Conjugated microporous poly(phenylene butadiynylene)s

High surface area porous poly(phenylene butadiynylene) networks were obtained (BET surface area up to 842 m(2) g(-1)) by the palladium-catalyzed homocoupling of 1,3,5-triethynylbenzene and 1,4-diethynylbenzene.     

Tetrabutylammonium Halides as Selectively Bifunctional Catalysts Enabling the Syntheses of Recyclable High Molecular Weight Salicylic Acid-Based Copolyesters

To synthesize high molecular weight poly(phenolic ester) via a living ring-opening polymerization (ROP) of cyclic phenolic ester monomers remains a critical challenge due to serious transesterification and back-biting reactions. Both phenolic ester bonds in monomer and polymer chains are highly active, and it is difficult so far to distinguish them. In this work, an unprecedented selectively bifunctional catalytic system of tetra-n-butylammonium chloride (TBACl) was discovered to mediate the syntheses of high molecular weight salicylic acid-based copolyesters via a living ROP of salicylate cyclic esters (for poly(salicylic methyl glycolide) (PSMG), M_n=361.8 kg/mol, Ð<1.30). Compared to previous catalysis systems, the side reactions were suppressed remarkably in this catalysis system because phenolic ester bond in monomer can be selectively cleaved over that in polymer chains during ROP progress. Mechanistic studies reveal that the halide anion and alkyl-quaternaryammonium cation work synergistically, where the alkyl-quaternaryammonium cation moiety interacts with the carbonyl group of substrates via non-classical hydrogen bonding. Moreover, these salicylic acid-based copolyesters can be recycled to dimeric monomer under solution condition, and can be recycled to original monomeric monomers without catalyst under sublimation condition.     

Photosynthesis of Benzonitriles on BiOBr Nanosheets Promoted by Vacancy Associates

Photocatalytic organic functionalization reactions represent a green, cost-effective, and sustainable synthesis route for value-added chemicals. However, heterogeneous photocatalysis is inefficient in directly activating ammonia molecules for the production of high-value-added nitrogenous organic products when compared with oxygen activation in the formation of related oxygenated compounds. In this study, we report the heterogeneous photosynthesis of benzonitriles by the ammoxidation of benzyl alcohols (99 % conversion, 93 % selectivity) promoted using BiOBr nanosheets with surface vacancy associates. In contrast, the main reaction of catalysts with other types of vacancy sites is the oxidation of benzyl alcohol to benzaldehyde or benzoic acid. Experimental measurements and theoretical calculations have demonstrated a specificity of vacancy type with respect to product selectivity, which arises from the adsorption and activation of NH₃ and O₂ that is required to promote subsequent C−N coupling and oxidation to nitrile. This study provides a better understanding of the role of vacancies as catalytic sites in heterogeneous photocatalysis.     

Properties of alkali metal atoms deposited on a MgO surface: a systematic experimental and theoretical study

The adsorption of small amounts of alkali metal atoms (Li, Na, K, Rb, and Cs) on the surface of MgO powders and thin films has been studied by means of EPR spectroscopy and DFT calculations. From a comparison of the measured and computed g values and hyperfine coupling constants (hfccs), a tentative assignment of the preferred adsorption sites is proposed. All atoms bind preferentially to surface oxide anions, but the location of these anions differs as a function of the deposition temperature and alkali metal. Lithium forms relatively strong bonds with MgO and can be stabilized at low temperatures on terrace sites. Potassium interacts very weakly with MgO and is stabilized only at specific sites, such as at reverse corners where it can interact simultaneously with three surface oxygen atoms (rubidium and cesium presumably behave in the same way). Sodium forms bonds of intermediate strength and could, in principle, populate more than a single site when deposited at room temperature. In all cases, large deviations of the hfccs from the gas-phase values are observed. These reductions in the hfccs are due to polarization effects and are not connected to ionization of the alkali metal, which would lead to the formation of an adsorbed cation and a trapped electron. In this respect, hydrogen atoms behave completely differently. Under similar conditions, they form (H(+))(e(-)) pairs. The reasons for this different behavior are discussed.     

Porous carbon and carbon/metal oxide microfibers with well-controlled pore structure and interface

A "brick-and-mortar" assembly approach for creating porous carbon and carbon/metal oxide fibers on the micron scale with well-defined pore structure and interface is presented. A series of monodisperse silica@polyacrylonitrile (PAN) and silica@metal oxide@PAN core/shell particles were synthesized by emulsion polymerization and assembled into organic-inorganic composite fibers through a simple ice-templating strategy with the assistance of polyvinyl alcohol. Porous carbon and carbon/metal oxide fibers with well-controlled pores and interfaces were created by oxidative stabilization and carbonization of composite fibers followed by removal of silica cores with hydrofluoric acid or concentrated alkali. The pore structure and the carbon/metal oxide interfaces of the fibers impart to the fibers' lightweight and potential applications in catalysis, electrochemical energy, and gas or liquid separations and storage.     

Lewis acid stabilized methylidene and oxoscandium complexes

The methylidene scandium complex (PNP)Sc(mu3-CH2)(mu2-CH3)2[Al(CH3)2]2 (PNP = N[2-P(CHMe2)2-4-methylphenyl]2-) can be prepared from the reaction of (PNP)Sc(CH3)2 and 2 equiv of Al(CH3)3. The Lewis acid stabilized methylidenes candium complex has been crystallographically characterized, and its bonding scheme analyzed by DFT. In addition, we report preliminary reactivity studies of the Sc-CH2 ligand with substrates such as H2NAr and OCPh2. While the former results in an Br?nsted acid-base reaction, the latter reagent produces the olefin H2C CPh2 along with the novel oxoscandium complex (PNP)Sc(mu3-O)(mu2-CH3)2[Al(CH3)2]2, quantitatively.     

A dinuclear Ni(I) system having a diradical Ni2N2 diamond core resting state: synthetic, structural, spectroscopic elucidation, and reductive bond splitting reactions

One-electron reduction of the square-planar nickel precursor (PNP)NiCl ( 1) (PNP (-) = N[2-P(CHMe 2) 2-4-methylphenyl] 2) with KC 8 effects ligand reorganization of the pincer ligand to assemble a Ni(I) dimer, [Ni(mu 2-PNP)] 2 ( 2), containing a Ni 2N 2 core structure, as inferred by its solid-state X-ray structure. Solution magnetization measurements are consistent with a paramagnetic Ni(I) system likely undergoing a monomer <--> dimer equilibrium. The room-temperature and 4 K solid-state X-band electron paramagnetic resonance (EPR) spectra display anisotropic signals. Low-temperature solid-state X-band EPR data at 4 K reveal rhombic values g z = 1.980(4), g x = 2. 380(4), and g y = 2.225(4), as well as a forbidden signal at g = 4.24 for the Delta M S = 2 half field transition, in accord with 2 having two weakly interacting metal centers. Utilizing an S = 1 model, full spin Hamiltonian simulation of the low-temperature EPR spectrum on the solid sample was achieved by applying a nonzero zero-field-splitting parameter ( D = 0.001 cm (-1)), which is consistent with an S = 0 ground state with a very closely lying S = 1 state. Solid-state magnetization data also corroborate well with our solid-state EPR data and reveal weak antiferromagnetic behavior ( J = -1.52(5) cm (-1)) over a 2-300 K temperature range at a field of 1 Tesla. Evidence for 2 being a masked "(PNP)Ni" scaffold originates from its reaction with N 2CPh 2, which traps the Ni(I) monomer in the form of a T-shaped species, Ni(PNPNNCPh 2), a system that has been structurally characterized. The radical nature of complex 2, or its monomer component, is well manifested through the plethora of cooperative H-X-type bond cleavage reactions, providing the nickel(II) hydride (PNP)NiH and the corresponding rare functionalities -OH, -OCH 3, -PHPh, and -B(catechol) integrated into the (PNP)Ni moiety in equal molar amounts. In addition to splitting H 2, compound 2 can also engage in homolytic X-X bond cleavage reactions of PhXXPh to form (PNP)Ni(XPh) (X = S or Se).     

Promoted colorimetric response of spirooxazine derivative: a simple assay for sensitive mercury(II) detection

Research on Chemical Intermediates - A spirooxazine derivative 1,3-dihydro-1,3,3-trimethyl-spiro[2-H-indole-2-2′-[2H-1,4] oxazino [2,3-f] [1, 10] phenanthroline] (compound 1) was explored as...