Showing papers on "Denticity published in 2010"
TL;DR: The experimental data suggest that mefenamic acid acts as deprotonated monodentate ligand coordinated to Co(II) ion through a carboxylato oxygen as well as showing good binding propensity to human or bovine serum albumin protein having relatively high binding constant values.
Abstract: Cobalt(II) complexes with the non-steroidal anti-inflammatory drug mefenamic acid in the presence or absence of nitrogen donor heterocyclic ligands (2,2′-bipyridine, 1,10-phenanthroline or pyridine) have been synthesized and characterized with physicochemical and spectroscopic techniques. The experimental data suggest that mefenamic acid acts as deprotonated monodentate ligand coordinated to Co(II) ion through a carboxylato oxygen. The crystal structures of tetrakis(methanol)bis(mefenamato)cobalt(II), 1 and (2,2′-bipyridine)bis(methanol)bis(mefenamato)cobalt(II), 2 have been determined by X-ray crystallography. The EPR spectra of complexes 1 and 2 in frozen solution reveal that they retain their structures. UV study of the interaction of the complexes with calf-thymus DNA (CT DNA) has shown that the complexes can bind to CT DNA and bis(methanol)bis(pyridine)bis(mefenamato)cobalt(II) exhibits the highest binding constant. Competitive study with ethidium bromide (EB) has shown that the complexes can displace the DNA-bound EB indicating that they bind to DNA in strong competition with EB. The cyclic voltammograms of the complexes recorded in dmso solution and in the presence of CT DNA in 1 : 2 dmso : buffer (containing 150 mM NaCl and 15 mM trisodium citrate at pH 7.0) solution have shown that they can bind to CT DNA by the intercalative binding mode. Mefenamic acid and its cobalt(II) complexes exhibit good binding propensity to human or bovine serum albumin protein having relatively high binding constant values. The antioxidant activity of the compounds has been evaluated indicating their high scavenging activity against hydroxyl free radicals and superoxide radicals.
210 citations
TL;DR: Bacterial activity of acyl-hydrazone and its complexes were studied against gram-positive bacteria: Staphylococcus aureus, Bacillus subtilis and gram-negative bacteria: Pseudomonas aeruginosa, Escherichia coli by using minimum inhibitory concentrations (MICs) method.
205 citations
TL;DR: The new luminescent PMMA-doped Eu(CPFHP)(3)(DDXPO) complex shows considerable promise for polymer light-emitting diode and active polymer optical fiber applications.
Abstract: A novel efficient antenna complex of Eu3+ [Eu(CPFHP)3(DDXPO)] supported by a highly fluorinated carbazole-substituted β-diketonate ligand, namely, 1-(9H-carbazol-2-yl)-4,4,5,5,5-pentafluoro-3-hydroxypent-2-en-1-one (CPFHP) and the 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene oxide (DDXPO) ancillary ligand, has been synthesized, structurally characterized, and its photoluminescent behavior examined. The single-crystal X-ray diffraction analysis of Eu(CPFHP)3(DDXPO) revealed that this complex is mononuclear, and that the central Eu3+ ion is surrounded by eight oxygen atoms, six of which are provided by the three bidentate β-diketonate ligands. The remaining two oxygen atoms are furnished by the chelating phosphine oxide ligand. The coordination polyhedron is best described as that of a distorted square antiprism. The photophysical properties of Eu(CPFHP)3(DDXPO) benefit from adequate protection of the metal by the ligands with respect to non-radiative deactivation as well as an efficient ligand-to-metal ...
192 citations
TL;DR: In this paper, a one pot, multi-component CuAAC reaction has been developed for the generation of alkyl, benzyl or aryl substituted bi and tridentate pyridyl-1,2,3-triazole ligands from their corresponding halides, sodium azide and alkynes in excellent yields.
158 citations
TL;DR: The ligand exchange reaction is incomplete, although a strong optical activity is induced to the resulting clusters, and the monodentate thiophenol exchange was found to be faster, and more ligands were exchanged when compared to BINAS.
Abstract: The thiolate-for-thiolate ligand exchange reaction between the stable Au38(2-PET)24 and Au40(2-PET)24 (2-PET: 2-phenylethanethiol) clusters and enantiopure BINAS (BINAS: 1,1′-binaphthyl-2,2′-dithiol) was investigated by circular dichroism (CD) spectroscopy in the UV/vis and MALDI mass spectrometry (MS). The ligand exchange reaction is incomplete, although a strong optical activity is induced to the resulting clusters. The clusters are found to be relatively stable, in contrast to similar reactions on [Au25(2-PET)18]− clusters. Maximum anisotropy factors of 6.6 × 10−4 are found after 150 h of reaction time. During the reaction, a varying ratio between Au38 and Au40 clusters is found, which significantly differs from the starting material. As compared to Au38, Au40 is more favorable to incorporate BINAS into its ligand shell. After 150 h of reaction time, an average of 1.5 and 4.5 BINAS ligands is found for Au38 and Au40 clusters, respectively. This corresponds to exchange of 3 and 9 monodentate 2-PET ligan...
151 citations
TL;DR: The carbon azides capable of binding to the catalytic copper center at the alkylated azido nitrogen in a chelatable fashion were indeed shown to be superior substrates under the reported conditions and led to the hypothesis of an additional effect of chelating azides on the efficiencies of Cu(OAc)(2)-accelerated AAC reactions, which is to facilitate the rapid reduction ofCu(II) to highly catalytic Cu(I) species.
Abstract: We described in a previous communication a variant of the popular Cu(I)-catalyzed azide-alkyne cycloaddition (AAC) process where 5 mol % of Cu(OAc)(2) in the absence of any added reducing agent is sufficient to enable the reaction. 2-Picolylazide (1) and 2-azidomethylquinoline (2) were found to be by far the most reactive carbon azide substrates that convert to 1,2,3-triazoles in as short as a few minutes under the discovered conditions. We hypothesized that the abilities of 1 and 2 to chelate Cu(II) contribute significantly to the observed high reaction rates. The current work examines the effect of auxiliary ligands near the azido group other than pyridyl for Cu(II) on the efficiency of the Cu(OAc)(2)-accelerated AAC reaction. The carbon azides capable of binding to the catalytic copper center at the alkylated azido nitrogen in a chelatable fashion were indeed shown to be superior substrates under the reported conditions. The chelation between carbon azide 11 and Cu(II) was demonstrated in an X-ray single-crystal structure. In a limited set of examples, the ligand tris(benzyltriazolylmethyl)amine (TBTA), developed by Fokin et al. for assisting the original Cu(I)-catalyzed AAC reactions, also dramatically enhances the Cu(OAc)(2)-accelerated AAC reactions involving nonchelating azides. This observation leads to the hypothesis of an additional effect of chelating azides on the efficiencies of Cu(OAc)(2)-accelerated AAC reactions, which is to facilitate the rapid reduction of Cu(II) to highly catalytic Cu(I) species. Mechanistic studies on the AAC reactions with particular emphasis on the role of carbon azide/copper interactions will be conducted based on the observations reported in this work. Finally, the immediate utility of the product 1,2,3-triazole molecules derived from chelating azides as multidentate metal coordination ligands is demonstrated. The resulting triazolyl-containing ligands are expected to bind with transition metal ions via the N(2) nitrogen of the 1,2,3-triazolyl group to form nonplanar coordination rings. The Cu(II) complexes of bidentate T1 and tetradentate T6 and the Zn(II) complex of T6 were characterized by X-ray crystallography. The structure of [Cu(T1)(2)(H(2)O)(2)](ClO(4))(2) reveals the interesting synergistic effect of hydrogen bonding, π-π stacking interactions, and metal coordination in forming a one-dimensional supramolecular construct in the solid state. The tetradentate coordination mode of T6 may be incorporated into designs of new molecule sensors and organometallic catalysts.
145 citations
TL;DR: A rational design will be needed to tune the emission energies of the Pt(N( ∧)C(∧)N)X complexes over a wide range while maintaining their high luminescent efficiency.
Abstract: In order to investigate the ground state and excited state properties of Pt(N∧C∧N)X, we have prepared a series of Pt complexes, where N∧C∧N aromatic chelates are derivatives of m-di(2-pyridinyl)benzene (dpb) and X are monoanionic and monodentate ancillary ligands including halide and phenoxide. Facile synthesis of platinum m-di(2-pyridinyl)benzene chloride and its derivatives, using controlled microwave heating, was reported. This method not only shortened the reaction time but also improved the reaction yield for most of the Pt complexes. Two Pt(N∧C∧N)X complexes have been structurally characterized by X-ray crystallography. The change of functional group does not affect the structure of the core Pt(N∧C∧N)Cl fragment. Both molecules pack as head-to-tail dimers, each molecule of the dimer related to the other by a center of inversion. The electrochemical studies of all Pt complexes demonstrate that the oxidation process occurs on the metal-phenyl fragment and the reduction process is associated with the e...
131 citations
TL;DR: The Ni (II)Fe(II) complexes, lacking appropriate Ni-Fe-S cluster structures, are not site analogues, but their synthesis and reactivity provide the first demonstration that molecular Ni(II)...Fe( II) sites and bridges can be attained, a necessity in the biomimetic chemistry of C-clusters.
Abstract: A singular feature of the catalytic C-cluster of carbon monoxide dehydrogenase is a sulfide-bridged Ni...Fe locus where substrate is bound and transformed in the reversible reaction CO + H(2)O right harpoon over left harpoon CO(2) + 2H(+) + 2e(-). A similar structure has been sought in this work. Mononuclear planar Ni(II) complexes [Ni(pyN(2)(Me2))L](1-) (pyN(2)(Me2) = bis(2,6-dimethylphenyl)-2,6-pyridinedicarboxamidate(2-)) derived from a NNN pincer ligand have been prepared including L = OH(-) (1) and CN(-) (7). Complex 1 reacts with ethyl formate and CO(2) to form unidentate L = HCO(2)(-) (5) and HCO(3)(-) (6) products. A binucleating macrocycle was prepared which specifically binds Ni(II) at a NNN pincer site and five-coordinate Fe(II) at a triamine site. The Ni(II) macrocyle forms hydroxo (14) and cyanide complexes (15) analogous to 1 and 7. Reaction of 14 with FeCl(2) alone and with ethyl formate and 15 with FeCl(2) affords molecules with the Ni(II)-L-Fe(II) bridge unit in which L = mu(2):eta(1)-OH(-) (17) and mu(2):eta(2)-HCO(2)(-) (18) and -CN(-) (19). All bridges are nonlinear (17, 140.0 degrees ; 18, M-O-C 135.9 degrees (Ni), 120.2 degrees (Fe); 19, Ni-C-N 170.3 degrees , Fe-N-C 141.8 degrees ) with Ni...Fe separations of 3.7-4.8 A. The Ni(II)Fe(II) complexes, lacking appropriate Ni-Fe-S cluster structures, are not site analogues, but their synthesis and reactivity provide the first demonstration that molecular Ni(II)...Fe(II) sites and bridges can be attained, a necessity in the biomimetic chemistry of C-clusters.
125 citations
TL;DR: Newly synthesized phenol based novel Schiff base polydentate symmetric ligand and two complexes showed good biological activity against all tested bacteria and yeast strains.
125 citations
TL;DR: In this paper, two diphenylphosphine-substituted benzimidazoles featuring an ethylene or a methylene linker between the benzidazole and the phosphine have been prepared.
109 citations
TL;DR: An unusual Ni-/Cu-mediated alkyne homocoupling reaction, directed through the cavity of a bidentate macrocyclic ligand by chelated metal ions to furnish rotaxanes in excellent (up to 95%) yields is reported.
Abstract: We report on an unusual Ni-/Cu-mediated alkyne homocoupling reaction, directed through the cavity of a bidentate macrocyclic ligand by chelated metal ions to furnish [2]rotaxanes in excellent (up to 95%) yields. This is the first active metal template reaction to employ an octahedral coordination geometry metal ion, Ni(II), and the study provides some interesting mechanistic insights into the mixed bimetallic reaction mechanism. The mixed-metal catalyst system was discovered serendipitously when Cu(I) was added to a Ni(II)-catalyzed alkyne homocoupling reaction in an attempt to facilitate chloride−acetylide ligand exchange. The role of Cu(I) in the reaction is, in fact, quite different from that originally intended. The effectiveness of having both nickel and copper present can be rationalized by the nature of a π-activated, σ-bonded, bimetallic intermediate in which the substitution of Ni(II) for one Cu(I) ion in the classic bimetallic Glaser reaction mechanism apparently aids reductive elimination of th...
TL;DR: This expansion to 348 ligands captures known ligand space for this class of monodentate two-electron donor ligands well, and principal component analysis (PCA) of the descriptors are used to derive an improved map of ligandspace.
TL;DR: An integrated solution to catalyst discovery that combines a diversity-oriented ligand synthesis, a catalyst-generation process driven by self-assembly and, finally, a combinatorial iterative library deconvolution strategy to identify the optimal catalyst is reported.
Abstract: Monodentate ligands with complementary hydrogen bonding units can self-assemble to form pseudo-bidentate ligands. Here, a combinatorial approach to the synthesis and analysis of reactions using these ligands allows the rapid identification of the most suitable ligand pair for highly selective rhodium-catalysed asymmetric hydrogenation.
TL;DR: In this paper, Ferrocene-appended copper(II) complexes [Cu(Fc-tpyramid)B](B)](ClO4)2 (1−3) and [cu(Phtpy)(dppz)](Dppz)2 ·MeCN (3a·MeCN) were characterized by X-ray crystallography.
TL;DR: The resulting PAA-g-MEA capped water-soluble QDs with relatively small hydrodynamic diameters possess higher photoluminescence quantum yields than the initial hydrophobic QDs, extraordinary stability over extended periods of time and over a broad pH range (3-14), salt concentrations (up to saturated NaCl solution), and thermal treatment at 100 degrees C.
Abstract: We have designed and synthesized a multidentate polymer ligand used for water-solubilization of luminescent quantum dots (QDs). The synthesis of the multidentate ligand (PAA-g-MEA) was based on several thiol groups grafted to a linear polymer chain through a simple carboxy-amine coupling reaction between poly(acryl acid) (PAA) and mercaptoethylamine (MEA). Water-soluble QDs capped with these PAA-g-MEA ligands were prepared via ligand exchange from the original hydrophobic ones. The resulting PAA-g-MEA capped water-soluble QDs with relatively small hydrodynamic diameters possess higher photoluminescence quantum yields than the initial hydrophobic QDs, extraordinary stability over extended periods of time and over a broad pH range (3-14), salt concentrations (up to saturated NaCl solution), and thermal treatment at 100 degrees C.
TL;DR: Three new 4-benzyloxy benzoic acid derivatives have been employed as ligands for the support of six lanthanide coordination compounds with the aim of testing the influence of electron releasing (-OMe) or electron withdrawing (-NO(2)) substituents on the photophysical properties.
Abstract: Three new 4-benzyloxy benzoic acid derivatives [4-benzyloxy benzoic acid = HL1; 3-methoxy-4-benzyloxy benzoic acid = HL2; 3-nitro-4-benzyloxy benzoic acid = HL3] have been employed as ligands for the support of six lanthanide coordination compounds [Tb3+ = 1–3; Eu3+ = 4–6] with the aim of testing the influence of electron releasing (-OMe) or electron withdrawing (-NO2) substituents on the photophysical properties. The new complexes have been characterized by a variety of spectroscopic techniques and two of the Tb3+ complexes [1 and 2] have been structurally authenticated by single-crystal X-ray diffraction. Compounds 1 and 2 crystallize in the monoclinic space group P21/n and their molecular structures consist of homodinuclear species that are bridged by two oxygen atoms from two benzoate ligands. In the case of 1, the carboxylate ligands coordinate to the central Tb3+ ion in bidentate chelating and bidentate bridging modes. By contrast, three different coordination modes (bidentate chelating, bidentate bridging and monodentate) are observed in the case of compound 2. Examination of the packing diagrams for 1 and 2 revealed the presence of a one-dimensional molecular array that is held together by intermolecular hydrogen-bonding interactions. The incorporation of an electron-releasing substituent on position 3 of 4-benzyloxy benzoic acid increases the electron density of the ligand and consequently improves the photoluminescence of the Tb3+ complexes. On the other hand, the presence of an electron-withdrawing group at this position dramatically decreases the overall sensitization efficiency of the Tb3+-centered luminescence due to dissipation of the excitation energy by means of a π*-n transition of the NO2 substituent along with the participation of the ILCT bands. The weaker photoluminescence of the Eu3+ complexes is attributable to the poor match of the triplet energy levels of the 4-benzyloxy benzoic acid derivatives with that of the emitting level of the central metal ion.
TL;DR: In this article, first principles molecular dynamics simulations based on the density functional theory and the Car-Parrinello method were used to study the structures and dynamics of the hydrated Mg(2+) ion and of the solvated MgHCO(3)(+) and MgCO(4) complexes in aqueous solution.
Abstract: We report first principles molecular dynamics simulations based on the density functional theory and the Car-Parrinello method to study the structures and dynamics of the hydrated Mg(2+) ion and of the solvated MgHCO(3)(+) and MgCO(3) complexes in aqueous solution. According to these simulations, the first hydration shell of the hydrated magnesium ion consists of six water molecules, whereas in the solvated magnesium bicarbonate and magnesium carbonate complexes the Mg(2+) is mostly five-coordinated, which indicates that when coordinated to magnesium the HCO(3)(-) and CO(3)(2-) anions reduce its the coordination sphere. Our simulations show that the structures of the most stable monomers of magnesium bi-carbonate and magnesium carbonate in solution are Mg[eta(1)-HCO(3)](H(2)O)(4)(+) and Mg[eta(1)-CO(3)](H(2)O)(4), i.e. the preferred hydration number is four, while the (bi-)carbonate is coordinated to the magnesium in a monodentate mode. The analysis of the exchange processes of the water molecules in the first and second hydration shell of Mg(2+) shows that the HCO(3)(-) or CO(3)(2-) ligands affect the dynamics of the magnesium coordination spheres by making its hydration shell more "labile". Furthermore, molecular dynamics simulations of the non-associated Mg(2+)/Cl(-) pair in water suggest that, despite negligible differences in the coordination spheres of Mg(2+), the chloride anion has a significant influence on the water exchange rates in the second hydration shell of Mg(2+).
TL;DR: The ligand cleavage of the Os derivative was significantly slower than of its Ru analogue, which could explain its higher activity in in vitro anticancer assays.
Abstract: Hydroxypyr(id)ones are versatile ligands for the synthesis of organometallic anticancer agents, equipping them with fine-tunable pharmacological properties Herein, we report on the preparation, mode of action, and in vitro anticancer activity of Ru(II)- and Os(II)-arene complexes with alkoxycarbonylmethyl-3-hydroxy-2-pyridone ligands The hydrolysis and binding to amino acids proceed quickly, as characterized by NMR spectroscopy and ESI mass spectrometry However, the reaction with amino acids causes cleavage of the pyridone ligands from the metal center because the amino acids act as multidentate ligands A similar behavior was also observed during the reactions with the model proteins ubiquitin and cytochrome c, yielding mainly [protein + M(eta(6)-p-cymene)] adducts (M = Ru, Os) Notably the ligand cleavage of the Os derivative was significantly slower than of its Ru analogue, which could explain its higher activity in in vitro anticancer assays Furthermore, the reaction of the compounds to 5'-GMP was characterized and coordination to the N7 of the guanine moiety was demonstrated by (1)H NMR spectroscopy and X-ray diffraction analysis CDK2/Cyclin A protein kinase inhibition studies revealed potent activity of the Ru and Os complexes
TL;DR: In this paper, a novel Schiff base (HL = 3-(4′-ethylazomethinobenzene sulphonamide)-4-methoxy-1,2,5-thiadiazole) derived from condensation of sulphametrole and varelaldehyde is reported and characterized based on elemental analyses, IR, solid reflectance, magnetic moment, molar conductance, and thermal analysis.
TL;DR: In this article, five new coordination polymers were synthesized under hydrothermal conditions by reactions of corresponding Cd(II) or Zn(II)-clusters with the mixed multidentate ligands of 1,2,4,5-tetrakis(imidazol-1-ylmethyl)benzene (L) and 1,3-5-benzenetricarboxylic acid (H3BTC), 1, 3-5benzenetriacetic acid(H3BTA), and H4BTEC
Abstract: Five new coordination polymers, namely, [Cd(L)0.5(HBTC)]·0.2H2O (1), [Cd3(L)2(BTA)2(H2O)2]·H2O (2), [Cd2(L)0.5(BTEC)]·H2O (3), [Zn3(L)(BTC)2(H2O)2]·3H2O (4), and [Zn2(μ2-OH)(L)0.5(BTA)]·H2O (5) were synthesized under hydrothermal conditions by reactions of corresponding Cd(II) or Zn(II) salts with the mixed multidentate ligands of 1,2,4,5-tetrakis(imidazol-1-ylmethyl)benzene (L) and 1,3,5-benzenetricarboxylic acid (H3BTC), 1,3,5-benzenetriacetic acid (H3BTA), 1,2,4,5-benzenetetracarboxylic acid (H4BTEC), respectively. The complexes were characterized by single crystal X-ray diffraction, IR, and thermogravimetric and elemental analyses. The Cd(II) complex 1 is a two-dimensional (2D) network with infinite one-dimensional (1D) Cd-HBTC2− chains linked together by L ligands, while the Zn(II) complex 4 with the same mixed ligands has a three-dimensional (3D) structure. The Cd(II) complex with BTA3− and L ligands (2) features an unusual 3D framework, and the Zn(II) complex 5 shows a 3D structure with (63)2(42,84...
TL;DR: The initial surface chemistry and growth mechanisms of the atomic layer deposition (ALD) of metallic copper on SiO(2) surfaces are investigated using an amidinate precursor (copper(I) di-sec-butylacetamidinate, [Cu((s)Bu-amd)](2)) and molecular hydrogen.
Abstract: The initial surface chemistry and growth mechanisms of the atomic layer deposition (ALD) of metallic copper on SiO(2) surfaces are investigated using an amidinate precursor (copper(I) di-sec-butylacetamidinate, [Cu((s)Bu-amd)](2)) and molecular hydrogen. Using in situ Fourier transform infrared spectroscopy together with calculations based on density functional theory, we show that the initial surface reaction of [Cu((s)Bu-amd)](2) with hydroxylated SiO(2) takes place by displacement of one of the sec-butylacetamidinate ligands at a surface -OH site, thus forming a Si-O-Cu-((s)Bu-amd) surface species, evident by the stretching vibrations of Si-O-Cu and the chelating -NCN- bonds. Molecular hydrogen exposure during a subsequent pulse dissociates most of the sec-butylacetamidinate ligands bound to surface Cu, which releases free amidine vapor, leaving Cu atoms free to agglomerate on the surface and thus opening more reactive sites for the next [Cu((s)Bu-amd)](2) pulse. Copper agglomeration is evident in the IR absorbance spectra through the partial recovery of the intensity of SiO(2) optical phonon modes upon H(2) reduction, which was lost after the reaction of [Cu((s)Bu-amd)](2) with the initial SiO(2) surface. The thermally activated ligand rearrangement from a bridging to a monodentate structure occurs above 220 degrees C through hydrogenation of the ligand by surface hydroxyl groups after exposure to a [Cu((s)Bu-amd)](2) pulse. As Cu particles grow with further ALD cycles, the activation temperature is lowered to 185 degrees C, and hydrogenation of the ligand takes place after H(2) pulses, catalyzed by Cu particles on the surface. The surface ligand rearranged into a monodentate structure can be removed during subsequent Cu precursor or H(2) pulses. Finally, we postulate that the attachment of dissociated ligands to the SiO(2) surface during the [Cu((s)Bu-amd)](2) pulse can be responsible for carbon contamination at the surface during the initial cycles of growth, where the SiO(2) surface is not yet completely covered by copper metal.
TL;DR: Monomeric zinc silylamido and ethyl complexes bearing tetradentate aminophenolato ligands efficiently initiated the ring-opening polymerization of rac-lactide, and the polymerization runs were better controlled in the presence of isopropanol, giving atactic PLAs end-capped with isoprostyl ester and hydroxyl groups.
Abstract: Monomeric zinc silylamido and ethyl complexes bearing tetradentate aminophenolato ligands [(DNNO)ZnR] (D = NMe2, OMe; R = N(SiMe3)2 (1–5, 8), Et (6, 7, 9, 10)), were isolated from the reaction of Zn[N(SiMe3)2]2 or ZnEt2 and one equivalent of aminophenols {aryl-CH2N[(CH2)2NMe2]CH2-phenol} in moderate to high yields. The monomeric nature of these complexes was further confirmed by X-ray diffraction studies of silylamido complexes 1, 3 and ethyl complexes 7, 9, 10. The methoxy or N,N-dimethylamino group of the aryl unit does not coordinate with the metal center in the solid state, only the remaining three donors of the ligand and silylamido or ethyl group interact with zinc center constructing a distorted tetrahedral coordination geometry at the metal center. All these zinc complexes efficiently initiated the ring-opening polymerization of rac-lactide, and the polymerization runs were better controlled in the presence of isopropanol, giving atactic PLAs end-capped with isopropyl ester and hydroxyl groups. The structure of the ancillary ligands showed some influence on the catalytic activity and selectivity of the corresponding zinc complexes. The introduction of bulky ortho-substituents on the phenoxy unit resulted in a decrease of the polymerization rate, whereas the isotactic dyad selectivity in the ROP of rac-lactide was enhanced.
TL;DR: The crystal structures of the zinc complexes (Zn2L14 and Zn2l24) are also reported in this article, showing the presence of distorted trigonal bipyramidal and tetrahedral coordination geometry about the metal ions.
TL;DR: Six Cu(II) complexes of 2-(2-(ethylcarbamothioyl)hydrazinyl)-2-oxo-N-phenylacetamide (H(3)APET) have been prepared and characterized by elemental analyses, spectral as well as magnetic and thermal measurements, which revealed that the ligand acts as ON bidentate, ONS tridentate or ONNS tetradentate forming structure.
TL;DR: Two new nickel(II) [Ni(L)(2)] and copper(II] complexes have been synthesized with bidentate NO donor Schiff base ligand (2-{(Z)-[furan-2-ylmethyl]imino]methyl}-6-methoxyphenol) (HL) and both complexes Ni(L) and Cu(L(2) have been characterized by elemental analyses, IR, UV-vis, (1)H,
TL;DR: In this article, a new generation of heterogeneous bidentate P(III) ligands containing nitrogen was used for base-free Pd(II) catalyzed C-C bond formation through Heck coupling reaction.
TL;DR: A palladium(0) NHC complex Pd0(LH1)2(MA) (MA = maleic anhydride) was prepared from the amide-imidazolium salt [LH 1H2]Cl (H1 = NH proton; H2 NCHN proton) as mentioned in this paper.
TL;DR: A series of multifunctional (mercaptomethyl)silanes of the general formula type R(n)Si(CH(2)SH)(4-n) (n = 0-2; R = organyl) was synthesized to disclose a new mechanism for the formation of dihydrogen catalyzed by these compounds, whereby one sulfur atom was protonated in the catalytic cycle.
Abstract: A series of multifunctional (mercaptomethyl)silanes of the general formula type RnSi(CH2SH)4−n (n = 0−2; R = organyl) was synthesized, starting from the corresponding (chloromethyl)silanes. They were used as multidentate ligands for the conversion of dodecacarbonyltriiron, Fe3(CO)12, into iron carbonyl complexes in which the deprotonated (mercaptomethyl)silanes act as μ-bridging ligands. These complexes can be regarded as models for the [FeFe] hydrogenase. They were characterized by elemental analyses (C, H, S), NMR spectroscopic studies (1H, 13C, 29Si), and single-crystal X-ray diffraction. Their electrochemical properties were investigated by cyclic voltammetry to disclose a new mechanism for the formation of dihydrogen catalyzed by these compounds, whereby one sulfur atom was protonated in the catalytic cycle. The reaction of the tridentate ligand MeSi(CH2SH)3 with Fe3(CO)12 yielded a tetranuclear cluster compound. A detailed investigation by X-ray diffraction, electrochemical, Raman, Mossbauer, and su...
TL;DR: The results suggest that an axial donor can lower |A(z)|, in contrast to what was previously believed on the basis of the "additivity rule", and this explains the anomalous behaviour of the V(IV)O complexes formed by N-{2-[(2-pyridylmethylene)amino]phenyl}pyridine-2-carboxamide (Hcapca) and several amidrazone derivatives.
Abstract: The previously unreported equilibrium in aqueous solution between the V IV O square pyramidal and trans octahedral form with an axial water molecule for a number of bidentate ligands with (N,O) and (O,O) donor sets (6-methylpicolinic (6-mepicH) and 6-methyl-2,3-pyridinedicarboxylic (6-me-2,3-pdcH 2 ) acids, dipyridin-2-ylmethanol (Hdpmo) and 1,2-dimethyl-3-hydroxy-4(1 H )-pyridinone (Hdhp)) has been demonstrated by the combined application of EPR spectroscopy and DFT methods. The EPR spectra suggest that, with increasing ionic strength, the equilibrium is shifted towards the formation of the pentacoordinated species and values of K ≈4.0 and 7.0 for the systems containing 6-methyl-2,3-pyridinedicarboxylic acid and dipyridin-2-ylmethanol were
measured. DFT calculations performed with Gaussian 03 and ORCA software predict the 51 V anisotropic hyperfine coupling constant along the z axis (A z ), which can be used to demonstrate the
presence of an axially bound ligand trans to the V=O bond. The results suggest that an axial donor (charged or
not) can lower |A z |, in contrast to what was previously believed on the basis of the “additivity rule”, and this explains the anomalous behaviour of the V IV O complexes formed by N -{2-[(2-pyridylmethylene)amino]phenyl}-pyridine-2-carboxamide (Hcapca) and several amidrazone derivatives. The decrease
in |A z | for the axial binding of a solvent molecule is mainly a result of the reduction of |A iso | and this was also observed when the solid [VO(6-methylpicolinato) 2 ] was dissolved in
DMSO or DMF. The variations in the structural (V=O, V-O and V-N distances, O-V-O and N-V-N angles, and the trigonality index t) and spectroscopic (|A z |, |A iso | and v (V=O)) properties as a function of the axial VOH 2 distance ( R ) are also presented. Finally, the electronic structures of the pentaand hexacoordinated complexes are discussed.
TL;DR: The studies on compounds 2-5 support the amended hypothesis that upon increasing Zn (2+) concentration, compound 1 first undergoes fluorescence enhancement because of the formation of a 2:1 (ligand to Zn(2+)) complex which slows down the PET quenching process.
Abstract: 1,2,3-Triazol-4-yl (triazolyl)-containing tetradentate ligand 1 undergoes fluorescence enhancement upon binding to zinc ion (Zn2+) in both organic (acetonitrile) and aqueous solutions. A 1:1 complex of 1 with a trigonal bipyramidal Zn2+ was characterized by X-ray crystallography. The cyclic voltammogram (CV) of 1 suggests that an intramolecular photoinduced electron transfer (PET) process is thermodynamically feasible which would quench the fluorescence of the 2-anthryltriazolyl fluorophore. On the basis of the X-ray and CV data, it was initially postulated that the 1:1 binding between Zn2+ and ligand 1 shuts down the PET quenching pathway of the free ligand, which leads to the fluorescence enhancement of 1. However, the nuance of the interaction between 1 and Zn2+ was revealed by isothermal titration calorimetry (ITC) and 1H NMR titration experiments. A two-step binding process was observed which proceeds through an intermediate species of 2:1 (ligand/Zn2+) stoichiometry. Upon close examination of the fl...