Akio Tajiri

Inter-ring overlap integrals in dimer complexes of phthalocyanines and porphyrins

Abstract Overlap integrals of phthalocanine (Pc) and porphyrin (Pp) dimers were calculated on changing the distance and rotation angle between two macrocycles. The HOMOs of Pc 2− and Pp 2− are both a 1u and were found to give large overlap integrals. The origin of this strong overlap was clarified by a comparison between the four-orbital model and the perimeter model.

An analysis of paramagnetic shifts in proton NMR spectra of non-radical lanthanide(III)-phthalocyanine sandwich complexes

Abstract Proton NMR spectra of [NBu4] [Ln(III)Pc2] ([NBu4] = tetra (n-butyl)ammonium; Ln = Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Tm, Er, Yb and Lu; Pc = phthalocyanine) are reported. Analysis of NMR and UV-visible spectra suggests a highly symmetrical structure for [LnPc2]− in solution. Contact shifts and pseudo-contact shifts were separated from the observed paramagnetic shifts by a statistical analysis and the results compared with data from other LSR complexes.

Electrochemistry of ferric ruthenocyanide (Ruthenium Purple), and its electrocatalysis for proton reduction

Abstract Electrochemistry of ferric ruthenocyanide (Ruthenium Purple, RP) was studied in acidic solutions containing a sodium salt (NaH 2 PO 4 or NaCl). Two kinds of redox peaks for the Fe III/II couple were clearly seen in a Na + solution, originating from a composite structure of both Fe 4 III [Ru II (CN) 6 ] 3 (insoluble) and Fe III [Ru II (CN) 6 ] − (soluble). In repeated CV scans in a NaCl solution, it was found that only the couple of the redox peak assigned to the insoluble form remains unchanged under the steady state. The ratio of the insoluble form was estimated by coulometry as ca. 40% of the initial coated unit cells of the RP. Efficient electrocatalytic H 2 formation was found to take place with the aid of the RP although this electrocatalysis was dependent on the type of sodium salt employed. In order to investigate the dominant factor affecting the overall kinetics in the H + reduction catalysis, the dependences of both the catalytic activity and the electron transfer rate in the RP film were studied in a NaH 2 PO 4 solution as a function of the coated amount. It was found that the overall kinetics are not dominated by electron transfer in the RP film.

Synthesis and intramolecular pericyclization of 1-azulenyl thioketones.

Several azulene-substituted thioketones, 1-thiobenzoylazulene (1a) and di(1-azulenyl) thioketone (2a) and their derivatives (1b and 2b-d) with alkyl substituents on each azulene ring, were prepared and their intramolecular pericyclization reaction was examined. The thioketones with a 3-alkyl substituent on each azulene ring exhibited the presumed pericyclization reaction under thermal and acid-catalyzed conditions, although the cases of the 1-azulenyl thioketones without the 3-alkyl substituents afforded a complex mixture under similar conditions. The intramolecular reaction following the intramolecular hydrogen transfer afforded the products 13b, 14b, and 14c. The products 13b and 14b were converted into the corresponding cations 18(+) and 19(+), which have structural similarity with that of the phenalenyl cation. These cations exhibited the expected two-step reduction waves upon CV, although the ESR analysis revealed that the neutral radical state did not have the presumed high stability.

Reaction of azulenes with 1-trifluoromethanesulfonylpyridinium trifluoromethanesulfonate (TPT) and synthesis of the parent azulene

2-Azulenyl trifluoromethanesulfonate was prepared by the reaction of 2-hydroxyazulene with trifluoromethanesulfonic anhydride in the presence of triethylamine as a base. Under the use of pyridine, 1-trifluoromethanesulfonylpyridinium trifluoromethanesulfonate further reacted with 2-azulenyl trifluoromethanesulfonate to give 1-(1-trifluoromethanesulfonyl-1,4-dihydropyridin-4-yl)azulenyl trifluoromethanesulfonate. Moreover, we found that azulenes also reacted with 1-trifluoromethanesulfonylpyridinium trifluoromethanesulfonate to give 4-(1-azulenyl)-1,4-dihydropyridine derivatives and 6-(1-azulenyl)-1-trifluoromethanesulfonyl-1-aza-hexa-1,3,5-triene depending on the reaction conditions. 2-Azulenyl trifluoromethanesulfonate was converted finally into the parent azulene in excellent yield by palladium-catalyzed reduction using formic acid as a reducing reagent.

Electrochemical hydrogen evolution by catalyst membrane composed of platinum, alkyl viologen and Nafion: consideration of the kinetically dominant factor based on understanding of electron-mediating ability of the viologen molecule

Abstract Electrocatalytic H 2 formation was carried out by using a Nafion membrane (Nf) embedding a Pt catalyst as well as an alkyl viologen (denoted as RV 2+ ; alkyl group (R): methyl, ethyl, propyl, heptyl, or dodecyl group). The H + reduction catalyzed by the Pt via the electrogenerated RV + was investigated. In order to understand the electron-mediating characteristic of the RV 2+ on kinetic aspect, turnover numbers (TON) of the RV 2+ for H 2 formation as well as electron transport kinetics (represented by the apparent diffusion coefficient of electron, D app ) of the mediator were studied with respect to RV 2+ concentration. In any RV 2+ system, both the TON and the D app exhibited a similar dependence on the concentration, showing that the overall kinetics is dominated by the electroreduction process of the mediator. When applying both the tetrachloroplatinate(II) (Pt 0 in catalytically active state) and the viologen mediator to the H 2 formation system, the TON was found to be controlled by the D app .

The absolute configuration of homotropone and its iron tricarbonyl complexes

Abstract Optical resolution of homotropone ( 1 ) and its Fe(CO)3 complexes ( 2, 3 ) was carried out by HPLC. The absolute configuration of the resolved exo complex (+)- 2 was determined by single crystal X-ray diffraction analysis, which was applied to establish the absolute configuration of the endo isomer (−)- 3 . The absolute configuration of homotropone (−)- 1 was established from theoretical and experimental considerations.

HPLC optical resolution of tricarbonyl(2,3-dihydrotropone)iron and its absolute configuration

Abstract Optical resolution of (±)-tricarbonyl(2,3-dihydrotropone)iron was carried out, and the absolute configuration was determined by X-ray diffraction and CD spectroscopic studies.

Voltammetric study of electrocatalysis for dioxygen reduction by trinuclear rutheniumammine complex confined in a polymer membrane

Abstract Electrocatalytic O 2 reduction was studied using a modified electrode coated with a Nafion membrane (Nf) dispersing a trinuclear ruthenium ammine complex ([(NH 3 ) 5 Ru III ORu IV (NH 3 ) 4 ORu III (NH 3 ) 5 ]Cl 6 , Ru-red). When measuring cyclic voltammogram under O 2 atmosphere (at 0.5 mV s −1 ), catalytic currents due to O 2 reduction were found to develop below −0.2 V (vs. Ag/AgCl). Since Ru-red undergoes irreversible decomposition into the mononuclear complexes via the reduced state (Ru III –Ru III –Ru III ) (∼−0.1 V), it is suggested that the electrocatalysis originates from the decomposed species (initial active species: Ru II (NH 3 ) 5 (OH 2 ) and Ru II (NH 3 ) 4 (OH 2 ) 2 ) rather than from the Ru-red. Although the present electrocatalyst was also applied to H 2 O 2 reduction system, the catalytic activity was found to be poor from the voltammetric behavior. It appeared that the kinetics of the electrocatalysis is much faster in the O 2 reduction than in the H 2 O 2 one. A selective and direct catalysis for O 2 reduction into H 2 O was suggested from a ring–disk voltammogram to take place by an aggregate of the mononuclear ruthenium complexes in the polymer matrix. In addition, it was found that electrocatalytic O 2 reduction involves a slow kinetic process, so that factors affecting the overall kinetics were discussed in terms of the catalysis mechanism.

Optically active hexacarbonyl(2-methyltropone)diiron; reaction mechanism of tricarbonyl(7-methyltropone)-iron with Fe2(CO)9

Abstract An optically active di-π-allyl hexacarbonyldiiron complex was prepared for the first time starting from racemic 7-methyltroponeFe(CO)3. The reaction mechanism of (substituted tropone)Fe(CO)3 with Fe2(CO)9 was discussed.