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1. Two-compartment kinetic Monte Carlo modelling of electrochemically mediated ATRP

   https://doi.org/10.1039/C8RE00156A  

   D'hooge, Dagmar R.; Fantin, Marco; Magenau, Andrew J.; Konkolewicz, Dominik; Matyjaszewski, Krzysztof (November 2018, Reaction Chemistry & Engineering)

   For electrochemically mediated atom transfer radical polymerization (eATRP), novel mechanistic insights are formulated based on a two-compartment kinetic Monte Carlo model in which catalyst concentration gradients between a large “bulk” compartment away from the electrode and a very small compartment around the electrode are accounted for to reflect the concept of the Nernst diffusion layer. The mass transport of deactivator catalyst to the electrode and its electrochemical reduction at the electrode are treated separately to enable the model to explicitly distinguish between limitations of mass transport and limitations due to intrinsic chemical reactivity. The model is applied to eATRP of methyl acrylate at 298 K with Cu II Br 2 /Me 6 TREN (Me 6 TREN: tris((2-dimethylamino)ethyl)amine) and eATRP of n -butyl acrylate at 317 K with Cu II Br 2 /TPMA (TPMA: tris(2-pyridylmethyl)amine). Diffusional limitations on termination need to be accounted for to properly reflect the eATRP kinetics and the microstructural properties of the obtained polymers. In most cases, an eATRP with mixed chemical and mass transport control is obtained. 

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2. Redox-switchable atom transfer radical polymerization

   https://doi.org/10.1039/c8cc09209e  

   Dadashi-Silab, Sajjad; Lorandi, Francesca; Fantin, Marco; Matyjaszewski, Krzysztof (January 2019, Chemical Communications)

   Temporal control in atom transfer radical polymerization (ATRP) relies on modulating the oxidation state of a copper catalyst, as polymer chains are activated by L/Cu I and deactivated by L/Cu II . (Re)generation of L/Cu I activator has been achieved by applying a multitude of external stimuli. However, switching the Cu catalyst off by oxidizing to L/Cu II through external chemical stimuli has not yet been investigated. A redox switchable ATRP was developed in which an oxidizing agent was used to oxidize L/Cu I activator to L/Cu II , thus halting the polymerization. A ferrocenium salt or oxygen were used to switch off the Cu catalyst, whereas ascorbic acid was used to switch the catalyst on by (re)generating L/Cu I . The redox switches efficiently modulated the oxidation state of the catalyst without sacrificing control over polymerization. 

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3. Open-air green-light-driven ATRP enabled by dual photoredox/copper catalysis

   https://doi.org/10.1039/D2SC04210J  

   Szczepaniak, Grzegorz; Jeong, Jaepil; Kapil, Kriti; Dadashi-Silab, Sajjad; Yerneni, Saigopalakrishna S.; Ratajczyk, Paulina; Lathwal, Sushil; Schild, Dirk J.; Das, Subha R.; Matyjaszewski, Krzysztof (October 2022, Chemical Science)

   Photoinduced atom transfer radical polymerization (photo-ATRP) has risen to the forefront of modern polymer chemistry as a powerful tool giving access to well-defined materials with complex architecture. However, most photo-ATRP systems can only generate radicals under biocidal UV light and are oxygen-sensitive, hindering their practical use in the synthesis of polymer biohybrids. Herein, inspired by the photoinduced electron transfer-reversible addition–fragmentation chain transfer (PET-RAFT) polymerization, we demonstrate a dual photoredox/copper catalysis that allows open-air ATRP under green light irradiation. Eosin Y was used as an organic photoredox catalyst (PC) in combination with a copper complex (X–Cu II /L). The role of PC was to trigger and drive the polymerization, while X–Cu II /L acted as a deactivator, providing a well-controlled polymerization. The excited PC was oxidatively quenched by X–Cu II /L, generating Cu I /L activator and PC˙ + . The ATRP ligand (L) used in excess then reduced the PC˙ + , closing the photocatalytic cycle. The continuous reduction of X–Cu II /L back to Cu I /L by excited PC provided high oxygen tolerance. As a result, a well-controlled and rapid ATRP could proceed even in an open vessel despite continuous oxygen diffusion. This method allowed the synthesis of polymers with narrow molecular weight distributions and controlled molecular weights using Cu catalyst and PC at ppm levels in both aqueous and organic media. A detailed comparison of photo-ATRP with PET-RAFT polymerization revealed the superiority of dual photoredox/copper catalysis under biologically relevant conditions. The kinetic studies and fluorescence measurements indicated that in the absence of the X–Cu II /L complex, green light irradiation caused faster photobleaching of eosin Y, leading to inhibition of PET-RAFT polymerization. Importantly, PET-RAFT polymerizations showed significantly higher dispersity values (1.14 ≤ Đ ≤ 4.01) in contrast to photo-ATRP (1.15 ≤ Đ ≤ 1.22) under identical conditions. 

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4. Encapsulation of tricopper cluster in a synthetic cryptand enables facile redox processes from Cu ^I Cu ^I Cu ^I to Cu ^II Cu ^II Cu ^II states

   https://doi.org/10.1039/D0SC05441K  

   Zhang, Weiyao; Moore, Curtis E.; Zhang, Shiyu (March 2021, Chemical Science)

   null (Ed.)

   One-pot reaction of tris(2-aminoethyl)amine (TREN), [Cu I (MeCN) 4 ]PF 6 , and paraformaldehyde affords a mixed-valent [ TREN4 Cu II Cu I Cu I (μ 3 -OH)](PF 6 ) 3 complex. The macrocyclic azacryptand TREN4 contains four TREN motifs, three of which provide a bowl-shape binding pocket for the [Cu 3 (μ 3 -OH)] 3+ core. The fourth TREN caps on top of the tricopper cluster to form a cryptand, imposing conformational constraints and preventing solvent interaction. Contrasting the limited redox capability of synthetic tricopper complexes reported so far, [ TREN4 Cu II Cu I Cu I (μ 3 -OH)](PF 6 ) 3 exhibits several reversible single-electron redox events. The distinct electrochemical behaviors of [ TREN4 Cu II Cu I Cu I (μ 3 -OH)](PF 6 ) 3 and its solvent-exposed analog [ TREN3 Cu II Cu II Cu II (μ 3 -O)](PF 6 ) 4 suggest that isolation of tricopper core in a cryptand enables facile electron transfer, allowing potential application of synthetic tricopper complexes as redox catalysts. Indeed, the fully reduced [ TREN4 Cu I Cu I Cu I (μ 3 -OH)](PF 6 ) 2 can reduce O 2 under acidic conditions. The geometric constraints provided by the cryptand are reminiscent of Nature's multicopper oxidases (MCOs). For the first time, a synthetic tricopper cluster was isolated and fully characterized at Cu I Cu I Cu I ( 4a ), Cu II Cu I Cu I ( 4b ), and Cu II Cu II Cu I ( 4c ) states, providing structural and spectroscopic models for many intermediates in MCOs. Fast electron transfer rates (10 5 to 10 6 M −1 s −1 ) were observed for both Cu I Cu I Cu I /Cu II Cu I Cu I and Cu II Cu I Cu I /Cu II Cu II Cu I redox couples, approaching the rapid electron transfer rates of copper sites in MCO. 

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5. p ‐Substituted Tris(2‐pyridylmethyl)amines as Ligands for Highly Active ATRP Catalysts: Facile Synthesis and Characterization

   https://doi.org/10.1002/anie.202004724  

   Enciso, Alan E.; Lorandi, Francesca; Mehmood, Arshad; Fantin, Marco; Szczepaniak, Grzegorz; Janesko, Benjamin G.; Matyjaszewski, Krzysztof (June 2020, Angewandte Chemie International Edition)

   Abstract A facile and efficient two‐step synthesis ofp‐substituted tris(2‐pyridylmethyl)amine (TPMA) ligands to form Cu complexes with the highest activity to date in atom transfer radical polymerization (ATRP) is presented. In the divergent synthesis,p‐Cl substituents in tris(4‐chloro‐2‐pyridylmethyl)amine (TPMA^3Cl) were replaced in one step and high yield by electron‐donating cyclic amines (pyrrolidine (TPMA^PYR), piperidine (TPMA^PIP), and morpholine (TPMA^MOR)) by nucleophilic aromatic substitution. The [Cu^II(TPMA^NR2)Br]⁺complexes exhibited larger energy gaps between frontier molecular orbitals and >0.2 V more negative reduction potentials than [Cu^II(TPMA)Br]⁺, indicating >3 orders of magnitude higher ATRP activity. [Cu^I(TPMA^PYR)]⁺exhibited the highest reported activity for Br‐capped acrylate chain ends in DMF, and moderate activity toward C−F bonds at room temperature. ATRP ofn‐butyl acrylate using only 10–25 part per million loadings of [Cu^II(TPMA^NR2)Br]⁺exhibited excellent control. 

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