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

Optically pure cyclophanes possessing a 1,3-dicarbonyl moiety were conveniently synthesized from alkanedioyl dichloride in four steps. The intramolecular [4+2]cycloaddition of bis(acylketene)s generated by thermal decomposition of bis(4,6-dioxo-1,3-dioxane) proceeded smoothly, giving cyclophane pyranones in high yields. The compounds possessing 7−10 bridging methylenes were resolved by imine formation with (R)-1-phenylethylamine, followed by basic hydrolysis. These cyclophanes are optically active versions of acetylacetone or salicylaldehyde and formed complexes with metals such as copper and europium. X-ray analysis of the chiral copper complex indicated the pentacoordinated structure of the copper metal with syn configuration of the two bridging chains.

Convenient Synthesis of Chiral Cyclophanes that Can Coordinate to Metals

Chemistry of organosilicon compounds. 193. Intramolecular cyclotrimerization of macrocylic and acyclic triynes with Group 6 metal carbonyls. The formation of fulvene and benzene

Planar Hexasilylbenzene Dianion with Thermally Accessible Triplet State

A series of oligo(1,1-silole)s, Me3Si[SiC4Me4]n SiMe3 (3: n=3, 4:n=4, 5:n=5) were synthesized and characterized. X-ray diffraction analysis of tersilole 3 revealed that the pentasilane backbone has almost all-trans conformation. The oligo(1,1-silole)s show distinct UV absorptions due to σ-σ*, σ-π*, and π-π* transitions.

Synthesis and Structure of a Series of Oligo[1,1-(2,3,4,5-tetramethylsilole)]s

1,3-Thiaza- and 1,3-selenaza-1,3-butadienes bearing several substituents at the C-2 and C-4 positions were generated through thermal cycloreversion of 6H-1,3,5-oxathiazines or 6H-1,3,5-oxaselenazines, respectively, and the heterodienes were efficiently trapped by using acetylenic dienophiles. When 6H-1,3,5-oxathiazines or 6H-1,3,5-oxaselenazines were heated in the presence of nucleophiles, such as alcohols or thiols, the corresponding 1,4-adducts of the heterodienes with the nucleophiles were obtained in good yields. On the other hand, heating of 6H-1,3,5-oxathiazines or 6H-1,3,5-oxaselenazines in the absence of trapping agents afforded several products which originated from the in situ generated 1,3-chalcogenaza-1,3-butadienes; also the heterodienes were not isolated or observed directly as the monomeric forms at all.

Chizuko Kabuto

Papers

Convenient Synthesis of Chiral Cyclophanes that Can Coordinate to Metals

Chemistry of organosilicon compounds. 193. Intramolecular cyclotrimerization of macrocylic and acyclic triynes with Group 6 metal carbonyls. The formation of fulvene and benzene

Planar Hexasilylbenzene Dianion with Thermally Accessible Triplet State

Synthesis and Structure of a Series of Oligo[1,1-(2,3,4,5-tetramethylsilole)]s

Generation of 1,3-Chalcogenaza-1,3-butadienes by Thermal Cycloreversion of 2,4,6-Trisubstituted 6H-1,3,5-Oxachalcogenazines