Iron’s abundance motivates its use in sustainable catalyst systems that also offer complementary reactivity manifolds compared to precious metals. However, the challenging reduction of benchmark iron ...

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Plastics pervade every aspect of modern life, yet effective mechanical recycling remains a major challenge. This is, in part, because of the mechanical forces that are involved in reprocessing, which break polymer chains and generate mechanoradicals, leading to a reduction in molecular weight and diminished material properties. This work introduces a robust strategy to capture and redirect these reactive intermediates, enabling value-preserving recycling pathways for widely used polymers polystyrene (PS) and poly(methyl methacrylate) (PMMA). By employing ball milling to induce chain scission, we demonstrate that mechanoradicals can be trapped by bis(butyl trithiocarbonate), yielding polymers with trithiocarbonate (TTC) end groups. Polymers degraded via ball milling showed significant reduction in molecular weight, ≈90% lower than the pristine polymers. These low molecular weight, TTC-functionalized polymers then served as macroinitiators for light-mediated controlled polymerization or, in the case of PMMA, as mediators for depolymerization under mild conditions. Chain extension of the degraded materials led to restored or increased molecular weight compared to the pristine polymers. Shear oscillatory rheology experiments revealed a recovery of entangled polymer properties, as evidenced by the reappearance of the rubbery plateau. We further showed that this “capture-and-repair” strategy is compatible with multiple cycles of degradation and chain extension, achieving repeated molecular weight recovery over three cycles. Additionally, we found that ball milling alone lowers the thermal depolymerization temperature of PMMA, enabling up to ≈44% depolymerization at 220 °C. Together, these findings highlight mechanoradical capture as a promising strategy to both enhance circularity and improve overall performance of mechanically recycled plastics.

The stereoselective functionalization of C–H bonds represents a central challenge in modern organic synthesis. Despite decades of innovation in C–H activation chemistry, methods for Z-selective functi...

The photoinduced accumulation of redox equivalents is a challenging requirement for artificial photosynthesis. Now a molecule has been developed in which the sequential absorption of photons results i...

Photoredox catalysis driven by visible light has improved chemical synthesis by enabling milder reaction conditions and unlocking distinct reaction mechanisms. Despite the transformative impact, visib...

The development of N,N-diaryl dihydrophenazine organic photoredox catalysts (PCs) has enabled numerous examples of organocatalyzed atom transfer radical polymerization (O-ATRP) of methyl methacrylate (MMA) monomer to polymers with low dispersity (Đ < 1.30) and near-unity initiator efficiency (I* ∼ 100%), as well as small molecule synthesis. In this work, we investigate the influence of core substitution (CS) by alkyl, aryl, and heteroatom groups on singlet excited state reduction potential (ES1°*). We observe that a highly reducing ES1°* is in part a result of a locally excited (LE)-dominated hybridized local and charge transfer (HLCT) excited state in CS PCs, which is influenced by the identity of the core substituent. Additionally, the PCs that possess a LE-dominated HLCT character maintain a relatively oxidizing PC radical cation oxidation potential (E1/2) for deactivation in O-ATRP compared to fully LE PCs reported in prior work. For example, a thiophenol core substituted (heteroatom CS, HetCS) PC shows the most negative ES1°* (−2.07 V vs SCE), more LE character (Stokes shift = 124 nm), and has an oxidizing PC radical cation (E1/2 = 0.30 V vs SCE). The CS PCs with improved properties, including more negative ES1°*, perform best in O-ATRP of MMA with the HetCS PC showing the best control in both DMAc (Đ = 1.08, I* = 89%) and EtOAc (Đ = 1.06, I* = 97%). Additionally, the HetCS PC was found to mediate the controlled polymerization of n-butyl acrylate (n-BA) (Đ = 1.24, I* = 97%), which has remained challenging in O-ATRP without supplemental deactivation strategies. An aryl CS PC was found to have moderate control as low as 1 ppm PC, indicating facilitation of low PC loadings (Đ = 1.33, I* = 69%). The relationship between excited state character, ES1°*, and polymerization control observed in this work provides a foundation for increasing the utility of phenazine PCs across photoredox catalysis.

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PdII-catalyzed C(sp3)−H arylation of saturated heterocycles with a wide range of aryl iodides is enabled by an N-heterocyclic carbene (NHC) ligand. A C−H insertion step by the PdII/NHC complex in the....

On February 7, the Trump administration moved to cut billions of dollars in funding from the National Institutes of Health (NIH) and National Science …

Due to their prevalence in pharmaceuticals and natural products, vicinally functionalized motifs are highly sought-after. Traditionally, these fragments are synthesized from alkene precursors via oxidation reactions. However, complementary syntheses via a C–C bond-forming approach are underexplored. Herein, we disclose a unified approach for accessing these motifs by acetal reagents made from affordable, prefunctionalized starting materials. We have demonstrated the wide applicability of this methodology to a variety of molecularly complex substrates. Additionally, the coupled products can be employed in one-pot cyclizations to synthesize a variety of lactones.

Many important synthetic-oriented works have proposed excited organic radicals as photoactive species, yet mechanistic studies raised doubts about whether they can truly function as photocatalysts. This skepticism originates from the formation of (photo)redox-active degradation products and the picosecond decay of electronically excited radicals, which is considered too short for diffusion-based photoinduced electron transfer reactions. From this perspective, we analyze important synthetic transformations where organic radicals have been proposed as photocatalysts, comparing their theoretical maximum excited state potentials with the potentials required for the observed photocatalytic reactivity. We summarize mechanistic studies of structurally similar photocatalysts indicating different reaction pathways for some catalytic systems, addressing cases where the proposed radical photocatalysts exceed their theoretical maximum reactivity. Additionally, we perform a kinetic analysis to explain the photoinduced electron transfer observed in excited radicals on subpicosecond time scales. We further rationalize the potential anti-Kasha reactivity from higher excited states with femtosecond lifetimes, highlighting how future photocatalysis advancements could unlock new photochemical pathways.

Selective semi-hydrogenation to generate alkenes from alkynes is an invaluable method to access olefins for materials, pharmaceuticals, and nat-ural products. Electrochemical transition-metal-catalyze...

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Photoredox catalysis is important in modern organic chemistry and the development of new synthetic methods. Mechanistic insights, particularly with photoredox chain reactions, are underdeveloped. This study combines quantum yield (QY) measurements, transient absorption spectroscopy (TAS), and electrochemical analysis to rigorously characterize the mechanism and rate constants of a ruthenium-catalyzed photoredox chain [4 + 2] cyclization between trans-anethole and isoprene. TAS and steady-state photochemical measurements (QY studies) reveal the role of oxygen in chain propagation as a secondary electron acceptor. The key kinetic competition between chain propagation and termination is identified by TAS and explored with kinetic modeling.

Herein, we introduce a new platform for alkene carboxy-alkylation. This reaction is designed around CO2•– addition to alkenes followed by radical polar crossover, which enables alkylation through carbanion attack on carbonyl electrophiles. We discovered that CO2•– adds to alkenes faster than it reduces carbonyl electrophiles and that this reactivity can be exploited by accessing CO2•– via hydrogen atom transfer from formate. This photocatalytic system transforms vinylarenes and carbonyl compounds into a diverse array of substituted γ-lactone products. Furthermore, indoles can be engaged through dearomative carboxy-alkylation, delivering medicinally relevant C(sp3)-rich heterocyclic scaffolds. Mechanistic studies reveal that the active photocatalyst is generated in situ through a photochemically induced reaction between the precatalyst and DMSO. Overall, we have developed a three-component alkene carboxy-alkylation reaction enabled by the use of formate as the CO2•– precursor.

The reduction of abundant benzene rings to scarce C(sp3)-rich motifs is invaluable for drug design, as C(sp3) content is known to correlate with clinical success. Cyclohexenes are attractive targets, ...