Search results for "PHENOLS"
showing 10 items of 766 documents
Self-assembly of programmed building blocks into structurally uniform dendrimers.
2005
Selective and independent dimerization of tri- and tetraurea derivatives was used to build up dendritic assemblies which are uniform in size and structure. Dendrimers with the total molecular masses of about 25 000 g/mol were obtained. The existence of uniform assemblies was proved by 1H and 1H DOSY NMR experiments and also by dynamic light scattering.
Heptacoordinated Molybdenum(VI) Complexes of Phenylenediamine Bis(phenolate): A Stable Molybdenum Amidophenoxide Radical
2013
The syntheses, crystallographic structures, magnetic properties, and theoretical studies of two heptacoordinated molybdenum complexes with N,N′-bis(3,5-di-tert-butyl-2-hydroxyphenyl)-1,2-phenylenediamine (H4N2O2) are reported. A formally molybdenum(VI) complex [Mo(N2O2)Cl2(dmf)] (1) was synthesized by the reaction between [MoO2Cl2(dmf)2] and H4N2O2, whereas the other molybdenum(VI) complex [Mo(N2O2)(HN2O2)] (2) was formed when [MoO2(acac)2] was used as a molybdenum source. Both complexes represent a rare case of the MoVI ion without any multiply bonded terminal ligands. In addition, molecular structures, magnetic measurements, ESR spectroscopy, and density functional theory calculations ind…
Isostructural Dinuclear Phenoxo-/Acetato-Bridged Manganese(II), Cobalt(II), and Zinc(II) Complexes with Labile Sites: Kinetics of Transesterification…
2012
Using the dinucleating phenol-based ligand 2,6-bis[3-(pyridin-2-yl)pyrazol-1-ylmethyl]-4-methylphenol] (HL(2)), in its deprotonated form, the six new dinuclear complexes [M(II)(2)(L(2))(μ-O(2)CMe)(2)(MeCN)(2)][PF(6)] (M = Mn (2a), Co (3a), Zn (4a)) and [M(II)(2)(L(2))(μ-O(2)CMe)(2)(MeCN)(2)][BPh(4)] (M = Mn (2b), Co (3b), Zn (4b)) have been synthesized. Crystallographic analyses on 2b·2MeCN, 3b·2MeCN, and 4b·2MeCN reveal that these complexes have closely similar μ-phenoxo bis(μ-carboxylato) structures. The physicochemical properties (absorption and ESI-MS spectral data, 2a,b, 3a,b, and 4a,b; (1)H NMR, 4a,b) of the cations of 2a-4a are identical with those of 2b-4b. Each metal ion is termina…
Oxidation of substituted phenols using copper(II) metallatriangles formed through ligand sharing
2014
Reaction of N(2),N(2')-bis-[(1-butyl-benzimidazol-2yl)methyl]biphenyl-2,2'-dicarboxamide (L) with CuX2⋅nH2O in methanol leads to the assembly of four trinuclear Cu(II) complexes with the general formula [Cu3(L)3X3]⋅3X⋅nH2O⋅mMeCN, where X=Cl(-), Br(-), NO3(-) and C6H5COO(-) and n=0-5, m=0-8 (compounds 1-4, respectively). The structure of one of the complex contains three Cu(II) metal ions at the corners of an equilateral triangle. Each of the copper(II) are coordinated through two benzimidazolyl imine N-atoms and two amide carbonyl O-atoms and the apical position is occupied by an anionic nitrate ion, leading to a distorted square pyramidal environment. The magnetic susceptibility data were …
Tungsten(VI) complexes with aminobis(phenolato) [O,N,O] donor ligands.
2004
The reaction between trisdiolatotungsten(VI) complex [W(eg)(3)] (1) (eg = 1,2-ethanediolato dianion) and phenolic ligand precursor methylamino-N,N-bis(2-methylene-4,6-dimethylphenol) (H(2)L(Me)) or methylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol) (H(2)L(tBu)) affords monomeric oxotungsten complex [WO(eg)(L(Me))] (2) or [WO(eg)(L(tBu))] (3), respectively. These complexes react further with chlorinating reagents, which leads to the displacement of ethanediolato ligands from the complex units and formation of cis and trans isomers of the corresponding dichloro complexes [WOCl(2)(L(Me))] (4) and [WOCl(2)(L(tBu))] (5), respectively. Identical dichloro complexes were also prepared by …
Characterization of phenolic pellets for ESR dosimetry in photon beam radiotherapy
2017
This work deals with the dosimetric features of a particular phenolic compound (IRGANOX 1076 ® ) for dosimetry of clinical photon beams by using electron spin resonance (ESR) spectroscopy. After the optimization of the ESR readout parameters (namely modulation amplitude and microwave power) to maximise the signal without excessive spectrum distortions, basic dosimetric properties of laboratory-made phenolic dosimeters in pellet form, such as reproducibility, dose–response, sensitivity, linearity and dose rate dependence were investigated. The dosimeters were tested by measuring the depth dose profile of a 6 MV photon beam. A satisfactory intra-batch reproducibility of the ESR signal of the …
Triphenylphosphane Pt(II) complexes containing biologically active natural polyphenols: Synthesis, crystal structure, molecular modeling and cytotoxi…
2016
Platinum complexes bearing phosphane ligands in cis configuration with deprotonated flavonoids (3-hydroxyflavone, quercetin) and deprotonated ethyl gallate were synthesized starting from cis-[PtCl2(PPh3)(2)]. In all cases, O,O' chelate structures were obtained. While quercetin and ethyl gallate complexes are quite stable in solution, the 3-hydroxyflavonate complex undergoes a slow aerobic photodegradation in solution with formation of salicylic and benzoic acids. The X-ray diffraction structures of quercetin and ethyl gallate complexes are reported. Cell cycle studies (in the dark) of the complexes in two human cell lines revealed that the cytotoxic activity of the complex bearing 3-hydroxy…
Experimental and Computational Studies of Hydrogen Bonding and Proton Transfer to [Cp*Fe(dppe)H]
2005
The present contribution reports experimental and computational investigations of the interaction between [Cp*Fe(dppe)H] and different proton donors (HA). The focus is on the structure of the proton transfer intermediates and on the potential energy surface of the proton transfer leading to the dihydrogen complex [Cp*Fe(dppe)(H2)]+. With p-nitrophenol (PNP) a UV/Visible study provides evidence of the formation of the ion-pair stabilized by a hydrogen bond between the nonclassical cation [Cp*Fe(dppe)(H2)]+ and the homoconjugated anion ([AHA]-). With trifluoroacetic acid (TFA), the hydrogen-bonded ion pair containing the simple conjugate base (A-) in equilibrium with the free ions is observed…
Self-Sorting Dimerization of Tetraurea Calix[4]arenes
2007
Calix[4]arenes substituted by four urea functions are self-complementary molecules that spontaneously combine in apolar solvents in the presence of an ammonium salt to form dimeric capsules held together by a belt of hydrogen bonds. In the presence of tetraethylammonium salts, the Et4N+ cation is included as a guest. The sorting between dimeric capsules formed in a mixture of calix[4]arenes directly depends on the steric crowding of the substituents grafted on the urea groups whether aromatic derivatives or aliphatic chains linking urea functions in mono-, di-, or tetraloop structures. Simple rules allow one to anticipate which capsules will be exclusively formed when calix[4]arenes are mix…
Molecules with New Topologies Derived from Hydrogen-Bonded Dimers of Tetraurea Calix[4]arenes
2008
Tetraurea calix[4]arenes 2 have been synthesized in which two adjacent aryl urea residues are connected to a loop by an aliphatic chain -O-(CH(2))(n)-O-. The remaining urea residues have a bulky 3,5-di-tert-butylphenyl residue and an omega-alkenyloxyphenyl residue. Since this bulky residue cannot pass through the loop, only one homodimer (22) is formed in apolar solvents, for steric reasons, in which the two alkenyl residues penetrate the two macrocyclic loops. Covalent connection of these alkenyl groups by olefin metathesis followed by hydrogenation creates compounds 3, which consist of molecules with hitherto unknown topology. Their molecular structure was confirmed by (1)H NMR spectrosco…