Room-temperature phosphorescence of a supercooled liquid: kinetic stabilisation by desymmetrisation

Achieving organic room-temperature phosphorescence (RTP) in a solvent-free liquid state is a challenging task because the liquid state provides a less rigid environment than the crystal. Here, we report that an unsymmetrical heteroaromatic 1,2-diketone forms an organic RTP liquid. This diketone exists as a kinetically stable supercooled liquid, which resists crystallisation even under pricking or shearing stresses, and remains as a liquid for several months. The unsymmetrical diketone core is flexible, with eight distinct conformers possible, which prevents nucleation and growth for the liquid–solid transition. Interestingly, the thermodynamically stable crystalline solid-state was non-emissive. Thus, the RTP of the diketone was found to be liquiefaction-induced. Single-crystal X-ray structure analysis revealed that the diminished RTP of the crystal is due to insufficient intermolecular interactions and restricted access to an emissive conformer. Our work demonstrates that flexible unsymmetrical skeletons are promising motifs for bistable liquid–solid molecular systems, which are useful for the further development of stimuli-responsive materials that use phase transitions.

Metal-free, single-component, unsymmetrical 1,2-diketone exhibits liquefaction-induced room-temperature phosphorescence. Desymmetrisation provides the supercooled liquid with notable kinetic stability and phase-dependent phosphorescence properties.     

Three-component carboacylation of alkenes via cooperative nickelaphotoredox catalysis

Various commercially available acyl chlorides, aldehydes, and alkanes were exploited for versatile three-component 1,2-carboacylations of alkenes to forge two vicinal C–C bonds through the cooperative action of nickel and sodium decatungstate catalysis. A wealth of ketones with high levels of structural complexity was rapidly obtained via direct functionalization of C(sp²)/C(sp³)–H bonds in a modular manner. Furthermore, a regioselective late-stage modification of natural products showcased the practical utility of the strategy, generally featuring high resource economy and ample substrate scope.

Various commercially available acyl chlorides, aldehydes, and alkanes were exploited for versatile three-component 1,2-carboacylations of alkenes to forge two vicinal C–C bonds through the cooperative action of nickel and sodium decatungstate catalysis.     

C2-ketonylation of carbohydrates via excited-state palladium-catalyzed 1,2-spin-center shift

C2-ketonyl-2-deoxysugars, sugars with the C2-hydroxyl group replaced by a ketone side chain, are important carbohydrate mimetics in glycobiology and drug discovery studies; however, their preparation remains a vital challenge in organic synthesis. Here we report the first direct strategy to synthesize this class of glycomimetics from readily available 1-bromosugars and silyl enol ethers via an excited-state palladium-catalyzed 1,2-spin-center shift (SCS) process. This step-economic reaction features broad substrate scope, has a high functional group tolerance, and can be used in late-stage functionalization of natural product- and drug-glycoconjugates. Preliminary experimental and computational mechanistic studies suggested a non-chain radical mechanism involving photoexcited palladium species, a 1,2-SCS process, and a radical Mizoroki–Heck reaction.

The excited-state palladium-catalyzed 1,2-spin-center shift process streamlines the synthesis of C2-ketonyl sugars. This step-economic reaction has a broad scope and allows late-stage functionalization of natural product- and drug-glycoconjugates.     

Buffering the local pH via single-atomic Mn–N auxiliary sites to boost CO2 electroreduction

Electrocatalytic CO₂ reduction driven by renewable energy has become a promising approach to rebalance the carbon cycle. Atomically dispersed transition metals anchored on N-doped carbon supports (M-N-C) have been considered as the most attractive catalysts to catalyze CO₂ to CO. However, the sluggish kinetics of M-N-C limits the large-scale application of this type of catalyst. Here, it is found that the introduction of single atomic Mn–N auxiliary sites could effectively buffer the locally generated OH⁻ on the catalytic interface of the single-atomic Ni–N–C sites, thus accelerating proton-coupled electron transfer (PCET) steps to enhance the CO₂ electroreduction to CO. The constructed diatomic Ni/Mn–N–C catalysts show a CO faradaic efficiency of 96.6% and partial CO current density of 13.3 mA cm⁻² at −0.76 V vs. RHE, outperforming that of monometallic single-atomic Ni–N–C or Mn–N–C counterparts. The results suggest that constructing synergistic catalytic sites to regulate the surface local microenvironment might be an attractive strategy for boosting CO₂ electroreduction to value-added products.

An effective strategy is developed to regulate the local microenvironment of single atomic Ni–N–C sites for accelerating CO₂ to CO conversion. The Ni/Mn–N–C catalysts shows a CO faradaic efficiency of 96.6% due to the accelerated reaction kinetics.     

Annulative coupling of vinylboronic esters: aryne-triggered 1,2-metallate rearrangement

A stereoselective annulative coupling of a vinylboronic ester ate-complex with arynes producing cyclic borinic esters has been developed. An annulation reaction that proceeded through the formation of two C–C bonds and a C–B bond was realized by exploiting a 1,2-metallate rearrangement of boronate triggered by the addition of a vinyl group to the strained triple bond of an aryne. The generated aryl anion would then cyclize to a boron atom to complete the annulation cascade. The annulated borinic ester could be converted to boronic acids and their derivatives by oxidation, halogenation, and cross-coupling. Particularly, halogenation and Suzuki–Miyaura coupling proceeded in a site-selective fashion and produced highly substituted alkylboronic acid derivatives.

A stereoselective annulative coupling of a vinylboronic ester ate-complex with arynes producing cyclic borinic esters has been developed.     

Directed,nickel-catalyzed 1,2-alkylsulfenylation of alkenyl carbonyl compounds

We report a regioselective, nickel-catalyzed syn-1,2-carbosulfenylation of non-conjugated alkenyl carbonyl compounds with alkyl/arylzinc nucleophiles and tailored N–S electrophiles. This method allows the simultaneous installation of a variety of C(sp³) and S(Ar) (or Se(Ar)) groups onto unactivated alkenes, which complements previously developed 1,2-carbosulfenylation methodology in which only C(sp²) nucleophiles are compatible. A bidentate directing auxiliary controls regioselectivity, promotes high syn-stereoselectivity with a variety of E- and Z-internal alkenes, and enables the use of an array of electrophilic sulfenyl (and seleno) electrophiles. Among compatible electrophiles, those with N-alkyl-benzamide leaving groups were found to be especially effective, as determined through comprehensive structure–reactivity mapping.

Electrophilic sulfenylating agents enable the three-component nickel-catalyzed 1,2-alkylsulfenylation of alkenyl carbonyl compounds with high regio- and diastereoselectivity.     

Coordination modulated on-off switching of flexibility in a metal–organic framework

Stimuli-responsive metal–organic frameworks (MOFs) exhibit dynamic, and typically reversible, structural changes upon exposure to external stimuli. This process often induces drastic changes in their adsorption properties. Herein, we present a stimuli-responsive MOF, 1·[CuCl], that shows temperature dependent switching from a rigid to flexible phase. This conversion is associated with a dramatic reversible change in the gas adsorption properties, from Type-I to S-shaped isotherms. The structural transition is facilitated by a novel mechanism that involves both a change in coordination number (3 to 2) and geometry (trigonal planar to linear) of the post-synthetically added Cu(i) ion. This process serves to ‘unlock’ the framework rigidity imposed by metal chelation of the bis-pyrazolyl groups and realises the intrinsic flexibility of the organic link.

Stimuli-responsive metal–organic frameworks (MOFs) exhibit dynamic structural changes upon exposure to external stimuli. Here the coordination geometry of a post-synthetically added metal ion drastically changes the adsorption properties.     

Organocatalytic asymmetric azidation of sulfoxonium ylides: mild synthesis of enantioenriched α-azido ketones bearing a labile tertiary stereocenter

Disclosed here is a catalytic asymmetric azidation reaction for the efficient synthesis of α-azido ketones bearing a labile tertiary stereocenter. With a superb chiral squaramide catalyst, a mild asymmetric formal H–N₃ insertion of α-carbonyl sulfoxonium ylides proceeded with excellent efficiency and enantioselectivity. This organocatalytic process not only complements the previous α-azidation approaches for the formation of quaternary stereocenters and mostly for 1,3-dicarbonyl compounds, but also has advantages over the well-known metal-catalyzed asymmetric carbene insertion chemistry using α-diazocarbonyl compounds. Detailed mechanistic studies via control reactions and NMR studies provided important insights into the reaction pathway, which features reversible protonation and dynamic kinetic resolution. The curiosity in mechanism also led to the development of a simplified alternative protocol with a cheaper HN₃ source.

An organocatalytic asymmetric H–N₃ insertion of α-carbonyl sulfoxonium ylides has been developed, providing efficient access to α-azido ketones bearing labile tertiary stereocenters and complementing the metal carbene insertion chemistry.     

Timing matters: pre-assembly versus post-assembly functionalization of a polyoxovanadate–organic cuboid

The pre-assembly and post-assembly approaches in the functionalization of a polyoxovanadate–organic cuboid, [{V₆S}₈(QPTC)₈{V₃}₂]¹⁰⁻, are discussed. We have shown that the two pathways have led to distinctly different systems, with either an expanded or contracted interior void space, when phenylphosphonate is introduced at different stages of the self-assembly. One leaves the cuboid framework largely intact, whereas the other results in a compact, twisted cuboid. Kinetic factors will have to be considered in the equilibrium of these complex processes. Furthermore, the exceptional stability of these polyoxometalate–organic systems facilitates mass spectrometric characterization, which confirms the composition of the complexes and also indicates that the methoxide groups on the vanadium cluster nodes are labile. The results will help deepen the mechanistic understanding of the formation mechanisms of polyoxovanadate-based metal–organic cages and other functionalized polyoxovanadate clusters in general.

Introducing functional groups at different stages in the assembly of a metal–organic cage has led to two distinct, endo-functionalized products, a result attributed to kinetic trapping in a process generally operating under thermodynamic control.     

The development of a comprehensive toolbox based on multi-level,high-throughput screening of MOFs for CO/N2 separations

The separation of CO/N₂ mixtures is a challenging problem in the petrochemical sector due to the very similar physical properties of these two molecules, such as size, molecular weight and boiling point. To solve this and other challenging gas separations, one requires a holistic approach. The complexity of a screening exercise for adsorption-based separations arises from the multitude of existing porous materials, including metal–organic frameworks. Besides, the multivariate nature of the performance criteria that needs to be considered when designing an optimal adsorbent and a separation process – i.e. an optimal material requires fulfillment of several criteria simultaneously – makes the screening challenging. To address this, we have developed a multi-scale approach combining high-throughput molecular simulation screening, data mining and advanced visualization, as well as process system modelling, backed up by experimental validation. We have applied our recent advances in the engineering of porous materials'' morphology to develop advanced monolithic structures. These conformed, shaped monoliths can be used readily in industrial applications, bringing a valuable strategy for the development of advanced materials. This toolbox is flexible enough to be applied to multiple adsorption-based gas separation applications.

The separation of challenging mixtures through adsorption is a multidimensional problem that requires a holistic approach. Our toolbox combines experiments, molecular and process simulations with data visualization to find optimal, porous materials.     

Enantioselective palladaelectro-catalyzed C–H olefinations and allylations for N–C axial chirality

Enantioselective palladaelectro-catalyzed C–H alkenylations and allylations were achieved with easily-accessible amino acids as transient directing groups. This strategy provided access to highly enantiomerically-enriched N–C axially chiral scaffolds under exceedingly mild conditions. The synthetic utility of our strategy was demonstrated by a variety of alkenes, while the versatility of our approach was reflected by atroposelective C–H allylations. Computational studies provided insights into a facile C–H activation by a seven-membered palladacycle.

Enantioselective palladaelectro-catalyzed C–H alkenylations and allylations were achieved by the means of an easily-accessible amino acid for the synthesis of N–C axially chiral indole biaryls.     

Fluorine in metal-catalyzed asymmetric transformations: the lightest halogen causing a massive effect

This review aims at providing an overview of the most significant applications of fluorine-containing ligands reported in the literature starting from 2001 until mid-2021. The ligands are classified according to the nature of the donor atoms involved. This review highlights both metal–ligand interactions and the structure–reactivity relationships resulting from the presence of the fluorine atom or fluorine-containing substituents on chiral catalysts.

This review provides an overview of the most significant applications of fluorine-tagged ligands, including metal–ligand interactions, structure–reactivity relationships, and transition state models, in metal-catalyzed asymmetric transformations.     

Sulfur stereogenic centers in transition-metal-catalyzed asymmetric C–H functionalization: generation and utilization

Transition-metal-catalyzed enantioselective C–H functionalization has emerged as a powerful tool for the synthesis of enantioenriched compounds in chemical and pharmaceutical industries. Sulfur-based functionalities are ubiquitous in many of the biologically active compounds, medicinal agents, functional materials, chiral auxiliaries and ligands. This perspective highlights recent advances in sulfur functional group enabled transition-metal-catalyzed enantioselective C–H functionalization for the construction of sulfur stereogenic centers, as well as the utilization of chiral sulfoxides to realize stereoselective C–H functionalization.

This perspective highlights sulfur functional groups enabled enantioselective C–H functionalization for the construction of sulfur stereogenic centers, and the utilization of chiral sulfoxide to realize stereoselective C–H functionalization.     

Oxygen harvesting from carbon dioxide: simultaneous epoxidation and CO formation

Due to increasing concentrations in the atmosphere, carbon dioxide has, in recent times, been targeted for utilisation (Carbon Capture Utilisation and Storage, CCUS). In particular, the production of CO from CO₂ has been an area of intense interest, particularly since the CO can be utilized in Fischer–Tropsch synthesis. Herein we report that CO₂ can also be used as a source of atomic oxygen that is efficiently harvested and used as a waste-free terminal oxidant for the oxidation of alkenes to epoxides. Simultaneously, the process yields CO. Utilization of the atomic oxygen does not only generate a valuable product, but also prevents the recombination of O and CO, thus increasing the yield of CO for possible application in the synthesis of higher-order hydrocarbons.

Selective formation of atomic oxygen to form epoxides in a waste free process is reported. Simultaneously generating carbon monoxide from carbon dioxide for further use.     

Carbon–carbon bond activation by B(OMe)3/B2pin2-mediated fragmentation borylation

Selective carbon–carbon bond activation is important in chemical industry and fundamental organic synthesis, but remains challenging. In this study, non-polar unstrained Csp²–Csp³ and Csp²–Csp² bond activation was achieved by B(OMe)₃/B₂pin₂-mediated fragmentation borylation. Various indole derivatives underwent C2-regioselective C–C bond activation to afford two C–B bonds under transition-metal-free conditions. Preliminary mechanistic investigations suggested that C–B bond formation and C–C bond cleavage probably occurred in a concerted process. This new reaction mode will stimulate the development of reactions based on inert C–C bond activation.

Non-polar unstrained Csp²–Csp³ and Csp²–Csp² bond activation was achieved via B(OMe)₃/B₂pin₂-mediated fragmentation borylation, in which C–C bond activation occurred regioselectively at the C2-position in various substituted indoles.     

Visible-light-induced transition metal and photosensitizer free decarbonylative addition of amino-arylaldehydes to ketones

The decarbonylative-coupling reaction is generally promoted by transition metals (via organometallic complexes) or peroxides (via radical intermediates), often at high temperatures to facilitate the CO release. Herein, a visible-light-induced, transition metal and external photosensitizer free decarbonylative addition of benzaldehydes to ketones/aldehydes at room temperature is reported. Tertiary/secondary alcohols were obtained in moderate to excellent yields promoted by using CsF under mild conditions. The detailed mechanistic investigation showed that the reaction proceeded through photoexcitation–decarbonylation of the aldehyde to generate an aromatic anion, followed by its addition to ketones/aldehydes. The reaction mechanism was verified by the density functional theory (DFT) calculations.

A visible-light-induced, transition-metal and external photosensitizer free decarbonylative addition of benzaldehydes to ketones/aldehydes via anion intermediates at room temperature is developed.     

Color-tunable persistent luminescence in 1D zinc–organic halide microcrystals for single-component white light and temperature-gating optical waveguides

Information security of photonic communications has become an important societal issue and can be greatly improved when photonic signals are propagated through active waveguides with tunable wavelengths in different time and space domains. Moreover, the development of active waveguides that can work efficiently at extreme temperatures is highly desirable but remains a challenge. Herein, we report new types of low-dimensional Zn(ii)–organic halide microcrystals with fluorescence and room-temperature phosphorescence (RTP) dual emission for use as 1D color-tunable active waveguides. Benefiting from strong intermolecular interactions (i.e., hydrogen bonds and π–π interactions), these robust waveguide systems exhibit colorful photonic signals and structural stability at a wide range of extreme simulated temperatures (>300 K), that covers natural conditions on Earth, Mars, and the Moon. Both experimental and theoretical studies demonstrate that the molecular self-assembly can regulate the singlet and triplet excitons to allow thermally assisted spectral separation of fluorescence and RTP, in combination with the single-component standard white-light emission. Therefore, this work demonstrates the first use of metal–organic halide microcrystals as temperature-gating active waveguides with promising implications for high-security information communications and high-resolution micro/nanophotonics.

1D zinc–organic halide microcrystals exhibiting thermally assisted spectral separation of fluorescence and phosphorescence could be used as single-component standard white-light and temperature-gating active waveguides.     

Cobalt-catalyzed intramolecular decarbonylative coupling of acylindoles and diarylketones through the cleavage of C–C bonds

We report here cobalt–N-heterocyclic carbene catalytic systems for the intramolecular decarbonylative coupling through the chelation-assisted C–C bond cleavage of acylindoles and diarylketones. The reaction tolerates a wide range of functional groups such as alkyl, aryl, and heteroaryl groups, giving the decarbonylative products in moderate to excellent yields. This transformation involves the cleavage of two C–C bonds and formation of a new C–C bond without the use of noble metals, thus reinforcing the potential application of decarbonylation as an effective tool for C–C bond formation.

A method for cobalt–N-heterocyclic carbene catalytic systems for the intramolecular decarbonylative coupling of ketones was achieved.     

Copper-catalyzed radical cascade reaction of simple cyclobutanes: synthesis of highly functionalized cyclobutene derivatives

Cyclobutenes as versatile and highly valuable synthons have been widely applied in synthesis. Although various methods for their synthesis have been well established, new strategies for the construction of the cyclobutene skeleton from simple substrates are still highly desirable. Starting from simple cyclobutanes, the construction of the cyclobutene skeleton especially introducing multiple functional groups simultaneously had never been achieved. Here, we developed a novel radical cascade strategy for the synthesis of highly functionalized cyclobutenes directly from cyclobutanes involving rare cleavage of four or five C–H bonds and formation of two C–N/C–S or three C–Br bonds. With copper as catalyst and N-fluorobenzenesulfonimide (NFSI) as oxidant, a wide range of diaminated, disulfonylated and tribrominated cyclobutene derivatives were efficiently synthesized.

A novel radical cascade strategy for the synthesis of highly functionalized cyclobutenes directly from cyclobutanes involving rare four or five C–H bonds cleavage and two C–N/C–S or three C–Br bonds formation has been successfully developed.     

Zn(ii)-Coordination-driven self-assembled nanoagents for multimodal imaging-guided photothermal/gene synergistic therapy

Synergistic photothermal therapy (PTT) with gene therapy (GT) has drawn emerging interest in the improvement of cancer therapeutic efficiency, while the co-delivery of photothermal agents (PTAs) and therapeutic genes by an integrated nanoplatform, with controllability and biodegradability, is still challenging and urgently desired. Herein, a multi-functional metal–organic framework (MOF) based PTT–GT platform (siRNA@PT-ZIF-8) was developed, which was constructed with siRNA, a near-infrared (NIR) responsive organic dye IR780 derivative (IR780-1), and 2-methylimidazole (2-MIM) by a facile one-pot self-assembly method. This “all-in-one” system of siRNA@PT-ZIF-8 enabled not only photothermal/photoacoustic/fluorescence multimodal imaging but also tumor microenvironment responsiveness for specific and on-demand release of therapeutic cargos, overcoming the inherent limitations of free gene or organic PTA molecules (e.g., short blood circulation half-life and weak stability) in conventional PTT and GT. This nanoplatform provides an efficient and safe strategy for cancer theranostics, and the one-step assembly strategy favors personalized formulation design for diverse demands in cancer management.

siRNA@PT-ZIF-8 was prepared by one pot self-assembly for tri-mode imaging guided mild-temperature photothermal synergetic gene therapy.