Photoredox-Catalyzed Reduction of Halogenated Arenes in Water by Amphiphilic Polymeric Nanoparticles

The use of organic photoredox catalysts provides new ways to perform metal-free reactions controlled by light. While these reactions are usually performed in organic media, the application of these catalysts at ambient temperatures in aqueous media is of considerable interest. We here compare the activity of two established organic photoredox catalysts, one based on 10-phenylphenothiazine (PTH) and one based on an acridinium dye (ACR), in the light-activated dehalogenation of aromatic halides in pure water. Both PTH and ACR were covalently attached to amphiphilic polymers that are designed to form polymeric nanoparticles with hydrodynamic diameter DH ranging between 5 and 11 nm in aqueous solution. Due to the hydrophobic side groups that furnish the interior of these nanoparticles after hydrophobic collapse, water-insoluble reagents can gather within the nanoparticles at high local catalyst and substrate concentrations. We evaluated six different amphiphilic polymeric nanoparticles to assess the effect of polymer length, catalyst loading and nature of the catalyst (PTH or ACR) in the dechlorination of a range of aromatic chlorides. In addition, we investigate the selectivity of both catalysts for reducing different types of aryl-halogen bonds present in one molecule, as well as the activity of the catalysts for C-C cross-coupling reactions. We find that all polymer-based catalysts show high activity for the reduction of electron-poor aromatic compounds. For electron-rich compounds, the ACR-based catalyst is more effective than PTH. In the selective dehalogenation reactions, the order of bond stability is C-Cl > C-Br > C-I irrespective of the catalyst applied. All in all, both water-compatible systems show good activity in water, with ACR-based catalysts being slightly more efficient for more resilient substrates

Biorenewable circularity aids sustainability of plastics

Closed-loop recycling of plastics is a key technology for a sustainable future. Researchers have now created biorenewable plastics that outperform fossil-based analogues and meet criteria for circularity

Direct C-H trifluoromethylation of (hetero)arenes in water enabled by organic photoredox-active amphiphilic nanoparticles

Photoredox-catalyzed chemical conversions are predominantly operated in organic media to ensure good compatibility between substrates and catalysts. Yet, when conducted in aqueous media, they are an attractive, mild, and green way to introduce functional groups into organic molecules. We here show that trifluoromethyl groups can be readily installed into a broad range of organic compounds by using water as the reaction medium and light as the energy source. To bypass solubility obstacles, we developed robust water-soluble polymeric nanoparticles that accommodate reagents and photocatalysts within their hydrophobic interior under high local concentrations. By taking advantage of the high excited state reduction potential of N-phenylphenothiazine (PTH) through UV light illumination, the direct C−H trifluoromethylation of a wide array of small organic molecules is achieved selectively with high substrate conversion. Key to our approach is slowing down the production of CF 3 radicals during the chemical process by reducing the catalyst loading as well as the light intensity, thereby improving effectiveness and selectivity of this aqueous photocatalytic method. Furthermore, the catalyst system shows excellent recyclability and can be fueled by sunlight. The method we propose here is versatile, widely applicable, energy efficient, and attractive for late-stage introduction of trifluoromethyl groups into biologically active molecules

Compartmentalized Polymers for Catalysis in Aqueous Media

The field of polymer science has advanced to a point where precise control over a polymer's chain length, dispersity, and microstructure permits to access compartmentalized polymers that catalyze a range of reactions efficiently and selectively in aqueous media. We here summarize how we unveiled the relation between the primary structure of amphiphilic polymers and their folding/collapse processes into compartmentalized structures in water. In addition, we discuss how these insights allowed us to access active catalysts that function in water and complex cellular media. After obtaining profound knowledge, we achieved enzyme-like activity and selectivity in these synthetic catalytic systems and improved their stability in complex media. We envisage that polymer-based catalytic systems will become accessible that cooperate in concert with enzymes for multistep cascade catalysis in water or induce novel ways to activate drugs in diseased tissue.</p

Electronic Activity Tuning of Acyclic Guanidines for Lactide Polymerization

Novel aromatic guanidine-based organocatalysts for the ring-opening of l-lactide were synthesized and applied in comprehensive polymerization experiments and kinetic studies. The introduction of electronically active substituents led to a significant change in activity by 2 orders of magnitude. The formed polylactide is featured with narrow polydispersity and high end-group fidelity, both characteristics that are typical for living polymerizations. Besides that, using linear free-energy relationships and DFT calculations revealed new insights into the polymerization mechanism. The formation of an adduct consisting of the catalyst and initiator/chain end turned out to be the rate-limiting step

Closed-Loop Recyclable High-Performance Polyimine Aerogels Derived from Bio-Based Resources

Organic aerogels are an intriguing class of highly porous and ultralight materials which have found widespread applications in thermal insulation, energy storage, and chemical absorption. These fully cross-linked polymeric networks, however, pose environmental concerns as they are typically made from fossil-based feedstock and the recycling back to their original monomers is virtually impossible. In addition, organic aerogels suffer from low thermal stability and potential fire hazard. To overcome these obstacles and create next-generation organic aerogels, a set of polyimine aerogels containing reversible chemical bonds which can selectively be cleaved on demand is prepared. As precursors, different primary amines and cyclophosphazene derivatives made from bio-based reagents (vanillin and 4-hydroxybenzaldehyde) to elevate the thermal stability and reduce the environmental impact are used. The resulting polyimine aerogels exhibit low shrinkage, high porosity, large surface area, as well as pronounced thermal stability and flame resistance. More importantly, the aerogels show excellent recyclability under acidic conditions with high monomer recovery yields and purities. This approach allows for preparation of fresh aerogels from the retrieved building blocks, thus demonstrating efficient closed-loop recycling. These high-performance, recyclable, and bio-based polyimine aerogels pave the way for advanced and sustainable superinsulating materials

Enlightening Materials with Photoswitches

Incorporating molecular photoswitches into various materials provides unique opportunities for controlling their properties and functions with high spatiotemporal resolution using remote optical stimuli. The great and largely still untapped potential of these photoresponsive systems has not yet been fully exploited due to the fundamental challenges in harnessing geometrical and electronic changes on the molecular level to modulate macroscopic and bulk material properties. Herein, progress made during the past decade in the field of photoswitchable materials is highlighted. After pointing to some general design principles, materials with an increasing order of the integrated photoswitchable units are discussed, spanning the range from amorphous settings over surfaces/interfaces and supramolecular ensembles, to liquid crystalline and crystalline phases. Finally, some potential future directions are pointed out in the conclusion. In view of the exciting recent achievements in the field, the future emergence and further development of light-driven and optically programmable (inter)active materials and systems are eagerly anticipated. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Closed-loop Recycling of Poly(Imine-Carbonate) Derived from Plastic Waste and Bio-based Resources

Abstract: Closed-loop recycling of polymers represents the key technology to convert plastic waste in a sustainable fashion. Efficient chemical recycling and upcycling strategies are thus highly sought-after to establish a circular plastic economy. Here, we present the selective chemical depolymerization of polycarbonate by employing a vanillin derivative as bio-based feedstock. The resulting di-vanillin carbonate monomer was used in combination with various amines to construct a library of reprocessable poly(imine-carbonate)s, which show tailor-made thermal and mechanical properties. These novel poly(iminecarbonate) s exhibit excellent recyclability under acidic and energy-efficient conditions. This allows the recovery of monomers in high yields and purity for immediate reuse, even when mixed with various commodity plastics. This work provides exciting new insights in the design of bio-based circular polymers produced by upcycling of plastic waste with minimal environmental impact

Photoswitchable polymerization catalysis:state of the art, challenges, and perspectives

\u3cp\u3eAdjusting the length, composition, and microstructure of a polymer during the process of its formation in principle allows achieving the desired properties, thereby enabling custom-design of the thus generated polymer for its targeted function. Over the past years, different stimuli have been applied to manipulate responsive catalyst systems in situ; among them light takes center stage as perhaps the most promising stimulus. Here, we highlight recent progress in the area of photoswitchable polymerization catalysis. In particular, we focus on the challenge of combining photoswitchable and catalytically active units in a manner that both entities are somehow coupled and interact, yet also retaining their switching and catalysis functions under suitable conditions. We introduce the requirements for an ideal case of a photoswitchable polymerization catalyst system and use them to analyze the current state of the art. Based on our analysis of the status quo, we point to scientific challenges in the field and sketch perspectives including potential applications.\u3c/p\u3