The highly enantioselective synthesis of functionalized helicenes and helicene-like molecules have been achieved via rhodium-catalyzed [2+2+2] cycloaddition reactions. The rhodium-catalyzed enantioselective intramolecular [2+2+2] cycloaddition of 2-naphthol-linked triynes afforded helicene-like molecules in good yields and ee values. The more sterically encumbered reaction, the rhodium-catalyzed enantioselective double intramolecular [2+2+2] cycloaddition of a 2-naphthol-linked hexayne, also proceeded to give a helicene-like molecule with high ee value, although the product yield was low. Not only intramolecular cycloaddition reactions but also intermolecular ones were accomplished by combinations of electron-rich tetraynes and electron-poor diynes to give - and helicene-like molecules and helicenes in varying yields and ee values.
The highly enantioselective synthesis of functionalized –helicenes and helicene-like molecules have been achieved via the cationic rhodium(I)/chiral bisphosphine complex-catalyzed intramolecular and intermolecular [2+2+2] cycloaddition reactions.
In this account, the emergence of a new family of porous solid-state materials based on carbon and nitrogen is discussed. This started with the observation that carbon nitride, a polymeric material with a composition close to C3N4, is not only unexpectedly thermally and chemically stable, but a semiconductor at the same time and able to catalyze a variety of chemical reactions, such as Diels–Alder cyclizations, oxidations, and photochemical water splitting. Carbon nitride is however already sufficiently reviewed but related materials with similar potential have essentially been not sufficiently covered. The remaining structures are manifold and cover the range from on the one hand covalent triazine frameworks (CTFs) as new semiconducting porous solid-state materials to the other porous nitrogen-doped carbons (NdCs) as catalysts which are known to be applicable in a variety of electrocatalytic reactions. CTFs are porous polymeric frameworks constituted of triazine rings and other aromatic rings. Chemical binding motifs and crystal structures can be used to control the band structure of such an (organic) solid-state material. Porous NdCs are usually made by adding nitrogen sources to classical carbonization recipes, and they are attracting a lot of interest because of their catalytic activity for electrochemical processes, such as oxygen reduction reaction (ORR). This account will summarize state-of-the-art work on those systems being next-generation catalysts for different kinds of reactions, which are affordable and high-performance catalysts with unique principle for emergence of catalytic activities, combining theoretical and experimental studies together with basic and applied science in a range of scientific fields from chemistry to physics. Indeed, the first exploration of the above materials as candidates for components of fuel cells and rechargeable metal–air batteries are discussed.
This account will summarize state-of-the-art work on carbon- and nitrogen-based porous solids, being affordable and high-performance catalysts, combining theoretical and experimental studies together with basic and applied science in a range of scientific field from chemistry to physics.
This report describes the synthesis and structural features of supramolecular assemblies of s-hydrindacene (1,2,3,5,6,7-hexahydro-s-indacene), such as macrocycles with directionally persistent peripheral functionality, allosteric receptors, adrenaline receptors, and rotaxane molecular shuttles. These hydrindacene-based assemblies also exhibit allostericity due to induced polarization of amides or to entropy-driven switching between the imine and hydrogen bonds.
Synthesis and structural features of supramolecular assemblies of s-hydrindacene (1,2,3,5,6,7-hexahydro-s-indacene), such as macrocycles with directionally persistent peripheral functionality, allosteric receptors, adrenaline receptors, and rotaxane molecular shuttles are described.
Solution-phase synchrotron X-ray absorption spectroscopy (XAS) is a powerful tool for structural and mechanistic investigations of paramagnetic organoiron intermediates in solution-phase reactions. For paramagnetic organotransition metal intermediates, difficulties are often encountered with conventional NMR- and EPR-based analyses. By using solution-phase XAS, we succeeded in identifying the organoiron species formed in the reaction of iron bisphosphine with mesitylmagnesium bromide, MesMgBr, and 1-bromodecane in a [FeX2(SciOPP)]-catalyzed Kumada–Tamao–Corriu (KTC)-type cross-coupling reaction. X-ray absorption near-edge structure (XANES) spectra showed that the resulting aryliron species possessed a divalent oxidation state. Extended X-ray absorption fine structure (EXAFS) demonstrated that the solution-phase molecular geometries of these species are in satisfactory agreement with the crystallographic geometries of [FeIIBrMes(SciOPP)] and [FeIIMes2(SciOPP)]. By combining GC-quantitative analysis and solution-phase XAS, the cross-coupling reactivities of these aryliron species were successfully investigated in the reaction with 1-bromodecane under stoichiometric and catalytic conditions.
Solution-phase molecular structures of organoiron intermediates of Kumada–Tamao–Corriu-type cross-coupling were illuminated by X-ray absorption spectroscopy. The intermediacy of halomesityl iron complex of [FeIIBrMes(SciOPP)] and dimesityl iron complex of [FeIIMes2(SciOPP)] was adequately elucidated with formal nonredox FeII/FeII catalytic cycle.
One-dimensional spin-crossover (SCO) polymers of formula [FeII(NH2-trz)3](CnH2n+1SO3)2·xH2O (trz: 4-substituted-1,2,4-triazole; n = 1–9) have been synthesized. They displayed hysteretic SCO transition around 280–350 K. The spin transition temperatures (T1/2) in the heating and cooling processes increased, and the hysteresis width became narrower with increasing alkyl chain length (n). From the analysis of EXAFS, the nearest-neighbor Fe–Fe distance decreased with increasing n, and it had a close relationship with T1/2. This is highly indicative of the increase of intrachain interaction of [FeII(NH2-trz)3] with n being attributed to the uniaxial chemical pressure effect induced by van der Waals force between alkyl chains, so-called “fastener effect.” To elucidate the physicochemical effect on T1/2, the ligand field and Racah parameter (B) were estimated by analysing the pre-edge region in Fe-K edge XANES spectra based on the ligand-field theory. B decreased with increasing n, which was closely consistent with the behavior of T1/2 and 57Fe Mössbauer isomer shift (IS). Judging from these results, a covalency between FeII 3d and ligand π* orbital is enhanced by the fastener effect, leading to the expansion of the 3d orbital, i.e. the remarkable decrease of B and IS, which is the dominating factor on T1/2 in our system.
We found that incorporation of alkaline earth metal oxides into Ag-loaded Ta2O5 (Ag/Ta2O5) suppresses the H2 production from overall water splitting for the photocatalytic conversion of CO2 by using H2O as an electron donor. Four different combinations of the photocatalysts (Ag/MO/Ta2O5 (M = Mg, Ca, Sr, or Ba)) were utilized; of these, the highest amount of CO was generated over Ag-loaded SrO-modified Ta2O5 (Ag/SrO/Ta2O5) with the evolution of a stoichiometric amount of O2. It was demonstrated that the presence of low quantities of SrO considerably enhanced the selectivity toward CO evolution. We also confirmed that a Ag cocatalyst increased the selectivity toward CO evolution and relatively small Ag nanoparticles maximized the selectivity toward CO evolution. It was therefore concluded that the particle size of the Ag cocatalysts should be controlled, and alkaline earth metal oxides should be introduced into Ag/Ta2O5 in order to achieve high conversion of CO2 and good selectivity toward O2 evolution.
Direct alkylation via the cleavage of the ortho C–H bonds by a nickel-catalyzed reaction of aromatic amides containing an 8-aminoquinoline moiety as the directing group with alkyl halides is reported. Various alkyl halides, including benzyl, allyl, alkyl, and methyl halides (or pseudo halides) participate as electrophilic coupling partners. The reaction shows a high functional group compatibility. The reaction proceeds in a highly regioselective manner at the less hindered C–H bonds in the reaction of meta-substituted aromatic amides, irrespective of the electronic nature of the substituent. The mechanism responsible for the C–H alkylation reaction is discussed based on the results obtained in a variety of mechanistic experiments.
In this paper, we investigated the effects of substitution at the 5-position of an asymmetric BODIPY cation sensor to tune its spectroscopic, photophysical, and cation-sensing properties. We introduced substituent groups with differing electron density at the 5-position of 3-[bis(pyridine-2-ylmethyl)amino]-BODIPY, which contains a cation recognition moiety at the 3-position of the BODIPY core, to develop four sensors which all exhibited distinctive ratiometric spectral changes in the presence of Cu2+. Aromatic substitution increased the Stokes shift. Substitution with the electron-withdrawing sulfonylphenyl group resulted in the highest fluorescence quantum yield, largest absorption coefficient, and largest spectral shift in the presence of Cu2+. The sulfonylphenyl-substituted sensor also exhibited excellent selectivity for Cu2+.
Gas-phase acidities (GA) of 2-phenyl- and 2-p-nitrophenyl-substituted fluoroalkanes, ArCH2Rf and ArCH(Rf1)Rf2, were calculated at the B3LYP/6-311+G(d,p) level of theory. The GA values of the fluoroalkanes having no fluorine atom at the β-position of the conjugate acid anion center were correlated linearly with the corrected number of fluorine atoms contained in the fluorinated alkyl group (Rf), indicating that these acidities were determined by accumulated inductive effect of fluorine atoms. The GA values of ArCH(CF3)21 and ArCH(C2F5)22 also conformed to the line, indicating negligible or no contribution of β-fluorine negative hyperconjugation to the stability of both carbanions. On the basis of this linear relationship, the extent of β-fluorine negative hyperconjugation involved in the acidity of fluoroalkanes having β-fluorine was evaluated quantitatively. It was concluded that the contribution of β-fluorine negative hyperconjugation to acidity of aryl-substituted fluoroalkanes is complementary to stabilization effects by the aryl group as well as accumulated inductive effect of fluorine atoms contained in the fluorinated alkyl group.
The solubility and ice melting point of a binary system containing water and D-allose (D-All), the C3 epimer of D-glucose, were investigated and, for the first time, a binary phase diagram was constructed in the temperature range −2 to 70 °C. It was found that D-All formed the dihydrate below 32 °C as a thermodynamically stable solid in equilibrium with the solution phase. X-ray single-crystal analysis confirmed that D-All molecules in the dihydrate form a β-D-pyranose ring in 4C1 conformation. The crystal system (orthorhombic), space group (P212121, #19), and number of sugar molecules per unit cell (Z = 4) were the same as those of D-All anhydride (stable Form I). The unit cell length of the c axis for D-All dihydrate was ca. 2.8 Å longer than that for D-All anhydride due to the incorporation of water molecules, whereas the differences in length of the a and b axes were within 0.7 Å. Conversion from the dihydrate to the anhydride of D-All was easily attained by heating D-All dihydrate above 75 °C or by storing it over P2O5 in a desiccator for ca. 4 h.
In this article, we have demonstrated that π–π stacking interactions can be synchronized through the rapid hydration of π-conjugated molecules, generating a sort of metastable state. The self-assembly process of the group of molecules activated with the same timing was directly correlated to the spatial pathway along the microflow channel. Various micrometer-sized molecular architectures having desired molecular packing, therefore, can be created through the precise regulation of the flowing self-assembly field in a top-down fashion, where the hysteresis of the spatial pathway was recorded in the resultant assemblies.
Reactions of a ruthenium(II) complex containing quinoline-2-carbaldehyde (pyridine-2-carbonyl)hydrazone (HL), trans(P,P)-[RuCl2(PPh3)2(HL)] (1), and 3d-metal(II) chlorides resulted in heterodimetallic complexes, [RuCl2(PPh3)2(µ-L)MCl2] (2M, M = Mn, Fe, Co, Ni, Cu, and Zn), in which the deprotonated hydrazonate (L−) bridged two metal ions in the µ-1(Ru)κ2N,O:2(M)κ3N′,N′′,N′′′ mode. The coordination bond lengths around the Ru and M centers suggested that the oxidation states in the complexes 2M could be assigned as RuIII and MII; this was also supported by magnetic, electrochemical, and spectroscopic measurements. In addition, oxidation of complex 1 by (NH4)2[Ce(NO3)6] gave the corresponding mononuclear RuIII complex with the deprotonated hydrazonate, trans(P,P)-[RuCl2(PPh3)2(L)] (3). It is suggested that oxidation of the Ru center lead to the concerted deprotonation from the hydrazone ligand. Addition of excess HClO4 to complex 3 gave a doubly protonated RuIII complex, 4(ClO4)2; in this complex the hydrazonate moiety was not protonated, but both the quinolyl and pyridyl N atoms were protonated. Complexes 3 and 42+ could be interconverted by the addition of acid or base without changing the oxidation state of the Ru center.
Logarithms of stability constants, log β, of copper(II) complexes with tripeptides containing glycine, glutamic acid, and histidine were modelled with 3χv connectivity index. The model developed on complexes with tripeptides formed of Gly and Glu yielded S.E. = 0.47, 0.38, and 0.55, depending on whether CuL, CuH−1L, or CuH−2L complexes were taken as referent. The model was also applied to complexes with tripeptides containing His, S.E. = 1.47, 1.39, and 1.80. Although a somewhat worse result for G/E/H tripeptide complexes, much bigger range of their log β’s (29.648), in contrast to 16.671 for G/E tripeptide complexes, has to be borne in mind.
We have recently reported a novel pseudo-dumbbell-type molecular beacon probe (Probe 1) possessing polyamine-connected deoxyuridine (U) and silylated pyrene. The probe showed weak fluorescence signal while it stayed alone. Fluorescence signal of the probe was increased in the presence of the complementary DNA. In this study, we prepared new molecular beacons, Probe 2 and Probe 3, possessing the elongated stem portion of Probe 1. In addition, one U in Probe 2 is substituted by anthraquinone-bearing deoxyuridine residue (Y) in Probe 3. Probe 4 is essentially the same as Probe 1 but one deoxyguanosine in the loop portion of Probe 1 is substituted by deoxyinosine in Probe 4. In Probe 5, 3′-terminal deoxycytidine of Probe 3 is substituted by deoxyadenosine. The fluorescence signal of these probes is effectively quenched in the absence of target DNA. Among all, Probe 3 shows the most effective quenching. On the other hand, the signal is substantially increased in the presence of complementary DNA. The ratio of signal to background in case of Probe 3 is the highest. All these probes also recognize single nucleotide alternation in the target DNA to a different extent. The sequence recognition ability of Probe 3 is also the highest among all the probes.