A two-dimensional amide-linked covalent organic framework anchored Pd catalyst for Suzuki-Miyaura coupling reaction in the aqueous phase at room temperature

Microwave-Assisted One-Step Synthesis of Palladium-Encapsulated Covalent Organic Frameworks for Heterogeneous Catalysis

Metal-encapsulated covalent organic frameworks (metal/COFs) represent an emerging paradigm in heterogeneous catalysis. However, the time-intensive (usually 4 or more days) and tedious multi-step synthesis of metal/COFs remains a significant stumbling block for their broad application. To address this challenge, we introduce a facile microwave-assisted in situ metal encapsulation strategy to cooperatively combine COF formation and in situ palladium(II) encapsulation in one step. With this unprecedented approach, we synthesize a diverse range of palladium(II)-encapsulated COFs (termed Mw-Pd/COF) in the air within just an hour. Notably, this strategy is scalable for large-scale production (~0.5 g). Leveraging the high crystallinity, porosity, and structural stability, one representative Mw-Pd/COF exhibits remarkable activity, functional group tolerance, and recyclability for the Suzuki-Miyaura coupling reaction at room temperature, surpassing most previously reported Pd(II)/COF catalysts with respect to catalytic performance, preparation time, and synthetic ease. This microwave-assisted in situ metal encapsulation strategy opens a facile and rapid avenue to construct metal/COF hybrids, which hold enormous potential in a multitude of applications including heterogeneous catalysis, sensing, and energy storage.

Root-inspired grafting of wood surfaces with hyperbranched polymers for enhanced interfacial adhesion with impregnated decorative paper

A root-like waterborne hyperbranched polymer, synthesized from diethylenetriamine (DETA) and methyl acrylate (MA) monomers, was inspired by the effect of solidifying soil with tree roots. This polymer was then blended with aqueous isocyanate SK615, known as MD-HBP-NH2, to serve as a surface modifier for blockboards. The blockboards were treated with a modifier to enhance the interfacial adhesion with melamine-formaldehyde (MF) resin-impregnated decorative paper, thereby preventing surface cracks. The polycondensation reaction temperatures of the modifiers were compared. These results indicated that a hyperbranched root-structured polymer emulsion was formed through Michael addition reactions. Following this modification, the blockboards demonstrated enhanced planeness and dimensional stability. Furthermore, the isocyanate groups reacted with the exposed hydroxyl groups, and the amino groups reacted with the aldehyde groups in the MF resin, thereby enhancing the interfacial bonding strength between the wood and the impregnated decorative paper. At a polycondensation temperature of 155 °C, optimal overall performance was attained, with the ability to penetrate the wood surface to a depth of 1.28 mm, and exhibited superior surface crack resistance. Moreover, this waterborne hyperbranched polymer modifier is eco-friendly, green, and non-toxic, with lower levels of volatile organic compounds. This presents a promising avenue for the development of eco-friendly modifiers to prevent surface cracking in wood-based panels with impregnated decorative paper.

Green and Facile Preparation of Covalent Organic Frameworks Based on Reaction Medium for Advanced Applications

Covalent organic frameworks (COFs), as a new class of crystalline, well-ordered, and porous materials with intermittent constructions, are formed via organic structural parts connected through covalent bonds. These materials have been employed in several fields comprising pollutant adsorption and separation, catalysis, electrical conductivity, gas storage, etc. The preparation of COFs is mainly applied in tubes with high temperatures and degassing treatment. Furthermore, the reaction medium is involved in toxic organic solvents like toluene, dioxane, mesitylene, acetonitrile, and so on. Hence, discovering clean medium and green approaches has attracted wide attention. Recently, facile, less dangerous, and greener methods have been developed for COFs synthesis in diverse applications like performing the reaction at ambient temperature or employing aqueous solvents, ionic liquids, and a mixture of organic solvents/water. This review article summarizes the eco-friendly production approaches of COFs for diverse applications.

Palladium nanoparticles-confined pore-engineered urethane-linked thiol-functionalized covalent organic frameworks: a high-performance catalyst for the Suzuki Miyaura cross-coupling reaction

Covalent organic frameworks (COFs) are potential templates for the synthesis of nanomaterials owing to the versatility of their structure. Most of the reported COFs comprise imine linkages. Herein, we report for the first time the synthesis of a urethane-linked COF (UCOF) using monoformylphloroglucinol and 1,4-phenylene diisocyanate as monomers. Furthermore, the UCOF was functionalized with cysteamine to introduce free dangling thiol groups into the cavity. The latter played a critical role in fixing the active metal efficiently and facilitating the confined growth of small metal nanoparticles (∼4-6 nm) with a high surface area leading to a pore-engineered heterogeneous Pd catalyst (PdNPs@UCOF-SH). The COF and Pd catalyst were characterized using various analytical techniques such as CP-MAS NMR, FTIR, PXRD, BET, FEG-SEM, HRTEM, XPS, TGA, and ICP-AES. The as-prepared UCOF-SH-supported Pd nanoparticles showed excellent catalytic activity in the Suzuki Miyaura cross-coupling reaction under mild conditions with low catalyst loading and eco-friendly solvents. The scope was extended to various aryl boronic acids and aryl halides (I, Br, and Cl). The halo-substituted and non-halo biaryl derivatives were obtained in good to excellent yields, within a shorter reaction time, avoiding the homocoupling of aryl boronic acid. The pore-engineered COF-derived catalyst is selective and easily recycled up to 10 runs without significant loss of catalytic activity. This reveals the robust nature of the PdNPs@UCOF-SH catalyst and the sustainability of the process which opens a new frontier for several catalytic applications.

Preparation and Tribological Properties of Bismaleimide Matrix Composites Reinforced with Covalent Organic Framework Coated Graphene Nanosheets

The poor compatibility between the polymer matrix and complex modification processes greatly affects the excellent tribological properties of graphene in the polymer matrix. In this study, a covalent organic framework (COF)-coated graphene hybrid lubricating filler (G/COFs) was synthesized in situ using a sample one-step mechanochemical synthesis process. This was used to improve the tribological properties of bismaleimide (BMI) resin. The morphology and microstructure of the G/COFs hybrid were characterized, and the effect of the added amount on the tribological properties of the G/COFs/BMI composites was studied. The results showed that the G/COFs hybrid could improve the stability of the friction coefficient and decrease the volume wear rate of BMI composites. Compared to the neat BMI, the 0.6 wt% G/COFs/BMI composites showed optimal tribological performance, with the friction coefficient and volume wear rate decreasing from 0.35 to 0.14 and from 48 × 10^-6 to 10.6 × 10^-6 mm³/(N‧m), respectively. In addition, the G/COFs/BMI composites showed lower friction coefficient fluctuations and volume wear rates than G/BMI composites. This is mainly attributed to the fact that the deposition of COFs can not only effectively prevent the aggregation of graphene nanosheets, but can also significantly improve the compatibility and interfacial bond between the graphene and BMI matrix. Moreover, the good synergistic effect between the lamellar COFs and graphene nanosheets can generate high-quality self-lubricating transfer films during the friction process. The excellent dispersibility, efficient chemical functionalization, better friction reduction and wear-resistance properties, and facile preparation method make graphene/COFs hybrid nanoparticles promising as an excellent lubricating filler.

Cellulose derived Pd nano-catalyst for efficient catalysis

Using green, environmentally friendly and resource-rich cellulose as a raw material, a ligand-free and highly dispersed palladium (Pd) nano-catalyst was successfully prepared in a facile way. A variety of characterization results showed that the Pd nanoparticles (NPs) were uniformly spread on the cellulose nanoporous microspheres, with an average particle size of ∼2.75 nm. As a carrier, cellulose microspheres with nanoporous structure and rich -OH groups greatly promoted the attachment and distribution of the highly dispersed Pd NPs, along with the diffusion and exchange of reactants, so as to greatly promote the catalytic activity. In the Suzuki-Miyaura coupling reaction, the catalyst of C-Pd exhibited excellent catalytic activity (TOF up to 2126 h-1), broad applicability, and good recyclability with almost no active loss in 6 continuous runs. This utilizing of bioresources to build catalyst materials is important for sustainable chemistry.

Organocatalytic synthesis of (Het)biaryl scaffolds via photoinduced intra/intermolecular C(sp2)-H arylation by 2-pyridone derivatives

A unique N,O-bidentate ligand 6-oxo-1,6-dihydro-pyridone-2-carboxylic acid dimethylamide (L1) catalyzed direct C(sp²)-H (intra/intermolecular) arylation of unactivated arenes has been developed to expedite access to (Het)biaryl scaffolds under UV-irradiation at room temperature. The protocol tolerated diverse functional groups and substitution patterns, affording the target products in moderate to excellent yields. Mechanistic investigations were also carried out to better understand the reaction pathway. Furthermore, the synthetic applicability of this unified approach has been showcased via the construction of biologically relevant 4-quinolone, tricyclic lactam and sultam derivatives.

A novel 2D mesoporous phosphazene-anthraquinone-based covalent organic polymer: synthesis, characterization and supercapacitor applications

A novel phosphazene anthraquinone-based covalent organic polymer (HD-1) was successfully designed and synthesized through a simple polymerization reaction. The as-prepared material was used as an electrode active material for a supercapacitor.