Hideki Saitoh

Effect of intramolecular π–π and CH–π interactions between ligands on structure, electrochemical and spectroscopic properties of fac-[Re(bpy)(CO)3(PR3)]+(bpy = 2,2′-bipyridine; PR3= trialkyl or triarylphosphines)

Intramolecular pi-pi and CH-pi interactions between the bpy and PR3 ligands of fac-[Re(bpy)(CO)3(PR3)]+ affect their structure, and electrochemical and spectroscopic properties. Intramolecular CH-pi interaction was observed between the alkyl groups on the phosphine ligand (R =nBu, Et) and the bpy ligand, and intramolecular pi-pi and CH-pi interactions were both observed between the aryl group(s) on the phosphorus ligand (R =p-MeOPh, p-MePh, Ph, p-FPh, OPh) and the bpy ligand, while no such interactions were found in the trialkylphosphite complexes (R = OiPr, OEt, OMe). The intramolecular interactions distort the pyridine rings of the bpy ligand as long as 3.7 x 10(-2)A in crystals. Molecular orbital calculations of the bpy ligand suggest that this distortion decreases the energy gap between its pi and pi* orbitals. An absorption band attributed to the pi-pi*(bpy) transition of the distorted rhenium complexes, measured in a KBr pellet, was red-shifted by 1-5 nm compared to the complexes without the distorted bpy ligand. Even in solution, similar red shifts of the pi-pi*(bpy) absorption were observed. The redox potential E1/2(bpy/bpy*-) of the complexes with the trialkylphosphine and triarylphosphine ligand are shifted positively by 110-120 mV and 60-80 mV respectively, compared with those derived from the electron-attracting property of the phosphorus ligand. In contrast with these properties, three nu(CO) IR bands, which are sensitive to the electron density on the central rhenium because of pi-back bonding, were shifted to higher energy, and a Re(I/II)-based oxidation wave was observed at a more positive potential according to the electron-attracting property of the phosphorus ligand.

Synthesis and properties of [Ru(tpy)(4,4′-X2bpy)H]+ (tpy=2,2′:6′,2″-terpyridine, bpy=2,2′-bipyridine, X=H and MeO), and their reactions with CO2

Abstract A novel type of hydrido complex [Ru(tpy)(4,4′-X2bpy)H]+ (X=H and MeO) was synthesized. The stronger hydridic character of the complexes compared with [Ru(bpy)2(L)H]+ type complexes (L=CO, PPh3 and AsPh3) was demonstrated by the relatively high chemical shifts of RuH in the 1H NMR spectra and by higher reactivities with CO2. The reactions of [Ru(tpy)(4,4′-X2bpy)H]+ with CO2 occurred at second-order rate constants varying from (4.69±0.02) to (5.51±0.04)×10−3 M−1 s−1 depending on both solvent and X, giving the formato complexes [Ru(tpy)(4,4′-X2bpy)(OCHO)]+ quantitatively. The rate constant was increased with the increase of solvent acceptor number, and the reaction of [Ru(tpy){4,4′-(MeO)2bpy}H]+ with CO2 was found to be 3.6 times faster than that of [Ru(tpy)(bpy)H]+. These results suggest that nucleophilic attack of the hydride ligand to the carbon atom of CO2 is the rate determining step for the formation of the formato complex. The structure of the formato complex [Ru(tpy)(bpy)(OCHO)](PF6) was determined by X-ray crystallographic analysis.

Polymorphism of Acrylic and Methacrylic Acid Esters Containing Long Fluorocarbon Chains and Their Polymerizability

The molecular aggregation of acrylic and methacrylic acid esters containing long-fluorocarbon chains: 2-(perfluoroalkyl)ethyl acrylate (FFnEA) and 2-(perfluoroalkyl)ethyl methacrylate (FFnEMA) (F(CF2)nCH2CH2OCOC(X)=CH2, where X=H, CH3 and n=6, 8, 10) was investigated by differential scanning calorimetry (DSC) and temperature controlled X-ray powder diffraction measurement. These compounds exhibited some characteristic polymorphic behaviors depending on the length of fluorocarbon chain and the α-position methyl group. The solid-state polymerization by γ-ray irradiation was studied for these compounds in the various crystal forms. In the solid-state polymerization, highest polymerizability was observed in the crystal form that exists in the highest temperature region for each compound.

DSC and X-ray studies on side-chain crystallization of comb-like polymers

Thermal properties of acrylate and methacrylate monomers containing long-fluorocarbon chains (H(CF2)nCH2OCOCH=CH2, (FnA) and H(CF2)nCH2OCOC(CH3)=CH2, (FnMA), wheren=6, 8, 10) and their comb-like polymers have been investigated by differential scanning calorimeter (DSC) and X-ray diffraction. The comb-like polymers (PF10A and PF10MA) with sufficiently long-fluorocarbon chains showed a simple melting and crystallizing behavior. For the fusion of PF10A in 1st heating, enthalpy change δHf was 18 kJ mol−1 and entropy change δSf was 45 J K−1 mol−1, while for PF10MA the values δHf and δSf were 5.3 kJ mol−1 and 14 J K−1 mol−1, respectively. Melted PF8A crystallized slowly, whereas PF8MA with same fluorocarbon chain and also both of PF6A and PF6MA with shorter fluorocarbon chains can hardly crystallize by the aggregation of side-chains. Effects of the length of side-chain and the flexibility of main chain on the side-chain crystallization of comb-like polymers are clear. Crystallization process of the methacrylate monomers was sensitively affected by the scanning rate of DSC measurement and the length of fluorocarbon chains.

Characterization of microstructure of polyethylenes by differential scanning calorimetry

Abstract The microstructures of polyethylenes (PEs) were investigated by differential scanning calorimetry (DSC). Homogeneous and inhomogeneous blends of three types of PEs, that is, low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), were used for measurement. The thermal behavior of samples suggests that homogeneous blends of HDPE and LDPE or LLDPE have a metastable microstructure which is caused by the co-crystallization of two different types of PEs. The single endothermic peak, due to the fusion of the homogeneous blend, is observed in the first heating and is not completely split into the peaks of respective components PEs by the second heating. From the result, it is thought that the molecular chains of PEs are entangled during the co-crystallization and they are not completely loosened by the first melting. The relation between the microstructures and the thermal behavior revealed by DSC has been discussed.

Identification of Polyethylene by Differential Scanning Calorimetry: Application to forensic science

A forensic sample consisting of melt-recrystallized polymers that was recovered from the scene of a fire in a factory was identified by differential scanning calorimetry. The factory commonly used two kinds of film sheets, A and B, made by different manufacturers. It was necessary to decide whether the forensic sample related to material A or B. The forensic sample and reference samples of materials A and B were subjected to infrared spectroscopy and pyrolysis gas chromatograph mass spectrometry measurements, which revealed their polyethylene nature. The thermal behaviour of the samples was examined by differential scanning calorimetry (DSC) and they were found to be blends of two kinds of polyethylenes, low-density polyethylene and linear low-density polyethylene. The samples could be identified and distinguished from each other via the DSC measurements.

Investigation of the thermal degradation mechanisms of poly(styrene-co-methacrylonitrile)s by flash pyrolysis and TG–FTIR measurements

Abstract Thermal degradation mechanisms of polystyrene, polymethacrylonitrile, and their random copolymers have been investigated by flash pyrolysis by Py-GC–MS and by programmed temperature TG–FTIR. The thermal degradation mechanisms of the copolymers are discussed in terms of the competition between depolymerization and back-biting reaction on the basis of bond dissociation energies of C–C and C–H bonds ( Q C–C and Q C–H ) in the polymer chains. The activation energy of pyrolysis ( ΔE a ) obtained by Ozawas plot and Q C–C values was increased with the content of methacrylonitrile units in the copolymer chain, although the onset temperatures of loss of sample mass in TG curves shifted to the lower temperature region. These phenomena have been explained in terms of the change of the ratio of depolymerization to back-biting reaction depending on chemical structure and degradation temperature.

Influence of molecular arrangement on the γ-ray-irradiation solid-state polymerization of 1-octadecyl vinyl ether with a characteristic polymorphism

The polymorphic behavior of 1-octadecyl vinyl ether was investigated by DSC and X-ray diffraction measurements under various temperatures. In DSC measurement of 1-octadecyl vinyl ether in the temperature range of −30 to approximately 50°C, four transition peaks were observed on heating, whereas three transition peaks appeared on cooling. The phase-transition behavior was investigated by the repeating scanning DSC measurements. It was concluded that this compound exhibited four crystalline modifications: α, sub α, β0, and β1. It was confirmed by the temperature-controlled X-ray diffraction measurement that these phase transitions are attributed to the change of crystal systems from hexagonal packing (α form) to a distorted orthorhombic (O⟂′) system (β1 form) via orthorhombic (O⟂) (sub α form) and intermediate β0 form, although the β0 form has not yet been clarified. In the γ-ray-irradiation solid-state polymerization for these crystal forms of this compound, the polymerizability of the sub α form is higher than that of other forms, and that of the α form is lowest. The polymerizability demonstrated an unusual increase at a temperature of −83.6°C, probably because the cationic polymerization mechanism is dominant over that of the free radical.

Structure and properties of constituents in hexane extract of frankincense

Frankincense has a unique odor and is an important fragrance material for Japanese incense. The constituents of frankincense vary according to the species of tree from which the resin is derived. The aroma profile of the frankincense used in Japanese incense showed that the important odor components were diterpenes, and incensole and its derivatives. These compounds have not been previously recognized as important odor compounds, and the relative stereochemistry of the diterpenes has not been assigned. We investigated the stereochemical structures of these compounds through synthetic studies with respect to 2. Incensole epoxide was isolated as pure crystals, and its structure was determined by single-crystal X-ray diffraction. The stereochemistry of the diterpenes was assigned by synthetic methods. Incensole and incensole acetate in the hexane extracts gradually oxidized to their epoxides, although this was not observed in the isolated pure compounds. These results indicate that incensole epoxides are not primary constituents of frankincense, but secondary products.

Solid-state thiotropolone: an extremely rapid intramolecular proton transfer.

Through variable-temperature solution-state NMR and molten- and solid-state CP/MAS (13)C NMR spectra, thiotropolone is found to exist as two rapidly equilibrated tautomeric structures, thione and enethiol, even in the solid state far below the melting point. The crystal structure shows an almost perpendicular packing, suggesting that the intramolecular hydrogen bond is dominant.