A series of π-conjugated alkynyl ligands based on quinoxaline and dibenzo[a,c]phenazine frameworks were synthesized and coordinated to gold(I) centers to investigate the influence of ligand structure and metal coordination on the photophysical and electronic properties of the resulting systems. The target ligands, 2,3-bis(4-ethynylphenyl)-6-methylquinoxaline (L1), 2,7-diethynyl-11-methyldibenzo[a,c]phenazine (L2), and 3,6-diethynyl-11-methyldibenzo[a,c]phenazine (L3), were prepared via Sonogashira cross-coupling reactions followed by deprotection of trimethylsilyl-protected alkynes. Subsequent reaction with AuCl(PCy₃) in the presence of potassium tert-butoxide afforded the corresponding binuclear gold(I) alkynyl complexes. Single-crystal X-ray diffraction of Au–L1 confirms a linear two-coordinate Au(I) geometry and a conjugated Au–CC–aryl framework. Photophysical investigations revealed that extending π-conjugation from the quinoxaline to the phenazine core induces a bathochromic shift in both absorption and emission. Coordination to gold(I) further amplifies this effect, resulting in red-shifted emission maxima, with Au–L3 exhibiting the most significant shift to 518 nm. This is accompanied by substantially larger Stokes shifts, indicating enhanced excited-state stabilization. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations corroborate the experimental trends, showing that gold coordination reduces the HOMO–LUMO gap and introduces metal-to-ligand charge transfer (MLCT) character. Furthermore, the heavy-atom effect of gold promotes efficient intersystem crossing, leading to stabilized triplet states. Nonlinear optical (NLO) property calculations demonstrate a significant enhancement in first hyperpolarizability (β) for the phenazine-based complexes, particularly Au–L3(β =5720 a.u.), establishing these systems as potential candidates for optoelectronic applications.
The present study describes a simple and efficient synthesis of cyclic carbonates through the incorporation of CO2 into epoxides using the synergistic combination of Cu-BTC/ZnBr2 in the presence of triethylamine (TEA) at atmospheric pressure. Notably, the methodology avoids the use of tetrabutylammonium bromide (TBAB) while operating at atmospheric CO2 pressure. DFT calculations and energy profile suggests that the reaction follows a two step mechanism in which the first step involves the activation of epoxide substrate through the coordination of oxygen atom with Cu-MOF and ZnBr2, followed by the nucleophilic attack of the bromide ions to open the ring. In the second step, CO2 insertion followed by ring closure provides the desired cyclic carbonate. This approach provides a simple, efficient and a scalable strategy for cyclic carbonate synthesis from CO2, contributing to the development of a sustainable carbon circular economy.
Palladium chemistry has been shown to be a promising tool for the synthesis of 3-aminoindoles, and further mechanistic studies are desirable to advance this field. In this manuscript, density functional theory (DFT) calculations were performed to investigate the mechanism and origin of regioselectivity of Pd-catalyzed bisamination reactions with ynamides and diaziridinone. It was found that the favorable mechanism proceeds via oxidative addition of the Ar-I bond, migratory insertion of ynamides, Ar-H activation, oxidative addition of di-tert-butyldiaziridinone and C-N reductive elimination. The Ar-H activation goes through the Cs2CO3-assisted concerted metallation-deprotonation (CMD) mechanism. The insertion of ynamides is irreversible and controls the regioselectivity. The calculation results revealed that the oxidative addition of di-tert-butyl diaziridinone to Pd(II) yields a high-valent Pd(IV) intermediate, accompanied by the cleavage of the N-N bond in di-tert-butyl diaziridinone via a concerted three-membered cyclic transition state. Subsequent transformation through reductive elimination and β-N elimination affords the desired indole product. The rate determining step of this reaction is the oxidative addition of di-tert-butyl diaziridinone. Distortion-interaction analysis were performed to demonstrate the origin of regioselectivity in this reaction.
A magnetic catalyst comprising Fe3O4 nanoparticles (NPs) was synthesized using a co‑precipitation method and analyzed through FT-IR, XRD, SEM, TEM, VSM, TGA, UV–Vis, and EDX. Strong magnetic responsiveness was confirmed by VSM measurements, which demonstrated a saturation magnetization of 60.5 emu g⁻¹. TEM investigation revealed spherical particles with a size distribution of 7.5–20 nm (average size 14.1 nm). Using TBAB as a co-catalyst and PEG-400 as a green solvent, the Fe3O4 NPs effectively catalyzed the cycloaddition of CO2 with different epoxides under mild circumstances (50 mg catalyst, 100 mg TBAB, 0.1 g PEG-400, 100 °C, 1 atm CO2, 3 h). High to excellent conversions (55–99%) were obtained for the comparable cyclic carbonates. In comparison to traditional carbonate‑formation methods, this approach offers faster reaction times, superior product yields, and ease of operation, making it suitable for large-scale applications. Furthermore, the Fe3O4 catalyst can be recycled over six cycles without a notable reduction in yields or loss of activity.
A series of heterobimetallic dimers with the general formula [Pt2(PP)2(μ-Cl)2][BArF24]2 (PP = 1,1′-bis(phosphino)ferrocene; BArF24 = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate)) were prepared by the reaction of the corresponding metal dichlorides, [Pt(PP)Cl2], with Na[BArF24]. These dimers were characterized via multinuclear NMR spectroscopy, elemental analysis and in several cases by X-Ray crystallography and 57Fe Mössbauer spectroscopy. In addition, the oxidative electrochemistry of these compounds was examined. The addition of the monodentate phosphines (PR3) to these dimers generally led to the symmetric cleavage of the dimers and the formation of [Pt(PP)Cl(PR3)][BArF24] compounds. However, for particularly bulky 1,1′-bis(phosphino)ferrocene or monodentate phosphine ligands, no reaction was observed. The [Pt(PP)Cl(PR3)][BArF24] compounds were characterized by multinuclear NMR spectroscopy, elemental analysis and in many instances, X-ray crystallography. The oxidation of these compounds was examined by cyclic voltammetry. The compounds typically exhibit a single oxidative wave the potential of which is influenced by the PP and PR3 ligands. The exception is [Pt(dppf)(PFcPh2)Cl][BArF24] which exhibits two oxidative waves due to the two inequivalent iron centers. Several of these compounds were also characterized by 57Fe Mössbauer spectroscopy.
Direct C–H sulfidation offers a step-economical approach for constructing heteroaryl sulfides by converting native C–H bonds into C–S bonds without prior substrate functionalization. This review summarizes advances reported from 2015 to 2025 in the C–H sulfidation of heterocycles, focusing on different catalytic and promoter systems rather than a single protocol. The covered methodologies include transition-metal catalysis, copper- and palladium-based systems, iodine-mediated and metal-free reactions, oxidative cross-dehydrogenative coupling, photoredox catalysis, electrochemical methods, and recyclable heterogeneous or nanocatalytic platforms. The discussion is organized according to catalyst type, sulfur source, heterocycle class, regioselectivity, and synthetic applicability. Representative substrates include indoles, imidazopyridines, pyrroles, quinolines, pyridines, thiophenes, benzothiazoles, purines, and pyrazoles. Key challenges include substrate-dependent selectivity, limited scalability, metal recovery, oxidant requirements, and sulfur-source compatibility. Future directions emphasize safer sulfur donors, earth-abundant catalysts, electrochemical or oxidant-free methods, recyclable systems, and broader site-selective protocols.
1,2,3-Benzoselenadiazoles are a significant class of selenium-containing fused heterocycles, characterized by a 1,2,3-selenadiazole ring annulated to a benzene core. These compounds, along with their derivatives, can be synthesized through several established methods. Common approaches include: (i) the condensation of (E)-1-((2-iodophenyl)diazenyl)piperazine with BuLi in the presence of selenium or SeBr₄, (ii) diazotization of 2-aminobenzeneselenol using nitrous acid (HNO₂), and (iii) oxidative cyclization of hydrazones or semicarbazones employing SeO₂ in acetic acid. In addition to these methods, a range of newer synthetic strategies has been developed, highlighting the versatility and continued interest in this class of compounds.
Organic synthesis is vital to upholding the tenets of green chemistry, as it reduces waste generation, leverages inexpensive, abundant starting materials, and supports the use of reusable catalysts. Lately, catalysis derived from biological sources has gained traction as a viable approach, thanks to its minimal ecological footprint, lower toxicity, and cost-effectiveness. Chitosan and its derivatives, in particular, stand out among bio-based materials for their robust promise as eco-friendly catalytic supports. Chitosan continues to attract significant interest owing to its unique properties and broad potential applications. Each year, publications and patents on this polymer show steady growth, reflecting increasing research momentum. This review article outlines the latest advancements and noteworthy developments (2020–2025) in the usage of chitosan and its derivatives as bio-based supports for metal immobilization in Sonogashira reactions. It covers methodologies for immobilizing metal nanoparticles (Pd, Au, Cu, Ti, and Co) or metal ions on unmodified chitosan, chitosan blended with organic and inorganic polymers, and ligand-functionalized chitosan variants.
A novel and efficient heterogeneous catalytic system based on Fe₃O₄/MWCNTs–Dop/Phen–MnCl₂ nanocatalyst has been developed for the synthesis of propargylamines via A³ coupling reactions of aldehydes, terminal alkynes, and secondary amines. The catalyst was rationally designed by immobilizing Mn(II) species onto a multifunctional dopamine/phenanthroline ligand framework anchored on Fe₃O₄-decorated multi-walled carbon nanotubes. This ligand combination was deliberately selected due to the complementary properties of its constituent components: dopamine provides robust surface anchoring through its catecholic hydroxyl groups while simultaneously offering N-donor coordination capabilities, whereas phenanthroline contributes rigid bidentate coordination geometry that stabilizes the Mn(II) center and prevents aggregation, thereby maximizing catalytic efficiency. This synergistic bifunctional ligand architecture combines exceptional metal coordination strength, high surface area accessibility, and magnetic recoverability within a single integrated nanostructure. Comprehensive characterization using FT-IR, XRD, TGA, BET, VSM, SEM, TEM, EDX, ICP-OES, and XPS analyses confirmed the structural integrity, mesoporosity, and well-dispersed nature of the active sites. Under optimized aqueous conditions at reflux, the catalyst exhibited excellent catalytic activity, affording propargylamines in high yields (89–99%) within short reaction times. Broad substrate scope was achieved, demonstrating high tolerance toward electron-donating and electron-withdrawing substituents as well as heteroaromatic systems. Mechanistic investigations revealed a cooperative activation pathway involving Mn(II)-mediated alkyne activation coupled with iminium ion formation. Notably, the catalyst demonstrated outstanding recyclability, retaining high activity over nine consecutive cycles with negligible Mn leaching. The innovation of this work resides in the strategic integration of a magnetic MWCNT-supported Mn(II) system with a dual-function Dop/Phen ligand platform, establishing a green, efficient, and economically viable catalytic approach for A³ coupling reactions in aqueous medium.
Long-wavelength-emitting iridium complexes are commonly developed by introducing strong intramolecular donor–acceptor (D–A) interactions, extending π conjugation, or incorporating specific heteroatoms. Although effective, these approaches often lead to increased structural complexity and more demanding synthesis. In this work, we adopt a molecular design strategy based on three bidentate ligands with distinct formal charge states (−2, −1, and 0) to construct a series of heteroleptic Ir(III) complexes. The asymmetric acac derivatives can coordinate in different orientations, resulting in the formation of coordination isomers. Accordingly, four complexes were obtained: Ir(C^C)(N^N)(acac-CF3) (Ir-1a), Ir(N^N)(C^C)(acac-CF3) (Ir-1b), Ir(C^C)(N^N)(acac-Th) (Ir-2a), and Ir(N^N)(C^C)(acac-Th) (Ir-2b). Despite their relatively simple molecular structures, these complexes show distinct deep-red/near-infrared emission with maxima ranging from 662 to 704 nm, mainly arising from intramolecular ligand-to-ligand charge-transfer character. OLEDs based on these emitters further exhibit promising electroluminescent performance, highlighting the potential of this tri-valence-state ligand design strategy for developing long-wavelength electroluminescent materials.
Palladium-catalyzed alkoxycarbonylation has evolved into a powerful and adaptable method for ester synthesis, distinguished by its exceptional efficiency, selectivity, and broad substrate scope. Recent years have witnessed remarkable progress in both mechanistic understanding and catalyst design, particularly through the development of advanced ligand frameworks that enable precise control over reactivity and selectivity. These innovations have paved the way for milder reaction conditions and enhanced compatibility with complex and sensitive functional groups. Ongoing research also addresses practical aspects such as catalyst stability, process scalability, and operational simplicity. Furthermore, the integration of modern synthetic technologies—including flow chemistry, renewable carbon sources, and computational modeling—has further elevated the versatility and industrial potential of this transformation. This review provides a comprehensive overview of recent advancements, highlights their synthetic significance, and critically evaluates current limitations, including catalyst loading, recyclability, and solvent choices, to provide a balanced perspective on the methodology’s environmental profile.
Tellurazole and pyridine are privileged heterocyclic scaffolds in medicinal chemistry, widely recognized as versatile building blocks for therapeutic agents due to their broad and diverse pharmacological profiles. The strategic fusion of these moieties has led to the development of a promising class of tellurium-containing heterocycles, namely benzotellurazoles and tellurazolopyridines. Tellurazolopyridines encompass several structural isomers, including tellurazolo[5,4-b]pyridines and quaternary tellurazolo[3,2-a]pyridin-4-ium salts. These fused systems exhibit enhanced biological activities, such as potent antioxidant, angiotensin-converting enzyme (ACE) inhibitory, antitumor, rodenticidal, insecticidal, fungicidal, and bactericidal effects. Such activities are largely attributed to the distinctive redox behavior of tellurium in combination with the electronic and structural features of the pyridine ring. This review presents a comprehensive overview of the design strategies, synthetic approaches, and biological evaluations of benzotellurazoles, tellurazolopyridines, and their corresponding salts.
A comprehensive DFT/TD-DFT and in silico investigation was performed on a series of nine 4-methylsulfonylbenzyl-substituted Ru(II) N-heterocyclic carbene (NHC) complexes previously synthesized experimentally. Geometry optimizations carried out at the B3LYP/def2-TZVP and PBE0/def2-TZVP levels showed excellent agreement with available X-ray data, confirming the stability of the pseudo-octahedral Ru(II) coordination sphere. Frontier molecular orbital analysis revealed HOMO–LUMO energy gaps ranging from 3.95–4.18 eV B3LYP and 4.63–4.88 eV PBE0, indicating high kinetic stability with moderate substituent-dependent electronic modulation. Global reactivity descriptors identified complex 1 h as exhibiting the most favorable balance between stability and chemical reactivity. NBO, MEP, and APT analyses confirmed efficient electron delocalization and metal-to-ligand charge transfer (MLCT), with electron-rich Ru and donor atoms acting as the principal reactive sites. TD-DFT calculations predicted intense absorption bands at 290–293 nm B3LYP and 273–277 nm PBE0, mainly arising from π→π* transitions with partial MLCT character. The investigated complexes also displayed remarkable nonlinear optical responses, with first-order hyperpolarizabilities reaching 1.15 × 104 x 10–33 esu, approximately 30 times larger than that of urea, highlighting their potential for photonic and optoelectronic applications. In silico pharmacokinetic evaluation using SwissADME and ProTox-III predicted favorable drug-likeness and low toxicity, while molecular docking against the 5V4G target demonstrated strong binding affinities, with complexes 1a, 1b, 1 g, and particularly 1 h exhibiting the most favorable interaction profiles. The present study elucidates the relationships between molecular structure, electronic properties, and biological performance of Ru(II)-NHC complexes and identifies 1 h as the most promising candidate for future biological investigations, whereas 1e exhibits the strongest nonlinear optical response.
A porphyrin-based metallacycle, namely [Au₂(1)₂](PF6)2, was synthesized using zinc(II) porphyrin 1 bearing two peripheral N-heterocyclic carbene (NHC) ligands on the meso positions 5 and 15. The dimeric complex was formed through coordination-driven assembly with Ag(I), followed by transmetallation with Au(I). The two porphyrins adopt a cofacial yet flexible arrangement, and spectroscopic studies revealed solvent-dependent behaviour. DFT calculations showed that the metallacycle can expand to accommodate 1,4-diazabicyclo[2.2.2]octane (DABCO). Proton NMR experiments confirmed the encapsulation of DABCO with rapid exchange compared to the related porphyrin-based metallacage constructed from a zinc(II) porphyrin bearing four peripheral NHC ligands on the meso positions 5, 10, 15 and 20.
A mixed-linker amino-functionalized copper-based metal-organic framework (NH2Cu-MOF) was successfully prepared by an ultrasound-assisted green method and used as an efficient heterogeneous catalyst for O-arylation reactions. The framework was constructed using benzene-1,3,5-tricarboxylic acid (BTC) and amino-functionalized BTC (NH2-BTC) as mixed organic linkers in an ethanol-water medium under mild conditions. The incorporation of amino-functionalized linkers generated structural defects and introduced additional active functionalities, enhancing the accessibility and catalytic activity of Cu sites. The successful formation of NH2Cu-MOF was confirmed by FT-IR, XPS, and XRD analyses, while SEM, BET, and TGA studies demonstrated its nanoscale morphology, porous structure, and thermal stability. The catalytic activity of NH2Cu-MOF was investigated in O-arylation reactions using water as an environmentally benign solvent. The catalyst exhibited high activity toward a wide range of substrates, affording diaryl ether products in good to excellent yields under mild reaction conditions. Moreover, the catalyst exhibited excellent recyclability, maintaining significant activity over multiple reaction cycles. These results exhibit that mixed-linker functionalization is as an effective strategy for designing robust and efficient Cu-based MOF catalysts for green organic transformations.
