Search

The synthesis of branched gold nanoparticles (AuNPs) with shape- and size-specific optical properties requires effective control of the particle formation mechanism using appropriate reducing agents and protective agents that prevent particle aggregation in solution. In this context, the heterogeneous synthesis of AuNPs using solid surfaces of graphene oxides and metal–organic frameworks has attracted much attention. These materials are characterized by their ability to immobilize and stabilize the particles grown on the surface without the need for additional protective agents. However, the shape- and size-selective synthesis of AuNPs using solid surfaces remains challenging. Herein, we report the shape-selective one-step synthesis of monodisperse branched AuNPs using a metal–macrocycle framework (MMF), a porous molecular crystal of Pd II3 -tris(phenylenediamine) macrocycle. Konpeito-Shaped branched AuNPs with uniform size were obtained on the surface of MMF by mixing HAuCl4·4H2O, L -ascorbic acid and MMF microcrystals. Spectroscopic and microscopic observations confirmed that MMF promoted the reduction of gold by its reductive activity as well as acted as a solid support to electrostatically immobilize the pseudo-seed particles for further growth on the crystal surface. In addition, the MMF also served as a substrate for in situ high-speed AFM imaging due to the effective immobilization of AuNPs on the surface, allowing direct visualization of the particle growth. Since the chemical structural features of MMF allow the growth of branched AuNPs via pseudo-seeding, this approach would provide new synthetic methods for obtaining a variety of gold nanostructures. [ABSTRACT FROM AUTHOR]

Porous crystals with well‐defined active metal centers on the pore surface have high potential as heterogeneous metal catalysts. We have recently demonstrated that a porous molecular crystal, metal‐macrocycle framework (MMF), catalyzes olefin migration reactions by photoactivation of its PdIICl2 moieties exposed on the crystalline channel surface. Herein we report a mechanistic study of the photoinduced olefin migration reactions at the PdII active centers of MMF. Several experiments, including a deuterium scrambling study, revealed that olefin migration is catalyzed via an alkyl mechanism by in situ generated Pd−H species on the channel surface during photoirradiation. This proposed mechanism was further supported by DFT and ONIOM calculations. [ABSTRACT FROM AUTHOR]

Keywords: mechanism; metallacycles; olefin migration; palladium; photoactivation EN mechanism metallacycles olefin migration palladium photoactivation 174 174 1 02/03/21 20210201 NES 210201 B One-dimensional crystalline channels b with well-defined active metal centers hold great potential as heterogeneous catalysts. Experimental and theoretical studies revealed that the olefin migration was catalyzed via an alkyl mechanism by in situ generated Pd-H species on the channel ceiling through photoirradiation. Mechanism, metallacycles, olefin migration, palladium, photoactivation. [Extracted from the article]

Metal-organic cages and capsules exhibit space-specific functions based on their discrete hollow structures. To acquire enzyme-like asymmetric or intricate structures, they have been modified by desymmetrization with two or more different ligands. There is a need to establish new strategies that can desymmetrize structures in a simple way using only one type of ligand, which is different from the mixed-ligand approach. In this study, a strategy was developed to form interconvertible stereoisomers using the unsymmetric macrocyclic ligand benzimidazole[3]arene. Single-crystal X-ray diffraction analysis revealed that the isomers assembled with silver tetrafluoroborate afforded a conformationally heteroleptic Ag 6 L 4 capsule with an intricate structure. The six Ag ions in the capsule were desymmetrized, resulting in significantly different coordination geometries. Remarkably, the capsule encapsulates a single tetrafluoroborate anion via multipoint C-H···F-B hydrogen bonds in both the solid and solution states, suggesting that anions of appropriate size and shape can act as a template for the capsule formation. These results demonstrate that the use of isomerizable and unsymmetric ligands is the effectiveness of constructing highly dissymmetric supramolecular structures from a single ligand.

A nanosized confined space with well-defined functional surfaces has great potential to control the efficiency and selectivity of catalytic reactions. Herein we report that a 1,6-diene, which normally forms an intramolecular [2+2] cycloadduct under photoirradiation, preferentially undergoes a photoinduced olefin migration in a porous crystal, metal-macrocycle framework (MMF), and alternatively [2+2] cycloaddition is completely inhibited in the confined space. A plausible reaction mechanism for olefin migration triggered by the photoinduced dissociation of the Pd-Cl bond is suggested based on UV-vis diffuse reflectance spectroscopy, single-crystal XRD, and MS-CASPT2 calculation. The substrate scope of the photoinduced olefin migration in MMF was also examined using substituted allylbenzene derivatives.

A new series of calix[ n ]arene analogues, benzimidazole[3]arenes, was rationally synthesized by Cu II -catalyzed post-macrocyclization transformation of a tris( o -phenylenediamine) macrocycle, and fully characterized by NMR, MS, and single-crystal X-ray diffraction (XRD) analyses. The resulting syn - and anti -benzimidazole[3]arenes have a bowl-shaped and a warped structure, respectively, in their crystalline states, and both display a dynamic inversion behavior in solution. This modification resulted in strong fluorescence due to the generated benzimidazole moieties. The mechanistic study of the post-macrocyclization transformation demonstrated that the formation of both benzimidazole[3]arenes was catalyzed, via triimine intermediates, by Cu II ions in air through oxidation and cyclization of the tris( o -phenylenediamine) macrocycle.