Despite the great potential of radical chemistry in organic synthesis, N‐heterocyclic carbene (NHC)‐catalyzed reactions involving radical intermediates are not well explored. This communication ...reports the three‐component coupling of aroyl fluorides, styrenes and the Langlois reagent (CF3SO2Na) to give various β‐trifluoromethylated alkyl aryl ketones with good functional group tolerance in moderate to high yields by cooperative photoredox/NHC catalysis. The alkene acyltrifluoromethylation proceeds via radical/radical cross coupling of ketyl radicals with benzylic C‐radicals. The ketyl radicals are generated via SET reduction of in situ formed acylazolium ions whereas the benzylic radicals derive from trifluoromethyl radical addition onto styrenes.
Photoredox and NHC catalysis in concert: A novel strategy for the preparation of β‐trifluoromethylketones via radical alkene acyltrifluoromethylation has been developed. The three‐component cascades proceed under mild conditions with readily available aroyl fluorides, styrenes and the Langlois reagent as the reaction partners.
Methods that enable site selective acylation of sp
C-H bonds in complex organic molecules are not well explored, particularly if compared with analogous transformations of aromatic and vinylic sp
C-H ...bonds. We report herein a direct acylation of benzylic C-H bonds by merging N-heterocyclic carbene (NHC) and photoredox catalysis. The method allows the preparation of a diverse range of benzylic ketones with good functional group tolerance under mild conditions. The reaction can be used to install acyl groups on highly functionalized natural product derived compounds and the C-H functionalization works with excellent site selectivity. The combination of NHC and photoredox catalysis offers options in preparing benzyl aryl ketones.
We report the efficient carboxylation of bromides and triflates with K2CO3 as the source of CO2 in the presence of an organic photocatalyst in combination with a nickel complex under visible light ...irradiation at room temperature. The reaction is compatible with a variety of functional groups and has been successfully applied to the synthesis and derivatization of biologically active molecules. In particular, the carboxylation of unactivated cyclic alkyl bromides proceeded well with our protocol, thus extending the scope of this transformation. Spectroscopic and spectroelectrochemical investigations indicated the generation of a Ni0 species as a catalytic reactive intermediate.
Not only good for plants, CO2 (formed in situ from K2CO3) and light enabled the efficient and mild carboxylation of bromides and triflates in the presence of an organic fluorophore and a nickel complex (see scheme). A variety of functional groups were tolerated, and non‐activated cyclic alkyl bromides reacted well. The synthesis and derivatization of biologically active molecules demonstrated the applicability of the method in multistep synthesis.
We report herein that thermodynamic and kinetic isomerization of alkenes can be accomplished by the combination of visible light with Co catalysis. Utilizing Xantphos as the ligand, the most stable ...isomers are obtained, while isomerizing terminal alkenes over one position can be selectively controlled by using DPEphos as the ligand. The presence of the donor–acceptor dye 4CzIPN accelerates the reaction further. Transformation of exocyclic alkenes into the corresponding endocyclic products could be efficiently realized by using 4CzIPN and Co(acac)2 in the absence of any additional ligands. Spectroscopic and spectroelectrochemical investigations indicate CoI being involved in the generation of a Co hydride, which subsequently adds to alkenes initiating the isomerization.
A mild and highly efficient translocation of alkenes by dual visible‐light‐cobalt catalysis has been developed. By the proper choice of ligands, isomerization over one position or more than one position with tolerance of a variety of functional groups can be selectively achieved.
A vast amount of energy can be extracted from the untapped low‐grade heat from sources below 100 °C and the Gibbs free energy from salinity gradients. Therefore, a process for simultaneous and direct ...conversion of these energies into electricity using permselective membranes was developed in this study. These membranes screen charges of ion flux driven by the combined salinity and temperature gradients to achieve thermo‐osmotic energy conversion. Increasing the charge density in the pore channels enhanced the permselectivity and ion conductance, leading to a larger osmotic voltage and current. A 14‐fold increase in power density was achieved by adjusting the ionic site population of covalent organic framework (COF) membranes. The optimal COF membrane was operated under simulated estuary conditions at a temperature difference of 60 K, which yielded a power density of ≈231 W m−2, placing it among the best performing upscaled membranes. The developed system can pave the way to the utilization of the enormous supply of untapped osmotic power and low‐grade heat energy, indicating the tremendous potential of using COF membranes for energy conversion applications.
A process for simultaneous and direct conversion of energy from the low‐gradient heat and salinity differences into electricity was developed using ionic covalent‐organic‐framework membranes. A higher membrane charge density enables greater ion‐transport resistance. The optimal thermo‐osmotic energy conversion device offers a power density of 231 W m−2 with a temperature difference.
Potassium ion batteries (KIBs) have emerged as a promising energy storage system, but the stability and high rate capability of their electrode materials, particularly carbon as the most investigated ...anode ones, become a primary challenge. Here, it is identified that pitch‐derived soft carbon, a nongraphitic carbonaceous species which is paid less attention in the battery field, holds special advantage in KIB anodes. The structural flexibility of soft carbon makes it convenient to tune its crystallization degree, thereby modulating the storage behavior of large‐sized K+ in the turbostratic carbon lattices to satisfy the need in structural resilience, low‐voltage feature, and high transportation kinetics. It is confirmed that a simple thermal control can produce structurally optimized soft carbon that has much better battery performance than its widely reported carbon counterparts such as graphite and hard carbon. The findings highlight the potential of soft carbon as an interesting category suitable for high‐performance KIB electrode and provide insights for understanding the complicated K+ storage mechanisms in KIBs.
The cycling stability of anode materials in potassium‐ion batteries (KIBs) is challenged by the large size of K+ itself. The findings not only demonstrate the promising potential of soft carbon as a category suitable for high‐performance KIB electrodes, but also provide insights into the complicated K+ storage mechanisms in carbon anodes of KIBs.
Serum samples from patients convalescing after SARS-CoV-2 infection and after vaccination with BBIBP-CorV or CoronaVac in China neutralized pseudoviruses expressing spike proteins from the B.1.1.7 ...variant at levels that were similar to those from the wild-type (Wuhan) isolate but lower than those from the B.1.351 variant.
Abstract
Insufficient access to clean water and resources has emerged as one of the most pressing issues affecting people globally. Membrane‐based ion separation has become a focal point of research ...for the generation of fresh water and the extraction of energy elements. This Review encapsulates recent advancements in the selective ion transport of covalent organic framework (COF) membranes, accomplished by strategically pairing diverse monomers to create membranes with various pore sizes and environments for specific purposes. We first discuss the merits of using COF materials as a basis for fabricating membranes for ion separation. We then explore the development of COF membranes in areas such as desalination, acid recovery, and energy element extraction, with a particular emphasis on the fundamental principles of membrane design. Lastly, we address both theoretical and practical challenges, as well as potential opportunities in the targeted design of ion‐selective membranes. The goal of this Review is to stimulate future investigative efforts in this field, which is of significant scientific and strategic importance.
In this paper, we study nuclearity of semigroup crossed products for quasi-lattice ordered groups. We show the relationships among nuclearity of the semigroup crossed product, amenability of the ...quasi-lattice ordered group and nuclearity of the underlying $C^*$-algebra. KCI Citation Count: 0
The 2,3-dihydrobenzofuran scaffold is widely found in natural products and biologically active compounds. Herein, dearomatizing 2,3-fluoroaroylation of benzofurans with aroyl fluorides as ...bifunctional reagents to access 2,3-difunctionalized dihydrobenzofurans is reported. The reaction that occurs by cooperative NHC/photoredox catalysis provides 3-aroyl-2-fluoro-2,3-dihydrobenzofurans with moderate to good yield and high diastereoselectivity. Cascades proceed via radical/radical cross-coupling of a benzofuran radical cation generated in the photoredox catalysis cycle with a neutral ketyl radical formed through the NHC catalysis cycle. The redox-neutral transformation exhibits broad substrate scope and high functional group compatibility. With anhydrides as bifunctional reagents, dearomatizing aroyloxyacylation of benzofurans is achieved and the strategy can also be applied to N-acylated indoles to afford 3-aroyl-2-fluoro-dihydroindoles.
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