M.R. Torres

Chemistry of Rh(I) complexes based on mesogenic 3,5-disubstituted pyrazole ligands. X-ray crystal structures of 3,5-di(4-n-butoxyphenyl)pyrazole (Hpzbp2) and [Rh(μ-pzR2)(CO)2]2 (R = C6H4OCnH2n+1, n = 10, 12) compounds. Part II

Abstract Four new 3,5-disubstituted pyrazoles Hpz R2 containing long-chain 4- n -alkyloxyphenyl substituents [R=C 6 H 4 OC n H 2 n +1 ; n =4 ( 1 ), 6 ( 2 ), 12 ( 5 ), 14 ( 6 )] have been prepared and characterised. All of them showed mesomorphic behaviour, the stability and the range of the mesophases increasing with the length of the chain on the pyrazole. The X-ray structure of Hpz bp2 ( 1 ) showed a highly linear molecular shape. Related results were deduced for the remained Hpz R2 and the structural consequences agree with the observed mesomorphic properties. The mesogenic pyrazoles Hpz R2 ( 1 – 6 ) were used as ligands towards [RhCl(CO) 2 ] and [Rh(CO) 2 ] fragments. [RhCl(CO) 2 (Hpz R2 )] complexes ( 7 – 12 ) showed some physical properties dependant on the long-chained pyrazoles, and related to different molecular arrays in the solid state. In all cases these compounds evolved to [Rh(μ-pz R2 )(CO) 2 ] 2 in solution. The pyrazolate Rh(I) complexes [Rh(μ-pz R2 )(CO) 2 ] 2 ( 13 – 18 ) had the usual boat conformation, as deduced by the crystal structure of two of these derivatives [ n =10 ( 16 ), 12 ( 17 )]. The packing arrangement has both layer and columnar characteristics. No mesophases have been detected for any of the Rh(I) complexes.

Mesogenic Pd(II) complexes based on 3-substituted pyrazol ligands

Abstract A new family of linear Pd(II) complexes based on pyrazoles containing long-chain substituents at the third position has been prepared and their mesomorphic properties studied. The crystalline structure of one of these compounds is described as a representative example of a very elongated and straight molecule.

Polymorphism and metal–metal interactions on [Rh(Cl)(CO)2(HpzR)] complexes

The novel pyrazoles containing 3-[4- n -hexyloxyphenyl] (hp), 3-[4- n -octyloxyphenyl] (op) and 3-[4- n -decyloxyphenyl] (dp) substituents, Hpz R (R=hp, op, dp; 1 – 3 ), and their corresponding Rh(I) compounds [Rh(Cl)(LL)(Hpz R )] (LL=2,5-norbornadiene NBD, 1,5-cyclooctadiene COD, 2CO; R=hp, op, dp; 4 – 12 ) have been prepared and characterised. The influence of the pyrazol substituent on the properties of the Rh(I) complexes has been analysed. Two crystalline polymorphs (yellow and red) have been isolated for [Rh(Cl)(CO) 2 (Hpz dp )] ( 12 ) in contrast to the single red crystalline form isolated for the related complexes [Rh(Cl)(CO) 2 (Hpz R )] (R=hp, op; 10 and 11 ). X-ray crystal structures of the red forms of 10 – 12 as well as the yellow one of 12 have been solved. The red compounds display one-dimensional stacking of square-planar molecules with metal–metal interactions along the c -axis. The yellow form consists of dimeric unities held together by Cl bridges, and without the one-dimensional metal–metal contacts. In both cases an intramolecular hydrogen bond was present, being stronger in the yellow form than in the red one. Thermochromic behaviour has also been observed for these dicarbonyl complexes. No liquid crystals properties were found for the new compounds, however, the double melting behaviour observed for 10 – 12 could be closely related to mesomorphism.

2-Anilinopyridinate of Cu(I) and adducts of 2-anilinopyridine and metal acetates.: Crystal structure of Cu2(μ-OAc)4(PhNHpy)2

Abstract The adducts of M(OAc)2·nH2O (M=Cu, Co, Ni, Zn) with 2-anilinopyridine, M(OAc)2(PhNHpy), have been synthesized and characterized. The X-ray crystal structure of Cu2(μ-OAc)4(PhNHpy)2 shows the dimer structure of Cu2(μ-OAc)4(H2O)2 with the PhNHpy ligand in the axial positions of the water molecules. It is antiferromagnetic (2J=−286 cm−1). Signals of the triplet state are observed in its EPR spectrum and the zero field splitting parameter (D=0.33 cm−1) has been calculated. The electronic spectra and the strong antiferromagnetism of the cobalt (2J=−324 cm−1) and nickel (2J=−382 cm−1) compounds allow to propose also a dimeric structure for them. By excess of ligand, in the anionic form, the Cu(I) compound Cu(PhNpy) was obtained for which a dinuclear structure with a lineal coordination in Cu(I) is proposed.

Silver pyrazole complexes with tunable liquid crystals and luminescent properties

New silver ionic complexes based on pyrazole ligands of the type [Ag(Hpz2R(n))2][A] (Hpz2R(n) = 3,5-bis(4-alkyloxyphenyl)pyrazole; R = C6H4OCnH2n+1; [A] = CH3-p-C6H4SO3− (PTS), CF3SO3− (OTf)) (type I) are liquid crystal materials exhibiting photoluminescence in the solid state, in solution and in the mesophase. By way of contrast, the related counterparts [Ag(HpzR(n))2][A] (HpzR(n) = 3-(4-alkyloxyphenyl)pyrazole; R = C6H4OCnH2n+1; [A] = CH3-p-C6H4SO3− (PTS), CF3SO3− (OTf)) (type II), containing monosubstituted pyrazole ligands, are not mesomorphic but also behave as luminescent materials. The crystalline structures of 5 and 10, as representative examples of classes I and II, have been solved. Molecular “H” or “Z” shapes, depending on the cis or trans orientation of the NH groups of the pyrazole ligands, were found, respectively. The first type gave rise to a layer-planar network, while a corrugated layer was found for complex 10, these features being related to the mesomorphic behaviour of both kinds of compounds. The mesomorphic and luminescent properties of complexes I and II were compared with those of related compounds containing the less sterically-demanding counteranions PF6−, NO3− and BF4−, described in our previous work. In all cases, the effect of the counteranions, as well as the substitution on the pyrazole groups, were analyzed for their corresponding properties.

Chemoselective Michael reactions on pyroglutamates. Expeditious synthesis of spiro-bis-γ-lactams as β-turn peptidomimetics

Abstract Starting from pyroglutamic acid, the synthesis of spiro-bis-γ-lactams, using as key step a chemoselective Michael reaction of pyroglutamates is reported. Thus, the reaction of N -BOC- l -methyl pyroglutamate with LiHMDS gives the enolates at C4 which react with several Michael acceptors. On the other hand, N -benzyl- l -methyl pyroglutamate reacts under the same conditions, to give the ester enolate which reacts with Michael acceptors leading to quaternized derivatives. The synthesis of the bicyclic spirolactams results from a reduction of the nitro group present in these derivatives which directly gives the spiro compounds. These final compounds may act as β-turn mimetics, as they have torsion angles which are in the range of β-turns of type II and II′.

Acetato and formato copper(II) paddle-wheel complexes with nitrogen ligands

Compounds Cu(AcO)2(pydz) (1), Cu(HCOO)2(pymd)1/2 (2), Cu(AcO)2(pymd)1/2 (3), and Cu(AcO)2(4,4′-bipy)1/2 (4) were obtained by reactions of Cu(AcO)2⋅H2O and Cu(HCOO)2 ⋅ 4H2O with pyridazine, pyrimidine, or 4,4′-bipyridine. In all the studied structures, the paddle-wheel units [Cu2[µ-RCOO)4] are present. Coppers show a square pyramidal coordination determined by four oxygens in the equatorial positions and a nitrogen in the axial position. Compound 1 consists of centrosymmetric dimeric molecules. Compounds 2 and 3 instead consist of zig-zag chains of [Cu2[µ-RCOO)4] units linked by bridging pyrimidine molecules. The chains run in the (1 0 1) and (1 1 −2) directions in 2 and 3, respectively. By crystallization of a solution of 4 in chloroform, Cu(AcO)2(4,4′-bipy)1/2 ⋅ 1/2CHCl3 (5) was obtained. It consists of monodimensional chains of [Cu2(µ-CH3COO)4] units linked by bridging 4,4′-bipy molecules. The chains, of two different types, run parallel to the b-axis in the crystal. Two chlorines of each CHCl3 molecule are close to two oxygens of two parallel chains. The packing can be described as sheets parallel to the (1 0 −1) plane. Magnetic properties and electron paramagnetic resonance spectra have been studied.

Structural Studies of Two Tinuvin ® P Analogs: 2-(2,4-Dimethylphenyl)-2H-benzotriazole and 2-Phenyl-2H-benzotriazole

2-(2,4-Dimethylphenyl)-2H-benzotriazole (1) has been synthesized in a three step procedure starting from 2,4-dimethyl-N-(2-nitrophenyl)benzamide via a 5-(2,4- dimethylphenyl)-1-(2-nitrophenyl)-1H-tetrazole intermediate. Its structure and those of Tinuvin P and 2-phenyl-2H-benzotriazole (5) have been studied by multinuclear NMR (1H-, 13C- and 15N-) in solution and in the solid state. X-ray diffraction analysis of 1 and 5 allowed to us establish the molecular conformation around the single bond connecting the two aromatic systems, in agreement with the conclusions drawn from the NMR study. In the case of 1 ab initio geometry optimization was achieved at the Hartree-Fock HF/6- 31G** and DFT B3LYP/6-31G** levels.

Fluorination Effects on NOS Inhibitory Activity of Pyrazoles Related to Curcumin

A series of new (E)-3(5)-[β-(aryl)-ethenyl]-5(3)-phenyl-1H-pyrazoles bearing fluorine atoms at different positions of the aryl group have been synthesized starting from the corresponding β-diketones. All compounds have been characterized by elemental analysis, DSC as well as NMR (1H, 13C, 19F and 15N) spectroscopy in solution and in solid state. Three structures have been solved by X-ray diffraction analysis, confirming the tautomeric forms detected by solid state NMR. The in vitro study of their inhibitory potency and selectivity on the activity of nNOS and eNOS (calcium-calmodulin dependent) as well as iNOS (calcium-calmodulin independent) isoenzymes is presented. A qualitative structure–activity analysis allowed the establishment of a correlation between the presence/absence of different substituents with the inhibition data proving that fluorine groups enhance the biological activity. (E)-3(5)-[β-(3-Fluoro-4-hydroxyphenyl)-ethenyl]-5(3)-phenyl-1H-pyrazole (13), is the best inhibitor of iNOS, being also more selective towards the other two isoforms.

Syntheses, structures, and magnetic properties of dinuclear/1-D copper(II) acetato and formato derivatives with methylpyrazine and dimethylpyrazine

In this study, {[Cu2(µ-HCO2)4](µ-Mepyrz)} n (1), [Cu2(µ-HCO2)4(Mepyrz)2] (2), {[Cu2(µ-AcO)4](µ-Mepyrz)} n (3), [Cu2(µ-AcO)4(Mepyrz)2] (4), [Cu2(µ-AcO)4(2,3-Me2pyrz)2] (5), [Cu2(µ-AcO)4(2,6-Me2pyrz)2] (6), and {[Cu2(µ-AcO)4](µ-2,5-Me2pyrz)} n (7) have been synthesized and characterized by chemical analysis and electronic spectroscopy. Compounds 2, 4, 5, and 6, characterized by single-crystal X-ray diffraction, are composed of molecular dimers based on a paddle-wheel motif with two coppers, four syn–syn carboxylates, and two ligands coordinated to copper in the axial positions. In 7, chains of [Cu2(µ-AcO)4] dimers with 2,5-Me2pyrz as bridging ligands are formed. Magnetic properties and electron paramagnetic resonance results of the compounds are also described.