Cristina Fernández-Castaño

Unexpected Staudinger reaction of α-azidoacetonitriles α-phenyl substituted with triphenylphosphine. Preparation, X-ray crystal and molecular structures of a phosphazine, an aminophosphonium carbanion salt and a phosphazide, with (Z)-configuration

Abstract Staudinger reaction of α-azidophenylacetonitrile with triphenylphosphine in 1:2 molar ratio provides the triphenylphosphazine 4 derived from α-diazophenylacetonitrile, whereas in 2:1 molar ratio the final product is found to be the aminotriphenylphosphonium salt of phenylmalononitrile 6 . However, the Staudinger reaction of α-azidodiphenylacetonitrile with triphenylphosphine affords the corresponding (Z)-phosphazide 17 . The crystal and molecular structures of compounds 4,6 , and 17 have been determined by X-ray analysis. Compound 17 is the first isolated phosphazide which presents the (Z)-configuration with respect to the central N-N bond of the PN 3 C moiety (P-N-N-N=0.0(3)°).

Porphyrins with four azole substituents in meso positions: X-ray crystal structure of Meso-tetrakis-(1-benzylpyrazol-4-yl)-porphyrin at 200 K

Abstract Several new porphyrins have been prepared in improved yields using an established method which was adapted to formylpyrazoles bearing on the pyrazole N 1 -nitrogen protective groups. The deprotection of N-para -methoxybenzyl and SEM protected meso -pyrazolylporphyrins afforded the first known pyrazolylporphyrins with pyrazole free N H groups. The crystal and molecular structure of meso -tetrakis-1-(benzyl-pyrazol-4-yl)porphyrin 4a has been solved by X-ray analysis. The porphyrin core displays a similar pattern of bond distances and angles to that of meso -tetraphenylporphyrin itself. The pyrazole rings are almost perpendicular to the macrocyclic ring in such a way that the nitrogen lone pairs of the pyrazole N 2 atoms are situated, up, down, down, up, with regard to it (ααββ atropisomer).

Self-assembly of NH-pyrazoles via intermolecular N—H⋯N hydrogen bonds

The crystal structures of two NH-pyrazole derivatives forming intermolecular N-H.N hydrogen bonds are reported: 5-methyl-4-(3-methylpyrazol-5-yl)pyrazol-3-ol, C(8)H(10)N(4)O (P1), and 3-methyl-5-dihydro-1H-naphtho[1,2-d]pyrazole hemihydrochloride, C(12)H(12)N(2).-C(12)H(13)N(2)(+).Cl(-) (P2). 26 other structures are surveyed in order to obtain a deeper insight into the ways NH-pyrazoles self-assemble by means of intermolecular N-H.N hydrogen bonds in molecular crystals. A limited number of compounds form chains or dimers via homonuclear N(+)-H.N positive-charge-assisted hydrogen bonds, typical of proton sponges, which can be remarkably short [e.g. N.N 2.714 (3), N-H 1.09 (3), H.N 1.63 (3) Å, N-H.N 169 (3) degrees in (P2)]. Most pyrazoles, however, pack via neutral N-H.N bonds which are formally assisted by resonance (resonance-assisted hydrogen bond, RAHB) through the.N=C-C=C-NH. iminoenamine fragment, contained in the ring, giving rise to dimers, trimers, tetramers and infinite chains of pyrazole molecules. Surprisingly, the resonance does not appear to shorten the N-H.N bond with respect to the accepted mean value N.N 2.97 (10) Å for non-resonant N-H.N bonds. It is shown that this is due to the internal pi-delocalization of the pyrazole ring, which can be hardly increased by the hydrogen-bond interaction, except in symmetrically 3,5-substituted pyrazoles which display N.N distances as short as 2.82 Å, identical C-C and C-N distances in the two halves of the pyrazole molecule, and typical phenomena of N-H.N dynamical proton disorder, detectable by (15)N-CP/MAS solid-state NMR.

The X-ray crystal and molecular structure of 3,5-di-tert-butylpyrazole hydrochloride at 200 K

Abstract The title compound 1 H ,2 H -3,5-di- tert -butylpyrazolium chloride ( 2 ) was prepared by reacting 1 H -3,5-di- tert -butylpyrazole ( 1 ) with hydrochloric acid in methanol. The molecules of 2 are arranged in the crystal in dimers bridged by the chlorine ion through strong and quite linear hydrogen bonds. Several surveys were performed via the Cambridge Structural Database searching for N + (sp 2 ) ue5f8 HCl − interactions and for pseudo-rings in which two chlorine ions were hydrogen bonded by two water molecules, both hydrogen atoms of each molecule being involved in the contacts.

Tautomerism of 1-(2′,4′-dinitrophenyl)-3-methyl-2-pyrazolin-5-one: theoretical calculations, solid and solution NMR studies and X-ray crystallography

To gain a better understanding of the tautomerism of 1-(2′,4′-dinitrophenyl)-3-methyl-2-pyrazolin-5-one, 2, different studies were performed. In order to simulate the gas phase, several MO calculations at the semiempirical (AM1 and PM3) and abinitio (HF/6-31G* and B3LYP/6-31G*) levels were carried out on the different tautomers of this compound and on those of the corresponding 1-phenyl derivative 4. The 1H and 13C NMR spectra were recorded in solution for compound 2. Finally, to investigate the solid state, 13C CPMAS NMR studies and the crystal structure analysis of this pyrazolinone and that of its isomer [1-(2′,4′-dinitrophenyl)-3-hydroxy-5-methylpyrazole, 3, whose chemical structure was incorrectly reported in the literature] were performed. In solution, the most abundant tautomer for both pyrazolinones, 2 and 4, depends on the solvent used. For compound 2 it was found that the CH tautomer was the most stable in the gas and solid states as opposed to its 1-phenyl analogue, which appears as the CH form in the gas phase and as NH and OH tautomers in the crystal.

Synthesis and structural studies of symmetric and unsymmetric adamantylmethyleneazines

The synthesis and spectroscopic properties (1H, 13C and 15N NMR, in solution and in the solid state) of six new 1-adamantylmethylene azines are reported. The crystal and molecular structures of 1-adamantylcarbaldehyde azine and 1-adamantyl methyl ketone azine, which exist in the solid state in the E,E-configuration, were determined by x-ray analysis. The geometric characteristics of the azine central bridge and the preferred configuration with regard to it (E,E, E,Z or Z,Z) were investigated by means of the crystallographic data retrieved from the Cambridge Structural Database and ab initio quantum chemical calculations. Copyright

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).

Unexpected Staudinger reaction of α-azidophenylacetonitrile and triphenylphosphine: synthesis and crystal structure of aminotriphenylphosphonium salt of phenylmalononitrile

Staudinger reaction of α-azidophenyiacetonitrile with triphenylphosphine in 1:2 molar ratio provides the triphenylphosphinazine derived from α-diazophenylacetonitrile, whereas in 2:1 molar ratio the final product is found to be the aminotriphenylphosphonium salt of phenylmalononitrile; X-ray structure analysis of this salt indicates that the anion and cation interact with one another via hydrogen bonding.

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.

Aromatic propellenes. Part 3. NMR, X-ray crystallography and semi-empirical calculations on the conformational isomerism of 1,2,4,5-tetrakis (pyrazol-1′-yl)-3,6-bis(3″,5″-dimethylpyrazol-1′-yl) benzene

The molecular and crystal structures of two crystalline forms of 1,2,4,5-tetrakis(pyrazol-1′-yl)-3,6-bis(3″,5″-dimethylpyrazol-1″-yl) benzene and one inclusion complex with two molecules of acetic acid were determined by x-ray analysis. The acetic acid forms dimers through symmetry centers and the only interactions in the structures are mainly due to weak C(SINGLE BOND)H…N interactions. All 14 possible conformations of the pyrazole with regard to the benzene ring were explored by means of AM1 semi-empirical calculations. The observed conformation in the crystal structures agrees fairly well with the most stable conformation which presents the pyrazole rings with the N(2) alternating between both sides of the phenyl plane. These calculations allow one to identify the minor isomer present in solution together with the major isomer corresponding to the crystal structure.