305 research outputs found
Synthesis, Characterization and Olefin/CO Exchange Reactions of Pyrazolylborato Complexes of Copper(I)
No full textNew bis(pyrazolyl)borato olefin complexes of copper(I) of general formula Cu[BH2(3,5-(CF3)2Pz)2]-
(olefin) have been prepared (olefins: coe = cyclooctene, van = 4-vinylanisole, clsty = 4-chlorostyrene,
tevs = triethylvinylsilane, fn = fumaronitrile). The structures of Cu[BH2(3,5-(CF3)2Pz)2](L), L = coe,
van, tevs, fn, have been determined by X-ray diffraction methods. Considering the two N atoms of the
bis(pyrazolyl)borate ligand and the midpoint of the C–C double bond of the coordinated olefin, the
compounds with L = coe, van and tevs contain a copper atom in a trigonal planar coordination. A
coordination polymer with N-coordinated fumaronitrile and tetrahedral coordination of copper atoms
is obtained in the case of L = fn. The carbonylation reactions of Cu[BH2(3,5-(CF3)2Pz)2](olefin)
(olefin = coe, clsty, van, tevs), Cu[BH2(3,5-(CF3)2Pz)2](olefin) + CO↔Cu[BH2(3,5-(CF3)2Pz)2](CO)
+ olefin, have been studied gas volumetrically and the thermodynamical parameters of the equilibria
for the displacement of the coordinated olefin by carbon monoxide have been determined. These data
for copper(I) are compared with those reported in the literature
Carbonyl clusters with a capping methylidyne phosphonate ligand crystal structure of [CO3(CO)9{η1-μ3-[CP(O) (OEt)2]}]
No full textThe bridging methylidyne clusters [Co-3(CO)(9)(eta(1)-mu(3)-[CP(O)(OR)(2)])] 1 (R = Et) and 3 (R = SiMe3) with alpha-phosphoryl substituents have been synthesized by reaction of Cl3C-P(O)(OR)(2) with Co-2(CO)(8), followed by protonation. Cluster 3 was also obtained by the reaction of 1 with Me3SiBr. The structure of 1 has been determined by X-ray crystallography. The donor properties of the P=O function toward Lewis acids such as [Cp2MCl](+) (M = Ti, Zr) were used to assemble early-late metal systems. (C) 1997 Elsevier Science S.A
Synthesis, X-ray structural analysis, antibacterial and DNA-binding studies of a lanthanum bis-(5,5′-dimethyl-2,2′-bipyridine) complex
No full textA new complex with the formula [La(5,5′-dmbpy) 2 (NO 3 ) 3 ] (a) [where (5,5′-dmbpy = 5,5′-dimethyl-2,2′-bipyridine)] has been synthesized. The compound was characterized by cyclic voltammetry, elemental analysis and spectroscopic methods (IR, UV–Vis, 1 H-NMR). Single crystals adapted for X-ray diffraction analysis were recorded by slow crystallization from a methanol solution. The complex is neutral being the lanthanum cation chelated by two bipyridine derivative neutral ligands and three bidentate nitrate groups. Electronic spectra show the transition of both ligand field and charge transfer bands. The fluorescence properties of the compound have been studied. The interactions of complex with FS-DNA (salmon sperm DNA) have been studied using UV–Vis, fluorescence spectroscopies and gel electrophoresis. The above-mentioned techniques were used in physiological buffer having pH 7.2. The binding constant (K b ) for interaction in (a) with DNA was obtained using UV–Vis spectroscopies (K b = 1.2 × 10 5 ) and fluorescence spectroscopies (K b = 1.50 × 10 5 ). The binding constant (K b ), the number of binding sites for each 1000 nucleotides (n) and the apparent bio molecular quenching constant (k q ) for FS-DNA were obtained through Stern–Volmer equation. Thermodynamic parameters data (∆H°, ΔS° and ΔG°) showed that hydrogen bonding and van der Waals interactions have an important function in the interaction of DNA–La(III) complex, and the binding mode is the groove binding. The DNA binding of La(III) complex is spontaneous as suggested by the negative ΔG°. Moreover, the DNA cleavage has been studied using agarose gel electrophoresis. The antibacterial effects of complex (a) have also been examined in vitro against standard bacterial strains
Bench-top experiment on Fucus reproduction in response to temperature
No full textFucus reproduction in response to temperature assessed as % change in conceptacles over the experimental duration of 5 weeks: Temperature levels 0, 5,10,15,20, 25°C; period Apr 2013, replucation 4; details and data in Graiff et al 2017
A Reinterpretation of the Imidazolate Au(I) Cyclic Trinuclear Compounds Reactivity with Iodine and Methyl Iodide with the Perspective of the Inverted Ligand Field Theory
No full textCoinage metal cyclic trinuclear compounds (CTCs) are an emerging class of metal coordination compounds that are valuable for many fine optoelectronic applications, even though the reactivity dependence by the different bridging ligands remains somewhat unclear. In this work, to furnish some hints to unravel the effect of substituents on the chemistry of Au(I) CTCs made of a specific class of bridging ligand, we have considered two imidazolate Au(I) CTCs and the effect of different substituents on the pyrrolic N atoms relative to classic metal oxidations with I2 or by probing electrophilic additions. Experimental suggestions depict a thin borderline between the addition of MeI to the N-methyl or N-benzyl imidazolyl CTCs, which afford the oxidized CTC in the former and the ring opening of the CTC and the formation of carbene species in the latter. Moreover, the reactions with iodine yield to the oxidation of the metal centers for the former and just of a metal center in the latter, even in molar excess of iodine. The analysis of the bond distances in the X-ray crystal structures of the oxidized highlights that Au(III)-C and Au(III)-N bonds are longer than observed for Au(I)-C and Au(I)-N bonds, as formally not expected for Au(III) centers. Computational studies converge on the attribution of these discrepancies to an additional case of inverted ligand field (ILF), which solves the question with a new interpretation of the Au(I)-ligand bonding in the oxidized CTCs, which furnishes a new interpretation of the Au(I)-ligand bonding in the oxidized CTCs, opening a discussion about addition/oxidation reactions. Finally, the theoretical studies outputs depict energy profiles that are compatible with the experimental results obtained in the reaction of the two CTCs toward the addition of I2, MeI, and HCl
A reinterpretation of the Imidazolate Au(I) Cyclic Trinuclear Compounds reactivity with iodine and methyl iodide with the perspective of the Inverted Ligand Field Theory
No full textCoinage metal cyclic trinuclear compounds (CTCs) are an emerging class of metal coordination compounds that are valuable for many fine optoelectronic applications, even though the reactivity dependence by the different bridging ligands remains somewhat unclear. In this work, to furnish some hints to unravel the effect of substituents on the chemistry of Au(I) CTCs made of a specific class of bridging ligand, we have considered two imidazolate Au(I) CTCs and the effect of different substituents on the pyrrolic N atoms relative to classic metal oxidations with I2 or by probing electrophilic additions. Experimental suggestions depict a thin borderline between the addition of MeI to the N-methyl or N-benzyl imidazolyl CTCs, which afford the oxidized CTC in the former and the ring opening of the CTC and the formation of carbene species in the latter. Moreover, the reactions with iodine yield to the oxidation of the metal centers for the former and just of a metal center in the latter, even in molar excess of iodine. The analysis of the bond distances in the X-ray crystal structures of the oxidized highlights that Au(III)-C and Au(III)-N bonds are longer than observed for Au(I)–C and Au(I)–N bonds, as formally not expected for Au(III) centers. Computational studies converge on the attribution of these discrepancies to an additional case of inverted ligand field (ILF), which solves the question with a new interpretation of the Au(I)–ligand bonding in the oxidized CTCs, which furnishes a new interpretation of the Au(I)-ligand bonding in the oxidized CTCs, opening a discussion about addition/oxidation reactions. Finally, the theoretical studies outputs depict energy profiles that are compatible with the experimental results obtained in the reaction of the two CTCs toward the addition of I2, MeI, and HCl
Manganese(III) complexes with tetradentate O^C^C^O ligands: Synthesis, characterization and catalytic studies on the CO2 cycloaddition with epoxides
No full textA novel class of manganese(III) complexes bearing bis(NHC)-bis(phenolate) (O^C^C^O) type ligands was successfully synthesized. Three differently substituted imidazolium salts (with 2-hydroxyphenyl, (H4L1)Br2, 5‐tert‐butyl‐2-hydroxyphenyl, (H4L2)Br2, and 3,5-di‐tert‐butyl‐2-hydroxyphenyl, (H4L3)Br2, groups) were prepared as precursors of the (O^C^C^O) ligands and a convenient high-yield complexation reaction using manganese(III) acetate was developed. Electrospray ionization mass spectrometry (ESI-MS) and single-crystal X-ray diffraction (SC-XRD) data confirm the formation of the complexes of general formula [MnBrL1–3] and clarify their coordination geometry. The complexes were studied as homogeneous catalysts in the cycloaddition of CO2 to benzyl glycidyl ether (BGE) to form the corresponding cyclic carbonate, using tetrabutylammonium bromide (TBAB) or bis(triphenylphosphine)iminium bromide (PPNBr) as co-catalysts. The complex [MnBrL3] shows the highest activity, and kinetic investigations revealed a pseudo-first order dependence with respect to BGE under neat conditions. The temperature effect was also investigated using the Eyring and Arrhenius equations and the activation parameters for the neat reaction using [MnBrL3] and TBAB were experimentally determined (ΔH‡ = 11.2 kcal·mol-1 and ΔS‡ = -50 cal·mol-1·K-1). On the basis of the performed mechanistic studies and DFT investigations, a catalytic cycle which involves the CO2 1,2-insertion as the rate determining step is proposed
Bench-top experiment on Fucus relative growth of thallus tips in response to temperatures
No full textMean daily Fucus relative growth of thallus tips (%/d) in response to temperatures under a photon fluence rate of 130 µmol m-² s-² in a 16:8 h L/D: Temperature levels 5, 10, 15, 20, 24, 26, 27, 28, 29°C; period Apr 2014; replication 4; details and data in Graiff et al 2015
Rhodium(I), palladium(II), and platinum(II) complexes containing new mixed phosphane-phosphite ligands - Effect of the catalytic system stability on the enantioselective hydroformylation of styrene
No full textThe new mixed phosphane-phosphite ligands 1 and 2, derived from 3,3′-di-tert-butyl-2,2′-dihydroxy-5,5′-dimethoxybiphenyl and (S)-binaphthol, respectively, reacted with [Rh(COD)(THF)2]CF3SO3 to give the compounds [Rh(COD)(1)]CF3SO3 and [Rh(COD)(2)]CF3SO3 in which the ligands 1 and (S)-2 are chelated to the rhodium centre. The reaction with [Rh(CO)2Cl]2 gave two different products, [Rh(CO)2(L)Cl] and [Rh(CO)(L)Cl] [L = 1 and (S)-2], containing L as a chelate. On the basis of the IR and NMR spectroscopic data, the proposed structure of the pentacoordinate species is a trigonal bipyramide in which the phosphane-phosphite ligand assumes an equatorial-axial coordination. The reactions of 1 and 2 with [Pd(C6H5CN)2Cl2] and [Pt(COD)I2] gave the corresponding compounds [Pd(L)Cl2] and [Pt(L)I2] in which the ligands are chelated to the metal centre. The crystal structure of the chloroform solvate of [Pd(L)Cl2] was fully characterised by an X-ray study. The chiral ligands (S)-2 and (S)-3 [derived from the orthobis(trimethylsilyl)-substituted (S)-binaphthol] were tested in the hydroformylation of styrene. The results obtained were discussed in light of the catalytic system stability
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