Pilar Cornago

The annular tautomerism of the curcuminoid NH-pyrazoles

The structures of four NH-pyrazoles, (E)-3,5-bis[β-(4-hydroxy-3-methoxyphenyl)-ethenyl]-1H-pyrazole (3), (E)-3(5)-[β-(4-hydroxy-3-methoxyphenyl)-ethenyl]-5(3)-methyl-1H-pyrazole (4), (E)-3(5)-[β-(4-hydroxy-3-methoxyphenyl)-ethenyl]-4,5(3)-dimethyl-1H-pyrazole (5) and (E)-3(5)-[β-(3,4-dimethoxyphenyl)-ethenyl]-4-methyl-5(3)-phenyl-1H-pyrazole (8), have been determined by X-ray crystallography. Compounds that have a phenol residue crystallize forming sheets that are stabilized by a complex pattern of hydrogen bonds between a unique tautomer (4), or by a 2 : 1 mixture of both tautomers (5) (these tautomers being identical in the case of 3). Pyrazole 8, which lacks OH groups, crystallizes in cyclic dimers that are stabilized by N–H⋯N hydrogen bonds. The tautomerism in solution and in the solid state was determined by 13C and 15N CPMAS NMR spectroscopy. For compounds 4, 5 and 8, the solid state results agree with those observed by crystallography; the most abundant tautomer in solution coincides with the tautomer present in the solid state (4 and 8) or with the most abundant tautomer in the crystal (5).

Structure of NH-benzazoles (1H-benzimidazoles, 1H- and 2H-indazoles, 1H- and 2H-benzotriazoles)

The structure and properties (crystallography, NMR, theoretical calculations) of the three N-unsubstituted benzazoles (1H-benzimidazoles, 1H- and 2H-indazoles, 1H- and 2H-benzotriazoles) have been reviewed for the period 2000–2012 with some results from previous years. The study of these compounds will greatly increase in the coming years and it is expected that the present review will contribute to it.

Complexes of rhodium and iridium derived from 2,5-bis(pyrazol-1'-yl)-1,4-dihydroxybenzene

Abstract The behaviour of the ligand 2,5-bis(pyrazol-1′-yl)-1,4-dihydroxybenzene (H 2 LL) towards Rh I , Ir I , Rh III and Ir III complexes is reported. This compound with two OH groups might act as a neutral ligand (H 2 LL), as a monoanionic ligand (HLL − ) or as a dianionic ligand (LL 2− ). Complexes of all the three kinds have been isolated. In the case of H 2 LL, the compounds are not organometallic complexes but clathrates. The crystal and molecular structure of the host-guest complex [{(η 5 -C 5 Me 5 )RhCl} 2 -(μ-Cl) 2 ]-H 2 LL ( 6a ) is reported. Both the host and the guest have crystallographic C i symmetry. No metal-H 2 LL chemical bonds are present, and van der Waals interactions between host and guest molecules govern the crystal packing. An heterobimetallic derivative [IrRh(η 5 -C 5 Me 5 )Cl 2 (LL)] ( 7c ) has been isolated.

The Structure of a Non-Symmetric Disordered Tetramer: A Crystallographic and Solid State Multinuclear NMR Study of the Properties of 3(5)-Ethyl-5(3)-Phenyl-1H-Pyrazole

The X-ray structure and the solid-state NMR measurements, mainly 15N CPMAS of the labelled compound, allow to determine the static and dynamic properties of 3(5)-ethyl-5(3)-phenyl-1H-pyrazole. The compound is a tetramer formed by three 5-ethyl-3-phenyl-1H-pyrazole and one 3-ethyl-5-phenyl-1H-pyrazole tautomers in dynamic equilibrium with the complementary situation.

1-Benzoylazoles: an experimental (NMR and crystallography) and theoretical study

Five N-benzoylazoles (imidazole, pyrazole, indole, benzimidazole and carbazole) have been prepared following modified literature procedures. Their NMR spectra in solution ( 1 H, 1 3 C and 1 5 N) have been measured. The crystal structures of 1-benzoylindole and 9-benzoylcarbazole have been determined by X-ray crystallography and the corresponding 1 3 C NMR spectra in the solid state have been measured by the CPMAS technique. Whereas 1-benzoylindole presents a standard behaviour, 9-benzoylcarbazole shows an unexpected 1 3 C CPMAS spectrum with additional splittings. In order to understand this fact, the 1 H and 1 3 C NMR spectra in dimethylether at -143°C (130 K) have been recorded and ab initio calculations (RHF/6-311G * * ) carried out. The corresponding absolute shieldings (GIAO/ RHF/6-311G * * ) together with the X-ray structure and the 1 3 C chemical shifts at low temperature have been used to discuss the CPMAS spectrum. We propose that the supplementary splittings of this spectrum are due to its conglomerate structure.

Aromatic propellenes. Synthesis, X-Ray structures and conformational study of polypyrazolylpyridines

Abstract The crystal and molecular structures of three pentapyrazolylpyridines pz5py, dmpz5py and pz4dmpzpy (pz = pyrazol-1′-yl, dmpz = 3,5-dimethylpyrazol-1′-yl) have been determined by X-Ray crystallography. The two pyrazole rings close to the pyridine nitrogen tend to be as coplanar as possible with the pyridine plane. Two different conformations with the nitrogen lone pairs of pyrazole N2 directed towards or opposite to the N1 nitrogen of pyridine, are present in the crystals. Semiempirical AM1 calculations have been performed to evaluate the stability of these conformations which appear to be present also in solution ( 1 H and 13 C NMR and dipole moments).

Synthesis, structure (NMR and mass spectrometry) and conformational analysis of heterocyclic analogues of dibenzo[a,e]cycloocta-1,5-diene: 5,6,12,13-tetrahydrobispyrazolo[1,2-a:1′,2′-e][1,2,5,6]tetraazocinediium dihalides

Several 5,6,12,13-tetrahydrobispyrazolo[1,2-a:1′,2′-e][1,2,5,6] tetraazocinediium dihalides 4a–d and 8 are prepared from pyrazole, 3,5-dimethylpyrazole, 4-(1-adamantyl)pyrazole and campho[2,3-c]pyrazole by stepwise alkylation with 1,2-dibromoethane or 1,2-dichloroethane. Their structural characterization has been achieved by NMR and mass spectrometry. Dynamic NMR spectroscopy allowed the measurement of the barrier for the chair–chair interconversion in the case of the parent compound 4a and the 1,3,8,10-tetramethyl derivative 4b. These barriers as well as the preferred chair conformation are rationalized through semi-empirical and molecular mechanics calculations with regard to dibenzo[a,e]cycloocta-1,5-diene. The study of doubly charged bispyrazolium salts allows demonstration of their reduction by addition of a hydride ion [C+++ H–→(C + H)+] during FABMS experiments.

The structure of β-diketones related to curcumin determined by X-ray crystallography, NMR (solution and solid state) and theoretical calculations

Structural data are reported on sixteen ketoenols of β-diketones: solution NMR, solid-state NMR (CPMAS and MAS) and X-ray crystallography (four compounds, where three are new). The emphasis is on the tautomerism between both ketoenols, in solution and in the solid state. GIAO/B3LYP/6-311++G(d,p) and Quantum ESPRESSO (QE) calculations were used and compared. For average values, the GIAO/DMSO-PCM is enough, but splittings can only be approached by using QE. A case of rotational disorder has been analyzed. Some anomalies related to C–F bonds and to the C–CF3 group have been detected.

Pyridyl and pyridiniumyl β-diketones as building blocks for palladium(II) and allyl–palladium(II) isomers. Multinuclear NMR structural elucidation and liquid crystal behaviour

A series of novel β-diketone ligands bearing alkyloxyphenyl R = C6H4OCnH2n+1 and pyridyl substituents at 1 and 3 positions of the β-diketone core [HLR(n)py] have been prepared and structurally characterized. The corresponding β-diketonate complexes [Pd(κ2-LR(n)py)2] were isolated as a mixture of cis and trans isomers each of them exhibiting the ligand in a NO- or OO-bidentate coordinative mode which were established by multinuclear NMR studies (1H, 13C and 15N). However none of those characteristics were determining to achieve liquid-crystalline properties on the new complexes. By contrast reactions of the aforementioned ligands [HLR(n)py] or those containing the pyridiniumyl substituent [HLR(n)pyH]+ towards the allyl–palladium fragment were successful to afford ionic metallomesogenic materials isolated as PF6 salts of [Pd(η3-C3H5)(κ2-HLR(n)py)][PF6] (I) and [Pd(η3-C3H5)(κ2-LR(n)pyH)][PF6] (II) types. Structural characterization and mesomorphic properties were established by multinuclear NMR and the use of DSC and POM techniques. In complexes I and II the corresponding β-diketone ligands were coordinated as neutral bidentate NO-donor or zwitterionicOO-donor systems, respectively. Complexes of type II exhibit a range of the SmC mesophases significantly greater than that found in the type I.

Aromatic propellenes. Part 10. Conformational study of hexa(imidazol-1-yl)benzene and hexakis(2-methylimidazol-1-yl)benzene by means of NMR and AM1 calculations

Abstract Hexa(imidazol-1-yl)benzene, (imz) 6 bz, and hexakis(2-methylimidazol-1-yl)benzene, (mimz) 6 bz, have been synthesized from hexafluorobenzene and imidazole or 2-methylimidazole anions in tetrahydrofuran. The stabilities of the eight possible conformers of (imz) 6 bz and (mimz) 6 bz have been estimated by semi-empirical calculations at the AM1 level. In both compounds, the absolute minimum corresponds to the conformation in which the β nitrogen lone pair of consecutive imidazole rings is alternately oriented to opposite sides of the benzene plane. While in (imz) 6 bz only the ring signals corresponding to a unique imidazole were observed, the presence of the eight conformers in (mimz) 6 bz has been established by 1 H and 13 C NMR spectroscopy.