Near‐stoichiometric O2 binding on metal centers in Co(salen) nanoparticles

Co(salen) [cobaltous bis(salicylaldehyde)ethylenediamine] complexes are well‐known O₂ carriers in solution. In the solid phase, these complexes exhibit some O₂ binding but detailed studies have been complicated because few of the known polymorphs of Co(salen) actually bind O₂. The O₂ binding results for nanoparticulate Co(salen) are presented in this study. Rod‐shaped Co(salen) nanoparticles, roughly 100 nm in diameter, were recrystallized by spraying a methylene chloride solution of commercially obtained Co(salen) into supercritical carbon dioxide. Temperature‐programmed desorption, thermogravimetric analysis, and a Rubotherm magnetic suspension balance measurements reveal a reversible O₂ uptake of ～1.51 mmol/(g nanoparticles) at 25°C, consistent with a binding stoichiometry involving a bridging peroxo unit between two Co centers. In contrast, no measurable O₂ uptake was observed with the commercial Co(salen). These results clearly show the potential for bottom‐up design of nanoparticulate metal complexes for enhanced O₂ storage and other applications. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Supramolecular π–π assembly of a neutral [Cu(salen)] complex via the templating effect of an ionic inorganic complex Na2[Cu(mnt)2] forming a framework type material having well-defined channels

A classical ionic inorganic complex Na₂[Cu(mnt)₂] (mnt²⁻ = maleonitriledithiolate = 1,2-dicyanoethylenedithiolate), that acts as a template in assembling neutral [Cu(salen)] (salen = bis(salicylidene)ethylenediamine) complexes forming a framework type arrangement, is accommodated in the channel formed in the crystal structure of a new type of host–guest compound [Cu(salen)]₄ · Na₂[Cu(mnt)₂] (1). The non-covalent supramolecular interactions among [Cu(salen)] complexes and between [Cu(salen)] and [Cu(mnt)₂]²⁻ complexes in the crystal lattice of 1 result in weak antiferromagnetic coupling.     

Co(salen) supported on graphene oxide for oxidation of lignin

Co(salen) was supported on graphene oxide (GO) (Co‐GO) by covalently grafting. Spectroscopy analyses confirmed its successful synthesis. Co‐GO demonstrated a high activity in the cleavage of βO4 linkage in lignin model compounds. The catalyst was also effective in depolymerizing an organosolv lignin polymer. The polymer residues were separated, and extensively analyzed by FTIR and NMR in order to understand the various structural changes of the polymer occurring versus catalyst. In catalytic oxidation, the βO4 ether linkages were cleaved and the side‐chains were oxidized occurring in the polymer. The polymer was thus converted into smaller monomers called degradation products which were detected by GC‐MS. The evolution of the polymer found that Co‐GO exhibited a significant catalytic effect as compared with Co‐NaY, Co‐MCM‐48, Co‐SSZ‐13. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44133.     

A recoverable catalyst Co(salen) in zeolite Y for the synthesis of methyl N-phenylcarbamate by oxidative carbonylation of aniline

A green process for the synthesis of methyl N-phenylcarbamate (MPC) by the oxidative carbonylation of aniline was studied. In this process, Co(salen) complexes were successfully encapsulated in zeolite Y by a flexible ligand method. The heterogeneous catalysts were characterized by AAS, BET, IR, TGA, XRD and XPS. The catalytic activities of the encapsulated catalysts and their homogeneous analogues were examined in the oxidative carbonylation of aniline to MPC. Under the conditions of aniline (11 mmol), encapsulated catalyst (0.5 g), KI (0.365 g), CO/O₂ ratio 9:1, 4 MPa, 170 °C, 3 h, Co(salophen)(OH)₂–Y catalyst shows the highest activity with the conversion of 67.1% and the selectivity of 77.3%. Co(salophen)(OH)₂–Y could be recycled at least five times and no significant loss of catalytic activity was observed.     

Catalytic oxidation of olefins with hydrogen peroxide catalyzed by [Fe(III)(salen)Cl] complex covalently linked to polyoxometalate

The catalytic activity of a hybrid compound [Fe(salen)-POM] (1) consisting of Fe(III)(salen)Cl [H₂salen = N,N′-bis(salicylidene)ethylenediamine] complex covalently linked to a Keggin type polyoxometalate, K₈SiW₁₁O₃₉, (POM) was studied in the oxidation of various olefins in acetonitrile, using hydrogen peroxide as oxygen source. While, [Fe(salen)-POM] catalyst showed moderate to good catalytic activity and product selectivity in the oxidation reactions, the complex Fe(III)(salen)Cl showed poor catalytic activity in these reactions. The effect of other parameters such solvent, oxidant, temperature and the metal type in Schiff base complex were also investigated.     

Two new homometallic coordination polymers based on a carboxylate-functionalized salen ligand

Two new homometallic coordination polymers 1 and 2 have been prepared by the directly one-step hydrothermal reactions of a carboxylate-functionalized salen ligand with Zn(II) and Co(II) ions, respectively. 1 exhibits a 3D open framework built by [Zn₄(μ₄-O)(carboxylate)₈] units and double Zn-salen ligands, while 2 shows a 1D chain structure constructed by cobalt ions and the ligand derived from the hydrolysis to one CN bond of salen ligand. The preliminary fluorescence measurements of 1–2 show the influence of structure on the property.     

Novel molecular architecture constructed on the skeleton of salen and salophen containing Zn(II) 2,2′-bipyridyl

The complexes of Zn(II)2,2′-bipyridine diacetate with salen (LH₂) and salophen (L′H₂) have been characterized in which complex with L′H₂ in DMSO has yielded a novel one-dimensional molecular architecture of micrometer length.     

A new softening agent for melt spinning of softwood kraft lignin

Kraft lignin obtained from the pulping of wood is an interesting new precursor material for carbon fiber production because of its high carbon content and ready availability. However, continuous spinning of softwood kraft lignin (SKL) has been impossible because of its insufficient softening characteristics and neat hardwood kraft lignin (HKL) has required extensive pretreatments to enable fiber formation. Softwood kraft lignin permeate (SKLP) and hardwood kraft lignin permeate (HKLP), fractionated by membrane filtration, were continuously melt spun into fibers. To improve the spinnability of SKL and HKL, HKLP was added as a softening agent. SKL‐ and HKL‐based fibers were obtained by adding 3–98 wt % HKLP. A suitable temperature range for spinning was 20–85°C above the T_g of the lignin samples, and this range gave a flawless appearance according to the SEM analysis. Smooth, homogeneous fibers of SKLP, HKLP, and SKL with HKLP were successfully processed into solid carbon fibers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Discrete versus In Situ‐Generated Aluminum‐Salen Catalysts in Enantioselective Cyanosilylation of Ketones: Role of Achiral Ligands

The monometallic species {Salen}AlX (X=Me, 2a , b ; X=Cl, 4a , b ; O‐i‐Pr, 5a,b ) and open bimetallic species {Salen}[AlMe₂]₂ ( 3a , b ) that result from binary combinations between an aluminum precursor [trimethylaluminum, dimethylaluminum chloride, aluminum tris(isopropoxide)] and a diprotio {Salen}H₂ pro‐ligand 1a , b ( a =1R,2R‐cyclohexyl‐salen; b =1R,2R‐diphenylethylene‐salen) have been isolated. The crystal structures of 3b , 4b and of μ‐oxo species [{diphenylethylene‐salen}Al]₂O ( 6b ) are reported. The discrete species 2 – 5a,b have been individually evaluated in the asymmetric cyanosilylation of acetophenone. It is shown that, in several cases, these discrete catalysts display dramatically different performances than the catalyst systems in situ‐generated from the binary combinations. The influence of the achiral ligand X on both the enantioselectivity and activity of the cyanosilylation reaction has been investigated, resulting in the definition of a highly active and productive hexafluoro‐2‐propoxide‐based catalyst for a variety of aryl alkyl ketones (TON up to 470, TOF up to 140 h⁻¹ at −20 °C for acetophenone).     

Hexachloroplatinate(IV) anion-induced cucurbit[5]uril and cucurbit[8]uril supramolecular assemblies with linear channels

Two Q[n]-based porous compounds, Q[5]·[PtCl₆]^2 −·2H₃O·12H₂O and 2Q[8]·[PtCl₆]^2 −·2H₃O·74H₂O in cooperating the hexachloroplatinate(IV) anion ([PtCl₆]^2 −) as an inorganic structure directing agent are demonstrated. The driving forces for the formation of such novel Q[n]-based porous compounds are considered to be the outer surface interactions of Q[n]s, including dipole interactions between Q[n]s and ion-dipole interactions between [PtCl₆]^2 − anions and Q[n]s. Moreover, the Q[5]-based porous compound displays absorption distinctness for tetrachloromethane, whereas the Q[8]-based porous compound displays absorption distinctness for methanol.     

Synthesis and crystal structures of two new inorganic–organic hybrid polyoxomolybdate complexes: [Himi]4[{Co(imi)2(H2O)2}Mo7O24] · 4H2O and [Zn(imi)4]2[(imi)2Mo8O26] · 6H2O

The two new inorganic–organic hybrid polyoxomolybdate complexes [Himi]₄[{Co(imi)₂(H₂O)₂}Mo₇O₂₄] · 4H₂O (1) and [Zn(imi)₄]₂[(imi)₂Mo₈O₂₆] · 6H₂O (2) (imi = imidazole) have been prepared by conventional aqueous solution synthesis. Compound 1 consists of heptamolybdate anions [Mo₇O₂₄]⁶⁻ covalently linked by [CoN₂O₄]²⁺ octahedra into one-dimensional zigzag-shaped chains. The zigzag-shaped chains are further linked together via the hydrogen-bonding interactions to form a 2D supramolecular framework. Compound 2 is build up of an imidazole-coordinated octamolybdate anion, two imidazole coordinating zinc cations and lattice water molecules to form a three-dimensional framework via complex hydrogen-bonding.     

Oxidation of cycloalkanes with molecular oxygen in the presence of salen metallocomplexes in thermomorphic conditions

The oxidation of cycloalkanes with molecular oxygen, catalyzed by two groups of metallosalen complexes, was studied. The first group consisted of salen complexes with different metals such as Mn, Fe, Co, Ni, Cu, Zn, while the second group was composed of manganese salen complexes with different substituents (t-butyl electron-donating substituents and/or electron-withdrawing perfluoroalkyl substituents). Mn, Fe and Co salen complexes are the most active catalysts, while Ni, Cu and Zn salen complexes are far less efficient. The introduction of t-butyl electron-donating substituents into Mnsalen complex increases the catalytic activity and catalysts solubility in the reaction mixture. The introduction of perfluoroalkyl electron-withdrawing substituents enhances the catalytic activity and renders the solubility of the catalyst temperature dependent (thermomorphic behaviour), thus allowing one to recover them easily after the reaction by simply cooling the system to room temperature. The synthesis of two new manganese salen complexes with perfluoroalkyl substituents was elaborated.     

Gold(I)‐Catalyzed Tandem Alkoxylation/Lactonization of γ‐Hydroxy‐α,β‐Acetylenic Esters

The formation of 4‐alkoxy‐2(5H)‐furanones was achieved via tandem alkoxylation/lactonization of γ‐hydroxy‐α,β‐acetylenic esters catalyzed by 2 mol% of [2,6‐bis(diisopropylphenyl)imidazol‐2‐ylidine]gold bis(trifluoromethanesulfonyl)imidate [Au(IPr)(NTf₂)]. The economic and simple procedure was applied to a series of various secondary propargylic alcohols allowing for yields of desired product of up to 95%. In addition, tertiary propargylic alcohols bearing mostly cyclic substituents were converted into the corresponding spiro derivatives. Both primary and secondary alcohols reacted with propargylic alcohols at moderate temperatures (65–80 °C) in either neat reactions or using 1,2‐dichloroethane as a reaction medium allowing for yields of 23–95%. In contrast to [Au(IPr)(NTf₂)], reactions with cationic complexes such as [2,6‐bis(diisopropylphenyl)imidazol‐2‐ylidine](acetonitrile)gold tetrafluoroborate [Au(IPr)(CH₃CN)][BF₄] or (μ‐hydroxy)bis{[2,6‐bis(diisopropylphenyl)imidazol‐2‐ylidine]gold} tetrafluoroborate or bis(trifluoromethanesulfonyl)imidate – [{Au(IPr)}₂(μ‐OH)][X] (X=BF₄, NTf₂) – mostly stop after the alkoxylation. Analysis of the intermediate proved the exclusive formation of the E‐isomer which allows for the subsequent lactonization.     

An unprecedented mixed valence cobalt(III)/cobalt(II) ion-pair complex ([CoCO3(bipy)2]2[Co(DCA)2]⋅16H2O) with two novel water tapes

An unprecedented mixed valence cobalt(III)/cobalt(II) ion-pair complex, [CoCO₃(bipy)₂]₂[Co(DCA)₂]⋅16H₂O (1) [bipy = 2,2′-bipyridine, DCA = demethylcantharidate, exo-1,4-epoxy-cyclohexyl-2,3-dicarboxylate group, (C₈H₈O₅)^2 −], has been synthesized and characterized by elemental analysis, IR, UV–vis, Thermogravimetric analysis (TGA) and single crystal X-ray diffraction. The crystal structure of 1 consists of three independent molecular moieties: [CoCO₃(bipy)₂]⁺, [Co(DCA)₂]^2–, and water molecules of crystallization. Interestingly, two novel water tapes, one comprises of alternate cyclic water tetramer and octamer, the other is constructed by alternate cyclic water hexamer and carboxylate–water hybrid octamer [(H₂O)₂(COO)₂]^2 −, have been detected for the first time in the host framework of 1. The two novel water tapes are linked together by the DCA and carbonate ligands via hydrogen bonds into a 2D water layer, and then the water layers assemble complex ions ([CoCO₃(bipy)₂]⁺ and [Co(DCA)₂]^2 −) through hydrogen bonds, π–π interactions and electrostatic interactions to form the overall 3D metal–organic framework structure.     

Multiple metal coordinating behaviour of the tetrapodal ligand 1,1,1,1-tetrakis[(salicylaldimino)methyl]methane

The tetrapodal ligand 1,1,1,1-tetrakis[(salicylaldimino)methyl]methane (H₄tsam) has been introduced for the first time for metal complexation. Two zinc(II) complexes[Zn₂(tsam)] (1) and [Zn₃(Htsam)₂]·2C₇H₈ (2) have been obtained by reacting zinc acetylacetonate with the ligand in the presence of triethylamine, while a cobalt(III) complex [Co(Htsam)]·CH₃CN·H₂O (3) is obtained when Co(ClO₄)₂·6H₂O is reacted in air. All the compounds have been characterized by their elemental analyses and ESI-MS, IR, UV-VIS and ¹H NMR spectra. The X-ray crystal structures of H₄tsam, 2 and 3 have been determined. Compounds 1 and 2 exhibit fluorescence in solution and the lifetimes of their luminescence decay have been measured. Thermal analysis (TGA, DTA) of 2 with regard to loss of encapsulated toluenes and redox behaviour of 3 have been studied.     

Salen homonuclear and heteronuclear lanthanide(III) complexes with near-infrared (NIR) luminescence

Two lanthanide complexes are achieved by utilizing H₂salen/acac ligands (H₂salen = N,N′-ethylenebis(salicylideneimine), acac = acetylacetonate). They are homonuclear [Nd₄(μ₃-OH)₂(salen)₂(acac)₆(CH₃OH)₂]·CH₃OH (1) and heteronuclear [NdYb(salen)₂(acac)₂] (2). The structures of the two complexes were determined by X-ray crystallographic studies and their photophysical properties were investigated. The homonuclear Nd₄ complex exhibits characteristic metal-centered NIR emission. The heteronuclear NdYb shows ‘dual emission’ from both neodymium(III) and ytterbium(III) ions.     

Synthesis and in vivo Evaluation of Fluorine‐18 and Iodine‐123 Pyrazolo[4,3‐e]‐1,2,4‐triazolo[1,5‐c]pyrimidine Derivatives as PET and SPECT Radiotracers for Mapping A2A Receptors

Imaging agents that target adenosine type 2A (A_2A) receptors play an important role in evaluating new pharmaceuticals targeting these receptors, such as those currently being developed for the treatment of movement disorders like Parkinson′s disease. They are also useful for monitoring progression and treatment efficacy by providing a noninvasive tool to map changes in A_2A receptor density and function in neurodegenerative diseases. We previously described the successful evaluation of two A_2A‐specific radiotracers in both nonhuman primates and in subsequent human clinical trials: [¹²³I]MNI‐420 and [¹⁸F]MNI‐444. Herein we describe the development of both of these radiotracers by selection from a series of A_2A ligands, based on the pyrazolo[4,3‐e]‐1,2,4‐triazolo[1,5‐c]pyrimidine core of preladenant. Each of this series of 16 ligands was found to bind to recombinant human A_2A receptor in the low nanomolar range, and of these 16, six were radiolabeled with either fluorine‐18 or iodine‐123 and evaluated in nonhuman primates. These initial in vivo results resulted in the identification of 7‐(2‐(4‐(4‐(2‐[¹⁸F]fluoroethoxy)phenyl)piperazin‐1‐yl)ethyl)‐2‐(furan‐2‐yl)‐7H‐pyrazolo[4,3‐e][1,2,4]triazolo[1,5‐c]pyrimidin‐5‐amine ([¹⁸F]MNI‐444) and 7‐(2‐(4‐(2‐fluoro‐4‐[¹²³I]iodophenyl)piperazin‐1‐yl)ethyl)‐2‐(furan‐2‐yl)‐7H‐imidazo[1,2‐c]pyrazolo[4,3‐e]pyrimidin‐5‐amine ([¹²³I]MNI‐420) as PET and SPECT radiopharmaceuticals for mapping A_2A receptors in brain.     

Syntheses,crystal structures and luminescent investigations of cobalt(II) and zinc(II) complexes with 2-propyl-4,5-dicarboxylate-imidazole (H3PIDC)

Presented in this communication are four metal complexes based on 2-propyl-4,5-dicarboxylate-imidazole (H₃PIDC), including two Co(II) coordination compounds, [Co(H₂PIDC)₂(H₂O)₂] · 4H₂O (1) and 2[Co(H₂PIDC)₂(H₂O)₂] · 5H₂O (2), as well as two Zn(II) coordination compounds, [Zn(H₂PIDC)₂(H₂O)₂] · 4H₂O (3) and 2[Zn(H₂PIDC)₂(H₂O)₂] · 7H₂O (4). They contain the same coordinated unit of [M(H₂PIDC)₂(H₂O)₂] (M = Zn or Co). Interestingly, among these four complexes, 1 and 2, or 3 and 4 crystallized in different space group, which may be related with the number of the crystallized H₂O molecules.     

[3H]UR‐DE257: Development of a Tritium‐Labeled Squaramide‐Type Selective Histamine H2 Receptor Antagonist

A series of new piperidinomethylphenoxypropylamine‐type histamine H₂ receptor (H₂R) antagonists with different substituted “urea equivalents” was synthesized and characterized in functional in vitro assays. Based on these data as selection criteria, radiosynthesis of N‐[6‐(3,4‐dioxo‐2‐{3‐[3‐(piperidin‐1‐ylmethyl)phenoxy]propylamino}cyclobut‐1‐enylamino)hexyl]‐(2,3‐³H₂)propionic amide ([³H]UR‐DE257) was performed. The radioligand (specific activity: 63 Ci mmol^?1) had high affinity for human, rat, and guinea pig H₂R (hH₂R, Sf9 cells: K_d, saturation binding: 31 nM , kinetic studies: 20 nM ). UR‐DE257 revealed high H₂R selectivity on membranes of Sf9 cells, expressing the respective hH_xR subtype (K_i values: hH₁R: >10 000 nM , hH₂R: 28 nM , hH₃R: 3800 nM , hH₄R: >10 000 nM ). In spite of insurmountable antagonism, probably due to rebinding of [³H]UR‐DE257 to the H₂R (extended residence time), the title compound proved to be a valuable pharmacological tool for the determination of H₂R affinities in competition binding assays.     

The Synthesis and Characterization of Melamine Based and [Fe/CrSalen] or [Fe/CrSalophen] Capped Polimer Schiff Base Complexes

In this study, by using previously reported monomer complexes [(2-(4-carboxybenzimino)-4,6-diamino-1,3,5-triazine)(salen/salophenFeIII)], [(2-(4-carboxybenzimino)-4,6-diamino-1,3,5-triazine)(salen/salophenCrIII)], [(2-(3,4-dihydroxybenzimino)-4,6-diamino-1,3,5-triazine)(salen/salophenFeIII)] and [(2-(3,4-dihydroxybenzimino)-4,6-diamino-1,3,5-triazine)(salen/salophenCrIII)] obtained by Uysal and Uçan (J Inc Phenom Macrocycl Chem, in press), sixteen new polimer Fe(III) and Cr(III) complexes involving tetradentate Schiff bases N,N′-bis (salicylidene)ethylenediamine-(salenH₂) or bis(salicylidene)-o-phenylenediamine-(salophenH₂) with 2-(4-carboxybenzimino)-4,6-diamino-1,3,5-triazine or 2-(3,4-dihydroxybenzimino)-4,6-diamino-1,3,5-triazine (Uysal and Uçan, J Inc Phenom Macrocycl Chem, in press) and terephthaldehyde or glutaraldehyde have been synthesized and characterized by means of elemental analysis, ¹H N.M.R., FT-IR spectrscopy, MS, thermal analyses and magnetic susceptibility measurements. The complexes have also been characterized as low-spin distorted octahedral Fe(III) and Cr(III) bridged by catechol and/or COO^? groups.