Hiroaki Wasada

Preparation, characterization, and reactivity of dinitrogen molybdenum complexes with bis(diphenylphosphino)amine derivative ligands that form a unique 4-membered P-N-P chelate ring.

Five dinitrogen-molybdenum complexes bearing bis(diphenylphosphino)amine derivative ligands (L(R)) that form a unique 4-membered P-N-P chelate ring, trans-[Mo(N(2))(2)(L(R))(2)] (2(R): R = Ph, Xy, p-MeOPh, 3,5-iPr(2)Ph, iPr), were prepared for the purpose of binding a dinitrogen molecule. The corresponding two dichloride-molybdenum complexes, trans-[MoCl(2)(L(R))(2)] (1(R): R = Ph, Xy), were also prepared as comparisons. FT-IR spectra of 2(R) were measured and compared the ν(N≡N) values. Moreover, X-ray crystal structure determination of 1(R) (R = Ph, Xy) and 2(R) (R = Xy, 3,5-iPr(2)Ph) is performed. These experimental results indicated that the coordinated dinitrogen molecule gets easily influenced by the N-substitutent of diphosphinoamine ligand. In addition, to investigate the effect of the properties of the diphosphinoamine ligand for the dinitrogen molybdenum complexes, we performed DFT calculations that focused on the difference of N-substituent, the dihedral angle between P-N-P plane and N-substituent aryl group, and the P-N-P bite angle. This calculation revealed that the competition between the back-donation from metal to dinitrogen and that from metal to ligand was affected by P-N-P bite angle and the dihedral angle of N-substituent of ligand. In order to examine the reactivity with respect to conversion of dinitrogen to ammonia, protonation and trimethylsilylation reactions of the coordinated dinitrogens were carried out for 2(R).

REACTION MECHANISM OF WATER EXCHANGE ON DI- AND TRIVALENT CATIONS OF THE FIRST TRANSITION SERIES AND STRUCTURAL STABILITY OF SEVEN-COORDINATE SPECIES

Abstract We studied the structural stability of heptahydrated trivalent cations of the first transition series from scandium to cobalt as model intermediary species in associative reaction pathways for the water exchange of the hexahydrated cations by ab initio molecular orbital methods. All the structures of heptacoordination are pentagonal bipyramidal with a distorted equatorial plane. The heptahydrated di- and trivalent cations with the same d-electron configuration are similar to each other for the structure and the structural stability which are strongly dependent on their d electron configurations. The associative mechanism is possible for the water-exchange reactions of the hexahydrated trivalent cations from scandium to cobalt, because the seven-coordinate species are located at the local minima or at the saddle points on the potential energy surface. The intrinsic reaction coordinates of the water-exchange reactions on the hexahydrated vanadium(II) and chromium(II) ions support the cis and trans attack of the associative mechanisms. The hexahydrated trivalent cations with d3 and d6 configurations [chromium(III) and cobalt(III)] prefer a cis attack, while manganese(III) with a d4 configuration prefers trans attack during the operative associative process of the water-exchange reaction.

Ab initio MO study on the potential energy surfaces of low-lying excited states of protonated Schiff base retinal

Abstract The potential energy surface of the protonated Schiff base of retinal has been calculated at the state-average complete active space self-consistent field (sa-CASSCF) level of theory to elucidate the mechanism of the trans – cis photoisomerization of the chromophore in bacteriorhodopsin. We treated two molecular systems, i.e., protonated N -methyl Schiff base retinal (C 21 H 32 N + ) and its simplified model compound, C 12 H 16 N + . We used the 6-31g split-valence basis set. To clarify the effect of the protein and hydrogen bonding with water, the same molecular system with a negative point charge or with a water molecule in the vicinity of the Schiff base was also calculated. The results show that the electrostatic environment of the protein works to produce a favorable potential energy surface for the lowest excited state of the chromophore, leading to efficient trans – cis photoisomerization.

Hydrogen trapping state associated with the low temperature thermal desorption spectroscopy peak in hydrogenated nanostructured graphite

Hydrogenated nanostructured graphite has been reported to exhibit a characteristic peak at around 600–800 K in thermal desorption spectroscopy (TDS). The origin of this peak is still controversial. We have reexamined it based on a combination Fourier transform infrared (FT-IR), electron diffraction, and electron energy-loss spectroscopy (EELS) study. The FT-IR spectrum of HNG exhibited an unknown broad absorption band at very low frequencies around 660 cm−1, which almost disappeared by annealing up to 800 K. Electron diffraction as well as plasmon peaks in EELS detected unusual shrinkage and subsequent expansion of the graphene interlayer distance by hydrogen incorporation and desorption with annealing, which were well correlated with the change in intensity of the 660 cm−1 IR band. An energetically stable configuration was found by theoretical model calculations based on GAUSSIAN03. All the present results are consistent with our previous studies, which suggested that hydrogen is loosely trapped between ...

Synthesis of Azepines via a [6 + 1] Annulation of Ynenitriles with Reformatsky Reagents

A protocol for the direct synthesis of azepines using a hafnium(III)-catalyzed [6 + 1] annulation of N-tethered ynenitriles with Reformatsky reagents is reported. A broad range of 3-amino-2,7-dihydro-1H-azepine-4-carboxylates 4aa-4he were obtained in high yields and with excellent functional group tolerance. The copper-mediated reactions of isolable Blaise intermediates (enamino esters 3), uniquely underwent 5-endo cyclization to afford the β-2,5-dihydropyrrolyl α,β-unsaturated esters 5aa-5fc, which exhibit anticancer activity.

FORMATION OF THE TRIMER ION CORE IN THE HETEROGENEOUS RARE GAS CLUSTER IONS

Thermochemical stabilities of the cluster ions composed of mixed rare gases were measured using a pulsed-electron beam high pressure mass spectrometer. The formation of trimer ion cores, i.e., A+(B)2 and A2+(B)1, was found when A and B are next to each other in the Periodic Table. This trend is similar to that for the pure rare gas cluster ions, i.e., the formation of ion core Rg3+ for Rg=He, Ne, Ar, Kr, and Xe. Although Ar and Xe are not next to each other in the Periodic Table, the formation of the trimer ion core is found for Xe+(Ar)2. This may be due to the fact that the ionization potentials of Ar and Xe are close to each other. The bond energies of larger cluster ions A+(B)2(B)n−2 and A2+(B)1(B)n−1 were found to be similar to those of homogeneous cluster ions (B)3+(B)n−3. The experimental bond energies were confirmed by ab initio calculations with a modified G2(MP2) method [e.g., 0.2 kcal/mol (expt) and 0.3 kcal/mol (theory) for Ar2+⋅He].

SOLVATION STRUCTURE OF SOLVATED CU(I) IONS IN NON-AQUEOUS SOLVENTS AS STUDIED BY EXAFS AND AB INITIO MOLECULAR ORBITAL METHODS

The structure parameters around the Cu(I) ion in pyridine (PY), 4-methylpyridine (4MPY), 2-methylpyridine (2MPY), 2,6-dimethylpyridine (26DMPY), and acetonitrile (AN) were determined by the extended X-ray absorption fine structure (EXAFS) method. The solvation structures of the Cu(I) ion in PY, 4MPY, and AN are 4-coordinate tetrahedral with Cu-N bond lengths of 205, 205, and 200 pm, respectively. In the case of 2MPY and 26DMPY, the Cu(I) ion has a 3-coordinate triangular structure with a Cu-N bond length of 201 pm. Such a decrease in the coordination number was interpreted in terms of the bulkiness of the solvent molecules. In order to clarify the most stable solvation structure of the Cu(I) ion, we carried out ab initio molecular orbital calculations for the solvation system of [Cu(NCH)n]+ (n = 1 - 6 ) where the steric effect is negligible. The Gibbs free energy of solvation was the smallest in the case of n = 4 and the 4-coordinate tetrahedral solvation of the Cu(I) ion was theoretically evaluated as most stable. The enthalpy of solvation monotonously decreases with increasing n, while the entropy of solvation proportionally increases. Although a larger gain of enthalpy is observed for the octahedral structure rather than the tetrahedral one, the entropic loss for the former overcomes the enthalpic gain.