ACS Combinatorial Science最新文献

A unique class of tridentate diaryltriazine ligand-containing gold(III) complexes with thermally activated delayed fluorescence (TADF) and/or thermally stimulated delayed phosphorescence (TSDP) properties has been designed and synthesized. With a simple structural modification on the coordination of carbazole moiety in the monodentate ligand, a large spectral shift of ∼160 nm (ca. 4900 cm^–1) spanning from sky blue to red emissions has been demonstrated in solid-state thin films. Three-state or four-state models have been employed in fitting the emission lifetimes of the gold(III) complexes at various temperatures. The findings clearly indicate the presence of three emitting states, S₁, T₁, and T₁′, suggesting the coexistence of TADF, phosphorescence, and TSDP. Notably, a minor structural change in the donor moiety between phenylcarbazolyl and diphenylaminoaryl has been demonstrated to turn on/off the TSDP, resulting in TADF-TSDP-phosphorescence or TADF-phosphorescence emitters. The TADF and/or TSDP properties have also been supported by temperature-dependent ultrafast transient absorption studies, with the direct observation of reverse intersystem crossing (RISC) and reverse internal conversion (RIC) and the determination of the activation parameters and excited state dynamics. Solution-processed and vacuum-deposited organic light-emitting devices (OLEDs) have been prepared, in which sky blue emitting devices based on 5 exhibit an operational lifetime LT₇₀ ∼ 5 times longer than the previously reported sky blue emitting analogue that shows only TSDP property. These results have provided valuable insights into the manipulation of the excited states via rational molecular design toward the realization of gold(III)-based TSDP and/or TADF materials with multiple radiative decay pathways that show enhanced radiative decay rate constants (k_r) for practical OLED applications.

The chemistry of the Meisenheimer complexes is of fundamental interest in organic chemistry. While the nitro group has been extensively employed to facilitate the formation and stabilization of Meisenheimer complexes, the analogous application of more user-friendly ester groups has remained an unexplored frontier. Herein, we report ester-stabilized Meisenheimer complexes, which have remarkable air-, moisture-, and thermo-stability. Moreover, the isolable and well-defined Meisenheimer intermediates exhibit divergent reactivity for dearomatization reactions, including modular 1,4-additions, dearomative (2 + 3) cycloadditions, and even higher-order (4 + n) cycloadditions. These methodologies enabled rapid access to complicated cyclohexane derivatives with multiple all-carbon quaternary centers and interesting structure topologies.

Transition metal carbenes have emerged as versatile intermediates for various types of alkylations. While reactions of metal carbene species with alkenes have been extensively studied, most examples focus on cyclopropanation and allylic C–H insertion. Herein, we present the first example of a catalytic strategy for the carbene-involved regioselective remote C–H alkylation of internal olefins by synergistically combining two iridium-mediated reactivities of olefin chain walking and carbenoid migratory insertion. The present method, utilizing sulfoxonium ylides as a bench-stable robust carbene precursor, was found to be effective for a series of olefins tethered with alkyl chains, heteroatom substituents, and complex biorelevant moieties. Combined experimental and computational studies revealed that reversible iridium hydride-mediated olefin chain walking proceeds to lead to a terminal alkyl-Ir intermediate, which then forms a carbenoid species for the final migratory insertion, resulting in regioselective terminal-alkylated products.

The unstable lithium (Li)/electrolyte interface, causing inferior cycling efficiency and unrestrained dendrite growth, has severely hampered the practical deployment of Li metal batteries (LMBs), particularly in carbonate electrolytes. Herein, we present a robust approach capitalizing on a dynamic supramolecular elastomer (DSE) interface layer, which is capable of being reduced with Li metal to spontaneously form strong Li⁺ ion-dipole interaction, thereby enhancing interfacial stability in carbonate electrolytes. The soft phase in the DSE structure enables fast Li⁺ transport via loosely coordinated Li⁺–O interaction, while the hard phase, rich in electronegative lithiophilic sites, drives the generation of fast-ion-conducting solid electrolyte interface components, including Li₃N and Li₂S. Furthermore, the dynamically resilient DSE network composed of soft and hard phases protects Li anodes from electrolyte corrosion and accommodates volume changes during cycling. All features of the DSE layer synergistically facilitate uniform Li⁺ deposition and suppress Li dendrite propagation, ensuring a stable and dendrite-free Li anode. Consequently, the symmetric Li||Li cell incorporating the DSE layer achieves cycling stability exceeding 6000 h under 1 mA cm^–2 and 1 mA h cm^–2 conditions. Furthermore, full cell pairing DSE/Li anode with LiFePO₄ (LFP) or high-voltage LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cathodes exhibits high-efficiency Li deposition and cycling stability, even under constrained conditions of limited Li (40 μm) and ultrahigh loading NMC811 cathode (21.5 mg cm^–2). This study underscores the effectiveness of the ion-dipole interaction-enabled DSE network in developing stable, high-energy-density LMBs.

New methods for the enantioselective synthesis of N-alkylated indoles and their derivatives are of great interest because indoles are pivotal structural elements in biologically active molecules and natural products. They are also versatile intermediates in organic synthesis. Among well-established asymmetric hydroamination methods, the asymmetric hydroamination with indole-based substrates is a formidable challenge. This observation is likely due to the reduced nucleophilicity of the indole nitrogen. Herein, a unique nickel-catalyzed enantio- and branched-selective hydroamination of 2-azadienes with indoles and structurally related N-heterocycles is reported for the generation of enantioenriched N,N-aminals. Salient features of this reaction include good yields, mild reaction conditions, high enantioselectivities, and broad substrate scope (60 examples, up to 96% yield and 99% ee). The significance of this approach with indoles and other N-heterocycles is demonstrated through structural modification of natural products and drug molecules and the preparation of enantioenriched N-alkylated indole core structures. Mechanistic studies reveal that olefin insertion into a Ni–H bond in the hydroamination is the enantio-determining step and oxidative addition of the N–H bond may be the turnover-limiting step.

Experimental and theoretical techniques were used to investigate the mechanism of pyridine C–H activation by diarylboryl/bis(phosphine) PBP pincer complexes of Ir. The critical intermediate (PBP)IrCO (4) contains a three-coordinate, Ir-bound boron that retains Lewis acidity in the perpendicular direction. Coordination of pyridine to this boron center in 4 leads to fast insertion of Ir into the 2-CH bond of pyridine, providing a different topology of direction than the conventional directed C–H activation where both the directing group coordination and C–H activation happen at the same metal center. Beyond this critical sequence, the system possesses significant complexity in terms of possible isomers and pathways, which have been thoroughly explored. Kinetic and thermodynamic preferences for the activation of differently substituted pyridines were also investigated. In experimental work, the key intermediate 4 is accessed via elimination of benzene from a phenyl/hydride containing precursor (PB^PhP)IrHCO (3). Density functional theory (DFT) investigations of the mechanism of benzene loss from 3 revealed the possibility of a genuinely new type of mechanism, whereby the Ph–H bond is made in a concerted process that is best described as C–H reductive elimination from boron, assisted by the transition metal (TMARE). For Ir, this pathway was predicted to be competitive with the more conventional pathways involving C–H reductive elimination from Ir, but still higher in energy barrier. However, for the Rh analog 3-Rh, TMARE was calculated to be the preferred pathway for benzene loss and this prediction was experimentally corroborated through the study of reaction rates and the kinetic isotope effect.

Cyclopropane-based high-energy fuels possess high intramolecular energy and density, and their precise synthesis is a critical challenge. However, owing to the highest strain in the cyclopropane structure (compared to other four- or five-membered rings, etc.), metal-carbene intermediates form with difficulty, resulting in poor catalytic selectivity for its synthesis. Herein, through rational design of π−π stacking between the Pd organic complex and graphene, we report a single-site Pd catalyst for precise synthesis of multicyclopropane-based high-energy fuels. It is discovered that π−π stacking enhanced the electrophilicity of Pd through a weak metal−support interaction, thus promoting the formation of Pd═C carbene active intermediates. Meanwhile, the adsorption between the active centers and intermediates was enhanced via π−π stacking. These two respects led to almost twice selectivity for cyclopropanation reaction up to 80.5% as that without π−π stacking. This work provides an effective strategy of π−π noncovalent interactions for regulating C−C coupling reaction selectivity.

Improving the use of platinum in propane dehydrogenation catalysts is a crucial aspect to increasing the efficiency and sustainability of propylene production. A known and practiced strategy involves incorporating more abundant metals in supported platinum catalysts, increasing its activity and stability while decreasing the overall loading. Here, using colloidal techniques to control the size and composition of the active phase, we show that Pt/Cu alloy nanoparticles supported on alumina (Pt/Cu/Al₂O₃) displayed elevated rates for propane dehydrogenation at low temperature compared to a monometallic Pt/Al₂O₃ catalyst. We demonstrate that the enhanced catalytic activity is correlated with a higher surface Cu content and formation of a Pt-rich core and Cu-rich shell that isolates Pt sites and increases their intrinsic activity. However, rates declined on stream because of dynamic metal diffusion processes that led to a more uniform alloy structure. This transformation was only partially inhibited by adding excess hydrogen to the feed stream. Instead, cobalt was introduced to provide trimetallic Pt/Cu/Co catalysts with stabilized surface structure and stable activity and higher rates than the original Pt/Cu system. The structure–activity relationship insights in this work offer improved knowledge of propane dehydrogenation catalyst development featuring reduced Pt loadings and notable thermal stability for propylene production.

Increasing the interface area between organic semiconductor photocatalysts and electrolyte by fabricating nanoparticles has proven to be an effective strategy to increase photocatalytic hydrogen production activity. However, it remains unclear if increasing the internal interface by the introduction of porosity has as clear benefits for activity. To better inform future photocatalyst design, a series of polymers of intrinsic microporosity (PIMs) with the same conjugated backbone were synthesized as a platform to independently modulate the variables of porosity and relative hydrophilicity through the use of hydrophilic alcohol moieties protected by silyl ether protecting groups. When tested in the presence of ascorbic acid and photodeposited Pt, a strong correlation between the wettable porosity and photocatalytic activity was found, with the more wettable analogue of two polymers of almost the same surface area delivering 7.3 times greater activity, while controlling for other variables. Transient absorption spectroscopic (TAS) investigation showed efficient intrinsic charge generation within 10 ps in two of the porous polymers, even without the presence of ascorbic acid or Pt. Detectable hole polarons were found to be immediately extracted by added ascorbic acid, suggesting the generation of reactive charges at regions readily accessible to electrolyte in the porous structures. This study directs organic semiconductor photocatalysts design toward more hydrophilic functionality for addressing exciton and charge recombination bottlenecks and clearly demonstrates the advantages of wettable porosity as a design principle.