Kazuyuki Kasuga

Transfer hydrogenation of a variety of ketones catalyzed by rhodium complexes in aqueous solution and their application to asymmetric reduction using chiral Schiff base ligands

The rhodium complex [Cp ∗ Rh(bpy)Cl]Cl shows efficient catalytic activity in the transfer hydrogenation of a wide variety of ketones in aqueous formic acid solution under mild reaction conditions. In the asymmetric reduction using chiral Schiff base ligands, the asymmetric induction was observed in reduction of dialkyl ketones as well as aryl ketones, among which ortho-chloroacetophenone gave the highest ee of 84%.

3-(2-Pyridyl)-2-pyrazoline derivatives: novel fluorescent probes for Zn2+ ion

Abstract Spectroscopic studies revealed that 3-(2-pyridyl)-2-pyrazoline derivatives have rather strong affinity toward divalent transition metal ions, but have almost no interaction with alkali and alkaline-earth metal ions. In the case of the 5-(4-cyanophenyl) derivative, enhancement of the fluorescence intensity was observed upon addition of the Zn 2+ ion, while most of other transition metal ions caused complete quenching.

Molecular and electronic ground and excited structures of heteroleptic ruthenium polypyridyl dyes for nanocrystalline TiO2 solar cells

Heteroleptic ruthenium complexes of the type cis-[Ru(H2dcbpy)(L)(NCS)2], where H2dcbpy = 4,4′-dicarboxy-2,2′-bipyridine and L = 1,10-phenanthroline (phen) (1) or dipyrido[3,2-a∶2′,3′-c]-phenazine (dppz) (2), were synthesized and their photochemical properties were investigated. The complexes showed a broad and intense metal-to-ligand charge transfer (MLCT) transition band in the visible region. The complexes were anchored to nanocrystalline TiO2 film electrodes, and the photovoltaic properties of the resulting dye-sensitized solar cells were characterized and compared with the properties of cells prepared with cis-(NBu4)2[Ru(Hdcbpy)2(NCS)2] (N719). The efficiency of the 2-sensitized solar cell was 20% lower than that of the 1-sensitized solar cell, but neither was as efficient as the N719-sensitized solar cell. The electronic structures of the complexes were investigated by means of a time-dependent density functional theory method in an effort to better understand their effectiveness in TiO2-based photoelectrochemical cells. The calculation results indicated that the character of the MLCT transitions in the long wavelength region differed between 1 and2, although their energy levels are nearly the same in the protonated forms. It was suggested that the performance of the 2-sensitized solar cell could be improved by the introduction of electron-donating groups on the dppz ligand of 2.

Synthesis of novel crownophanes containing two phenolic moieties via a tandem claisen rearrangement

Abstract A series of crownophanes containing two phenolic moieties within a macrocyclic ring have been successfully synthesized by a one-step thermal reaction from the corresponding macrocyclic polyethers by using a “Tandem Claisen Rearrangement”.

Double Claisen rearrangement: A new route to novel ligands for metal ions

Abstract Successive double Claisen Rearrangement of 2-aryloxymethyl-3-aryloxy-1-propene leads to the corresponding 2-(O-hydroxyaryl)methyl-3-(O-hydroxymethyl)-1-propene derivatives which exhibit excellent extractabllity for heavy metal ions.

Selective Liquid Membrane Transport of Lead(II) by an Acyclic Polyether Dicarboxylic Acid Ionophore.

The effects of the chain structure and substitutents in six acyclic polyether dicarboxylic acids and one acyclic polyether carboxylic acid upon the efficiency and selectivity of pH-driven Pb(2+) transport in a bulk chloroform membrane system have been assessed. Among the carriers, 1,2-bis[2-(o-carboxyphenoxy)ethoxy]-4-tert-butylbenzene (1) is found to exhibit high selectivity for transport of Pb(2+) compared with alkali metal cations and a variety of other divalent metal ion species. Ionophore 1 also extracts Pb(2+) from aqueous solution into chloroform with the loss of two protons. A 1:1 complex of Pb(2+) with di-ionized 1 was isolated.

Transport of monosaccharides through a liquid membrane mediated by lipophilic alkaline earth metal complexes

Abstract Lipophilic alkaline earth metal complexes, prepared from the corresponding metal hydroxides and phosphoric acid diesters, are quite effective for the transport of some monosaccharides, especially ribose, across a chloroform liquid membrane under neutral conditions.

Systematic evaluation of HOMO energy levels for efficient dye regeneration in dye-sensitized solar cells

Thirty ruthenium complexes of the types [Ru(tctpy)(C^N)NCS] and [Ru(tctpy)(N^O)NCS] (C^N = cyclometalating ligand and N^O = pyridinecarboxylate and its derivatives) were synthesized and evaluated to identify the highest occupied molecular orbital (HOMO) energy level (EHOMO) for efficient dye regeneration in dye-sensitized solar cells. EHOMO of these complexes was systematically tuned by changing the electron-donating ability of the C^N and N^O ligands. For complexes with an EHOMO in the potential range more negative than 0.5 V vs. a saturated calomel electrode (SCE), the incident photon-to-current conversion efficiency (IPCE) increased with a positive shift in EHOMO but could not exceed 70%, suggesting that rapid dye regeneration is difficult. On the other hand, high IPCEs above 70% were often observed for complexes with an EHOMO more positive than 0.5 V vs. SCE. It is thus concluded that there is a threshold for efficient electron transfer near 0.5 V vs. SCE (ΔG2 ≈ 0.3 eV) for the series of these sensitizers.

Synthesis and Electrochemical Properties of 2,6-Bis(quinoline-2-yl)pyridyl Ruthenium Complexes as Near-Infrared Sensitizers for Dye-Sensitized Solar Cells

New ruthenium(II)–polypyridyl complexes 1a–1d (1a: X= Y= H, 1b: X= H, Y= Cl, 1c: X= H, Y= Me, 1d: X= COOH, Y= H) having 2,6-bis(4-carboxyquinolin-2-yl)pyridine derivatives as ligands were synthesized as sensitizers for dye-sensitized solar cells (DSCs) and their photophysical and photochemical properties were characterized. The photovoltaic performance of DSCs sensitized with 1a–1d was found to be different. The DSC sensitized with 1a exhibits higher efficiency and IPCE value than those sensitized with 1b–1d. The APCE value of the DSC sensitized with 1a was almost 80% in the 500–800 nm range. Therefore, the performance of the DSC sensitized with 1a might improve if the adsorption of 1a on the TiO2 surface could be appropriately controlled by investigation of dye immersion condition or introduction of bulky substituents on the ligand in order to suppress dye aggregation.

Structure and photochemical properties of ruthenium complexes having dimethyl-substituted DPPZ or TPPHZ as a ligand

Novel ruthenium complexes having 4,7-dimethyl-substituted DPPZ or TPPHZ as a ligand have been synthesized: the methyl groups on the ligands exert a shielding effect on the phenazine nitrogens which prevents solvent-quenching.