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PubMed2006

Role of donor and secondary interactions in the structures and thermal properties of alkaline-earth and rare-earth metal pyrazolates.

The addition of neutral coligands to reduce the aggregation and improve the volatility of potential heavy alkaline-earth metal chemical vapor deposition (CVD) precursors has typically resulted in liberation of the coligand upon heating. A new series of dinuclear alkaline-earth and rare-earth metal pyrazolates, bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)calcium] (1), bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)strontium] (2), and bis[bis(3,5-di-tert-butylpyrazolato)bis(tetrahydrofuran)barium] (3), have been obtained from our previous donor-free oligonuclear complexes [{M(3,5-tBu2pz)2}n] (5, M = Ca, n = 3; 6, M = Sr, n = 4; 7, M = Ba, n = 6) by treatment with tetrahydrofuran (THF). Compounds 1-3, as well as the europium analogue bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)europium(II)] (4), can also be prepared by direct reaction of the metals and pyrazole in THF and anhydrous liquid ammonia. Recrystallization from hexane led to single crystals of 2-4, while the powder diffraction pattern of 1 revealed it to be isostructural with the previously published bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)ytterbium(II)] (8), providing important insight into differences and similarities between the two groups of metals. Detailed structural analysis of the compounds reveals secondary interactions including pi-bonding and agostic interactions, which are considered essential in stabilizing the metal complexes. The direct comparison of structural features and thermal properties (as evaluated by thermogravimetric analysis and sublimation studies) of the donor-free oligonuclear and the donor-containing dinuclear species offers a better understanding of the role of donors and secondary interactions.

Journal Article↗
PubMed1997

Silver(I) Pyrazolates. Synthesis and X-ray and (31)P-NMR Characterization of Triphenylphosphine Complexes and Their Reactivity toward Heterocumulenes.

Silver(I) pyrazolate was reacted with triphenylphosphine, leading to the dinuclear [Ag(2)(pz)(2)(PPh(3))(2)] and [Ag(2)(pz)(2) (PPh(3))(3)] complexes (Hpz = pyrazole), which were extensively characterized by (31)P-NMR methods and single-crystal X-ray analyses. Crystals of [Ag(2)(pz)(2)(PPh(3))(2)] are triclinic, space group P&onemacr;, with a = 9.567(2) Å, b = 11.440(2) Å, c = 10.073(2) Å, alpha = 93.59(2) degrees, beta = 64.01(2) degrees, gamma = 107.24(2) degrees, Z = 1, and D(calc) = 1.539 g.cm(-)(3); final R = 0.028 for 2532 independent reflections having F > 4sigma(F). They contain centrosymmetric dimers with trigonally coordinated silver atoms, which are 3.870(1) Å apart. Crystals of [Ag(2)(pz)(2) (PPh(3))(3)] are triclinic, space group P&onemacr;, with a = 9.752(2) Å, b = 14.163(2) Å, c = 20.450(2) Å, alpha = 101.84(1) degrees, beta = 99.83(2) degrees, gamma = 100.68(2) degrees, Z = 2, and D(calc) = 1.424 g.cm(-)(3); final R = 0.025 for 7075 independent reflections having F > 4sigma(F). Each molecule contains two inequivalent silver ions, bearing one and two phosphines, respectively, and a Ag(&mgr;-pz)(2)Ag ring with a rare twisted conformation. Both complexes readily react with heterocumulenes such as CS(2), COS, CO(2), and RNCO, affording new derivatives, the nature of which is dependent on the experimental conditions. Single-crystal X-ray analysis of [Ag(pz-CS(2))(PPh(3))(2)] has shown the unexpected S,S coordination of the pyrazolecarbodithioate fragment. Its crystals are triclinic, space group P&onemacr;, with a = 10.329(4) Å, b = 13.082(2) Å, c = 14.284(3) Å, alpha = 86.71(2) degrees, beta = 75.14(2) degrees, gamma = 74.79(2) degrees, Z = 2, and D(calc) = 1.431 g.cm(-)(3); final R = 0.028 for 5179 independent reflections having F > 4sigma(F).

Journal Article↗
PubMed2001

A solid-state NMR, X-ray diffraction, and ab initio computational study of hydrogen-bond structure and dynamics of pyrazole-4-carboxylic acid chains.

Using high-resolution solid-state (15)N CMAS NMR, X-ray crystallography, and ab initio calculations, we have studied the structure of solid pyrazole-4-carboxylic acid (1). The crystal structure was determined at 295 and 150 K. Molecules of 1 are located on a two-fold axis, implying proton disorder of the NH and OH groups; no phase transition was observed between these two temperatures. The compound forms quasi-linear ribbons in which the molecules are linked by cyclic hydrogen bonds between pyrazole and carboxylic acid groups with disordered hydrogen-bonded protons. Crystallography is unable to decide whether the disorder is dynamic or static. NMR shows that this disorder is dynamic, that is, consisting of very fast degenerate double proton transfers between two rapidly interconverting O-H.N and O.H-N hydrogen bridges. However, at low temperature, NMR shows a proton disorder-order transition where the protons are preferentially localized on given nitrogen and oxygen atoms. An amorphous phase exhibiting proton order is observed when the compound is precipitated rapidly. In this case, the defects are annealed by moderate heating. Ab initio calculations performed on oligomers of 1 show that the O-H.N hydrogen bridge is about 0.064 A shorter and less bent ( approximately 171 degrees ) than the O.H-N hydrogen bridge ( approximately 150 degrees ). For an isolated ribbon, this result leads to structures with localized protons, either to a cycle with about 200 molecules, or to a quasi-linear ribbon involving an undulated structure, or to a combination of both motifs. Only the undulated structure is compatible with the linear ribbon observed by X-ray crystallography, where the fast proton transfer in the high-temperature phase is assisted by the motions of the undulated chain. A disordered structure is assigned to the amorphous phase, which exhibits the combination of the curved and the undulated motifs.

Journal Article↗
PubMed2000

A new germanium-based linker for solid phase synthesis of aromatics: synthesis of a pyrazole library

An efficient synthesis of chlorogermane linker 12 is described. Economic introduction of germanium into this linker is accomplished by insertion of dichlorogermylene [from germanium(IV) chloride] into the homobenzylic C-Cl bond of 4-(2-chloroethyl)phenol 1. Using linker 12, transmetalation with lithiated 4-acetophenone, 3-acetophenone, and 4-(4'methoxy)biphenyl followed by Mitsunobu-type coupling to Argogel gives functionalized resins 14, 16, and 18, respectively. Treatment of resin 18 with TFA, ICl, Br2, or NCS effects clean ipso-degermylation releasing biphenyls 19-22, respectively. Resins 14 and 16 are employed for the parallel synthesis of a library of pyrazoles by enaminone formation (using Bredereck's reagent), condensative ring-closure (using a series of monosubstituted hydrazines), and cleavage (using TFA and Br2). Analysis of this library reveals the influence of the hydrazine substituent on both the regioselectivity of ring-closure and the propensity for electrophilic substitution at the 4-position of the pyrazoles during ipso-degermylative cleavage.

Journal Article↗
PubMed2004

Synthesis and relative stability of 3,5-diacyl-4,5-dihydro-1H-pyrazoles prepared by dipolar cycloaddition of enones and alpha-diazoketones.

An unusual reaction process that produced unexpected heterocyclic systems by a fragmentation-recombination mechanism is described. Thus treatment of the triketone, 3-acetyl-2,6-heptanedione, 1, with methanesulfonyl azide gave, in addition to the expected alpha-diazo ketone 3a, the dihydropyrazole 3c and its oxidation product, the pyrazole 3d. We propose that the initially formed alpha-diazo ketone 3a fragments into the simple alpha-diazomethyl ketone and methyl vinyl ketone which then undergo an intermolecular [2,3]-dipolar cycloaddition. Analogous treatment of the trifluoromethyl trione 2 again afforded a pyrazole 4c. Further experiments were carried out to lend evidence to our mechanistic hypothesis. Thus alpha-diazoacetophenone 5 and MVK underwent a [2,3]-dipolar cycloaddition under mild conditions to give the two regioisomeric dihydropyrazoles 6a and 6b. Interestingly these were formed in a 2:1 ratio, which suggested that 6a was more stable than 6b. The structures of 6a and 6b were optimized by using the B3LYP density functional method and the 6-31G* basis set and isomer 6a was predicted to be 1.5 kcal/mol more stable than isomer 6b. This energy difference could be rationalized by the greater capacity of the acetyl group than the benzoyl group to conjugate with the hydrazone. This difference in conjugation is reflected by key bond length differences. Thus we have discovered a novel fragmentation-cycloaddition process. We have also presented evidence for the mechanism of the formation of the dihydropyrazoles and carried out calculations to support these findings.

Journal Article↗
PubMed2006

Intertrimer and intratrimer metallophilic and excimeric bonding in the ground and phosphorescent States of trinuclear coinage metal pyrazolates: a computational study.

The interactions present in cyclic trinuclear coinage metal pyrazolates were studied computationally. Cuprophilic interaction was found to bind the singlet ground state of the dimer of trimers [[Cu(Pz)](3)](2), overcoming electrostatic repulsion. The large variation in intertrimer separations found in the literature for coinage metal pyrazolates is consistent with the relatively weak metallophilic interaction. The emissive triplet excited-state geometry of [[M(Pz)](3)](2) is predicted by density functional calculations to show major geometric distortion caused by Jahn-Teller instability and excimeric M-M bonding. Large calculated Stokes' shifts, which are also observed for experimental models, are consistent with significant excited-state distortions for these materials. The major finding derived from the present study is that the intertrimer M...M contraction in the emissive T(1) state is much more than the intratrimer contraction in all [[M(Pz)](3)](2) models, giving rise to a lower T(1) --> S(0) phosphorescence energy in these models than in analogous monomer-of-trimer models. The observations made here point to a great potential for rationally tuning the emission properties of trinuclear coinage metal complexes through choice of the metal and ligands.

Journal Article↗
PubMed2006

Novel synthesis of highly functionalized pyrazolines and pyrazoles by triphenylphosphine-mediated reaction of dialkyl azodicarboxylate with allenic esters.

[reaction: see text] Reaction of the Huisgen zwitterion, derived from triphenylphosphine and dialkyl azodicarboxylate, with allenic esters affords highly functionalized pyrazolines and pyrazoles. The crystal structure of pyrazoline derivative 7a showed extensive C-H...O interactions. Pyrazole formation proceeds via a novel nitrogen to carbon migration of the carboalkoxy group.

Journal Article↗
PubMed2005

Neutral Cu4N12 and Ag4N12 metallacycles with a para-cyclophane framework assembled from copper(I) and silver(I) pyrazolates and pyridazine.

Trinuclear copper(I) and silver(I) pyrazolates {[3,5-(CF3)2Pz]M}3 (M = Cu and Ag) react with pyridazine to give neutral, tetranuclear metallacycles with a para-cyclophane core whereas benzo[c]cinnoline fails to break the cyclic pyrazolate trimers under similar conditions, and affords a metalla-propellane featuring both two- and three-coordinate metal sites.

Journal Article↗
PubMed2005

Rhenium oxo compounds containing eta2-pyrazolate ligands.

Reaction of potassium salts of sterically demanding pyrazolates (pz = bis-3,5-tert-butylpyrazolate, pz= bis-3,5-tert-butyl-4-methylpyrazolate) with Re2O7 affords soluble eta2-pyrazolate complexes of the type [(eta2-pz)ReO3(THF)n](1: pz, n= 1 and 2: pz, n= 0). They were characterized by spectroscopic methods and by X-ray crystallography confirming the eta2-coordinate ligands. Complex 1 employing the ligand with a proton in the 4-position retains one molecule of THF, whereas the additional methyl group in 2 leads to the base-free compound 2. Compound 1 reacts with pyridine and 3,5-dimethylpyridine to form Lewis base adducts of the type [(eta2-pz)ReO3(L)](3: L = py; 4: L = 3,5-Me2py). The pronounced sensitivity towards water of these complexes is demonstrated by the reaction of 1 with one equivalent of water forming the corresponding pyrazolium perrhenate [ReO4][pzH2](5). Its solid state structure shows a hydrogen bonded dimeric assembly. Catalytic activity of 1 is established in oxygen atom transfer-reactions (OAT) from dimethylsulfoxide to triphenylphosphine, and in epoxidations of cyclooctene employing bis(trimethylsilyl) peroxide (BTSP).

Journal Article↗
PubMed2002

(Acetonitrile)[2,6-bis(pyrazol-1-yl)pyridine](isonicotinamide)copper(II)-tetrafluoroborate-acetonitrile (1/2/2).

Molecules of the title compound, [Cu(C(2)H(3)N)(C(11)H(9)N(5))(C(6)H(6)N(2)O)](BF(4))(2).2C(2)H(3)N, comprise (acetonitrile)[2,6-bis(pyrazol-1-yl)pyridine](isonicotinamide)copper(II) cations, tetrafluoroborate anions and lattice acetonitrile molecules. The cations have distorted square-pyramidal geometries in which the N(3)-donor, viz. 2,6-bis(pyrazol-1-yl)pyridine, and the N-donor, viz. the isonicotinamide ligand, occupy the four basal positions, with the coordinated acetonitrile N-donor atom occupying the apical position. Pairs of cations are linked by N-H.F hydrogen bonds through tetrafluoroborate anions, forming centrosymmetric dimers, which are further linked by C-H.O hydrogen bonds into two-dimensional undulating sheets, three of which interpenetrate to generate a two-dimensional network.

Journal Article↗
PubMed2003

1-Bromo-2,6-bis[(pyrazol-1-yl)methyl]benzene.

The title compound, C(14)H(13)BrN(4), has a planar central unit, (C)(2)C(6)H(3)Br, the pendant pyrazole rings forming dihedral angles of 83.8 (3) and 89.3 (3) degrees with this plane. The pyrazole rings are oriented such that there is an approximate twofold axis coincident with the C-Br bond.

Journal Article↗
PubMed2004

Di-mu-iodo-bis{[1,1'-methylenebis(3,5-dimethyl-1H-pyrazole-kappaN2)]copper(I)}.

In the title compound, [Cu2I2(C11H16N4)2], each of the two crystallographically equivalent Cu atoms is tetrahedrally coordinated by two N atoms from one 1,1'-methylenebis(3,5-dimethyl-1H-pyrazole) ligand and two bridging iodide anions. The molecule has a crystallographic center of symmetry located at the mid-point of the Cu...Cu line. One H atom of the CH2 group of the 1,1'-methylenebis(3,5-dimethyl-1H-pyrazole) ligand interacts with an iodide ion in an adjacent molecule to afford pairwise intermolecular C-H...I contacts, thereby forming chains of molecules running along the [101] direction.

Journal Article↗
PubMed2006

Bis[bis(3-phenylpyrazol-1-yl)(pyrazol-1-yl)methane]copper(II) bis(perchlorate) acetonitrile disolvate.

The title copper(II) complex, [Cu(C22H18N6)2](ClO4)2.2C2H3N, comprises two neutral substituted tris(pyrazol-1-yl)methane ligands bonded to a central Cu(II) ion, which is positioned on a crystallographic inversion center. Six Cu-N bonds are arranged in a distorted octahedral fashion. The unsubstituted pyrazole rings on each ligand are oriented trans with respect to each other, interdigitated with the two 3-phenylpyrazole rings of the other ligand.

Journal Article↗
PubMed2006

3-[5-(4-Bromophenyl)-1H-pyrazol-3-ylamino]-5,5-dimethylcyclohex-2-en-1-one-(Z)-3-(4-bromophenyl)-3-chloroacrylonitrile (2/1): a stoichiometric cocrystal of a reaction product with one of its early precursors.

The title compound, 2C17H18BrN3O.C9H5BrClN, was crystallized from the reaction between 5,5-dimethylcyclohexane-1,3-dione, triethyl orthoformate and 5-amino-3-(4-bromophenyl)pyrazole, which had itself been prepared from the reaction between (Z)-3-(4-bromophenyl)-3-chloroacrylonitrile and hydrazine. The compound is a stoichiometric 2:1 cocrystal of the reaction product 3-[5-(4-bromophenyl)-1H-pyrazol-3-ylamino]-5,5-dimethylcyclohex-2-en-1-one and the early reactant (Z)-3-(4-bromophenyl)-3-chloroacrylonitrile. The two independent molecules of cyclohex-2-en-1-one are linked by N-H...N and N-H...O hydrogen bonds into complex bilayers and the molecules of acrylonitrile are trapped within large cavities in the substructure formed by the cyclohex-2-en-1-one molecules.

Journal Article↗
PubMed2006

A pyrazole derivative potently inhibits lymphocyte Ca2+ influx and cytokine production by facilitating transient receptor potential melastatin 4 channel activity.

3,5-Bis(trifluoromethyl)pyrazole derivative (BTP2) or N-[4-3, 5-bis(trifluromethyl)pyrazol-1-yl]-4-methyl-1,2,3-thiadiazole-5-carboxamide (YM-58483) is an immunosuppressive compound that potently inhibits both Ca2+ influx and interleukin-2 (IL-2) production in lymphocytes. We report here that BTP2 dosedependently enhances transient receptor potential melastatin 4 (TRPM4), a Ca2+-activated nonselective (CAN) cation channel that decreases Ca2+ influx by depolarizing lymphocytes. The effect of BTP2 on TRPM4 occurs at low nanomolar concentrations and is highly specific, because other ion channels in T lymphocytes are not significantly affected, and the major Ca2+ influx pathway in lymphocytes, ICRAC, is blocked only at 100-fold higher concentrations. The efficacy of BTP2 in blocking IL-2 production is reduced approximately 100-fold when preventing TRPM4-mediated membrane depolarization, suggesting that the BTP2-mediated facilitation of TRPM4 channels represents the major mechanism for its immunosuppressive effect. Our results demonstrate that TRPM4 channels represent a previously unrecognized key element in lymphocyte Ca2+ signaling and that their facilitation by BTP2 supports cell membrane depolarization, which reduces the driving force for Ca2+ entry and ultimately causes the potent suppression of cytokine release.

Anilides↗
PubMed1996

Synthesis and cytoprotective antiulcer activity of 2- or 4-(1H-pyrazol-1-yl)pyrimidine derivatives related to mepirizole and dulcerozine.

(1H-Pyrazol-1-yl)-, (1H-imidazol-1-yl)-, and (1H-1,2,4-triazol-1-yl)pyrimidines were prepared and evaluated for cytoprotective antiulcer activity. Among them, 4-methoxy-6-methyl-2-(1H-pyrazol-1-yl)pyrimidine (18) showed potent inhibition of the HCl-ethanol-induced and water-immersion stress-induced ulcers in rats, as well as low acute toxicity.

Administration, Oral↗
PubMed1990

Synthesis and platelet aggregation inhibitory effects of N-[(1H-pyrazol-1-yl)alkyl]benzoylamides.

A series of N-[(1H-pyrazol-1-yl)alkyl]benzoylamides was synthesized and tested in vitro for their inhibitory effects on adenosine diphosphate-, collagen-, arachidonic acid- and thrombin-induced aggregation of human platelets. Among them, N-[(1H-pyrazol-1-yl)butyl]benzoylamide (Ve) was found to have the most potent inhibitory activity. The structure-activity relationships are reported. The biological activity of the title compounds is reported in parallel with that of a known inhibitor of thromboxane A2 synthetase.

Chemical Phenomena↗
PubMed1998

[Antimicrobial activity of (N-salicylidene-DL-aspartate- and (N-salicylidene-L-asparaginate)-copper complexes with pyrazole-type ligands].

By a reaction of salicylaldehyde (Scl) with the corresponding amino acids and by the next complexation reaction of the formed Schiff bases with Cu2+ ions in an aqueous-alcoholic medium, aqua (N-salicylideneaminoalkanoato)copper(II) complex chelates of the composition Cu(Scl-DL-Asp(2-)) (H2O)2, Ip and Cu(Scl-L-Asn(2-)(H2O), In were prepared. The monodiazole complexes with pyrazole IIp and IIn (as monohydrate) as well as with 3,5-dimethylpyrazole IIIp a IIIn were prepared by replacing the molecule of H2O in the parent aquacomplexes with the diazoles under the same reaction conditions. Using a routine dilution micromethod, the antimicrobial activity of the prepared complexes and free diazoles was tested against Staphylococcus aureus, Escherichia coli and Candida albicans. Only a significant antistaphylococcus activity was found (highest for the complex IIn; MIC = 39 micrograms/cm3). All chelates (Ip,n-IIIp,n) were more effective (MIC = 39-156 micrograms/cm3) than both pyrazole (312 micrograms/cm3)and 3,5-dimethylpyrazole (625 micrograms/cm3) alone. The relationship between the coordination-chemical properties and the biological effects of the complexes studied is discussed.

Anti-Bacterial Agents↗