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ABSTRACT: Efficient light harvesting: Cyclometalated ruthenium complexes were synthesized and evaluated in a dye-sensitized solar cell as near-IR sensitizers. Tuning of the HOMO energy level by structural modifications of the ligand improved the conversion efficiency of the cells based on these complexes to up to 10.7 %.
Angewandte Chemie International Edition 05/2012; 51(30):7528-31. · 13.45 Impact Factor
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ABSTRACT: Deuterium-labelled compounds were prepared by (transfer) deuterogenation of unsaturated compounds using H(2) or HCO(2)H in acidic D(2)O as deuterium source with almost quantitative yields and high deuterium contents under mild reaction conditions via heterolytic cleavage of H(2) (or decomposition of HCO(2)H) and rapid H(+)/D(+) exchange using iridium catalysts with 4,4'-dihydroxy-2,2'-bipyridine.
Dalton Transactions 09/2009; · 3.84 Impact Factor
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ABSTRACT: Transfer hydrogenation catalyzed by an iridium catalyst with 4,4'-dihydroxy-2,2'-bipyridine (DHBP) in an aqueous formate solution exhibits highly pH-dependent catalytic activity and chemoselectivity. The substantial change in the activity is due to the electronic effect based on the acid-base equilibrium of the phenolic hydroxyl group of DHBP. Under basic conditions, high turnover frequency values of the DHBP complex, which can be more than 1000 times the value of the unsubstituted analogue, are obtained (up to 81 000 h(-1) at 80 degrees C). In addition, the DHBP catalyst exhibits pH-dependent chemoselectivity for alpha,beta-unsaturated carbonyl compounds. Selective reduction of the C=C bond of enone with high activity are observed under basic conditions. The ketone moieties can be reduced with satisfactory activity under acidic conditions. In particular, pH-selective chemoselectivity of the C=O versus C=C bond reduction was observed in the transfer hydrogenation of cinnamaldehyde.
Chemistry 12/2008; 14(35):11076-81. · 5.93 Impact Factor
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ABSTRACT: New strategy for the simultaneous tuning of catalytic activity and water solubility of complex catalysts is described on the basis of an acid−base equilibrium between pyridinol and pyridinolate as the catalyst ligands. Herein, half-sandwich complexes with 4,4‘-dihydroxy-2,2‘-bipyridine (DHBP) or 4,7-dihydroxy-1,10-phenanthroline (DHPT) served as highly efficient and recyclable catalysts for the hydrogenation of bicarbonate in water. The oxyanion generated from the phenolic hydroxy group shows strong electronic donation and polarity, which play significant roles in the catalytic activity and water solubility, respectively. As a result, turnover frequencies (TOF) up to 42 000 h-1 and turnover numbers (TON) up to 222 000 have been obtained by using iridium catalysts under 6 MPa at 120 °C. Furthermore, an iridium DHPT catalyst was spontaneously precipitated at the end of the reaction. Iridium leaching was found to be 0.11 ppm (1.2% of the loaded catalyst), and the added base was completely consumed. The recovered catalyst could be recycled for four cycles with high catalytic activity. Consequently, the catalyst was homogeneous and highly activated at the beginning of the reaction, whereas it was heterogeneous and deactivated at the end. The catalytic system offers an environmentally benign process with high efficiency, easy separation, catalyst recycling, waste-free process, and aqueous catalysis.
01/2007;
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ABSTRACT: Reverse electron transfer from TiO2 to I2 in nanocrystalline TiO2 films with coadsorbed [NBu4]2[cis-Ru(Hdcbiq)2(NCS)2] (1; [NBu4]+ = tetrabutylammonium cation; H2dcbiq = 4,4‘-dicarboxy-2,2‘-biquinoline) and [NBu4]2[cis-Ru(Hdcbpy)2(NCS)2] (2; H2dcbpy = 4,4‘-dicarboxy-2,2‘-bipyridine) was investigated. The apparent electron lifetime decreased when 1 was coadsorbed with 2 on TiO2. The incident monochromatic photon-to-current conversion efficiency and the open-circuit photovoltage decreased substantially even when a small amount of 1 was coadsorbed with 2 on TiO2. The reduction of 1 on TiO2 was spectroelectrochemically observed at a potential that was more positive than the energy of the conduction band edge of the TiO2 films. These results suggest that the injected electron from photoexcited complex 2 reacted with I2 through 1. Reverse electron transfer from TiO2 to I2 depended not only on the electron density but also on the amount of 1 adsorbed on TiO2. Therefore, we assumed that the injected electron was trapped by 1 on TiO2 and then reacted with I2. If an injected electron diffused randomly in TiO2, the relative cross-section (σtrap) of electron trapping by 1 on TiO2 would be expected to be 1 and to be the same as that of trapping by 2. However, the σtrap value was much larger than expected, which indicates that the electron in TiO2 predominantly reacted with I2 through 1.
12/2006;
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ABSTRACT: The catalyst recycling in the conversion of CO2 into formate using the iridium complex with 4,7-dihydroxy-1,10-phenanthroline as a catalyst precursor is described. The catalyst precursor was dissolved in an aqueous KOH solution under CO2 pressure prior to the reaction, but was precipitated spontaneously at the end of the reaction. The acidification by the generation of formate caused the transformation from the water-soluble deprotonated form into the water-insoluble protonated form. When the reaction was carried out at 60 degrees C for 20 h using 0.1 M KOH solution under 6 MPa of H2:CO2 (1:1), the catalyst precursor was precipitated spontaneously and the added KOH was consumed completely. The catalyst was recovered by filtration, and the product was obtained by the evaporation of the filtrate. Iridium leaching into the filtrate was found to be 0.11 ppm (<2% of the loaded Ir). The recovered catalyst retained high catalytic activity for four cycles. Consequently, the CO2 conversion using the complex is an environmentally benign process, whose significant features are as follows: (i) catalyst recycling by self-precipitation/filtration, (ii) waste-free process, (iii) the easy isolation of the product, (iv) high efficiency under relatively mild conditions, and (v) aqueous catalysis without the use of organic materials. Furthermore, we have demonstrated the significant roles of the oxyanion generated from the acidic phenolic hydroxyl on the catalyst ligand, which are the catalyst recovery by acid-base equilibrium, as well as the water-solubility by its polarity and the catalyst activation by its electron-donating ability.
Journal of the American Chemical Society 09/2005; 127(38):13118-9. · 9.91 Impact Factor
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ABSTRACT: Half-sandwich Ru(II), Ir(III), and Rh(III) complexes with 4,7-dihydroxy-1,10-phenanthroline are highly efficient catalysts for hydrogenation of bicarbonate in alkaline aqueous solution without an amine additive. The generation of an oxyanion by deprotonation of the two hydroxy substituents on the catalyst ligand caused a dramatic enhancement of catalytic activity, due to its strong electron-donating ability, as well as imparting water solubility.
02/2004;
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04/2002;
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12/1997;
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ABSTRACT: 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%.
Journal of Molecular Catalysis A: Chemical.
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ABSTRACT: Half-sandwich complexes with 4,4′-dihydroxy-2,2′-bipyridine (DHBP) or 4,7-dihydroxy-1,10-phenanthroline (DHPT) are highly efficient catalysts for the hydrogenation of bicarbonate in an alkaline aqueous solution without an amine additive. The generation of an oxyanion by the deprotonation of the two hydroxy substituents on the catalyst ligand caused a dramatic enhancement of catalytic activity due to the strong electron-donating ability of the oxyanion. Turnover frequencies (TOF) up to 42,000 h−1 and turnover numbers (TON) up to 222,000 have been obtained by using iridium catalysts under 6 MPa at 120 °C. The production of formate (TOF = 3.5 h−1) was observed even under ambient conditions (0.1 MPa, 30 °C).
Journal of Photochemistry and Photobiology A: Chemistry. 182(3):306-309.
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Tetrahedron Letters 39(52):9699-9702. · 2.68 Impact Factor
