Carboxylic Group-Assisted Proton Transfer in Gold-Mediated Thiolation of Alkynes

Combined experimental and theoretical studies revealed a complex mechanistic picture in which the carboxylic group-assisted proton transfer from acetic acid to an alkyne molecule is the key step in the unique gold-mediated alkyne transformation that leads to the formation of <i>gem</i>-disubstituted vinyl gold complexes. The structures of the complexes were unambiguously established using NMR spectroscopy (in solution) and X-ray diffraction (in the solid state). ESI-MS study of the reaction mixture revealed multiple gold-containing complexes and clusters. Investigation of the MS² fragmentation patterns of the selected ions suggested the involvement of gold acetylides in the transformation. Further treatment of the complexes with protic acid led to the discovery of a novel route for the gold-mediated alkyne hydrothiolation

Carboxylic Group-Assisted Proton Transfer in Gold-Mediated Thiolation of Alkynes

Combined experimental and theoretical studies revealed a complex mechanistic picture in which the carboxylic group-assisted proton transfer from acetic acid to an alkyne molecule is the key step in the unique gold-mediated alkyne transformation that leads to the formation of <i>gem</i>-disubstituted vinyl gold complexes. The structures of the complexes were unambiguously established using NMR spectroscopy (in solution) and X-ray diffraction (in the solid state). ESI-MS study of the reaction mixture revealed multiple gold-containing complexes and clusters. Investigation of the MS² fragmentation patterns of the selected ions suggested the involvement of gold acetylides in the transformation. Further treatment of the complexes with protic acid led to the discovery of a novel route for the gold-mediated alkyne hydrothiolation

Cytotoxic Activity of Salicylic Acid-Containing Drug Models with Ionic and Covalent Binding

Three different types of drug delivery platforms based on imidazolium ionic liquids (ILs) were synthesized in high preparative yields, namely, the models involving (i) ionic binding of drug and IL; (ii) covalent binding of drug and IL; and (iii) dual binding using both ionic and covalent approaches. Seven ionic liquids containing salicylic acid (SA-ILs) in the cation or/and in the anion were prepared, and their cytotoxicity toward the human cell lines CaCo-2 (colorectal adenocarcinoma) and 3215 LS (normal fibroblasts) was evaluated. Cytotoxicity of SA-ILs was significantly higher than that of conventional imidazolium-based ILs and was comparable to the pure salicylic acid. It is important to note that the obtained SA-ILs dissolved in water more readily than salicylic acid, suggesting benefits of possible usage of traditional nonsoluble active pharmaceutical ingredients in an ionic liquid form

Facile Hydrolysis of Nickel(II) Complexes with N‑Heterocyclic Carbene Ligands

Metal complexes with N-heterocyclic carbene ligands (NHC) are ubiquitously used in catalysis, where the stability of the metal–ligand framework is a key issue. Our study shows that Ni-NHC complexes may undergo facile decomposition due to the presence of water in organic solvents (hydrolysis). The ability to hydrolyze Ni­(NHC)₂X₂ complexes decreases in the order of NHC = 1,2,4-triazolium > benzimidazolium ≈ imidazolium. Depending on the ligand and substituents, the half reaction time of the complex decomposition may change from several minutes to hours. The nature of the halogen is also an important factor, and the ability for decomposition of the studied complexes decreases in the order of Cl > Br > I. NMR and MS monitoring revealed that Ni-NHC complexes in the presence of water undergo hydrolysis with Ni–C_carbene bond cleavage, affording the corresponding <i>N</i>,<i>N</i>′-dialkylated azolium salts and nickel­(II) hydroxide. These findings are of great importance for designing efficient and recyclable catalytic systems, because trace water is a common contaminant in routine synthetic applications

Pd-NHC Catalytic System for the Efficient Atom-Economic Synthesis of Vinyl Sulfides from Tertiary, Secondary, or Primary Thiols

Vinyl sulfides represent an important class of compounds in organic chemistry and materials science. Atom-economic addition of thiols to the triple bond of alkynes provides an excellent opportunity for environmentally friendly processes. We have found that well-known and readily available Pd-NHC complex (IMes)­Pd­(acac)Cl is an efficient catalyst for alkyne hydrothiolation. The reported technique provides a general one-pot approach for the selective preparation of Markovnikov-type vinyl sulfides starting from tertiary, secondary, or primary aliphatic thiols, as well as benzylic and aromatic thiols. In all the studied cases, the products were formed in excellent selectivity and good yields

Adducts of N‑Heterocyclic Drugs, Niacin, Allopurinol, and Amiloride, with 2,4-Pyridinedicarboxylic Acid Coformer

A co-crystallization of three drug molecules, niacin (3-pyridine-carboxylic acid = NIA), allopurinol (pyrazolo­(3,4-d)­pyrimidin-4-one = ALP), and amiloride (3,5-diamino-6-chloro-pyrazine-2-carbonyl)-guanidine = AMI), with the same coformer, 2,4-pyridine­dicarbox­ylic acid (PDA), resulted in three new crystalline products, (NIA)­(PDA) (<b>1</b>), (ALP)₂­(PDA)·​1.5H₂O (<b>2</b>), and (AMI)₂­(PDA)₂­(H₂O)₂ (<b>3</b>). The formation of new phases was confirmed by IR spectra and X-ray single-crystal and powder diffraction analysis. The proton transfer resulted in the zwitterionic co-crystal <b>1</b>. In co-crystal <b>2</b>, neutral ALP molecules existed in the oxo-tautomeric form. Compound <b>3</b> crystallizes as the salt with the guanidinium cationic part as in the started amiloride hydrochloride hydrate, and the PDA coformer as the zwitterionic pyridinium dicarboxylate anion. Thus, the diversity of the PDA coformer ionization states included the neutral, zwitterion, and zwitterion anionic forms. All compounds were layered structures where the heterocyclic molecules were linked in the H-bonded corrugated layers stabilized by the diverse conventional and charge-assisted hydrogen bonds with π–π stacking interactions between the layers supported by the mediated water molecules in <b>2</b> and <b>3</b>

Evidence of Low-Temperature Phase Transition in Tetracene–Tetracyanoquinodimethane Complex

Multitemperature X-ray diffraction and vibrational spectroscopic studies of tetracene–tetracyanoquinodimethane (TCNQ) charge transfer cocrystals have revealed the existence of a reversible phase transition in the temperature interval 150–200 K. It was shown that a new monoclinic polymorph of the cocrystal exists above that temperature range, with a structure that is very similar to the one previously described in the literature as being triclinic. The crystal structures of the two polymorphs were also calculated with periodic density functional theory quantum chemical calculations, and their geometries were compared to the experimental ones. The degree of charge transfer in both polymorphs was characterized using alteration in the bond lengths of the TCNQ molecule and frequency shifts obtained from vibrational spectroscopy data

Mild and Regioselective Hydroxylation of Methyl Group in Neocuproine: Approach to an N,O-Ligated Cu₆ Cage Phenylsilsesquioxane

The self-assembly synthesis of Cu­(II)-silsesquioxane involving 2,9-dimethyl-1,10-phenanthroline (neocuproine) as an additional N ligand at copper atoms was performed. The reaction revealed an unprecedented aerobic hydroxylation of only one of the two methyl groups in neocuproine to afford the corresponding geminal diol. The produced derivative of oxidized neocuproine acts as a two-centered N,O ligand in the assembly of the hexacopper cage product [Cu₆(Ph₅Si₅O₁₀)₂·(C₁₄H₁₁N₂O₂)₂] (<b>1</b>), coordinating two of the six copper centers in the product. Two siloxanolate ligands [PhSi­(O)­O]₅ in the cis configuration coordinate to the rest of the copper­(II) ions. Compound <b>1</b> is a highly efficient homogeneous precatalyst in the oxidation of alkanes and alcohols with peroxides

Reaction of α‑Bromo Enones with 1,2-Diamines. Cascade Assembly of 3‑(Trifluoromethyl)piperazin-2-ones via Rearrangement

A facile one-pot synthesis of 3-trifluoromethylated piperazin-2-ones has been achieved by the treatment of trifluoromethyl 2-bromo enones with N,N′-disubstituted ethylenediamines in trifluoroethanol. The mechanism of this unexpected reaction is discussed in terms of multistep processes involving formation of captodative aminoenone as a key intermediate. The unique influence of trifluoromethyl group on the reaction path was demonstrated

Solution Processing of Methylammonium Lead Iodide Perovskite from γ‑Butyrolactone: Crystallization Mediated by Solvation Equilibrium

The chemical origin of solvents typically used for preparation of hybrid lead halide perovskitesdimethyl sulfoxide (DMSO), dimethylformamide (DMF), and γ-butyrolactone (GBL)strongly influences the process of perovskite crystallization because of the formation of intermediate adducts with different structures and morphology. The composition and crystal structures of the adducts depend on the coordination and binding ability of the solvents and the ratio of the precursors. New adducts of perovskite and GBL with either an unusual cluster structure, (MA)₈(GBL)_<i>x</i>[Pb₁₈I₄₄], or an adduct, (MA)₂(GBL)₂Pb₃I₈, similar to those observed for DMF and DMSO are described for the first time. Complex equilibriums between chemical species existing in perovskite solutions are revealed by Raman spectroscopy. As a result, new features of the perovskite crystallization through intermediate adduct phases are discussed, and effective perovskite deposition pathways are suggested