Graphite oxide (GO) and its derivatives have been studied using 13C and 1H NMR. NMR spectra of GO derivatives confirm the assignment of the 70 ppm line to C−OH groups and allow us to propose a new structural model for GO. Thus we assign the 60 ppm line to epoxide groups (1,2-ethers) and not to 1,3-ethers, as suggested earlier, and the 130 ppm line to aromatic entities and conjugated double bonds. GO contains two kinds of regions:  aromatic regions with unoxidized benzene rings and regions with aliphatic six-membered rings. The relative size of the two regions depends on the degree of oxidation. The carbon grid is nearly flat; only the carbons attached to OH groups have a slightly distorted tetrahedral configuration, resulting in some wrinkling of the layers. The formation of phenol (or aromatic diol) groups during deoxygenation indicates that the epoxide and the C−OH groups are very close to one another. The distribution of functional groups in every oxidized aromatic ring need not be identical, and both ...

Structure of Graphite Oxide Revisited

Synthetic Principles for Bandgap Control in Linear pi-Conjugated Systems.

2.5. Stabilization of IL Emulsions by Nanoparticles 2623 3. Hydrogenations in ILs 2623 3.1. Hydrogenation on IL-Stabilized Nanoparticles 2623 3.1.1. Hydrogenation of 1,3-Butadiene 2623 3.1.2. Hydrogenation of Alkenes and Arenes 2624 3.1.3. Hydrogenation of Ketones 2624 3.2. Homogeneous Catalytic Hydrogenation in ILs 2624 3.3. Hydrogenation of Functionalized ILs 2625 3.3.1. Selective Hydrogenation of Polymers 2625 3.4. Asymmetric Hydrogenations 2626 3.4.1. Enantioselective Hydrogenation 2626 3.5. Role of the ILs Purity in Hydrogenation Reactions 2628

Catalysis in ionic liquids

The increasing demand to produce enantiomerically pure pharmaceuticals, agrochemicals, flavors, and other fine chemicals has advanced the field of asymmetric catalytic technologies.1,2 Among all asymmetric catalytic methods, asymmetric hydrogenation utilizing molecular hydrogen to reduce prochiral olefins, ketones, and imines, have become one of the most efficient methods for constructing chiral compounds.3 The development of homogeneous asymmetric hydrogenation was initiated by Knowles4a and Horner4b in the late 1960s, after the discovery of Wilkinson’s homogeneous hydrogenation catalyst [RhCl(PPh3)3]. By replacing triphenylphosphine of the Wilkinson’s catalystwithresolvedchiralmonophosphines,6Knowles and Horner reported the earliest examples of enantioselective hydrogenation, albeit with poor enantioselectivity. Further exploration by Knowles with an improved monophosphine CAMP provided 88% ee in hydrogenation of dehydroamino acids.7 Later, two breakthroughs were made in asymmetric hydrogenation by Kagan and Knowles, respectively. Kagan reported the first bisphosphine ligand, DIOP, for Rhcatalyzed asymmetric hydrogenation.8 The successful application of DIOP resulted in several significant directions for ligand design in asymmetric hydrogenation. Chelating bisphosphorus ligands could lead to superior enantioselectivity compared to monodentate phosphines. Additionally, P-chiral phosphorus ligands were not necessary for achieving high enantioselectivity, and ligands with backbone chirality could also provide excellent ee’s in asymmetric hydrogenation. Furthermore, C2 symmetry was an important structural feature for developing new efficient chiral ligands. Kagan’s seminal work immediately led to the rapid development of chiral bisphosphorus ligands. Knowles made his significant discovery of a C2-symmetric chelating bisphosphine ligand, DIPAMP.9 Due to its high catalytic efficiency in Rh-catalyzed asymmetric hydrogenation of dehydroamino acids, DIPAMP was quickly employed in the industrial production of L-DOPA.10 The success of practical synthesis of L-DOPA via asymmetric hydrogenation constituted a milestone work and for this work Knowles was awarded the Nobel Prize in 2001.3k This work has enlightened chemists to realize * Corresponding author. 3029 Chem. Rev. 2003, 103, 3029−3069

New Chiral Phosphorus Ligands for Enantioselective Hydrogenation

Asymmetric 1,3-Dipolar Cycloaddition Reactions

Stabile Tetrakis(trialkylsilyl)disilylene; Synthese, Röntgenstrukturanalyse und UV/VIS‐Spektren

Crystal structures of molecular complexes of 2-chloro-11,11,12,12-tetracyanoanthraquinodimethane with benzene (1:1) and pyrene(2:1)

Axially chiral 2′-methoxy-1,1′-binaphthyl-2-carboxylic acid (1) was effectively utilized as chiral derivatizing agent for discrimination of enantiomeric alcohols and amines by 1H NMR with the aid of Eu(fod)3. Among a pair of the diastereomeric esters or amides prepared from (aS)-1 and an α-chiral alcohol or amine, the methoxyl protons of the (aS,R)-diastereomer showed the larger lanthanoid-induced downfield shift than those of the (aS,S)-counterpart. Thus, addition of up to 0.5–1.0 equiv amount of Eu(fod)3 caused base-line separation of those protons, allowing determination of the enantiomeric purities and assignment of the absolute configurations of the enantiomeric alcohols and amines. An X-ray crystallographic analysis of the amide ((aS,S)-2) obtained from (aS)-1 and (S)-1-phenylethylamine showed structural resemblance between the amides and esters of 1. Steric models which explain the NMR behavior of the diastereomeric esters and amides are presented based on X-ray analyses. Also reported are two meth...

Use of Axially Chiral 2′-Methoxy-1,1′-binaphthyl-2-carboxylic Acid as Chiral Derivatizing Agent for Discrimination of Enantiomeric Alcohols and Amines by 1H NMR

1,1,2,2,9,9,10,10-Octamethyl-1,2,9,10-tetrasila[2.2]paracyclophane, the first [2.2]paracyclophane bridged by heteroatoms, has been prepared. UV, IR, and 1H- 13C- and 29Si-NMR spectral together with X-ray crystallographic data are recorded. The compound displays a strong σπ mixing between Si–Si bonds and aromatic rings as evidenced by a large red shift in UV spectra.

Octamethyltetrasila[2.2]paracyclophane. Cyclophanes Bridged by Polysilanes

β-(N,N-Dimethylcarbamoylselenenyl)- and β-(N,N-dimethylcarbamoyltellurenyl)alkenyl ketones were converted into isoselenazoles and isotellurazole Te-oxides, respectively, simply by treating with hyd...

Chizuko Kabuto

Papers

Stabile Tetrakis(trialkylsilyl)disilylene; Synthese, Röntgenstrukturanalyse und UV/VIS‐Spektren

Crystal structures of molecular complexes of 2-chloro-11,11,12,12-tetracyanoanthraquinodimethane with benzene (1:1) and pyrene(2:1)

Use of Axially Chiral 2′-Methoxy-1,1′-binaphthyl-2-carboxylic Acid as Chiral Derivatizing Agent for Discrimination of Enantiomeric Alcohols and Amines by 1H NMR

Octamethyltetrasila[2.2]paracyclophane. Cyclophanes Bridged by Polysilanes

Synthesis of Isochalcogenazole Rings by Treating β-(N,N-Dimethylcarbamoylchalcogenenyl)alkenyl Ketones with Hydroxylamine-O-sulfonic Acid