Showing papers on "Denticity published in 2009"
TL;DR: In this paper, a full literature account is given on work describing the transition-metal catalyzed vinyl or addition polymerization to polynorbornene covering the years of 2001 to the beginning of 2008.
312 citations
TL;DR: In this paper, a comprehensive review of homoleptic transition metal complexes of bulky bidentate N-aryl-o-iminoquinonato type ligands involving comparison with o-quinonato analogues is presented.
299 citations
TL;DR: A new type of carbonylation of the ortho C-H bonds in aromatic amides 1, in which the pyridin-2-ylmethylamino moiety functions as a bidentate directing group, can be achieved.
Abstract: A new type of carbonylation of the ortho C−H bonds in aromatic amides 1, in which the pyridin-2-ylmethylamino moiety functions as a bidentate directing group, can be achieved The presence of ethylene as a hydrogen acceptor and also of H2O, probably for the generation of an active catalytic species, is required A wide variety of functional groups, including methoxy, amino, ester, ketone, cyano, chloro, and even bromo substituents, can be substituted for aromatic amides The complex 9 was isolated by the stoichiometric reaction of 1b and Ru3(CO)12, in which 1b binds to one Ru atom in the expected N,N fashion and the carbonyl oxygen binds to the other Ru atom as an O donor
236 citations
TL;DR: In this paper, surface modification of nanocrystalline TiO2 particles (45 A) with bidentate benzene derivatives, that is, 2-hydroxybenzoic acid, 2,5-dihydroxy benzoic amino acid, 3,4-dhydroxy benzene acid, and catechol was found to alter optical properties of nanoparticles.
Abstract: Surface modification of nanocrystalline TiO2 particles (45 A) with bidentate benzene derivatives, that is, 2-hydroxybenzoic acid, 2,5-dihydroxybenzoic acid, 2,3-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, and catechol was found to alter optical properties of nanoparticles. The formation of the inner-sphere charge transfer (CT) complexes results in a red shift of the semiconductor absorption compared to unmodified nanocrystallites. The binding structures were investigated by using FTIR spectroscopy. The investigated ligands have the optimal geometry for chelating surface Ti atoms, resulting in ring coordination complexes (catecholate or salycilate type of binuclear bidentate binding), thus restoring six-coordinated octahedral geometry of surface Ti atoms. From the Benesi−Hildebrand plot, the stability constants at pH 2 of the order 103 M−1 have been determined.
207 citations
TL;DR: An exceedingly sterically demanding, rigid, and chiral NHC ligand was prepared and structurally characterized, and the ability to use aryl chloride substrates in intramolecular palladium-catalyzed alpha-arylations reveals its unique reactivity.
Abstract: An exceedingly sterically demanding, rigid, and chiral NHC ligand, IBiox[(−)-menthyl] (1), was prepared and structurally characterized With a buried volume of ∼50%, this ligand arguably represents one of the most sterically demanding monodentate ligands The ability to use aryl chloride substrates in intramolecular palladium-catalyzed α-arylations reveals its unique reactivity Moreover, C2-symmetric 1 allows the highly enantioselective formation of oxindoles with up to 99% ee
187 citations
TL;DR: The dependence of the denticity and geometry of pyridine-2,6-dicarboxylate, as well as of the composition of Pydc-containing complexes, was studied as a function of the nature of the A atom, the molar ratio Pyd c:A and the presence of neutral or acidic ligands in the reaction mixture.
Abstract: Compounds (299) containing 494 symmetrically independent pyridine-2,6-dicarboxylate moieties have been investigated. Among them the structures of Na(3)[Nd(Pydc)(3)].14H(2)O and Na(3)[Er(Pydc)(3)].11.5H(2)O, where H(2)Pydc is pyridine-2,6-dicarboxylic acid, were determined by single-crystal X-ray diffraction, while the others were taken from the Cambridge Structural Database. The characteristics of any complex by means of the ;method of crystallochemical analysis' are described, and the coordination types of all the Pydc ions and crystallochemical formulae of all the compounds were determined. Although the ion can act as a mono-, bi-, tri-, tetra- and pentadentate ligand, 96% of Pydc ions are coordinated to the central A atom in the tridentate-chelating mode. The dependence of the denticity and geometry of pyridine-2,6-dicarboxylate, as well as of the composition of Pydc-containing complexes, was studied as a function of the nature of the A atom, the molar ratio Pydc:A and the presence of neutral or acidic ligands in the reaction mixture.
149 citations
TL;DR: It is found that overall ligands presenting higher coordination numbers (dithiolane) exhibit much better stability to excess added salt and against competition from DTT compared to their monodentate counterparts.
Abstract: The colloidal stability of gold nanoparticles (AuNPs) cap-exchanged with either monothiol- or dithiolane-terminated PEG-OCH3 ligands was investigated. Three distinct aspects were explored: (1) effects of excess salt concentration; (2) ligation competition by dithiothreitol (DTT); and (3) resistance to sodium cyanide digestion. We found that overall ligands presenting higher coordination numbers (dithiolane) exhibit much better stability to excess added salt and against competition from DTT compared to their monodentate counterparts. Resistance to NaCN digestion indicated that there is a balance between coordination number and density of ligand packing on the NP surface. For smaller NPs, where a larger surface curvature reduces the ligand packing density, a higher coordination number is clearly beneficial. In comparison, a higher ligand density allowed by the smaller curvature for larger nanocrystals makes monothiol−PEG-capped NPs more resistant to cyanide digestion. The present study indicates that balanc...
141 citations
TL;DR: Bis-acyl-/aroyl-hydrazones can be divided into two basic structural categories: those derived from a dihydrazide and those that are derived from dialdehyde (or diketone).
132 citations
TL;DR: A series of ruthenium(II) complexes have been prepared by using bidentate chelating N-heterocyclic carbene (NHC) ligands that feature different donor groups as mentioned in this paper.
124 citations
TL;DR: Preliminary results on the use of these complexes as initiators for the polymerisation of rac-lactide are reported, and suggest different initiation mechanisms are occurring for the two metals, in agreement with the different silylation reactivity observed.
Abstract: The synthesis of magnesium and zinc complexes of bidentate anionic alkoxide ligands with saturated-backbone carbene groups is reported. Mono(ligand) and bis(ligand) complexes [M(LR)N″]2 and [M(LR)2] (M = Mg, Zn, N″ = N(SiMe3)2, LR = [OCMe2CH2{CNCH2CH2NR}] R = iPr, Mes, Dipp) have been isolated, and some structurally characterised and compared with the new unsaturated carbene complex [Mg(L)2]. Reactions with silyl halides show either addition across the metal carbene bond, or across the metal alkoxide bond, in accordance with the metals’ electronegativity difference: the metal alkoxide bonds are stronger for MgII complexes, for which the carbene is silylated to form zwitterionic [MgI(Me3SiLR)N″] (Me3SiLR = OCMe2CH2{Me3SiCNCH2CH2NR}) while the metal-bound alkoxide group is silylated in the ZnII complexes forming [ZnI(Me3SiOLR)N″] (Me3SiOLR = Me3SiOCMe2CH2{CNCH2CH2NR}). The proligand [HLR] is silylated at the alcohol group, forming the iodide salt [Me3SiOCMe2CH2{HCNCH2CH2NR}]I.Preliminary results on the use of these complexes as initiators for the polymerisation of rac-lactide are reported, and suggest different initiation mechanisms are occurring for the two metals, in agreement with the different silylation reactivity observed. The polymerisation reactions are facile at room temperature even without an initiator, and yield polymers of reasonable molecular weight and heterotacticity and with good PDI. These are the first magnesium NHC complexes demonstrated to effect lactide polymerisation.Also, an adduct instead of the anticipated potassium alkoxycarbene is generated from the reaction of the proligand [HLR] with potassium amide KN″; this has been structurally characterised.
113 citations
TL;DR: Indium trichloride, benzyl alcohol, and triethylamine generate a catalyst in situ for the room temperature polymerization of D,L- lactide affording highly heterotactic polylactide of controlled molecular weight and narrow molecular weight distribution.
TL;DR: In this article, the cytotoxic activity of diamine bis(phenolato) ligands was investigated with three families of Ti(IV) complexes and the potential connection between cytotoxicity and hydrolytic behavior was found.
TL;DR: In this article, a bulky ligand, 2,3,6,7-anthracenetetracarboxylic acid (H4ata), was used to react with ZnII ions under different conditions, yielding four new coordination polymers.
Abstract: In our efforts to investigate polydentate ligands bearing bulky backbones, we used a bulky ligand, 2,3,6,7-anthracenetetracarboxylic acid (H4ata), to react with ZnII ions under different conditions, yielding four new coordination polymers, {[Zn(ata)0.5(DMF)(H2O)]·DMF·H2O}n (1), {[Zn(ata)0.5(4,4′-bipy)0.5(DMF)]·DMF}n (2), {[Zn(ata)0.5(azpy)0.5(DMF)]·DMF}n (3), and {[Zn(ata)0.5(4,4′-bipy)(DMAC)]·(DMA)0.5}n (4) (DMF = N,N-dimethylformamide, 4,4′-bipy = 4,4′-bipyridine, azpy = 4,4′-azopyridine, DMAC = N,N-dimethylacetamide, DMA = dimethylamine), which were characterized by IR and single crystal X-ray diffraction. Complex 1 forms a two-dimensional (2D) network with (4,4) topology assembled by ata4− ligands and ZnII ions. Complexes 2 and 3 are three-dimensional (3D) frameworks with {83}2{85;10} topology containing infinite 2D networks pillared by 4,4′-bipy and azpy, respectively. Complex 4 takes a 2D structure with (4,4) net containing infinite one-dimensional chains constructed by ZnII ions with 4,4′-bipy and ...
TL;DR: Interestingly, the [VIVO(SAA)(bpy)] complex selectively inhibits PTP1B over the other two phosphatases (approximate ninefold selectivity against SHP-1 and about twofold selectivities against TCPTP).
Abstract: A series of oxovanadium complexes with mixed ligands, a tridentate ONO-donor Schiff base ligand [viz., salicylidene anthranilic acid (SAA)], and a bidentate NN ligand [viz., 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), dipyrido[3,2-a:2',3'-c]phenazine (dppz), or 7-methyldipyrido[3,2-a:2',3'-c]phenazine (dppm)], have been synthesized and characterized by elemental analysis, electrospray ionization mass spectrometry, UV-vis spectroscopy, Fourier transform IR spectroscopy, EPR spectroscopy, and X-ray crystallography. Crystal structures of both complexes, [V(IV)O(SAA)(bpy)].0.25bpy and [V(IV)O(SAA)(phen)].0.33H(2)O, reveal that oxovanadium(IV) is coordinated with one nitrogen and two oxygen atoms from the Schiff base and two nitrogen atoms from the bidentate planar ligands, in a distorted octahedral geometry (VO(3)N(3)). The oxidation state of V(IV) with d(1) configuration was confirmed by EPR spectroscopy. The speciation of VO-SAA-bpy in aqueous solution was investigated by potentiomtreic pH titrations, and the results revealed that the main species are two ternary complexes at a pH range of 7.0-7.4, and one is the isolated crystalline complex. The complexes have been found to be potent inhibitors against human protein tyrosine phosphatase 1B (PTP1B) (IC(50) approximately 30-61 nM), T-cell protein tyrosine phosphatase (TCPTP), and Src homology phosphatase 1 (SHP-1) in vitro. Interestingly, the [V(IV)O(SAA)(bpy)] complex selectively inhibits PTP1B over the other two phosphatases (approximate ninefold selectivity against SHP-1 and about twofold selectivity against TCPTP). Kinetics assays suggest that the complexes inhibit PTP1B in a competitive and reversible manner. These suggest that the complexes may be promising candidates as novel antidiabetic agents.
TL;DR: This series of azido complexes demonstrates that the flexibility of the dpa ligand plays an important role in directing the structures of the final products.
Abstract: By employing a flexible molecule, 2,2′-dipyridylamine (dpa), as a bidentate coligand, three azide-bridged one-dimensional coordination polymers, [M(dpa)(N3)2]n (M = Cu, 1·Cu; Co, 2·Co) and [Ni(dpa)(OAc)0.5(N3)1.5(H2O)]n (3·Ni), have been successfully synthesized and structurally and magnetically characterized. They show versatile one-dimensional chain structures. 1·Cu is an EO-N3 bridged uniform chain; 2·Co is an alternative chain linked by two EO-N3 and two EE-N3 bridges. Interestingly, 3·Ni is a zigzag chain linked alternatively by one EE-N3 and a novel 3-fold bridge, which is composed of two EO-N3 and one acetate group. This series of azido complexes demonstrates that the flexibility of the dpa ligand plays an important role in directing the structures of the final products. Magnetic studies reveal dominant intrachain antiferromagnetic couplings in compound 1·Cu. Compounds 2·Co and 3·Ni are weak ferromagnets due to the spin canting, with critical temperatures of 12.4 and 32.5 K, respectively.
TL;DR: Three new solid complexes have been synthesized by the reaction of rare earth(III) nitrate with the first ligand curcumin (HL) and the second ligand 1,10-phenanthroline-5,6-dione (L') in alcohol solution and it was found that the cleavage process of plasmid DNA was sensitive to pH, however, adding radical scavengers almost had no effect on the DNA cleavage reaction.
TL;DR: The stereochemistry of ten-coordinate rare-earth and transition-metal compounds is studied from the point of view of continuous shape measures (CShM) and derived tools and some ligand topologies are seen to consistently favor usually neglected ideal polyhedra, such as the capped trigonal cupola.
Abstract: The stereochemistry of ten-coordinate rare-earth and transition-metal compounds is studied from the point of view of continuous shape measures (CShM) and derived tools. A total of 19 ideal ten-vertex polyhedra belonging to 12 different symmetry point groups have been considered, from which nine are retained for the description of the stereochemistries of all studied compounds. The structures of the coordination spheres are analyzed by families, according to the denticity and topology of the ligands. Some ligand topologies are seen to consistently favor usually neglected ideal polyhedra, such as the capped trigonal cupola.
TL;DR: The complex [(p-cym)Ru(bpm)(py)][PF(6)](2) is the first ruthenium(ii) arene complex that can selectively photodissociate a monodentate ligand (py) when excited with visible light and form a reactive aqua derivative able to bind to a DNA base.
TL;DR: In this article, the O,P-type phosphinophenol ligands were found to readily react with 1 equiv of AlMe3 to afford in high yields the corresponding Al chelate complexes.
TL;DR: The synthesis of a variety of 2-(1H-1,2,3-triazol-4-yl)-pyridines by click chemistry is demonstrated to provide straightforward access to mono-functionalized ligands, highlighting the synthetic potential of this class of bidentate ligands with respect to polymer chemistry or the attachment onto surfaces and nanoparticles.
Abstract: The synthesis of a variety of 2-(1H-1,2,3-triazol-4-yl)-pyridines by click chemistry is demonstrated to provide straightforward access to mono-functionalized ligands. The ring-opening polymerization of epsilon-caprolactone initiated by such a mono-functionalized ligand highlights the synthetic potential of this class of bidentate ligands with respect to polymer chemistry or the attachment onto surfaces and nanoparticles. The coordination to Ru(II) ions results in homoleptic and heteroleptic complexes with the resultant photophysical and electrochemical properties strongly dependent on the number of these ligands attached to the Ru(II) core.
TL;DR: In this article, four new solvent-induced Cu(II) complexes with the chemical formulae [{Cu(HL)(CH3OH)2Cu]· CH3OH (1), [{(CU(HL))2(CH3CH2CH 2CH2OH) 2}Cu] (2), [CuL(H2O)}2Cu2]· 2CH3 CH2CH2H2OH (3) and [(CUH2C 2C2C2O] (4), where H4L = 6
TL;DR: Thermodynamic and kinetic stability data are determined for the formation of complexes with AAZTA and the lanthanoid metal ions, and other divalent metal ions of interest for this application, allowing its potentially safe use as contrast agent in magnetic resonance imaging.
Abstract: The heptadentate ligand 1,4-bis(hydroxycarbonylmethyl)-6-[bis(hydroxycarbonylmethyl)]amino-6-methylperhydro-1,4-diazepine (AAZTA) and its derivatives were recently reported to give stable complexes with Gd(3+) with superior efficiency as MRI contrast agents. Nevertheless, only preliminary data are available on the coordination behavior of this interesting ligand. In this work, thermodynamic and kinetic stability data are determined for the formation of complexes with AAZTA and the lanthanoid metal ions, and other divalent metal ions of interest for this application. The AAZTA ligand binds the lanthanoid ions with log K(ML) values of 17.53-21.85 with its affinity steadily increasing from La(3+) to Lu(3+), suggesting that the seven-membered skeleton is better suited to accommodate smaller metal ions. Even though the denticity is lower, the stability of the heavier lanthanoid complexes is comparable to those of the classical ligand diethylenetriaminepentaacetic acid (DTPA). The transmetalation reactions of [Gd(AAZTA)](-) with Cu(2+) and Eu(3+) predominantly occur through proton-assisted dissociation of the complex. The role of the direct attack of Cu(2+) or Eu(3+) in the exchange reactions is limited, although the formation of dinuclear complexes decreases the proton-assisted dissociation. Near physiological conditions, [Gd(AAZTA)](-) is significantly more inert than [Gd(DTPA)](2-), allowing its potentially safe use as contrast agent in magnetic resonance imaging.
TL;DR: The new scorpionate complexes 3 and 4 are shown to act as catalyst precursors for the peroxidative oxidation ofcyclohexane to cyclohexanol and cyclo hexanone, under mild conditions (at room temperature and using an aqueous solution of H2O2) reaching TON values up to 186 in NCMe/H2O.
Abstract: Reactions between CuCl2 and the functionalized scorpionate 2,2,2-tris(1-pyrazolyl)ethanol HOCH2C(pz)31 (pz = pyrazolyl) or 2,2,2-tris(1-pyrazolyl)ethyl methanesulfonate CH3SO2OCH2C(pz)32 yield the corresponding water soluble CuII complexes [CuCl2{HOCH2C(pz)3}] 3 or [CuCl2{CH3SO2OCH2C(pz)3}]24. In 3 the scorpionate ligand shows the typical N,N,N-coordination mode, whereas in the dinuclear complex 4 it binds the metal as a bidentate species. Compounds 1-4 have been characterized by IR, far-IR, elemental analysis and (for 2-4) single crystal X-ray diffraction. The new scorpionate complexes 3 and 4 are shown to act as catalyst precursors for the peroxidative oxidation of cyclohexane to cyclohexanol (main product) and cyclohexanone, under mild conditions (at room temperature and using an aqueous solution of H2O2) reaching TON values up to 186 in NCMe/H2O. Their hydrosolubility allows them to operate also in pure aqueous media (without any organic solvent, although less effectively), a rare feature of significance towards a green alkane oxidation process.
TL;DR: In this article, a new multifunctional semirigid Schiff-base ligand comprising two pyridyl (Py) and two benzimidazolyl (Bim) donor groups, 1,2-bis, has been synthesized, with which 10 coordination polymers of different transition metal ions, namely, {[AgL]CF3SO3·CH3OH}n,
Abstract: A new multifunctional semirigid Schiff-base ligand comprising two pyridyl (Py) and two benzimidazolyl (Bim) donor groups, 1,2-bis(1-(1-(pyridine-3-ylmethyl)benzimidazol-2-yl)ethylidene)hydrazine (L), has been synthesized, with which 10 coordination polymers of different transition metal ions, namely, {[AgL]CF3SO3·CH3OH}n (1), {[Ag2L](p-CH3C6H4SO3)2·2CH3OH}n (2), {[Hg3LCl6]·CHCl3}n (3), [HgLBr2]n (4), {[CdL(CH3CO2)2H2O]·1.5H2O}n (5), [CdLI2]n (6), {[MnL(H2O)4](ClO4)2·H2O}n (7), [MnL(p-CH3C6H4SO3)2]n (8), {[ZnL2(CH3CN)2(H2O)2](CF3SO3)2}n (9), and {[ZnL2(CH3CH2OH)2(H2O)2](p-CH3C6H4SO3)2}n (10) have been prepared and characterized by elemental analyses, IR spectroscopy, powder X-ray diffraction, and single-crystal X-ray diffraction. In complexes 1, 2, and 3, L acts as a tetradentate ligand to connect four metal ions that show the same coordination environment in 1 or different coordination environments in 2 and 3, generating two-dimensional (2D) networks of the (4, 4) net topology. In complexes 4−8, L acts as...
TL;DR: Iridium(III) complexes with two ppy (ppy = 2-phenylpyridine) and one functionalized 2,2′-bipyridyl ligand containing a bidentate or terdentate binding group were synthesized, and their photophysical and luminescence sensing properties to heavy metal ions were studied as mentioned in this paper.
TL;DR: One-pot metal promoted reactions between salicylaldehyde and 4-methyl-1,3-phenylenediamine in the presence of metal salts acting as template agents yield zinc(II) Salicylaldimine complexes, which exhibit antimicrobial activity against Staphylococcus aureus in a minimum inhibitory concentration (MIC) experiment.
TL;DR: The perrhenate bound to Ln is included in the CB6 cavity, thus providing the first case of inclusion of a tetrahedral oxoanion in this macrocycle.
Abstract: The reaction of uranyl and lanthanide nitrates with cucurbit[6]uril (CB6) in the presence of perrhenic acid and under hydrothermal conditions yields the novel heterometallic uranyl-lanthanide molecular complexes [UO2Ln(CB6)(ReO4)2(NO3)(H2O)7](ReO4)2 (Ln = Sm, Eu, Gd, Lu). Both metal cations are bound to carbonyl groups of the same CB6 portal, one for UO22+ and two for Ln3+. The uranium atom is also bound to one monodentate perrhenate ion and three aquo ligands, while the lanthanide is bound to one monodentate perrhenate and one nitrate ions, and four aquo ligands. Not only are these complexes rare examples of ReO4− bonding to f element ions, but the perrhenate bound to Ln is included in the CB6 cavity, thus providing the first case of inclusion of a tetrahedral oxoanion in this macrocycle.
TL;DR: The results explain why aliphatic C-H donors are observed to function as competitive binding sites in solution and suggest that such C- H...anion contacts should be considered as possible contributors when evaluating the denticity of an anion receptor.
Abstract: Electronic structure calculations, MP2/aug-cc-pVDZ, are used to determine C-H...Cl- hydrogen bond energies for a series of XCH3 donor groups in which the electron-withdrawing ability of X is varied over a wide range of values. When attached to polarizing substituents, aliphatic CH groups are moderate-to-strong hydrogen bond donors, exhibiting interaction energies comparable to those obtained with O-H and N-H groups. The results explain why aliphatic C-H donors are observed to function as competitive binding sites in solution and suggest that such C-H...anion contacts should be considered as possible contributors when evaluating the denticity of an anion receptor.
TL;DR: Comparison of the details of the compound structures, their DNA binding, and their toxicity allows the exploration of structure–activity relationships that might be used to guide optimization of the activity of agents of this class of compounds.
Abstract: Various interaction modes between a group of six ruthenium polypyridyl complexes and DNA have been studied using a number of spectroscopic techniques. Five mononuclear species were selected with formula [Ru(tpy)L1L2](2−n)+, and one closely related dinuclear cation of formula [{Ru(apy)(tpy)}2{μ-H2N(CH2)6NH2}]4+. The ligand tpy is 2,2′:6′,2″-terpyridine and the ligand L1 is a bidentate ligand, namely, apy (2,2′-azobispyridine), 2-phenylazopyridine, or 2-phenylpyridinylmethylene amine. The ligand L2 is a labile monodentate ligand, being Cl−, H2O, or CH3CN. All six species containing a labile L2 were found to be able to coordinate to the DNA model base 9-ethylguanine by 1H NMR and mass spectrometry. The dinuclear cationic species, which has no positions available for coordination to a DNA base, was studied for comparison purposes. The interactions between a selection of four representative complexes and calf-thymus DNA were studied by circular and linear dichroism. To explore a possible relation between DNA-binding ability and toxicity, all compounds were screened for anticancer activity in a variety of cancer cell lines, showing in some cases an activity which is comparable to that of cisplatin. Comparison of the details of the compound structures, their DNA binding, and their toxicity allows the exploration of structure–activity relationships that might be used to guide optimization of the activity of agents of this class of compounds.
TL;DR: The vanadyl complex exhibited excellent in vitro anti-tumor activity against leukemia comparable to that of cisplatin, inducing cell death by apoptosis with IC(50) values in the micromolar range.