Pyrazole Complexes Research Articles

Structural and 57Fe-Mössbauer characterization of mononuclear ferrous and ferric pyrazole complexes

The reactions of FeX3 (X=Cl and Br) and pz∗H (pz∗H=pyrazole, or substituted pyrazole) in CH2Cl2 have led to three types of mononuclear complexes: mer-[FeX3(pz∗H)3], trans-[FeX2(pz∗H)4]− and trans-[FeX2(pz∗H)4]. The latter type, containing FeII-centers results from spontaneous reduction of the FeIII starting material. The X-ray crystal structures of eleven such complexes and the 57Fe-Mössbauer spectra of three of them are reported.

Coordination versus Coupling of Dicyanamide in Molybdenum and Manganese Pyrazole Complexes

The reactions of cis-[MoCl(η(3)-methallyl)(CO)(2)(NCMe)(2)] (methallyl = CH(2)C(CH(3))CH(2)) with Na(NCNCN) and pz*H (pzH, pyrazole, or dmpzH, 3,5-dimethylpyrazole) lead to cis-[Mo(η(3)-methallyl)(CO)(2)(pz*H)(μ-NCNCN-κ(2)N,N)](2) (pzH, 1a; dmpzH, 1b), where dicyanamide is coordinated as bridging ligand. Similar reactions with fac-[MnBr(CO)(3)(NCMe)(2)] lead to the pyrazolylamidino complexes fac-[Mn(pz*H)(CO)(3)(NH═C(pz*)NCN-κ(2)N,N)] (pzH, 2a; dmpzH, 2b), resulting from the coupling of pyrazol with one of the CN bonds of dicyanamide. The second CN bond of dicyanamide in 2a undergoes a second coupling with pyrazole after addition of 1 equiv of fac-[MnBr(CO)(3)(pzH)(2)], yielding the dinuclear doubly coupled complex [{fac-Mn(pzH)(CO)(3)}(2)(μ-NH═C(pz)NC(pz)=NH-κ(4)N,N,N,N)]Br (3). The crystal structure of 3 reveals the presence of two isomers, cis or trans, depending on whether the terminal pyrazoles are coordinated at the same or at different sides of the approximate plane defined by the bridging bis-amidine ligand. Only the cis isomer is detected in the crystal structure of the perchlorate salt of the same bimetallic cation (4), obtained by metathesis with AgClO(4). All the N-bound hydrogen atoms of the cations in 3 or 4 are involved in hydrogen bonds. Some of the C-N bonds of the pyrazolylamidino ligand have a character intermediate between single and double, and theoretical studies were carried out on 2a and 3 to confirm its electronic origin and discard packing effects. Calculations also show the essential role of bromide in the planarity of the tetradentate ligand in the bimetallic complex 3.

Metal‐Ion Permeation in Congested Nanochannels: The Exposure Effect of Ag+ Ions on the Phosphorescent Properties of a Gold(I)–Pyrazolate Complex that is Confined in the Nanoscopic Channels of Mesoporous Silica

An organometallic/silica nanocomposite of a 1D cylindrical assembly of a trinuclear gold(I)-pyrazolate complex ([Au(3)Pz(3)]) that was confined inside the nanoscopic channels of hexagonal mesoporous silica ([Au(3)Pz(3)]/silica(hex)), emitted red light with a luminescence center at 693 nm upon photoexcitation at 276 nm owing to a Au(I)-Au(I) metallophilic interaction. When a film of [Au(3)Pz(3)]/silica(hex) was dipped into a solution of Ag(+) in tetrahydrofuran (THF), the resulting nanocomposite material (Ag@[Au(3)Pz(3)]/silica(hex)) emitted green light with a new luminescence center at 486 nm, which was characteristic of a Au(I)-Ag(I) heterometallic interaction. Changes in the emission/excitation and XPS spectra of Ag@[Au(3)Pz(3)]/silica(hex) revealed that Ag(+) ions permeated into the congested nanochannels of [Au(3)Pz(3)]/silica(hex), which were filled with the cylindrical assembly of [Au(3)Pz(3)].

Synthesis, characterization, and anticancer activity of ruthenium-pyrazole complexes

A series of new water soluble Ru(III) pyrazole complexes mer-[RuCl3(DMSO-S)(pyz)2] 1, mer-[RuCl3(DMSO-S)(DMSO-O)(pyz)] 2, mer-[RuCl3(bpy)(dmpyz)] 3, and mer-[RuCl3(DMSO-S)(dmpyz)2] 4 (pyz=pyrazole; dmpyz=3,5-dimethylpyrazole, bpy=2,2’-bipyridine) have been synthesized and characterized by use of a combination of spectroscopy (IR and UV-visible), X-ray diffraction, and cyclic voltammetry. The molecular X-ray structure of all reported compounds (1–4) revealed distorted octahedral coordination around ruthenium. The cytotoxicity assay on human breast cancer cells (MCF7) demonstrated that compounds 1 and 4 affect cell viability, whereas compounds 2 and 3 do not show appreciable activity. The IC50 values for 1 and 4 lie within the range of 71–32μM in MCF7 cells.

Steric-influenced fluxionality in monomeric two and three coordinate copper(I) complexes with a trans-chelating bis-pyrazole ligand

Two new trans-chelating bispyrazolyl ligands, LH, where LH=1,3-bis-(3,5-dimethyl-pyrazol-1-ylmethyl)-2,3-dihydro-1H-perimidine, and LCHPh2, where LCHPh2=2-benzhydryl-1,3-bis-(3,5-dimethyl-pyrazol-1-ylmethyl)-2,3-dihydro-1H-perimidine, and their two and three coordinate copper(I) derivatives [Cu(LH)](ClO4) (3·ClO4), [Cu(LCHPh2)](ClO4) (4·ClO4), and [Cu(LH)I] (5) were prepared and structurally characterized by X-ray crystallography. The variable-temperature 1H NMR spectra showed that complex 4·ClO4 is rigid, whereas complexes 3·ClO4 and 5 are nonrigid in CH2Cl2 solution. This suggests that the steric bulk of the 2-substituents in the dihydroperimidine moiety could impart some steric effects upon the fluxional behavior of individual two and three coordinate copper(I)–pyrazole complexes, in comparison with the rigid three coordinate copper(I) complex [Cu(LPh)I] (2) and dynamic two coordinate copper(I) complex [Cu(LPh)](ClO4) (1·ClO4) found previously [17]. To the best of our knowledge, complex 5 represents the first example of a dynamic monomeric three coordinate copper(I) complex.

Dinuclear Rh(ii) pyrazolates as CVD precursors for rhodium thin films

New dinuclear rhodium(II) pyrazolate (Pz) complexes of formula Rh(2)(3-R,5-R'Pz)(4)·2L (R = R' = CF(3), L = H(2)O (1), CH(3)CN (2)) and Rh(2)(3-R,5-R'Pz)(4) (R = R' = (t)Bu (3); R = CF(3), R' = (t)Bu (4)) have been synthesized from the interaction of the lithium salt of the corresponding pyrazole with Rh(2)(OAc)(4) in diethyl ether. The complexes were characterized by X-ray crystallography and spectroscopic methods. They were further evaluated as precursors for the chemical vapor deposition (CVD) of Rh thin films using H(2) as the carrier gas. The resulting films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).

Rhodium pyrazolate complexes as potential CVD precursors

Reaction of 3,5-(CF(3))(2)PzLi with [Rh(μ-Cl)(η(2)-C(2)H(4))(2)](2) or [Rh(μ-Cl)(PMe(3))(2)](2) in Et(2)O gave the dinuclear complexes [Rh(η(2)-C(2)H(4))(2)(μ-3,5-(CF(3))(2)-Pz)](2) (1) and [Rh(2)(μ-Cl)(μ-3,5-(CF(3))(2)-Pz) (PMe(3))(4)] (2) respectively (3,5-(CF(3))(2)Pz = bis-trifluoromethyl pyrazolate). Reaction of PMe(3) with [Rh(COD)(μ-3,5-(CF(3))(2)-Pz)](2) in toluene gave [Rh(3,5-(CF(3))(2)-Pz)(PMe(3))(3)] (3). Reaction of 1 and 3 in toluene (1 : 4) gave moderate yields of the dinuclear complex [Rh(PMe(3))(2)(μ-3,5-(CF(3))(2)-Pz)](2) (4). Reaction of 3,5-(CF(3))(2)PzLi with [Rh(PMe(3))(4)]Cl in Et(2)O gave the ionic complex [Rh(PMe(3))(4)][3,5-(CF(3))(2)-Pz] (5). Two of the complexes, 1 and 3, were studied for use as CVD precursors. Polycrystalline thin films of rhodium (fcc-Rh) and metastable-amorphous films of rhodium phosphide (Rh(2)P) were grown from 1 and 3 respectively at 170 and 130 °C, 0.3 mmHg in a hot wall reactor using Ar as the carrier gas (5 cc min(-1)). Thin films of amorphous rhodium and rhodium phosphide (Rh(2)P) were grown from 1 and 3 at 170 and 130 °C respectively at 0.3 mmHg in a hot wall reactor using H(2) as the carrier gas (7 cc min(-1)).

Lanthanoid and Alkaline Earth Complexes Involving New Substituted Pyrazolates

From the pyrazoles 3,5-di-(2′-furanyl)pyrazole (fu2pzH), 3-phenyl-5-(2′-thienyl)pyrazole (PhtpzH) and 3-(2′-furanyl)-5-(2′′-naphthyl)pyrazole (funappzH), a range of alkaline earth and lanthanoid pyrazolate complexes has been prepared by redox transmetallation/protolysis reactions between free metals, Hg(C6F5)2 and the pyrazoles, by reaction of I2‐activated metals with the pyrazoles, and in one case by a similar reaction of unactivated metal, in the donor solvents tetrahydrofuran (thf) and 1,2-dimethoxyethane (dme). Thus the divalent [Ca(Phtpz)2(thf)4], [Ba(Phtpz)2(thf)4] and [Ca(funappz)2(thf)4]·(thf) complexes, the heteroleptic [Yb(Phtpz)I(thf)4] and the trivalent [La(fu2pz)3(thf)3]·2thf complex have been prepared and structurally characterized, as well as the dme complexes [Yb(Phtpz)2(dme)2] and [Eu(Phtpz)3(dme)2]. Highlights include the first trans-[LnII(pz)I(thf)4] complex, a rare transoid [Ln(pz)2(dme)2] complex and a complex with both chelating and unidentate dme. In all cases, the Phtpz complexes exhibit pronounced positional disorder of the 2-thienyl and phenyl groups in the solid state, as do the two polymorphs of the parent pyrazole.

Perspective: the potential of pyrazole-based compounds in medicine

Pyrazoles are widely used as core motifs for a large number of compounds for various applications such as catalysis, agro-chemicals, building blocks of other compounds and in medicine. The attractiveness of pyrazole and its derivatives is their versatility that allows for synthesis of a series of analogues with different moieties in them, thus affecting the electronics and by extension the properties of the resultant compounds. In medicine pyrazole is found as a pharmacophore in some of the active biological molecules. While pyrazole derivatives have been extensively studied for many applications including anticancer, antimicrobial, anti-inflammatory, antiglycemic, anti-allergy and antiviral, much less has been reported on their metal counterparts in spite of the fact that metals have been shown to impart activity to ligands. Thus this perspective is intended to demonstrate the potential of pyrazole and pyrazolyl metal complexes in the areas of drug discovery and development. Several examples, that include palladium, platinum, copper, gold, zinc, cobalt, nickel, iron, copper, silver and gallium complexes, are used to bolster the above point. For the purposes of this review three areas are discussed, that is pyrazole metal complexes as: (i) anticancer, (ii) antibacterial/parasitic and (iii) antiviral agents.

Template Sol-Gel Synthesis of Phosphorescent Mesoporous Silica Film Nanocomposites Using an Amphiphilic Gold (I) Pyrazolate Complex

Herein novel mesoporous silica film nanocomposites are successfully synthesized by using phosphorescent columnar assembly of an amphiphilic trinuclear gold (I) pyrazolate complex [Au3Pz3] as a functional template in the sol-gel synthesis. By controlling the molar ratios of silica source tetrabutylorthosilicate (TBOS) to [Au3Pz3] in an acidic aqueous alcohol solution from 60:1 to 20:1, highly ordered phosphorescent nanocomposites can be fabricated with hexagonal [Au3Pz3]/silicahexand lamellar [Au3Pz3]/silicalamsilicates.

Hypersensitivity in the 4f–4f absorption spectra of tris (acetylacetonato) neodymium(III) complexes with imidazole and pyrazole in non-aqueous solutions. Effect of environment on hypersensitive transitions

The optical absorption spectra of [Nd(acac) 3(H 2O) 2]·H 2O, [Nd(acac) 3(im) 2] and [Nd(acac) 3(pz) 2] (where acac is the anion of acetylacetone, im is imidazole and pz is pyrazole) complexes in the visible region have been analyzed. The transition 4G 5/2← 4I 9/2 located near the middle of the visible region (17,500 cm −1) is hypersensitive. Its behavior is in sharp contrast to many other typically weak and consistently unvaried, normal 4f–4f transitions. It is overlapped by a less intense transition 2G 7/2← 4I 9/2. The band shapes of the hypersensitive transition show remarkable changes on passing from aqueous solution to various non-aqueous solutions, which is the result of changes in the environment about the Nd(III) ion in the various solutions and suggests coordination of a solvent molecules. Pyridine has been found especially effective in promoting 4f–4f electric-dipole intensity. The DMSO invades the complexes and replaces the water molecules and heterocyclic amines from the coordination sphere. Two DMSO molecules coordinate and the complexes acquire similar structure, [Nd(acac) 3(DMSO) 2] in solution. The oscillator strength and the band shape of the hypersensitive transition of all the complexes remains the same in this solvent. The IR spectra and the NMR spectra of the complexes have also discussed.

ChemInform Abstract: β‐Protic Pyrazole and N‐Heterocyclic Carbene Complexes: Synthesis, Properties, and Metal—Ligand Cooperative Bifunctional Catalysis

AbstractReview: ca. 150 refs.

β‐Protic Pyrazole and N‐Heterocyclic Carbene Complexes: Synthesis, Properties, and Metal–Ligand Cooperative Bifunctional Catalysis

This Minireview provides an overview of the chemistry of pyrazole and N-heterocyclic carbene (NHC) complexes bearing an NH group at the β-position to the metal. The synthesis and structures as well as the Brønsted acidic nature of the β-NH group are described in detail. These complexes are attractive candidates for novel metal-ligand cooperative bifunctional catalysts, which would benefit highly effective molecular and energy transformations.

Phosphomolybdate cluster based solids mediated by transition metal complexes

Reaction of molybdate and phosphate precursors in the presence of 3d transition metal ions and pyrazole ( pz) under hydrothermal condition resulted in the crystallization of four new phosphomolybdate cluster based solids: ( pz) 2[{Co( pz) 4} 5{P 2Mo 5O 23} 2]·6H 2O ( 1), ( pz){Ni( pz) 4(H 2O) 2}[{Ni( pz) 4} 5{P 2Mo 5O 23} 2]·2H 2O ( 2), {Cu( pz) 4(H 2O) 2}[{Cu( pz) 4}{Cu( pz) 4(H 2O)}{P 2Mo 5O 23}]·2H 2O ( 3) and ( pz)[{Zn( pz) 3} 3{P 2Mo 5O 23}]·2H 2O ( 4). In all the solids, a metal complex {M( pz) n } covalently links{P 2Mo 5O 23} clusters to form a chain. The dimensionality of the structures differs in the way the chains link or self assemble with counter ions and water molecules. To the best of our knowledge, 4 is the first example of a zinc complex incorporated with {P 2Mo 5O 23} cluster. The paper discusses the self assembly occurring between in situ metal pyrazole complex and phosphomolybdate clusters through coordinate/covalent and noncovalent interactions during crystallization of a particular solid.

Synthesis, Structure, and Proton-Transfer Reactions of Brønsted Acidic Pyridylpyrazole Complexes of Ruthenium

Abstract A reaction of [{Cp*Ru(μ3-Cl)}4] (Cp*: η5-C5(CH3)5) with 5-phenyl-3-(2-pyridyl)-1H-pyrazole (PhpypzH) afforded a chelating pyrazole complex [Cp*RuCl(PhpypzH)] (2) bearing an NH proton at the β-position to the metal. Treatment of 2 with an equimolar amount of silver nitrite followed by anion exchange with KOTf (OTf: OSO2CF3) gave the pyrazolato–nitrosyl complex [Cp*Ru(NO)(Phpypz)](OTf) (3) through a proton shift from the pyrazole ligand to the nitrite ion. In contrast, simple ligand exchange took place in the reaction of silver nitrite and [Cp*RuCl(bipy)] (bipy: 2,2′-bipyridine) without the protic chelate ligand to give the nitro complex [Cp*Ru(NO2-κN)(bipy)] (4). Protonation of 4 with triflic acid led to the formation of the nitrosyl complex [Cp*Ru(NO)(bipy)](OTf)2 (5). The pyrazolato complex 3 was also obtained by the reaction of [Cp*Ru(NO)Cl2] with PhpypzH and KOTf in water. Reversible protonation of 3 resulted in the formation of the dicationic pyrazole complex [Cp*Ru(NO)(PhpypzH)](OTf)2 (6). The detailed structures of 2–4 and 6 have been determined by X-ray crystallography.

Oxalate Bridged Copper Pyrazole Complex Templated Anderson-Evans Cluster Based Solids

The synthesis of four new Anderson-Evans type cluster based solids was carried out from an aqueous solution containing sodium molybdate, chromium chloride, cupric chloride and pyrazole at room temperature: [{Cr3O(CH3COO)6(H2O)3}2{H7CrMo6O24}]·24H2O, 1; [{Cu2(ox)(pz)4}{H7CrMo6O24}]·11H2O, 3; [{Cu(pz)2(H2O)2}{Cu2(ox)(pz)4}{H5CrMo6O24}]·8H2O, 4; and [{Cu(pz)3Cl}{Cu2(ox)(pz)4}{H6CrMo6O24}]·8H2O, 5. In 1, the discrete Anderson-Evans cluster aggregates with trimeric chromium acetate cationic complex through supramolecular interactions. In 3–5, the Anderson-Evans cluster is covalently linked into a 1D chain through oxalate bridged copper pyrazole units. In 3, the chains are further stabilized by water oligomers. In 4 and 5, the chains are covalently linked into 2D sheets by different copper pyrazole complexes. The oxalate molecules in 3–5 are probably generated in situ in the reaction medium, through a reductive coupling of dissolved carbon dioxide assisted by copper pyrazole units.

Halide and Nitrite Recognizing Hexanuclear Metallacycle Copper(II) Pyrazolates

Halide-centered hexanuclear, anionic copper(II) pyrazolate complexes [trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)X](-), X = Cl, Br, I are isolated in a good yield from the redox reaction of the trinuclear copper(I) pyrazolate complex [μ-Cu(3)((3,5-CF(3))(2)pz)(3)] with a halide source such as PPh(3)AuCl or [Bu(4)N]X, X = Cl, Br, or I, in air. X-ray structures of the anion-centered hexanuclear complexes show that the six copper atoms are bridged by bis(3,5-trifluoromethyl)pyrazolate and hydroxyl ligands above and below the six copper atom plane. The anions are located at the center of the cavity and weakly bound to the six copper atoms in a μ(6)-arrangement, Cu-X = ~3.1 Å. A nitrite-centered hexanuclear copper(II) pyrazolate complex [trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)(NO(2))](-) was obtained when a solution of [PPN]NO(2) in CH(3)CN was added dropwise to the trinuclear copper(I) pyrazolate complex [μ-Cu(3)((3,5-CF(3))(2)pz)(3)] dissolved in CH(3)CN, in air. Blue crystals are produced by slow evaporation of the acetonitrile solvent. The X-ray structure of [PPN][trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)(NO(2))] complex shows the nitrite anion sits in the hexanuclear cavity and is perpendicular to the copper plane with a O-N-O angle of 118.3(7)°. The (19)F and (1)H NMR of the pyrazolate ring atoms are sensitive to the anion present in the ring. Anion exchange of the NO(2)(-) by Cl(-) can be observed easily by (1)H NMR.

Crystal field and exchange interactions in rare earth transition metal salen compounds containing bipyridine, pyrazole complexes

Crystal field parameters for Pr 3+ in {[Ni(salen)Pr–(hfac) 3](H 2O)} (noted as NiPr) and {[Ni(salen)Pr(hfac) 3(pyr)]–(CHCl 3)} (noted as NiPrpyr) have been found from a fit to the thermal variation in the magnetic susceptibility of NiPr and NiPrpyr. The nature of exchange interaction in [Cu(salen)Pr(hfac)3(pyr)] (noted as CuPrpyr), {[{Cu(salen)Pr(hfac) 3} 2(pyz)](H 2O) 3} (noted as Cu 2Pr 2pyz) and {[{Cu(salen)Pr(hfac) 3} 2(bpy)]–(CHCl 3) 2} (noted as Cu 2Pr 2bpy, bpy=4,4_-bipyridine) have been found using the derived results for NiPr and NiPrpyr. All the exchange interactions give significant contribution to the thermal variation in magnetic susceptibility below 50 K. The contribution due to Pr–Cu interaction is positive while that of the Cu–Cu and Pr–Pr interactions are negative. The behaviors below 10 K for Pr–Cu and Pr–Pr are difficult to explain, and point to a possible change in structure of CuPrpyr, Cu 2Pr 2pyz and Cu 2Pr 2bpy below 10 K. The theoretical thermal variations in the magnetic specific heat of NiPr and NiPrpyr are computed and discussed.

ChemInform Abstract: Pyrazole and (Pyrazol‐1‐yl)metal Complexes as Carbon—Carbon Coupling Catalysts

AbstractReview: 156 refs.

Self‐Repair of a One‐Dimensional Molecular Assembly in Mesoporous Silica by a Nanoscopic Template Effect

Upon confinement of a trinuclear gold(I) pyrazolate complex in a hexagonal silicate channel, the luminescence center formed by a AuI–AuI metallophilic interaction is not only protected against thermal disruption but also strongly encouraged to self-recover from a heat-induced structural damage. This nanoscopic template effect is negligible for a lamellar silica framework.