Crystal structure and Hirshfeld surface analysis of 2-{[(E)-(3-cyclobutyl-1H-1,2,4-triazol-5-yl)imino]methyl}phenol

The title compound, C13H14N4O, was developed using the reaction of salicylaldehyde and 3-amino-5-cyclobutyl-1,2,4-triazole in ethanol under microwave irradiation. This eco-friendly microwave-promoted method proved to be efficient in the synthesis of 2-{[(E)-(3-cyclobutyl-1H-1,2,4-triazol-5-yl)imino]methyl}phenol in good yields and purity. The title compound is a Schiff base that exists in the phenol–imine tautomeric form and adopts an E configuration. The three independent molecules in the asymmetric unit (A, B and C) are not planar, the cyclobutyl and the phenol-imine rings are twisted to each other making a dihedral angle of 67.8 (4)° in molecule A, 69.1 (2)° in molecule B and 89.1 (2)° in molecule C. In each molecule an intramolecular O—H...N hydrogen bond is present, forming an S(6) ring motif. A Hirshfeld surface analysis was performed to investigate the contributions of the different intermolecular contacts within the supramolecular structure. The major interactions are H...H (53%), C...H (19%) and N...H (17%) for molecule A, H...H (50%), N...H (20%) and C...H (20%) for molecule B and H...H (57%), C...H (14%) and N...H (13%) for molecule C.

Crystal structure and Hirshfeld surface analysis of (Z)-2-{[(2,4-dimethylphenyl)imino]methyl}-4-methylphenol

The title compound, C16H17NO, is a Schiff base that exists in the enol–imine tautomeric form and adopts a Z configuration. The molecule is non-planar, with the twisted rings making a dihedral angle of 39.92 (4)°. The intramolecular O—H...N hydrogen bond forms an S(6) ring motif. In the crystal, molecules are linked by C—H...π interactions and very weak π-π stacking interactions also help to consolidate the crystal packing. A Hirshfeld surface analysis was performed to investigate the contributions of different intermolecular contacts within the supramolecular structure. The major contributions are from H...H (65%), C...H (19.2%) and O...H (6.6%) interactions.

Monoazo (Monohydrazone) pigments based on acetoacetanilides

The monoazoacetoacetanilide series of pigments, traditionally known as Hansa Yellows, are long-established products that entered the market in the early twentieth century. They are mostly inexpensive products offering bright colors of moderate intensity covering the entire yellow area of the spectrum, good lightfastness, but inferior solvent resistance. The technical properties of the pigments may be explained by their molecular structures, which adopt the ketohydrazone tautomeric form, and their crystal structures. Their good lightfastness is attributed mainly to intramolecular hydrogen-bonding, while their generally inferior fastness to organic solvents is explained by the relatively weak intermolecular interactions in the crystal structure. The monoazoacetanilide pigments are synthesized by the traditional two-stage process of diazotization of a primary aromatic amine, followed by an azo coupling reaction of the resulting diazonium salt with an acetoacetanilide coupling component. Their main use is in decorative paints, although a few products are suitable for printing inks.

Disazo (Bishydrazone) pigments based on pyrazolones

The most important classical orange organic pigments are disazopyrazolones, also referred to as diarylide oranges. The first pigment in this series, CI Pigment Orange 13, was discovered in 1910 although it was a further 20 years before it was introduced as a commercial product. Currently, two orange disazopyrazolones are extremely important industrial organic pigments, while two red products are of lesser importance. The products are structurally analogous to the disazoacetoacetanilides (diarylide yellows), which are discussed in a separate chapter. For example, they are symmetrical compounds that exist in the bis-ketohydrazone tautomeric form. The pigments also exhibit similar technical and color properties compared with disazoacetoacetanilide pigments, for example providing high color strength and transparency, features that determine their importance as printing ink pigments. They are manufactured in a process that parallels those used for the disazoacetoacetanilide (diarylide) yellows, but with coupling components containing the pyrazolone heterocyclic system, in place of acetoacetanilides.

One- and two-dimensional PbII compounds resulting from reaction of PbBr2 and Pb(SCN)2 with pyrimidine-2-thione

Pyrimidine-2-thione (HSpym) reacts with lead(II) thiocyanate and lead(II) bromide in N,N-dimethylformamide (DMF) to form poly[(μ-isothiocyanato-κ2 N:S)(μ4-pyrimidine-2-thiolato-κ6 N 1,S:S:S:S,N 3)lead(II)], [Pb(C4H3N2S)(NCS)] n or [Pb(Spym)(NCS)] n , (I), and the polymeric one-dimensional (1D) compound catena-poly[[μ4-bromido-di-μ-bromido-(μ-pyrimidine-2-thiolato-κ3 N 1,S:S)(μ-pyrimidine-2-thione-κ3 N 1,S:S)dilead(II)] N,N-dimethylformamide monosolvate], {[Pb2Br3(C4H3N2S)(C4H4N2S)]·C3H7NO} n or {[Pb2Br3(Spym)(HSpym)]·DMF} n , (IIa), respectively. Poly[μ4-bromido-di-μ3-bromido-(μ-pyrimidine-2-thiolato-κ3 N 1,S:S)(μ-pyrimidine-2-thione-κ3 N 1,S:S)dilead(II)], [Pb2Br3(C4H3N2S)(C4H4N2S)] n or [Pb2Br3(Spym)(HSpym)] n , (IIb), could be obtained as a mixture with (IIa) when using a lesser amount of solvent. In the crystal structures of the pseudohalide/halide PbII stable compounds, coordination of anionic and neutral HSpym has been observed. Both Spym− (in the thiolate tautomeric form) and NCS− ligands were responsible for the two-dimensional (2D) arrangement in (I). The Br− ligands establish the 1D polymeric arrangement in (IIa). Eight-coordinated metal centres have been observed in both compounds, when considering the Pb...S and Pb...Br interactions. Both compounds were characterized by FT–IR and diffuse reflectance spectroscopies, as well as by powder X-ray diffraction. Compound (IIa) and its desolvated version (IIb) represent the first structurally characterized PbII compounds containing neutral HSpym and anionic Spym− ligands. After a prolonged time in solution, (IIa) is converted to another compound due to complete deprotonation of HSpym. The structural characterization of (I) and (II) suggests HSpym as a good candidate for the removal of PbII ions from solutions containing thiocyanate or bromide ions.

Stabilization of an elusive tautomer by metal coordination

The solid-state isolation of the different tautomers of a chemical compound can be a challenging problem. In many cases, tautomers with an energy very close to the most stable one cannot be isolated (elusive tautomers). In this article, with reference to the 4-methyl-7-(pyrazin-2-yl)-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole ligand, for which the elusive 3H-tautomer has an energy only 1.4 kcal mol−1 greater than the most stable 2H form, we show that metal complexation is a successful and reliable way for stabilizing the elusive tautomer. We have prepared two complexes of the neutral ligand with CuBr2 and ZnBr2, namely, aquabromidobis[4-methyl-7-(pyrazin-2-yl)-3H-[1,2,4]triazolo[3,2-c][1,2,4]triazole]copper(II) bromide trihydrate, [CuBr(C8H7N7)2(H2O)]Br·3H2O, and dibromido[4-methyl-7-(pyrazin-2-yl)-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole][4-methyl-7-(pyrazin-2-yl)-3H-[1,2,4]triazolo[3,2-c][1,2,4]triazole]zinc(II) monohydrate, [ZnBr2(C8H7N7)2]·H2O. The X-ray analysis shows that, in both cases, the elusive 3H-tautomer is present. The results of the crystallographic analysis of the two complexes reflect the different coordination preferences of CuII and ZnII. The copper(II) complex is homotautomeric as it only contains the elusive 3H-tautomer of the ligand. The complex can be described as octahedral with tetragonal distortion. Two 3H-triazolotriazole ligands are bis-chelated in the equatorial plane, while a water molecule and a bromide ion in elongated axial positions complete the coordination environment. The zinc(II) complex, on the other hand, is heterotautomeric and contains two bromide ions and two monodentate ligand molecules, one in the 2H-tautomeric form and the other in the 3H-tautomeric form, both coordinated to the metal in tetrahedral geometry. The observation of mixed-tautomer complexes is unprecedented for neutral ligands. The analysis of the X-ray molecular structures of the two complexes allows the deduction of possible rules for a rational design of mixed-tautomer complexes.

Crystal structure and molecular docking study of (E)-2-{[(E)-2-hydroxy-5-methylbenzylidene]hydrazinylidene}-1,2-diphenylethan-1-one

The title compound, C22H18N2O2, is a Schiff base that exists in the phenol–imine tautomeric form and adopts an E configuration with respect to the C=N bond. The molecular structure is stabilized by an O—H...N hydrogen bond, forming an S(6) ring motif. In the crystal, pairs of C—H...O hydrogen bonds link the molecules to form inversion dimers. Weak π–π stacking interactions along the a-axis direction provide additional stabilization of the crystal structure. The molecule is non-planar, the aromatic ring of the benzaldehyde residue being nearly perpendicular to the phenyl and 4-methylphenol rings with dihedral angles of 88.78 (13) and 82.26 (14)°, respectively. A molecular docking study between the title molecule and the COVID-19 main protease (PDB ID: 6LU7) was performed, showing that it is a potential agent because of its affinity and ability to adhere to the active sites of the protein.

Synthesis of Phosphonates, Phosphinates and Tertiary Phosphine Oxides by Pd- or Ni-Catalyzed Microwave-Assisted P–C Coupling Reactions without the Addition of Conventional Ligands

Microwave (MW)-assistance may be a powerful tool also in the Hirao P–C coupling reactions of vinyl/aryl halides with dialkyl phosphites in the presence of Pd-catalysts/P-ligands elaborated forty years ago. This review surveys the development of this reaction by showing the expansion of the reagents and catalysts, as well as the information accumulated. The stress was laid on the “green” aspects, the simplification of the catalyst systems, and the reliable mechanistic details in order to be able to establish the optimum conditions. The best protocol involves the use of some excess of the >P(O)H reagent to ensure the PdII→Pd0 reduction and, via its trivalent tautomeric form (>POH) also the P-ligand. The overall rate is the result of two factors, the activity of the catalyst complex formed, and the reactivity of the reactants in the P–C coupling reactions. Both components are influenced by the nature of the aryl substituents in Ar2P(O)H. NiII salts may also be used as the catalyst precursor, however, despite the PdII→Pd0→PdII route, in this case, a NiII→NiIV→NiII sequence was proved.