Proof of Concept: Interface of Recyclable Organogels with Embedded Palladium Nanoparticles Catalyzing Suzuki–Miyaura Coupling in Water at Room Temperature

Abstract

A sustainable approach for C–C cross-coupling reaction at room temperature in water has been developed to avoid tedious Pd separation, reduce the carbon footprint, and save energy. Another important aspect is the catalyst recycling and easy product separation. α,γ-Hybrid peptides were designed to selectively use as a ligand for C–C cross-coupling catalysts as well as to form organogels. The peptides form antiparallel sheet-like structures in the solid state. The peptide containing m -aminobenzoic acid, glycine, and dimethylamine forms a whitish gel in toluene, and co-gelation with Pd(OAc) 2 results in light brown gel, which acts as a biphasic catalyst for Suzuki–Miyaura cross-coupling at room temperature in water by mild shaking. The organic–inorganic hybrid gel was characterized by rheology, field-emission scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray analyses. On completion of the cross-coupling reaction, the basic aqueous layer (containing products) above the gel can be simply decanted and the intact organic–inorganic hybrid gel can be recycled by topping-up fresh reactants multiple times. The reaction permitted a range of different substitution patterns for aryl and heterocyclic halides with acid or phenol functional groups. Both electron-donating- and electron-withdrawing-substituted substrates exhibited good results for this transformation. The findings inspire toward a holistic green technology for Suzuki–Miyaura coupling reaction and an innovative avenue for catalyst recycling and product isolation.

Synthesis of 2,5‐Diphenyl‐2H‐[1,2,3]triazole‐4‐carboxylic Acid Appended Phenylalanine for Thixotropic Metallogelation and Stiffness Manipulation

“…Thixotropy sweeps were performed at an angular frequency of 10 rad/s and consecutively with a 0.1 % and 50 % strain. For all experiments, gels were prepared in 0.2 mL volume in 5 mL Sterilin vials [30] …”

Mechanically Robust Hybrid Gel Beads Loaded with “Naked” Palladium Nanoparticles as Efficient, Reusable, and Sustainable Catalysts for the Suzuki–Miyaura Reaction

“…Inspired by this work, we developed an active LMWG, DBS-CONHNH 2 , not only capable of removing precious-metal cations from waste water down to ppb levels but also able to spontaneously reduce them in situ to their elemental form, storing them as NPs inside its network . When loaded with Pd(II), the resulting gel with embedded Pd(0)-NPs has been used for Suzuki–Miyaura, Heck, and Sonogashira cross-couplings with excellent yields, good functional group tolerability, and green reaction conditions. − Recently, Haldar and co-workers used a similar strategy to develop a self-assembled organogel in toluene, which accumulates PdNPs and catalyzes Suzuki–Miyaura cross-coupling reactions when brought into contact with an aqueous solution of reagents …”

“…50−52 Recently, Haldar and co-workers used a similar strategy to develop a self-assembled organogel in toluene, which accumulates PdNPs and catalyzes Suzuki−Miyaura cross-coupling reactions when brought into contact with an aqueous solution of reagents. 53 As for many LMWGs, however, DBS-CONHNH 2 suffers from low mechanical stability. A widely used method to improve the strength of gels is to form hybrid gels composed of two gelators�for example, using an LMWG to give function and a polymer gelator (PG) to provide robustness.…”

“… 50 − 52 Recently, Haldar and co-workers used a similar strategy to develop a self-assembled organogel in toluene, which accumulates PdNPs and catalyzes Suzuki–Miyaura cross-coupling reactions when brought into contact with an aqueous solution of reagents. 53 …”

A Triazole‐Based Covalent Gel Loaded with Cu/Pd Bimetallic Nanoparticles for Efficient Catalytic Cross‐Coupling Reactions

“…Gels possess hierarchical pore structure, providing micropores for anchoring the catalytic center and macropores for efficient mass transfer [38–40] . However, because of the instability of gels under harsh conditions, a few gel systems have been reported to catalyze cross‐coupling reactions and suffer from low catalytic efficiency [41,42] . Therefore, it is important to construct a stable gel‐based catalytic system that can tolerate harsh conditions and has high catalytic efficiency.…”