During the development of new synthetic organic reactions by the use of group 4–7 metals, we twice encountered a reproducibility problem. The key factor was trace amounts of second metal elements that contaminated the first, main metals, i.e., nickel in chromium and lead in zinc. We had determined the standard procedures for these reactions and they were adopted in Organic Syntheses. The difference in the source of zinc, i.e., contamination by a catalytic amount of lead, proved to affect both the reactivity of the Simmons–Smith reaction and the formation of alkylzinc from the corresponding iodides. By using the concept of catalytic effects of the second metals, we developed a method to use manganese metal and applied this to sequential radical and anionic reactions. In addition, allylic aluminum species were prepared smoothly from allylic halides and aluminum by addition of an indium salt, the second element. In this account, I describe how the synthetic methods were discovered and developed, with an emphasis on the stories behind the communications and articles.
During the development of new synthetic reactions, I accidentally discovered that trace amounts of second metals that contaminated the first, main metals affected the reduction of organic halides. I describe it with an emphasis on the stories behind the original papers.
C–H direct arylation reactions of thieno[3,2-b]thiophenes (TT) with dibromo-substituted aromatic compounds afforded five different kinds of TT-based conjugated polymers, including donor–acceptor and dye-containing polymers. Although various thiophene-based polymers have been synthesized previously via polycondensation using direct arylation reactions, our research demonstrates the first direct arylation polycondensation procedure using a TT monomer. The physical properties of the obtained polymers were evaluated by using UV–vis absorption spectroscopy and cyclic voltammetry. The dye-containing polymer showed photovoltaic responses in a bulk heterojunction solar cells with a fullerene derivative.
Polycondensation via C–H direct arylation afforded thienothiophene-based polymers including donor–acceptor and dye-containing conjugated polymers. The obtained polymers were evaluated in terms of absorption, electrochemical, and photovoltaic properties.
A vesicle that exhibited the extrusion and contraction of a pseudopod-like structure under a pH gradient was studied. The vesicle is composed of oleate and oleic acid, and transforms from a double-spherical shape to a disk-like shape after numerous cyclic shape changes, including the reversal and rotation of the double-spherical vesicle. A pseudopod-like structure is extruded from the vesicle toward a pH gradient, created by NaOH diffusion, and is then contracted. This reversible motion is repeated many times. Notably, NaCl diffusion produces a monotonic and irreversible extrusion. The difference between the two systems could be explained by the cation permeability across the membrane. A mathematical model that accounted for this characteristic reproduced the experimental results semi-quantitatively. Vesicles exhibiting amoeboid-like behaviors, which may be useful in the design of amphiphilic molecular assemblies with biomimetic characteristics, have rarely been reported and are poorly understood. The present study may provide significant insight into the design of such biomimetic vesicles.
Fluorophores with intramolecular charge-transfer (ICT) character in the excited state exhibit significant solvatochromism of their fluorescence. Here, we report an example for such compounds, a benzophosphole P-oxide bearing an electron-donating p-(diphenylamino)phenyl group at the 3-position. While this compound shows only subtle dependence of the absorption maximum on the solvent polarity (λmax = 383–392 nm), its emission maximum is significantly red-shifted upon increasing the solvent polarity (cyclohexane: λem = 457 nm; DMF: λem = 598 nm). Most notably, the fluorescence quantum yields gradually increase with increased Stokes shifts, ultimately reaching ΦF = 0.28 in DMF. This trend is fundamentally different from that observed for the corresponding 2-(diphenylamino)phenyl-substituted benzophosphole congener, for which applications as a fluorescent bioimaging probe were previously demonstrated. In this study, the origins of this striking difference are examined by a combined experimental and theoretical approach. Our results suggest that the observed difference arises from a significant contribution of quinoidal resonance forms in the ICT excited state, which suppresses nonradiative decay and hence increases the quantum yield in polar solvents.
Time-odd interactions in molecules may give rise to a current along the bonds connecting the atoms. In a graph representation of a molecule the analogue of these currents corresponds to directed edges. We consider the distribution of currents in polycyclic molecules, using a minimal cycle basis. The irreducible representations of this basis in the automorphism group of the molecular graph delineate specific magnetic multipoles. This is illustrated for the case of corazulene with fourfold symmetry which may sustain a magnetic octopole. It is further shown how breaking of the fourfold symmetry can give rise to the induction of an octopolar magnetic moment by a homogeneous magnetic field. Two conjugated polycyclic hydrocarbon systems showing an induced octopolar moment are investigated by ab initio current density calculations.
We demonstrated that the sequential structural control of nanoparticles of an open-framework coordination polymer, copper hexacyanoferrate (CuHCF). The structural control has been achieved by adding the component ions not only in dispersion phase but also in the thin film form. The CuHCF nanoparticles (NPs) in the dispersion phase changed chemical composition and enhanced dispersibility with capturing [Fe(CN)6]3− anions. On the other hand, the NPs in the thin film were reversibly turned to the original state by capturing Cu2+ cations. Through the sequential processes, all of the synthesized CuHCF NPs were utilized for the high-quality electrochemical electrode for without electrochemical side reaction. This process will contribute the preparation of various electrochemical devices such as electrochromic devices, secondary batteries and biosensors.
We have fabricated diluted magnetic semiconductors (DMSs) based on organic–inorganic layered perovskite-type compounds, in which multiple quantum well structures were formed. DMSs were synthesized by substituting a small fraction of the Pb2+ ions in the inorganic layers with Mn2+ or Cu2+. XRD, ESR, and magnetization results indicate that the samples form mixed crystals. The Mn-doped samples exhibited paramagnetism down to 10 K, whereas the Cu-doped samples exhibited ferromagnetism at temperatures lower than ca. 15 K. In addition, a clear exciton peak was observed in the absorption spectrum of each sample. These results indicate that self-organized DMS quantum wells were successfully fabricated.
The metallacyclic compound was isolated by chemical reduction after selective protection of a single CO ligand in a dicarbonylruthenium(II) complex bearing the redox-active bidentate pyridyl ligand, 2-(2-pyridyl)-1,8-naphthyridine. Spectroscopic and X-ray structural analyses of the metallacycle revealed hydrogenation of the naphthyridine unit.
We report simple preparation of viscoelastic gels induced by multiple intermolecular interactions using low-molecular-weight aromatic sulfonates and alkylammoniums in water. The flow properties of the gels could be controlled between viscoelastic gel to high-viscosity liquid by changing the number of sulfonates and the length of alkyl chain among the components. Rheology evaluations of these viscoelastic materials showed significant differences of G′ and G′′ depending on the components. Also, spin–lattice relaxation, T1 in swollen-resin magic angle spinning 13C NMR well supported the differences of the viscoelastic gels in “hardness” according to the strength of hydrophobic interactions and π–π interactions contributed to the hydrogelation by alkyl chains and aromatic rings, respectively. Furthermore, we demonstrated a possibility for self-healing of a viscoelastic gel prepared with sodium 1,3,6-naphthalene trisulfonate and hexadecyltrimethylammonium bromide.
The catalytic activity of alkali metal- and alkaline earth metal-modified NaY zeolites for production of acrylic acid and methyl acrylate from methyl lactate was investigated. The reaction pathways and the role of the alkali metals in acrylate production are discussed.
The ligand coupling reaction (LCR) of hypervalent pentacoordinate antimony compounds (ArnTol5−nSb; Ar = p-trifluoromethylphenyl, Tol = p-methylphenyl; n = 0–5) was analyzed via the long-range-corrected density functional theory. Although previous experimental or computational investigations have suggested apical–apical or equatorial–equatorial coupling of ArnTol5−nSb compounds, the present results lead to apical–equatorial coupling. The biased experimental ratios of the coupling products, which were grounds for apical–apical coupling, can be explained by the stability of the transition-state (TS) structure for the apical–equatorial coupling, where n–π* interaction plays an important role to the stabilization. We further investigated the potential energy surface of H5Sb, for which the intrinsic reaction coordinate (IRC) from the TS structure for LCR indicates the equatorial–equatorial coupling. It is found that the valley-ridge transition occurs along the IRC near the TS structure and the transverse vibrational mode with imaginary frequency, orthogonal to the IRC, directs to the reactant structure corresponding to the apical–equatorial coupling.
Cyclic compounds consisting of two 1,8-anthrylene units and two ethenylene linkers were studied as π-conjugated compounds. Three derivatives having substituents (H, Me, and Ph) at the linker moieties were synthesized by Suzuki–Miyaura coupling of the corresponding diethenylanthracene boronic esters with 1,8-diiodo-10-mesitylanthracene. The X-ray analysis and DFT calculations revealed that all the compounds had nonplanar cyclic frameworks where the two ethenylene linkers were syn to the anthracene units. Exchanges between the two syn forms were observed from the line shape changes in the 1H NMR signals of the mesityl group. Their barriers increased in the order of H, Ph, and Me compounds from 34 to 70 kJ mol−1. The effects of substituents on the molecular structure, dynamic behavior, and electronic properties are discussed.
We developed a capillary electrophoretic (CE) method for the kinetic study of intermolecular interactions. Neither immobilization nor chemical modification, e.g., fluorescence labelling, of solute and ligand molecules is required. A concept of chromatographic capillary electrophoresis (CCE) was introduced as an experimental CE procedure. In the CCE mode, the migration of solute–ligand complex in a capillary is stopped. Only solute molecules migrate and are detected. New moment equations were developed, which were essential for determining association and dissociation rate constants from elution peak profiles measured under the CCE conditions. The combination of the CCE concept and the moment theory leads to the CE method, i.e., moment analysis by CCE (MACCE). However, because it was hard to really perform CE experiments under the CCE conditions, we also developed practical experimental and data analysis procedures for the MACCE measurement. The reaction rate constants were analytically determined by the MACCE method for the formation and dissociation of the inclusion complex between thymol and sulfated-β-cyclodextrin. It is unnecessary to fit elution curves numerically calculated to those experimentally measured for determining the rate constants. It was demonstrated that the MACCE method was effective for the kinetic study of intermolecular interactions.
The intra- and intermolecular reactivity of triplet sumanenetrione 31, which contains a curved π-system, were investigated to characterize the triplet aromatic ketone. The lowest ππ* triplet energy and lifetime were determined from phosphorescence measurements at 77 K to be 196 kJ mol−1 and 9.5 ms in methylcyclohexane, respectively. The transient ππ* triplet state 31 was detected by laser flash photolysis at 293 K and found to be significantly short-lived, e.g., 53.9 µs in degassed benzene, compared to a planar ππ* triplet ketone such as fluorenone triplet (500 µs). The fast intersystem crossing process (ISC) of 31 was attributed to the curved structure of the sumanenetrione, which enhances spin-orbit coupling (SOC). The ππ* character was proven by its negligible quenching by isopropanol, i.e., kq < 4.50 × 103 M−1 s−1, although the quenching rate constants for molecular oxygen and triethylamine in benzene were high: 1.0 × 109 M−1 s−1 and 4.0 × 108 M−1 s−1. The ππ* character of the triplet state was also proven by the relatively small electron spin resonance zero-field splitting parameter, |D|/hc, in toluene at 78 K, which was found to be 0.0621 cm−1. The |E|/hc parameter was determined to be 0.0071 cm−1.