N-heterocyclic Carbene Adducts Research Articles

Visible light-mediated organocatalyzed 1,3-aminoacylation of cyclopropane employing N-benzoyl saccharin as bifunctional reagent

The carboamination of unsaturated molecules using bifunctional reagents is considered an attractive approach for the synthesis of nitrogen-containing compounds. However, bifunctional C–N reagents have never been employed in the carboamination of cyclopropane. In this study, we use an N-heterocyclic carbene (NHC), N-benzoyl saccharin, as a bifunctional reagent and a photoredox catalyst for a dual-catalyzed 1,3-aminoacylation of cyclopropane. NHCs play multiple roles, functioning as Lewis base catalysts to activate C–N bonds, promoting the oxidative quenching process of PC*, and acting as efficient acyl radical transfer catalysts for the formation of C–C bonds. The oxidative quenching process between the excited-state PC* and acyl NHC adduct is the key to the photooxidation generality of aryl cyclopropanes.

Mono-Ortho-Beryllated Carbodiphosphoranes: Synthesis, Structure, Bonding and Reactivity.

The reaction of organoberyllium compounds with hexaphenylcarbodiphosphorane yields mono-ortho-beryllated complexes, which feature a double dative Be=C bond. The bonding situation in these compounds together with a simple carbodiphosphorane and an N-heterocyclic carbene adduct was analysed with energy decomposition analysis in combination with natural orbital for chemical valence as well as with quantum theory of atoms-in-molecules. Furthermore, the driving forces accountable for mono-ortho-beryllation were elucidated along with the reactivity of the Be=C bond.

Polymer Mechanochemistry on Reactive Species Generated from Mechanochemical Reactions†

Comprehensive SummaryPolymer mechanochemistry on reactive species has attracted more and more attentions over the past 20 years, as the mechanochemical generation of reactive species has a great potential in developing different polymeric materials for various purposes, such as stress detection, self‐healing, self‐strengthening, controllable degradation and release of small molecules. In this review, we first discuss the recent progress on polymer mechanochemistry of the reactive species that are generated from the mechanochemical reactions of mechanophores. Five types of reactive species, including radical, zwitterion, ionic, carbene and neutral intermediates, and their applications were reviewed in detail. Since mechanochemical reactions are sensitive to the mechanophore structure and polymer framework, we then discuss how mechanophore isomerism, polymer structure, polymer attachment point, and polymer architecture influence the mechanophore activation. At last, we provide our perspectives on the polymer mechanochemistry of reactive species. Key ScientistsIn the 1930s, a seminal work by Staudinger showed that the molecular weight of poly(styrene) reduced after mastication. However, polymer mechanochemistry mainly focused on the destructive effects of mechanical force, until Moore reported that the azo‐mechanophore was cleaved selectively upon sonication in 2005. Afterwards, his group also found that mechanical force changed the reaction pathway of benzocyclobutene and made spiropyran display purple color under stress. In 2009, Sijbesma revealed that metal–NHC could be used as a latent catalyst to catalyze transesterification and polymerization. Subsequently, the Craig group disclosed the special mechanical reactivity of perfluorocyclobutane in 2011 and examined the influence of polymer backbone on the reactivity of epoxides in 2012. Later, they also reported that the lever‐arm effect enhanced gDBC or gDCC mechanochemistry. Since 2015, Otsuka's group has developed a series of mechanophores that generated various carbon radicals and showed different colors under mechanical force. De Bo subsequently investigated the effect of regio‐ and stereochemistry on the reactivity of furan–maleimide adduct in 2017, and he examined the different mechanisms of the mechanical activation of tetrafluorobenzene–NHC (N‐heterocyclic carbene) adduct in 2020. During that time, the Choi group explored the influence of polymer architecture on the mechanophore activation, and Robb's group utilized a furan‐maleimide adduct to achieve the release of different small molecules. In 2020, Göstl and Herrmann employed the scission of the disulfide within polymers to release drugs and reporting molecules by ultrasound, and the Chen group also investigated the mechanochemistry of diselenides which afforded selenium radicals. In 2021, Boydston's group realized the “flex‐activation” of NHC‐carbodiimide to release NHC small molecules. Recently, the Chen group achieved multistate mechanochromism by combining two Rh structures together through a conjugated connector. In addition, Robb designed a furan‐maleimide adduct to mechanically give a donor–acceptor Stenhouse adduct that reacted with different amines to display various colors. This review has focused on the chemistry of reactive species that are generated from mechanochemical reactions.

NHC-Stabilized Mixed Group 13/14/15 Element Hydrides.

The syntheses of novel N-heterocyclic carbene (NHC) adducts of group 13, 14 and 15 element hydrides are reported. Salt metathesis reactions between NaPH2 and IDipp ⋅ GeH2 BH2 OTf (1) (IDipp=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) led to mixtures of the two isomers IDipp ⋅ GeH2 BH2 PH2 (2 a) and IDipp ⋅ BH2 GeH2 PH2 (2 b); by altering the reaction conditions an almost exclusive formation of 2 b was achieved. Attempts to purify mixtures of 2 a and 2 b by re-crystallization from THF afforded a salt [IDipp ⋅ GeH2 BH2 ⋅ IDipp][PHGeH2 BH2 PH2 BH2 GeH2 ] (4) that contains the novel anionic cyclohexyl-like inorganic heterocycle [PHGeH2 BH2 PH2 BH2 GeH2 ]- . In addition, the borane adducts IDipp ⋅ GeH2 BH2 PH2 BH3 (3 a) and IDipp ⋅ BH2 GeH2 PH2 BH3 (3 b) as even longer chain compounds were obtained from reactions of 2 a/2 b with H3 B ⋅ SMe2 and were studied by NMR spectroscopy. Accompanying DFT computations give insight into the mechanism and energetics associated with 2 a/2 b isomerization as well as their decomposition pathways.

Trigonal bipyramidal or square planar? Density functional theory calculations of iron bis(dithiolene) N-heterocyclic carbene complexes.

Density functional theory (DFT) calculations of 57 iron bis(dithiolene)-N-heterocyclic carbene adducts were conducted to determine what parameters predict, and possibly influence, the coordination of these aforementioned adducts. The parameters considered herein include three different types of nuclear magnetic resonance (C-NMR, Se-NMR, and P-NMR) isotropic chemical shifts, the Tolman Electronic Parameter (TEP), the Huynh Electronic Parameter (HEP), and the percent buried volume (%Vbur) of the different N-heterocyclic carbenes (NHCs) calculated from DFT. These parameters were selected based upon prior literature connection to σ-donor ability, π-acidity, and steric effects. The computed values of the properties were compared via multivariable linear regression models to see which properties best predict the Addison τ parameter-a measure of whether the complex would assume the square pyramidal or trigonal bipyramidal geometry. It was determined that a combination of TEP and %Vbur are the best predictors of the τ value, for the parameters considered herein. The inclusion of additional parameters yields mild improvement to the statistical models for the prediction of the τ value.

Photophysics and photochemistry of thermally activated delayed fluorescence emitters based on the multiple resonance effect: transient optical and electron paramagnetic resonance studies.

The photochemistry of two representative thermally activated delayed fluorescence (TADF) emitters based on the multiple resonance effect (MRE) (DABNA-1 and DtBuCzB) was studied. No significant TADF was observed in fluid solution, although the compounds have a long-lived triplet state (ca. 30 μs). We found that these planar boron molecules bind with Lewis bases, e.g., 4-dimethylaminopyridine (DMAP) or an N-heterocyclic carbene (NHC). A new blue-shifted absorption band centered at 368 nm was observed for DtBuCzB upon formation of the adduct; however, the fluorescence of the adduct is the same as that of the free DtBuCzB. We propose that photo-dissociation occurs for the DtBuCzB-DMAP adduct, which is confirmed by femtosecond transient absorption spectra, implying that fluorescence originates from DtBuCzB produced by photo-dissociation; the subsequent in situ re-binding was observed with nanosecdon transient absorption spectroscopy. No photo-dissociation was observed for the NHC adduct. Time-resolved electron paramagnetic resonance (TREPR) spectra show that the triplet states of DABNA-1 and DtBuCzB have similar zero field splitting (ZFS) parameters (D = 1450 MHz). Theoretical studies show that the slow ISC is due to small SOC and weak Herzberg-Teller coupling, although the S1/T1 energy gap is small (0.14 eV), which rationalizes the lack of TADF.

Uncovering Nitrosyl Reactivity at N-Heterocyclic Carbene Center.

N-heterocyclic carbenes (NHCs) have garnered much attention due to their unique properties, such as strong σ-donating and π-accepting abilities, as well as their transition-metal-like reactivity toward small molecules. In 2015, we discovered that NHCs can react with nitric oxide (NO) gas to form radical adducts that resemble transition metal nitrosyl complexes. To elucidate the analogy between NHC and transition metal NO adducts, here we have undertaken a systematic investigation of the electron- and proton-transfer chemistry of [NHC-NO]• (N-heterocyclic carbene nitric oxide radical) compounds. We have accessed a suite of compounds, comprised of [NHC-NO]+, [NHC-NO]-, [NHC-NOH]0, and [NHC-NHOH]+ species. In particular, [NHC-NO]- was isolated as potassium and lithium ion adducts. Most interestingly, a monomeric potassium [NHC-NO]- compound was isolated with the assistance of 18-crown-6, which is the first instance of a monomeric alkali N-oxyl compound to the best of our knowledge. Our results demonstrate that [NHC-NO]• exhibits redox behavior broadly similar to metal nitrosyl complexes, which opens up more possibilities for utilizing NHCs to build on the known reactivity of metal complexes.

Biological potential of vinyl/allyl substituted imidazole-based N-heterocyclic carbene adducts: synthesis, spectral and X-ray crystallographic structural characteristics

Biological potential of vinyl/allyl substituted imidazole-based N-heterocyclic carbene adducts: synthesis, spectral and X-ray crystallographic structural characteristics

Photoredox Catalysis-Enabled Sulfination of Alcohols and Bromides.

Sulfinates are important lynchpin intermediates in pharmaceutical production; however, their synthesis via photoredox catalysis is challenging because of their facile oxidation. We herein disclose a photocatalytic strategy for the direct conversion of alcohols and alkyl bromides into alkyl sulfinates. These transformations are enabled by the utilization of easily oxidized radical precursors─namely, alcohol N-heterocyclic carbene adducts and N-adamantyl aminosupersilane─that facilitate efficient synthesis of the oxidatively labile sulfinate products. A broad range of functional groups are amenable to the reported transformations, providing rapid access to sulfonamides, sulfonyl halides, sulfones, and sulfonic acids. The utility of these methods is further demonstrated via the late-stage diversification of natural products and drugs into pharmaceutically relevant sulfonamides and "clickable" sulfonyl fluorides. In summary, this work illustrates the potential of novel radical precursors to expand the breadth of photoredox transformations.

Cytotoxic, Thrombolytic and Antibacterial Evaluation of Synthesized Substituted and Un-Substituted Selenium-N-Heterocyclic Carbene Adducts

Alkyl-substituted azolium salts (1-8) and their Se-N-heterocyclic carbene (Se-N-Het-C) adducts (9-12) were obtained in very reasonable yields. All synthesized azolium salts and their Se-N-Het-C adducts were characterized by different spectroscopic techniques such as FT-IR, 1HNMR, 13CNMR, and elemental analysis. It was found that all synthesized Se-N-Het-C adducts were stable at room temperature in both air and moisture. In-vitro these compounds (5-12) were assessed for their antimicrobial potential against Bacillus subtilis (B. subtilis), Macrococcus brunensis (M. brunensis), and Bacillus cereus (B. cereus) in vitro. Results of MIC and inhibition zone values revealed that the majority of the Selenium N-Heterocyclic carbene adducts were active against Bacillus subtilis (B. subtilis) than Macrococcus brunensis (M. brunensis) and Bacillus cereus (B. cereus) whereas opposite in the azolium salts (5-8). Compounds 5-8 have an inhibition zone of 16and#177;0.1-26and#177;0.3mm against all tested bacterial strains while selenium-NHC adducts 9-12 have a zone of inhibition (16and#177;0.2 to 25 and#177; 0.4mm). Adduct 12 showed good activity against all tested strains with ZI values 25 and#177; 0.1, 22and#177; 0.5, 17 and#177; 0.3 mm and MIC values 17 and#177; 0.2, 16 and#177; 0.4 and 18 and#177; 0.3 and#181;g/mL against Bacillus subtilis (B. subtilis), Macrococcus brunensis (M. brunensis) and Bacillus cereus (B. cereus) respectively. Adduct 10 showed the highest thrombolysis i-e 86.9% and adduct 12 showed good hemolysis i-e 0.51%. Overall results of thrombolysis and cytotoxicity studies revealed that the compounds are safe for preclinical studies of mouse blood in vitro.

N‐Heterocyclic Carbene‐Assisted Reversible Migratory Coupling of Aminoborane at Magnesium

A combined synthetic and theoretical investigation of N-heterocyclic carbene (NHC) adducts of magnesium amidoboranes is presented, which involves a rare example of reversible migratory insertion within a normal valent s-block element. The reaction of (NHC)Mg(N(SiMe3 )2 )2 (1) and dimethylamine borane yields the tris(amide) adduct (NHC-BN)Mg(NMe2 BH3 )(N(SiMe3 )2 ) (2; NHC-BN = NHC-BH2 NMe2 ). In addition to Me2 N=BH2 capture at the NHC C-Mg bond, mechanistic investigations suggest the likelihood of aminoborane migratory insertion from an RMg(NMe2 BH2 NMe2 BH3 ) intermediate. To elucidate these processes, the carbene complexes (NHC)Mg(NMe2 BH3 )2 (8) and (NHC)Mg(NMe2 BH2 NMe2 BH3 )2 (9) were synthesized, and a dynamic migration of Me2 N=BH2 between Mg-N and NHC C-Mg bonds was observed in 9. This unusual reversible migratory insertion is presumably induced by dissimilar charge localization in the - {NMe2 BH2 NMe2 BH3 } anion, as well as the capacity of NHCs to reversibly capture Me2 N=BH2 in the presence of Lewis acidic magnesium species.

On the reactivity of Al-group 11 (Cu, Ag, Au) bonds.

Reactions of the seven-membered heterocyclic potassium diamidoalumanyl, [K{Al(SiNDipp)}]2 (SiNDipp = {CH2SiMe2NDipp}2; Dipp = 2,6-di-isopropylphenyl), with a variety of Cu(I), Ag(I) and Au(I) chloride N-heterocyclic carbene (NHC) adducts are described. The resultant group 11-Al bonded derivatives have been characterised in solution by NMR spectroscopy and, in the case of [{SiNDipp}Al-Au(NHCiPr)] (NHCiPr = N,N'-di-isopropyl-4,5-dimethyl-2-ylidene), by single crystal X-ray diffraction. Although similar reactions of LAgCl and LAuCl, where L is a more basic cyclic alkyl amino carbene (CAAC), generally resulted in reduction of the group 11 cations to the base metals, X-ray analysis of [(CyCAAC)AgAl(SiNDipp)] (CyCAAC = 2-[2,6-bis(1-methylethyl)phenyl]-3,3-dimethyl-2-azaspiro[4.5]dec-1-ylidene) provides the first solid-state authentication of an Ag-Al σ bond. The reactivity of the NHC-supported Cu, Ag and Au alumanyl derivatives was assayed with the isoelectronic unsaturated small molecules, N,N'-di-isopropylcarbodiimide and CO2. While these reactions generally provided products consistent with nucleophilic attack of the group 11 atom at the electrophilic heteroallene carbon centre, treatment of the NHC-supported copper and silver alumanyls with N,N'-di-isopropylcarbodiimide yielded less symmetric Cu-C and Ag-C-bonded isomers. In contrast to the previously described copper and silver alumanyl derivatives, [(NON)Al(O2C)M(Pt-Bu3)] (M = Cu or Ag; NON = 4,5-bis(2,6-di-isopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene), which were prone to facile CO extrusion and formation of carbonate derivatives, the NHC-supported dioxocarbene species, [(NHCiPr)M(CO2)Al(SiNDipp)] (M = Cu, Ag, Au), are all stable at room and moderately elevated temperatures. The stabilising role of the NHC co-ligand was, thus, assessed by preparation of the t-Bu3P adducted copper-alumanyl, [(t-Bu3P)CuAl(SiNDipp)]. Treatment of this latter compound, which was also structurally characterised by X-ray analysis, with both N,N'-di-isopropylcarbodiimide and CO2 again provided smooth heteroallene insertion and formation of the relevant Cu-C-bonded products. Although both compounds were quite stable at room temperature, heating of [(t-Bu3P)Cu(CO2)Al(SiNDipp)] at 60 °C induced elimination of CO and formation of the analogous carbonate, [(t-Bu3P)Cu(OCO2)Al(SiNDipp)], which was identified by 13C and 31P NMR spectroscopy. Reflective of the more reliable nucleophilic behaviour of the gold centres in these group 11 alumanyls, computational (QTAIM and NBO) analysis highlighted a lower level of covalency of the Al-Au linkage in comparison to the analogous Al-Cu and Al-Ag interactions. Although substitution of the co-ligand significantly perturbs the charge distribution across the Cu-Al bond of [LCuAl(SiNDipp)] (L = NHCiPr or t-Bu3P), only a negligible difference is observed between the phosphine-coordinated copper systems derived from either the [SiNDipp]- or (NON)-based alumanyl ligands. Computational mapping of the reaction profiles arising from treatment of the various group 11 alumanyls with N,N'-di-isopropylcarbodiimide indicates that the observed formation of the Cu-N and Ag-N bound isomers do not provide the thermodynamic reaction outcome. In contrast, examination of the CO2-derived reactions, and their potential toward CO extrusion and subsequent carbonate formation, implies that the identity of the co-ligand exerts a greater influence on this aspect of reactivity than the architecture of the diamidoalumanyl anion.

Experimental and Computational Study on Photophysical Properties of Mesoionic Chalcogenones.

N-Heterocyclic carbene adducts with main group elements (NHC=E) have aroused great interest and have been widely investigated in coordination chemistry. Among them, N-heterocyclic carbene adducts with chalcogens (NHC=Ch) have been known for a long time. Their investigations mostly focused on synthesis, coordination chemistry and electrochemistry. Their photophysical properties still remain unexplored. In this work, the photophysical properties of mesoionic carbene adducts with sulfur and selenium have been investigated both in solution and solid state. These compounds showed blue fluorescence in dichloromethane. While in solid state, orange to red room-temperature phosphorescence can be observed, and dual emission was found in mesoionic thiones. Furthermore, time-dependent density functional theory (TD-DFT) calculations were used to obtain insights into the luminescent mechanism.

Design, DFT studies, antimicrobial and antioxidant potential of Binuclear N-heterocyclic Carbene (NHCs) complexes, Probing the aspect of DNA interaction through In-vitro and In-silico approach

N-heterocyclic carbene (NHC) adducts have shown remarkable biological potential for numerous medical applications. With an aim to improve biological potential of benzimidazolium salts, newer analogues of benzimidazole and their silver complexes were synthesized and characterized. Synthesized salts (L1-L2) and silver complexes (C1-C2) were confirmed through elemental analysis, UV–visible spectroscopy, FTIR, 1H NMR &13C NMR spectroscopy. The compounds C1 & C2 were found stable in solution form for studied time period when examined spectroscopically and showed optimum lipophilicity when measured for their partition coefficient through flask shake method. Synthesized compounds showed good antimicrobial potential against gram positive bacterial strain S. Aureus with IC50 2.02±0.12 and 2.11±0.13 µM respectively while 2.11±0.1 and 2.28±0.17 µM against gram negative bacterial strain E. Coli for C1 and C2 respectively. The interaction study of the related compounds with DNA was predicted by molecular docking study, which confirmed that the studied compound C1 (-8.04 kcal/mol) has a higher binding energy than compound C2 (-4.23 kcal/mol); Also, the compound C1 exhibits a better affinity against to DNA than Ethidium bromide (-7.68 kcal/mol) and cisplatin (-6.21 kcal/mol).The claim was practically assured through spectroscopic and viscometeric method which confirmed that compounds have good affinity for DNA with binding constant kb, 5.78×104 M-1 and 6.84×104 M-1 for C1 and C2 respectively.

Indirect Access to Carbene Adducts of Bismuth- and Antimony-Substituted Phosphaketene and Their Unusual Thermal Transformation to Dipnictines and [(NHC)2OCP][OCP

The synthesis and thermal redox chemistry of the first antimony (Sb)– and bismuth (Bi)–phosphaketene adducts are described. When diphenylpnictogen chloride [Ph2PnCl (Pn = Sb or Bi)] is reacted with sodium 2-phosphaethynolate [Na[OCP]·(dioxane)x], tetraphenyldipnictogen (Ph2Pn–PnPh2) compounds are produced, and an insoluble precipitate forms from solution. In contrast, when the N-heterocyclic carbene adduct (NHC)–PnPh2Cl is combined with [Na[OCP]·(dioxane)x], Sb– and Bi–phosphaketene complexes are isolated. Thus, NHC serves as an essential mediator for the reaction. Immediately after the formation of an intermediary pnictogen–phosphaketene NHC adduct [NHC–PnPh2(PCO)], the NHC ligand transfers from the Pn center to the phosphaketene carbon atom, forming NHC–C(O)P-PnPh2 [Pn = Sb (3) or Bi (4)]. In the solid state, 3 and 4 are dimeric with short intermolecular Pn–Pn interactions. When compounds 3 and 4 are heated in THF at 90 and 70 °C, respectively, the pnictogen center PnIII is thermally reduced to PnII to form tetraphenyldipnictines (Ph2Pn–PnPh2) and an unusual bis-carbene-supported OCP salt, [(NHC)2OCP][OCP] (5). The formation of compound 5 and Ph2Pn–PnPh2 from 3 or 4 is unique in comparison to the known thermal reactivity for group 14 carbene–phosphaketene complexes, further highlighting the diverse reactivity of [OCP]− with main-group elements. All new compounds have been fully characterized by single-crystal X-ray diffraction, multinuclear NMR spectroscopy (1H, 13C, and 31P), infrared spectroscopy, and elemental analysis (1, 2, and 5). The electronic structure of 5 and the mechanism of formation were investigated using density functional theory (DFT).

N-Heterocyclic carbene, carbodiphosphorane and diphosphine adducts of beryllium dihalides: synthesis, characterisation and reduction studies.

Reaction of several N-heterocyclic carbenes, a carbodiphosphorane, and bis(diphenylphosphino)ethane (DPPE) with [BeX2(OEt2)2] (X = Br or I) have yielded a variety of beryllium dihalide adduct complexes, all of which were crystallographically characterised. Attempts to reduce the compounds to low oxidation state beryllium complexes using a variety of reducing agents have been carried out, but were of limited success. However, reaction of [(IPr)BeBr2] (IPr = :C{(DipNCH)2}; Dip = 2,6-diisopropylphenyl) with the aluminium(i) heterocycle, [:Al(DipNacnac)] (DipNacnac = [HC(MeCNDip)2]-) afforded the adduct complex, [{(IPr)(Br)Be(μ-H)}2], while reduction of [(IPr)BeBr2] with potassium naphthalenide gave the beryllium naphthalenediyl complex, [(IPr)Be(C10H8)]. Furthermore, reaction of [{(DPPE)BeI2}∞], with [:Al(DipNacnac)] led to insertion of the Al centre of the heterocycle into a Be-I bond, and formation of a rare example of an Al-Be bonded complex, [(DPPE)(i)Be-Al(i)(DipNacnac)].

Synthesis and characterization of partially substituted NHC supported alane adducts using triflate or chloride salts

Use of an aldiminium-based triflate salt as group transfer reagent to an N-heterocyclic carbene (NHC) adduct with alane [(IPr)AlH3] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene) led to the substitution of a hydride by triflate and subsequently to the formation of [(IPr)AlH2OTf] (1), which is the first structurally characterized aluminum dihydride triflate compound and the first (trifluoromethanesulfonyl)oxyalane NHC adduct. The related reaction with aldiminium-based chloride salt resulted in similar substitution and formation of mixed products [(IPr)AlH2Cl] and [(IPr)AlHCl2], which co-crystallized in the form of [(IPr)AlH3−xClx], x = 1, 2 (2). This proves that aldiminium-based salts are suitable reagents in alane chemistry. In addition, the adduct [(IPr)AlCl3] (4) was also prepared from AlCl3 and IPr carbene.

Synthesis in combination with Biological and Computational evaluations of selenium-N-Heterocyclic Carbene compounds

Bis-imidazolium salts and their Se-NHC adducts were designed, synthesized, and characterized by various spectroscopic techniques. Density Functional Theory (DFT) was applied on designed molecules through the basis set of hybrid functional B3LYP/6-31 G level of theory. To estimate the structural properties of tested compounds and their influence on biological applications, the HOMO and LUMO energy levels and their energy gaps were calculated. Theoretical studies were used to elaborate on the optical properties of salts and respective selenium adducts. The synthesized salts and N-Heterocyclic carbenes adducts of selenium (Se-NHCs) were tested in vitro against the Breast Adenocarcinoma cell line (MCF-7) by cell viability measurements. It was found that the N-alkylated substitutions on imidazolium salts have more significant free radical scavenging property whereas the reverse case was observed in the selenium compounds. All the compounds except M1 were not showing prominent cytotoxicity against cancerous cell lines.

Reactive Extrusion and Magnesium (II) N-Heterocyclic Carbene Catalyst in Continuous PLA Production.

Reactive extrusion and magnesium (II) N-heterocyclic carbene catalyst are successfully employed in continuous polylactide synthesis. The possibility of using six-membered N-heterocyclic carbene adducts to act as efficient catalysts towards the sustainable synthesis of poly(l-lactide) through ring-opening polymerization of l-lactide (LA) is first investigated in bulk batch reactions. Under optimized solvent-free conditions, polylactide (PLA) of moderate to high molecular weights and excellent optical activities are successfully achieved. These promising results are further applied in the continuous production of PLA in an extruder.

Synthesis of pentafluorobenzene-based NHC adducts and their catalytic activity in the microwave-assisted reactions of aldehydes

N-Heterocyclic carbenes (NHCs) have been widely used in organometallic chemistry as ligands, as well as standalone organocatalysts in various reactions, mostly using aromatic aldehydes as substrates. We have previously demonstrated the efficiency of azolium-2-carboxylate zwitterions in the hydroxymethylation of aldehydes, especially aliphatic aldehydes, under microwave irradiation. In the present work, we report a series of pentafluorobenzene-based NHC adducts and their efficiency in the hydroxymethylation and self-condensation of aliphatic and aromatic aldehydes using microwave irradiation. The free carbenes are released under the reaction conditions and 1,3-dimesityl-2-(perfluorophenyl)imidazolidine and 1,3-bis(2,6-dimethylphenyl)-2-(perfluorophenyl)imidazolidine proved to be the most potent precatalysts.