH)]·MeOH (1·MeOH and 2·MeOH), [MoO2(L1 or 2)(D)] [D = pyridine, (1a and 2a), 3-methylpyridine, (1b and 2b) and 4-methylpyridine, (1c and 2c)], binuclear [{MoO2(L1 or 2)}2(D)] (D = 4,4′-bipyridine (1d, 1d′ and 2d), and polynuclear complexes [MoO2(L1 or 2)]n (3 and 4) were synthesized by solution based reactions of enaminones (H2L1 = 3-(2-hydroxy-4-methylphenylamino)-1-phenylbut-2-en-1-one; H2L2 = 3-(2-hydroxy-5-methylphenylamino)-1-phenylbut-2-en-1-one) with the dioxobis(acetylacetonato)molybdenum(VI) complex, [MoO2(acac)2]. Reactions of the mononuclear complexes 1·MeOH and 2·MeOH with pyridine and its derivatives resulted in corresponding mononuclear [MoO2(L1 or 2)(D)] or binuclear [{MoO2(L1 or 2)}2(D)] complexes. In case of [{MoO2(L1)}2(4,4-bpy)] two polymorphic forms are obtained (1d and 1d′). The cross-linked transformations of [MoO2(L1 or 2)(D)] complexes in solution or when exposed to vapors of N-heterocyclic bases have been explored. Crystal and molecular structures of ten complexes (1·MeOH, 2·MeOH, 1a–d, 1d′, 2b–d) were determined by the single-crystal X-ray diffraction analysis. Enaminone ligands and their molybdenum complexes were characterized by elemental and TG analysis, IR and NMR spectroscopy and screened for their in vitro cytotoxic and antibacterial activities. None of the tested compounds showed cytotoxic ability against THP-1 and HepG2 cell lines. Compounds 1·MeOH, 1b, 2·MeOH, 2a and 3, exhibited weak antibacterial activity on Moraxella catarrhalis strain while other complexes did not show antibacterial properties towards Staphylococcus aureus, Enterococcus faecalis and Escherichia coli bacteria.

Combinatorial Synthesis of Acacen-Type Ligands and Their Coordination Compounds.

A highly modular synthetic method for the preparation of acacen-type ligands and their coordination compounds was developed. A series of 46 acacen-type ligands were synthesized by a combinatorial acid-catalyzed transamination between six primary diamines and eight enaminones. The bis-enaminone products were used as tetradentate ligands for coordination of copper(II), nickel(II), cobalt(II), and palladium(II). Dependence of the preferred E- or Z-configuration of the enaminone ligand on the α-substituent of the enaminone moiety in solution was determined by NMR and confirmed by X-ray diffraction. The copper(II) complexes were tested for their suitability as catalysts in 3 + 2 cycloaddition of azomethine imine to methyl propiolate.

A versatile ethanolamine-derived trifluoromethyl enaminone ligand for the elaboration of nickel(II) and copper(II)–dysprosium(III) multinuclear complexes with magnetic properties

Abstract A Ni(II) tetranuclear cubane-like complex and a mixed Cu(II)–Dy(III) nonanuclear complex have been synthesized from a common ethanolamine-derived trifluoromethyl enaminone ligand. The resulting polynuclear architectures exhibit interesting magnetic properties arising from the metallic architecture, especially Single-Molecule Magnet (SMM) behavior. The crystal structures of the [Ni 4 ] and [Dy 3 Cu 6 ] complexes were refined by single-crystal X-ray diffraction analyses and correlated to variable-temperature magnetic susceptibility data. Redox properties of the Ni(II) tetranuclear complex have been also investigated. The [Dy 3 Cu 6 ] complex results from the condensation of three {Dy 2 Cu 2 } cubane-like moieties giving rise to nonanuclear architectures. By changing the global charge of the Cu–Dy nonanuclear complex (from cationic to neutral), compared with those previously reported in the literature, the magnetic properties have been disturbed. This work should contribute to improve the SMM synthesis strategy.

Quenching of Fluorescence in Bodipy‐Derived Trifluoromethyl Enaminone Ligands upon Coordination to Copper(II)

AbstractThe synthesis of two trifluoromethyl‐derived enaminone ligands, L1H (bidentate) and L2H2, (tridentate), which bear a fluorescent 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (Bodipy) moiety, leads to the preparation and characterization of two CuII complexes {[Cu(L1)2]·2(CH2Cl2) (A) and [Cu4(L2)4]·4(C4H8O2) (B)} that exhibit different architectures. The magnetic properties of the cubane‐like complex B evidence a dominant ferromagnetic behavior characterized by exchange coupling constants J1 = +20.56(3) cm–1 and J2 = –10.29(2) cm–1. Indeed, whereas the luminescence properties of the Bodipy‐derived trifluoromethyl enaminones L1H and L2H2 are typical of the Bodipy skeleton, the emission is totally quenched in both mononuclear (A) and cubane (B) CuII complexes. To elucidate this quenching phenomenon, the Rehm–Weller equation has been used based on experimental cyclic voltammetry redox potential measurements. The result remains ambiguous for complexes A and B, and the origin of the quenching phenomenon, photoinduced electron transfer (PET) versus energy transfer (Förster or Dexter), cannot be deduced.

Synthesis of heteroaryl containing sulfides via enaminone ligand assisted, copper-catalyzed C–S coupling reactions of heteroaryl thiols and aryl halides

The C–S cross coupling reactions between electron deficient heteroaryl thiols and aryl halides have been smoothly performed to provide various heteroaryl containing sulfides in the presence of copper catalyst and enaminone ligand.

8-Aminoquinoline and 2-aminopyridine trifluoromethyl-derived enaminone ligands and their Co(II), Ni(II) and Zn(II) metal complexes: Structural arrangements due to F⋯H interactions

Two tridentate trifluoromethylated enaminones derived from 8-aminoquinoline and 2-aminopyridine L1H and L2H have been designed as ligands that can exhibit multiple coordination centers. Five new complexes 1–5 based on transition metals (CoII, NiII and ZnII) were prepared and their crystal structure and redox properties have been studied. The role of the trifluoromethyl moieties and their ability to form F⋯H intra- and inter-complexes bonds leading to multidimensional networks have been also featured.

Unexpected lanthanide cation selectivity of bis-β-ketovinylated diaza-18-crown-6 and open-chain diamines: cooperative effect of the second keto group

New diaza-18-crown-6 based ligands were prepared by the β-ketovinylation of diaza-18-crown-6 by TMS-protected ynones. The obtained N,N′-bis-(3-oxo-3-arylpropen-1-yl)-7,16-diaza-18-crown-6 ligands (aryl = p-MeOC6H4, p-Me2NC6H4) selectively bind the Ln3+ in preference to main group cations, showing high Ln3+/Zn2+ and Ln3+/Pb2+ selectivities (from 2 to 5.5 in log βML values determined by UV-spectrophotometric titration in CH3OH). The Me2N-derivative is also a holmium-selective fluoro-ionofore, as its intense emission is almost completely quenched by Ho3+ salts at concentrations as low as 10−5 mol l−1. The monoazacrown analogs with only one enaminone group complex less strongly with Ln3+ and are less selective, but bis-β-ketovinylated open-chain diamines (N,N′-dibenzyl-3,6-dioxaoctane-1,8-diamine and N,N′-dibenzyldecane-1,10-diamine) show almost the same binding constants with La3+ (log βML = 3.5–3.7) and Pb2+ (log βML = 1.6) as the corresponding diaza-18-crown-6 derivative. This and the changes observed in the 1H NMR spectra of the azacrown enaminone ligands in the presence of La3+ indicate the exocyclic coordination of Ln3+ with the carbonyl oxygens of the side arms. Rotation around the =C–N bond is restricted in enaminone ligands and especially in their complexes with Ln3+, which allows to explain the observation of two sub-sets of signals in the 1H NMR spectra of bis-β-ketovinylated diaza-18-crown-6 in the presence of La(NO3)3 by the existence of two rotamers of the ligands. Diaza-18-crown-6 and open-chain diamines with two β-ketovinyl side arms selectively bind rare earth group cations in preference to main group cations (Pb2+, Zn2+ and Ba2+) through the exocyclic coordination of Ln3+ with the carbonyl oxygens of the side arms. The presence of the second β-ketovinyl group is essential, as ligands with only one β-ketovinyl group do not show such selectivity.

Bidentate and Tetradentate β‐Aminovinyl Trifluoromethylated Ketones and Their Copper(II) Complexes: Synthesis, Characterization and Redox Chemistry

AbstractNew polyfunctional bidentate and tetradentate trifluoromethylated enaminone ligands that bear redox‐active and photosensitive moieties were synthesized in moderate to good yields and their coordination chemistry with copper(II) was examined. The crystal structures revealed the formation of mononuclear CuII complexes with all ligands, where the metal ion is located in almost perfect to distorted square planar environments. The deviation from an ideal square plane influences the redox potentials of the metal centre within the complex as demonstrated by cyclic voltammetry. For all the complexes, a stable CuI species was evidenced by a quasireversible reduction step at potentials from –0.48 to –1.08 V (potential standards E0), but the most stable CuI species originated from the CuII complex with the tetradentate ligand. UV/Vis absorption spectra revealed no major differences between the ligands and their CuII complexes.

Single End‐to‐End Azidocopper(II) Chain Based on an Electroactive Ligand: A Structural, Electrochemical, Magnetic and Ab Initio Study

AbstractBy combining azide and the (Z)‐1,1,1‐trifluoro‐4‐(quinolin‐8‐ylamino)but‐3‐en‐2‐one enaminone ligand, HL, an azido‐bridged copper(II) one dimensional polymer was synthesized in a one‐pot reaction. The solved and refined crystal structure evidenced the unusual single and asymmetric end‐to‐end coordination mode of the azide ion. The redox properties of this complex were studied by cyclic voltammetry, andoxidation of the azido bridge was evidenced. Magneticmeasurements, combined with magnetostructural‐driven analysis revealed a weak ferromagnetic interaction between the copper(II) ions within the N3–‐bridged chains, complemented by an antiferromagnetic interaction between the chains mediated by π–π interactions. A survey of the scarce literature of single end‐to‐end azido bridges, associated with quantum chemical ab initio calculations, was carried out to tentatively identify the relevant parameters driving the weak intrachain exchange interaction.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The new molybdenum(V) complexes with differently N-substituted β′-hydroxy-β-enaminones

Six new dinuclear complexes of molybdenum(V) have been prepared by the reaction of [Mo2O3(acac)4] (acac=acetylacetonate ion) with the polydentate ligands, β′-hydroxy-β-enaminones. The complexes are coordinated by two enaminone ligands via two donor oxygen atoms as in the analogous β-diketonates. The octahedral coordinations around the molybdenum atoms are completed by the monodentate solvent molecules D (methanol, ethanol, 2-propanol). The complexes of the general formulae [Mo2O4L2(ROH)2]·2ROH (complex 1b) and [Mo2O4L2(ROH)2]·ROH (complex 2a) were easily losing solvated alcohol molecules. All complexes were characterized by elemental analysis, IR, and some of them by one- and two-dimensional NMR spectra (in case 1a) and by X-ray crystallography (1a, 1b and 2a).