Taisuke Hamada

A novel photocatalytic asymmetric synthesis of (R)-(+)-1,1′-bi-2-naphthol derivatives by oxidative coupling of 3-substituted-2-naphthol with Δ-[Ru(menbpy)3]2+[menbpy = 4,4′-di(1R,2S,5R)-(–)-menthoxycarbonyl-2,2′-bipyridine], which posseses molecular helicity

The asymmetric synthesis of (R)-(+)-1,1′-bi-2-naphthol [or (R)-(+)-1,1 ′-bi-3-methoxy-2-naphthol] from 2-naphthol (or 3-methoxy-2-naphthol) is performed photocatalytically by using the chiral ruthenium complex, M(C3)-Δ-[Ru(menbpy)3]2+[M(C3)= counterclockwise molecular helicity along the C3 axis, menbpy = 4,4′-di(1R,2S,5R)-(–)-menthoxycarbonyl-2,2′-bipyridine] as a photosensitizer and[Co(acac)3](acac–= acetylacetonato) as an oxidant.

Photoinduced electron transfer between [Cu(dmphen)L2]+[dmphen = 2,9-dimethyl-1,10-phenanthroline, L = PPhn(C6H4OMe-p)3 –n(n= 0–3)] and methyl viologen

Photocatalytic reduction of methyl viologen (1,1′-dimethyl-4,4′-bipyridinium mv2+) was efficiently carried out with copper(I) complexes [Cu(dmphen)L2]+[dmphen = 2,9-dimethyl-1,10-phenanthroline, L = PPhn(C6H4OMe-p)3 –n, n= 0–3] upon irradiation of the metal-o-ligand charge-transfer band at around 360 nm. The quantum yield for reduction, φ(mv˙+), increases considerably in the order L = PPh3 PPh2-(C6H4OMe-p) < PPh(C6H4OMe-p)2 < P(C6H4OMe-p)3, i.e. in increasing order of the phosphine donation ability. The best quantum yield (0.1) was recorded when [Cu(dmphen){P(C6H4OMe-p)3}2]+ was used. Kinetic analysis and measurement of the lifetime of the excited copper(I) complex revealed the reason why φ(mv˙+) increases as the phosphine donation ability increases: first, the excited state becomes longer-lived and secondly, the charge-separation step becomes easier with increasing donation ability. The significant phosphine effects on the excited-state lifetime are discussed in terms of the solvent interaction with the copper(I) centre.

Synthesis of a new copper(I) complex, [Cu(tmdcbpy)2]+ (tmdcbpy = 4,4′,6,6′-tetramethyl-2,2′-bipyridine-5,5′-dicarboxylic acid), and its application to solar cells

A newly synthesized copper(I) complex, [Cu(tmdcbpy)2]+ (tmdcbpy = 4,4′,6,6′-tetramethyl-2,2′-bipyridine-5,5′-dicarboxylic acid), was applied to a solar cell with TiO2, which provided successful results, a photocurrent of about 4 mA cm−2, photovoltage of 630 mV and an IPCE (incident monochromatic photon-to-current conversion efficiency) value of 30%, under visible light irradiation from a AM 1.5G sunlight simulator (100 mW cm−2).

Enantioselective and photocatalytic oxidation of 1,1′-bi-2-naphthol with a chiral ruthenium complex which includes molecular helicity

Abstract 1,1′-Bi-2 -naphthol was oxidized catalytically and enantioselectively ( ≤ 15.2 % e.e.), by using the chiral ruthenium complex, Δ-[Ru (menbpy) 3 ] 2+ (menbpy = 4,4′-dimenthoxycarbonyl-2,2′-bipyridine) as a photocatalyst and [Co (acac) 3 ] (Hacac=pentane-2,4-dione) as an oxidant under photoirradiation.

Photoinduced electron transfer reaction between [Cu(dmp)P2]+or− (P=PPh3 or PPh2(m-C6H4SO3−) and viologen derivatives

Abstract The copper(I) complex, [Cu(dmp)P 2 ] +or− (dmp=2,9-dimethyl-l,10-phenanthroline, P=triphenylphosphine PPh 3 or diphenylphosphinobenzene- m -sulfonate PPh 2 ( m -C 6 H 4 SO 3 − )), catalytically photoreduces viologen derivatives, dicationic methylviologen MV 2+ and neutral propylviologen disulfonate PVS 0 . The quantum yield Φ(V°) for the viologen photoreduction is discussed on the basis of the lifetime of the photosensitiser, formation of the encounter complex, dissociation of the encounter complex to products, and back electron transfer in the encounter complex. When [Cu(dmp){PPh 2 ( m -C 6 H 4 SO 3 )} 2 ] − is used for the photoreduction of MV 2+ , the highest quantum yield (Φ(V°)=0.03) is obtained. Kinetic analysis and measurements of the excited state lifetime reveal that this best Φ(V°) value arises from the rapid formation of the encounter complex, owing to the attractive electrostatic interaction between anionic [Cu(dmp){PPh 2 ( m -C 6 H 4 SO 3 )} 2 ] − and cationic MV 2+ .

Methylviologen-pendant iron porphyrins as models of a reduction enzyme: six-electron reduction of nitrobenzene to anilineElectronic supplementary information (ESI) available: time-courses of reduction, UV-VIS spectral changes, cyclic voltammograms, EPR spectra, conversion and yield percentages for the reduction of p-nitroanisole. See http://www.rsc.org/suppdata/dt/b2/b211125j/

Methylviologen-pendant iron porphyrins, in which methylviologen was introduced to the meso-phenyl group through an amido-bridge at either the p- or m-position, were newly synthesized, in expectation that these methylviologen-pendant iron porphyrins would be good functional models of a multi-electron reductase such as nitrite reductase since the methylviologen-pendant can play the role of an electron-trapping and storage unit like the iron–sulfur cluster of the nitrite reductase. These iron porphyrins were successfully applied to the six-electron reduction of nitrobenzene to aniline, which is a model reaction of nitrite reduction to ammonia catalyzed by nitrite reductase. Both p- and m-methylviologen-pendant iron porphyrins give somewhat larger yields of aniline in the reduction of nitrobenzene and much larger yields of p-methoxyaniline in the reduction of p-nitroanisole than does normal iron tetraphenylporphyrin. Though normal iron tetraphenylporphyrin can not catalyze well the reduction of p-nitroanisole in the presence of the dioxygen molecule, these methylviologen-pendant iron porphyrins can catalyze well the reduction of p-nitroanisole and give a considerably larger yield of p-methoxyaniline even in the presence of the dioxygen molecule. These methylviologen-pendant iron porphyrins give a much larger yield of aniline in the reduction of nitrosobenzene and somewhat larger yield of aniline in the reduction of phenylhydroxylamine than does iron tetraphenylporphyrin. m-Methylviologen-pendant iron porphyrin exhibits higher catalytic activity than does the p-pendant one. The role of methylviologen moiety is discussed, based on cyclic voltammograms and UV-VIS spectra of these iron porphyrins.

Novel photoinduced asymmetric synthesis of Λ-[Co(acac)3] from Co(acac)2(H2O)2 and Hacac catalysed by racemic complexes of Δ- and Λ-[Ru(menbpy)3]2+{menbpy = 4,4′-Di-[(1R,2S,5R)-(–)-menthoxycarbonyl)]-2,2′-bipyridine; Hacac = pentane-2,4-dione}

The asymmetric synthesis of M(C3)-Λ-[Co(acac)3] has been realized by the oxidation of Co(acac)2(H2O)2 and Hacac with theracemicphotocatalystsof [Ru(menbpy)3]2+{menbpy = 4,4′-di-[(1R, 2S,5R)-(–)-menthoxycarbonyl]-2,2′-bipyridine} which predominates the helical chirality of M(C3)-Δ-[Ru(Menbpy)3]2+; the extent of the asymmetric induction by the helical photocatalyst has been enlarged by lowering the % v/v of EtOH-H2O or by raising the molar ratio of [Hacac]/[Co(acac)2(H2O)2].

Synthesis of a new chiral copper(I) complex and itsapplication to stereoselective photoreduction of[Co(edta)]- (H4edta =ethylenedinitrilotetraacetic acid)

A chiral bipyridine derivative, 4,4′-6,6′-tetramethyl-5,5′-bis[(S)-(-) -1-phenylethylcarbamoyl]-2,2′-bipyridine (L), was newly synthesized. Using its copper(I) complex, [CuL(PPh 3 ) 2 ] + , [Co(edta)] - (H 4 edta = ethylenedinitrilotetraacetic acid) was stereoselectively photoreduced upon irradiation with near-UV light (360–400 nm) corresponding to the metal-to-ligand charge transfer absorption band of the copper(I) complex, where the Λ enantiomer of [Co(edta)] - was preferentially reduced. The stereoselectivity of 42% enantiomeric excess was observed at 10% conversion, where the solvent was EtOH–water (75:25 v/v). This [Co(edta)] - photoreduction by [CuL(PPh 3 ) 2 ] + proceeds through both static and dynamic quenching mechanisms. Quenching experiments with the optical isomers, Δ- and Λ-[Co(edta)] - , clearly indicated that quenching takes place with little stereoselectivity, but charge separation and/or a reverse electron transfer occur stereoselectively.

Stereoselective molecular recognition of enantiomeric cobalt(III) complexes by novel photosensitizers of helical ruthenium(II) complexes

Abstract The stereoselective quenching of helical RU(II) complexes with Δ or Λ-Co(III) complexes was controlled by the molecular helicities of the both reactants. The quenching rate constant and stereoselectivity were affected by the EtOH content in the EtOH/H 2 O solvent with the maximum quenching rate ratio of k Δ q / k Λ q = 1.28.

Novel enantioselective photocatalysis by chiral, helical ruthenium(II) complexes

The enantioselective photoreduction of the helical substrates of rac-[Co(acac)3](acac –= acetylacetonato) and rac-[Co(edta)]–(edta4–= ethylenediaminetetraacetato) with the newly synthesized helical photocatalysts Δ-(or rac)-[Ru[Menbpy)32+{Menbpy = 4,4′-bis[(1R,2S,5R)-(–)-menthoxycarbonyl]-2,2′-bipyridine}, and Λ-(or Δ)-[Ru{(S or R)-PhEtbpy}3]2+{(S or R)-PhEtbpy = 4,4′-bis[(S)-(–) or (R)-(+)-1-phenylethylaminocarbonyl]-2,2′-bipyridine} was realized in the helical-shape recognition reaction with a maximum enantiomer rate ratio (KΔ;/KΛ) of 14.7 in 90%v/v EtOH-H2O at 25 °C.