Recent Submissions

  • Ambiguities in solvation free energies from cluster-continuum quasichemical theory: lithium cation in protic and aprotic solvents.

    Itkis, Daniil; Cavallo, Luigi; Yashina, Lada V; Minenkov, Yury (Physical chemistry chemical physics : PCCP, Royal Society of Chemistry (RSC), 2021-07-22) [Article]
    Gibbs free energies for Li+ solvation in water, methanol, acetonitrile, DMSO, dimethylacetamide, dimethoxyethane, dimethylformamide, gamma-butyrolactone, pyridine, and sulfolane have been calculated using the cluster-continuum quasichemical theory. With n independent solvent molecules S initial state forming the "monomer" thermodynamic cycle, Li+ solvation free energies are found to be on average 14 kcal mol-1 more positive compared to those from the "cluster" thermodynamic cycle where the initial state is the cluster Sn. We ascribe the inconsistency between the "monomer" and "cluster" cycles mainly to the incorrectly predicted solvation free energies of solvent clusters Sn from the SMD and CPCM continuum solvation models, which is in line with the earlier study of Bryantsev et al., J. Phys. Chem. B, 2008, 112, 9709-9719. When experimental-based solvation free energies of individual solvent molecules and solvent clusters are employed, the "monomer" and "cluster" cycles result in identical numbers. The best overall agreement with experimental-based "bulk" scale lithium cation solvation free energies was obtained for the "monomer" scale, and we recommend this set of values. We expect that further progress in the field is possible if (i) consensus on the accuracy of experimental reference values is achieved; (ii) the most recent continuum solvation models are properly parameterized for all solute-solvent combinations and become widely accessible for testing.
  • Observation of Negative Photoconductivity in Lead-Free Cs3Bi2Br9Perovskite Single Crystal

    Tailor, Naveen Kumar; Maity, Partha; Satapathi, Soumitra (ACS Photonics, American Chemical Society (ACS), 2021-07-21) [Article]
    Light exposure usually causes an increase in photoconductivity in perovskite semiconductors. However, we report here light-induced negative photoconductivity, followed by slow dark self-recovery in a lead-free Cs3Bi2Br9 perovskite single crystal. Femtosecond transient reflection (fs-TR) spectroscopy studies further reveal hole self-trapping at the Vk center (Br2– dimer) in the midband states of this vacancy-ordered perovskite. Subsequently, these charged defect states (Vk) trap photogenerated charge carriers and produce an internal electrical field, which essentially opposes the externally applied field, leading to negative photoconductivity. A highly sensitive prototype photodetector was fabricated with figure of merits estimated as responsivity (6.42 mA/W), detectivity (2.51 × 1012 Jones), and current in a dark to light ratio (∼20). Our observation of this retrospective photocurrent in optically active perovskite materials can be applied for developing highly sensitive detectors.
  • [Cu36H10(PET)24(PPh3)6Cl2] Reveals Surface Vacancy Defects in Ligand-Stabilized Metal Nanoclusters

    Dong, Chunwei; Huang, Renwu; Chen, Cailing; Chen, Jie; Nematulloev, Saidkhodzha; Guo, Xianrong; Ghosh, Atanu; Alamer, Badriah Jaber; Hedhili, Mohamed N.; Isimjan, Tayirjan T.; Han, Yu; Mohammed, Omar F.; Bakr, Osman (Journal of the American Chemical Society, American Chemical Society (ACS), 2021-07-13) [Article]
    Precise identification and in-depth understanding of defects in nanomaterials can aid in rationally modulating defect-induced functionalities. However, few studies have explored vacancy defects in ligand-stabilized metal nanoclusters with well-defined structures, owing to the substantial challenge of synthesizing and isolating such defective metal nanoclusters. Herein, a novel defective copper hydride nanocluster, [Cu36H10(PET)24(PPh3)6Cl2] (Cu36; PET: phenylethanethiolate; PPh3: triphenylphosphine), is successfully synthesized at the gram scale via a simple one-pot reduction method. Structural analysis reveals that Cu36 is a distorted half cubic nanocluster, evolved from the perfect Nichol’s half cube. The two surface copper vacancies in Cu36 are found to be the principal imperfections, which result in some structural adjustments, including copper atom reconstruction near the vacancies as well as ligand modifications (e.g., substitution, migration, and exfoliation). Density functional theory calculations imply that the above-mentioned defects have a considerable influence on the electronic structure and properties. The modeling suggests that the formation of defective Cu36 rather than the perfect half cube is driven by the enlargement of the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the nanocluster. The structural evolution induced by the surface copper atom vacancies provides atomically precise insights into the defect-induced readjustment of the local structure and introduces new avenues for understanding the chemistry of defects in nanomaterials.
  • Oriented Halide Perovskite Nanostructures and Thin Films for Optoelectronics

    Chen, Jie; Zhou, Yang; Fu, Yongping; Pan, Jun; Mohammed, Omar F.; Bakr, Osman (Chemical Reviews, American Chemical Society (ACS), 2021-07-12) [Article]
    Oriented semiconductor nanostructures and thin films exhibit many advantageous properties, such as directional exciton transport, efficient charge transfer and separation, and optical anisotropy, and hence these nanostructures are highly promising for use in optoelectronics and photonics. The controlled growth of these structures can facilitate device integration to improve optoelectronic performance and benefit in-depth fundamental studies of the physical properties of these materials. Halide perovskites have emerged as a new family of promising and cost-effective semiconductor materials for next-generation high-power conversion efficiency photovoltaics and for versatile high-performance optoelectronics, such as light-emitting diodes, lasers, photodetectors, and high-energy radiation imaging and detectors. In this Review, we summarize the advances in the fabrication of halide perovskite nanostructures and thin films with controlled dimensionality and crystallographic orientation, along with their applications and performance characteristics in optoelectronics. We examine the growth methods, mechanisms, and fabrication strategies for several technologically relevant structures, including nanowires, nanoplates, nanostructure arrays, single-crystal thin films, and highly oriented thin films. We highlight and discuss the advantageous photophysical properties and remarkable performance characteristics of oriented nanostructures and thin films for optoelectronics. Finally, we survey the remaining challenges and provide a perspective regarding the opportunities for further progress in this field.
  • Chelation enforcing a dual gold configuration in the catalytic hydroxyphenoxylation of alkynes

    Escayola, Sílvia; Poater, Jordi; Ramos, Miguel; Luque-Urrutia, Jesús Antonio; Duran, Josep; Simon, Sílvia; Solà, Miquel; Cavallo, Luigi; Nolan, Steven P.; Poater, Albert (Applied Organometallic Chemistry, Wiley, 2021-07-06) [Article]
    The functionalization of alkynes by Au (N-heterocyclic carbene, NHC) complexes via the hydrophenoxylation reaction is a paradigm for the discussion between mono and dual metal catalysis. With the aim of mimicking the framework containing two gold units, achieved with molecular boxes, two NHC ligands were joined here with a chelated chain and this motif was examined in the hydrophenoxylation/hydroalkoxylation reactions through DFT calculations. This synthetic motif transforms the standard hydrophenoxylation intermolecular reaction from an inter- into an intra-molecular nucleophilic attack, when forming the C–O bond. Various chain lengths were tested with regard to the coordination of the alkyne to the cationic NHC-gold(I) center.
  • Metal-Organic Frameworks: Molecules or Semiconductors in Photocatalysis?

    Kolobov, Nikta; Goesten, Maarten; Gascon, Jorge (Angewandte Chemie, Wiley, 2021-07-02) [Article]
    In the realm of solids, Metal-Organic Frameworks (MOFs) offer unique possibilities for a rationale-based engineering of tailored physical properties. These derive from the modular, molecular make-up of MOFs, which allows for the selection and modification of the organic and inorganic building units that construct them. The adaptable properties make MOFs interesting materials for photocatalysis, an area of increasing significance. But the molecular and porous nature of a MOs leaves the field, in some areas, juxtapositioned between semiconductor physics and homogeneous photocatalysis. While descriptors from both fields are applied in tandem, the gap between theory and experiment has widened in some area’s, and arguably needs fixing. Here we review, on the basis of the literature, where MOFs have shown to be similar to conventional semiconductors in photocatalysis, and where they have shown to be more like infinite molecules in solution. We do this from the perspective of band theory, which in the context of photocatalysis, covers both the molecular and nonmolecular principles of relevance.
  • Polyether-Based Block Co(ter)polymers as Multifunctional Lubricant Additives

    Hong, Frank T.; Ladelta, Viko; Gautam, Ribhu; Sarathy, Mani; Hadjichristidis, Nikos (ACS Applied Polymer Materials, American Chemical Society (ACS), 2021-06-30) [Article]
    A series of polyether-based diblock copolymers were synthesized by sequential organocatalytic ring-opening polymerization (ROP) of either hexene oxide (HO) or octene oxide (OO) as the first monomer with propylene oxide (PO) as the second monomer. In addition, one triblock terpolymer of OO, PO, and styrene oxide (SO) was synthesized following the same method. The ROP was catalyzed by triethyl borane (TEB)/(phosphazene base t-BuP2) with eicosanol as the initiator. The resulting co(ter)polymers have a low polydispersity index and good solubility in hydrocarbon-based oils and are metal-free. By blending polyoctene oxide (POO) and polyhexene oxide (PHO) homopolymers with a Group II base oil (AramcoPrima 230) (2.5 to 5.0 wt %), the viscosity index (VI) increased from 100 to 160, and the thermal stability enhanced up to 50 °C. By using diblock copolymers, POO-block-poly(propylene oxide) (POO-b-PPO) and PHO-block-PPO (PHO-b-PPO), instead of the homopolymers, the VI and the thermal stability are almost the same, but the oil exhibits superior lubrication performance, with friction and wear decreasing up to 46 and 86%, respectively. The addition of the PSO block to the POO-b-PPO chain (POO-b-PPO-b-PSO) further improves the thermal stability but worsens the rheological and tribological properties (i.e., VI, friction, and wear) of lubricating oils.
  • Polyether-Based Block Co(ter)polymers as Multifunctional Lubricant Additives

    Hong, Frank T.; Ladelta, Viko; Gautam, Ribhu; Sarathy, Mani; Hadjichristidis, Nikos (ACS Applied Polymer Materials, American Chemical Society (ACS), 2021-06-30) [Article]
    A series of polyether-based diblock copolymers were synthesized by sequential organocatalytic ring-opening polymerization (ROP) of either hexene oxide (HO) or octene oxide (OO) as the first monomer with propylene oxide (PO) as the second monomer. In addition, one triblock terpolymer of OO, PO, and styrene oxide (SO) was synthesized following the same method. The ROP was catalyzed by triethyl borane (TEB)/(phosphazene base t-BuP2) with eicosanol as the initiator. The resulting co(ter)polymers have a low polydispersity index and good solubility in hydrocarbon-based oils and are metal-free. By blending polyoctene oxide (POO) and polyhexene oxide (PHO) homopolymers with a Group II base oil (AramcoPrima 230) (2.5 to 5.0 wt %), the viscosity index (VI) increased from 100 to 160, and the thermal stability enhanced up to 50 °C. By using diblock copolymers, POO-block-poly(propylene oxide) (POO-b-PPO) and PHO-block-PPO (PHO-b-PPO), instead of the homopolymers, the VI and the thermal stability are almost the same, but the oil exhibits superior lubrication performance, with friction and wear decreasing up to 46 and 86%, respectively. The addition of the PSO block to the POO-b-PPO chain (POO-b-PPO-b-PSO) further improves the thermal stability but worsens the rheological and tribological properties (i.e., VI, friction, and wear) of lubricating oils.
  • Access to Ultrafast Surface and Interface Carrier Dynamics Simultaneously in Space and Time

    Zhao, Jianfeng; Nughays, Razan; Bakr, Osman; Mohammed, Omar F. (The Journal of Physical Chemistry C, American Chemical Society (ACS), 2021-06-29) [Article]
    Charge carrier dynamics at material surfaces and interfaces play a fundamental role in controlling the performance of photocatalytic reactions and photovoltaic devices; however, precise characterization of the surface dynamical properties of a material with nanometer (nm) and femtosecond (fs) spatial and temporal resolutions, respectively, is a precondition for profound understanding and is thus urgently needed. Many techniques have been developed to meet this demand, but barely any of them have simultaneous excellent surface sensitivity (depth resolution) and sufficient spatiotemporal resolutions, except for a one-of-a-kind second-generation scanning ultrafast electron microscope (S-UEM), which has been established and developed at KAUST to provide direct and controllable dynamical information about the ultrafast charge carrier dynamics and the localization of electrons and holes on the photoactive material surface and interfaces. In this feature article, the instrumentation, working principles, new capabilities, and unique applications of S-UEM in the ultrafast characterization of material surfaces and interfaces, including charge carrier injection, surface carrier diffusion, surface carrier trapping, and recombination, are systematically summarized and inspected. Future developments from both theoretical and experimental perspectives are also discussed.
  • 62-8: Invited Paper: High Color Gamut QDot ™ LCD Displays with Perovskite Quantum Dots: Devices Architecture, Performance and Reliability

    Sinatra, Lutfan; Lutfullin, Marat; Lentijo-Mozo, Sergio; Bakr, Osman (SID Symposium Digest of Technical Papers, Wiley, 2021-06-28) [Article]
    erovskite Quantum Dots (QDs) promise to deliver over 90% of Rec2020 color representation, the highest for RoHS compliant LCD displays. In this study, we strive to demonstrate the performance of LCD displays using QDot™ green emitting Perovskite QDs with various backlight architectures. Using different blue and red light sources, we fabricated four types of LCD display, which showed contrasting Rec2020 color gamut from 80 to 86 % and brightness from 1000 to 2000 nits. With these impressive metrics, Perovskite Quantum Dots paves the way for mass adoption of the technology in the display field.
  • Manipulation of hot carrier cooling dynamics in two-dimensional Dion–Jacobson hybrid perovskites via Rashba band splitting

    Yin, Jun; Naphade, Rounak; Maity, Partha; Gutierrez Arzaluz, Luis; Almalawi, Dhaifallah R.; Roqan, Iman S.; Bredas, Jean-Luc; Bakr, Osman; Mohammed, Omar F. (Nature Communications, Springer Science and Business Media LLC, 2021-06-28) [Article]
    AbstractHot-carrier cooling processes of perovskite materials are typically described by a single parabolic band model that includes the effects of carrier-phonon scattering, hot phonon bottleneck, and Auger heating. However, little is known (if anything) about the cooling processes in which the spin-degenerate parabolic band splits into two spin-polarized bands, i.e., the Rashba band splitting effect. Here, we investigated the hot-carrier cooling processes for two slightly different compositions of two-dimensional Dion–Jacobson hybrid perovskites, namely, (3AMP)PbI4 and (4AMP)PbI4 (3AMP = 3-(aminomethyl)piperidinium; 4AMP = 4-(aminomethyl)piperidinium), using a combination of ultrafast transient absorption spectroscopy and first-principles calculations. In (4AMP)PbI4, upon Rashba band splitting, the spin-dependent scattering of hot electrons is responsible for accelerating hot-carrier cooling at longer delays. Importantly, the hot-carrier cooling of (4AMP)PbI4 can be extended by manipulating the spin state of the hot carriers. Our findings suggest a new approach for prolonging hot-carrier cooling in hybrid perovskites, which is conducive to further improving the performance of hot-carrier-based optoelectronic and spintronic devices.
  • Cascade Electron Transfer Induces Slow Hot Carrier Relaxation in CsPbBr3 Asymmetric Quantum Wells

    Maity, Partha; Merdad, Noor A.; Yin, Jun; Lee, Kwangjae; Sinatra, Lutfan; Bakr, Osman; Mohammed, Omar F. (ACS Energy Letters, American Chemical Society (ACS), 2021-06-28) [Article]
    We report an engineering approach not only to delay hot carrier equilibrium but also to slow the cooling rate of CsPbBr3-based multiple quantum wells (MQWs), as evident from femtosecond transient absorption measurements and density functional theory calculations. Three energetically cascaded CsPbBr3 perovskite layers (stacked with thicknesses of 3, 7, and 20 nm for asymmetric MQWs and 20, 20, and 20 nm for symmetric MQWs) are separated by a 5 nm organic barrier of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline. Time-resolved data demonstrate that the sequential hot-electron transfer between CsPbBr3 layers mediates the delayed hot carrier equilibrium in the asymmetric MQWs. Interestingly, the delayed hot carrier equilibrium is followed by a much slower relaxation in asymmetric MQWs (40 ps) than symmetric ones (3.2 ps), which could be attributed to the decoupling of a hot electron–hole originating from hot electron transfer. Our findings provide a promising approach for efficient hot carrier extraction in solar cells that exceed the Shockley–Queisser limit.
  • Influence of the anionic ligands on properties and reactivity of Hoveyda-Grubbs catalysts

    Albalawi, Mona O.; Falivene, Laura; Jedidi, Abdesslem; Osman, Osman I.; Elroby, Shaaban A.; Cavallo, Luigi (Molecular Catalysis, Elsevier BV, 2021-06-26) [Article]
    Ruthenium based catalysts remain among the more successful complexes used in the catalysis of metathesis processes for the synthesis of new carbon-carbon bonds. The investigation of the influence of the different system moieties on its catalytic performance has led to important improvements in the field. To this extent, density functional theory (DFT) calculations have contributed significantly providing fundamental understandings to develop new catalysts. With this aim, we presented here a detailed computational study of how the nature of the anion ligand binding to the metal affects the global properties and reactivity of the catalyst. Geometric, energetic and electronic analysis have been performed to reach the key insights necessary to build structure-performance correlations.
  • A Random Forest Classifier for Protein-Protein Docking Models

    Barradas Bautista, Didier; Cao, Zhen; Vangone, Anna; Oliva, Romina; Cavallo, Luigi (Cold Spring Harbor Laboratory, 2021-06-24) [Preprint]
    Herein, we present the results of a machine learning approach we developed to single out correct 3D docking models of protein-protein complexes obtained by popular docking software. To this aim, we generated a set of ~7xE06 docking models with three different docking programs (HADDOCK, FTDock and ZDOCK) for the 230 complexes in the protein-protein interaction benchmark, version 5 (BM5). Three different machine-learning approaches (Random Forest, Supported Vector Machine and Perceptron) were used to train classifiers with 158 different scoring functions (features). The Random Forest algorithm outperformed the other two algorithms and was selected for further optimization. Using a features selection algorithm, and optimizing the random forest hyperparameters, allowed us to train and validate a random forest classifier, named CoDES (COnservation Driven Expert System). Testing of CoDES on independent datasets, as well as results of its comparative performance with machine-learning methods recently developed in the field for the scoring of docking decoys, confirm its state-of-the-art ability to discriminate correct from incorrect decoys both in terms of global parameters and in terms of decoys ranked at the top positions.
  • Intramolecular Electrochemical Oxybromination of Olefins for the Synthesis of Isoxazolines in Batch and Continuous Flow

    Prabhakar Kale, Ajit; Nikolaienko, Pavlo; Smirnova, Kristina; Rueping, Magnus (European Journal of Organic Chemistry, Wiley, 2021-06-23) [Article]
    A new electrochemical method for the synthesis of 2-isoxazolines is reported. The reaction operates under atmospheric conditions and tolerates air and moisture. The use of potassium bromide as both electrolyte and bromine source precludes the need for toxic, air-sensitive inorganic oxidants or transition metal catalysts.
  • Chemo- and enantioselective hetero-coupling of hydroxycarbazoles catalyzed by a chiral vanadium(v) complex

    Sako, Makoto; Higashida, Keigo; Kamble, Ganesh Tatya; Kaut, Kevin; Kumar, Ankit; Hirose, Yuka; Zhou, Da-Yang; Suzuki, Takeyuki; Rueping, Magnus; Maegawa, Tomohiro; Takizawa, Shinobu; Sasai, Hiroaki (ORGANIC CHEMISTRY FRONTIERS, Royal Society of Chemistry (RSC), 2021-06-23) [Article]
    The catalytic enantioselective oxidative hetero-coupling of arenols using a chiral vanadium(V) complex has been developed. The coupling of hydroxycarbazole derivatives with various arenols provided axially chiral biarenols with high chemo-, regio-, and enantioselectivities. The reaction took place under mild conditions and exhibited satisfactory functional group tolerance. Aerobic oxidative hetero-coupling with β-ketoesters also proceeded with high chemo- and stereoselectivities under slightly modified reaction conditions.
  • Delivery of Endothelial Cell-Laden Microgel Elicits Angiogenesis in Self-Assembling Ultrashort Peptide Hydrogels In Vitro

    Ramirez Calderon, Gustavo; Susapto, Hepi Hari; Hauser, Charlotte (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2021-06-18) [Article]
    Blood vessel generation is an essential process for tissue formation, regeneration, and repair. Notwithstanding, vascularized tissue fabrication in vitro remains a challenge, as current fabrication techniques and biomaterials lack translational potential in medicine. Naturally derived biomaterials harbor the risk of immunogenicity and pathogen transmission, while synthetic materials need functionalization or blending to improve their biocompatibility. In addition, the traditional top-down fabrication techniques do not recreate the native tissue microarchitecture. Self-assembling ultrashort peptides (SUPs) are promising chemically synthesized natural materials that self-assemble into three-dimensional nanofibrous hydrogels resembling the extracellular matrix (ECM). Here, we use a modular tissue-engineering approach, embedding SUP microgels loaded with human umbilical vein endothelial cells (HUVECs) into a 3D SUP hydrogel containing human dermal fibroblast neonatal (HDFn) cells to trigger angiogenesis. The SUPs IVFK and IVZK were used to fabricate microgels that gel in a water-in-oil emulsion using a microfluidic droplet generator chip. The fabricated SUP microgels are round structures that are 300–350 μm diameter in size and have ECM-like topography. In addition, they are stable enough to keep their original size and shape under cell culture conditions and long-term storage. When the SUP microgels were used as microcarriers for growing HUVECs and HDFn cells on the microgel surface, cell attachment, stretching, and proliferation could be demonstrated. Finally, we performed an angiogenesis assay in both SUP hydrogels using all SUP combinations between micro- and bulky hydrogels. Endothelial cells were able to migrate from the microgel to the surrounding area, showing angiogenesis features such as sprouting, branching, coalescence, and lumen formation. Although both SUP hydrogels support vascular network formation, IVFK outperformed IVZK in terms of vessel network extension and branching. Overall, these results demonstrated that cell-laden SUP microgels have great potential to be used as a microcarrier cell delivery system, encouraging us to study the angiogenesis process and to develop vascularized tissue-engineering therapies.
  • All-Polycarbonate Graft Copolymers with Tunable Morphologies by Metal-Free Copolymerization of CO2 with Epoxides

    Alagi, Prakash; Zapsas, Georgios; Hadjichristidis, Nikos; Hong, Sung Chul; Gnanou, Yves; Feng, Xiaoshuang (Macromolecules, American Chemical Society (ACS), 2021-06-18) [Article]
    Brush-type macromolecules (BMs) have attracted much attention over the past decades because of their unique properties and potential applications in nanoscience, drug-delivery systems, and photonics. A two-step strategy of synthesis of polycarbonate-grafted copolymers with either star-shaped or brushtyped morphologies using a “grafting from” approach is reported; the backbone in these all-polycarbonate graft copolymers is made of poly(cyclohexene carbonate) (PCHC), and the side grafts are made of poly(propylene carbonate) (PPC). In the first step, poly (vinyl-cyclohexene carbonate) (PVCHC) backbones of two different sizes (PVCHC35, PVCHC283) were prepared by copolymerization of vinyl-cyclohexene oxide (VCHO) with CO2 in the presence of triethylborane (TEB), using tetrabutyl ammonium succinate (TBAS) as the initiator. In the second step, the dangling vinyl double bonds of PVCHC were transformed into carboxylic acid groups. After partial neutralization of the latter using tetrabutyl ammonium hydroxide, the PPC grafts could be grown from the backbone carboxylic sites by copolymerization of propylene oxide (PO) with CO2 in the presence of TEB. Before attempting the synthesis of the above all-polycarbonate grafted copolymers, we check the viability of the above synthetic strategy by preparing graft copolymers made of a polymethacrylate backbone and PPC side grafts. In the latter case, the backbone was generated by reversible addition−fragmentation chain-transfer (RAFT) polymerization of methacrylic acid (MAA), followed by the growth of PPC side grafts using the backbone carboxylates as initiating sites. In both cases (PVCHC-g-PPC and PMAA-g-PPC), two types of architectures corresponding to two different morphologies were synthesized: star-shaped morphologies were obtained from rather short backbones, and relatively long grafts, on the one hand, and semiflexible cylinders were grown from rather long backbones and short grafts. These various structures were characterized by nuclear magnetic resonance (NMR) and gel permeation chromatography/light scattering (GPC/LS), and their morphologies were further investigated by atomic force microscopy (AFM). The reported synthetic method provides a robust way to synthesize well-defined polycarbonates with either star-type or brush-type morphologies and graft copolymers made of polyacrylate backbones and polycarbonate grafts. Thermal and mechanical properties of these graft copolymers were also investigated.
  • Non-metal with metal behavior: metal-free coordination-insertion ring-opening polymerization

    Wang, Xin; Xu, Jiaxi; Li, Zhenjiang; Liu, Jingjing; Sun, Jie; Hadjichristidis, Nikos; Guo, Kai (Chemical Science, Royal Society of Chemistry (RSC), 2021-06-15) [Article]
    The “coordination-insertion” ring-opening polymerization (ROP) mechanism has so far been the monopoly of metal catalysts. In this work, we present a metal-free “coordination-insertion” ROP of trimethylene carbonate (TMC) and ε-caprolactone (ε-CL), as well as their sequential block copolymerization, with N-trimethylsilyl-bis (trifluoromethanesulfonyl)imide (TMSNTf2) as the non-metallic initiator/catalyst. TMSNTf2 was proposed to work through an unprecedented metal-free “coordination-insertion” mechanism, which involves the coordination of monomer to the Si atom of TMSNTf2, the nucleophilic attack of the –NTf2 group on the coordinated monomer, and the cleavage of the acyl–oxygen bond of the monomer. The proposed metal-free “coordination-insertion” ROP was studied by NMR, SEC, and MALDI-TOF analyses. In addition, the TMSNTf2-mediated ROP of TMC and ε-CL led to linear and cyclic polymers following two-stage first-order polymerization processes, as evidenced by structural analyses and kinetics study, which further demonstrated the metal-free “coordination-insertion” mechanism.
  • Redox-Neutral Cross-Coupling Amination with Weak N-Nucleophiles: Arylation of Anilines, Sulfonamides, Sulfoximines, Carbamates, and Imines via Nickelaelectrocatalysis

    Zhu, Chen; Kale, Ajit Prabhakar; Yue, Huifeng; Rueping, Magnus (JACS Au, American Chemical Society (ACS), 2021-06-15) [Article]
    A nickel-catalyzed cross-coupling amination with weak nitrogen nucleophiles is described. Aryl halides as well as aryl tosylates can be efficiently coupled with a series of weak N-nucleophiles, including anilines, sulfonamides, sulfoximines, carbamates, and imines via concerted paired electrolysis. Notably, electron-deficient anilines and sulfonamides are also suitable substrates. Interestingly, when benzophenone imine is applied in the arylation, the product selectivity toward the formation of amine and imine product can be addressed by a base switch. In addition, the alternating current mode can be successfully applied. DFT calculations support a facilitated reductive elimination pathway.

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