Atroposelective Synthesis of Biaryl N-Oxides via Cu-Catalyzed De Novo Heteroaromatic N-Oxide Ring Formation.

Heteroaromatic N-oxides, renowned for their highly polar N─O bond and robust structure, exhibit significant bioactivities and have played a pivotal role in various drug development projects since the discovery of Minoxidil. Moreover, heteroaromatic N-oxides, featuring axially chiral biaryl frameworks, are indispensable as Lewis base catalysts and ligands in organic synthesis. Despite their importance, synthesizing these chiral compounds is challenging, necessitating chiral starting materials or resolution processes. Catalytic strategies rely on the functionalization of heteroaromatic N-oxide compounds, leading to products with a relatively limited skeletal diversity. This study introduces a Cu-catalyzed atroposelective method for synthesizing biaryl N-oxides via de novo heteroaromatic N-oxide ring formation. This mild and efficient approach achieves excellent stereoselectivities (up to 99:1 er), enabling the production of a wide array of N-oxides with novel heteroaromatic scaffolds. The axially chiral N-oxide product 3f demonstrates high stereoselectivity and recyclability as a Lewis base catalyst. Additionally, product 3e exhibits promising therapeutic efficacy against triple-negative breast cancer, with IC50 values of 4.8 and 5.2 µm in MDA-MB-231 and MDA-MB-468 cells, respectively. This research not only advances the synthesis of challenging chiral heteroaromatic N-oxides but also encourages further exploration of N-oxide entities in the discovery of bioactive small molecules.

Deoxygenative Geminal Silylboration of Amides Using Silylboronates: Synthesis and Use of α-Boryl-α-Silylalkylamines.

α-Silylalkylamines and α-borylalkylamines are versatile synthetic intermediates and attractive scaffolds found in pharmaceutical drugs and agrochemicals. Despite great progress on synthetic methods for preparation of α-silylalkylamines or α-borylalkylamines, there are no general strategies for preparation of α-boryl-α-silylalkylamines and the reactivity has not been explored. Here we report deoxygenative geminal silylboration of amides using silylboronates in the presence of alkoxide base catalyst, producing α-boryl-α-silylalkylamines. The silicon and boron groups in α-boryl-α-silylalkylamines are found to be utilized to chemoselective transformations, such as protonation and alkylation. This protocol serves various α-silylalkylamines and α-borylalkylamines from readily available amides.

Cyclic Multi-Site Chelation for Efficient and Stable Inverted Perovskite Solar Cells.

Trap-assisted non-radiative recombination losses and moisture-induced degradation significantly impede the development of highly efficient and stable inverted (p-i-n) perovskite solar cells (PSCs), which require high-quality perovskite bulk. In this research, we mitigate these challenges by integrating thermally stable perovskite layers with Lewis base covalent organic frameworks (COFs). The ordered pore structure and surface binding groups of COFs facilitate cyclic, multi-site chelation with undercoordinated lead ions, enhancing the perovskite quality across both its bulk and grain boundaries. This process not only reduces defects but also promotes improved energy alignment through n-type doping at the surface. The inclusion of COF dopants in p-i-n devices achieves power conversion efficiencies (PCEs) of 25.64% (certified 24.94%) for a 0.0748-cm2 device and 23.49% for a 1-cm2 device. Remarkably, these devices retain 81% of their initial PCE after 978 hours of accelerated aging at 85˚C, demonstrating remarkable durability. Additionally, COF-doped devices demonstrate excellent stability under illumination and in moist conditions, even without encapsulation.

Application of Mesoporous Carbon-Based Highly Dispersed K-O2 Strong Lewis Base in the Efficient Catalysis of Methanol and Ethylene Carbonate.

As an atom-economical reaction, the direct generation of dimethyl carbonate (DMC) and ethylene glycol (EG) via the transesterification of CH3OH and ethylene carbonate (EC) has several promising applications, but the exploration of carriers with high specific surface areas and novel heterogeneous catalysts with more basic sites remains a long-standing research challenge. For this purpose, herein, a nitrogen-doped mesoporous carbon (NMC, 439 m2/g) based K-O2 Lewis base catalyst (K-O2/NMC) with well-dispersed strongly basic sites (2.23 mmol/g, 84.5%) was designed and synthesized. The compositions and structures of NMC and K-O2/NMC were comprehensively investigated via Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption, CO2 temperature-programmed desorption, and contact angle measurements. The optimal structural configuration and electron cloud distribution of the K-O2/NMC catalyst were simulated using first-principles calculations. The electron transfer predominantly manifested as a flow from K-O to C-O/C-N, and the interatomic interactions between each atom were enhanced and exhibited a tendency for a more stable state after redistribution. Furthermore, the adsorption energies (Eads) of CH3OH at K-O-O and K-O-N sites were -1.4185 eV and -1.3377 eV, respectively, and the O atom in CH3OH exhibited a stronger adsorption tendency for the K atom at the K-O-O site. Under the optimal conditions, the EC conversion, DMC/EG selectivity, and turnover number/frequency were 80.9%, 98.6%/99.4%, and 40.5/60.8 h-1, respectively, with a reaction rate constant (k) of 0.1005 mol/(L·min). Results showed that the heterogeneous K-O2/NMC catalyst prepared herein greatly reduced the reaction cost while guaranteeing the catalytic effect, and the whole system required a lower reaction temperature (65 °C), a shorter reaction time (40 min), and a lower catalyst amount (2.0 wt % of EC). Therefore, K-O2/NMC can be used as a catalyst in different transesterification reactions.

23.81%-Efficiency Flexible Inverted Perovskite Solar Cells with Enhanced Stability and Flexibility via a Lewis Base Passivation.

Lewis base molecules bind the undercoordinated lead atoms at interfaces and grain boundaries, leading to the high efficiency and stability of flexible perovskite solar cells (PSCs). We demonstrated a highly efficient, stable, and flexible PSC via interface passivation using a Lewis base of tri(o-tolyl)phosphine (TTP). It not only induced an intimate interface contact and a complete deposition of the perovskite thin layers on hole transport layers (HTLs) but also led to a better perovskite with a raised crystallinity, fewer defects, and a better morphology, including fewer gullies, high uniformity, and low roughness. Furthermore, the TTP treatments induced a good alignment of energy levels among the perovskites, HTLs, and C60. The resultant flexible inverted PSCs exhibited a high power conversion efficiency (PCE) of 23.81%, which is one of the highest PCEs among these flexible inverted PSCs. Moreover, the optimized flexible PSCs exhibited high storage stability, superior operation stability, and enhanced mechanical flexibility. This study presents an effective method to substantially raise the PCE, stability, and mechanical flexibility of the flexible inverted perovskite photovoltaics.

Enhancing the Efficiency and Stability of Inverted Formamidinium-Cesium Lead-Triiodide Perovskite Solar Cells through Lewis Base Pretreatment of Buried Interfaces.

Mixed components of formamidinium(FA) and cesium (Cs)-based perovskite solar cells are the most hopeful for commercialization owing to their excellent operational and phase stabilities, especially for devices with inverted structure. The nonradiative recombination of carriers can be effectively suppressed through interface optimization, therefore, the performance of devices can be improved. Notably, the buried interface emerges as critical aspects such as charge transport, charge recombination kinetics, and morphology of perovskite films. This study focuses on a straightforward yet effective approach to overcome buried interface challenges between organic polymers (poly(-triarylamine) (PTAA) and FACs-based perovskite films. The PTAA substrate is pretreated with a Lewis base known as 2-butynoic acid (BA) with a C═O functional group. First, it can be an interfacial buffering layer, harmonizing stress mismatch between the perovskite and PTAA layers, consequently optimizing crystallization and improving perovskite film quality. Second, Pb2+ defect can be passivated at the buried interface of the perovskite film through binding with the C═O group of the BA molecule. This dual-function strategy leads to a substantial enhancement in both photoelectric conversion efficiency (PCE) and stability of devices. Finally, the PCE of the device-modified buried interface with BA reaches an impressive 23.33%. Furthermore, unencapsulated devices with BA treatment maintain approximately 94% of their initial efficiency after aging at maximum power point tracking for 1000 h.

Design, Preparation, and Implementation of Axially Chiral Benzotetramisoles as Lewis Base Catalysts for Asymmetric Cycloadditions.

Developing novel catalysts with potent activity is of great importance in organocatalysis. In this study, we designed and prepared a new class of benzotetramisole Lewis base catalysts (AxBTM) that have both central and axial chirality. This unique feature of these catalysts results in a three-dimensional microenvironment with multi-layers of chirality. The performance of the developed catalysts was tested in a series of cycloaddition reactions. These included the AxBTM-catalyzed (2+2) cycloaddition between α-fluoro-α-aryl anhydride with imines or oxindoles, and the sequential gold/AxBTM-catalyzed (4+2) cycloaddition of enynamides with pentafluorophenyl esters. The interplay between axial and central chirality had a collaborative effect in regulating the stereochemistry in these cycloadditions, leading to high levels of stereoselectivity that would otherwise be challenging to achieve using conventional BTM catalysts. However, the (2+2) and (4+2) cycloadditions have different predilections for axial and central chirality combinations.

Base-Stabilized Gallium Sulfides and Selenides Supported by a Bis(oxazolinyl)(phenyl)methanide Ligand.

Gallylene supported by a bis(oxazolinyl)(phenyl)methanide (Boxm) ligand was synthesized and structurally characterized. The reaction of this gallylene with triphenylphosphine sulfide/selenide yielded dimeric gallium sulfide and selenide. These compounds could be converted to monomeric terminal sulfide and selenide by coordination of an external Lewis base such as an N-heterocyclic carbene (NHC or IMe4) and 4-dimethylaminopyridiene (DMAP). These doubly-base-stabilized gallium sulfide/selenide reacted with phenyl isocyanate to give the corresponding cycloadducts by releasing the Lewis base, indicating the formation of a single-base-stabilized gallium sulfide/selenide intermediate.

Modulating Nucleation and Crystal Growth of Tin Perovskite Films for Efficient Solar Cells.

The performance of tin halide perovskite solar cells (PSCs) has been severely limited by the rapid crystallization of tin perovskites, which usually leads to an undesirable film quality. In this work, we tackle this issue by regulating the nucleation and crystal growth of tin perovskite films using a small Lewis base additive, urea. The urea-SnI2 interaction facilitates the formation of larger and more uniform clusters, thus accelerating the nucleation process. Additionally, the crystal growth process is extended, resulting in a high-quality tin perovskite film with compact morphology, increased crystallinity, and reduced defects. Consequently, the efficiency of tin PSCs is significantly increased from 10.42% to 14.22%. This work highlights the importance of manipulating the nucleation and crystal growth of tin perovskites to realize efficient tin PSCs.

Vacuum-Processed Propylene Urea Additive: A Novel Approach for Controlling the Growth of CH3NH3PbI3 Crystals in All Vacuum-Processed Perovskite Solar Cells.

In this study, we present a novel method for controlling the growth of perovskite crystals in the vacuum thermal evaporation process by utilizing a vacuum-processable additive, propylene urea (PU). By coevaporation of perovskite precursors with PU to form the perovskite layer, PU, acting as a Lewis base additive, retards the direct reaction between the perovskite precursors. This facilitates a larger domain size and reduced defect density. Following the removal of the residual additive, the perovskite layer, exhibiting improved crystallinity, demonstrates reduced charge recombination, as confirmed by a time-resolved microwave conductivity analysis. Consequently, there is a notable enhancement in open-circuit voltage and power conversion efficiency, increasing from 1.05 to 1.15 V and from 17.17 to 18.31%, respectively. The incorporation of a vacuum-processable and removable Lewis base additive into the fabrication of vacuum-processed perovskite solar cells offers new avenues for optimizing these devices.

Synergy of machine learning and density functional theory calculations for predicting experimental Lewis base affinity and Lewis polybase binding atoms.

Investigation of Lewis acid-base interactions has been conducted by ab initio calculations and machine learning (ML) models. This study aims to resolve two critical tasks that have not been quantitatively investigated. First, ML models developed from density functional theory (DFT) calculations predict experimental BF3 affinity with Pearson correlation coefficients around 0.9 and mean absolute errors around 10 kJ mol-1. The ML models are trained by DFT-calculated BF3 affinity of more than 3000 adducts, with input features readily obtained by rdkit. Second, the ML models have the capability of predicting the relative strength of Lewis base binding atoms in Lewis polybases, which is either an extremely challenging task to conduct experimentally or a computationally expensive task for ab initio methods. The study demonstrates and solidifies the potential of combining DFT calculations and ML models to predict experimental properties, especially those that are scarce and impractical to empirically acquire.

Using the phospha-Michael reaction for making phosphonium phenolate zwitterions.

The reactions of 2,4-di-tert-butyl-6-(diphenylphosphino)phenol and various Michael acceptors (acrylonitrile, acrylamide, methyl vinyl ketone, several acrylates, methyl vinyl sulfone) yield the respective phosphonium phenolate zwitterions at room temperature. Nine different zwitterions were synthesized and fully characterized. Zwitterions with the poor Michael acceptors methyl methacrylate and methyl crotonate formed, but could not be isolated in pure form. The solid-state structures of two phosphonium phenolate molecules were determined by single-crystal X-ray crystallography. The bonding situation in the solid state together with NMR data suggests an important contribution of an ylidic resonance structure in these molecules. The phosphonium phenolates are characterized by UV-vis absorptions peaking around 360 nm and exhibit a negative solvatochromism. An analysis of the kinetics of the zwitterion formation was performed for three Michael acceptors (acrylonitrile, methyl acrylate, and acrylamide) in two different solvents (chloroform and methanol). The results revealed the proton transfer step necessary to stabilize the initially formed carbanion as the rate-determining step. A preorganization of the carbonyl bearing Michael acceptors allowed for reasonable fast direct proton transfer from the phenol in aprotic solvents. In contrast, acrylonitrile, not capable of forming a similar preorganization, is hardly reactive in chloroform solution, while in methanol the corresponding phosphonium phenolate is formed.

Enantioselective Synthesis of Planar-Chiral Sulfur-Containing Cyclophanes by Chiral Sulfide Catalyzed Electrophilic Sulfenylation of Arenes.

An efficient catalytic asymmetric electrophilic sulfenylation reaction for the synthesis of planar-chiral sulfur-containing cyclophanes has been developed for the first time. This was achieved by using a new Lewis base catalyst and a new ortho-trifluoromethyl-substituted sulfenylating reagent. Using the substrates with low rotational energy barrier, the transformation proceeded through a dynamic kinetic resolution, and the high rotational energy barrier of the substrates allowed the reaction to undergo a kinetic resolution process. Meanwhile, this transformation was compatible with a desymmetrization process when the symmetric substrates were used. Various planar-chiral sulfur-containing cyclophanes were readily obtained in moderate to excellent yields with moderate to excellent enantioselectivities (up to 97 % yield and 95 % ee). This approach was used to synthesize pharmaceutically relevant planar-chiral sulfur-containing molecules. Density functional theory calculations showed that π-π interactions between the sulfenyl group and the aromatic ring in the substrate play a crucial role in enantioinduction in this sulfenylation reaction.

Chiral 4-MeO-Pyridine (MOPY) Catalyst for Enantioselective Cyclopropanation: Attenuation of Lewis Basicity Leads to Improved Catalytic Efficiency.

The design of pyridine-derived organocatalysts aims at the increase of their Lewis basicity, however such an approach is not always efficient. For example, strongly Lewis basic DMAP is completely inefficient as catalyst in the cyclopropanation reaction. Herein we disclose an alternative approach that relies on attenuation of DMAP Lewis basicity. Specifically, the replacement of 4-dimethylamino substituent in DMAP for 4-MeO group delivered a highly efficient catalyst for cyclopropanation of electron-deficient olefins with α-bromoketones. Kinetic studies provide compelling evidence that the superior catalytic efficiency of 4-MeO pyridine (MOPY) is to be attributed to the favorable balance between Lewis basicity and leaving group ability. The use of chiral, enantiomerically pure MOPY catalyst has helped to achieve high enantioselectivities (up to 91 : 9 er) in the previously unreported pyridine-catalyzed cyclopropanation reaction.

An N-Heterocyclic Quinodimethane: A Strong Organic Lewis Base Exhibiting Diradical Reactivity.

We report the preparation of a new organic σ-donor with a C6H4-linker between an N-heterocyclic carbene (NHC) and an exocyclic methylidene group, which we term N-heterocyclic quinodimethane (NHQ). The aromatization of the C6H4-linker provides a decisive driving force for the reaction of the NHQ with an electrophile and renders the NHQ significantly more basic than analogous NHCs or N-heterocyclic olefins (NHOs), as shown by DFT computations and competition experiments. In solution, the NHQ undergoes an unprecedented dehydrogenative head-to-head dimerization by C-C coupling of the methylidene groups. DFT computations indicate that this reaction proceeds via an open-shell singlet pathway revealing the diradical character of the NHQ. The product of this dimerization can be described as conjugated N-heterocyclic bis-quinodimethane, which according to cyclic voltammetry is a strong organic reducing agent (E1/2=-1.71 V vs. Fc/Fc+) and exhibits a remarkable small singlet-triplet gap of ΔES→T=4.4 kcal mol-1.

Enantioselective Construction of Eight-Membered N-Heterocycles from Simple 1,3-Dienes via Pd(0) Lewis Base Catalysis.

We report herein an unprecedented enantioselective (4+4) cycloaddition of simple 1,3-dienes with azadienes for the construction of fused eight-membered N-heterocycles. In this transformation, the π-Lewis basic Pd(0) catalyst achieves activation of 1,3-dienes to induce nucleophilic addition to azadienes followed by ring cyclization via a selective terminal allylic substitution. Furthermore, highly efficient and diastereoselective derivatizations of the eight-membered rings provide a facile access to diverse enantiopure fused tetra- to hexacyclic compounds with potential application in medicinal chemistry.

Enhanced Performance and High Resistance to Efficiency Degradation of Blue Quantum-Dot Light-Emitting Diodes Using the Lewis Base Blended Hole-Transporting Layers.

The distinctive characteristics of blue quantum dots (QDs) such as their deep valence band and large bandgap give rise to an elevated hole injection barrier between the hole transport layers (HTLs) and the QD active layer. This results in an imbalance of carrier transport and injection across the device, leading to a degrading performance in QD light-emitting diodes (QLEDs). In this paper, high-efficiency and low-efficiency degradation blue CdSe/CdS/ZnS QLEDs were fabricated by using the Lewis base, 1,2-bis(diphenylphosphino)ethane (DPPE), blended with poly(9-vinylcarbazole) (PVK) (DPPE:PVK) as HTLs. The device performance of blue QLEDs can be finely adjusted by manipulating the blending ratio between DPPE and PVK. When 4 wt % DPPE was blended with PVK (4 wt % DPPE:PVK) as the HTL, the device achieved its optimal performance. Compared to the device with neat PVK as the HTL, the turn-on voltage of blue QLEDs with the 4 wt % DPPE:PVK HTL is reduced from 3.21 to 2.9 V. The maximum current efficiency (CE) and external quantum efficiency (EQE) of blue QLEDs increase from 2.92 cd A-1 and 5.89% in neat PVK to 5.75 cd A-1 and 11.75% for the 4 wt % DPPE:PVK HTL. Furthermore, the QLEDs incorporating DPPE:PVK HTLs exhibited exceptional resistance to efficiency degradation (EQE = 8.83%@L = 12,000 cd m-2 for 4 wt % DPPE:PVK as the HTL and EQE = 2.80%@L = 12,000 cd m-2 for neat PVK as the HTL). A more in-depth analysis reveals that enhanced device performance results from the chelating and bridging effect of the bidentate ligand Lewis base DPPE. These effects strengthen the binding of free metal ions in the blue QDs, reduce the charge barriers, enhance the contact between the HTLs and the QD active layer, and ultimately improve hole injection.

Synthesis of ß-Amino Acid Derivatives via Enantioselective Lewis Base Catalyzed N-Allylation of Halogenated Amides with Morita-Baylis-Hillman Carbonates.

Trifluoro- and trichloroacetamides serving as pronucleophiles undergo enantioselective Lewis base catalyzed N-allylation with Morita-Baylis-Hillman carbonates to produce enantioenriched ß-amino acid derivatives. The reactions proceed as a kinetic resolution to give the allylation products and the remaining carbonates in good yields and high enantioselectivity. The obtained products are amenable to diastereoselective derivatization to produce a library of spiro-isoxazoline lactams.

Enhancing the Efficiency and Stability of Perovskite Solar Cells through Defect Passivation and Controlled Crystal Growth Using Allantoin.

In this study, we present a robust approach that concurrently manages crystal growth and defect passivation within the perovskite layer through the introduction of a small molecule additive─allantoin. The precise regulation of crystal growth in the presence of allantoin yields perovskite films characterized by enhanced morphology, larger grain size, and improved grain orientation. Notably, the carbonyl and amino groups present in allantoin passivate under-coordinated Pb2+ and I- defects, respectively, through molecular interactions. Trap density in the perovskite layer is measured, and it is 0.39 × 1016 cm-3 for the allantoin-incorporated device and 0.83 × 1016 cm-3 for the pristine device. This reduction in defects leads to reduced trap-assisted nonradiative recombination, as confirmed by the photoluminescence, transient photo voltage, and impedance measurements. As a result, when these allantoin-incorporated perovskite films are implemented as the active layer in solar cells, a noteworthy efficiency enhancement to 20.63% is attained, surpassing the 18.04% of their pristine counterparts. Furthermore, devices with allantoin exhibit remarkable operational stability, maintaining 80% of their efficiency even after 500 h of continuous illumination, whereas the pristine device degraded to 65% of its initial efficiency in 400 h. Also, allantoin-incorporated devices exhibited exceptional stability against high humidity and elevated temperatures.

Amino Pyridine Iodine as an Additive for Defect-Passivated Perovskite Solar Cells.

Defect passivation of the perovskite surface and grain boundary (GBs) has become a widely adopted approach to reduce charge recombination. Research has demonstrated that functional groups with Lewis acid or base properties can successfully neutralize trap states and limit nonradiative recombination. Unlike traditional Lewis acid-base organic molecules that only bind to a single anionic or cationic defect, zwitterions can passivate both anionic and cationic defects simultaneously. In this work, zwitterions organic halide salt 1-amino pyridine iodine (AmPyI) is used as a perovskite for defect passivation. It is found that a pair of amino lone electrons in AmPyI can passivate defects surface and GBs through hydrogen bonding with perovskite, and the introduced I- can bind to uncoordinated Pb2+ while also controlling the surface morphology of the film and improving the crystallinity. In the presence of the AmPyI additive, we obtained about 1.24 µm of amplified perovskite grains and achieved an efficiency of 23.80% with minimal hysteresis.