Despite worldwide interest from synthetic chemists, the rational design of catalytically active organoiron species remains problematic. While noble metal catalysis proceeds through diamagnetic low-spin intermediates, iron species are often in the high or intermediate spin states, which are paramagnetic and difficult to analyze. Possible spin change during catalysis also complicates the problem. This report describes two extremes for the catalyst design of iron complexes. One involves diamagnetic 14-electron iron(II) species useful for two-electron chemistry often seen in noble metal catalysis. The disilaferracyclic carbonyl complex 4 is a good catalyst precursor, and shows good catalytic performance for the hydrogenation and hydrosilylation of alkenes, and the hydrosilane reduction of carbonyl compounds. Based on DFT calculations, mechanisms involving σ-CAM (sigma-complex-assisted metathesis) for the hydrogenation and hydrosilane reduction are suggested. Further catalyst design inspired by the success of 4 led to the discovery of iron and cobalt catalyst systems composed of metal carboxylates and isocyanide ligands leading to a practical substitute for industrially useful platinum catalysts for hydrosilylation with hydrosiloxanes. The second approach involves paramagnetic 16-electron iron (II) catalyst species. A series of “(R3TACN)FeX2” complexes were prepared and found to be good catalysts for atom transfer radical polymerization, giving rise to well-controlled polymerization of styrene, methacrylates, and acrylates with high activity. Moreover, the catalyst could be easily removed from the polymer and was reusable. Mechanistic studies of iron-catalyzed cross-coupling reactions in collaboration with Nakamura and Takaya opened a new approach to the catalyst design of unknown spin states by using new analytical methods for paramagnetic species in the solution state.
Morphology of molecules and materials has significant impact on properties and functions. At molecular and nanometer scales, morphologies of molecules and their organized state are controlled by molecular design and synthesis. This account focuses on morphologies of crystalline and polymer materials from nanometer to macroscopic scales. A good model for morphology control is found in nature. Biominerals form inorganic–organic composites with hierarchically organized morphologies under mild conditions. We found the overlooked biological strategy for the morphogenesis from the nanocrystals and the macromolecules. Inspired by biological approaches, hierarchically organized morphologies of crystals were prepared through controlled growth in the presence of organic polymers. The bioinspired approaches are regarded as polymer-controlled crystallization. Recently, we developed the reverse approach, namely crystal-controlled polymerization. The hierarchical morphology control of organic and inorganic polymer materials was achieved by using crystals. Morphology design and control of materials have potential for improvement of performance and emergence of unprecedented properties. The present account summarizes basic findings of the overlooked biological strategy, polymer-mediated crystallization, and crystal-mediated polymerization.
A new series of highly π-extended dicyanomethylene-endcapped quinoidal S,N-heteroacenes (JH-quinoids) fused with thiophene and pyrrole rings have been designed and synthesized. The π-extension of the central S,N-heteroacene cores gives rise to significant red-shifted absorption maxima in solution without being affected by the long alkyl groups. The absorption maximum of JH10 with the longest quinoidal backbone in the thin film significantly red-shifted to the near-infrared region of 1260 nm as compared to that in solution (880 nm), indicating the formation of strong intermolecular interaction in the solid state. JH-quinoids maintain sufficiently low LUMO energy levels in the range of −4.09∼−4.22 eV regardless of the fused ring systems and substituents, while the HOMO energy levels increase with extending the length of S,N-heteroacenes; the highest HOMO energy level of JH10 is as high as −5.18 eV owing to the contributions from the nitrogen atoms and chalcogen. The molecular geometries of JH-quinoids optimized from the DFT calculations indicate their complete planar backbones and the trend of HOMO and LUMO energy levels variation is in good agreement with the cyclic voltammetry results. Consequently, the present JH-quinoids should be promising candidates for ambipolar organic semiconductors.
Copper(I) complexes bearing (R)-(+)-2,2′-bis(di-p-tolylphosphino)-1,1′-binaphthyl and 2,2′-bipyridine derivative ligands were newly synthesized and characterized. Despite many known copper(I) complexes bearing diimine and diphosphine ligands, which are well-investigated for their photofuntions, exhibit irreversible oxidation, the present complex shows clear spectral changes on oxidation and reduction reactions.
A mixed molecular layer composed of phospholipids and fatty acids (carbon number: 18) was investigated experimentally to understand the interaction between them depending on the number of double bonds in the fatty acids. The surface pressure–surface area (Π–A) isotherm for 1,2-di-oleoyl-sn-glycero-3-phosphocholine (DOPC) at an air/water interface characteristically changed with the addition of fatty acid, i.e., A at Π was not changed for oleic acid very much in comparison with other fatty acids. The degree of the decrease in A at Π for 1,2-di-stearoyl-sn-glycero-3-phosphocholine was not changed for stearic acid very much in comparison with other fatty acids, suggesting different responses to fatty acids between the two compounds. Attenuated total reflection Fourier transform infrared spectroscopy and differential scanning calorimetry were used to evaluate the interaction between DOPC and fatty acid molecules.
The gel-state dependencies of brown patterns of Mn–Fe-based Prussian blue analogues (PBAs) formed in water-glass gels by reaction–diffusion (RD) processes have been studied by using X-ray fluorescence and X-ray absorption near-edge structure spectroscopies. Three tubes containing admixtures of 0.25 M [Fe(CN)6]3− and 0.30 M acetic acid (A and B) or boric acid (C) in water-glass (9.1 (A) and 7.4 (B and C) mass%) were brought into contact with 0.20 M MnSO4 solution. Tube A formed periodic (but not genuine Liesegang) bands, whereas tubes B and C formed light-brown bands in the turbid zone (TZ). A lowered amount of water-glass (A → B) resulted in a more fluctuant distribution of the PBAs. [Mn(H2O)6]2+ ions were also present in the TZ of tube B and their content increased with distance from the gel-junction after stopping the RD process. Addition of boric acid (C) suppressed the RD processes in the gel, slowing down the formation of PBAs. It is likely that the areas of low PBA content in the TZ of tubes B and C generate the light-brown bands. FEFF calculations suggest that the most likely local structures of the predominant PBAs in tubes A/B and C are Mn(NCFe)2O4K2 and Mn(NCFe)2O4, respectively.
Two kinds of enediyne-cored polyphenylene dendrimer (mGn, pGn) were prepared as pure cis and trans isomers. In comparison to parent enediyne with no dendron substituents, the dendrimers exhibited highly efficient fluorescence emission with mutual cis–trans isomerization. Along with an increase in the generation of dendrons, decrease of Φiso and shortening of τS were observed, suggesting that dendrons affect cis–trans photoisomerization and deactivation from excited singlet state.
A shape-persistent macrocycle composed of carbazole and salphen, which has a discrete 1.4-nm-sized inner cavity, forms four thermotropic columnar liquid crystalline (LC) phases. Both the structure and dynamics of the macrocyclic mesogens in the LC phases were investigated by solid-state NMR. Variable temperature 1H and 13C magic-angle spinning (MAS) experiments reveal that the peripheral side chains exhibited narrow line widths throughout the columnar phases, indicating that the side chains behave like liquids among the columns. In sharp contrast, the NMR signals related to the macrocyclic mesogen became highly symmetric and similar to signals in solution with increasing temperature. These results revealed that the LC macrocycle with an inherent inner cavity gains more mobility around the mesogenic framework as the macrocycle underwent phase transitions.
Atomic charges are very useful variables in chemistry and biochemistry. However, there is no equation to give “exact” atomic charges. For evaluation of atomic charges, the criteria, (i) small dependency of basis sets, (ii) reproduction of electrostatic potential (ESP) determined by self-consistent field calculation, and (iii) small grid artifacts in charge fitting, have been often employed. Although ESP charge, which is one of the choices for atomic charges, satisfies the criteria (i) and (ii), it has been difficult to remove the grid artifacts. Recently, we proposed another ESP charge by including spatial electron density distribution. In this study, we computed the atomic charges about intramolecular transesterification in phosphorylated d-ribose and oxidation reaction of deoxytetranucleotide d(CGCG)2 with our method and showed that our method can satisfy the three criteria.
We investigated the anionic ring opening polymerization of ethylene oxide using a microflow system with a tubular reactor. Employing alkoxy anions as an initiator, the monoalkyl-ether terminated polyethylene glycols were obtained by the microfluidic system within 30 min of residence time, which is a remarkably shortened reaction time compared with a batch system. The use of a suitable micromixer is important to obtain monoalkyl-ether terminated PEGs in high yields and small PDIs. By comparison with a batch system, the anionic ROP in the microflow was quite smooth and the distribution of the obtained polymer was narrow with the use of MeONa as a catalyst.
In the presence of diphenyl sulfide, oxygen-oxidative polymerization of diphenyl disulfide gave highly crystalized poly(1,4-phenylene sulfide) (PPS) using a vanadyl-strong acid catalytic system. Effect of the sulfide, which was inactive to the vanadyl catalyst, was ascribed to the enhancement of the electrophilic substitution with a sulfonium cation onto a thiophenyl end. The finally purified PPS showed high crystallinity (Xc = 44%), which was even higher than that of the reagent grade PPS produced by the conventional polycondensation process.
Supercapacitors as a promising energy storage device have received significant attention. Here we report a facile, low cost and mass production strategy to prepare polyaniline (PANI)/molybdenum sulfide (MoSX) supercapacitor material by electrodeposition. More specifically, PANI was electrodeposited on glassy carbon (GC) through chrono amperometry followed by electrodeposition of MoSX via chrono potentiometry from ammonium tetrathiomolybdate ((NH4)2MoS4) precursor. This composite material was characterized by X-ray photoelectron spectrum, scanning electron microscopy and energy-dispersive X-ray spectroscopy. In addition, PANI/MoSX shows superior capacitance of 48.64 mF cm−2 at a current density of 56.62 µA cm−2 and long-term stability without any degradation during the 150 cycles. The enhanced capacitance observed is from the combination of electrochemical behaviors of PANI and MoSX.
Solvent self-diffusion coefficients Dw* and Dw are respectively determined by PGSE NMR in the bulk solvent and in suitably prepared aqueous micellar solutions of a series of commercial ethoxylated nonyl phenols (ENPs) at 298 and 317 K. The capability of ENP micelles for obstructing the free diffusion of solvent molecules is characterized by the obstruction ratio K = Dw/Dw*, which turns out to depend merely on the volume fraction of EO units present—regardless of significant changes in solute concentration, distribution of EO chain length, micellar aggregation number and temperature. The experiments are interpreted in terms of a renewed analytical model of ENP micellar structure, based on Tanford’s concept of hydrodynamic particle. The results from model fitting return the characteristic sizes of ENP monomers, support the ellipsoid shape of the micelles, indicate a stable EO shell, follow the trend in the variation of hydration number vs. the chain length predicted by thermal analysis in PEO solutions.
A series of halogen substituted nickel tmtaa (tmtaa: 7,16-dihydro-6,8,15,17-tetramethyldibenzo-[b,i][1,4,8,11] tetraazacyclotetradecine) complexes ([Ni(tmtaa-4X)], X = F, Cl, Br, I) have been prepared and characterized by X-ray crystallographic structure analysis. It was found that [Ni(tmtaa-4F)] formed one-dimensional stacked structure, [Ni(tmtaa-4Cl)] exhibited polymorphism, and [Ni(tmtaa-4Br)] and [Ni(tmtaa-4I)] incorporated crystallization solvent in its crystals. In particular, crystal to crystal phase transition was observed in [Ni(tmtaa-4Br)].