NOBF4 Research Articles

Nitrosation of 2-aryl-1-bromo-1-fluorocyclopropanes with nitrosonium tetrafluoroborate as an approach to the synthesis of 5-aryl-4-bromo-4-fluoroisoxazolines

Nitrosation of 2-aryl-1-bromo-1-fluorocyclopropanes with nitrosonium tetrafluoroborate as an approach to the synthesis of 5-aryl-4-bromo-4-fluoroisoxazolines

Synthesis of Furoxans (1,2,5‐oxadiazole 2‐oxides) from Styrenes and Nitrosonium Tetrafluoroborate in Non‐Acidic Media and Mechanistic Study

Diverse furoxans (1,2,5‐oxadiazole 2‐oxides) were synthesized from the corresponding styrenes using nitrosonium tetrafluoroborate as the nitrosation reagent in pyridine (basic media) or dichloromethane (neutral media). Acid‐sensitive functional groups were tolerated under these conditions. The probable reaction mechanism was elucidated. The experimental results support an ionic reaction pathway in contrast to the conventional acidic conditions with a radical mechanism.

Ferrier sulfamidoglycosylation of glycals catalyzed by nitrosonium tetrafluoroborate: Towards new carbonic anhydrase glycoinhibitors

Ferrier sulfamidoglycosylation of glycals catalyzed by nitrosonium tetrafluoroborate allowed the preparation of hydroxysulfamide glycosides in good yields with a good α stereoselectivity. A variety of mono-saccharide derivatives was synthesized using this new methodology leading to selective and powerful glycoinhibitors of the tumor associated carbonic anhydrases (CA, EC 4.2.1.1) isoforms CA IX and CA XII.

Efficient synthesis of the tetrasaccharide repeating unit of the O-antigen of Escherichia coli O174 strain

The tetrasaccharide repeating unit of the O-antigen of Escherichia coli O174 strain was synthesized applying sequential glycosylations of suitably functionalized monosaccharide intermediates. Activation of glycosyl trichloroacetimidate derivatives using nitrosyl tetrafluoroborate (NOBF4) has been used during the synthesis. The glycosylation steps were high yielding with satisfactory stereo outcome.

Surface engineered antifouling optomagnetic SPIONs for bimodal targeted imaging of pancreatic cancer cells.

Targeted imaging contrast agents for early pancreatic ductal adenocarcinoma diagnosis was developed using superparamagnetic iron oxide nanoparticles (SPIONs). For phase transfer of SPIONs, the hydrophobic SPIONs are first treated with tetrafluoroborate and then capped by bovine serum albumin (BSA) via ligand exchange. It was experimentally found that nitrosyl tetrafluoroborate pretreatment and proper structures of molecules are essential to the effective surface functionalization of SPIONs. Nonspecific binding was found to be significantly reduced by BSA surface functionalized hydrophobic SPIONs (BSA·SPIONs). The BSA·SPIONs were monodispersed with an average size of approximately 18.0 nm and stable in a wide pH range and various ionic strengths even after 7 days of storage. The longitudinal and transverse proton relaxation rate (r1, r2) values of the BSA·SPIONs were determined to be 11.6 and 154.2 s−1 per mM of Fe3+ respectively. The r2/r1 ratio of 13.3 ensured its application as the T2-weighted magnetic resonance imaging contrast agents. When conjugated with near-infrared fluorescent dye and monoclonal antibody, the dyeBSA·SPION-monoclonal antibody bioconjugates showed excellent targeting capability with minimal nonspecific binding in the bimodal imaging of pancreatic cancer cells. The experimental approach is facile, environmentally benign, and straightforward, which presents great promise in early cancer diagnosis.

Synthesis of Titanium Dioxide/Cadmium Sulfide Nanosphere Particles for Photocatalyst Applications

Semiconductor nanocomposites, which are composed of titanium dioxide (TiO2) nanorods, cadmium sulphide (CdS) nanoparticles (NPs), and Ni clusters, were synthesized. The following steps were adopted: (i) surfactant-capped TiO2 nanorods with controlled length were synthesized in an autoclave using oleic acid and amino hexanoic acid as surfactants. By using a ligand-exchange procedure, in which nitrosonium tetrafluoroborate (NOBF4) was used to replace the original surfactants, hydrophilic NOBF4–TiO2 nanorods were obtained; (ii) the resulting nanorods were deposited with CdS NPs and (iii) then deposited selectively with Ni clusters (as cocatalyst) on the nanocomposite surface. Under visible-light illumination of the nanocomposite, the generated electrons from the conduction band of CdS are transferred to TiO2 via TiO2/CdS interface, then to metallic Ni cluster. As a result, the electron–hole separation was highly enhanced, leading to a Ni–TiO2/CdS nanocomposite with high photocatalytic performance for the pro...

簡便な選択的ニトロソアレーンの合成

Nitroso compounds have drawn much attention of synthetic organic and biological chemists because of their usefulness as synthetic intermediate as well as interesting bioactivity. Here, a recent report about the simple and selective preparative method for nitrosoarenes using nitrosonium tetrafluoroborate is described. It provides versatile nitrosoarenes including heteroarenes which are not easily prepared by alternative method.

Assembly and Fiber Formation of a Gemini-Type Hexathienocoronene Amphiphile for Electrical Conduction

We report the synthesis, characterization, and self-assembly of a new gemini-type amphiphilic hexathienocoronene (HTCGemini), which owes its amphiphilicity to two hydrophobic dodecyl chains on one side of the HTC core and two hydrophilic triethylene glycol (TEG) chains on the other. Bearing a "softer" aromatic HTC core than the conventional hexa-peri-hexabenzocoronenes (HBC), and being more planar than contorted-hexabenzocoronenes (c-HBC), HTCGemini is demonstrated to yield various well-ordered assemblies in solution, at the liquid-solid interface, and in solid state by the use of different processing techniques. Regular fibers, helices, and tubes can be formed simply by processing from different solvents. At the liquid-solid interface, as visualized by scanning tunneling microscopy (STM), pairs of molecules adsorb very close to each other and arrange in the p2 plane group, driven by packing constraints and weak van der Waals interactions between adjacent molecules. HTCGemini also exhibits phase forming behavior in the bulk upon thermal treatment, resulting in a crystalline, herringbone-like columnar structure. Owning to an electron enriched aromatic core with respect to other reported coronenes, HTCGemini easily forms a stable radical cation, both in solution and in the bulk, upon oxidative doping with nitrosonium tetrafluoroborate (NOBF4). Furthermore, light irradiation of the blend film of HTCGemini and phenyl-C61-butyric acid methyl ester (PCBM) generates a prominent photocurrent which can be switched repeatedly with a large on/off ratio (6.0 × 10(4)). The self-assembled structures obtained from HTCGemini at different length scales have potential applications in optoelectronic devices, solar cells, and redox sensors.

Wet-Chemical Synthesis and Consolidation of Stoichiometric Bismuth Telluride Nanoparticles for Improving the Thermoelectric Figure-of-Merit

Bismuth telluride nanoparticles (NPs) have been synthesized using a low-temperature wet-chemical approach from bismuth(III) oleate and tri-n-octylphosphine telluride. The size and shape of the NPs can be controlled by adjusting the temperature, reaction time, and nature of the surfactants and solvents. Aromatic hydrocarbons (toluene, xylenes) and ethers (phenyl- and benzyl-ether) favor the formation of stoichiometric Bi2Te3 NPs of platelike morphology, whereas the presence of oleylamine and 1-dodecanethiol yields Bi-rich Bi2Te3 spherical NPs. XRD, IR, SEM, TEM, and SAED techniques have been used to characterize the obtained products. We show that the surfactants can be efficiently removed from the surface of the NPs using a two-step process employing nitrosonium tetrafluoroborate and hydrazine hydrate. The surfactant-free NPs were further consolidated into high density pellets using cold-pressing and field-assisted sintering techniques. The sintered surfactant-free Bi2Te3 showed electrical and thermal properties comparable to Bi2Te3 materials processed through conventional solid state techniques, and greatly improved over other nanostructured Bi2Te3 materials synthesized by wet-chemical approaches.

ChemInform Abstract: Nitrosyl Tetrafluoroborate Catalyzed Preparation of 2,3‐Unsaturated Glycosides and 2‐Deoxyglycosides of Hindered Alcohols, Thiols, and Sulfonamides.

AbstractD‐Glucal derivative (I) reacts with alcohols, thiols, and sulfonamides under conditions A) to provide 2,3‐unsaturated glycosides with high α‐selectivity.

Nitrosyl Tetrafluoroborate Catalyzed Preparation of 2,3-Unsaturated Glycosides and 2-Deoxyglycosides of Hindered Alcohols, Thiols, and Sulfonamides

Nitrosyl tetrafluoroborate (NOBF₄) has been successfully applied as an efficient organocatalyst for the preparation of 2,3-unsaturated and 2-deoxyglycosides of hindered alcohols, aryl thiols, and aryl sulfonamides from glycal derivatives under the Ferrier rearrangement conditions. Product yields and stereo-outcomes were very good.

ChemInform Abstract: Stereoselective Glycosylations by Nitrosyl Tetrafluoroborate‐Catalyzed Activation of Glycosyl Trichloroacetimidate Derivatives.

AbstractThe activation of glycosyl trichloroacetimidates by nitrosyl tetrafluoroborate provides an alternative to existing protocols for the activation of these compounds in multistep oligosaccharide synthesis.

Three-Component Heterocyclization of gem-Bromofluorocyclopropanes with NOBF4: Access to 4-Fluoropyrimidine N-Oxides

Novel three-component heterocyclization involving gem-bromofluorocyclopropanes, nitrosyl tetrafluoroborate, and a molecule of the solvent (nitrile) yielding previously unknown fluorinated pyrimidine N-oxides is described. A two-step synthetic approach to 4-fluoropyrimidine N-oxides from alkenes under mild conditions is developed using this reaction. Mechanistic aspects of the heterocyclization are discussed.

Stereoselective Glycosylations by Nitrosyl Tetrafluoroborate-Catalyzed Activation of Glycosyl Trichloroacetimidate Derivatives

Efficient stereoselective glycosylation conditions have been developed by using nitrosyl tetrafluoroborate (NOBF 4 ) promoted activation of glycosyl trichloroacetimidate derivatives. A ­series of mono- and disaccharide derivatives were synthesized in excellent yield, and high stereoselectivity at the glycosylation center was observed in every case.

Nitrosation of aryl and heteroaryltrifluoroborates with nitrosonium tetrafluoroborate.

Organotrifluoroborates have emerged as an alternative to toxic and air- and moisture-sensitive organometallic species for the synthesis of functionalized aryl and heteroaryl compounds. It has been shown that the trifluoroborate moiety can be easily converted into a variety of different substituents in a late synthetic stage. In this paper, we disclose a mild, selective, and convenient method for the ipso-nitrosation of organotrifluoroborates using nitrosonium tetrafluoroborate (NOBF(4)). Aryl- and heteroaryltrifluoroborates were converted into the corresponding nitroso products in good to excellent yields. This method proved to be tolerant of a broad range of functional groups.

Spectroscopic characterization of ligands on the surface of water dispersible NaGdF4:Ln3+ nanocrystals

For electronic or biomedical applications it is desirable to have ligand-free water-dispersible nanocrystals (NCs). The commonly used FTIR spectroscopy often provides a direct evidence for molecules on the surface. In some cases, however, the strong bands of solvent molecules may obscure the peaks of surface bounded ligands. We show that in this regard the emission spectroscopy may be used as a more reliable probing tool. The relevant information can be obtained from emission and excitation spectra, emission decay times as well as from analysis of relative efficiency of excitation energy transfer from Gd3+ to Eu3+ ions. Using these methods we tested samples obtained by various synthetic routes and indicated that only nitrosonium tetrafluoroborate (NOBF4) removes successfully the organic ligands from the nanocrystals surface, yielding organic ligand-free NCs dispersible in aqueous solutions. The conclusions drawn from emission spectroscopy are useful for interpretation of results of FTIR, Raman and NMR studies. The detailed assignment of FTIR peaks for oleate-capped and oleate-free NCs is also provided. Finally, we point to the risk of drawing erroneous conclusions about colloidal stability of nanocrystals if refractive indexes of NCs and medium are similar.

Rodlike Macromolecules through Spatial Overlapping of Thiophene Dendrons

Two novel dendritic macromonomers 7 and 8 functionalized with electroactive conjugated thiophene oligomers were synthesized by stepwise cross-coupling reactions and the introduction of a vinyl group at the focal point. Both macromonomers were polymerized into dendronized polymers 9 and 10 by using a radical polymerization method. The photophysical and redox behaviors of dendronized polymers 9 and 10 are significantly different from those of the corresponding macromonomers. This difference may result from the spatial overlapping of thiophene dendrons through π-π interactions when the dendrons are connected to a polymer backbone. The dendronized polymers can organize into large-area two-dimensional sheets with a thickness of 4.8 nm. Polymer 9, which has all-dendritic thiophene side chains, exhibited enhanced conductivity by partial doping with iodine or nitrosonium tetrafluoroborate (NOBF(4)). The novel amphiphilic dendronized polymer 15 was synthesized by the atom-transfer radical polymerization of macromonomer 7 from a poly(ethylene glycol) (PEG) macroinitiator and was found to have a self-organized structure in water.

A Generalized Ligand-Exchange Strategy Enabling Sequential Surface Functionalization of Colloidal Nanocrystals

The ability to engineer surface properties of nanocrystals (NCs) is important for various applications, as many of the physical and chemical properties of nanoscale materials are strongly affected by the surface chemistry. Here, we report a facile ligand-exchange approach, which enables sequential surface functionalization and phase transfer of colloidal NCs while preserving the NC size and shape. Nitrosonium tetrafluoroborate (NOBF4) is used to replace the original organic ligands attached to the NC surface, stabilizing the NCs in various polar, hydrophilic media such as N,N-dimethylformamide for years, with no observed aggregation or precipitation. This approach is applicable to various NCs (metal oxides, metals, semiconductors, and dielectrics) of different sizes and shapes. The hydrophilic NCs obtained can subsequently be further functionalized using a variety of capping molecules, imparting different surface functionalization to NCs depending on the molecules employed. Our work provides a versatile ligand-exchange strategy for NC surface functionalization and represents an important step toward controllably engineering the surface properties of NCs.

Mechanism of N(5)-Ethyl-flavinium Cation Formation Upon Electrochemical Oxidation of N(5)-Ethyl-4a-hydroxyflavin Pseudobase

We investigated the oxidation behavior of 5-ethyl-4a-hydroxy-3-methyl-4a,5-dihydrolumiflavin (pseudobase Et-FlOH) in acetonitrile with the aim of determining if the two-electron oxidized Et-FlOH(2+) undergoes a release of hydroxyl cation and the production of 5-ethyl-3methyllumiflavinium cation (Et-Fl(+)). The focus of this work is to investigate the possibility of using Et-FlOH as a catalyst for water oxidation. The cyclic voltammetry demonstrates that Et-FlOH exhibits two one-electron oxidation potentials at +0.95 and +1.4 V versus normal hydrogen electrode (NHE), with the second oxidation potential being irreversible. The production of Et-Fl(+) is observed in the cyclic voltammetry of Et-FlOH and has been previously assigned to the release of OH(+) from the two-electron oxidized Et-FlOH(2+). The results of our study show that this is not the case: (i) we performed bulk electrolysis of the electrolyte solution at +2 V and then added Et-FlOH to the electrolyzed solution. We found that Et-Fl(+) is produced from this solution, even though Et-FlOH itself was not oxidized; (ii) reactions of Et-FlOH with chemical oxidants (ceric ammonium nitrate, nitrosyl tetrafluoroborate, and tetrabutylammonium persulfate) demonstrate that Et-Fl(+) production occurs only in the presence of strong Lewis acids, such as Ce(4+) and NO(+) ions. On the basis of these results, we propose that the production of Et-Fl(+) in the electrochemistry of Et-FlOH occurs because of the shift in the Et-FlOH/Et-Fl(+) acid-base equilibrium in the presence of protons released during anodic oxidation. We identified two sources of protons: (i) oxidation of traces of water present in the acetonitrile releases oxygen and protons and (ii) two-electron oxidized Et-FlOH(2+) releases protons located on the N(5)-alkyl chain. The release of protons from Et-FlOH(2+) was confirmed by cyclic voltammetry of Et-FlOH in the presence of pyridine as a base. The first oxidation peak of Et-FlOH at +0.95 V is reversible in the absence of pyridine. The addition of pyridine leads to the shift of the oxidation potential to a less positive value, which is consistent with a proton-coupled electron transfer (PCET). Furthermore, the anodic current increases, and the cathodic peak becomes irreversible, giving rise to two additional reduction peaks at -0.2 and -1 V. The same reduction peaks were observed in the high scan rate cyclic voltammogram of Et-FlOH in the absence of pyridine, implying that the release of protons indeed occurs from Et-FlOH(2+). To determine which functional group of Et-FlOH(.+) is the source of protons, we performed DFT calculations at the B3LYP/6-311++G** level of theory for a reaction of Et-FlOH(.+) with pyridine and identified two proton sources: (i) the >N-CH(2)- group of the N(5) alkyl chain and (ii) the -OH group in the 4a-position of the radical cation. Because the appearance of new reduction peaks at -0.2 and -1.0 V occurs in the model compound that lacks -OH protons (Et-FlOMe), we conclude that the proton removal occurs predominantly from the >N-CH(2)- moiety.

Diruthenium Phenylacetylide Complexes Bearing para-/meta-Amino Phenyl Substituents

Presented herein is the synthesis and characterization of four diruthenium(II,III) compounds of formulas Ru2(Xap)4(C≡C-C6H4-4-NH2) (Xap is 2-anilinopyridinate, 1a; and 2-(3,5-dimethoxy)anilinopyridinate, 1b) and Ru2(Xap)4(C≡C-C6H4-3-NH2) (2a/2b). X-ray structural studies of compounds 1b and 2a revealed minimal changes in the coordination sphere of the Ru2 core. Voltammetric measurements showed that compounds 1 exhibit three one-electron redox processes: a reversible reduction of Ru2, a reversible oxidation of Ru2, and a quasi-reversible oxidation of an amino group. Compounds 2 display the same Ru2-based redox processes but not the −NH2 oxidation. Compounds 1a/1b were successfully converted to the corresponding diazonium salts [Ru2(Xap)4-(C≡C-C6H4-4-N2)](BF4) (3a/3b) via oxidation by nitrosonium tetrafluoroborate, which was generated in situ from t-BuONO and BF3. However, the attempt to convert compounds 2 to the corresponding diazonium salts was unsuccessful. DFT calculations of model compounds were perfo...