Search Results (11)

Silica-based sorbents covalently modified with polyhedral boron clusters represent a promising platform for highly selective separation materials, yet robust and synthetically accessible immobilization protocols remain underdeveloped. In this work, novel sorbents based on commercially available silica gels functionalized with closo-dodecaborate anions were synthesized and systematically characterized. Two immobilization strategies were compared: direct nucleophilic addition of surface aminopropyl groups to the nitrilium derivative (Bu₄N)[B₁₂H₁₁NCCH₃] and sol–gel condensation of a pre-formed boron-containing APTES-derived silane. Covalent attachment via amidine bond formation was confirmed by solution and MAS ¹¹B NMR spectroscopy, IR spectroscopy, elemental analysis/ICP-OES, and SEM. The direct grafting route afforded a boron loading of 4.5 wt% (≈20% of the theoretical capacity), with the efficiency limited by electrostatic repulsion between anionic amidine fragments on the negatively charged silica surface, whereas the APTES route gave lower absolute loading (0.085 mmol/g) due to the low specific surface area of the coarse silica support. Despite the moderate degree of functionalization, the resulting boron cluster–modified silica gels are attractive candidates for specialized chromatographic applications, where the unique hydrophobic and dihydrogen-bonding properties of closo-dodecaborates may enable selective retention of challenging analytes and motivate further optimization of surface morphology and immobilization conditions. Full article

This work explores a novel and efficient synthetic approach to a new class of boron cluster derivatives via the nucleophilic addition of stabilized phosphorus ylides, Ph₃P=CHR² (R² = COOEt, CN), to a series of nitrilium salts of the closo-decaborate anion, [2-B₁₀H₉NCR¹]⁻ (R¹ = Me, Et, ⁿPr, ⁱPr, Ph). The reaction proceeds regio- and stereospecifically, affording a diverse range of iminoacyl phosphorane derivatives, [2-B₁₀H₉NH=C(R¹)C(PPh₃)R²]⁻, in high isolated yields (up to 95%). The obtained compounds (10 examples) were isolated as tetrabutylammonium or tetraphenylphosphonium salts and thoroughly characterized by multinuclear NMR (¹¹B, ¹H, ¹³C, ³¹P), high-resolution mass spectrometry, and single-crystal X-ray diffraction. The reaction feasibility was found to be strongly influenced by the steric hindrance of the R¹ group. Furthermore, the practical utility of these novel hybrids was demonstrated by employing the [2-B₁₀H₉NH=C(CH₃)C(COOC₂H₅)=PPh₃]⁻ anion as a highly effective membrane-active component in ion-selective electrodes. The developed tetraphenylphosphonium (TPP⁺) sensor exhibited a near-Nernstian response, a low detection limit of 3 × 10⁻⁸ M, and excellent selectivity over a range of common inorganic and organic cations, showcasing the potential of closo-borate-based ionophores in analytical chemistry. Full article

In this work, a series of boronated amidines based on the closo-dodecaborate anion and amino acids containing an amino group in the side chain of the general formula [B₁₂H₁₁NHC(NH(CH₂)_nCH(NH₃)COOH)CH₃], where n = 2, 3, 4, were synthesized. These derivatives contain conserved α-amino and α-carboxyl groups recognized by the binding centers of the large neutral amino acid transporter (LAT) system, which serves as a target for the clinically applied BNCT agent para-boronophenylalanine (BPA). The paper describes several approaches to synthesizing the target compounds, their acute toxicity studies, and tumor uptake studies in vivo in two tumor models. The promising compound [B₁₂H₁₁NHC(NH(CH₂)₂CH(NH₃)COOH)CH₃]*3H₂O demonstrates low toxicity (LD₅₀ in a range from 150 to 300 mg/kg) and excellent solubility and also shows selective uptake in experimental melanoma in laboratory mice (T/N ratio remained >3 up to 60 min post-injection, with a maximum T/N of 6.2 ± 2.8 at 45 min). Full article

By reacting nitrilium derivative of the closo-dodecaborate anion, Bu₄N[B₁₂H₁₁N≡CR] (where R = Me, Et, nPr, iPr, p-tolyl), with lithium aluminum hydride (LiAlH₄), N-alkylammonium derivatives of the closo-dodecaborate anion, and Bu₄N[B₁₂H₁₁NH₂CH₂R], were obtained. The reduction reaction procedure was optimized, achieving yields close to quantitative (90–95%). The structure of the compound Bu₄N[B₁₂H₁₁NH₂CH₂CH₃] was determined using X-ray structural analysis. It was found that substituting lithium aluminum hydride (LiAlH₄) with sodium borohydride (NaBH₄) leads to the same products but only upon heating, while the reaction with LiAlH₄ proceeds at room temperature. Full article

The functionalization of copolyfluorenes containing dicyanophenanthrene units by closo-decaborate anion is described. Target copolyfluorenes were analyzed using SEM, UV-vis, luminescence, NMR, and Fourier-transform infrared (FTIR) spectroscopy. The effect of complexation with the closo-decaborate anion on the photophysical properties was studied both experimentally and theoretically. The PL data indicate an efficient charge transfer from fluorene to the dicyanophenanthrene units coordinated to the closo-decaborate. The coordination of closo-decaborate clusters to the nitrile groups of copolyfluorenes provides an important route to new materials for sensors and light-emitting devices while, at the same time, serving as a platform for further study of the nature of boron clusters. Full article

The Ugi four-component reaction (Ugi-4CR) undoubtedly is the most prominent multicomponent reaction (MCRs) that has sparked organic chemists’ interest in the field. It has been widely used in the synthesis of diverse heterocycle molecules such as potential drugs, natural product analogs, pseudo peptides, macrocycles, and functional materials. The Ugi-4CRs involve the use of an amine, an aldehyde or ketone, an isocyanide, and a carboxylic acid to produce an α-acetamido carboxamide derivative, which has significantly advanced the field of isocyanide-based MCRs. The so-called intermediate nitrilium ion could be trapped by a nucleophile such as azide, N-hydroxyphthalimide, thiol, saccharin, phenol, water, and hydrogen sulfide instead of the original carboxylic acid to allow for a wide variety of Ugi-type reactions to occur.β In addition to isocyanide, there are alternative reagents for the other three components: amine, isocyanide, and aldehyde or ketone. All these alternative components render the Ugi reaction an aptly diversity-oriented synthesis of a myriad of biologically active molecules and complex scaffolds. Consequently, this review will delve deeper into alternative components used in the Ugi MCRs, particularly over the past ten years. Full article

The preparation of novel nitrilium derivatives of closo-dodecaborate anion [B₁₂H₁₁NCR]⁻, R = n-C₃H₇, i-C₃H₇, 4-C₆H₄CH₃, 1-C₁₀H₇ is described. Target compounds were obtained in good yields (up to 73%). The synthesis of target borylated nitrilium derivatives was characterised by the simplicity of the chemical apparatus and the absence of the necessity for the purification of desired compounds. The crystal structures of previously obtained [B₁₂H₁₁NCCH₃]⁻ and novel [B₁₂H₁₁NCC₃H₇]⁻ were established with the help of X-ray structure analysis. DFT-analysis of several nitrilium derivatives [B₁₂H₁₁NCR]⁻, R = CH₃, C₃H₇, 4-CH₃C₆H₄ was carried out. The main peculiarities of the C≡N bond of the exo-polyhedral substituent were revealed in terms of bond lengths, bond orders and atomic charges. The LUMO orbitals of the systems considered were examined for understanding of the electrophilic nature of the nitrilium derivatives of the closo-dodecaborate anion. Full article

In the present work, a convenient and straightforward approach to the preparation of borylated amidines based on the closo-dodecaborate anion [B₁₂H₁₁NCCH₃NHR]−, R=H, Alk, Ar was developed. This method has two stages. A nitrile derivative of the general form [B₁₂H₁₁NCCH₃]⁻ was obtained, using a modified technique, in the first stage. On the second stage the resulting molecular system interacted with primary amines to form the target amidine products. This approach is characterised by a simple chemical apparatus, mild conditions and high yields of the final products. The mechanism of the addition of amine to the nitrile derivative of the closo-dodecaborate anion was studied, using quantum-chemical methods. The interaction between NH₃ and [B₁₂H₁₁NCCH₃]⁻ ammonia was chosen as an example. It was found that the structure of the transition state determines the stereo-selectivity of the process. A study of the biological properties of borylated amidine sodium salts indicated that the substances had low toxicity and could accumulate in cancer cells in significant amounts. Full article

A series of novel cobalt bis(dicarbollide) based amidines were synthesized by the nucleophilic addition of primary and secondary amines to highly activated B-N⁺≡C–R triple bond of the propionitrilium derivative [8-EtC≡N-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)]. The reactions with primary amines result in the formation of mixtures of E and Z isomers of amidines, whereas the reactions with secondary amines lead selectively to the E-isomers. The crystal molecular structures of E-[8-EtC(NMe₂)=HN-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)], E-[8-EtC(NEt₂)=HN-3,3′-Co(1,2- C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)] and E-[8-EtC(NC₅H₁₀)=HN-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)] were determined by single crystal X-ray diffraction. Full article

The complexation reactions of nido-carboranyl amidine 10-PrNHC(Et)=HN-7,8-C₂B₉H₁₁ with different nickel(II) phosphine complexes such as [(PR₂R’)₂NiCl₂] (R = R’ = Ph, Bu; R = Me, R’ = Ph) were investigated. As a result, a series of novel half-sandwich nickel(II) π,σ-complexes [3-R’R₂P-3-(8-PrN=C(Et)NH)-closo-3,1,2-NiC₂B₉H₁₀] with the coordination of the carborane and amidine components was prepared. The acidification of obtained complexes with HCl led to the breaking of the Ni-N bond with formation of nickel(II) π-complexes [3-Cl-3-R’R₂P-8-PrNH=C(Et)NH-closo-3,1,2-NiC₂B₉H₁₀]. The crystal molecular structure of [3-Ph₃P-3-(8-PrN=C(Et)NH)-closo-3,1,2-NiC₂B₉H₁₀] was determined by single crystal X-ray diffraction. Full article

A novel one-pot multicomponent reaction to synthesize substituted imidazopyrazines is described. In brief, 1H-(imidazol-5-yl)-N-substituted methanamines react with aldehydes and isocyanides in methanol at room temperature to give imidazopyrazine derivatives in excellent yields. The imidazole nitrogen atom was able to intercept the nascent nitrilium ion, channeling the reaction toward to the sole formation of imidazopyrazines, suppressing the competitive formation of other possible side products deriving from the reaction with the high-energy nitrilium ion. The number of examples and the variability of the nature of isocyanides, aldehydes, and amine components herein employed, witness the robustness of this novel methodology. Full article