Stereoconvergent Direct Ring Expansion of Cyclopropyl Ketones to Cyclopentanones

Recyclization of the ring-opening species of alkyl cyclopropyl ketones to cyclopentanones, which proceeds through an unfavored 5-endo-trig cyclization predicted by Baldwin’s rules, is elusive. Herein, as assisted by a strong aryl donor and the Thorpe–Ingold strain on a quaternary cyclopropyl center, stereoconvergent direct ring expansion of cyclopropyl ketones to cyclopentanones promoted by TfOH or BF3·Et2O is described, providing a modular construction of polysubstituted cyclopentanones from aldehydes, alkyl methyl ketones, and α-keto esters within three steps

Stereoconvergent Direct Ring Expansion of Cyclopropyl Ketones to Cyclopentanones

Recyclization of the ring-opening species of alkyl cyclopropyl ketones to cyclopentanones, which proceeds through an unfavored 5-endo-trig cyclization predicted by Baldwin’s rules, is elusive. Herein, as assisted by a strong aryl donor and the Thorpe–Ingold strain on a quaternary cyclopropyl center, stereoconvergent direct ring expansion of cyclopropyl ketones to cyclopentanones promoted by TfOH or BF3·Et2O is described, providing a modular construction of polysubstituted cyclopentanones from aldehydes, alkyl methyl ketones, and α-keto esters within three steps

Monovalent Nickel-Mediated Radical Formation: A Concerted Halogen-Atom Dissociation Pathway Determined by Electroanalytical Studies

The recent success of nickel catalysts in stereoconvergent cross-coupling and cross-electrophile coupling reactions partly stems from the ability of monovalent nickel species to activate C­(sp3) electrophiles and generate radical intermediates. This electroanalytical study of the commonly applied (bpy)Ni catalyst elucidates the mechanism of this critical step. Data rule out outer-sphere electron transfer and two-electron oxidative addition pathways. The linear free energy relationship between rates and the bond-dissociation free energies, the electronic and steric effects of the nickel complexes and the electrophiles, and DFT calculations support a variant of the halogen-atom abstraction pathway, the inner-sphere electron transfer concerted with halogen-atom dissociation. This mechanism accounts for the observed reactivity of different electrophiles in cross-coupling reactions and provides a mechanistic rationale for the chemoselectivity obtained in cross-electrophile coupling over homocoupling

<b>Origins of Catalyst-Controlled Selectivity in Ag-Catalyzed Regiodivergent C–H Amination</b>

Ag-catalyzed nitrene transfer (NT) converts C–H bonds into valuable C–N bonds. These reactions offer a promising strategy for catalyst-controlled regiodivergent functionalization of different types of reactive C–H bonds, as the regioselectivity is tunable by varying the steric and electronic environments around the Ag nitrene, as well as the identity of the nitrene precursors and the tether length. Therefore, a unified understanding of how these individual factors affect the regioselectivity is key to the rational design of highly selective and regiodivergent C–H amination reactions. Herein, we report a computational study of various Ag-catalyzed NT reactions that indicates a concerted H-atom transfer (HAT)/C–N bond formation mechanism. A detailed analysis was carried out on the effects of the C–H bond dissociation enthalpy (BDE), charge transfer, ligand–substrate steric repulsions, and transition state ring strain on the stability of the C–H insertion transition states with different Ag nitrene complexes. The ancillary ligands on the Ag and the nitrene precursor identity both affect transition state geometries to furnish differing sensitivities to the BDE, tether length, and electronic effects of the reactive C–H bonds. Based on our understanding of the dominant factors that control selectivity, we established a rational catalyst and precursor selection approach for regiodivergent amination of diverse C–H bonds. The computationally predicted regiodivergent amination of β- and γ-C–H bonds of aliphatic alcohol derivatives was validated by experimental studies

<b>Origins of Catalyst-Controlled Selectivity in Ag-Catalyzed Regiodivergent C–H Amination</b>

Ag-catalyzed nitrene transfer (NT) converts C–H bonds into valuable C–N bonds. These reactions offer a promising strategy for catalyst-controlled regiodivergent functionalization of different types of reactive C–H bonds, as the regioselectivity is tunable by varying the steric and electronic environments around the Ag nitrene, as well as the identity of the nitrene precursors and the tether length. Therefore, a unified understanding of how these individual factors affect the regioselectivity is key to the rational design of highly selective and regiodivergent C–H amination reactions. Herein, we report a computational study of various Ag-catalyzed NT reactions that indicates a concerted H-atom transfer (HAT)/C–N bond formation mechanism. A detailed analysis was carried out on the effects of the C–H bond dissociation enthalpy (BDE), charge transfer, ligand–substrate steric repulsions, and transition state ring strain on the stability of the C–H insertion transition states with different Ag nitrene complexes. The ancillary ligands on the Ag and the nitrene precursor identity both affect transition state geometries to furnish differing sensitivities to the BDE, tether length, and electronic effects of the reactive C–H bonds. Based on our understanding of the dominant factors that control selectivity, we established a rational catalyst and precursor selection approach for regiodivergent amination of diverse C–H bonds. The computationally predicted regiodivergent amination of β- and γ-C–H bonds of aliphatic alcohol derivatives was validated by experimental studies

Air-Stable Conversion of Separated Carbon Nanotube Thin-Film Transistors from p-Type to n-Type Using Atomic Layer Deposition of High-κ Oxide and Its Application in CMOS Logic Circuits

Due to extraordinary electrical properties, preseparated, high purity semiconducting carbon nanotubes hold great potential for thin-film transistors (TFTs) and integrated circuit applications. One of the main challenges it still faces is the fabrication of air-stable n-type nanotube TFTs with industry-compatible techniques. Here in this paper, we report a novel and highly reliable method of converting the as-made p-type TFTs using preseparated semiconducting nanotubes into air-stable n-type transistors by adding a high-κ oxide passivation layer using atomic layer deposition (ALD). The n-type devices exhibit symmetric electrical performance compared with the p-type devices in terms of on-current, on/off ratio, and device mobility. Various factors affecting the conversion process, including ALD temperature, metal contact material, and channel length, have also been systematically studied by a series of designed experiments. A complementary metal−oxide−semiconductor (CMOS) inverter with rail-to-rail output, symmetric input/output behavior, and large noise margin has been further demonstrated. The excellent performance gives us the feasibility of cascading multiple stages of logic blocks and larger scale integration. Our approach can serve as the critical foundation for future nanotube-based thin-film macroelectronics

Engineered P450 Atom-Transfer Radical Cyclases are Bifunctional Biocatalysts: Reaction Mechanism and Origin of Enantioselectivity

New-to-nature radical biocatalysis has recently emerged as a powerful strategy to tame fleeting open-shell intermediates for stereoselective transformations. In 2021, we introduced a novel metalloredox biocatalysis strategy that leverages the innate redox properties of the heme cofactor of P450 enzymes, furnishing new-to-nature atom-transfer radical cyclases (ATRCases) with excellent activity and stereoselectivity. Herein, we report a combined computational and experimental study to shed light on the mechanism and origins of enantioselectivity for this system. Molecular dynamics and quantum mechanics/molecular mechanics (QM/MM) calculations revealed an unexpected role of the key beneficial mutation I263Q. The glutamine residue serves as an essential hydrogen bond donor that engages with the carbonyl moiety of the substrate to promote bromine atom abstraction and enhance the enantioselectivity of radical cyclization. Therefore, the evolved ATRCase is a bifunctional biocatalyst, wherein the heme cofactor enables atom-transfer radical biocatalysis, while the hydrogen bond donor residue further enhances the activity and enantioselectivity. Unlike many enzymatic stereocontrol rationales based on a rigid substrate binding model, our computations demonstrate a high degree of rotational flexibility of the allyl moiety in an enzyme–substrate complex and succeeding intermediates. Therefore, the enantioselectivity is controlled by the radical cyclization transition states rather than the substrate orientation in ground-state complexes in the preceding steps. During radical cyclization, anchoring effects of the Q263 residue and steric interactions with the heme cofactor concurrently control the π-facial selectivity, allowing for highly enantioselective C–C bond formation. Our computational findings are corroborated by experiments with ATRCase mutants generated from site-directed mutagenesis

Escape from Palladium: Nickel-Catalyzed Catellani Annulation

While Catellani reactions have become increasingly important for arene functionalizations, they have been solely catalyzed by palladium. Here we report the first nickel-catalyzed Catellani-type annulation of aryl triflates and chlorides to form various benzocyclobutene-fused norbornanes in high efficiency. Mechanistic studies reveal a surprising outer-sphere concerted metalation/deprotonation pathway during the formation of the nickelacycle, as well as the essential roles of the base and the triflate anion. The reaction shows a broad functional group tolerance and enhanced regioselectivity compared to the corresponding palladium catalysis

Acoustic Core–Shell Resonance Harvester for Application of Artificial Cochlea Based on the Piezo-Triboelectric Effect

The demand for flexible, efficient, and self-powered cochlear implants applied to remedy sensorineural hearing loss caused by dysfunctional hair cells remains urgent. Herein, we report an acoustic core–shell resonance harvester for the application of artificial cochleae based on the piezo-triboelectric effect. Integrating dispersed BaTiO3 particles as cores and porous PVDF-TrFE as shells, the acoustic harvest devices with ingenious core–shell structures exhibit outstanding piezo-triboelectric properties (Voc = 15.24 V, DAsc = 9.22 mA/m2). The acoustic harvest principle reveals that BaTiO3 nanocores resonate with sound waves and bounce against porous PVDF-TrFE microshells, thereby generating piezo-triboelectric signals. By experimental measurement and numerical modeling, the vibration process and resonance regulation of acoustic harvest devices were intensively investigated to regulate the influential parameters. Furthermore, the acoustic harvesters exhibit admirable feasibility and sensitivity for sound recording and show potential application for artificial cochlea

Acoustic Core–Shell Resonance Harvester for Application of Artificial Cochlea Based on the Piezo-Triboelectric Effect

The demand for flexible, efficient, and self-powered cochlear implants applied to remedy sensorineural hearing loss caused by dysfunctional hair cells remains urgent. Herein, we report an acoustic core–shell resonance harvester for the application of artificial cochleae based on the piezo-triboelectric effect. Integrating dispersed BaTiO3 particles as cores and porous PVDF-TrFE as shells, the acoustic harvest devices with ingenious core–shell structures exhibit outstanding piezo-triboelectric properties (Voc = 15.24 V, DAsc = 9.22 mA/m2). The acoustic harvest principle reveals that BaTiO3 nanocores resonate with sound waves and bounce against porous PVDF-TrFE microshells, thereby generating piezo-triboelectric signals. By experimental measurement and numerical modeling, the vibration process and resonance regulation of acoustic harvest devices were intensively investigated to regulate the influential parameters. Furthermore, the acoustic harvesters exhibit admirable feasibility and sensitivity for sound recording and show potential application for artificial cochlea