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1. Aluminium( iii ) dialkyl 2,6-bisimino-4 R -dihydropyridinates(−1): selective synthesis, structure and controlled dimerization

   https://doi.org/10.1039/C9DT00847K  

   Gallardo-Villagrán, Manuel ; Vidal, Fernando ; Palma, Pilar ; Álvarez, Eleuterio ; Chen, Eugene Y.-X. ; Cámpora, Juan ; Rodríguez-Delgado, Antonio ( June 2019 , Dalton Transactions)

   A family of stable and otherwise selectively unachievable 2,6-bisimino-4- R -1,4-dihydropyridinate aluminium (III) dialkyl complexes [AlR' 2 (4-R- i PrBIPH)] (R = Bn, Allyl; R′ = Me, Et, i Bu) have been synthesized, taking advantage of a method for the preparation of the corresponding 4- R -1,4-dihydropiridine precursors developed in our group. All the dihydropyrdinate(−1) dialkyl aluminium complexes have been fully characterized by 1 H- 13 C-NMR, elemental analysis and in the case 2′a , also by X-ray diffraction studies. Upon heating in toluene solution at 110 °C, the dimethyl derivatives 2a and 2′a dimerize selectively through a double cycloaddition. This reaction leads to the formation of two new C–C bonds that involve the both meta positions of the two 4- R -1,4-dihydropyridinate fragments, resulting the binuclear aluminium species [Me 2 Al(4-R- i PrHBIP)] 2 (R = Bn ( 3a ); allyl ( 3′a )). Experimental kinetics showed that the dimerization of 2′a obeys second order rate with negative activation entropy, which is consistent with a bimolecular rate-determining step. Controlled methanolysis of both 3a and 3′a release the metal-free dimeric bases, (4-Bn- i PrHBIPH) 2 and (4-allyl- i PrHBIPH) 2 , providing a convenient route to these potentially useful ditopic ligands. When the R′ groups are bulkier than Me ( 2b , 2′b and 2′c ), the dimerization is hindered or fully disabled, favoring the formation of paramagnetic NMR-silent species, which have been identified on the basis of a controlled methanolysis of the final organometallic products. Thus, when a toluene solution of [AlEt 2 (4-Bn- i PrBIPH)] ( 2b ) was heated at 110 °C, followed by the addition of methanol in excess, it yields a mixture of the dimer (4-Bn- i PrHBIPH) 2 and the aromatized base 4-Bn- i PrBIP, in ca . 1 : 2 ratio, indicating that the dimerization of 2b competes with its spontaneous dehydrogenation, yielding a paramagnetic complex containing a AlEt 2 unit and a non-innocent (4-Bn- i PrBIP) ˙− radical-anion ligand. Similar NMR monitoring experiments on the thermal behavior of [AlEt 2 (4-allyl- i PrBIPH)] ( 2′b ) and [Al i Bu 2 (4-allyl-iPrBIPH)] ( 2′c ) showed that these complexes do not dimerize, but afford exclusively NMR silent products. When such thermally treated samples were subjected to methanolysis, they resulted in mixtures of the alkylated 4-allyl- i PrBIP and non-alkylated i PrBIP ligand, suggesting that dehydrogenation and deallylation reactions take place competitively. 

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2. Microfluidic Synthesis of Elastomeric Microparticles: A Case Study in Catalysis of Palladium-Mediated Cross-Coupling

   Bennett, Jeffrey A ; Genzer, Jan ; Abolhasani, Milad ( October 2018 , 2018 AIChE Annual Meeting)

   Metal-mediated cross-coupling reactions offer organic chemists a wide array of stereo- and chemically-selective reactions with broad applications in fine chemical and pharmaceutical synthesis.1 Current batch-based synthesis methods are beginning to be replaced with flow chemistry strategies to take advantage of the improved consistency and process control methods offered by continuous flow systems.2,3 Most cross-coupling chemistries still encounter several issues in flow using homogeneous catalysis, including expensive catalyst recovery and air sensitivity due to the chemical nature of the catalyst ligands.1 To mitigate some of these issues, a ligand-free heterogeneous catalysis reaction was developed using palladium (Pd) loaded into a polymeric network of a silicone elastomer, poly(hydromethylsiloxane) (PHMS), that is not air sensitive and can be used with mild reaction solvents (ethanol and water).4 In this work we present a novel method of producing soft catalytic microparticles using a multiphase flow-focusing microreactor and demonstrate their application for continuous Suzuki-Miyaura cross-coupling reactions. The catalytic microparticles are produced in a coaxial glass capillary-based 3D flow-focusing microreactor. The microreactor consists of two precursors, a cross-linking catalyst in toluene and a mixture of the PHMS polymer and a divinyl cross-linker. The dispersed phase containing the polymer, cross-linker, and cross-linking catalyst is continuously mixed and then formed into microdroplets by the continuous phase of water and surfactant (sodium dodecyl sulfate) introduced in a counter-flow configuration. Elastomeric microdroplets with a diameter ranging between 50 to 300 micron are produced at 25 to 250 Hz with a size polydispersity less than 3% in single stream production. The physicochemical properties of the elastomeric microparticles such as particle swelling/softness can be tuned using the ratio of cross-linker to polymer as well as the ratio of polymer mixture to solvent during the particle formation. Swelling in toluene can be tuned up to 400% of the initial particle volume by reducing the concentration of cross-linker in the mixture and increasing the ratio of polymer to solvent during production.5 After the particles are produced and collected, they are transferred into toluene containing palladium acetate, allowing the particles to incorporate the palladium into the polymer network and then reduce the palladium to Pd0 with the Si-H functionality present on the PHMS backbones. After the reduction, the Pd-loaded particles can be washed and dried for storage or switched into an ethanol/water solution for loading into a micro-packed bed reactor (µ-PBR) for continuous organic synthesis. The in-situ reduction of Pd within the PHMS microparticles was confirmed using energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and focused ion beam-SEM, and TEM techniques. In the next step, we used the developed µ-PBR to conduct continuous organic synthesis of 4-phenyltoluene by Suzuki-Miyaura cross-coupling of 4-iodotoluene and phenylboronic acid using potassium carbonate as the base. Catalyst leaching was determined to only occur at sub ppm concentrations even at high solvent flow rates after 24 h of continuous run using inductively coupled plasma mass spectrometry (ICP-MS). The developed µ-PBR using the elastomeric microparticles is an important initial step towards the development of highly-efficient and green continuous manufacturing technologies in the pharma industry. In addition, the developed elastomeric microparticle synthesis technique can be utilized for the development of a library of other chemically cross-linkable polymer/cross-linker pairs for applications in organic synthesis, targeted drug delivery, cell encapsulation, or biomedical imaging. References 1. Ruiz-Castillo P, Buchwald SL. Applications of Palladium-Catalyzed C-N Cross-Coupling Reactions. Chem Rev. 2016;116(19):12564-12649. 2. Adamo A, Beingessner RL, Behnam M, et al. On-demand continuous-flow production of pharmaceuticals in a compact, reconfigurable system. Science. 2016;352(6281):61 LP-67. 3. Jensen KF. Flow Chemistry — Microreaction Technology Comes of Age. 2017;63(3). 4. Stibingerova I, Voltrova S, Kocova S, Lindale M, Srogl J. Modular Approach to Heterogenous Catalysis. Manipulation of Cross-Coupling Catalyst Activity. Org Lett. 2016;18(2):312-315. 5. Bennett JA, Kristof AJ, Vasudevan V, Genzer J, Srogl J, Abolhasani M. Microfluidic synthesis of elastomeric microparticles: A case study in catalysis of palladium-mediated cross-coupling. AIChE J. 2018;0(0):1-10. 

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3. 2D molybdenum and vanadium nitrides synthesized by ammoniation of 2D transition metal carbides (MXenes)

   https://doi.org/10.1039/c7nr06721f  

   Urbankowski, Patrick ; Anasori, Babak ; Hantanasirisakul, Kanit ; Yang, Long ; Zhang, Lihua ; Haines, Bernard ; May, Steven J. ; Billinge, Simon J. ; Gogotsi, Yury ( January 2017 , Nanoscale)

   MXenes are a rapidly growing class of 2D transition metal carbides and nitrides, finding applications in fields ranging from energy storage to electromagnetic interference shielding and transparent conductive coatings. However, while more than 20 carbide MXenes have already been synthesized, Ti 4 N 3 and Ti 2 N are the only nitride MXenes reported so far. Here by ammoniation of Mo 2 CT x and V 2 CT x MXenes at 600 °C, we report on their transformation to 2D metal nitrides. Carbon atoms in the precursor MXenes are replaced with N atoms, resulting from the decomposition of ammonia molecules. The crystal structures of the resulting Mo 2 N and V 2 N were determined with transmission electron microscopy and X-ray pair distribution function analysis. Our results indicate that Mo 2 N retains the MXene structure and V 2 C transforms to a mixed layered structure of trigonal V 2 N and cubic VN. Temperature-dependent resistivity measurements of the nitrides reveal that they exhibit metallic conductivity, as opposed to semiconductor-like behavior of their parent carbides. As important, room-temperature electrical conductivity values of Mo 2 N and V 2 N are three and one order of magnitude larger than those of the Mo 2 CT x and V 2 CT x precursors, respectively. This study shows how gas treatment synthesis such as ammoniation can transform carbide MXenes into 2D nitrides with higher electrical conductivities and metallic behavior, opening a new avenue in 2D materials synthesis. 

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4. Enabling High-Rate Long-lifespan Lithium-Sulfur Batteries via Stereolithography Technique and Oxidative Chemical Vapor Deposition

   Zhang, Yuxuan ; Lee, Sunghwan ( June 2022 , 64th Electronic Materials Conference)

   Enhancing battery energy storage capability and reducing the cost per average energy capacity is urgent to satisfy the increasing energy demand in modern society. The lithium-sulfur (Li-S) battery is especially attractive because of its high theoretical specific energy (around 2600 W h kg-1), low cost, and low toxicity.1 Despite these advantages, the practical utilization of lithium-sulfur (Li-S) batteries to date has been hindered by a series of obstacles, including low active material loading, shuttle effects, and sluggish sulfur conversion kinetics.2 The traditional 2D planer thick electrode is considered as a general approach to enhance the mass loading of the Li-S battery.3 However, the longer diffusion length of lithium ions, which resulted in high tortuosity in the compact stacking thick electrode, decreases the penetration ability of the electrolyte into the entire cathode.4 Although an effort to induce catalysts in the cathode was made to promote sulfur conversion kinetic conditions, catalysts based on transition metals suffered from the low electronic conductivity, and some elements (i.e.: Co, Mn) may even absorb and restrict polysulfides for further reaction. 5 To mitigate the issues listed above, herein we propose a novel sulfur cathode design strategy enabled by additive manufacturing and oxidative chemical vapor deposition (oCVD). 6,7 Specifically, the cathode is designed to have a hierarchal hollow structure via a stereolithography technique to increase sulfur usage. Microchannels are constructed on the tailored sulfur cathode to further fortify the wettability of the electrolyte. The as-printed cathode is then sintered at 700 °C in an N2 atmosphere in order to generate a carbon skeleton (i.e.: carbonization of resin) with intrinsic carbon defects. The intrinsic carbon defects are expected to create favorable sulfur conversion conditions with sufficient electronic conductivity. In this study, the oCVD technique is leveraged to produce a conformal coating layer to eliminate shuttle effects. Identified by scanning electron microscopy and energy-dispersive X-ray spectroscopy mapping characterizations, the oCVD PEDOT is not only covered on the surface of the cathode but also on the inner surface of the microchannels. High-resolution x-ray photoelectron spectroscopy analyses (C 1s and S 2p orbitals) between pristine and modified samples demonstrate that a high concentration of the defects has been produced on the sulfur matrix after sintering and posttreatment. In-operando XRD diffractograms show that the Li2S is generated in the oCVD PEDOT-coated sample during the charge and discharge process even with a high current density, confirming an eminent sulfur conversion kinetic condition. In addition, ICP-OES results of lithium metal anode at different states of charge (SoC) verify that the shuttle effects are excellently restricted by oCVD PEDOT. Overall, the high mass loading (> 5 mg cm-2) with an elevated sulfur utilization ratio, accelerated reaction kinetics and stabilized electrochemical process have been achieved on the sulfur cathode by implementing this innovative cathode design strategy. The results of this study demonstrate significant promises of employing pure sulfur powder with high electrochemical performance and suggest a pathway to the higher energy and power density battery. References: 1 Chen, Y. Adv Mater 33, e2003666. 2 Bhargav, A. Joule 4, 285-291. 3 Liu, S. Nano Energy 63, 103894. 4 Chu, T. Carbon Energy 3. 5 Li, Y. Matter 4, 1142-1188. 6 John P. Lock. Macromolecules 39, 4 (2006). 7 Zekoll, S. Energy & Environmental Science 11, 185-201. 

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5. LixSiON (x = 2, 4, 6): a novel solid electrolyte system derived from agricultural waste

   https://doi.org/10.1039/D0GC02580A  

   Zhang, X. ; Temeche, E. ; Laine, R. M. ( October 2020 , Green chemistry)

   A set of LixSiON (x = 2, 4, 6) polymer precursors to a novel solid-state electrolyte system were synthesized starting from rice hull ash (RHA), an agricultural waste, providing a green route towards the assembly of all solid-state batteries (ASSBs). Silica, ∼90 wt% in RHA, can be catalytically (alkali base) dissolved (20–40 wt%) in hexylene glycol (HG) and distilled directly from the reaction mixture as the spirosiloxane [(C6H14O2)2Si, SP] at 200 °C. SP can be lithiated using controlled amounts of LiNH2 to produce LixSiON oligomers/polymers with MWs up to ∼1.5 kDa as characterized by FTIR, MALDI-ToF, multinuclear NMR, TGA-DTA, XRD, XPS, SEM and EDX. XPS analyses show that Li contents depend solely on added LiNH2 but found N contents are only ≤1 at%. NH2 likely is removed as NH3 during sample preparation (vacuum/ overnight). In contrast, MALDI indicates N contents of ∼5–30 at% N with shorter drying times (vacuum/ minutes). 7Li NMR positive chemical shifts suggest that precursor bound Li+ ions dissociate easily, ben- eficial for electrochemical applications. The 7Li shifts correlate to Li contents as well as Li+ conductivities. 1H, 13C and 29Si NMRs of the Li6SiON precursor show fluxional behavior implying high Li+ mobility. Dense microstructures are observed for Li4SiON and Li6SiON pellets heated to 200 °C/2 h/N2. Impedance studies suggest that ionic conductivities increase with Li content; the Li6SiON precursor offers the highest ambient conductivity of 8.5 × 10−6 S cm−1 after heating to 200 °C/2 h/N2. 

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