Search results for "BOX"

Synthesis and characterization of mono- and binuclear copper(II) complexes with 2,2′:6′,2″-terpyridine (terpy) and carboxylates: X-ray crystal struct…

1987

Abstract Perchlorate and hexafluorophosphate salts of monomeric [Cu(terpy)(OOCH)(OH2)]+ and dimeric [Cu(terpy)(OOCR)]22+ cations (terpy = 2,2′:6′,2″-terpyridine, R = CH3 or C2H5) have been synthesized and characterized by IR, electronic and ESR spectra, and analytical data. Spectroscopic results indicate a five-coordinate, close-to-square pyramidal geometry around the copper(II) ion. The half-field absorption in the ΔMs = 2 region of powdered X-band ESR spectra has been observed for the dimeric species. The crystal structure of [Cu(terpy)(OOCH)(OH2)](ClO4) has been determined by X-ray diffraction methods. The compound crystallizes in the space group P21/c with unit-cell dimensions: a = 7.34…

Straightforward synthesis of donor-stabilised phosphenium adducts from imidazolium-2-carboxylate and their electronic properties

2007

Cationic imidazolium-2-phosphanes were obtained by the addition of a chlorophosphane (R2PCl, R = Ph, iPr or Cy) to 1,3-dimethylimidazolium-2-carboxylate without the need for a purification step. An additional anion exchange reaction with KPF6 led to the corresponding halide-free ligands in excellent yields. The molecular structure of one of them was examined both in the solid state and in solution. The lone pair of electrons on the phosphorus atom is not delocalised to the imidazolium fragment and thus remains available for further metal coordination. As such compounds can be described as phosphenium cations stabilised by a N-heterocarbene donor base, the electronic properties of the Lewis …

Molecular self-assembly on an insulating surface: interplay between substrate templating and intermolecular interactions

2012

We report on molecular self-assembly of biphenyl-4,4'-dicarboxylic acid (BPDCA) on CaCO3(10 (1) over bar4) under ultra-high vacuum conditions. Two-dimensional, ordered islands are obtained upon deposition at room temperature, coexisting with a streaky structure that is ascribed to individual, mobile molecules forming a two-dimensional gas-like phase. High-resolution non-contact atomic force microscopy (NC-AFM) images of the molecular islands reveal an ordered inner structure that is dominated by rows of molecules aligned side by side running along the [(42) over bar 61] crystallographic direction. A detailed analysis of these rows exhibits inter-row distances that are multiples of the calci…

One‐Dimensional Coordination Polymers of Mn II , Cu II , and Zn II Supported by Carboxylate‐Appended (2‐Pyridyl)alkylamine Ligands – Structure and Ma…

2009

Four new complexes [MnII(L1OO)(H2O)][ClO4]·2H2O (1), [ZnII(L1OO)][ClO4]·2H2O (2), [CuII(L3OO)][CF3SO3]·H2O (3), and [ZnII(L3OO)][ClO4] (4) (L1OO– = 3-[(2-(pyridine-2-yl)ethyl){2-(pyridine-2-yl)methyl}amino]propionate; L3OO– = 3-[(2-(pyridine-2-yl)ethyl){(dimethylamino)ethyl}amino]propionate) have been synthesized and characterized by elemental analysis, IR, and UV/Vis spectroscopy. Structural analysis revealed that 1, 3, and 4 are one-dimensional chain-like coordination polymers. In 1 distorted octahedral MnN3O3 and in 3 square-pyramidal CuN3O2 coordination is satisfied by three nitrogen atoms and an appended carboxylate oxygen atom of the ligand, and an oxygen atom belonging to the carboxy…

Salt effects on the protonation of l-histidine and l-aspartic acid: a complex formation model

1991

Abstract Protonation constants of l -histidine (histidinate: his − ) and l -aspartic acid (aspartate: asp 2− ) were determined potentiometrically, using the (H + ) glass electrode, in aqueous tetraethylammonium iodide (Et 4 NI), calcium chloride and sodium chloride solutions, at 0 −3 and 10 ⩽, T ⩽, 45 ° C. Differences in protonation constants determined in different salt media were explained by a complex formation model and, according to this model, the presence of the following species was hypothesized: Ca(his) + , CaH(his) 2+ , CaH 2 (his) 3+ Na(his) 0 , H 3 (his)X + , H 2 (his)X 0 , Et 4 N(his) 0 , Et 4 NH(his) + , Ca(asp) 0 , CaH(asp) + , CaH 2 (asp) 2+ , Na(asp) − , NaH(asp) 0 , H 3 (a…

A novel and selective fluoride opening of aziridines by XtalFluor-E. synthesis of fluorinated diamino acid derivatives.

2015

The selective introduction of fluorine onto the skeleton of an aminocyclopentane or cyclohexane carboxylate has been developed through a novel and efficient fluoride opening of an activated aziridine ring with XtalFluor-E. The reaction proceeded through a stereoselective aziridination of the olefinic bond of a bicyclic lactam and regioselective aziridine ring opening with difluorosulfiliminium tetrafluoroborate with the neighboring group assistance of the sulfonamide moiety to yield fluorinated diamino acid derivatives. The method based on the selective aziridine opening by fluoride has been generalized to afford access to mono- or bicyclic fluorinated substances.

1991

The thermal degradation mechanisms of amphiphilic acrylic copolymers containing mesogenic pyrimidine side chains and hydrophilic 2-hydroxyethyl acrylate (HEA) main-chain spacer units were investigated by thermogravimetry (TG) and pyrolysis-field ionization mass spectrometry (Py-FIMS). The degradation behaviour of these polymers depends on the amount of HEA incorporated. Thermogravimetry revealed that the main decomposition occurs in a single step for the pyrimidine homopolymer, whereas with increasing HEA content a two-step process evolves. The major products identified by Py-FIMS are two alcohols and one olefin split from the aromatic side chains. Depolymerization is only a minor degradati…

1,2,4-Triazoles. Improved synthesis of 5-substituted 4-amino-3-mer-cato-(4H)-1,2,4-triazoles and a facile route to 3,6-disubstituted 1,2,4-triazolo[3…

1997

The reaction of thiocarbohydrazide with carboxylic acids at the melting temperature allows an improved preparation of the S-substituted 4-amino-3-mercapto-1,2,4-triazole heterocycles. The crude 4-amino-5-mercapto-1,2,4-triazoles react easily with carboxylic acids or carboxylic acid chlorides to afford the 1,2,4-triazolo[3,4-fc][1,3,4]thiadiazole ring system.

Reaction of lithium enediolates with perfluoroketene dithioacetals. Synthesis of α-trifluoromethyl γ-dicarboxylic acid derivatives

2004

The reaction of perfluoroketene dithioacetals with dianions of carboxylic acids proceeds through the substitution of the vinylic fluoride. The preparative value of this reaction depends strongly on the reaction and work-up conditions, the optimisation of which led to use LDA as a base and multiple extraction techniques. The overall process may be considered as a formal synthesis of α-trifluoromethyl γ-dicarboxylic acid derivatives.

Stereoselective synthesis of unsaturated and functionalized L-NHBoc amino acids, using Wittig reaction under mild phase-transfer conditions.

2012

The stereoselective synthesis of a new amino acid phosphonium salt was described by quaternization of melting triphenylphosphine with the γ-iodo NHBoc-amino ester, derived from L-aspartic acid. The deprotection of the carboxylic acid function to afford the phosphonium salt with a free carboxylic acid group was achieved by a palladium-catalyzed desallylation reaction. This phosphonium salt was used in the Wittig reaction with aromatic or aliphatic aldehydes and trifluoroacetophenone, under solid-liquid phase-transfer conditions in chlorobenzene and in the presence of K(3)PO(4) as weak base, to afford the corresponding unsaturated amino acids without racemization. Thus, the reaction with subs…