Cu(II)-Mediated Sulfonylation of (Hetero)arenes with TosMIC Using Monodentate Directing Groups

Monodentate chelation-assisted direct ortho-C–H sulfonylation of (hetero)arenes using TosMIC as the novel sulfonylating reagent has been developed. A broad range of substrates, including indolines, indoles, 2-phenylpyridines, and others were well tolerated to afford the corresponding products in moderate to good yields. Mechanistic studies revealed that the sulfonyl radical might be involved. Inspired by the above discovery, preliminary para-C–H sulfonylation of naphthalene substrate was also successfully realized. The current protocol featured with cheap metal catalysis, good functional group compatibility, and operational convenience

Chiral CNN Pincer Palladium(II) Complexes with 2‑Aryl-6-(oxazolinyl)pyridine Ligands: Synthesis, Characterization, and Application to Enantioselective Allylation of Isatins and Suzuki–Miyaura Coupling Reaction

A series of chiral 2-aryl-6-(oxazolinyl)­pyridine (aryl = phenyl or 1-naphthyl) ligands <b>2a</b>–<b>f</b> were conveniently prepared from commercially available 6-bromo-2-picolinaldehyde in two steps. Reaction of <b>2a</b>–<b>f</b> with PdCl₂ in toluene in the presence of sodium bicarbonate afforded the corresponding CNN pincer Pd­(II) complexes <b>3a</b>–<b>f</b> via aryl C–H bond activation of the related ligands. All of the new compounds have been fully characterized by elemental analysis (MS for ligands), ¹H and ¹³C NMR, and IR spectra. In addition, the molecular structures of Pd­(II) complexes <b>3c</b>–<b>f</b> have been determined by X-ray single-crystal diffraction. The obtained chiral pincer catalysts were successfully used in the asymmetric allylation of isatins with allyltributyltin, giving the corresponding 3-allyl-3-hydroxyoxindoles in high yields with enantioselectivities of up to 86% ee. These pincers could also catalyze the asymmetric Suzuki–Miyaura coupling reaction to provide the axially chiral biaryl products in good yields with good stereoselectivities (up to 68% ee)

PCN Pincer Palladium(II) Complex Catalyzed Enantioselective Hydrophosphination of Enones: Synthesis of Pyridine-Functionalized Chiral Phosphine Oxides as NC_sp³O Pincer Preligands

A series of chiral PCN pincer Pd­(II) complexes <b>VI</b>–<b>XIII</b> with aryl-based aminophosphine–imidazoline or phosphinite–imidazoline ligands were synthesized and characterized. They were examined as enantioselective catalysts for the hydrophosphination of enones. Among them, complex <b>IX</b>, which features a Ph₂PO donor as well as an imidazoline donor with (4<i>S</i>)-phenyl and <i>N</i>-Tol-<i>p</i> groups, was found to be the optimal catalyst. Thus, in the presence of 2–5 mol % of complex <b>IX</b> a wide variety of enones reacted smoothly with diarylphosphines to give the corresponding chiral phosphine derivatives in high yields with enantioselectivities of up to 98% ee. In particular, heteroaryl species such as 2-thienyl-, 2-furyl-, and 2-pyridinyl-containing enones that have a strong coordination ability to the Pd center were also appropriate substrates for the current catalytic system. For example, hydrophosphination of 2-alkenoylpyridines with diphenylphosphine followed by oxidation with H₂O₂ afforded the corresponding pyridine-functionalized chiral phosphine oxides in good yields with good to excellent enantioselectivities (10 examples, up to 95% ee). Furthermore, it had been demonstrated that the obtained pyridine-containing phosphine oxide acted as a tridentate ligand in the reaction with PdCl₂ to form an intriguing NC_sp³O pincer Pd­(II) complex via C_sp³–H bond activation, which to our knowledge is the first example of a chiral DC_sp³D′ Pd pincer (D ≠ D′; D and D′ denote donor atoms such as P, N, etc.)

Chiral CNN Pincer Palladium(II) Complexes with 2‑Aryl-6-(oxazolinyl)pyridine Ligands: Synthesis, Characterization, and Application to Enantioselective Allylation of Isatins and Suzuki–Miyaura Coupling Reaction

A series of chiral 2-aryl-6-(oxazolinyl)­pyridine (aryl = phenyl or 1-naphthyl) ligands <b>2a</b>–<b>f</b> were conveniently prepared from commercially available 6-bromo-2-picolinaldehyde in two steps. Reaction of <b>2a</b>–<b>f</b> with PdCl₂ in toluene in the presence of sodium bicarbonate afforded the corresponding CNN pincer Pd­(II) complexes <b>3a</b>–<b>f</b> via aryl C–H bond activation of the related ligands. All of the new compounds have been fully characterized by elemental analysis (MS for ligands), ¹H and ¹³C NMR, and IR spectra. In addition, the molecular structures of Pd­(II) complexes <b>3c</b>–<b>f</b> have been determined by X-ray single-crystal diffraction. The obtained chiral pincer catalysts were successfully used in the asymmetric allylation of isatins with allyltributyltin, giving the corresponding 3-allyl-3-hydroxyoxindoles in high yields with enantioselectivities of up to 86% ee. These pincers could also catalyze the asymmetric Suzuki–Miyaura coupling reaction to provide the axially chiral biaryl products in good yields with good stereoselectivities (up to 68% ee)

Regioselective 2,2,2-Trifluoroethylation of Imidazopyridines by Visible Light Photoredox Catalysis

A visible-light-induced C-3 selective trifluoroethylation of imidazoheterocycles using 1,1,1-trifluoro-2-iodoethane as trifluoroethyl radical sources was developed. The methodology enables the introduction of a trifluoroethyl group in a fast and efficient reaction under mild conditions with excellent regioselectivities and high functional group tolerance

Enantiomeric Separations of Chiral Sulfonic and Phosphoric Acids with Barium-Doped Cyclofructan Selectors via an Ion Interaction Mechanism

New cyclofructan-6 (CF6)-based chiral stationary phases (CSPs) bind barium cations. As a result, the barium-complexed CSPs exhibit enantioselectivity toward 16 chiral phosphoric and sulfonic acids in the polar organic mode (e.g., methanol or ethanol mobile phase containing a barium salt additive). Retention is predominantly governed by a strong ionic interaction between the analyte and the complexed barium cation as well as hydrogen bonding with the cyclofructan macrocycle. The log <i>k</i> versus log [X], where [X] = the concentration of the barium counteranion, plots for LARIHC–CF6-P were linear with negative slopes demonstrating typical anion exchange behavior. The nature of the barium counteranion also was investigated (acetate, methanesulfonate, trifluoroacetate, and perchlorate), and the apparent elution strength was found to be acetate > methanesulfonate > trifluoroacetate > perchlorate. A theory based upon a double layer model was proposed wherein kosmotropic anions are selectively adsorbed to the cyclofructan macrocycle and attenuate the effect of the barium cation. van’t Hoff studies for two analytes were conducted on the LARIHC–CF6-P for three of the barium salts (acetate, trifluoroacetate, and perchlorate), and the thermodynamic parameters governing retention and enantioselectivity are discussed. Interestingly, for the entropically driven separations, enantiomeric selectivity can increase at higher temperatures, even with decreasing retention

Chiral Bis(imidazolinyl)phenyl NCN Pincer Rhodium(III) Catalysts for Enantioselective Allylation of Aldehydes and Carbonyl–Ene Reaction of Trifluoropyruvates

Chiral NCN pincer rhodium­(III) complexes with bis­(imidazolinyl)­phenyl ligands were found to be effective catalysts for the allylation of a variety of electronically and structurally diverse aldehydes with allyltributyltin, giving the corresponding optically active homoallylic alcohols in high yields with enantioselectivities of up to 97% <i>ee</i>. These complexes were also applied in the carbonyl–ene reaction of ethyl or methyl trifluoropyruvate with various 2-arylpropenes. With the aid of silver trifluoromethanesulfonate, the pincer rhodium­(III) catalysts could catalyze the reaction to provide the corresponding chiral α-hydroxy-α-trifluoromethyl esters in good yields with high stereoselectivities (up to 95% <i>ee</i>)

Enantioselective Hydrophosphination of Enones with Diphenylphosphine Catalyzed by Bis(imidazoline) NCN Pincer Palladium(II) Complexes

A series of chiral NCN pincer Pd­(II) complexes with 1,3-bis­(2′-imidazolinyl)­phenyl (Phebim) ligands were synthesized via the C–H activation or oxidative addition method. A dinuclear macrocyclic Pd­(II) complex was also prepared by reaction of the Phebim-H ligand with PdCl₂. All of the new compounds were fully characterized, and X-ray single-crystal structures were obtained for two of the complexes. The Pd­(II) complexes were successfully applied to enantioselective hydrophosphination of various enones with diphenylphosphine, providing optically active phosphine derivatives in good yields with enantioselectivities of up to 94% ee

Visual Gustation via Regulable Elastic Photonic Crystals

The unique structural sensitivity of photonic crystals (PCs) endows them with stretchable or elastic tunability for light propagation and spontaneous emission modulation. Hydrogel PCs have been demonstrated to have biocompatibility and flexibility for potential human health detection and environmental security monitoring. However, current elastic PCs still possess a fixed elastic modulus and uncontrollable structural colors based on a tunable elastic modulus, posing considerable challenges for in situ detection, particularly in wearable or portable sensing devices. In this work, we introduced a novel chemo-mechanical transduction mechanism embedded within a photonic crystal nanomatrix, leading to the creation of structural colors and giving rise to a visual gustation sensing experience. By utilizing the captivating structural colors generated by the hydrogel PC, we employ abundant optical information to identify various analytes. The finite element analysis proved the electric field distribution in the PC matrix during stretch operations. The elastic-optical behaviors with various chemical cosolvents, including cations, anions, saccharides, or organic acids, were investigated. The mechanism of the Hofmeister effect regulating the elasticity of hydrogels was demonstrated with the network nanostructure of the hydrogels. The hydrogel PC matrix demonstrates remarkable capability in efficiently distinguishing a wide range of cations, anions, saccharides, and organic acids across various concentrations, mixtures, and even real food samples, such as tastes and soups. Through comprehensive research, a precise relationship between the structural colors and the elastic modulus of hydrogel PCs has been established, contributing to the biomatching elastic-optics platform for wearable devices, a dynamic environment, and clinical or health monitoring auxiliary

New Type of 2,6-Bis(imidazo[1,2‑<i>a</i>]pyridin-2-yl)pyridine-Based Ruthenium Complexes: Active Catalysts for Transfer Hydrogenation of Ketones

Neutral and cationic ruthenium­(II) complexes bearing a symmetrical 2,6-bis­(imidazo­[1,2-<i>a</i>]­pyridin-2-yl)­pyridine were synthesized and structurally characterized by NMR analysis and X-ray crystallographic determinations. These complexes have exhibited good catalytic activity in the transfer hydrogenation of ketones. In refluxing isopropyl alcohol, the conversion of the substrates reached up to 99%, and a TOF value of 356 400 h^–1 with 0.1 mol % catalyst was achieved