Binuclear aluminum complexes with amine–imine type ligands derived from 1,3-benzenedialdehyde: synthesis,structures and their catalytic properties in ring-opening polymerization

Reaction of 1,3-bis(imino)benzenes with a stoichiometric amount of LiAlH₄ in THF yields iminoaminobenzenes L1 and L2. Further reaction of iminoaminobenzenes L1 and L2 with an equivalent of AlR₃ in toluene affords macrocyclic binuclear aluminum complexes 1a, 1b, and 2a. These macrocyclic aluminum complexes were characterized by ¹H NMR, ¹³C NMR, and IR spectroscopy. The molecular structures of 1a, 1b, and 2a were further confirmed by X-ray crystallography. X-ray diffraction analysis revealed that 1a, 1b, and 2a adopted a distorted tetrahedral geometry around aluminum. These complexes have efficient activities toward ring-opening polymerization of ε-caprolactone in the presence of benzyl alcohol.     

Synthesis and characterization of aluminum and zinc complexes supported by pyrrole-based ligands and catalysis of the aluminum complexes toward the ring-opening polymerization of ?-caprolactone

Reaction of quinolin-8-amine with 1H-pyrrole-2-carbaldehyde or 5-tert-butyl-1H-pyrrole-2-carbaldehyde catalyzed by HCO₂H forms N-((1H-pyrrol-2-yl)methylene)quinolin-8-amine (≡ HL, 3a) or N-((5-tert-butyl-1H-pyrrol-2-yl)methylene)quinolin-8-amine (≡ HL′, 3b). Treatment of 3a and 3b respectively with AlMe₃ or AlEt₃ in toluene affords corresponding aluminum complexes LAlMe₂ (4a), L′AlMe₂ (4b) and LAlEt₂ (4c). Reaction of 3a and 3b with an equivalent of ZnEt₂ in toluene generates L₂Zn and L′₂Zn, respectively. A related compound N-((1H-pyrrol-2-yl)methylene)-2-(3,5-dimethyl-1H-pyrazol-1-yl)benzenamine (≡ HL″, 7) was prepared by reaction of 2-(3,5-dimethyl-1H-pyrazol-1-yl)benzenamine with 1H-pyrrole-2-carbaldehyde in the presence of HCO₂H. Reaction of 7 with AlMe₃ gives L″₂AlMe (8), and with ZnEt₂ yields L″₂Zn (9). All new compounds were characterized by NMR spectroscopy and elemental analysis. The structures of complexes 4b, 5b and 8 were additionally characterized by single crystal X-ray diffraction analyses. Complexes 4a-4c, and 8 were proved to be active catalysts for the ring-opening polymerization (ROP) of ?-caprolactone (?-CL) in the presence of BnOH. The kinetic study of the polymerization reactions catalyzed by 4a and 8 was performed.     

Synthesis, structure and norbornene polymerization behavior of nickel complexes bearing two β-ketoiminato chelate ligands

A series of nickel(II) complexes bearing two nonsymmetric bidentate β-ketoiminato chelate ligands have been prepared, and the structures of complexes [(2,6-Me₂C₆H₃)NC(CH₃)C(H)C(Ph)O]₂Ni (4a) and [(2,6-Me₂C₆H₃)NC(CH₃)C(H)C(CF₃)O]₂Ni (4c) have been confirmed by X-ray crystallographic analysis. These nickel(II) complexes were investigated as catalysts for the vinylic polymerization of norbornene. Using modified methylaluminoxane (MMAO) as a cocatalyst, these complexes display very high activities and produce high molecular weight polymers. Catalytic activity of up to 1.16 × 10⁴ kg/mol_Ni · h and the viscosity-average molecular weight of polymer of up to 870 kg/mol were observed. Catalyst activity, polymer yield, and polymer molecular weight could be controlled over a wide range by the variation of the reaction parameters such as Al/Ni molar ratio, norbornene/catalyst molar ratio, monomer concentration, polymerization reaction temperature and time.     

Synthesis of rhodium–carbonyl complexes bearing a novel P,N-chelating ligand of Schiff-base type

Schiff-base type N,P-chelating ligands, phosphorus analogues of imino–anilido ligands, were designed and synthesized as a new type of ligands toward transition metals, and the rhodium–carbonyl complexes bearing the novel imino–phosphido and phosphaalkenyl-anilido ligands were synthesized as stable crystalline compounds. Their structures were definitively revealed by X-ray crystallographic analysis, showing the unique electronic features of the ligands. In addition, the effective trans-influence of the phosphorus atom was suggested on the basis of the structural parameters and spectroscopic features of the isolated complexes.     

Cationic palladium(II)–acetylacetonate complexes bearing pyridinyl imine ligands as catalysts for the hydroamination of phenylacetylene and polymerization of norbornene

Acetylacetonate palladium(II) complexes bearing pyridinyl imine ligands [Pd(acac)(L)]BF₄ were synthesized via nitrile displacement in [Pd(acac)(MeCN)₂]BF₄ by the bidentate ligands L of type 2-C₅H₄N–CH=N–(CH₂)_nOMe or 2-C₅H₄N–CH=N–Ar. The structures of complexes were analyzed by X-ray diffractometry, NMR, and DFT. The complexes catalyze hydroamination of phenylacetylene with aniline to give the Markovnikov imine product as well as polymerization of norbornene.     

Titanium complexes bearing aromatic-substituted β-enaminoketonato ligands: Syntheses, structure and olefin polymerization behavior

A series of titanium complexes [(Ar)NC(CF₃)CHC(R)O]₂TiCl₂ (4b: Ar = -C₆H₄OMe(p), R = Ph; 4c: Ar = -C₆H₄Me(p), R = Ph; 4d: Ar = -C₆H₄Me(o), R = Ph; 4e: Ar = α-Naphthyl, R = Ph; 4f: Ar = -C₆H₅, R = t-Bu; 4g: Ar = -C₆H₄OMe(p); R = t-Bu; 4h: Ar = -C₆H₄Me(p); R = t-Bu; 4i: Ar = -C₆H₄Me(o); R = t-Bu) has been synthesized and characterized. X-ray crystal structures reveal that complexes 4b, 4c and 4h adopt distorted octahedral geometry around the titanium center. With modified methylaluminoxane (MMAO) as a cocatalyst, complexes 4b-c and 4f-i are active catalysts for ethylene polymerization and ethylene/norbornene copolymerization, and produce high molecular weight polyethylenes and ethylene/norbornene alternating copolymers. In addition, the complex 4c/MMAO catalyst system exhibits the characteristics of a quasi-living copolymerization of ethylene and norbornene with narrow molecular weight distribution.     

Transition metal complexes with Schiff-base ligands: 4-aminoantipyrine based derivatives–a review

The survey highlights structural properties and biological studies of transition metal complexes derived from 4-aminoantipyrine. The most important results of extensive studies (syntheses, spectral, magnetic, redox, structural characteristics, antimicrobial and DNA cleavage) of the metal complexes with heterocyclic Schiff bases of 4-aminoantipyrine with some aldehydes and oximes are reviewed.     

Correction to: Macrocycles in dual role: ancillary ligands in metal complexes and organocatalysts for the ring‑opening polymerization of lactide

Journal of Inclusion Phenomena and Macrocyclic Chemistry - A correction to this paper has been published: https://doi.org/10.1007/s10847-021-01060-y     

Synthesis,spectral, and thermal studies of oxomolybdenum(V) Schiff-base complexes derived from heterocyclic β-diketone

Six mononuclear Mo(V) Schiff-base complexes were prepared by the reaction of MoCl₅ with Schiff bases, namely HL¹–HL³ and HL⁴–HL⁶, such as 5-hydroxy-3-methyl-1(2-chloro)phenyl-1H-pyrazolone-4-carbaldehyde (I), 5-hydroxy-3-methyl-1(3-chloro)phenyl-1H-pyrazolone-4-carbaldehyde (II), and 5-hydroxy-3-methyl-1(3-sulfoamido)phenyl-1H-pyrazolone-4-carbaldehyde (III) with ethanolamine and propanolamine, respectively, in aqueous ethanolic medium. The resulting complexes have been characterized by elemental analyses, molar conductance, FT-IR, ¹H-NMR, electronic, electron spin resonance (ESR) spectra, magnetic susceptibility, and thermal study. The molar conductivity data show them to be non-electrolytes. IR and ¹H-NMR spectral data suggest that the ligand is a dibasic bidentate with ON donor toward metal ion. Electronic, magnetic, and ESR spectral data suggest that the oxomolybdenum(V) complexes have distorted octahedral geometry. One chloride coordinated to molybdenum is confirmed by thermal study.     

Unbridged bidentate aluminum complexes supported by diaroylhydrazone ligands: Synthesis,structure and catalysis in polymerization of ε-caprolactone and lactides

A series of novel diaroylhydrazone aluminum complexes have been synthesized and well-defined structurally, and their catalytic performance in the polymerization of ε-caprolactone and lactides have also been evaluated. Complexes [(L^1–4)₂AlMe] ( 1 – 4 ) {[L¹ = (3,5-^tBu₂–2-OMe-C₆H₂)CH=NNCOC₆H₅], [L² = (3,5-^tBu₂–2-OMe-C₆H₂)CH=NNCO(C₆H₄–4-OCH₃)], [L³ = (3,5-^tBu₂–2-OMe-C₆H₂)CH=NNCO(C₆H₄–4-Br)] and [L⁴ = (2-OMe-C₆H₄)CH=NNCO(C₆H₄–4-^tBu)]} were prepared through treatment of AlMe₃ with the corresponding proligands L^1–4H in molar ratios of 1: 1 or 1: 2. Chemical structures of all the complexes were well-defined by elemental analysis, NMR spectra as well as single-crystal X-ray study. Complexes [(L^1–4)₂AlMe] ( 1 – 4 ) in this work represent the first examples of aluminum complexes of aroylhydrazone ligands with crystallographic characterization. Specifically, they are all in monomeric form with a penta-coordinated aluminum center, including two approximately co-planar five-membered metallacycles with aluminum. Introduced bulky tert-butyl substituents in aroylhydrazone ligands could affect the geometry around the central metal which is a distorted square-based pyramid in complexes 1 – 3 while being a trigonal bipyramidal in complex 4 , thus affecting their catalytic behaviors. The complexes can successfully catalyze the ring-opening polymerization of ε-caprolactone and _L-lactide under mild conditions without any activator. In addition, complexes 1 – 4 could also polymerize rac-lactide, affording atactic polylactides with high conversions and good controllability in relatively short reaction time.     

Synthesis and characterization of a series of chiral NHC–Pd complexes derived from l-phenylalanine

The synthesis of a series of chiral Pd(L)PyBr₂ (3a–3e) and Pd(L)PyCl₂ (4d and 4e) complexes from l-phenylalanine is presented (L = (S)-3-allyl-4-benzyl-1-(2,6-diisopropylphenyl)-imidazolin-2-ylidene (a), (S)-4-benzyl-1-(2,6-diisopropylphenyl)-3-(naphthalen-2-ylmethyl)imidazolin-2-ylidene (b), (S)-4-benzyl-3-(biphenyl-4-ylmethyl)-1-(2,6-diisopropylphenyl)imidazolin-2-ylidene (c), (S)-4-benzyl-1-(2,6-diisopropylphenyl)-3-(naphthalen-1-ylmethyl)imidazolin-2-ylidene (d) or (S)-4-benzyl-1-(2,6-diisopropylphenyl)-3-(2,4,6-trimethylbenzyl)imidazolin-2-ylidene (e). The complexes were characterized by physicochemical and spectroscopic methods, and the X-ray crystal structures of 3a–3c and 4d are reported. In each case, there is a slightly distorted square-planar geometry around palladium, which is surrounded by imidazolylidene, two trans halide ligands and a pyridine ligand. There are π–π stacking interactions in the crystal structures of these complexes. Complex 3a showed good catalytic activity in the Cu-free Sonogashira coupling reaction under aerobic conditions.     

Ring-opening polymerization of ε-caprolactone by lithium piperazinyl-aminephenolate complexes: synthesis, characterization and kinetic studies

A series of lithium complexes were prepared from 2(N-piperazinyl-N'-methyl)-2-methylene-4-R'-6-R-phenols ([ONN](RR')) and characterized through elemental analysis, (1)H and (13)C{(1)H} NMR spectroscopy, and X-ray crystallography. Treatment of the ligands with n-butyllithium afforded {Li[ONN](RR')}(3) [R = Me, R' = (t)Bu, (1); R = R' = (t)Bu (2); R = R' = (t)Am, (3), (t)Am = C(CH(3))(2)CH(2)CH(3)], with trimetallic structures in the solid-state as shown by single-crystal X-ray diffraction. The reactivity of these complexes in the ring-opening polymerization of ε-caprolactone (ε-CL), as well as the influences of monomer concentration, monomer/Li molar ratio, polymerization temperature and time, was studied. Rates of polymerization were first order with respect to both monomer and lithium concentrations, and activation energies for the reactions were determined. MALDI-TOF MS analysis revealed that transesterification had occurred during the polymerization.     

Bimetallic aluminum alkyl complexes as highly active initiators for the polymerization of ε-caprolactone

Two dinuclear aluminum alkyl complexes supported by a piperazidine-bridged bis(phenolato) group were prepared, and both complexes exhibited extremely high activity for the ring-opening polymerization of ε-caprolactone. In the presence of benzyl alcohol (BnOH), the polymerization accelerated dramatically.     

Biological aspects of Schiff base–metal complexes derived from benzaldehydes: an overview

Schiff bases are stable imines containing C=N, where N is bonded to an alkyl or aryl group, but not with hydrogen and are prepared by condensation of aliphatic or aromatic primary amine with carbonyl compounds. They have the general formula R₁R₂C?=?NR₃, where R₃?≠?H. The presence of the basic donor N atom and the stability of the imine function render Schiff bases as the most favored ligands that have the ability to stabilize metal ions in different oxidation states. The chelating environment in a Schiff base profoundly influences the electron distribution in the coordination sphere of metal in a complex and thereby regulates the property of the compounds in a big way. The structural diversity in some of the metal complexes with multidentate Schiff base ligands has triggered a wide range of applications of this class of compounds in sensors, catalysis, biology, medicines, and photonics. This review compiles the synthesis and biological activities (antimicrobial, antioxidant, anticancer, antitubercular, DNA interaction studies) of benzaldehyde-based Schiff bases and their metal complexes.     

Synthesis,spectroscopic and thermal investigation of Schiff-base complexes of Cu(II) derived from heterocyclic β-diketone with various primary amines

The mononuclear complex [Cu(PMFP)(bipy)]ClO₄ was prepared by reaction of Cu(NO₃)₂·5H₂O with ligand PMFP and 2,2′-bipyridine. The corresponding Schiff bases were prepared by condensation of [Cu(PMFP)(bipy)]ClO₄ with ethylenediamine, ethanolamine and glycine with general formula [Cu(PMFP-SB)(bipy)]ClO₄ (where PMFP?=?1-phenyl-3-methyl-4-formyl-2-pyrazolin-5one; bipy?=?2,2′-bipyridine). All the compounds have been characterized by elemental analysis, magnetic susceptibility, conductometry measurements and ¹H-NMR, FT-IR, ESR, electronic spectra and mass spectrometry. Electronic spectra and magnetic susceptibility measurements indicate square planar stereochemistry. Thermal stability, order of kinetics, heat capacity and activation energy of thermal degradation for these complexes were determined by TGA and DSC. Hamiltonian and bonding parameters from ESR spectra indicate the metal ligand bonding is partially covalent.     

Highly stable performance of supercapacitors using microporous carbon derived from phenol–melamine–formaldehyde resin

A series of microporous carbons were prepared by simple carbonization and activation of phenol–melamine–formaldehyde resin. The morphology, surface area, and elemental composition of the samples were investigated by scanning electron microscope, Brunauer–Emmett–Teller measurement, Raman spectra, and elemental analysis, respectively. Electrochemical characteristics were evaluated by cyclic voltammograms, galvanostatic charge/discharge, and electrochemical impedance spectroscopy measurements in 6.0?mol?L^?1 KOH. The microporous carbon activated by KOH presented a high specific capacitance of 202?F?g^?1 at a scan rate of 2?mV?s^?1. Furthermore, the KOH-activated microporous carbon electrode exhibited durable operation, the total loss of capacitance after 20,000 cycles is 2% at a current density of 500?mA?g^?1. The good electrochemical performance of the activated carbon was ascribed to well-developed micropores, high surface area, larger pore volume as well as oxygen groups.     

Synthesis,characterization and biological activity of copper(II) complexes with ligands derived from β-amino acids

Transition Metal Chemistry - Two copper(II) complexes with ligands derived from β-amino acids, 2-(1-aminocyclohexyl)acetic acid L1 and 2-(1-amino-4-(tert-butyl)cyclohexyl)acetic acid L2, were...     

Metal complexes of hybrid oxygen-arsenic ligands—VI. Stabilization of manganese(II)-arsine complexes using ligands from o-R2AsC6H4CO2Na

A reaction of MnCl₂·4H₂O with o-R₂AsC₆H₄CO₂ Na in 1:2 molar ratio in 95% EtOH yields four manganese(II)-monotertiaryarsine complexes [Mn(o-Me₂AsC₆H₄CO₂)Cl]·0.5H₂O, [Mn(o-R₂AsC₆H₄CO₂)₂(H₂O)₂]·nH₂O (n = O and R = Ph or p-tolyl; n = 1 and R = Et). The stabilization of these four complexes is significant in view of the only two already known.     

Synthesis and characterization of novel titanium complexes bearing [ONX]-type β-enaminoketonato ligands and their application to ethylene (co)polymerization

A series of novel titanium complexes bearing tridentate β-enaminoketonato chelating ligands of type, [R(2)NC(CF(3))C(H)CR(1)O]TiCl(3) (2a: R(1) = Ph, R(2) = -C(6)H(4)OMe(o); 2b: R(1) = Ph, R(2) = -C(9)H(6)N; 2c: R(1) = Ph, R(2) = -C(6)H(4)SMe(o); 2d: R(1) = Ph, R(2) = -C(6)H(4)SPh(o); 2e: R(1) = (t)Bu, R(2) = -C(6)H(4)SPh(o)) and [R(2)NC(R(1))C(H)C(CF(3))O]TiCl(3) (2f: R(1) = Ph, R(2) = -C(6)H(4)PPh(2)(o)) were prepared from TiCl(4) by treating with one equiv of deprotonated ligands in toluene. The reaction of 1a with equivalent of TiCl(4) in THF afforded another complex, C(6)H(4)OMeNC(CF(3))C(H)CPhO]TiCl(3)(thf) (3a), in addition to formation of the dichloride complex 4a, [C(6)H(4)(OMe)NC(CF(3))C(H)CPhO](2)TiCl(2). After deprotonation by alkali-metal hydride at -78 °C in diethyl ether, ligand 1a could react with 0.5 equiv of TiCl(4) to form the exclusive and clean dichloride complex 4a in high yield. These complexes were identified by NMR and mass spectra as well as elemental analyses. X-ray diffraction studies on these new trichloride complexes revealed a distorted octahedral coordination of the central metal with three chlorine atoms in a mer disposition. Dichloride complex 4a also adopted a distorted octahedral geometry around the titanium center. Two chlorine atoms are situated in the cis position, as seen in the bond angles for Cl(1)-Ti-Cl(2) (92.64(7)°). The O atom on the heterocyclic group was not coordinated with Ti. When activated by modified methylaluminoxane (MMAO), complexes 2a-e exhibited moderate to high activity towards ethylene (co)polymerization, giving relatively high molecular weight polymers with unimodal molecular weight distribution.