Storing electrons from H2 for transfer to CO2, all at room temperature.

We present an Ir complex that extracts electrons from H2 at room temperature and stores them as a H2-derived energy carrier (H2EC) at room temperature. Furthermore, we demonstrate that this complex reduces CO2 to a metal-CO22- species at room temperature, and present the first electrospray ionisation mass spectrum for this compound.

H2-driven reduction of CO2 to formate using bacterial plasma membranes.

Bacterial membranes shield the intracellular compartment by selectively allowing unwanted substances to enter in, which in turn reduces overall catalytic efficiency. This report presents a model system using the isolated plasma membranes of Citrobacter sp. S-77 that harbor oxygen-stable [NiFe]hydrogenase and [Mo]formate dehydrogenase, which are integrated into a natural catalytic nanodevice through an electron transfer relay. This naturally occurring nanodevice exhibited selectivity and efficiency in catalyzing the H2-driven conversion of CO2 to formate with the rate of 817 mmol·L-1·gprotein-1·h-1 under mild conditions of 30 °C, pH 7.0, and 0.1 MPa. When the isolated plasma membranes of Citrobacter sp. S-77 was immobilized with multi-walled carbon nanotubes and encapsulated in hydrogel beads of gellan-gum cross-linked with calcium ions, the catalyst for formate production remained stable over 10 repeated uses. This paper reports the first case of efficient and selective formate production from H2 and CO2 using bacterial plasma membranes.

2D Coordination Network of Trioxotriangulene with Multiple Redox Abilities and Its Rechargeable Battery Performance.

A three-fold symmetric trioxotriangulene derivative with three pyridyl groups as coordinating sites was designed and synthesized. In a cyclic voltammetry measurement, the trioxotriangulene skeleton exhibited a multi-stage redox ability from neutral radical to radical tetra-anion species. In the zinc complex of monoanion species, three pyridyl groups coordinated to the zinc ion to build up a two-dimensional coordination network with a cavity larger than 12 Å in diameter. This complex was utilized as a cathode active material of a lithium ion battery, and it exhibited a capacity of ca. 60 mAh g-1 per the weight of the active material with a stable cycling performance up to 1000 cycles. This work shows that the coordination network formed by the trioxotriangulene-based ligand was effective in the improvement of cycle performance of the organic rechargeable battery.

Redox behaviour of the ß-dihydroporphycene cobalt complex: study on the effect of hydrogenation of the ligand.

The dihydrogenated porphycene cobalt(ii) complex was synthesized and electrochemical experiments were carried out. The one-electron reduction of the complex proceeded at the central metal to afford the Co(i) species; in contrast, for the non-hydrogenated porphycene cobalt(ii) complex, the one-electron reduction gave the ligand reduced radical anion species. The reactivity of the one-electron reduced species with alkyl halides showed clear differences between the complexes. Hydrogenation of the ß-position of the porphycene makes it possible to generate a central cobalt reduced species possessing a higher reactivity than the ligand reduced radical anion species.

Cobalt-Carbon Bond Formation Reaction via Ligand Reduction of Porphycene-Cobalt(II) Complex and Its Noninnocent Reactivity.

The interesting redox properties and reactivity of metalloporphycene have been studied for decades; however, the detailed experimental investigation on the reactivity and reaction mechanism under inert condition combined with theoretical calculations had not been performed so far. In this study, the novel reactivity of the reduced form of the cobalt porphycene with alkyl halides to form cobalt-carbon (Co-C) bonds was revealed. Under electrochemical reductive conditions, not the central cobalt, but the ligand was reduced and reacted with alkyl halides to afford the cobalt-alkyl complexes under N2 atmosphere in a glovebox. The reaction mechanism was clarified by the combination of experimental and theoretical studies that the porphycene ligand works as a noninnocent ligand and allows the SN2-type Co-C bond formation. This result provides us the possibility of the reaction triggered by the reduction of ligand with macrocyclic π-conjugated system, not by the reduction of metal.

An Azulene-Fused Tetracene Diimide with a Small HOMO-LUMO Gap.

A newly prepared tetraazulene-fused tetracene diimide (TA-fused TDI) showed absorption in the near-IR region owing to the effective extension of the π-conjugated system as well as a large two-photon absorption cross-section (σ(2) =2140 GM) at 950 nm. Four reversible reduction processes and n-type semiconductivity were also confirmed as attractive electronic properties of this compound.

A Stable Organic π-Radical of a Zinc(II)-Copper(I)-Zinc(II) Complex of Decaphyrin.

A Zn(II) -Cu(I) -Zn(II) heterotrimetal complex of decaphyrin was synthesized by stepwise metalations: metalation of a [46]decaphyrin with Zn(II) ions to produce a 46π decaphyrin bis(Zn(II) ) complex and its subsequent metalation with Cu(II) ion. In the second metalation step, it has been shown that Cu(II) ion is reduced to a Cu(I) ion in the complex and a dianionic bis(Zn(II) ) containing [46]decaphyrin ligand is oxidized to the corresponding monoanionic [45]decaphyrin ligand, indicating a non-innocent nature of the decaphyrin ligand. Despite the radical nature, the heterotrimetal complex is fairly stable under ambient conditions and exhibits almost no intermolecular magnetic interaction, owing to extensive delocalization of an unpaired electron in the large π-conjugated circuit of decaphyrin moiety.

Solvent- and temperature-dependent conformational changes between Hückel antiaromatic and Möbius aromatic species in meso-trifluoromethyl substituted [28]hexaphyrins.

We investigated the photophysical properties of figure-eight-like meso-hexakis(trifluoromethyl) [26]- and [28]hexaphyrins(1.1.1.1.1.1) denoted as TFM26H and TFM28H, respectively, using steady-state and time-resolved spectroscopy along with theoretical calculations to explore their electronic and magnetic natures depending on their molecular aromaticity. TFM26H exhibited a well-resolved absorption feature and intense fluorescence, both of which were neither solvent- nor temperature-dependent. These optical properties were in agreement with its Hückel's [4n + 2] aromaticity as observed in typical aromatic porphyrinoids. The S(1)-state lifetime of ~50 ps for TFM26H in solution was shorter than those in planar aromatic hexaphyrins (>100 ps) presumably due to nonplanar figure-eight geometry of TFM26H. However, TFM28H exhibited remarkable changes in solvent- and temperature-dependent absorption spectra as well as excited-state lifetimes indicating that a dynamic equilibrium occurs between the two conformational species. With the help of quantum mechanical geometry optimization and vertical excitation energy calculations, we found that the figure-eight double-sided conformer observed in the solid-state and single-sided distorted one could be the best candidates for the two conformers, which should be Hückel antiaromatic and Möbius aromatic species, respectively, based on their optical characteristics, molecular orbital structures, and excited-state lifetimes. Conformational dynamics between these two conformers of TFM28H was scrutinized in detail by temperature-dependent (1)H NMR spectra in various solvents, which showed that the conformational equilibrium was quite sensitive to solvents and that a conformational change faster than the NMR time-scale occurs even at 173 K.

Neutral radical and singlet biradical forms of meso-free, -keto, and -diketo hexaphyrins(1.1.1.1.1.1): effects on aromaticity and photophysical properties.

We have investigated the electronic structures and photophysical properties of 5,10,20,25-tetrakis(pentafluorophenyl)-substituted hexaphyrin(1.1.1.1.1.1) (1) and its meso-keto (2) and meso-diketo derivatives (3) using various spectroscopic measurements. In conjunction with theoretical calculations, these analyses revealed fundamental structure-property relationships within this series, including unusual ground-state electronic structures with neutral, monoradical, and singlet biradical character. The meso-free species 1 is a representative 26 π-electron aromatic compound and shows characteristic spectroscopic features, including a sharp Soret band, well-defined Q-like bands, and a moderately long excited state lifetime (τ = 138 ps). In contrast, the meso-keto derivative 2 displays features characteristic of a neutral monoradical species at the ground state, including the presence of lower energy absorption bands in the NIR spectral region and a relatively short excited-state lifetime (13.9 ps). The meso-diketo 3 exhibits features similar to those of 2, specifically NIR absorptions and a short excited-state lifetime (9.7 ps). Compound 3 is thus assigned as being a ground-state singlet biradicaloid. Two photon absorption (TPA) measurements revealed comparatively large σ(2) values of 600 GM for 2 and 1600 GM for 3 with excitation at λ(ex) =1600 nm as compared to that observed for 1 (σ(2): 360 GM). The enhanced nonlinear optical properties of 2 and 3 are rationalized in terms of the open-shell electronic configuration allowing a large, field-induced fluctuation in the electron density (i.e., a large polarization). This interpretation is supported by theoretical evaluations of the static second hyperpolarizabilities (γ) and γ density analyses. Furthermore, nucleus-independent chemical shift (NICS) and harmonic oscillator model of aromaticity (HOMA) values and anisotropy of the induced current density (AICD) plots revealed a clear distinction in terms of the aromatic character of 1-3. Importantly, the open-shell radicaloid 2 and singlet biradicaloid 3 can be formally regarded as 27 π-electron nonaromatic and 26 π-electron aromatic species, respectively, constrained within a dominant 28 π-electron conjugated network. On the basis of the combined experimental and theoretical evidence, it is concluded that the meso-carbonyl groups of 2 and 3 play an important role in perturbing the macrocyclic π-conjugation of the parent hexaphyrin structure 1. In particular, they lead to the imposition of intrinsic radical and biradical character on the molecule as a whole and thus easy-to-discern modifications of the overall electronic effects.

A stable non-Kekulé singlet biradicaloid from meso-free 5,10,20,25-tetrakis(pentafluorophenyl)-substituted [26]hexaphyrin(1.1.1.1.1.1).

A meso,meso-diketohexaphyrin was isolated and characterized as a chemically stable non-Kekulé singlet biradicaloid. Two unpaired electrons are seemingly delocalized on two tripyrrolic units separated by C=O bonds. These results underscore the potential of expanded porphyrins to achieve unique electronic states.

Multiple conformational changes of beta-tetraphenyl meso-hexakis(pentafluorophenyl) substituted [26] and [28]hexaphyrins(1.1.1.1.1.1).

Beta-tetraphenyl meso-hexakis(pentafluorophenyl) substituted [26]hexaphyrin is conformationally flexible between rectangular and figure-of-eight shapes and its two-electron reduced [28]hexaphyrin takes figure-of-eight conformations, which are changed, upon protonation, to twisted conformations with distinct Möbius aromaticity.

Homo- and heterobismetal complexes of 5-Hydroxy-10,15,25,30-tetrakis(pentafluorophenyl)-substituted [26]hexaphyrin(1.1.1.1.1.1).

Metalation of meso-free 5,10,20,25-tetrakis(pentafluorophenyl)-substituted [26]hexaphyrin(1.1.1.1.1.1) (4) with Cu(II) and Zn(II) ions afforded homodinuclear complexes 6 and 7, respectively. A demetalation-remetalation protocol provided monozinc(II) complex 9 selectively, from which copper(II)-zinc(II) heterodinuclear complex 10 was prepared effectively.