Syntheses, structures, and coordination chemistry of phosphole-containing hybrid calixphyrins: promising macrocyclic P,N2,X-mixed donor ligands for designing reactive transition-metal complexes

The syntheses, structures, and coordination chemistry of phosphole-containing hybrid calixphyrins (P,N2,X-hybrid calixphyrins) and the catalytic activities of their transition-metal complexes are reported. The 5,10-porphodimethene type 14pi-P,(NH)2,X- and 16pi-P,N2,X-hybrid calixphyrins (X = O, S, NH) are prepared via acid-promoted dehydrative condensation between a sigma4-phosphatripyrrane and the corresponding 2,5-bis[hydroxy(phenyl)methyl]heteroles followed by DDQ oxidation. Both spectroscopic and crystallographic data of the hybrid calixphyrins have revealed that the conformation and size of the macrocyclic platforms as well as the oxidation state of the -conjugated pyrrole-heterole-pyrrole (N-X-N) units vary considerably depending on the combination of heteroles. The sigma3-P,(NH)2,S- and sigma3-P,N2,S-hybrids react with Pd(OAc)2 and Pd(dba)2, respectively, to afford the same Pd(II)-P,N2,S-hybrid complex, in which the calixphyrin platform is regarded as a dianionic ligand. In the complexation with [RhCl(CO)2]2 in dichloromethane, the sigma3-P,N2,S-hybrid behaves as a neutral ligand to afford an ionic Rh(I)-P,N2,S-hybrid complex, whereas the sigma3-P,N2,NH-hybrid behaves as an anionic ligand to produce Rh(III)-P,N3-hybrid complexes. In the latter reaction, it is likely that a neutral Rh(I)-P,N3-hybrid complex, generated as a highly nucleophilic intermediate, undergoes C-Cl bond activation of the solvent. The complexation of AuCl(SMe2) with the sigma3-P,N2,X-hybrids (X = S, NH) leads to the formation of the corresponding Au(I)-monophosphine complexes. The spectral data and crystal structures of these metal complexes exhibit the hemilabile nature of the phosphole-containing hybrid calixphyrin platforms derived from the flexible phosphole unit and the redox active N-X-N units. The hybrid calixphyrin-palladium and -rhodium complexes catalyze the Heck reaction and hydrosilylations, respectively, implying that the metal center in the core is capable of activating the substrates under appropriate reaction conditions. The present results demonstrate the potential utility of the phosphole-containing hybrid calixphyrins as a new class of macrocyclic P,N2,X-mixed donor ligands for designing highly reactive transition-metal complexes.     

Theoretical study of pyrazolate-bridged dinuclear platinum(II) complexes: interesting potential energy curve of the lowest energy triplet excited state and phosphorescence spectra

Four kinds of 3,5-dialkylpyrazolate(R2pz)-bridged dinuclear platinum(II) complexes [Pt2(mu-R2pz)2(dfppy)2] (dfppy=2-(2,4-difluorophenyl)pyridine; R2pz=pyrazolate in 1, 3,5-dimethylpyrazolate in 2, 3-methyl-5- tert-butylpyrazolate in 3, and 3,5-bis(tert-butyl)pyrazolate in 4) were theoretically investigated by the DFT(B3PW91) method. The Stokes shift of their phosphorescence spectra was discussed on the basis of the potential energy curve (PEC) of the lowest energy triplet excited state (T1). This PEC significantly depends on the bulkiness of substituents on pz. In 1 and 2, bearing small substituents on pz, one local minimum is present in the T1 state besides a global minimum. The local minimum geometry is similar to the S0-equilibrium one. The T1 state at this local minimum is characterized as the pi-pi* excited state in dfppy, where the dpi orbital of Pt participates in this excited state through an antibonding interaction with the pi orbital of dfppy; in other words, this triplet excited state is assigned as the mixture of the ligand-centered pi-pi* excited and metal-to-ligand charge transfer excited state ((3)LC/MLCT). The geometry of the T1-global minimum is considerably different from the S0-equilibrium one. The T1 state at the global minimum is characterized as the triplet metal-metal-to-ligand charge transfer ((3)MMLCT) excited state, which is formed by the one-electron excitation from the dsigma-dsigma antibonding orbital to the pi* orbital of dfppy. Because of the presence of the local minimum, the geometry change in the T1 state is suppressed in polystyrene at room temperature (RT) and frozen 2-methyltetrahydrofuran (2-MeTHF) at 77 K. As a result, the energy of phosphorescence is almost the same in these solvents. In fluid 2-MeTHF at RT, on the other hand, the geometry of the T1 state easily reaches the T1-global minimum. Because the T1-global minimum geometry is considerably different from the S0-equilibrium one, the phosphorescence occurs at considerably low energy. These are the reasons why the Stokes shift is very large in fluid 2-MeTHF but small in polystyrene and frozen 2-MeTHF. In 3 and 4, bearing bulky tert-butyl substituents on pz, only the T1-global minimum is present but the local minimum is not. The electronic structure of this T1-global minimum is assigned as the (3)MMLCT excited state like 1 and 2. Though frozen 2-MeTHF suppresses the geometry change of 3 and 4 in the T1 state, their geometries moderately change in polystyrene because of the absence of the T1-local minimum. As a result, the energy of phosphorescence is moderately lower in polystyrene than in frozen 2-MeTHF. The T1-global minimum geometry is much different from the S0-equilibrium one in 3 but moderately different in 4, which is interpreted in terms of the symmetries of these complexes and the steric repulsion between the tert-butyl group on pz and dfppy. Thus, the energy of phosphorescence of 3 is much lower in fluid 2-MeTHF than in frozen 2-MeTHF like 1 and 2 but that of 4 is moderately lower; in other words, the Stokes shift in fluid 2-MeTHF is small only in 4.     

Heteropolynuclear complexes of 3,5-dimethylpyrazolate [Pt2M4(Me2pz)8] (M = Ag, Cu). Highly luminescent character of the triplet excited state based on mixed-metal cores

The platinum dimer and heteropolynuclear platinum complexes of 3,5-dimethylpyrazolate, [Pt2M4(mu-Me2pz)8] [M = H (1), Ag (2), Cu (3)], were synthesized and structurally characterized. They exhibit yellow, sky-blue, and orange luminescence, respectively, in the solid state. The absorption bands of 2 and 3 are mainly assigned to the combination of the metal-metal-to-ligand charge-transfer and [Pt2 --> Pt2M4] transitions by the time-dependent density functional theory (DFT) method. DFT calculations also indicate that the emissive states of 2 and 3 are 3[Pt2 --> Pt2Ag4] and 3[Cu(d) --> Pt2Cu4], respectively.     

Phase reduction approach to synchronisation of nonlinear oscillators

Systems of dynamical elements exhibiting spontaneous rhythms are found in various fields of science and engineering, including physics, chemistry, biology, physiology, and mechanical and electrical engineering. Such dynamical elements are often modelled as nonlinear limit-cycle oscillators. In this article, we briefly review phase reduction theory, which is a simple and powerful method for analysing the synchronisation properties of limit-cycle oscillators exhibiting rhythmic dynamics. Through phase reduction theory, we can systematically simplify the nonlinear multi-dimensional differential equations describing a limit-cycle oscillator to a one-dimensional phase equation, which is much easier to analyse. Classical applications of this theory, i.e. the phase locking of an oscillator to a periodic external forcing and the mutual synchronisation of interacting oscillators, are explained. Further, more recent applications of this theory to the synchronisation of non-interacting oscillators induced by common noise and the dynamics of coupled oscillators on complex networks are discussed. We also comment on some recent advances in phase reduction theory for noise-driven oscillators and rhythmic spatiotemporal patterns.     

Global existence of small solutions for the fourth-order nonlinear Schrödinger equation

We consider the Cauchy problem for the fourth-order nonlinear Schrödinger equation

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where \(n=1,2\). We prove global existence of small solutions under the growth condition of \(f\left( u\right) \) satisfying \(\left| \partial _{u}^{j}f\left( u\right) \right| \le C\left| u\right| ^{p-j},\) where \(p>1+\frac{4}{n},0\le j\le 3\).

     

Total synthesis of azumamide A and azumamide E, evaluation as histone deacetylase inhibitors, and design of a more potent analogue

The unprecedented diastereoselective Mannich reaction of a Z-allylsulfoximine was a key step in the total synthesis of the marine natural products azumamide A and E, and an unnatural analogue. Their relative potency as histone deacetylase inhibitors was evaluated and found to correlate with predicted zinc-binding affinity. [reaction: see text]     

Organo[2-(hydroxymethyl)phenyl]dimethylsilanes as mild and reproducible agents for rhodium-catalyzed 1,4-addition reactions

Stable and reusable tetraorganosilicon reagents, alkenyl-, aryl-, and silyl[2-(hydroxymethyl)phenyl]dimethylsilanes, undergo 1,4-addition reactions to alpha,beta-unsaturated carbonyl acceptors under mild rhodium-catalysis. The reaction tolerates a diverse range of functional groups and is applicable to gram-scale synthesis. Use of a chiral diene ligand allows the achievement of the corresponding enantioselective transformations using the tetraorganosilicon reagents, providing the silicon-based approach to optically active ketones and substituted piperidones that serve as synthetic intermediates of pharmaceuticals. A rhodium alkoxide species is suggested to be responsible for a transmetalation step on the basis of the observed kinetic resolution of a racemic chiral phenylsilane in the enantioselective 1,4-addition reaction under the rhodium-chiral diene catalysis.     

On the critical nonlinear damped wave equation with large initial data

We study the nonlinear damped wave equation

(0.1)     

Synthesis and micromechanical properties of flexible, self-supporting polymer-SiO2 nanofilms

Large-scale, self-supporting ultrathin films composed of an elastomeric polyacrylate network interpenetrated by a silica (SiO2) network were synthesized and characterized. The organic network was first photopolymerized and the silica structure was subsequently developed in situ in the preformed organic gel. Composition and morphology of the hybrid interpenetrated network (IPN) nanofilms were characterized by infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy and compared with the case of zirconia (ZrO2) hybrid IPN reported earlier. Young modulus, ultimate tensile strength, and ultimate tensile elongation were determined for different organic/inorganic molar ratios and give some insights on how the composition of the nanofilms influence their robustness and self-supporting properties.     

Phosphatidylcholine vesicle-mediated decomposition of hydrogen peroxide

The decomposition of hydrogen peroxide (H2O2) was examined in aqueous solution (50 mM Tris-HCl buffer, pH 7.4, containing 100 mM NaCl) at 25 degrees C in pure buffer or in the presence of either vesicles or micelles formed from various phosphatidylcholines (PCs). In the absence of PCs, more than 90% of the initially added H2O2 (1.0 mM) remained intact after incubation for 120 h. The effect of the PCs on the decomposition of H2O2 was studied by using different PCs that varied in terms of number of carbon atoms in the two acyl chains n as well as in terms of the degree of unsaturation. PCs with short hydrocarbon chains (n = 4, 6-8) were dissolved in the buffer solution in the form of nonassociated monomers or as micelles in equilibrium with monomers at a fixed PC concentration of 10 mM. The presence of these short-chain PCs slightly enhanced the H2O2 decomposition rate. Micelles formed by non-lipid detergents (sodium cholate, Triton X-100, and sodium dodecylsulfate) had a similar effect. In marked contrast, PCs with long hydrocarbon chains (n > or = 10) dispersed in buffer solution as vesicles (liposomes) significantly enhanced the rate of H2O2 decomposition, with the most effective PC being 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) at 25 degrees C. This indicates that the packing density of the PC molecules influences the reactivity, presumably through the direct interaction of the PC assemblies with H2O2 molecules. Furthermore, in the case of vesicles formed from PCs with unsaturated acyl chains (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC; 1,2-dioleoyl-sn-glycero-3-phosphocholine, DOPC), carbon-carbon double bond oxidation did not occur extensively under the conditions used. This indicates that the observed effect of PCs on the decomposition of H2O2 is indeed related to the assembly structure (vesicle vs micelles vs monomers) and is clearly not related to the presence of unsaturated hydrocarbon chains. Fluorescence polarization measurements of two fluorescent probes embedded either in the acyl chain region of the vesicles (DPH, 1,6-diphenyl-1,3,5-hexatriene) or on the surface of the vesicles (TMA-DPH, 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene iodide) show that the presence of H2O2 leads to a decrease in the fluidity of the lipid-water surface and not to a change in the fluidity of the hydrophobic region of the vesicle bilayer. This indicates that the decomposition of H2O2 is triggered through interactions between H2O2 and the polar head group area of PC vesicles.