We have successfully achieved the electron-transfer (ET) state of 9-mesityl-10-methylacridinium ion, produced by a single step photoinduced electron transfer, which has a much longer lifetime (e.g., 2 h at 203 K) and higher energy (2.37 eV) than that of the natural system without loss of energy due to multistep electron-transfer processes.

Visible light irradiation of the absorption band of 9-mesityl-10-methylacridinium ion (Acr+-Mes) in an O2-saturated acetonitrile (MeCN) solution containing 9,10-dimethylanthracene results in formation of oxygenation product, i.e., dimethylepidioxyanthracene (Me2An-O2). Anthracene and 9-methylanthracene also undergo photocatalytic oxygenation with Acr+-Mes to afford the corresponding epidioxyanthracenes under the photoirradiation. In the case of anthracene, the further photoirradiation results in formation of anthraquinone as the final six-electron oxidation product, via 10-hydroxyanthrone, accompanied by generation of H2O2. When anthracene is replaced by olefins (tetraphenylethylene and tetramethylethylene), the photocatalytic oxygenation of olefins affords the corresponding dioxetane, in which the O-O bond is cleaved to yield the corresponding ketones. The photocatalytic oxygenation of anthracenes and olefins is initiated by photoexcitation of Acr+-Mes, which results in formation of the electron-transfer state: Acr*-Mes*+, followed by electron transfer from anthracenes and olefins to the Mes*+ moiety together with electron transfer from the Acr* moiety to O2. The resulting anthracene and olefin radical cations undergo the radical coupling reactions with O2*- to produce the epidioxyanthracene (An-O2) and dioxetane, respectively.

Critical biological electron-transfer processes involving high-valent oxometal chemistry occur widely, for example in haem proteins [oxoiron(IV); Fe(IV)(O)] and in photosystem II. Photosystem II involves Ca(2+) as well as high-valent oxomanganese cluster species. However, there is no example of an interaction between metal ions and oxoiron(IV) complexes. Here, we report new findings concerning the binding of the redox-inactive metal ions Ca(2+) and Sc(3+) to a non-haem oxoiron(IV) complex, [(TMC)Fe(IV)(O)](2+) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane). As determined by X-ray diffraction analysis, an oxo-Sc(3+) interaction leads to a structural distortion of the oxoiron(IV) moiety. More importantly, this interaction facilitates a two-electron reduction by ferrocene, whereas only a one-electron reduction process occurs without the metal ions. This control of redox behaviour provides valuable mechanistic insights into oxometal redox chemistry, and suggests a possible key role that an auxiliary Lewis acid metal ion could play in nature, as in photosystem II.

A new cupric-superoxo complex [LCu II (O 2 •− )] + , which possesses particularly strong O-O and Cu-O bonding, is capable of intermolecular C-H activation of the NADH analogue 1-benzyl-1,4-dihydronicotinamide (BNAH). Kinetic studies indicate a first-order dependence on both the Cucomplex and BNAH with a deuterium kinetic isotope effect (KIE) of 12.1, similar to that observed for certain copper monooxygenases.Copper(I) reactions with molecular oxygen play fundamental roles in many chemical and biological processes.1 , 2 Copper-dependent proteins perform a diverse array of oxidative and oxygenative reactions. This has inspired considerable efforts in the design of novel ligands and copper coordinated complexes as well as the study of ligand-copper(I) dioxygen adducts to elucidate their structures, electronic characteristics and substrate reactivity.2 -4 Compared to binuclear copper-dioxygen derived species, mononuclear analogues have been synthetically challenging and hence are less understood.3 , 5 However, they are fundamentally important and are directly relevant to copper proteins including dopamine-β-monooxygenase (DβM) and peptidlyglycine-α-hydroxylating monooxygenase (PHM).6 These enzymes possess a so-called non-coupled binuclear active site,7 which comprises two Cu centers separated by ~11Å. Dioxygen binding and substrate hydroxylation occur at one of the copper sites (designated Cu M ). In an important PHM X-ray structure, a dioxygen derived species presumed to be an end-on bound cupric superoxide species (i.e., Cu II -O-O •− ) resides adjacent to an inhibitory substrate analog.6c Along with biochemical,6a,b , 8 chemical and computational studies,5 , 9 the cupric-superoxo species is thought by many to be the reactive intermediate responsible for initiating oxidation via hydrogen-atom abstraction. However, other species have been considered as important intermediates in enzymatic turnover, either prior to or following substrate attack, including cuprichydroperoxo (Cu II -− OOH)10 and high-valent cupryl (Cu II -O• <-> Cu III =O) (1) is unreactive toward a number of commonly employed C-H substrates, such as dihydroanthracene, xanthene and 10-methyl-9,10-dihydroacridine -substrates possessing C-H bonds significantly weaker than those found for DBM and PHM substrates (dopamine, 85 kcal/mol; hippuric acid, 87 kcal/mol).6b However, the addition of an excess of 1-benzyl-1,4-dihydronicotinamide (BNAH) -an NADH analogue, which is both a strong H-atom (H (Figure 3b). This gives a kinetic isotope effect (KIE) of 12.1. This KIE value is comparable to that (KIE = 10) reported for C-H bond cleavage of BNAH by a trans-dioxomanganese(V) porphyrin.20 Product analysis of the [LCu II (O 2 •− )] + /BNAH reaction (following quenching with HCl at −130 °C)15 confirms that BNAH has undergone oxidation by 1. The substrate's 4' C-H bond has been oxidatively cleaved to form 1-benzylnicotinamidium ion (BNA + ) in 42% yield ( 1 H-NMR), based on the initial copper concentration (Scheme 1). Additionally, upon acidification, ...

Rates of electron transfer from a series of one-electron reductants to a nonheme oxoiron(IV) complex, [(N4Py)Fe(IV)(O)](2+), are enhanced as much as 10(8)-fold by addition of metal ions such as Sc(3+), Zn(2+), Mg(2+), and Ca(2+); the metal ion effect follows the Lewis acidity of metal ions. The one-electron reduction potential of [(N4Py)Fe(IV)(O)](2+) is shifted to a positive direction by 0.84 V in the presence of Sc(3+) ion (0.20 M).

Long live the state! Photoexcitation of a zinc chlorin–fullerene dyad with a short linkage results in the formation of the ultra‐long‐lived charge‐separated (CS) state by a one‐step photoinduced electron transfer without loss of energy, which is inevitable for charge separation by multistep electron‐transfer processes. The lifetime of the charge‐separated state was 120 s in frozen PhCN at −150 °C (see picture).

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Photocatalytic hydrogen evolution with a ruthenium metal catalyst under basic conditions (pH 10) has been made possible for the first time by using 2-phenyl-4-(1-naphthyl)quinolinium ion (QuPh(+)-NA), dihydronicotinamide adenine dinucleotide (NADH), and Ru nanoparticles (RuNPs) as the photocatalyst, electron donor, and hydrogen-evolution catalyst, respectively. The catalytic reactivity of RuNPs was virtually the same as that of commercially available PtNPs. Nanosecond laser flash photolysis measurements were performed to examine the photodynamics of QuPh(+)-NA in the presence of NADH. Upon photoexcitation of QuPh(+)-NA, the electron-transfer state of QuPh(+)-NA (QuPh(•)-NA(•+)) is produced, followed by formation of the π-dimer radical cation with QuPh(+)-NA, [(QuPh(•)-NA(•+))(QuPh(+)-NA)]. Electron transfer from NADH to the π-dimer radical cation leads to the production of 2 equiv of QuPh(•)-NA via deprotonation of NADH(•+) and subsequent electron transfer from NAD(•) to QuPh(+)-NA. Electron transfer from the photogenerated QuPh(•)-NA to RuNPs results in hydrogen evolution even under basic conditions. The rate of electron transfer from QuPh(•)-NA to RuNPs is much higher than the rate of hydrogen evolution. The effect of the size of the RuNPs on the catalytic reactivity for hydrogen evolution was also examined by using size-controlled RuNPs. RuNPs with a size of 4.1 nm exhibited the highest hydrogen-evolution rate normalized by the weight of RuNPs.