scholarly journals Synthesis of axially chiral gold complexes and their applications in asymmetric catalyses

2013 ◽  
Vol 9 ◽  
pp. 2224-2232 ◽  
Author(s):  
Yin-wei Sun ◽  
Qin Xu ◽  
Min Shi
Keyword(s):  
Aromatic Ring ◽  
Functional Group ◽  
Phosphine Ligands ◽  
Gold Complexes ◽  
Hindered Rotation ◽  
X Ray ◽  
Catalytic Activities ◽  
Axially Chiral

Several novel chiral N-heterocyclic carbene and phosphine ligands were prepared from (S)-BINOL. Moreover, their ligated Au complexes were also successfully synthesized and characterized by X-ray crystal diffraction. A weak gold-π interaction between the Au atom and the aromatic ring in these gold complexes was identified. Furthermore, we confirmed the formation of a pair of diastereomeric isomers in NHC gold complexes bearing an axially chiral binaphthyl moiety derived from the hindered rotation around C–C and C–N bonds. In the asymmetric intramolecular hydroamination reaction most of these chiral Au(I) complexes showed good catalytic activities towards olefins tethered with a NHTs functional group to give the corresponding product in moderate yields and up to 29% ee.

scholarly journals Synthesis of chiral mono(N-heterocyclic carbene) palladium and gold complexes with a 1,1'-biphenyl scaffold and their applications in catalysis

2011 ◽  
Vol 7 ◽  
pp. 555-564 ◽  
Author(s):  
Lian-jun Liu ◽  
Feijun Wang ◽  
Wenfeng Wang ◽  
Mei-xin Zhao ◽  
Min Shi
Keyword(s):  
Crystal Structure ◽  
Coupling Reactions ◽  
Gold Complexes ◽  
X Ray ◽  
Catalytic Activities ◽  
Axially Chiral

Axially chiral mono(NHC)–Pd(II) and mono(NHC)–Au(I) complexes with one side shaped 1,1'-biphenyl backbone have been prepared from chiral 6,6'-dimethoxybiphenyl-2,2'-diamine. The complexes were characterized by X-ray crystal structure diffraction. The Pd(II) complex showed good catalytic activities in the Suzuki–Miyaura and Heck–Mizoroki coupling reactions, and the (S)-Au(I) complexes also showed good catalytic activities in the asymmetric intramolecular hydroamination reaction to give the corresponding product in moderate ee.

Titanocene and ansa-titanocene complexes bearing 2,6-bis(isopropyl)phenoxide ligand(s). Syntheses, characterization and use in catalytic dehydrocoupling polymerization of phenylsilane

2011 ◽  
Vol 76 (1) ◽  
pp. 75-94 ◽  
Author(s):  
Michal Horáček ◽  
Jan Merna ◽  
Róbert Gyepes ◽  
Jan Sýkora ◽  
Jiří Kubišta ◽  
...  
Keyword(s):  
Variable Temperature ◽  
Titanocene Dichloride ◽  
Spectroscopic Methods ◽  
Rotation Barrier ◽  
X Ray Diffraction ◽  
Hindered Rotation ◽  
Catalytic Behavior ◽  
X Ray ◽  
Catalytic Activities ◽  
H Nmr

Aryloxychloro and bis(aryloxy) titanocenes of general formula L2TiCl2–x(OAr′)x where L = η5-C5H5 (x = 1 (1) and 2 (2)), L2 = SiMe2(η5-C5H4)2 (x = 1 (3) and 2 (4)), and Ar′ = 2,6-(CHMe2)2C6H3 were prepared by the reaction of corresponding titanocene dichloride with LiOAr′ and characterized by spectroscopic methods and compound 3 by single crystal X-ray diffraction analysis. The bulky aryloxy ligand in 1 and 3 exerts a hindered rotation around the Ti–O bond on the 1H NMR time scale, resulting in its dynamic behavior in CDCl3 solution. Variable temperature NMR measurements proved the rotation barrier in 3 (ΔG‡298 = 13.9 ± 0.3 kcal/mol) to be lower than that in 1 (ΔG‡298 = 14.7 ± 0.2 kcal/mol) as a consequence of the more open titanocene shell in the ansa-structure of 3. The catalytic behavior of complexes 1–4, [(η5-C5H5)2TiCl2] and [{SiMe2(η5-C5H4)2}TiCl2], was examined in dehydrocoupling polymerization of phenylsilane under comparable conditions, showing a remarkable higher activity for the titanocene complexes with regards to the ansa-titanocene ones. The order of catalytic activities 2 ~ 1 > [(η5-C5H5)2TiCl2] >> [{SiMe2(η5-C5H4)2}TiCl2] ~ 3 ~ 4 reveals the aryloxy ligands to have an enhancing effect on activity in the titanocene series.

Photocatalytic activity of TiO2 synthesized by anodization and anodic spark deposition

MRS Advances ◽  
2020 ◽  
Vol 5 (61) ◽  
pp. 3141-3152
Author(s):  
Alma C. Chávez-Mejía ◽  
Génesis Villegas-Suárez ◽  
Paloma I. Zaragoza-Sánchez ◽  
Rafael Magaña-López ◽  
Julio C. Morales-Mejía ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Photocatalytic Activity ◽  
Surface Characteristics ◽  
Amorphous Solids ◽  
X Ray Diffraction ◽  
X Ray ◽  
Catalytic Activities ◽  
Anodic Spark Oxidation ◽  
Porous Surfaces ◽  
Scanning Electron

AbstractSeveral photocatalysts, based on titanium dioxide, were synthesized by spark anodization techniques and anodic spark oxidation. Photocatalytic activity was determined by methylene blue oxidation and the catalytic activities of the catalysts were evaluated after 70 hours of reaction. Scanning Electron Microscopy and X Ray Diffraction analysis were used to characterize the catalysts. The photocatalyst prepared with a solution of sulfuric acid and 100 V presented the best performance in terms of oxidation of the dye (62%). The electric potential during the synthesis (10 V, low potential; 100 V, high potential) affected the surface characteristics: under low potential, catalyst presented smooth and homogeneous surfaces with spots (high TiO2 concentration) of amorphous solids; under low potential, catalyst presented porous surfaces with crystalline solids homogeneously distributed.

Axially Chiral Bis(α-amino Acid)s and Their Deamino Analogues. Synthesis and Configurational Assignment

1998 ◽  
Vol 63 (2) ◽  
pp. 211-221 ◽  
Author(s):  
Miloš Tichý ◽  
Luděk Ridvan ◽  
Miloš Buděšínský ◽  
Jiří Závada ◽  
Jaroslav Podlaha ◽  
...  
Keyword(s):  
Amino Acid ◽  
Nmr Spectra ◽  
Building Blocks ◽  
X Ray Diffraction ◽  
Amino Groups ◽  
X Ray ◽  
Configurational Assignment ◽  
Symmetry Properties ◽  
Axially Chiral ◽  
Polymeric Structures

The axially chiral bis(α-amino acid)s cis-2 and trans-2 as possible building blocks for polymeric structures of novel type of helicity were prepared. Their configuration has been determined by NMR spectroscopy and, in the case of the trans-isomer, confirmed by single-crystal X-ray diffraction. Analogous pair of stereoisomeric diacids cis-3 and trans-3, devoid of the amino groups, was also prepared and their configuration assigned. The observed differences in the NMR spectra of cis- and trans-isomers of 2 and 3 are discussed from the viewpoint of their different symmetry properties.

scholarly journals X-ray Photoelectron Spectroscopy Analysis of Chitosan–Graphene Oxide-Based Composite Thin Films for Potential Optical Sensing Applications

Polymers ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 478
Author(s):  
Wan Mohd Ebtisyam Mustaqim Mohd Daniyal ◽  
Yap Wing Fen ◽  
Silvan Saleviter ◽  
Narong Chanlek ◽  
Hideki Nakajima ◽  
...  
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Graphene Oxide ◽  
Photoelectron Spectroscopy ◽  
Functional Group ◽  
Optical Sensing ◽  
Composite Thin Films ◽  
Cobalt Ions ◽  
X Ray ◽  
Sensing Applications

In this study, X-ray photoelectron spectroscopy (XPS) was used to study chitosan–graphene oxide (chitosan–GO) incorporated with 4-(2-pyridylazo)resorcinol (PAR) and cadmium sulfide quantum dot (CdS QD) composite thin films for the potential optical sensing of cobalt ions (Co2+). From the XPS results, it was confirmed that carbon, oxygen, and nitrogen elements existed on the PAR–chitosan–GO thin film, while for CdS QD–chitosan–GO, the existence of carbon, oxygen, cadmium, nitrogen, and sulfur were confirmed. Further deconvolution of each element using the Gaussian–Lorentzian curve fitting program revealed the sub-peak component of each element and hence the corresponding functional group was identified. Next, investigation using surface plasmon resonance (SPR) optical sensor proved that both chitosan–GO-based thin films were able to detect Co2+ as low as 0.01 ppm for both composite thin films, while the PAR had the higher binding affinity. The interaction of the Co2+ with the thin films was characterized again using XPS to confirm the functional group involved during the reaction. The XPS results proved that primary amino in the PAR–chitosan–GO thin film contributed more important role for the reaction with Co2+, as in agreement with the SPR results.

scholarly journals Crystallization and preliminary X-ray characterization of the 2,4′-dihydroxyacetophenone dioxygenase fromAlcaligenessp. 4HAP

2014 ◽  
Vol 70 (6) ◽  
pp. 823-826 ◽  
Author(s):  
G. Beaven ◽  
A. Bowyer ◽  
P. Erskine ◽  
S. P. Wood ◽  
A. McCoy ◽  
...  
Keyword(s):  
Synchrotron Radiation ◽  
Formic Acid ◽  
Molecular Oxygen ◽  
Aromatic Ring ◽  
Bond Cleavage ◽  
Its Sequence ◽  
Hydroxybenzoic Acid ◽  
X Ray

The enzyme 2,4′-dihydroxyacetophenone dioxygenase (or DAD) catalyses the conversion of 2,4′-dihydroxyacetophenone to 4-hydroxybenzoic acid and formic acid with the incorporation of molecular oxygen. Whilst the vast majority of dioxygenases cleave within the aromatic ring of the substrate, DAD is very unusual in that it is involved in C—C bond cleavage in a substituent of the aromatic ring. There is evidence that the enzyme is a homotetramer of 20.3 kDa subunits each containing nonhaem iron and its sequence suggests that it belongs to the cupin family of dioxygenases. By the use of limited chymotrypsinolysis, the DAD enzyme fromAlcaligenessp. 4HAP has been crystallized in a form that diffracts synchrotron radiation to a resolution of 2.2 Å.

Observations of TiO2 Surfaces Using Totally Reflected X-ray In-plane Diffraction Under UV Irradiation

2002 ◽  
Vol 751 ◽  
Author(s):  
T. Horiuchi ◽  
H. Ochi ◽  
K. Kaisei ◽  
K. Ishida ◽  
K. Matsushige
Keyword(s):  
Uv Irradiation ◽  
Uv Light ◽  
Plane Surface ◽  
Signal To Noise Ratio ◽  
High Surface ◽  
Ultra Violet ◽  
High Signal ◽  
X Ray ◽  
Force Microscopy ◽  
Catalytic Activities

ABSTRACTSurface lattice displacements of titanium dioxide (TiO2: rutile) during ultra-violet (UV) light irradiation have been investigated using a total reflection x-ray diffraction, which provides a high signal to noise ratio (S/N) and superior in-plane surface diffraction. Under the environments in vapors of H2O, CH3OH, C2H5OH and C3H6OH, the photo-catalytic activities of TiO2 (110), (100) and (001) surfaces subject to UV irradiation have been measured. It is found that the diffraction peaks and their full width half maxima (FWHMs) show some peculiarities with respect to the photo-catalytic activities in both surface lattices and adsorbed molecules in vapors. Furthermore, Kelvin force microscopy (KFM) has showed that there exists a very high surface potential, probably due to surface atom displacements induced by UV irradiation. With regard to the origin of the photo-catalytic activities, the induced surface potentials are discussed.

ChemInform Abstract: Palladium-Catalyzed Asymmetric Allylic Alkylation of Indoles by C-N Bond Axially Chiral Phosphine Ligands.

ChemInform ◽  
2013 ◽  
Vol 44 (41) ◽  
pp. no-no
Author(s):  
Takashi Mino ◽  
Miho Ishikawa ◽  
Kenji Nishikawa ◽  
Kazuya Wakui ◽  
Masami Sakamoto
Keyword(s):  
Phosphine Ligands ◽  
Allylic Alkylation ◽  
Asymmetric Allylic Alkylation ◽  
Axially Chiral ◽  
Chiral Phosphine Ligands ◽  
Palladium Catalyzed

Structural Investigation of a Configurationally Stable Seven-Membered Bridged Biaryl of Relevance for Atroposelective Biaryl Syntheses*

2003 ◽  
Vol 58 (2-3) ◽  
pp. 231-236 ◽  
Author(s):  
Gerhard Bringmann ◽  
Robert-Michael Pfeifer ◽  
Christian Rummey ◽  
Thomas Pabst ◽  
Dirk Leusser ◽  
...  
Keyword(s):  
Total Synthesis ◽  
Ring Opening ◽  
Structural Investigation ◽  
X Ray Diffraction ◽  
Cleavage Reaction ◽  
Perfect Agreement ◽  
X Ray ◽  
Ether Bridge ◽  
Axially Chiral ◽  
Aromatic Systems

The atroposelective ring opening of lactone-bridged biaryl systems is the key step in the total synthesis of a series of axially chiral biaryl natural products and useful reagents or catalysts for asymmetric synthesis. For a more in-depth understanding of the mechanism and stereochemical course of this remarkable cleavage reaction, a seven-membered ether analog of such useful biaryl lactones has been investigated structurally, both experimentally, by X-ray diffraction analysis, and by ab initio calculations (B3LYP/6-31G*). In a nearly perfect agreement, both methods show that these seven-membered bridged biaryls do not constitute helicene-like distorted molecules, but ‘true’ biaryls, whose sufficiently long lactone or ether bridge allows the two aromatic systems to adopt a large dihedral angle to each other, without any noticeable deviation from planarity for the two aromatic systems - in contrast to related six-membered analogs, which can rather be considered as helicene-like twisted polycyclic systems.

scholarly journals Molecular iodine-catalyzed one-pot multicomponent synthesis of 5-amino-4-(arylselanyl)-1H-pyrazoles

2018 ◽  
Vol 14 ◽  
pp. 2789-2798 ◽  
Author(s):  
Camila S Pires ◽  
Daniela H de Oliveira ◽  
Maria R B Pontel ◽  
Jean C Kazmierczak ◽  
Roberta Cargnelutti ◽  
...  
Keyword(s):  
Multicomponent Reaction ◽  
Functional Group ◽  
Diazo Compound ◽  
Molecular Iodine ◽  
Multicomponent Synthesis ◽  
One Pot ◽  
X Ray ◽  
Dehydrogenative Coupling ◽  
Reflux Temperature

A one-pot iodine-catalyzed multicomponent reaction has been developed for the selective preparation of 5-amino-4-(arylselanyl)-1H-pyrazoles from a diverse array of benzoylacetonitriles, arylhydrazines and diaryl diselenides. The reactions were conducted in MeCN as solvent at reflux temperature under air. The methodology presents a large functional group tolerance to electron-deficient, electron-rich, and bulky substituents and gave the expected products in good to excellent yields. The synthesized 1,3-diphenyl-4-(phenylselanyl)-1H-pyrazol-5-amine was submitted to an oxidative dehydrogenative coupling to produce a diazo compound confirmed by X-ray analysis.

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