Synthesis, stereochemistry, and reactions of 2,5-diphenylsilacyclopentenes

1,1-Disubstituted derivatives of 2,5-diphenylsilacyclopent-3-enes, namely those having the 1,1-diphenyl, 1,1-dimethyl, 1-alkoxy-1-methyl and 1,1-dialkoxy, were prepared by a one-pot reaction of (1E, 3E)-1,4-diphenyl-1,3-butadiene and dichlorosilanes in the presence of magnesium. Each silacyclopentene was formed as a mixture of one trans and two cis isomers. 1-Ethoxy-1-methyl-2,5-diphenylsilacyclopent-3-ene and 1,1-diethoxy-2,5-diphenylsilacyclopent-3-ene were reacted with optically active alcohols to furnish the corresponding diastereomers. The absolute configuration of one of these diastereomers was determined by X-ray structure analysis. The mixture of cis and trans diastereomers was lithiated by lithium diisopropylamide (LDA) to obtain the trans forms selectively, with the stereoselectivity being determined by NOE experiments.     

Superoxide ion formation process on reduced MoO3---TiO2

Two novel Mo⁵⁺ ions, different from either the D_2d symmetry Mo⁵⁺ on anatase or the D_2hMo⁵⁺ on rutile, appeared on partially reduced molybdenum oxide supported on -titanic acid. The oxygen molecule is held on one of these novel Mo⁵⁺ ions but is not reduced to the superoxide ion. Oxygen is reduced to O⁻₂ entirely by the Mo⁴⁺ ion formed from the D_2d symmetry ion and the O⁻₂ is subsequently stabilized after moving to a Ti⁴⁺-site.     

Novel cluster ions from magnesium and zinc acetates in filament heated in-beam electron impact mass spectrometry

Mass spectral peaks of cluster ions believed to be due to penta-μ-acetato-μ₄-oxo-tetramagnesium and tri-μ-acetato-μ₃-oxo-trimagnesium, or the corresponding zinc compounds, were detected when magnesium acetate or zinc acetate was heated on a tungsten filament and impacted at the same time by an electron beam. Structures of these non-transition metal complexes are analogues of the so-called ‘electron-sponge’ complexes, [Ru₃O(OAc)₆L₃]. Previously reported new cluster ions from lithium acetate are formulated by similar structures.     

Formation of CN(B2Σ) by the electron impact dissociation of HCN. measurements near threshold

Emission spectra of the CN violet band system (B²Σ—X²Σ) were observed by the electron impact on HCN with several impact energies near the threshold. The formation of CN(B) by the dissociative excitation of HCN was investigated. The threshold energy agreed essentially with that obtained by the photodissociation measurements by Okabe et al. The excitation function and the dependence of the vibrational populations of CN(B) on the electron energy were obtained. These results suggest that an optically allowed state contributes to the formation of CN(B) from HCN as a main precursor.     

Non-surface activity and micellization of ionic amphiphilic diblock copolymers in water. Hydrophobic chain length dependence and salt effect on surface activity and the critical micelle concentration

We reported previously (Macromolecules 2003, 36, 5321; Langmuir, 2004, 20, 7412) that amphiphilic diblock copolymers having polyelectrolytes as a hydrophilic segment show almost no surface activity but form micelles in water. In this study, to further investigate this curious and novel phenomenon in surface and interface science, we synthesized another water-soluble ionic amphiphilic diblock copolymer poly(hydrogenated isoprene)-b-sodium poly(styrenesulfonate) PIp-h2-b-PSSNa by living anionic polymerization. Several diblock copolymers with different hydrophobic chain lengths were synthesized and the adsorption behavior at the air/water interface was investigated using surface tension measurement and X-ray reflectivity. A dye-solubilization experiment was carried out to detect the micelle formation. We found that the polymers used in this study also formed micelles above a certain polymer concentration (cmc) without adsorption at the air-water interface under a no-salt condition. Hence, we further confirmed that this phenomenon is universal for amphiphilic ionic block copolymer although it is hard to believe from current surface and interface science. For polymers with long hydrophobic chains (more than three times in length to hydrophilic chain), and at a high salt concentration, a slight adsorption of polymer was observed at the air-water interface. Long hydrophobic chain polymers showed behavior "normal" for low molecular weight ionic surfactants with increasing salt concentration. Hence, the origin of this curious phenomenon might be the macroionic nature of the hydrophilic part. Dynamic light scattering analysis revealed that the hydrodynamic radius of the block copolymer micelle was not largely affected by the addition of salt. The hydrophobic chain length-cmc relationship was found to be unusual; some kind of transition point was found. Furthermore, very interestingly, the cmc of the block copolymer did not decrease with the increase in salt concentration, which is in clear contrast to the fact that cmc of usual ionic small surfactants decreases with increasing salt concentration (Corrin-Harkins law). These behaviors are thought to be the special, but universal, characteristics of ionic amphiphilic diblock copolymers, and the key factor is thought to be a balance between the repulsive force from the water surface by the image charge effect and the hydrophobic adsorption.     

Estimation of equilibrium structure and anharmonicity by use of changes in the rz structure by isotopic substitution and vibrational excitation: I. General formulation and application to OCl2

A general formulation is presented on the differences in the average (r_z) structure caused by isotopic substitution and vibrational excitation; the differences in the average structure for both bonded and nonbonded atomic pairs are represented as linear combinations of quadratic average values of the Cartesian displacement coordinates. This method is applicable to a joint analysis of spectroscopic and electron diffraction data so that the equilibrium geometrical parameters and effective anharmonic constants for polyatomic molecules can be estimated even when only a limited number of rotational constants for isotopic species and vibrationally excited states are available. Its application to OCl₂ molecule as an example is discussed.     

Preparation and properties of phosphaethynes bearing bulky aryl groups with electron-donating substituents at the para position

Phosphaethynes bearing a 2,6-di-tert-butyl-4-(dimethylamino)phenyl, 2,6-di-tert-butyl-4-methoxyphenyl, or 2,6-di-tert-butylphenyl group were prepared. A (31)P NMR spectroscopic investigation of the chemical shifts indicated that electron-donating groups at the para position cause shifts to a higher field. Bathochromic shifts caused by the electron-donating groups were apparently observed in UV-vis spectra. The structure of 2-[2,6-di-tert-butyl-4-(dimethylamino)phenyl]-1-phosphaethyne was analyzed by X-ray crystallography.     

Regiocontrolled addition of arylboronic acids to allenes using palladium and platinum catalysts

Studies about the regiocontrolled addition of arylboronic acids to allenes using a palladium or a platinum catalyst have been described. The selectivity of the reaction can be altered by the choice of the metal reagent and base. Contrary to the formation of endo-olefinic products in the reactions using hydroxopalladium complex, predominant production of exo-olefinic products was observed by the reaction with hydroxoplatinum complex.     

Curve-structured phenalenyl chemistry: synthesis, electronic structure, and bowl-inversion barrier of a phenalenyl-fused corannulene anion

We have demonstrated the features of curve-structured phenalenyl chemistry, for the first time. A phenalenyl-fused corannulene anion has been designed by the annelation of a six-memberd ring across peri-positions of corannulene and generated as a stable species in a degassed solution. The 1H and 13C NMR spectra have shown the highly symmetrical structure and high-field shifts of protons and carbons at the asterisked positions in the chemical structure, indicating the occurrence of large negative charge densities at these positions. These results well agree with the HOMO picture and the electrostatic potential surface, demonstrating the phenalenyl anion-type electronic structure is retained in the curved-surface pi-system. The calculated bowl-inversion barrier of the anion (11.3 kcal/mol) is larger than that of corannulene (9.2 kcal/mol) because of peri-annelation of the corannulene skeleton. The calculations of the barriers of the neutral radical (12.6 kcal/mol), radical dianion (8.1 kcal/mol), and trianion (5.4 kcal/mol) of the phenalenyl-fused corannulene have exhibited a stepwise flattening of the curvature with increase in negative charge. Therefore, we have revealed that the bowl-inversion barrier of the anion is governed by the setoff of the peri-annelation and negative charge effects.