Karol Erfurt

Hydrogen-bond-rich ionic liquids as effective organocatalysts for Diels–Alder reactions

The synthesis and characterisation of new hydrogen-bond-rich ionic liquids and studies of their catalytic performance in Diels–Alder reactions are described. D-Glucose and chloroalcohols were used as the raw materials and as the sources of hydroxyl groups for the synthesis of ionic-liquid cations, whereas weakly coordinating bis(trifluoromethylsulfonyl)imide was used as the anion. The new ionic liquids were analysed by 1H and 13C NMR spectroscopy and by ESI-MS experiments, which confirmed their structures. In addition, the thermal data of the studied ionic liquids measured by differential scanning calorimetry and thermogravimetric analysis showed that these compounds tend to form a glass at temperatures in the range of −29 °C to −16 °C and are thermally stable from ambient temperature to at least 430 °C, most likely because of the presence of bis(trifluoromethylsulfonyl)imide anions. The performance of the ionic liquids in the model reaction of cyclopentadiene with diethyl maleate or methyl acrylate was investigated. The studied ionic liquids showed high activity even when present in catalytic amounts (4 mol% with respect to the dienophile). An increase in the number of hydroxyl groups present in the ionic liquid structure resulted in higher reaction rates.

Chemo-enzymatic Baeyer–Villiger oxidation in the presence of Candida antarctica lipase B and ionic liquids

A new method for the chemo-enzymatic Baeyer–Villiger oxidation of cyclic ketones to lactones has been developed. The influence of reaction parameters and the structure of various ionic liquids were studied. Free Candida antarctica lipase B or Novozyme-435 suspended in an ionic liquid was used as the catalytic phase. The reaction was carried out under mild conditions at room temperature using 30% aq. H2O2 as the oxidation agent. 1-Butyl-3-methyl bistriflimide was the most effective ionic liquid and increased the reaction rate compared to toluene. Lipase exhibited good stability, and the ionic liquid could be easily reused. Therefore, a general chemo-enzymatic method for the oxidation of cyclohexanones and cyclobutanones to obtain adequate lactones in high yields (79–95%) has been proposed.

Herbicidal ionic liquids derived from renewable sources

A novel family of sugar-based herbicidal ionic liquids has been synthesized and the physical properties of the obtained salts were characterized. The herbicidal function was introduced to the new ionic liquids by the anion (4-chloro-2-methylphenoxyacetate or 2,4-dichlorophenoxyacetate) while the potential biodegradability and non-toxicity originated from the cation (based on D-glucose).

Synthesis, photophysical properties and application in organic light emitting devices of rhenium(I) carbonyls incorporating functionalized 2,2′:6′,2′′-terpyridines

Several new rhenium(I) complexes [ReCl(CO)3(4′-R-terpy-κ2N)] incorporating 2,2′:6′,2′′-terpyridine-based ligands were successfully synthetized and characterized by IR, NMR (1H and 13C), UV-vis spectroscopy and single crystal X-ray analysis. The luminescent properties of [ReCl(CO)3(4′-R-terpy-κ2N)] were studied in solution and solid state, at 298 and 77 K. To better understand the photophysical properties of [ReCl(CO)3(4′-R-terpy-κ2N)], density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were performed. Preliminary studies towards application of these complexes in organic light emitting diodes (OLEDs) were carried out, including testing the possibility of electroluminescence intensity increase by including metallic nanowires in the structure design.

A facile route to well-defined imidazolium-based poly(ionic liquid)s of enhanced conductivity via RAFT

The synthesis of well-defined imidazolium-based poly(ionic liquid)s (PILs) by reversible addition–fragmentation chain transfer (RAFT) polymerization is demonstrated. Two specially designed monomeric ionic liquids (MILs), such as 1-methyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide [MVIM][NTf2] and 1-ethyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide [EVIM][NTf2] were polymerized with the 2,2′-azobisisobutyronitrile (AIBN) initiator in the presence of a trithiocarbonate RAFT agent. Depending on the varied ratios of the monomer to CTA ([monomer]/[CTA] = 100/1; 400/1; 1000/1) we obtained P[MVIM][NTf2] and P[EVIM][NTf2] homopolymers with the number-average molecular weights (Mn) in a broad range Mn = 2.5–340.0 kDa and Mn = 2.1–450.0 kDa, respectively. The controlled character of the polymerization of each ionic monomer was confirmed by the pseudo-first order kinetic, a linear increase in the Mn with conversion and relatively narrow dispersity indices (Đ = 1.09–1.37 for P[MVIM][NTf2] and Đ = 1.10–1.41 for P[EVIM][NTf2]). Additionally, the obtained macromolecules are characterized by the enhanced/or comparable conductivity in comparison with those reported in the literature [Wojnarowska et al., Macromolecules, 2014, 47, 4056–4065 and Fan et al., Macromolecules, 2016, 49, 4557–4570], indicating that we are able to produce polymers of high molecular weights characterized by relatively high conductivity (σdc ∼ 10−9 at Tg). Finally, we found quite unexpected evolution of Tgvs. Mn of the produced polymers in the limit of low molecular weight, which seems to correspond to those observed in the case of van der Waals polymers such as polystyrene or polyisobutylene.

1-Imidoalkylphosphonium salts with modulated Cα–P+ bond strength: synthesis and application as new active α-imidoalkylating agents

An effective synthesis of the hitherto unknown 1-imidoalkylphosphonium salts has been developed in the reported study. The crucial step in the method included the decarboxylative α-methoxylation of N-phthaloyl- or N-succinylamino acids to the corresponding N-(1-methoxyalkyl)imides, followed by the displacement of the methoxy group by the triarylphosphonium group through melting of the imide derivative with triarylphosphonium tetrafluoroborate. The imidoalkylating properties of the obtained 1-imidoalkylphosphonium salts were tested using the Tscherniac–Einhorn-type reaction with aromatic hydrocarbons as a model reaction. It was found that the Cα–P+ bond strength can be considerably reduced and the imidoalkylation of arenes can be markedly facilitated using 1-imidoalkylphosphonium salts derived from triarylphosphines with electron-withdrawing substituents such as tris(m-chorophenyl)phosphine, tris(p-chlorophenyl)phosphine and tris[p-(trifluoromethyl)phenyl]phosphine. Microwave irradiation also considerably facilitates the cleavage of the highly polar Cα–P+ bond.

Studies on the hard confinement effect on the RAFT polymerization of a monomeric ionic liquid. Unexpected triggering of RAFT polymerization at 30 °C

For the first time, the RAFT polymerization of a monomeric ionic liquid under hard confinement was successfully carried out. Consequently, macromolecules with well-defined chemical structures and narrow molecular weight distributions were obtained. Additionally, we reported the unique possibility of triggering RAFT polymerization at 30 °C. This novel strategy open alternative routes to the easy and simple manufacturing of polymers with defined geometries and highly specific properties according to our desired purpose, i.e., in industrial application as biosensors and electronic and electrical nanodevices.

1-(N-Acylamino)alkyltriarylphosphonium Salts with Weakened Cα-P+ Bond Strength—Synthetic Applications

The α-amidoalkylating properties of 1-(N-acylamino)alkyltriarylphosphonium salts with weakened Cα-P+ bond strength are discussed and examined. It is demonstrated that such type of phosphonium salts reacts smoothly with a diverse array of carbon- and heteroatom-based nucleophiles, including 1-morpholinocyclohexene, 1,3-dicarbonyl compounds, benzotriazole sodium salt, p-toluenesulfinate sodium salt, benzylamine, triarylphosphines, and other P-nucleophiles. Reactions are conducted at room temperature, in a short time (5–15 min) and mostly without catalysts. Simple work-up procedures result in good or very good yields of products. The structures of known compounds were established by spectroscopic methods and all new compounds have been fully characterized using 1H-, 13C-, 31P-NMR, IR spectroscopy, and high-resolution mass spectrometry. Mechanistic aspects of described transformations are also performed and discussed. It was demonstrated that unique properties make 1-(N-acylamino)alkyl-triarylphosphonium salts with weakened Cα-P+ bond strength interesting building blocks with great potential, especially in α-amidoalkylation reactions.

Novel Uridine Glycoconjugates, Derivatives of 4-Aminophenyl 1-Thioglycosides, as Potential Antiviral Compounds

A novel series of uridine glycoconjugates, derivatives of 4-aminophenyl 1-thioglycosides, was designed and synthesized. All compounds were evaluated in vitro for their antiviral activity against hepatitis C virus (HCV) and classical swine fever virus (CSFV), two important human and animal viral pathogens for which new or improved therapeutic options are needed. The antiviral activity of all synthesized compounds was confirmed using pseudo-plaque reduction assays in which a significant arrest of CSFV and HCV growth was observed in the presence of these compounds. Two of the synthesized compounds, 9 and 12, displayed a significant inhibitory effect on HCV and CSFV propagation with IC50 values of 4.9 and 13.5 µM for HCV and 4.2 and 4 µM for CSFV, respectively, with low cytotoxicity. Using various infection and replication models, we have shown that both compounds were able to significantly reduce viral genome replication by up to 90% with IC50 values in the low micromolar range. A structure activity analysis of the synthesized compounds showed that the high antiviral activity was attributed to the hydrophobicity of glycoconjugates and the introduction of elements capable to coordinate metal ions into the spacer connecting the sugar and uridine moiety, which can be useful in the development of new antiviral compounds in the future.