Synthesis, characterization and reactivity of a zwitterionic amine bridged bis(phenolate) lanthanide complex

A zwitterionic amine bridged bis(phenolate) ytterbium(III) complex was synthesized, and its reactivity with a zinc cluster was explored. The reaction of (C₅H₅)₃Yb(THF) with the amine bridged bis(phenol) HONNOH [ONNO = Me₂NCH₂CH₂N{CH₂-(2-O-C₆H₂-Bu^t₂-3,5)}₂] in a 1:2 M ratio in toluene at 80 °C produced the zwitterionic ytterbium complex [ONNO]Yb[ONNO(μ₄-H)] (1) in a high isolated yield. The reaction of ZnEt₂ with 1 equiv of PhCH₂OH gave a zinc cluster Zn₇Et₆(OCH₂Ph)₈ (2) in a good isolated yield. Complex 1 reacted with complex 2 in a 7:1 M ratio at room temperature to afford the unexpected ligand redistributed product [ONNO]Zn(THF) (3). These complexes were well characterized by elemental analyses, IR spectra and NMR spectroscopy in the case of complexes 2 and 3. The definitive molecular structures of complexes 2 and 3 were determined by single-crystal X-ray analyses.     

Lanthanide chloride complexes of amine-bis(phenolate) ligands and their reactivity in the ring-opening polymerization of epsilon-caprolactone

Reaction of two equivalents of n-BuLi with sterically demanding amine-bis(phenol) compounds, H(2)O(2)NN'(R) (Me(2)NCH(2)CH(2)N{CH(2)-3,5-R(2)-C(6)H(2)OH}(2); R = t-Bu or t-Pe (tert-pentyl)) yields isolable lithium complexes, Li(2)(O(2)NN'(R)), in good yields. Upon reaction with one equivalent of LnCl(3)(THF)(x), the lithium salts afford rare earth amine-phenolate chloride complexes in good yields, Ln(O(2)NN'(R))Cl(THF); Ln = Y, Yb, Ho, Gd, Sm, Pr. Crystals of Y(O(2)NN'(t-Bu))Cl(THF), 1, and Sm(O(2)NN'(t-Bu))Cl(DME), 2, suitable for single crystal X-ray crystallographic analysis were obtained. In contrast to previously reported [{Gd(O(2)NN'(t-Pe))(THF)(micro-Cl)}(2)] and related La and Sm complexes, these species are monomeric. 1 contains Y in a distorted octahedral environment bonded to two amine, two phenolate, one THF and one chloride donor. 2 contains Sm in a distorted capped trigonal prismatic environment bonded to two amine, two phenolate, two DME oxygens and one chloride donor. The Ln(O(2)NN'(t-Pe))Cl(THF) complexes were active initators for the controlled ring-opening polymerization of epsilon-caprolactone with a tendency to form low molecular weight cyclic polyesters (M(n) 3000-5000). The conversion rates, although slower than related amido and alkyl species, were different for monomeric and dimeric initiators. The size of the metal centre also affected the conversions and the molecular weights achieved.     

Synthesis,reactivity and structural characterization of lanthanide hydroxides stabilized by a carbon-bridged bis(phenolate) ligand

The synthesis of lanthanide hydroxo complexes stabilized by a carbon-bridged bis(phenolate) ligand 2,2’-methylene-bis(6-tert-butyl-4-methylphenoxo) (MBMP²⁻) was described, and their reactivity toward phenyl isocyanate was explored. Reactions of (MBMP)Ln(C₅H₅)(THF)₂ with a molar equiv. of water in THF at −78 °C afforded the bis(phenolate) lanthanide hydroxides as dimers [{(MBMP)Ln(μ-OH)(THF)₂}₂] [Ln = Nd (1), Yb (2)] in high yields. Complexes 1 and 2 reacted with phenyl isocyanate in THF, after workup, to give the desired O−H addition products, [(MBMP)Ln(μ-η¹:η²-O₂CNHPh)(THF)₂]₂ [Ln = Nd (3), Yb (4)] in excellent isolated yields. These complexes were well characterized, and the molecular structures of complexes 2 to 4 were determined by X-ray crystallography. The ytterbium atom in complex 2 is coordinated to six oxygen atoms to form a distorted octahedral geometry, whereas each metal center in complexes 3 and 4 is seven-coordinated, and the coordination geometry can be best described as a distorted pentagonal bipyramid.     

三(2,6-二叔丁基-4-甲基-苯氧基)镧催化ε-己内酯低温聚合特征及与环碳酸酯嵌段共聚

摘要用三(2,6-二叔丁基-4-甲基-苯氧基)镧[La(OAr)₃]在-15 ℃引发ε-己内酯(CL)的开环聚合, 发现聚合体系具有活性聚合特征. 在第二步聚合过程中继续补加第二种单体三亚甲基环碳酸酯(TMC)或二甲基三亚甲基环碳酸酯(DTC), 可得到CL与环碳酸酯的嵌段共聚物.     

Highly chemoselective lipase from Candida sp. 99-125 catalyzed ring-opening polymerization for direct synthesis of thiol-terminated poly(ε-caprolactone)

Lipase from Candida sp. 99-125 catalyzed ring-opening polymerization of ε-caprolactone in the presence of 6-mercapto-1-hexanol was presented as a new metal-free approach for direct synthesis of welldefined thiol-terminated poly(ε-caprolactone). Remarkably, high chemoselectivity of lipase from Candida sp. 99-125 toward hydroxyl and thiol was exhibited and quantitative thiol fidelity over 90% was achieved. The tedious protecting/deprotecting steps for thiol and metal residue were avoided. The polymerizations with around 70% monomer conversion were conducted in bulk and toluene at relative low temperature of 40 ℃. Number-average molecular weight of resulted polymers ranged from 3000 to 4700 Da by changing the feed ratio between monomer and initiator. The structures of obtained thiolterminated poly(ε-caprolactone) were demonstrated by combining NMR and SEC analyses.     

Synthesis,structures, and characterization of copper(II), nickel(II), and cobalt(III) metal complexes derived from an asymmetric bidentate Schiff-base ligand

An asymmetric bidentate Schiff-base ligand (2-hydroxybenzyl-2-furylmethyl)imine (L–OH) was prepared. Three complexes derived from L–OH were synthesized by treating an ethanolic solution of the appropriate ligand with an equimolar amount of metallic salt. Three complexes, Cu₂(L–O^?)₂Cl₂ (1), Ni(L–O^?)₂ (2) and Co(L–O^?)₃ (3), have been structurally characterized through elemental analysis, IR, UV spectra and thermogravimetric analysis. Single crystal X-ray diffraction shows metal ions and ligands reacted with different proportions 1?:?1, 1?:?2 and 1?:?3, respectively, so copper(II), nickel(II), and cobalt(III) have different geometries.     

Synthesis,characterization, and catalytic properties of a cobalt(II) complex supported by an amine-bis(phenolate) ligand

A cobalt(II) complex [L′CoPy] 1 was prepared by the reaction of dimethylaminoethylamino-N,N-bis(2,4-dibromo)phenol (H₂L′) with CoCl₂. Electrochemical studies indicate that this complex is among the most efficient homogeneous catalysts for water reduction, with a turnover frequency of 917.7 mol of hydrogen per mole of catalyst per hour at an overpotential of 636.7 mV (pH 7.0). Additionally, under photoirradiation with blue light (λ _max = 469 nm), complex 1 in combination with [Ru(bpy)₃]Cl₂ and ascorbic acid (pH 4.0 in aqueous solution) also produces hydrogen with a turnover number of 4.9 × 10⁵ mol of H₂ per mol of catalyst.     

Titanium complexes bearing amine bis(phenolate) ligands: Synthesis,structure and catalysis in ring‐opening polymerization of lactide

Monomeric bis(isopropoxy) titanium complexes LTi(Oⁱ Pr)₂ (L =  ─ OC₆H₂–4‐R¹–6‐R²–2‐CH₂N[(CH₂)₂N(R³)₂]CH₂–4‐R⁴–6‐R⁵‐C₆H₂O ─ , R¹ = R² = ^t Bu, R³ = Et, R⁴ = R⁵ = Cl, (L¹)Ti(Oⁱ Pr)₂; R¹ = R² = Me, R³ = Et, R⁴ = R⁵ = Me, (L²)Ti(Oⁱ Pr)₂; R¹ = R² = ^t Bu, R³ = Et, R⁴ = OMe, R⁵ = ^t Bu, (L³)Ti(Oⁱ Pr)₂; R¹ = R⁴ = OMe, R³ = Et, R² = R⁵ = ^t Bu, (L⁴)Ti(Oⁱ Pr)₂; R¹ = R² = ^t Bu, R³ = Me, R⁴ = OMe, R⁵ = ^t Bu, (L⁵)Ti(Oⁱ Pr)₂) supported by amine bis(phenolate) ligands were synthesized and characterized using NMR spectroscopy and elemental analysis. The solid‐state structure of (L³)Ti(Oⁱ Pr)₂ was determined using single‐crystal X‐ray diffraction. (L^1–5)Ti(Oⁱ Pr)₂ were all found to initiate the ring‐opening polymerization of l ‐lactide and rac ‐lactide in a controlled manner at 110–160°C. As shown by kinetic studies, (L¹)Ti(Oⁱ Pr)₂ polymerized l ‐lactide faster than did (L^2–5)Ti(Oⁱ Pr)₂. In addition, good number‐average molecular weight and narrow polydispersity index (1.00–1.71) of polymers were also obtained. The microstructure of the polymers and a possible mechanism of coordination–insertion of polymerization were evidenced by MALDI‐TOF and ¹H NMR spectra of the polylactides.     

Ultrasonic-bath-assisted preparation of mononuclear copper(I) thiosemicarbazone complex particles: Crystal structure,characterization and antimicrobial activity

Particles of the copper(I) thiosemicarbazone complex [Cu(Brcatsc)(PPh3)2Cl]·CH3CN (1), Brcatsc = 2-bromo-3-phenylpropenalthiosemicarbazone, were synthesized by an ultrasonic-bath-assisted method and characterized by elemental analyses, NMR (¹H, ¹³C, and ³¹P) and FT-IR spectroscopies, X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The thermal stability of 1 was studied by thermal gravimetry analysis and its structure was determined by single crystal X-ray diffraction. The compound 1 is a mononuclear complex with the copper(I) ion coordinated in a distorted tetrahedral geometry by one S atom of Brcatsc, two P atoms of two PPh₃, and one Cl atom. The complex involves the Brcatsc thiosemicarbazone ligand in an S monodentate bonding mode. The antibacterial activity of the ligand and its copper(I) complex was studied against two gram-positive (Staphylococcus aureus and Enterococcus faecalis) and two gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria.     

A gadolinium(III) complex: synthesis,structure, photophysical profile and its role in the degradation of nitroaromatics

The synthesis and structural characterization of a gadolinium(III) complex with phenanthroline and thiocyanate ligands have been accomplished. The X-ray crystal structure reveals that Gd(III) in a slightly distorted square anti-prism coordinated with four thiocyanate ions and two phenanthroline molecules; one phenanthroline is protonated which compensates the charge of Gd(III) center. The crystal structure shows chemically significant non-covalent interactions like hydrogen bonding involving the thiocyanate ligand and π–π interactions between uncoordinated phenanthrolinium and coordinated phen. Investigation on the intermolecular interactions and crystal packing via Hirshfeld surface analysis reveals that close contacts are mainly associated with weak interactions. The fingerprint plots demonstrate that these weak interactions are important for crystal packing. The Gd(III) complex shows photophysical activity. The compound is capable of degrading toxic pollutants like nitroaromatics and may have far reaching consequences for cleaning these toxic pollutants from industrial effluents.     

Synthesis,structural characterization,and catalytic reactivity of a new molybdenum(VI) complex containing 1,3,4-thiadiazole derivative as a tridentate NNO donor ligand

A new cis-dioxo molybdenum(VI) complex was obtained by reaction of 2,4-dihydroxybenzylidene(5-N,N-methylphenylamino-1,3,4-thiadiazol-2-yl)hydrazone as ligand and [MoO₂(acac)₂] in methanol and was characterized by elemental analyses, ¹H NMR, IR, and electronic spectroscopic studies. The complex was also analyzed by single-crystal X-ray diffraction. The structure determination revealed a distorted octahedral coordination geometry around molybdenum in which the tridentate NNO donor (L^2–) is bonded to [MoO₂]²⁺ through phenolic oxygen, hydrazinic nitrogen, and thiadiazole nitrogen. The sixth coordination site is occupied by a weakly bonded methanol. The complex was tested as a catalyst for homogeneous epoxidation of olefins using tert-butyl hydrogen peroxide as an oxidant. In the homogeneous catalytic system, the reactions are efficiently carried out with high yields and selectivity.     

Synthesis,Crystal Structure,and Electrochemistry of Iron and Cobalt Complexes Supported by a Pentadentate Amine‐bis(phenolate) Ligand

The pentadentate amine‐bis(phenolate) ligand 6,6′‐(dipyridin‐2‐ylmethylazanediyl)bis(methylene)bis(2,4‐dimethylphenol) (H₂L) was prepared and characterized. This ligand readily coordinates with Fe^III or Co^III ions, and the resulting complexes [Fe^IIILCl] ( 1 ) and [Co^IIIL(H₂O)]Cl ( 2 ) were characterized by elemental analysis. X‐ray structural studies show that the ligand in complexes 1 and 2 acts as a pentadentate ligand, leaving one coordination side of the transition metal available for exogenous ligands such as chloride ion ( 1 ) or water ( 2 ) ligand, and the central metal atoms are hexacoordinate in a similar distorted octahedral arrangement. Electrochemical studies reveal that each of the complexes exhibits multiple redox processes in the potential window investigated. Complex 1 shows one reversible oxidative event at 0.32 V and one quasi‐reversible reduction event at –1.03 V, while the complex 2 displays one reversible oxidative event at 0.18 V and one quasi‐reversible reduction at –0.64 V.     

Study on carbon-hydrogen activation of ketones by Gold(III) complexes and the synthesis and characterization of two ketonylgold(III) complexes

The acetonylgold(III) compound [Au(ppy)(CH₂COCH₃)Cl] (1) (ppy = 2-phenylpyridine) was unexpectedly obtained during the crystallization process of Au(III) lactate complex [Au(ppy)(CH₃CHOHCOO⁻)Cl]. This new structure prompted us to further study the role of Au(III) complexes on the carbon-hydrogen activation of ketones. Complex [Au(ppy)(CH₂COCH₃)NO₃] (2) was synthesized by reacting [Au(ppy)(NO₃)₂] with acetone while the ketonyl Au(III) complex [Au(apd)Cl₂] (3) (Hapd = 2-acetylpyridine) was obtained through carbon-hydrogen bond activation of the acetyl group. The crystal structures of 1 and 2 have common features: a square-planar Au(III) centre coordinated by one five-membered chelate ring, one acetonyl ligand and one anion (chloride or nitrate). Both structures show that carbon-hydrogen activation of acetone by 2-phenylpyridine-Au(III) complexes leads to the formation of acetonyl-Au(III) complexes. The Au-CH₂ bond lengths (2.067(7) Å, 1 and 2.059(5) Å, 2) are similar to each other but longer than the Au-C (phenyl) bond lengths. The two softest ligands (carbanion) are also cis to each other in the thermodynamically most stable isomer. In complex 3, the σ-bonded acetyl group is confirmed by ¹³C DEPT NMR spectroscopy.     

Rare earth metal alkyl complexes bearing N,O,P multidentate ligands: Synthesis, characterization and catalysis on the ring-opening polymerization of l-lactide

Alkane elimination reactions of rare earth metal tris(alkyl)s, Ln(CH₂SiMe₃)₃(THF)₂ (Ln = Y, Lu) with the multidentate ligands HL^1-4, afforded a series of new rare earth metal complexes. Yttrium complex 1 supported by flexible amino-imino phenoxide ligand HL¹ was isolated as homoleptic product. In the reaction of rigid phosphino-imino phenoxide ligand HL² with equimolar Ln(CH₂SiMe₃)₃(THF)₂, HL² was deprotonated by the metal alkyl and its imino CN group was reduced to C-N by intramolecular alkylation, generating THF-solvated mono-alkyl complexes (2a: Ln = Y; 2b: Ln = Lu). The di-ligand chelated yttrium complex 3 without alkyl moiety was isolated when the molar ratio of HL² to Y(CH₂SiMe₃)₃(THF)₂ increased to 2:1. Reaction of steric phosphino β-ketoiminato ligand HL³ with equimolar Ln(CH₂SiMe₃)₃(THF)₂ afforded di-ligated mono-alkyl complexes (4a: Ln = Y; 4b: Ln = Lu) without occurrence of intramolecular alkylation or formation of homoleptic product. Treatment of tetradentate methoxy-amino phenol HL⁴ with Y(CH₂SiMe₃)₃(THF)₂ afforded a monomeric yttrium bis-alkyl complex of THF-free. The resultant complexes were characterized by IR, NMR spectrum and X-ray diffraction analyses. All alkyl complexes exhibited high activity toward the ring-opening polymerization of l-lactide to give isotactic polylactide with controllable molecular weight and narrow to moderate polydispersity.     

Synthesis in solvent-free conditions,characterization and biological activity of a new Schiff-base ligand and its Cu(II) complex

A new bis-imine Schiff base (N₈O₂ donor, LH₂) has been synthesized by melt condensation of 3-amino-1,2,4-triazole with 1,5-bis(2′-formylphenyl)-1,5-dioksapentane in 2 : 1 molar ratio, in solvent and solvent-free conditions. The ligand has been characterized using FTIR, UV–Vis, ¹H NMR, ¹³C NMR, mass spectra, elemental analysis, and thermal (TGA-DSC) techniques. A new complex of LH₂ with Cu(II) has been synthesized in solvent and solvent-free conditions. FTIR, UV–Vis mass spectra, and thermal analysis (TGA-DSC) have been used to characterize the Cu(II) complex. Thermal degradation showed that the final products were black carbon and metallic copper. Distorted octahedral geometry has been observed around CuLH₂Cl₂ · LH₂ and its Cu(II) complex have been screened for in vitro antifungal and antioxidant activities. Antioxidation was determined for their superoxide scavenging and reducing activities. The ligand and its Cu(II) complex have strong antifungal activity against Aspergillus niger. The compounds have significant superoxide anion radical scavenging activity and reducing power against various antioxidant systems in vitro.     

Synthesis and characterization of tetrahedrally and octahedrally coordinated mixed-valence Co(II)/Co(III) complex with thiosemicarbazone-based ligand

Synthesis, characterization, and X-ray crystal structure for a mixed-valence binuclear Co(II)/Co(III) complex with the dianionic dithiolate form of a pentadentate ligand 2,6-diacetylpyridinebis(thiosemicarbazone) are reported. A new synthetic methodology has been employed replacing usual cobalt(II) salts by [Co(NH₃)₅Cl]Cl₂ as a precursor. The coordination geometry of cobalt(II), CoN₂S₂, was found to be distorted tetrahedral, whereas the cobalt(III) coordination sphere, CoN₄S₂, is slightly distorted octahedral. The magnetic behavior and molar conductivity of the complex are in agreement with the mixed-valence state.