Annulation-Induced Hidden Reactivity of the 1,2,4-Triazole Backbone

Triazoles are an important class of compounds with widespread applications. Functionalization of the triazole backbone is thus of significant interest. In comparison to 1,2,3-triazoles, C−H activation-functionalization of the congeners 1,2,4-triazoles is surprisingly underdeveloped. Indeed, no such C−H activation-functionalization has been reported for 4-substituted 1,2,4-triazole cores. Furthermore, although denitrogenative ring-opening of 1,2,3-triazoles is well-explored, 1,2,4-triazole/triazolium substrates have not been known to exhibit N−N bond-cleaving ring-opening reactivity so far. In this work, we unveiled an unusual hidden reactivity of the 1,2,4-triazole backbone involving the elusive N−N bond-cleaving ring-opening reaction. This new reactivity was induced by a Satoh-Miura-type C−H activation-annulation at the 1,2,4-triazole motif appended with a pyridine directing group. This unique reaction allowed ready access to a novel class of unsymmetrically substituted 2,2′-dipyridylamines, with one pyridine ring fully-substituted with alkyl groups. The unsymmetrical 2,2′-dipyridylamines were utilized to access unsymmetrical boron-aza-dipyridylmethene fluorescent dyes. Empowered with desirable optical/physical properties such as large Stokes shifts and suitable hydrophobicity arising from optimal alkyl chain length at the fully-substituted pyridine-ring, these dyes were used for intracellular lipid droplet-selective imaging studies, which provided useful information toward designing suitable lipid droplet-selective imaging probes for biomedical applications.     

Enantioselective Synthesis of N−N Biaryl Atropisomers through Iridium(I)-Catalyzed C−H Alkylation with Acrylates

Enantioselective synthesis of N−N biaryl atropisomers is an emerging area but remains underexplored. The development of efficient synthesis of N−N biaryl atropisomers is in great demand. Herein, the construction of N−N biaryl atropisomers through iridium-catalyzed asymmetric C−H alkylation is reported for the first time. In the presence of readily available Ir precursor and Xyl-BINAP, a variety of axially chiral molecules based on indole-pyrrole skeleton were obtained in good yields (up to 98 %) with excellent enantioselectivity (up to 99 % ee). In addition, N−N bispyrrole atropisomers could also be synthesized in excellent yields and enantioselectivity. This method features perfect atom economy, wide substrate scope, and multifunctionalized products allowing diverse transformations.     

Aryne-Enabled C−N Arylation of Anilines

Anilines are potentially high-value arylating agents, but are limited by the low reactivity of the strong C−N bond. We show that the reactive intermediate benzyne can be used to both activate anilines, and set-up an aryl transfer reaction in a single step. The reaction does not require any transition metal catalysts or stoichiometric organometallics, and establishes a metal-free route to valuable biaryl products by functionalizing the aniline C−N bond.     

Direct C−C Double Bond Cleavage of Alkenes Enabled by Highly Dispersed Cobalt Catalyst and Hydroxylamine

The utilization of a single-atom catalyst to break C−C bonds merges the merits of homogeneous and heterogeneous catalysis and presents an intriguing pathway for obtaining high-value-added products. Herein, a mild, selective, and sustainable oxidative cleavage of alkene to form oxime ether or nitrile was achieved by using atomically dispersed cobalt catalyst and hydroxylamine. Diversified substrate patterns, including symmetrical and unsymmetrical alkenes, di- and tri-substituted alkenes, and late-stage functionalization of complex alkenes were demonstrated. The reaction was successfully scaled up and demonstrated good performance in recycling experiments. The hot filtration test, catalyst poisoning and radical scavenger experiment, time kinetics, and studies on the reaction intermediate collectively pointed to a radical mechanism with cobalt/acid/O₂ promoted C−C bond cleavage as the key step.     

Synergistic Nitrogen Binding Sites in a Metal-Organic Framework for Efficient N2/O2 Separation

Porous materials with d₃ electronic configuration open metal sites have been proved to be effective adsorbents for N₂ capture and N₂/O₂ separation. However, the reported materials remain challenging to address the trade-off between adsorption capacity and selectivity. Herein, we report a robust MOF, MIL-102Cr, that features two binding sites, can synergistically afford strong interactions for N₂ capture. The synergistic adsorption site exhibits a benchmark Q_st of 45.0 kJ mol⁻¹ for N₂ among the Cr-based MOFs, a record-high volumetric N₂ uptake (31.38 cm³ cm⁻³), and highest N₂/O₂ selectivity (13.11) at 298 K and 1.0 bar. Breakthrough experiments reveal that MIL-102Cr can efficiently capture N₂ from a 79/21 N₂/O₂ mixture, providing a record 99.99 % pure O₂ productivity of 0.75 mmol g⁻¹. In situ infrared spectroscopy and computational modelling studies revealed that a synergistic adsorption effect by open Cr(III) and fluorine sites was accountable for the strong interactions between the MOF and N₂.     

Transition Metal-Free Aromatic C−H,C−N,C−S and C−O Borylation

Aromatic organoboron compounds are highly valuable building blocks in organic chemistry. They were mainly synthesized through aromatic C−H and C−Het borylation, in which transition metal-catalysis dominate. In the past decade, with increasing attention to sustainable chemistry, numerous transition metal-free C−H and C−Het borylation transformations have been developed and emerged as efficient methods towards the synthesis of aromatic organoboron compounds. This account mainly focuses on recent advances in transition metal-free aromatic C−H, C−N, C−S, and C−O borylation transformations and provides insights to where further developments are required.     

Cu-Doped MoSi2N4 Monolayer as a Potential NH3 Sensor

Cu doped MoSi₂N₄ monolayer (Cu-MoSi₂N₄) was firstly proposed to analyze adsorption performances of common gas molecules including O₂, N₂, CO, NO, NO₂, CO₂, SO₂, H₂O, NH₃ and CH₄ via density functional theory (DFT) combining with non-equilibrium Green's function (NEGF). The electronic transport calculations indicate that Cu-MoSi₂N₄ monolayer has high sensitivity for CO, NO, NO₂ and NH₃ molecules. However, only NH₃ molecule adsorbs on the Cu-MoSi₂N₄ monolayer with moderate strength (−0.55 eV) and desorbs at room temperature (2.36×10⁻³ s). Thus, Cu-MoSi₂N₄ monolayer is demonstrated as a potential NH₃ sensor.     

Assembled Porphyrin-Based Multinuclear Ruthenium(II)-NNNN Complex Catalysts for Transfer Hydrogenation of Ketones

Multinuclear porphyrin-based ruthenium(II)-NNNN complexes were efficiently assembled by means of coordinatively unsaturated 16-electron mononuclear ruthenium(II)-pyrazolyl-imidazolyl-pyridine complex, zinc(II) meso-tetra(4-pyridyl)-porphyrin (ZnTPyP), and 4,4′-linked bipyridines. The resultant multinuclear (Ru₄ and Ru₈) porphyrin-based ruthenium(II)-NNNN complexes exhibited exceptionally high catalytic activity at as low as 0.008 mol % Ru loading for the transfer hydrogenation reaction of ketones in refluxing 2-propanol, reaching up to 99 % yields and 5.7×10⁶ h⁻¹ TOFs.     

Terpyridine Based Heteroleptic Ruthenium Complexes: Influence of Donor and Acceptor Ligands in Photosensitization

We report heteroleptic ruthenium complexes of terpyridine (tpy) ligands with directly linked carboxylic acid anchors. These complexes feature methyl or methoxy-substituted ^4′−Phtpy as donor ligands. We prepared these heteroleptic complexes from the ruthenium (II) precursor via a milder route to preclude the homoleptic complex formation. The donor−acceptor arrangement of tpy ligands in these ruthenium complexes renders visible light absorption giving metal and ligand-to-ligand charge transfer excitations at c.a. 490 nm. We evaluate the effect of the tpy donor substituents on the light-harvesting ability in Dye-Sensitized Solar Cells (DSSCs) and compare their photosensitizing ability with heteroleptic complexes bearing phenyl spacer at the acceptor end. Further, scrutinizing their photovoltaic performance, we studied their electron transfer kinetics in DSSCs using electrochemical impedance spectroscopy. This paper presents the structure-photosensitization relationship of these heteroleptic ruthenium complexes through a combined experimental and computational approach.     

Stereo- and Regiochemical Effect of N,N-Dialkylamide Extractants on the Speciation of Pu Complexes

The relationship between extractant stereochemistry and their extraction performance has only poorly been established. In order to address a part of this concern, we investigated the Pu(IV) liquid-liquid extraction (LLE) by using the N,N-di-(2-ethylhexyl)butyramide (DEHBA), as well as those of its position isomers. DEHBA (ββ-isomer) and N-(2-ethylhexyl)-N-(oct-3-yl)butyramide (EHOBA or αβ-isomer) were synthesized as a mixture of stereoisomer or stereoenriched (R,S)- and (S,S)-diastereoisomers, and were all assessed for Pu^IV LLE. The results showed that both the position and the stereoisomerism of the aliphatic substituents affect Pu^IV complexation and extraction. We found that Pu extraction is lowered by factor 2 to 4 when the ethyl branching group is closer to the complexing site. UV-vis spectroscopy showed that this extraction decrease was affected by steric hindrance inducing a deprivation of Pu inner sphere complex. Effect of stereoisomerism is highlighted for branching closer to the complexing site (α-position). Enantiopure DEHBA stereoisomers provided similar Pu extraction, whereas a slight decrease could be noticed for the more cluttered stereoenriched (αβ)-isomers, which was also concomitant with a smaller population of inner sphere complex. In contrast, the stereoisomers mixture led to a strong decrease of Pu extraction because of an antagonistic association in the mixed complexes.