Energy-Dispersive XAFS Studies on the Spontaneous Dispersion of PdO and the Formation of Stable Pd Clusters in Zeolites

Spontaneous dispersion and clustering processes of Pd were measured by means of the energy-dispersive EXAFS method. The spontaneous dispersion of bulky metal Pd into highly dispersed PdO was directly observed on the H-type zeolite in the atmosphere of O2. In contrast to H-type zeolites, simple oxidation of the agglomerated Pd was observed on Na-ZSM-5. The structural change of Pd was followed in the atmosphere of hydrogen. The clustering processes of metal Pd depended on the kind of zeolite, and these were categorized into three groups. The first group, i.e., Na-ZSM-5 and H-beta, showed monotonic agglomeration of metal Pd by increasing the reduction temperature. The second group consisted of H-ZSM-5 and H-mordenite where the formation of Pd6 clusters was found. On these zeolites, the generation of Pd6 clusters was reversibly observed upon the repetition of reduction and oxidation treatments. The third group consisted of H-Y and USY zeolites where the formation of Pd13 clusters was observed. From these findings, it was concluded that the crystal structure and acid sites of zeolites had profound influences on the dynamic behavior and the genesis of Pd clusters with various structures.     

Highly efficient chiral metal cluster systems derived from Ru3(CO)12 and chiral diiminodiphosphines for the asymmetric transfer hydrogenation of ketones

The chiral Ru cluster-based catalyst systems generated in situ from Ru3(CO)12 and chiral diiminodiphosphine tetradentate ligands effected asymmetric transfer hydrogenation of propiophenone in 2-propanol, leading to 1-phenyl-1-propanol in 94% yield and with 96% ee.     

A general and efficient method for the palladium-catalyzed cross-coupling of thiols and secondary phosphines

The general and efficient cross-coupling of thiols with aryl halides was developed utilizing Pd(OAc)₂/1,1′-bis(diisopropylphosphino)ferrocene as the catalyst. The substrate scope is broad and includes a variety of aryl bromides and chlorides, which can be coupled to aliphatic and aromatic thiols. This catalyst system has the widest substrate scope of any reported to date. The present catalyst system also enables the palladium-catalyzed coupling of secondary phosphines with aryl bromides and chlorides.     

Kinetic study on enzymatic s-oxygenation promoted by a reconstituted system with purified cytochrome P-450

Thioanisole derivatives ($\text{1a–e}$) were found to be oxygenated by a reconstituted system of purified cytochrome P-450 to give sulfoxides ($\text{2a–e}$). Logarithms of Vmax were found to be correlated linearly with one electron oxidation potentials of the sulfides (Ep) suggesting the oxygenation to proceed via one electron transfer from sulfides to the active species of the enzyme.     

Theoretical study of degree of covalency in some CoF6(n-) complexes (n = 4, 3, and 2)

On the basis of a high-quality LCAO MO SCF calculation, covalency versus ionicity of a Co–F bond in the CoF₆(n-) complexes, where n = 4, 3, and 2, is discussed. The overlap and gross atomic populations, delocalization of certain MOS, and the charge densities in the bond region as well as around F's all indicate that the covalency increases as n decreases or the valency of Co increases in these complexes.     

Synthesis, structure, and bonding properties of 5-carbaphosphatranes: a new class of main group atrane

1-Hydro-5-carbaphosphatrane (1) and 1-methyl-5-carbaphosphatrane (2), the first 5-carbon analogues of phosphatranes, were synthesized by a demethylation reaction of cyclic phosphinate 3. X-ray analysis revealed that 1 has a typical trigonal bipyramidal structure with hydrogen and carbon atoms at the apical position and three oxygen atoms at the equatorial positions, indicating that 1 is a phosphorane in the perfectly "anti-apicophilic" arrangement. Apical P-C and P-H bond lengths were 1.921(2) and 1.38(2) A, respectively. The (1)J(PH) value of 1 and the (1)J(PC)(P-CH(3)) value of 2 were 852 and 215 Hz, respectively, which are extraordinarily large for the apical coupling constants of phosphoranes, but close to those of the reported phosphatranes with a 5-nitrogen atom. IR and Raman spectra are also reported. Force constant calculations indicate the transannular bond in carbaphosphatrane is 3 times stronger than in silatrane, due to its covalent character.     

Radical Ions of Conjugated Polycyclic Hydrocarbons Containing Two Phenalenyl π-Systems

The radical cations and the radical of 1,2-bis(phenalen-1-ylidene)ethane ( 1 ), 1,2-bis(phenalen-1-ylidene)ethene ( 2 ) and pentaleno[1,2,3-cd: 4,5,6-c′ d′]diphenalene ( 3 ) have been characterized by ESR and ENDOR spectroscopy. The ease of formation of these radical ions and their π-spin distributions are interpreted in terms of a simple model correlates the frontier orbitals of 1, 2 and 3 with the nonbonding MO's of two phenalenyl π-systems.     

Reactions of aromatic nitro,nitroso, hydroxylamino azoxy,azo and hydrazo compounds with selenol

Relative reactivities of aromatic nitro, nitroso, hydroxylamino, azoxy, azo and hydrazo compounds in the reduction with RSe^? were found to fall in the following order :

     

Amphiphilic NaY zeolite particles loaded with niobic acid: Materials with applications for catalysis in immiscible liquid-liquid system

The catalytic potential of catalysts for acid-catalyzed reactions has been demonstrated by NaY zeolite loaded with alkylsilane-covered niobic acid in the liquid phase hydration of 1,2-epoxyoctane with water. The catalytic activity of the catalysts was correlated to the amphiphilic character of the solid catalyst particles. This revised version was published online in August 2006 with corrections to the Cover Date.     

Reduction of diaryl disulfides with 1-benzyl-1,4-dihydronicotinamide

Reduction of diaryl disulfides with 1-benzyl-1,4-dihydronicotinamide (BNAH) proceeded through a radical chain reaction, while dialkyl disulfides were found to be inert to BNAH.