Volcano-type correlation between particle size and catalytic activity on hydrodechlorination catalyzed by AuPd nanoalloy.

Although changing the size of metal nanoparticles (NPs) is a reasonable way to tune and/or enhance their catalytic activity, size-selective preparation of NPs possessing random-alloy morphology has been challenging because of the differences in the ionization potential of each metal ion. This study demonstrates a time-controlled aggregation-stabilization method for the size-selective preparation of random alloy NPs composed of Au and Pd, which are stabilized by poly(N-vinyl-2-pyrrolidone) (PVP). By adjusting the mixing time in the presence of a small amount of PVP, aggregation was induced to produce AuPd:PVP with sizes ranging between 1.2 and 8.2 nm at approximately 1 nm intervals. Transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), and extended X-ray absorption fine structure (EXAFS) analyses indicated the formation of various sizes of AuPd nanoalloys, and size-dependent catalytic activity was observed when hydrodechlorination of 4-chloroanisole was performed using 2-propanol as a reducing agent. AuPd:PVP with a size of 3.1 nm exhibited the highest catalytic activity. A comparison of the absorption edges of X-ray absorption near edge structure (XANES) spectra suggested that the electronic state of the Au and Pd species correlated with their catalytic activity, presumably affecting the rate-determining step.

Comparative bindings of lactones, lactide, and cyclic carbonates: experimental insights into the coordination step of polymerization.

Comparative bindings of several renowned monomers were investigated experimentally using B(C6F5)3 as a Lewis acid model for the coordination step in ring-opening polymerization. A complete series of the X-ray crystal structures of the B(C6F5)3 adducts with the monomers was reported. The X-ray structural studies and spectroscopic data revealed a coordination strength in the order lactones > tetrahydrofuran > cyclic carbonates > lactide.

Polymerization of ε-Caprolactone Using Bis(phenoxy)-amine Aluminum Complex: Deactivation by Lactide.

Polymerizations of biodegradable lactide and lactones have been the subjects of intense research during the past decade. They can be polymerized/copolymerized effectively by several catalyst systems. With bis(phenolate)-amine aluminum complex, we have shown for the first time that lactide monomer can deactivate the aluminum complex during the ongoing polymerization of ε-caprolactone to a complete stop. After hours of dormant state, the aluminum complex can be reactivated again by heating at 100 °C without the addition of any external chemicals still giving polymer with narrow dispersity. Studies using NMR, in situ FTIR, and single-crystal X-ray crystallography indicated that the coordination of the carbonyl group in lactyl unit was responsible for the unusual behavior of lactide. In addition, the unusual methyl-migration from methyl lactate ligand to the amine side chain of the aluminum complex was observed through intermolecular nucleophilic-attack mechanism.

The Impact of the Polymer Chain Length on the Catalytic Activity of Poly(N-vinyl-2-pyrrolidone)-supported Gold Nanoclusters.

Poly(N-vinyl-2-pyrrolidone) (PVP) of varying molecular weight (M w = 40-360 kDa) were employed to stabilize gold nanoclusters of varying size. The resulting Au:PVP clusters were subsequently used as catalysts for a kinetic study on the sized-dependent aerobic oxidation of 1-indanol, which was monitored by time-resolved in situ infrared spectroscopy. The obtained results suggest that the catalytic behaviour is intimately correlated to the size of the clusters, which in turn depends on the molecular weight of the PVPs. The highest catalytic activity was observed for clusters with a core size of ~7 nm, and the size of the cluster should increase with the molecular weight of the polymer in order to maintain optimal catalytic activity. Studies on the electronic and colloid structure of these clusters revealed that the negative charge density on the cluster surface also strongly depends on the molecular weight of the stabilizing polymers.

Fe, Ru, and Os complexes with the same molecular framework: comparison of structures, properties and catalytic activities.

A series of group 8 metal complexes with the same molecular framework, [M(PY5Me2)L]n+ (M = Fe, Ru, and Os; PY5Me2 = 2,6-bis[1,1-bis(2-pyridyl)ethyl]pyridine; L = monodentate ligand), were successfully synthesized and structurally characterized. The spectroscopic and electrochemical properties as well as the catalytic activity for water oxidation of these complexes were investigated.

Emission amplification by sumanene nanocrystals in an onigiri-type organic-organic assembly.

Core-shell assemblies of nanocrystals of sumanene (shell) and sumanenetrione (core) resembling onigiri (filled Japanese rice balls) were fabricated by stepwise reprecipitation. Optical properties of the onigiri-type assemblies showed that emissions from the core sumanenetrione nanocrystals were amplified through energy transfer from the shell sumanene nanocrystals through the nanocrystalline interface.

Bis[2,6-bis-(2-meth-oxy-phen-yl)pyridinium] di-µ-bromido-bis-[dibromidocuprate(II)].

The title salt, (C(19)H(18)NO(2))(2)[Cu(2)Br(6)], was obtained from an attempt to synthesize the copper(II) complex of 2,6-bis-(2-meth-oxy-phen-yl)pyridine (L) from a reaction between CuBr(2) and one equivalent of L in CH(2)Cl(2) at room temperature. The resulting compound is the salt of the 2,6-bis-(2-meth-oxy-phen-yl)pyridinium cation and 0.5 equivalents of a hexa-bromido-dicuprate(II) dianion. Both meth-oxy groups of the cationic pyridinium moiety are directed towards the N atom of the pyridine ring as a result of intra-molecular N-H⋯O hydrogen bonds. The centrosymmetric hexabromidodicuprate dianion possesses a distorted tetra-hedral geometry at the copper ion. The Cu-Br bond lengths are 2.3385 (7) and 2.3304 (7) Šfor the terminal bromides, whereas the bond length between the Cu atom and two bridging bromides is slightly longer [2.4451 (6) Å].