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21.
This paper reviews results from study of mononuclear ruthenium complexes capable of catalyzing the oxidation of water to molecular oxygen. These catalysts may be classified into three groups, with different rate laws associated with O2 evolution. In one class, O2 evolution proceeds via radical coupling of the oxygen atom of an RuV=O species with a hydroxocerium(IV) ion. O2 evolution catalyzed by the second class occurs via acid–base reaction of the oxygen atom of an RuV=O species with a water molecule. In the third group, the dominant mechanism is oxo–oxo radical coupling between two RuV=O species. Several significant properties of the oxidant Ce(IV) are also discussed, including the singlet biradical character of the hydroxocerium(IV) ion. 相似文献
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Kobayashi M Masaoka S Sakai K 《Dalton transactions (Cambridge, England : 2003)》2012,41(16):4903-4911
A new Pt(II)-based metalloviologen analog, [PtCl(Mepytpy)](2+) (abbreviated as PV(2+); Mepytpy(+) = 4'-(4-methyl-pyridinio)-2,2':6',2'-terpyridine), was synthesized and its spectroscopic and electrochemical properties were investigated. The structures of Mepytpy(+) and PV(2+) were solved by single-crystal X-ray diffraction analysis. Electrochemical studies in DMF (N,N-dimethylformamide) revealed that both the first and second reduction potentials of PV(2+) (E = -0.87 V vs. Fc/Fc(+) for PV(2+)/PV(+)˙; E = -1.31 V vs. Fc/Fc(+) for PV(+)˙/PV(0)) are nearly consistent with those of methylviologen (N,N'-dimetyl-4,4'-bipyridinium, MV(2+)) (E = -0.90 V vs. Fc/Fc(+) for MV(2+)/MV(+)˙; E = -1.28 V vs. Fc/Fc(+) for MV(+)˙/MV(0)), where the first reduction of PV(2+) is assigned as the reduction at the Mepytpy(+) ligand bound to the Pt(ii) ion. Upon the addition of a reducing agent Na(2)S(2)O(4) into an aqueous acetate buffer solution (pH = 5.0) of PV(2+), the generation of one-electron-reduced radical species (PV(+)˙) was spectrophotometrically observed and was assigned based on the time-dependent density functional theory (TD-DFT) calculations. The H(2)-evolving activity of PV(2+) was evaluated in the presence of a sacrificial electron donor (EDTA) in an aqueous acetate buffer solution (pH = 5.0). It was found that the stability of the metalloviologen PV(2+) during the photolysis is much higher than that of the parent compound [PtCl(tpy)](+). 相似文献
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Kimoto A Yamauchi K Yoshida M Masaoka S Sakai K 《Chemical communications (Cambridge, England)》2012,48(2):239-241
The Ru(V)==O species and other intermediates in O(2) evolution from water catalyzed by [Ru(terpy)(bpy)(OH(2))](2+) were spectrophotometrically characterized, and the spectral components observed were identified based on the TD-DFT calculations. Moreover, important insights into the rapid paths after the RDS were given by the DFT studies. 相似文献
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Ajayakumar G Kobayashi M Masaoka S Sakai K 《Dalton transactions (Cambridge, England : 2003)》2011,40(15):3955-3966
In our hopes to improve the photocatalytic efficiency of photo-hydrogen-evolving molecular devices, several new dyads and triads possessing a photosensitizing Ru(bpy)(phen)(2)(2+) (or Ru(phen)(3)(2+)) chromophore (abbreviated as Ru(II)) attached to both/either a phenothiazine moiety (abbreviated as Phz) and/or H(2)-evolving PtCl(2)(bpy) units (abbreviated as Pt), such as Phz-Ru(II)-Pt2 (triad), Ru(II)-Pt2 (dyad), and Ru(II)-Pt3 (dyad), were synthesized and their basic properties together with the photo-hydrogen-evolving characteristics were investigated in detail. The (3)MLCT phosphorescence from the Ru(II) moiety in these systems is substantially quenched due to the highly efficient photoinduced electron transfer (PET). Based on the electrochemical studies, the driving forces for the PET were estimated as -0.07 eV for Phz-Ru(II)-Pt2, -0.24 eV for Ru(II)-Pt2, and -0.22 eV for Ru(II)-Pt3, revealing the exergonic character of the PET in these systems. Luminescence lifetime studies revealed the existence of more than two decay components, indicative of a contribution of multiple PET processes arising from the presence of at least two different conformers in solution. The major luminescence decay components of the hybrid systems [τ(1) = 6.5 ns (Ru(II)-Pt2) and τ(1) = 1.04 ns (Phz-Ru(II)-Pt2) in acetonitrile] are much shorter than those of Phz-free/Pt-free Ru(bpy)(phen)(2)(2+) derivatives. An important finding is that the triad Phz-Ru(II)-Pt2 affords a quite long-lived charge separated (CS) state (τ(CS) = 43 ns), denoted as Phz(+)˙-Ru(Red)-Pt2, as a result of reductive quenching of the triplet excited state of Ru(bpy)(phen)(2)(2+) by the tethering Phz moiety, where Ru(Red) denotes Ru(bpy)(phen)(2)(+). Moreover, the lifetime of Phz(+)˙-Ru(Red)-Pt2 was observed to be much longer than that of Phz(+)˙-Ru(Red). The photocatalytic H(2) evolution from water driven by these systems was examined in an aqueous acetate buffer solution (pH 5.0) containing 4-19% dimethylsulfoxide (solubilising reagent) in the presence of EDTA as a sacrificial electron donor. Dyads Ru(II)-Pt2 and Ru(II)-Pt3 were found to exhibit improved photo-hydrogen-evolving activity compared to the heterodinuclear Ru-Pt dyads developed so far in our group. On the other hand, almost no catalytic activity was observed for Phz-Ru(II)-Pt2 in spite of the formation of a strongly reducing Ru(Red) site (Phz(+)˙-Ru(Red)-Pt2), indicating that the electron transfer from the photogenerated Ru(Red) unit to the PtCl(2)(bpy) unit is not favoured presumably due to the slow electron transfer rate in the Marcus inverted region. 相似文献
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Hironobu Ozawa Dr. Masayuki Kobayashi Bijitha Balan Dr. Shigeyuki Masaoka Dr. Ken Sakai Prof. Dr. 《化学:亚洲杂志》2010,5(8):1860-1869
The mechanism of photoinduced hydrogen evolution from water driven by the first photo‐hydrogen‐evolving molecular catalyst ( 1 ), given by a coupling of [Ru(bpy)2(5‐amino‐phen)]2+ and [PtCl2(4,4′‐dicarboxy‐bpy)] (bpy=2,2′‐bipyridine, phen=1,10‐phenanthroline), was investigated in detail. The H2 evolution rate was found to obey Michaelis–Menten enzymatic kinetics with regard to the concentration of EDTA (ethylenediamine tetra‐acetic acid disodium salt, sacrificial electron donor), which indicates that an ion‐pair formation between the dicationic 1 and the dianionic form of EDTA (pH 5) is a key step leading to H2 formation. A 2:1 coupling product of 1 and ethylenediamine (i.e., a {RuII2PtII2} complex 2 ) was found to show significantly higher photo‐hydrogen‐evolving (PHE) activity than 1 , which revealed the validity of the bimolecular activation proposed in our previous study. The PHE activity of 2 was also observed to be linear to the concentration of 2 , which indicates that H2 formation through the intermolecular path competes with the intramolecular path. Molecular orbital diagrams, conformational features, and Pt???H(water or acetic acid) hydrogen bonds were characterized by DFT calculations. 相似文献
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Yoshiaki Hidaka Tetsuo Higashihara Natsuhiko Ninomiya Hiromitsu Masaoka Takuji Nakamura Hiroyuki Kawano 《国际化学动力学杂志》1996,28(2):137-151
1,3-Butadiene (1,3-C4H6) was heated behind reflected shock waves over the temperature range of 1200–1700 K and the total density range of 1.3 × 10−5 −2.9 × 10−5 mol/cm3. Reaction products were analyzed by gas-chromatography. The concentration change of 1,3-butadiene was followed by UV kinetic absorption spectroscopy at 230 nm and by quadrupole mass spectrometry. The major products were C2H2, C2H4, C4H4, and CH4. The yield of CH4 for a 0.5% 1,3-C4H6 in Ar mixture was more than 10% of the initial 1.3-C4H6 concentration above 1500 K. In order to interpret the formation of CH4 successfully, it was necessary to include the isomerization of 1,3-C4H6 to 1,2-butadiene (1,2-C4H6) and to include subsequent decomposition of the 1,2-C4H6 to C3H3 and CH3. The present data and other shock tube data reported over a wide pressure range were qualitatively modeled with a 89 reaction mechanism, which included the isomerizations of 1,3-C4H6 to 1,2-C4H6 and 2-butyne (2-C4H6). © 1996 John Wiley & Sons, Inc. 相似文献
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Kobayashi K Ishikubo M Kanaizuka K Kosuge K Masaoka S Sakai K Nozaki K Haga MA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(25):6954-6963
Ru complexes bearing a bis-tridentate benzimidazolyl ligand have been synthesized. The dinuclear ones act as a bibasic acid with pK(a1)=4.36 and pK(a2)=5.90. The protonated form of the dinuclear complex exhibited two one-electron oxidations at +0.91 and +1.02 V versus the ferrocenium/ferrocene (Fc/Fc(+)) couple (the potential difference (ΔE)=0.11 V), but the di-deprotonated form showed two waves at +0.50 and +0.58 V versus Fc/Fc(+) (ΔE=0.08 V). Since the potential difference between two waves reflects the strength of the metal-metal interaction, the deprotonation of the benzimidazole moieties in the complexes weakened the Ru-Ru communication. The degree of electronic coupling between two metal centers, estimated from the intervalence charge transfer (IVCT) band, was greater for the protonated form. DFT calculations for the protonated and deprotonated forms of the dinuclear complex suggest that the Ru(II)-L(H(2)) π* interaction plays a key role in the Ru-Ru interaction. 相似文献