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Herein, a series of new Ag(I)-NHC complexes containing 1,3-dioxane group were synthesized by the direct reaction of Ag2O and benzimidazolium salts in light-free conditions. All Ag(I)-NHC complexes were spectrally characterized using 1H, 13C NMR, FT-IR, LC-MS, and elemental analysis. Additionally, the structures of compounds 1a and 1e were elucidated by the single X-ray diffraction techniques. Further, the synthesized Ag(I)-NHC complexes were evaluated for cytotoxicity study on the L-929 cells and the anticancer activity against the HCT 116 and MCF-7 cancer cell lines. Notably, 1a showed significant anticancer activity against HCT 116 with an IC50 of 6.37 ± 0.92 µg/mL compared to cisplatin (IC50 = 36.75 ± 1.76 µg/mL). 1c (IC50 = 3.21 ± 1.96 µg/mL) and 1e (IC50 = 3.72 ± 1.12 µg/mL) exhibited significant anticancer activity against MCF-7 cells and was similar to cisplatin (IC50 = 32.17 ± 2.85 µg/mL). Meanwhile, 1a and 1e displayed the highest selectivity index. Most importantly, the cell viability test showed that 1e induced neglectable cytotoxicity (IC50 = 36.38 ± 2.27 µg/mL) toward L-929 and was similar to cisplatin (IC50 = 36.11 ± 2.09 µg/mL). The anticancer activities of Ag(I)-NHC complexes vary depending on the substituent group of the silver complex and the cell line type. Moreover, the inhibitory mechanism of 1e was not dependent on caspase-associated apoptosis initiated by the lysosomal-mitochondrial pathway. Taken together, we conclude that this work provides a simple and rapid protocol for the synthesis of Ag(I)-NHC complexes and the featured Ag(I)-NHC complexes have an anticancer drug potential for biomedical applications.

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A new, cationic N-heterocyclic carbene RhI complex with a tetra-fluorido-borate counter-anion, [Rh(C8H12)(C8H15N3)(C18H15P)]BF4, has been synthesized and structurally characterized. There are two independent ion pairs in the asymmetric unit. Each complex cation exhibits a distorted square-planar conformation around the RhI atom. Bond lengths and bond angles are as expected for an Rh-NHC complex. There are several close, non-standard C-H⋯F hydrogen-bonding inter-actions between the ions. One of the tetra-fluorido-borate anions shows statistical disorder of the F atoms.

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Covalent organic frameworks linked by carbon-carbon double bonds (C=C COFs) are an emerging class of crystalline, porous, and conjugated polymeric materials with potential applications in organic electronics, photocatalysis, and energy storage. Despite the rapidly growing interest in sp2 carbon-conjugated COFs, only a small number of closely related condensation reactions have been successfully employed for their synthesis to date. Herein, we report the first example of a C=C COF, CORN-COF-1 (CORN = Cornell University), prepared by N-heterocyclic carbene (NHC) dimerization. In-depth characterization reveals that CORN-COF-1 possesses a two-dimensional layered structure and hexagonal guest-accessible pores decorated with a high density of strongly reducing tetraazafulvalene linkages. Exposure of CORN-COF-1 to tetracyanoethylene (TCNE, E1/2 = 0.13 V and -0.87 V vs. SCE) oxidizes the COF and encapsulates the radical anion TCNE•- and the dianion TCNE2- as guest molecules, as confirmed by spectroscopic and magnetic analysis. Notably, the reactive TCNE•- radical anion, which generally dimerizes in the solid state, is uniquely stabilized within the pores of CORN-COF-1. Overall, our findings broaden the toolbox of reactions available for the synthesis of redox-active C=C COFs, paving the way for the design of novel materials.

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Because of eco-friendliness, biodegradability and ease of modification, cellulose is deemed as alternative to unrenewable petroleum resources. Nonetheless, it is more indispensable to exploit corn cob cellulose produced from agricultural waste residue as supportive materials in green catalysis. In this study, a new magnetically benzimidazole functionalized cellulose/Fe3O4 derived from corn cob cellulose as a stabilizer agent (Fe3O4@CL-NHC) was prepared, and palladium was immobilized on this stabilizer (Fe3O4@CL-NHC-Pd). The catalyst was fully characterized by different techniques including TEM, SEM, and XPS analyses, etc. The abundant hydroxyl groups of cellulose provided uniform dispersion and high stability of palladium, while Fe3O4 as a support offered simple magnetic separation. High efficiency (up to 99 %) was demonstrated by this biocatalyst under green conditions in relatively short reaction times towards Suzuki reactions. Due to collaborative interactions of N-heterocyclic carbene and hydroxyl groups with palladium, the synthesized complex prevented metal leaching effectively (<1 %). Moreover, the magnetic property of this catalyst (43.0 emu g-1) provides facile recovery of this composite from the reaction mixture with great ease for several times, which overcomes issues of complicated work-up separation. This work offers a promising avenue to enriching the application of biopolymer from agricultural residue in the potential organic transformations.

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A new eco-friendly method for the synthesis of mono- and multifunctional organosulfur compounds, based on the process between ynals and thiols, catalyzed by bulky N-heterocyclic carbene (NHC), was designed and optimized. The proposed organocatalytic approach allows the straightforward formation of a broad range of thioesters and sulfenyl-substituted aldehydes in yields above 86%, in mild and metal-free conditions. In this study, thirty-six sulfur-based derivatives were obtained and characterized by spectroscopic methods.

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Hydrogen isotope exchange (HIE) via C-H activation constitutes an efficient method for the synthesis of isotopically-enriched compounds, which are crucial components of the drug discovery process and are extensively employed in mechanistic studies. A series of iridium(I) complexes, bearing a chelating phosphine-N-heterocyclic carbene ligand, was designed and synthesized for application in the catalytic HIE of challenging N- and O-aryl carbamates. A broad range of substrates were labeled efficiently, and applicability to biologically-relevant systems was demonstrated by labeling an ʟ-tyrosine-derived carbamate with excellent levels of deuterium incorporation. Combined theoretical and experimental studies unveiled intriguing mechanistic features within this process, in comparison to C-H activation and hydrogen isotope exchange catalysed by monodentate Ir(I) NHC/phosphine complexes.

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In this manuscript, literature reports on mono- and di-halogen (F, Cl, Br, and I) substituted at positions 4 or/and 4,5 imidazol-2-ylidene (NHC) metal complexes are discussed: particularly, their structural diversity with various metals (groups 6-13), important physicochemical properties, catalytic and medicinal/biological applications are reviewed. To our knowledge, there are no literature reports on group 4 and 5 metal complexes with this type of NHC ligands. Halogenated imidazol-2-ylidene metal complexes deserve special attention because halogens are the classic electron donating groups (mesomerically) in conjugated aromatic/heteroaromatic ring systems, but electron withdrawing inductively. However, they exhibit a significant electron withdrawing inductive effect, thus providing unique electronic properties. This is important for fine tuning of σ-donor abilities of the "carbenic" carbon of imidazol-2-ylidenes, which directly affect catalytic performance of their metal complexes. Other applications, advantages, and disadvantages of halogenated vs. unsubstituted imidazol-2-ylidene metal complexes are critically analyzed and summarized in this review.

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Due to the growing significance of sustainable and environmentally friendly organic transformations, there has been increasing interest in utilizing vitamins as catalysts owing to their green nature, biocompatibility, and ease of preparation. Among these, Vitamin B1, also known as thiamine stands out for its nonflammable, water-soluble, inexpensive, and non-toxic characteristics. This review summarized recent developments on the catalytic application of Vitamin B1 in organic transformations, particularly in facilitating C-C and C-X (N, O, S) bond formations, thus demonstrating its efficacy in synthesizing complex molecules. Vitamin B1 exhibits versatility in these reactions, functioning as both an organocatalyst as well as a co-catalyst or ligand with other metal catalysts. The review also delves into the application of thiamine diphosphate -dependent enzymes as catalysts in organic reactions, drawing inspiration from natural enzymatic processes. Additionally, the mechanistic intricacies of thiamine-catalyzed reactions and the roles of co-catalysts or additives are thoroughly examined, providing insights into reaction pathways and facilitating informed catalyst design strategies.

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Developing methods to directly transform C(sp3) -H bonds is crucial in synthetic chemistry due to their prevalence in various organic compounds. While conventional protocols have largely relied on transition metal catalysis, recent advancements in organocatalysis, particularly with radical NHC catalysis have sparked interest in the direct functionalization of "inert" C(sp3) -H bonds for cross C-C coupling with carbonyl moieties. This strategy involves selective cleavage of C(sp3) -H bonds to generate key carbon radicals, often achieved via hydrogen atom transfer (HAT) processes. By leveraging the bond dissociation energy (BDE) and polarity effects, HAT enables the rapid functionalization of diverse C(sp3)-H substrates, such as ethers, amines, and alkanes. This mini-review summarizes the progress in carbene organocatalytic functionalization of inert C(sp3)-H bonds enabled by HAT processes, categorizing them into two sections: 1) C-H functionalization involving acyl azolium intermediates; and 2) functionalization of C-H bonds via reductive Breslow intermediates.

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A stereoselective hydroxyallylation reaction of cyclopropenes with cyclopropanols is achieved under zinc-mediated conditions, affording densely functionalized cyclopropanes with excellent diastereocontrol over three contiguous stereocenters within and outside the cyclopropane ring. A racemic variant of the reaction is synergistically promoted by catalytic N-heterocyclic carbene (NHC) and organic base, whereas chiral amino alcohol-derived bifunctional NHC enables a catalytic enantioselective variant. The reaction likely involves the generation of enolized zinc homoenolate via ring-opening of zinc cyclopropoxide and enolization of the resulting homoenolate, followed by its addition to the cyclopropene as a prochiral allylzinc nucleophile. Our mechanistic investigations highlighted the transient nature of enolized homoenolate, which, once generated from thermodynamically predominant cyclopropoxide, immediately proceeds to allylzincation with cyclopropene. The NHC not only promotes the rate-determining generation of enolized homoenolate but also engages in the allylzincation process. The resulting cyclopropylzinc species undergoes partial in situ protonation while partially remaining intact, thereby leaving an opportunity for trapping with an external electrophile.

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A series of Au(I) complexes containing unsymmetrical N-heterocyclic carbene (imidazolylidene and benzimidazolylidene) functionalized with a xyloside group and an alkyl moiety (methyl and mesityl) was prepared using efficient procedures from D-xylose. Their characterization was carried out in solution by multinuclear NMR, HR-MS spectrometry and cyclic voltammetry, as well as in the solid state by means of single crystal X-ray diffraction analysis for two of them. Evaluation of their ability to inhibit bacterial growth showed a preference for a Gram-positive strain, Staphylococcus aureus, over a Gram-negative strain, Pseudomonas aeruginosa.

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A new neutral triazole-based N-heterocyclic carbene rhodium(I) complex [RhCl(C8H12)(C8H15N3)], has been synthesized and structurally characterized. The complex crystallizes with two mol-ecules in the asymmetric unit. The central rhodium(I) atom has a distorted square-planar coordination environment, formed by a cyclo-octa-1,5-diene (COD) ligand, an N-heterocyclic carbene (NHC) ligand, and a chlorido ligand. The bond lengths are unexceptional. A weak inter-molecular non-standard hydrogen-bonding inter-action exists between the chlorido and NHC ligands.

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To study the effect of a dye on the photoluminescence (PL) properties of metal complexes, a series of gold(I) complexes were synthesized, containing a 7-amino-4-methylcoumarin luminophore. The complexes are comprised of a coumarin moiety featuring different ancillary ligands, specifically N-heterocyclic carbenes, triphenylphosphine, and diphenyl-2-pyridylphosphine. The synthesized gold(I) complexes are luminescent both in solution and the solid state at room temperature and 77 K. Complexes of different nuclearity, i.e., mono-, di- and trinuclear compounds were synthesized. A clear trend between the nuclearity and the quantum yields can be seen. The coumarin dye not only improves the PL properties, but also enhances the luminescence of trinuclear clusters, which are otherwise known to be weak emitters in solution. The optical absorption properties were investigated in detail by quantum chemical calculations.

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N-Heterocyclic carbenes (NHCs) have become important tools in modern synthetic chemistry due to their versatility as organocatalysts and ligands in organometallic complexes. Since their first isolation and characterization, NHCs have demonstrated significant utility in various catalytic processes, offering advantages such as strong σ-electron donation and the ability to stabilize reactive intermediates. However, beyond their well-documented roles in catalysis, the potential of NHCs as stoichiometric reagents and synthetic building blocks remains an underexplored yet promising area. This Mini-review aims to shed light on these lesser-known applications of NHCs and their N-heterocyclic precursors or derivatives in organic synthesis. Furthermore, we discuss how the unique electronic and steric properties of NHCs can be harnessed to develop new synthetic methodologies or construct interesting organic frameworks. By highlighting these emerging uses, we hope to encourage further research into the non-catalytic applications of NHCs, broadening their scope and impact in synthetic chemistry.

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Three new tridentate copper(II) N-heterocyclic carbene (NHC) complexes have been obtained and characterized with symmetrical C-4 substitutions on their pendent pyridine rings. Substitutions including methyl (Me), methoxy (OMe), and chloro (Cl) groups, which extend the library pincer Cu-NHC complexes under investigation, modify the impact of pyridinyl basicity on NCN pincer complexes. Both ligand precursors and copper(II) complexes are characterized using a range of techniques, including nuclear magnetic resonance (NMR) spectroscopy for 1H, 13C, 31P, and 19F nuclei, electrospray ionization mass spectrometry (ESI-MS), X-ray crystallography, cyclic voltammetry, and UV-Vis spectroscopy. The pyridine substitutions lead to minimal changes to bond lengths and angles in the X-ray crystal structures of these related complexes; there is a pronounced impact on the electrochemical behavior of both the ligand precursors and copper complexes in the solution. The substitution in the pyridinyl units of these complexes show an impact on the catalytic reactivity of these complexes as applied to a model C-N bond-forming reaction (CEL cross-coupling) under well-established conditions; however, this observation does not correlate to the expected change in basicity in these ligands.

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Herein, we report the inaugural instance of NHSi-coordinated copper amide emitters (2-5). These complexes exhibit thermally activated delayed fluorescence (TADF) and singlet-triplet dual emission in anaerobic conditions. The NHSi-Cu-diphenylamide (2) complex demonstrates TADF with a very small ΔEST gap (0.01 eV), an absolute quantum yield of 11%, a radiative rate of 2.55×105 s-1, and a short τTADF of 0.45 µs in the solid state. The dual emissive complexes (3-5) achieve an absolute quantum yield of up to 20% in the solid state with a kISC rate of 1.82×108 s-1 and exhibit room temperature phosphorescence (RTP) with lifetimes up to 9 ms. The gradual decrease in the intensity of the triplet state of complex 3 under controlled oxygen exposure demonstrates its potential for future oxygen-sensing applications. Complexes 2 and 3 have been further utilized to fabricate converted LEDs, paving the way for future OLED production using newly synthesized NHSi-Cu-amides.

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Diradicals based on a meta-quinodimethane (m-QDM) scaffold generally have a triplet ground state and are rather scarce. Herein, m-QDM-based non-Kekulé diradicals [3,3'-(NHC)2BP] (3-NHC) (NHC = SIPr = C{N(Dipp)CH2}2; IPr = C{N(Dipp)CH}2, Me-IPr = C{N(Dipp)CMe}2; Dipp = 2,6-iPr2C6H3; BP = 1,1'-C6H3C6H3) featuring N-heterocyclic carbene (NHC) pendants are reported as crystalline solids. The EPR spectra of 3-NHC show both allowed (Dms = 1) and forbidden (Dms = 2; 'half-field') transitions characteristic for triplet diradicals. Variable temperature EPR studies however reveal a singlet ground state for 3-SIPr. Consistent with the EPR spectra, calculations predict a remarkably small (open-shell) singlet-triplet energy gap (ΔEST ≤ 0.26 kcal/mol) for the 3-NHC compounds. The calculated singlet diradical character for the ground states of the 3-NHC compounds amounts to ~99%.

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Catalytic activation of Caryl-O bonds is considered as a powerful strategy for the production of aromatics from lignin. However, due to the high reduction potentials of diaryl ether 4-O-5 linkage models, their single electron reduction remains a daunting challenge. This study presents the blue light-induced bifunctional N-heterocyclic carbene (NHC)-catalyzed one-electron reduction of diaryl ether 4-O-5 linkage models for the synthesis of trivalent phosphines. The H-bond between the newly devised bifunctional NHC and diaryl ethers is responsible for the success of the single electron transfer. Furthermore, this approach demonstrates selective one-electron reduction of unsymmetric diaryl ethers, oligomeric phenylene oxide, and lignin model.

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The JAK-STAT signalling pathway is primarily involved in cytokine signalling and induces various factors namely, erythropoietin, thrombopoietin, interferons, interleukins, and granulocyte colony-stimulating factors. These factors tremendously influenced understanding human health and illness, specifically cancer. Inhibiting the JAK/STAT pathway offers enormous therapeutic promises against cancer. Many JAK inhibitors are now being studied due to their efficacy in various cancer treatments. Further, the Nitrogen-heterocyclic (N-heterocyclic) scaffold has always shown to be a powerful tool for designing and discovering synthetic compounds with diverse pharmacological characteristics. The review focuses on several FDA-approved JAK inhibitors and their systematic categorization. The medicinal chemistry perspective is highlighted and classified review on the basis of N-heterocyclic molecules. Several examples of designing strategies of N-heterocyclic rings including pyrrolo-azepine, purine, 1H-pyrazolo[3,4-d]pyrimidine, 1H-pyrrolo[2,3-b]pyridine, pyrazole, thieno[3,2-d] pyrimidine, and, pyrimidine-based derivatives and their structure-activity relationships (SAR) are discussed. Among the various N-heterocyclic-based JAK inhibitors pyrimidine-containing compound 1 exhibited excellent inhibition activity against JAK2WT and mutated-JAK2V617F with IC50 of 2.01 and 18.84 nM respectively. Amino pyrimidine-containing compound 6 and thiopheno[3,2-d]pyrimidine-containing compound 13 expressed admirable JAK3 inhibition activity with IC50 of 1.7 nM and 1.38 nM respectively. Our review will support the medicinal chemists in refining and directing the development of novel N-heterocyclic-based JAK inhibitors.

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The activation of C-C bonds by transition-metal complexes is of continuing interest and acetonitrile (MeCN) has attracted attention as a cyanide source with comparatively low toxicity for organic cyanation reactions. A diiron end-on µ-η1:η1-CN-bridged complex was obtained from a crystallization experiment of an open-chain iron-NHC complex, namely, µ-cyanido-κ2C:N-bis{[(acetonitrile-κN)[3,3'-bis(pyridin-2-yl)-1,1'-(methylidene)bis(benzimidazol-2-ylidene)]iron(II)} tris(hexafluorophosphate), [Fe2(CN)(C2H3N)2(C25H18N6)2](PF6)3. The cyanide appears to originate from the MeCN solvent by C-C bond cleavage or through carbon-hydrogen oxidation.