Ligand Coupling Research Articles

ChemInform Abstract: Reductive Coupling of Carbon Monoxide and Alkyl Isocyanide Ligands in Early Transition Metal Complexes: A Review

ChemInform Abstract: Reductive Coupling of Carbon Monoxide and Alkyl Isocyanide Ligands in Early Transition Metal Complexes: A Review

ChemInform Abstract: Facile Oxidation of Sulfides to Sulfoxides Using Iodosobenzene and Benzeneseleninic Acid as a Catalyst.

Abstract Iodosobenzene in the presence of catalytic amount of benzeneseleninic acid oxidized various sulfides to sulfoxides through ligand coupling on the iodine atom in excellent yields in acetonitrile under mild conditions.

ChemInform Abstract: Aryllead Triacetates: Regioselective Reagents for N-Arylation of Amines.

Aryllead triacetates have been found to be regioselective reagents for the mono N-arylation of a range of aromatic, heterocyclic and aliphatic amines under mild and neutral conditions in a reaction catalysed by copper diacetate. The arylation of arylamines was unaffected by the steric hindrance of the arylamine but was dependent on the arylamine basicity. In addition, the position of oxidisable substituents on both the aryllead triacetate and the arylamine was found to be important due to a competing oxidation-reduction reaction. The arylation of heterocyclic amines proceeded in modest to good yields whilst aliphatic amines were arylated in poor to modest yields. The mechanism proposed for these reactions involves transfer of the aryl group onto copper forming a copper(III) intermediate which subsequently undergoes ligand coupling to give the N-arylated amine and the catalytic CuI species.

ChemInform Abstract: Application of Aryllead(IV) Derivatives to the Preparation of 3-Aryl-4- hydroxy-1-benzopyran-2-ones.

Aryllead triacetates are chemoselective and regioseiective reagents for the preparation of 3-aryl-4-hydroxy-1-benzopyran-2-ones in good to excellent yields by C-3 arylation of the preformed 4-hydroxy-1-benzopyran-2-one ring. This approach was applied to the high-yielding synthesis of naturally occurring examples. A radical mechanism was discounted and the mechanism proposed involves the ligand coupling of an intermediate possessing an enolate-to-lead bond to afford arylated products.

Coupling of Aromatic N-Heterocycles Mediated by Group 3 Complexes

Group 3 η2-N,C-pyridyl complexes supported by a ferrocene-diamide ligand have been known to mediate the coupling of η2-N,C-pyridyl and coordinated-pyridine ligands with a concomitant dearomatization of the pyridine ligand. Examples reported previously by us were limited to a few cases. In order to investigate the scope of the coupling reaction, various η2-N,C-pyridyl scandium complexes were isolated and characterized. Their reactivity toward other aromatic N-heterocycles is presented along with the characterization of the subsequent reaction products. The coupling reaction is favored by ortho substitution, the presence of fused aromatic rings on the pyridine ligand, and chelating substrates. In one instance, the product of the coupling reaction between a scandium η2-N,C-pyridyl complex and 7,8-benzoquinoline could not be isolated because a subsequent isomerization reaction was favored. The coupling reaction is not restricted to η2-N,C-pyridyl fragments, and it proceeds also from CH2 groups bound to the metal center and connected to a pyridine ligand. The reaction between η2-N,C-imidazolyl scandium complexes and 2,2′-bipyridine is also discussed.

Analysis of the Magnetic Coupling in M3(dpa)4Cl2Systems (M = Ni, Pd, Cu, Ag) by Ab Initio Calculations

The magnetic exchange parameter (J) of a series of neutral and oxidized trinuclear extended metal atom chain complexes [M(3)(dpa)(4)Cl(2)](0/1+), where dpa is the anion of di(2-pyridyl)amine, has been extracted employing the complete active space second-order perturbation theory (CASPT2). The computed magnetic coupling constant for Ni(3)(dpa)(4)Cl(2) (-98 cm(-1)) and the mono-oxidized Cu(3) complex (-35 cm(-1)) are in excellent agreement with the experimental estimates. This consistence is though not achieved for Cu(3)(dpa)(4)Cl(2), with three S = 1/2 magnetic centers, for which we surprisingly obtain 1/3 of the experimental value only. This worrying result and the possible sources for such large discrepancy are analyzed. The magnetic coupling has been also analyzed for the hypothetical complexes with Pd(3) and Ag(3) metal chains. Much larger couplings are obtained, which is ascribed to the larger spatial extent of the magnetic orbitals. Furthermore, we analyze the relative importance of the magnetic coupling paths through the sigma-system (through metal coupling) and the delta-system (through ligand coupling).

Study of Dynamic NO Ligands on Ruthenium Complexes

In this article, our study of dynamic NO ligands on ruthenium complexes has been reported. Transformation of NO ligand, linear NO+ and bent NO- form, is characteristic of NO ligand on transition metal complexes. However, such transformation and incorporation of NO ligand into organic molecules, the so-called dynamic NO ligands, have little observed. We found three types of the dynamic NO ligands. First topic is interconversion of NO ligand (linear NO+ and bent NO- form) in the chemistry of [2+2] cycloaddition reaction and protonation of vinylidene ruthenium complexes. In second topic, interesting reactivity of NO ligand on ruthenium complexes is described, where C–H activation and N–C coupling of NO ligand are included. Final attention is drawn to unprecedented N–N coupling of NO ligands on dinuclear ruthenium complexes. This N–N coupling is closely related with bacterial nitric oxide reductase (NOR). Use of the N–N coupling complexes achieved stepwise reproduction of the NOR catalytic process. These findings lead to new aspects in the chemistry of NO ligand on ruthenium complexes.

New reaction of β-diketiminatoeuropium complex: sterically induced oxidation–coupling of β-diketiminato ligands

Attempted synthesis of sterically demanding tris-beta-diketiminate complexes of europium led to oxidation-coupling of beta-diketiminates and the formation of the THF-solvated divalent europium complex Eu(L(2,6-Me(2)))(2)(THF) (L(2,6-Me(2)) = [{N(2,6-Me(2)C(6)H(3))C(Me)}(2)CH](-)), while the normal tris-beta-diketiminate complex Eu(L(2-Me))(3) for the less bulky ligand L(2-Me) ([{N(2-MeC(6)H(4))C(Me)}(2)CH](-)) was isolated by the same procedure.

Formation of epoxides from pentacoordinated organoarsenic compounds with a β-hydroxyethyl group

A series of pentacoordinated organoarsenic compounds (arsoranes) bearing a β-hydroxyethyl group (4a, 6a and 6b) was synthesized. The crystal structures were determined by single crystal X-ray analysis. Treatment of these arsoranes with KH almost quantitatively gave the corresponding epoxide. The reaction of 4a having an unsubstituted β-hydroxyethyl group with KH was monitored by 1H and 19F NMR in CD3CN, suggesting that a hexacoordinate arsenic anion was formed as the intermediate. However, a further stereochemical study of the epoxide formation suggested that the reaction proceeded in the SN2 manner and not in the ligand coupling reaction (LCR) of the intermediate hexacoordinate arsenic anion.

Spin‐Hamiltonian parameters and local lattice structure for Pd(I) center in γ‐irradiated bis(acetylacetonato)palladium(II)

AbstractThis paper reports on a theoretical analysis of spin‐Hamiltonian parameters and local lattice structure for Pd(I) center in γ‐irradiated Pd(II)(acac)2. Through the crystal‐ and ligand‐field theory, the microscopic spin‐Hamiltonian parameters and local molecular structure for Pd(I) center in the γ‐irradiated Pd(II)(acac)2 system have been studied by using the high‐order perturbation formulas and Newman's superposition model. Based on these calculations, it was found that the distance of the metal‐ligand bonds in the square planar complex for Pd(I) center in the γ‐irradiated Pd(II)(acac)2 system increases by 0.1Å. To understand the detailed physical and chemical properties of the [Pd(I)(acac)2]2– complex, the contributions of the spin‐orbit coupling of ligand to spin‐Hamiltonian parameters for Pd(I) ion are considered. The theoretical results are in reasonable agreement with the experimental values. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A Bimetallic Ru2Pt Complex Containing a Trigonal-Planar μ3-Carbido Ligand: Formation, Structure, and Reactivity Relevant to the Fischer−Tropsch Process

The bimetallic Ru(2)Pt complex [(Cp*Ru)(2)(mu(2)-NHPh)(mu(2)-H)(mu(3)-C)PtMe(PMe(3))(2)][OTf] (3; Cp* = eta(5)-C(5)Me(5)) containing a planar three-coordinate carbido ligand has been prepared in 93% yield by thermal isomerization of the bridging methylene precursor [(Cp*Ru)(2)Me(mu(3)-NPh)(mu(2)-CH(2))Pt(PMe(3))(2)][OTf] (2) via cleavage of the methylene C-H bonds. Exposure of the carbido complex 3 to carbon monoxide (1 atm) induced coupling of the carbido ligand with the nearby methyl and hydride ligands to produce the diruthenium ethylidene complex [(Cp*Ru)(2)(mu(2)-CHMe)(mu(2)-NHPh)(CO)(2)][OTf] (4) and the known triplatinum complex [Pt(CO)(PMe(3))](3). The crystal structures of 2, 3, and 4 (BPh(4) salt) are reported.

Preparation and characterization of a cellulose affinity membrane for human immunoglobulin G (IgG) purification

This paper reports the design, preparation and characterization of cellulose affinity membranes for antibody purification using a new methodology. Cellulose membranes were prepared from polymer-ionic liquid solutions, namely 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), by the water induced phase inversion process. After functionalization with a synthetic ligand 2-(3-aminophenol)-6-(4-amino-1-naphthol)-4-chloro- s-triazine (ligand 22/8), these were evaluated as affinity supports for human immunoglobulin G (IgG). Membranes were characterized in terms of morphology (SEM), porosity (mercury porosimetry), hydrophilicity (contact angle measurement), transport properties (permeability) and mechanical performance (DMA). Membranes prepared with varying cellulose contents (5 and 10 wt.% cellulose in ionic liquid solutions) lead to films with different properties. The 10 wt.% cellulose membrane presented enhanced morphological and mechanical properties, however, the morphology of this membrane was significantly altered after ligand coupling. Adsorption isotherms for human IgG onto 10 wt.% matrix activated with ligand 22/8 were obtained. Preliminary results showed that the bovine serum albumin (BSA), a model impurity, did not adsorb onto the membrane while up to 6 mg IgG/g was bound and 2 mg IgG/g recovered.

Surface Modification of PLGA Particles: The Interplay between Stabilizer, Ligand Size, and Hydrophobic Interactions

Therapeutic and diagnostic carriers can be functionalized with active targeters to induce tissue-specific delivery. However, the possible impact of adsorbed steric stabilizer such as the frequently used poloxamers (Pluronics) on surface modification of poly(D,L-lactide-co-glycolide) (PLGA) particles has not been examined so far. Therefore, three model ligands of different molecular weights (653; 36,000; 155,000 g/mol) covering the size range of important targeters were conjugated to the surface of PLGA microparticles in the presence of different concentrations of Pluronic F68 (0.01-5%, w/v). Flow cytometry and fluorimetric quantification revealed for all tested ligands that high Pluronic concentrations decreased the coupling efficiency to a half or even one-third of that achieved in the absence of stabilizer. Moreover, the reduction strongly depends on the ligand size and its propensity for hydrophobic interactions. Apart from that, a high degree of particle aggregation was observed with Pluronic concentrations below 0.1% (w/v). Thus, a compromise has to be found, which combines sufficient stability with the best possible ligand coupling efficiency. For the studied system, 0.1% (w/v) turned out to be the optimum concentration of Pluronic F68.

Formation and cross-linking of fibrinogen layers monitored with in situ spectroscopic ellipsometry

Thick matrices of fibrinogen with incorporation of a matrix metalloproteinase inhibitor were covalently bonded on functionalized silicon surfaces using an ethyl-3-dimethyl-aminopropyl-carbodiimide and N-hydroxy-succinimide affinity ligand coupling chemistry. The growth of the structure was followed in situ using dynamic ellipsometry and characterized at steady-state with spectroscopic ellipsometry. The growth was compared with earlier work on ex situ growth of fibrinogen layers studied by single wavelength ellipsometry. It is found that in situ growth and ex situ growth yield different structural properties of the formed protein matrix. Fibrinogen matrices with thicknesses up to 58 nm and surface mass densities of 1.6 μg/cm 2 have been produced.

Mechanism of the cobalt-catalyzed carbonylation of ethyl diazoacetate

Carbonyl cobalt complexes serve as catalysts or catalyst precursors for the facile and selective transformation of primary diazoalkanes into the corresponding ketene. The mechanism of this carbonylation reaction has been elucidated in the case of ethyl diazoacetate as model diazoalkane using octacarbonyl dicobalt as the catalyst precursor. Dinuclear cobalt complexes having ethoxycarbonylcarbene ligand(s) in bridging position(s) have been identified as active intermediary of the catalytic cycles and their relevant chemical properties have been explored. Key step of the carbonylation is the formation of the highly reactive ethoxycarbonylketene by intramolecular coupling of a carbonyl ligand with the ethoxycarbonylcarbene ligand. DFT calculations reveal that the ketene formation takes place via a rapid coupling of the carbene ligand with one terminal CO followed by coordination of an external carbon monoxide and by a facile intramolecular rearrangement and ketene elimination. The ethoxycarbonylketene can be in situ trapped by OH, NH, or CH acid compounds or by N-substituted imines. In the presence of ethanol diethyl malonate is the only product of the catalytic carbonylation of ethyl diazoacetate. On the bases of the kinetics of the composing steps of the catalytic cycles, localization of the rate-determining step(s) under various reaction conditions has been made.

Removal of heavy metals from solution using biocompatible polymers

Well characterised, hydrophobic, poly(vinylidene fluoride) and poly(sulfone) membranes, a physisorbed amphiphillic surfactant as an affi nity linker with covalently attached bio-specific ligands to demonstrate heavy metal ion binding and re-use is reported. Central to this technology are the easy to manufacture membranes and a biocompatible Pluronic™ surfactant that serves multiple functions, where it acts not only as an affi nity linker, preventing non-specific protein adsorption to the membrane surface but also non-covalently hydrophilises the membrane matrix. This work describes the fabrication and characterisation of non-porous, hydrophobic membranes for the attachment of a robust, bio-compatible ligand, in order to specifically chelate divalent cations (Cd2+, Ni2+, Zn2+, Cu+) and subsequently, histidine tagged proteins. These affi nity tags are frequently used by bioengineers and biochemists to produce recombinant enzymes, peptides, hormones and antibodies. Successful coupling of ligands to Pluronic was achieved followed by quantifi cation of the ligand binding sites on the surface. This technology is scalable (due to the multi-variant membrane module design), able to resist non-specific protein adsorption and can be regenerated and re-used (up to five times) with a simple anionic surfactant solution.

ChemInform Abstract: Selective Oxidative Ligand Coupling of Organoborates Bearing an Alkynyl Group.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Selective Oxidative Ligand Coupling of Organoborates Bearing an Alkynyl Group

Abstractmagnified imageSelective oxidative ligand coupling of alkynyl(triaryl)borates was achieved by treatment with ethoxyvanadyl dichloride [VO(OEt)Cl2] to form the spsp2 carbon‐carbon bond. A one‐pot procedure through the in situ preparation of the borate was demonstrated using triphenylborane and 1‐ethynyl‐4‐methoxybenzene.

Targeting of the β 2-adrenoceptor increases nonviral gene delivery to pulmonary epithelial cells in vitro and lungs in vivo

Coupling of targeting ligands to polyethylenimine (PEI) has been previously used to improve transfection efficiency of PEI gene vectors. Here, we show that the β 2-adrenoceptor (β 2-AR) agonist, clenbuterol (Clen), can be used to improve gene transfer efficiency of PEI gene vectors on alveolar epithelial cells in vitro and in the lungs of mice in vivo. Clenbuterol conjugated to fluorescein-labeled bovine serum albumin resulted in clenbuterol-specific cellular uptake predominantly into alveolar but not bronchial epithelial cells. Clen- g-PEI (4/1) conjugates were combined with increasing molar ratios of PEI for transfection. At optimized PEI- g-Clen/PEI composition, transfection efficiency on alveolar epithelial cells was up to 14-fold higher than for unmodified PEI and could be inhibited by an excess of free clenbuterol. No increase of transfection efficiency was observed on bronchial epithelial cells. Increasing the PEI- g-Clen/PEI molar ratio resulted in an increase of gene vector size, decrease of the zeta potential and cytotoxicity. Aerosol delivery of optimized PEI- g-Clen/PEI (1/5) gene vectors resulted in a significant 3-fold increase of gene expression in the lungs of mice compared with unmodified PEI gene vectors. We suggest that coupling of β 2-adrenoceptor ligands to nonviral gene vectors represents a promising approach to improve gene delivery to the lungs.

Electrochemistry of ruthenium(ii) complexes of 8-aminoquinoline

Oxidation of [Ru(NH(2)Q)(3)](2+) (NH(2)Q = 8-aminoquinoline) results in intermolecular coupling of 8-aminoquinoline ligands to yield an electroactive polymer. Oxidative polymerization is not observed for [Ru(bpy)(2)(NH(2)Q)](2+) (bpy = 2,2'-bipyridine), where only one 8-aminoquinoline ligand is present.