C9-Aryl-substituted berberine derivatives with tunable AIE properties for cell imaging application.

Berberine (BBR), a widely used isoquinoline alkaloid derived from natural sources, exhibits aggregation-induced emission (AIE) characteristics and has biological applications such as in selective lipid droplet imaging and photodynamic therapy. However, natural BBR suffers from low fluorescence quantum yield (ΦF) and monotonous emission wavelength. In this paper, a series of C9-position-aryl-substituted berberine derivatives with a D-A structure were designed and synthesized. The electronic effect of the substitution groups can tune the intramolecular charge transfer (ICT) effect of the berberine derivatives, resulting in bluish green to NIR (508-682 nm) luminescence with AIE characteristics and enhanced ΦF up to 36% in the solid state. Interestingly, berberine derivatives containing an amino or a pyridyl group can exhibit fluorescence response to TFA. Cell imaging of the berberine derivatives was conducted using Caco-2 cancer cells, demonstrating their multi-color and efficient wash-free imaging capabilities. This work presents a new strategy for developing novel berberine derivatives with tunable AIE properties for application in biological imaging.

Photoinduced radical cascade domino Heck coupling of N-aryl acrylamide with vinyl arenes enabled by palladium catalysis.

Here, a redox-neutral palladium-catalyzed photo-induced radical cascade domino Heck reaction of N-aryl acrylamide with vinyl arenes is described. A diverse range of bioactive oxindoles, featuring an all-carbon quaternary center, were synthesized. The reaction is proposed to proceed via an open-shell intermediate and occurs under mild reaction conditions, exhibiting excellent functional group tolerance. Importantly, the synthesized products can be readily transformed into biologically active molecules, including (±)-physostigmine and (±)-physovenine.

Photoinduced Nitrogen-to-Alkyl Radical Relay Heck Reaction of o-Alkylbenzamides with Vinyl Arenes by Palladium Catalysis.

Here, a palladium-catalyzed photoinduced N-to-alkyl radical relay Heck reaction of o-alkylbenzamides at benzylic sites with vinyl arenes is described. The reaction employs neither exogeneous photosensitizers nor external oxidants. It is proposed to proceed via a N-to-alkyl hybrid palladium-radical mechanism which occurs under mild conditions that are compatible with a wide range of functional groups. The products are easily transformed to azepinone derivatives, which are prevalent in pharmaceuticals and natural products.

Versatile halogenation via a CNHC

Stable cyclopalladated complexes containing an (sp3)C-Pd bond were synthesized via α-CH2 deprotonation and palladation of N-alkyl groups of carbene ligands bearing electron-withdrawing substituents. The strong electron donating strengths of the resulting CNHC^Csp3 chelators were experimentally identified, and the palladacycle underwent template-directed, versatile C-halogenation with X2.

Efficient Construction of Symmetrical Diaryl Sulfides via a Supported Pd Nanocatalyst-Catalyzed C-S Coupling Reaction.

Aryl sulfides play an important role in pharmaceuticals, biologically active molecules and polymeric materials. Herein, a general and efficient protocol for Pd@COF-TB (a kind of Pd nanocatalyst supported by a covalent organic framework)/DIPEA-catalyzed one-pot synthesis of symmetrical diaryl sulfides through a C-S coupling reaction from aryl iodides and Na2S2O3 is developed. More importantly, the addition of N,N-diisopropylethylamine (DIPEA) can not only enhance the catalytic activity of a Pd@COF-TB nanocatalyst, but also effectively inhibit the formation of biphenyl byproducts, which are a product of Ullmann reaction. Besides, it has been confirmed that the aryl Bunte salts generated in situ from Na2S2O3 and aryl iodides are the sulfur sources involved in this C-S coupling reaction. With the strategy proposed in this work, a variety of symmetrical diaryl sulfides could be obtained in moderate to excellent yields with a high tolerance of various functional groups. Moreover, a possible mechanism of this Pd nanoparticle-catalyzed C-S coupling reaction is proposed based on the results of controlling experiments.

Removal of wastewater phenolic compounds with triethylenetetramine functionalized polystyrene resin.

A polyamine functionalized polystyrene resin (PSATA) was prepared via condensation reaction of acetylated polystyrene resin with triethylenetetramine, which, upon NaBH4 reduction, produced PSATAR. In comparison with the PSATA, the PSATAR with more flexible amine groups shows improved structural properties, and the equilibrium adsorption capacities of phenol, 2-nitrophenol (ONP) and 2,4-dinitrophenol (DNP) in wastewater were up to 1.073, 1.832 and 1.901 mmol/g, respectively. Their adsorption isotherms fit well with the Freundlich model, indicating a multilayer, heterogeneous adsorption nature. Kinetic studies indicated that the adsorption of phenolic compounds conforms to the pseudo-second-order kinetics with the adsorption rate controlled by film diffusion for ONP and DNP, and intra-particle diffusion in the later stage for phenol.

Fused azole-thiazolines via one-pot cyclization of functionalized N-heterocyclic carbene precursors.

A one-pot two-step methodology was exploited to synthesize fused thiazoline-azolium salts via reactions of bromoalkyl-azolium salts with KSCN and NaOH. The synthetic feasibility and versatility was demonstrated by the high yield (>80%) preparation of 13 salts with different backbones, linkers and substituents. Using methylpropionato as an N-protecting group, the resulting salts could be further derivatized to their neutral azole-thiazolines. The reaction sequence proceeds via (i) Br → SCN substitution, (ii) N-heterocyclic carbene formation, (iii) carbene attack of the S atom and CN- displacement in the alkyl-S-C[triple bond, length as m-dash]N unit, and (iv) methyl acrylate elimination.

Synthesis of 9-O-arylated berberines via copper-catalyzed CAr-O coupling reactions.

Berberine is a widely used antimicrobial agent in clinic. However, a high dosage is often required due to its low lipophilicity and bioavailability. The current study explores the structural modifications of berberines with potentially lipophilic aryl groups to address this problem. A series of 15 9-O-aryl-substituted berberines (3a-o) and one 9-O-phenylene-bridged berberine dimer (5) was synthesized by copper-catalyzed cross-coupling of tetrahydroberberrubine and aryl iodides, followed by oxidation with I2.

Donor Strengths Determination of Pnictogen and Chalcogen Ligands by the Huynh Electronic Parameter and Its Correlation to Sigma Hammett Constants.

The suitability and accuracy of the Huynh electronic parameter (HEP) was further tested to reveal remote substituent effects in pyridines, which are located five or six bonds away from the reporter probe. These values show an excellent correlation to Hammett σ-constants of the respective substituents with coefficients of R2 =0.9856 (σm ) and R2 =0.9857 (σp ). Based on this observation, a methodology for the re-evaluation of certain Hammett constants with larger uncertainties has been proposed and demonstrated. Moreover, the scope of HEP was extended to various neutral pnictogen and chalcogen donors during which "transphobia effects" were revealed for mixed NHC complexes containing phosphites, arsine and stibine for the first time.

Tunable Copper-Catalyzed Reaction of C60 with 2-Ethoxycarbonylacetamides and Subsequent BF3·Et2O-Mediated Isomerization of the Generated Dihydrofuran-Fused Fullerenes to Fulleropyrrolidinones.

A tunable copper-catalyzed reaction of C60 with 2-ethoxycarbonylacetamides using air as the oxidant has been explored, which selectively affords methanofullerenes (2) and dihydrofuran-fused fullerenes (3) under the CuI/DMAP and CuCl/NMI catalytic systems, respectively. Furthermore, the generated dihydrofuran-fused fullerenes could be transformed to fulleropyrrolidinones (4 and 5) upon treatment with BF3·Et2O.

Ring-expanded N-heterocyclic carbenes as ligands in iron-catalysed cross-coupling reactions of arylmagnesium reagents and aryl chlorides.

The structure-activity relationship of expanded-ring N-heterocyclic carbenes (NHCs) in the iron-catalysed Kumada aryl-aryl coupling reaction was explored. This was achieved by comparing the catalytic performance of Fe-NHC catalysts generated in situ containing NHCs that differ in steric bulk. In particular, the influences of ring sizes (5-8) and N-aryl substituents were explored in terms of spectroscopic and structural features, which affect their %Vbur values. The three best performing ligands were found on a diagonal of a 5 × 4 structural matrix revealing an optimal steric bulk and significant influences of subtle steric variations on the catalytic activities.

A unified ligand electronic parameter based on 13C NMR spectroscopy of N-heterocyclic carbene complexes.

The properties and reactivities of transition metal complexes are rooted in the stereoelectronic properties of their ligands. While the bulk of a ligand can be easily evaluated and compared by the drawing of its Lewis structure, prediction on the electronic contributions is often less straightforward. Thus, several electronic parameters have been developed for the experimental evaluation of ligands throughout the years. This article accounts for the most recent one developed by the Huynh group, which employs 13C NMR spectroscopy to determine ligand donor strengths using N-heterocyclic carbene complexes. This parameter not only proves to be safer, more convenient and accurate in comparison to existing methodologies, but it also provides, in certain cases, more intuitive and reliable results. Furthermore, it is currently the only one that allows the direct comparison of various Werner-type and organometallic ligands on a unified scale.

Controlled access to a heterometallic N-heterocyclic carbene helicate.

Metallation of a pentadentate diNHC proligand bearing a dipropyl-pyridine-2,6-dicarboxamide with silver and gold affords mono- and dinuclear, double-stranded bis(NHC) complexes as useful building blocks for metallo-supramolecules. The digold(I) complex acts as a metallo-bis(pincer) ligand to furnish the first example of an organometallic NHC-helicate upon coordination to cobalt.

Determining the electron-donating properties of bidentate ligands by (13)C NMR spectroscopy.

A series of 15 mononuclear complexes [PdBr((i)Pr2-bimy)(L2)]PF6 (1-15) ((i)Pr2-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene, L2 = aromatic 1,2-diimines, diazabutadienes, or methylene-, ethylene- and propylene-bridged di-N-heterocyclic carbenes) and two dicarbene-bridged, dinuclear complexes [Pd2Br4((i)Pr2-bimy)2(diNHC)] (16 and 17) were synthesized and characterized by multinuclear NMR spectroscopy, electrospray ionization mass spectrometry, and in some cases X-ray diffraction analysis. The influence of the 15 bidentate ligands L2 on the (13)Ccarbene signals of the (i)Pr2-bimy reporter ligand in the chelate complexes was studied, on the basis of which a facile methodology for the donor strength determination of bidentate ligands was developed.

Highly modular access to functionalised metal-carbenes via post-modifications of a single bromoalkyl-substituted NHC-Pd(II) complex.

The synthesis of a bromopropyl-substituted NHC-Pd(II) complex, which can undergo exemplary and versatile 2nd and 3rd generation post-modifications easily affording 7 new functionalised NHC complexes, is demonstrated.

Influence of Schiff base and lanthanide metals on the synthesis, stability, and reactivity of monoamido lanthanide complexes bearing two Schiff bases.

The monoamido lanthanide complexes stabilized by Schiff base ligand L(2)LnN(TMS)(2) (L = 3,5-Bu(t)(2)-2-(O)-C(6)H(2)CH═N-8-C(9)H(6)N, Ln = Yb (1), Y (2), Eu (3), Nd (4), and La (5)) were synthesized in good yields by the reactions of Ln[N(TMS)(2)](3) with 1.8 equiv of HL in hexane at room temperature. It was found that the stability of 1-5 depends greatly on the size of the lanthanide metals with the increasing trend of Yb ≈ Y < Nd < La. The amine elimination of Ln[N(TMS)(2)](3) with the bulky bidentate Schiff base HL' (L' = 3,5-Bu(t)(2)-2-(O)-C(6)H(2)CH═N-2,6-Pr(i)(2)-C(6)H(3)) afforded the monoamido lanthanide complexes L'(2)LnN(TMS)(2) (Ln = Yb (9), Y (10), Nd (11), and La (12)). While the amine elimination with the less bulky Schiff base HL'' (L'' = 3,5-Bu(t)(2)-2-(O)-C(6)H(2)CH═N-2,6-Me(2)-C(6)H(3)) yielded the desired monoamido complexes with the small metals of Y and Yb, L''(2)LnN(TMS)(2) (Ln = Yb (13) and Y (14)), and the more stable tris-Schiff base complexes with the large metals of La and Nd, yielded L''(3)Ln as the only product. Complexes 1-14 were fully characterized including X-ray crystal structural analysis. Complexes 1-5, 10, and 14 can serve as the efficient catalysts for addition of amines to carbodiimides, and the catalytic activity is greatly affected by the lanthanide metals with the active sequence of Yb < Y < Eu ≈ Nd ≈ La.