Pyrazolyl Nitrogen Research Articles

Synthesis and catalytic activity of silver N-heterocyclic carbene complexes based on bis(3,5-dimethylpyrazol-1-yl)methyl-substituted pyridylimidazole

A series of N-heterocyclic carbene (NHC) silver complexes derived from 6-[bis(3,5-dimethylpyrazol-1-yl)methyl]-2-pyridylimidazole have been synthesized and characterized by physico-chemical and spectroscopic methods, and the structures of four complexes have been confirmed by X-ray structural analyses. The functionalized NHC is a monodentate ligand in (NHC)AgCl through the carbene carbon atom, and a bridging [C,N,N] tridentate ligand in (NHC)2Ag2(BF4)2 and (NHC)2Ag2(PF6)2 through two pyrazolyl nitrogens and the carbene carbon to form a metallomacrocycle, in which a head (carbene)– to tail (nitrogen) coordination mode to two silver atoms is observed. Preliminary catalytic tests show that these newly synthesized Ag–NHC complexes exhibit excellent catalytic activity at a low catalyst loading (0.1–1 mol%) in the aldehyde–amine–alkyne coupling reaction.

Dissociation of a tripodal pyridyl-pyrazole ligand and assortment of metal complex: Synthesis, structure, DFT, thermal stability, cytotoxicity, DNA cleavage, and molecular docking studies

A tripodal pyridyl-pyrazole based N,N,O donor ligand (L) has been designed, and it's copper(II) complex, [Cu(L1)Cl2]2.(dmpzH)2 (1) where dmpzH refers protonated dimethylpyrazole, and manganese(II) complex, [Mn(L)(Cl)2] (2)] have been synthesized and characterized by a combination of various spectroscopy, X-ray crystallography, electrochemical, thermogravimetric and density functional theory. The X-ray structure of 1 showed the copper(II) coordinated by the two sets of NO donors which had been assorted from the ligand (L) along with two bridging and one terminal chloride atoms. The distorted square-planar centrosymmetric structure of 1 is further stabilized by the hydrogen bonding with exogenous protonated pyrazole units that had been extracted from L. The title ligand retained its original structure when bound with Mn(II) giving a pseudo-octahedral geometry. The central Mn(II) was coordinated by two pyrazolyl nitrogen (N1, N7), one tertiary amine nitrogen (N3), one carbohydrazide oxygen atom O1, and two exogenous chloride ions in a cis disposition. Cytotoxicity experiments carried out in a series of human cell lines (IMR-32, HepG2 and HeLa) to confirm the apoptotic mechanism of cell death, predominantly in IMR-32. The DNA cleavage studies were then performed in the presence of the synthesized compounds to verify the influence of ligand structural features in their nuclease activity. Complex 2 was able to cause double-strand DNA scissions both in an oxidizing and reducing environment, whereas complex 1 broke the single-strand DNA in a reducing environment only, suggesting its potential anticancer therapeutics. To shed a better understanding of DNA-substrate interaction, a molecular docking study was performed.

The Influence of Aryl Substituents on the Supramolecular Structures and Photoluminescence of Cyclic Trinuclear Pyrazolato Copper(I) Complexes.

Cyclic trinuclear complexes with group 11 metal(I) ions are fascinating and important to coordination chemistry. One of the ligands known to form these cyclic trinuclear complexes is pyrazolate, which is a bridging ligand that coordinates many transition metal ions in a Npz–M–Npz linear mode (Npz = pyrazolyl nitrogen atom). In these group 11 metal(I) ions, copper is the most abundant metal. Therefore, polynuclear copper(I) complexes are very important in this field. The cyclic trinuclear copper(I) complex [Cu(3,5-Ph2pz)]3 (3,5-Ph2pz– = 3,5-diphenyl-1-pyrazolate anion) was reported in 1988 as a landmark complex, but its photoluminescence properties have hitherto not been described. In this study, we report the photoluminescence and two different polymorphs of [Cu(3,5-Ph2pz)]3 and its derivative [Cu(3-Me-5-Phpz)]3 (3-Me-5-Phpz– = 3-metyl-5-phenyl-1-pyrazale anion). The substituents in [Cu(3-Me-5-Phpz)]3 cause smaller distortions in the solid-state structure and a red-shift in photoluminescence due to the presence of intermolecular cuprophilic interactions.

Pincer-like pyrazole- and imidazole-pyridinyl compounds: Synthesis, characterisation, crystallographic and computational investigation

An array of pincer-like bis(pyrazole)pyridinyl (1–10) and bis(imidazole)pyridinyl compounds (11 and 12) with varying alkyl pendant arms was synthesised and spectroscopically characterised. The classic Knorr approach for the synthesis of pyrazoles was adopted to minimise experimental complications and to maximise yield. In general, the yield of compounds 1–8 increased as the n-alkyl arm length increased [1 (33.7%) < 2 (41.5%) < 3 (42.6%)…8 (80.5%)]. This was primarily attributed to the boiling points of their respective alkyl ketone reagents. In all cases tautomerism was evident in the 13C{1H} NMR spectra. The 13C resonances of the carbons adjacent to the pyrazolyl nitrogen atoms were broad and weak, revealing rapid pyrazolyl tautomerism in solution. Single crystal XRD analysis of 1 showed that, for the first time with the aid of an ethanol molecule, the compound was locked into a specific arrangement due to stabilisation via intermolecular hydrogen bonding. This was corroborated by DFT calculations which indicated mixed tautomer II (−497412 kcal.mol−1) to be further stabilised once it was brought in the presence of ethanol. Additionally, the energy gap between the HOMOs and LUMOs was computed and found to be 107.79, 111.22 and 116.29 kcal.mol−1 for structures I, II and III, respectively (265, 255 and 246 nm). This signifies that the π-π* electronic transition is red-shifted from structure III to I.

Synthesis and Structural Characterization of a Silver(I) Pyrazolato Coordination Polymer.

Coinage metal(I)···metal(I) interactions are widely of interest in fields such as supramolecular assembly and unique luminescent properties, etc. Only two types of polynuclear silver(I) pyrazolato complexes have been reported, however, and no detailed spectroscopic characterizations have been reported. An unexpected synthetic method yielded a polynuclear silver(I) complex [Ag(μ-L1Clpz)]n (L1Clpz− = 4-chloride-3,5-diisopropyl-1-pyrazolate anion) by the reaction of {[Ag(μ-L1Clpz)]3}2 with (nBu4N)[Ag(CN)2]. The obtained structure was compared with the known hexanuclear silver(I) complex {[Ag(μ-L1Clpz)]3}2. The Ag···Ag distances in [Ag(μ-L1Clpz)]n are slightly shorter than twice Bondi’s van der Waals radius, indicating some Ag···Ag argentophilic interactions. Two Ag–N distances in [Ag(μ-L1Clpz)]n were found: 2.0760(13) and 2.0716(13) Å, and their N–Ag–N bond angles of 180.00(7)° and 179.83(5)° indicate that each silver(I) ion is coordinated by two pyrazolyl nitrogen atoms with an almost linear coordination. Every five pyrazoles point in the same direction to form a 1-D zig-zag structure. Some spectroscopic properties of [Ag(μ-L1Clpz)]n in the solid-state are different from those of {[Ag(μ-L1Clpz)]3}2 (especially in the absorption and emission spectra), presumably attributable to this zig-zag structure having longer but differently arranged intramolecular Ag···Ag interactions of 3.39171(17) Å. This result clearly demonstrates the different physicochemical properties in the solid-state between 1-D coordination polymer and metalacyclic trinuclear (hexanuclear) or tetranuclear silver(I) pyrazolate complexes.

A heterometallic Cd/Ag/Se complex incorporating 3-ferrocenyl-5-(2-pyridyl)pyrazolato (fcpp) ligands: synthesis and structure of [Cd2{Ag(SePh)}2(μ3-OH2)2(μ2,η3-fcpp)4]·2C3H6O

Abstract A self-assembly reaction of Cd(NO3)2 · 4H2O, 3-ferrocenyl-5-(2-pyridyl)-pyrazole (Hfcpp), [Ag(SePh)] n , and Et3N in a mixed acetone-water solvent resulted in the formation of a heterometallic complex [Cd2{Ag(SePh)}2 (μ 3-OH2)2(μ 2,η 3-fcpp)4] · 2C3H6O (1) with a phenylselenolate ligand. The two cadmium and two silver centers are linked by four [μ 2,η 3-fcpp]− ligands and two μ 3-OH2 water molecules. Each Cd atom is in a slightly distorted octahedral coordination environment, while each Ag atom shows a distorted tetrahedral coordination geometry, which is composed of two pyrazolyl nitrogen atoms, one selenium atom, and one oxygen atom.

Synthesis and antimicrobial studies of half-sandwich arene platinum group complexes containing pyridylpyrazolyl ligands

The reaction of [(arene)MCl2]2 with pyridylpyrazolyl ligands (L1 and L2) in the presence of ammonium hexafluorophosphate leads to formation of cationic complexes having the general formula [(arene)M(L)Cl]PF6 {M = Ru, arene = p-cymene (1, 4); Cp*, M = Rh (2, 5); Cp*, M = Ir (3, 6); L = 2-(1H-pyrazol-1-yl)pyridine (L1), 2-(3,5-dimethyl-1H-pyrazol-1-yl)pyridine (L2)}. Similarly the reaction of [CpRu(PPh3)2Cl] and [(ind)Ru(PPh3)2Cl] (ind = η5-C9H7) with L1 and L2 yielded cationic complexes which have been formulated as [(Cp/ind)Ru(L)PPh3]PF6 (7–10). All these complexes were characterized by analytical and spectroscopic techniques. The pyridylpyrazolyl ligands coordinated metal through pyridyl and pyrazolyl nitrogens forming a six-membered metallacycle. The ligands as well as the complexes were evaluated for their in vitro antibacterial activity by agar well diffusion method against two Gram negative bacteria (Escherichia coli and Pseudomonas aeruginosa) and two Gram positive bacteria (Staphylococcus aureus and Bacillus thuriengiensis). Results show that the ligands and the complexes have significant antibacterial activity against Gram negative bacteria.

Syntheses and Crystal Structures of Copper(II) Bis(pyrazolyl)acetic Acid Complexes

The reaction of bis(pyrazol-1-yl)acetic acid (L) with copper(II) bromide provides two new complexes: [Cu(L-H)Br(µ-Br)]2 (1) and [Cu(L)2]⋅4H2O (2). Complex 1 is prepared by the stoichiometric reaction of L-H with copper(II) bromide in tetrahydrofuran. Dissolution of 1 in methanol causes its conversion into the bis-ligated complex (2), a highly hygroscopic material. Complex 2 can also be synthesized directly by the stoichiometric reaction of L-H with CuBr2 in methanol. Complex 1 is dimeric, interlinked by two bridging bromide ligands, and possesses terminal bromide ligands on each copper atom. The two pyrazolyl ligands in 1 coordinate with the nitrogen atoms to complete the coordination sphere of copper, resulting in a highly distorted geometry that lies between a trigonal bipyramidal or square pyramidal geometry with wide bond angles between the trans-oriented pyrazolyl nitrogen atoms and bromide ligands. Complex 2 assumes a pseudo-trigonal prismatic geometry with the deprotonated carboxylic acid that interacts weakly with copper. Reaction of bis(pyrazol-1-yl)acetic acid (L-H) with copper(II) bromide provides two new complexes: [Cu(L-H)Br(µ-Br)]2 (1) and [Cu(L)2]⋅4H2O (2), these compounds represent the first, well-defined, independent copper(II) compounds supported by the base bis(pyrazolyl)acetic acid ligand.

Synthesis and structural studies of arene ruthenium and Cp*Rh/Cp*Ir complexes containing pyridylpyrazole- and pyridylthiazole-based ligands

The reactions of [(arene)RuCl2]2 (arene = p-cymene or benzene) and [Cp*MCl2]2 (M = Rh or Ir) with N,N′-bidentate chelating ligands 2-[3-(2-pyridyl)pyrazolyl]pyrimidine (L1) and 4-phenyl-(2-pyridyl)thiazole (L2) leads to the formation of mononuclear complexes of general formula [(arene)/Cp*M(L)Cl]PF6. Eight such complexes have been prepared and characterized by spectroscopic techniques. In addition, five of the complexes were also characterized by single-crystal X-ray diffraction. These complexes have typical piano-stool geometries around the metal center, with five-membered metellacycles in which L1 and L2 both act as N,N′-chelating ligands. Moreover, L1 prefers to coordinate through its pyrimidine and pyrazolyl nitrogen atoms, rather than the pyridine nitrogen.

The synthesis and characterisation of coordination and hydrogen-bonded networks based on 4-(3,5-dimethyl-1H-pyrazol-4-yl)benzoic acid.

The synthesis, structural and thermal characterisation of a number of coordination complexes featuring the N,O-heteroditopic ligand 4-(3,5-dimethyl-1H-pyrazol-4-yl)benzoate, HL are reported. The reaction of H2L with cobalt(II) and nickel(II) nitrates at room temperature in basic DMF/H2O solution gave discrete mononuclear coordination complexes with the general formula {[M(HL)2(H2O)4]·2DMF} (M = Co (1), Ni (2)), whereas the reaction with zinc(II) nitrate gave [Zn(HL)2]∞, 3, a coordination polymer with distorted diamondoid topology and fourfold interpenetration. Coordination about the tetrahedral Zn(II) nodes in 3 are furnished by two pyrazolyl nitrogen atoms and two carboxylate oxygen atoms to give a mixed N2O2 donor set. Isotopological coordination polymers of zinc(II), {[Zn(HL)2]·2CH3OH·H2O}∞, 4, and cobalt(II), [Co(HL)2]∞, 5, are formed when the reactions are carried out under solvothermal conditions in methanol (80 °C) and water (180 °C), respectively. The reaction of H2L with cadmium(II) nitrate at room temperature in methanol gives {[Cd(HL)2(MeOH)2]·1.8MeOH}∞6, a 2-D (4,4)-connected coordination polymer, whereas with copper(II) the formation of green crystals that transform into purple crystals is observed. The metastable green phase [Cu3(HL)4(μ2-SO4)(H2O)3]∞, 7, crystallises with conserved binding domains of the heteroditopic ligand and contains two different metal nodes: a dicopper carboxylate paddle wheel motif, and, a dicopper unit bridged by sulfate ions and coordinated by ligand pyrazolyl nitrogen atoms. The resultant purple phase {[Cu(HL)2]·4CH3OH·H2O}∞, 8, however, has single copper ion nodes coordinated by mixed N2O2 donor sets with trans-square planar geometry and is threefold interpenetrated. The desolvation of 8 was followed by powder X-ray diffraction and single crystal X-ray diffraction which show desolvation induces the transition to a more closely packed structure while the coordination geometry about the copper ions and the network topology is retained. Powder X-ray diffraction and microanalysis were used to characterise the bulk purity of the coordination materials 1–6 and 8. The thermal characteristics of 1–2, 4–6 and 8 were studied by TG-DTA. This led to the curious observation of small exothermic events in networks 4, 6, and 8 that appear to be linked to their decomposition. In addition, the solid state structures of H2L and that of its protonated salt, H2L·HNO3, were also determined and revealed that H2L forms a 2-D hydrogen bonded polymer incorporating helical chains formed through N–HO and O–HN interactions, and that [H3L]NO3 forms a 1-D hydrogen-bonded polymer.

Hydroxide-bridged cubane complexes of nickel(II) and cadmium(II): magnetic, EPR, and unusual dynamic properties.

The reactions of M(ClO4)2·xH2O (M = Ni(II) or Cd(II)) and m-bis[bis(1-pyrazolyl)methyl]benzene (Lm) in the presence of triethylamine lead to the formation of hydroxide-bridged cubane compounds of the formula [M4(μ3-OH)4(μ-Lm)2(solvent)4](ClO4)4, where solvent = dimethylformamide, water, acetone. In the solid state the metal centers are in an octahedral coordination environment, two sites are occupied by pyrazolyl nitrogens from Lm, three sites are occupied by bridging hydroxides, and one site contains a weakly coordinated solvent molecule. A series of multinuclear, two-dimensional and variable-temperature NMR experiments showed that the cadmium(II) compound in acetonitrile-d3 has C2 symmetry and undergoes an unusual dynamic process at higher temperatures (ΔGLm‡ = 15.8 ± 0.8 kcal/mol at 25 °C) that equilibrates the pyrazolyl rings, the hydroxide hydrogens, and cadmium(II) centers. The proposed mechanism for this process combines two motions in the semirigid Lm ligand termed the “Columbia Twist and Flip:” twisting of the pyrazolyl rings along the Cpz–Cmethine bond and 180° ring flip of the phenylene spacer along the CPh–Cmethine bond. This dynamic process was also followed using the spin saturation method, as was the exchange of the hydroxide hydrogens with the trace water present in acetonitrile-d3. The nickel(II) analogue, as shown by magnetic susceptibility and electron paramagnetic resonance measurements, has an S = 4 ground state, and the nickel(II) centers are ferromagnetically coupled with strongly nonaxial zero-field splitting parameters. Depending on the Ni–O–Ni angles two types of interactions are observed: J1 = 9.1 cm(–1) (97.9 to 99.5°) and J2 = 2.1 cm(–1) (from 100.3 to 101.5°). “Broken symmetry” density functional theory calculations performed on a model of the nickel(II) compound support these observations.

Synthesis of N-heterocyclic carbene silver and palladium complexes bearing bis(pyrazol-1-yl)methyl moieties

A series of N-heterocyclic carbene (NHC) silver and palladium complexes derived from N-[bis(pyrazol-1-yl)methyl]phenyl-N′-benzylimidazolium and N-[bis(pyrazol-1-yl)methyl]phenoxy- methyl-N′-benzylimidazolium salts have been synthesized and characterized by elemental analysis, NMR spectroscopy and single-crystal X-ray diffraction. The NHCs functionalized by bis(pyrazol-1-yl)methyl groups show three different coordination modes in these complexes. N-[Bis(pyrazol-1-yl)methyl]phenyl-N′-benzylimidazol-2-ylidene (L) and N-[bis(3,5-dimethylpyrazol-1-yl)methyl]phenyl-N′-benzylimidazol-2-ylidene (L′) act as monodentate ligands through the carbene carbon in cationic complexes [L2Ag][AgCl2] and [L′4Ag3Br2][AgBr2]. A bridging [C,N] bidentate coordination mode, through one pyrazolyl nitrogen and the carbene carbon to two palladium centers, was observed in macrocyclic complex L′2Pd2Br2. While in the coordination polymer [L2Ag2]n[PF6]2n and macrocyclic complex [L′2Ag2][PF6]2, L and L′ act as bridging [C,N,N] tridentate ligands through two pyrazolyl nitrogens and the carbene carbon. Although N-[bis(pyrazol-1-yl)methyl]phenoxymethyl-N′-benzylimidazol-2-ylidene (L″) also acts as a bridging [C,N] bidentate ligand in L″2Ag2Cl2 and a bridging [C,N,N] tridentate ligand in L″2Ag2X2 (X = BF4 or PF6), like L′ and L in L′2Pd2Br2 as well as [L2Ag2]n[PF6]2n and [L′2Ag2][PF6]2, respectively, an obvious difference among them is present. L″ prefers to coordinate to two silver atoms in a head (carbene)–to tail (nitrogen) coordination mode, while L and L′ show head (carbene)–to head (carbene) and tail (nitrogen)–to tail (nitrogen) coordination modes to two silver atoms. Additionally, these silver complexes exhibit good catalytic activity in the three-component coupling reaction of alkyne, aldehyde and amine forming propargylamines.

Steric effects in pyrazole palladium(II) compounds: Synthetic, structural, and theoretical studies of a highly distorted octahedral palladium(II) pyrazole compound

Carbamoyl pyrazole compounds of palladium(II) chloride of the type [PdCl2L2] (where L=C3H3N2CONR2 or C5H7N2CONR2; R=CH3, C2H5 or iC3H7) have been synthesized and characterized by IR, 1H NMR, ES-MS, elemental analysis and single crystal X-ray diffraction methods. The centrosymmetric structure of [PdCl2(C3H3N2CON{C2H5}2)2] (2) shows that the palladium(II) ion is surrounded by two pyrazolyl nitrogen and two chlorine atoms in a square planar arrangement and the two nitrogen atoms of the carbamoyl group are weakly bonded to the metal centre in axial positions. In the centrosymmetric structure of [PdCl2(C5H7N2CON{C2H5}2)2] (5), the palladium(II) ion is surrounded by two pyrazole nitrogen and two chlorine atoms form a square planar arrangement and the two oxygen atoms of the carbamoyl group are weakly bonded to the metal centre in axial positions. The ligands are bonded through the soft pyrazole nitrogen to palladium(II) chloride in mutually trans positions. The carbamoyl pyrazole groups displayed an anti conformation. Theoretical studies on compound 5 show that the axial interactions involve donation from the filled pz orbital of the oxygen atom to the dxz orbital of the palladium(II) ion.

Ethylene and Styrene Carbon Monoxide Copolymerization Catalyzed by Pyrazolyl Palladium(II) Complexes

The pyrazolyl pyridylimine ligands [2-(3,5-dimethylpyrazol-1-yl)ethyl]pyridin-2-ylmethyleneimine (L1) and [2-(3,5-di-tert-butylpyrazol-1-yl)ethyl]pyridin-2-ylmethyleneimine (L2) and pyrazolyl thienylimine ligands [2-(3,5-dimethylpyrazol-1-yl)ethyl]thiophen-2-ylmethyleneimine (L3), [2-(3,5-di-tert-butyl-pyrazol-1-yl)ethyl]thiophen-2-ylmethyleneimine (L4), [2-(3,5-dimethylpyrazol-1-yl)ethyl]-2-bromothiophen-2-ylmethyleneimine (L5), and [2-(3,5-di-tert-butyl-pyrazol-1-yl)ethyl]-2-bromothiophen-2-ylmethyleneimine (L6) were synthesized by condensation of the appropriate pyrazolylamine and the corresponding aldehyde. Reactions of L1–L6 with [PdCl(Me)(cod)] gave the corresponding palladium(II) complexes [PdCl(Me)(L)] (where L = L1 (1a), L2 (2a), L3 (3a), L4 (4a), L5 (5a), L6 (6a)) in very good yields. The pyridylimine ligands L1 and L2 were found to coordinate via the imine and pyridine nitrogen atoms, while the thienylimine ligands L3–L6 coordinate via imine and pyrazolyl nitrogen atoms to the palladium. The ca...

Metal cation- and anion-induced assembly: structures and luminescent properties

Three complexes HgLBr2 (1), [HgLI2]·CH3CN (2) and HgL(SCN)2 (3) were synthesized by self-assembly of a multidentate ligand containing pyridyl and pyrazolyl groups, namely, 6-phenyl-4-(4-(1H-pyrazolyl)phenyl)-2,2′-bipyridine (abbreviated as L), with corresponding mercury(II) salts. While the ligand reacted with Cd(NCS)2 and Co(NCS)2, complexes [CdL2(NCS)2]·H2O (4) and [CoL2(NCS)2]·CH3OH (5) were obtained. The structures of these complexes were determined by X-ray crystallography. In 1 and 3, the hydrogen bonding or C–H⋯π interactions based on the anions and the pyrazolyl nitrogen atom contribute to the 2-D and 3-D structures, respectively. Compared with 1 and 3, no hydrogen bonding interaction based on the I− anion can be found in 2. As a result, only the C–H⋯N hydrogen bonding interactions based on the pyrazolyl nitrogen atom link the molecules to form a 1-D structure. In complexes 3–5, the difference in their structures is attributed to the different metal center ions with diverse coordination modes. The results reveal that the anions and metal ions have great impact on the final structures of the supramolecular architectures. The relationships between the structures and luminescent properties were investigated in detail.

Synthesis and catalytic activity of N-heterocyclic carbene silver complexes derived from 1-[2-(pyrazol-1-yl)phenyl]imidazole

Six mono- and dinuclear N-heterocyclic carbene (NHC) silver complexes based on 1-[2-(pyrazol-1-yl)phenyl]imidazole have been synthesized and characterized by elemental analysis and NMR spectroscopy, and their structures have been confirmed by single crystal X-ray diffraction. The N-functionalized carbene ligands exhibit versatile coordination modes in these silver complexes. N-[2-(3,5-Dimethylpyrazol-1-yl)phenyl]-N-benzylimidazol-2-ylidene (L) acts as a monodentate ligand through the carbene carbon in mononuclear LAgCl. While in dinuclear L2Ag2(PF6)2 and L′2Ag2(PF6)2 (L′ = N-[2-(pyrazol-1-yl)phenyl]-N-benzylimidazol-2-ylidene), L and L′ act as bridging bidentate ligands through the pyrazolyl nitrogen and the carbene carbon atoms to two silver atoms. Though, these two silver atoms have different coordination environments. In the former, one silver atom coordinates with two carbene carbons, the other coordinates with two pyrazolyl nitrogen atoms. In the latter, each silver atom coordinates with one carbene carbon and one pyrazolyl nitrogen atom, respectively. A dinuclear macrocyclic structure is observed in m-xylyl bridging tetradentate bis-NHC complexes L2Ag2(BF4)2 and (L)CH2C6H4CH2(L)Ag2(BF4)2, in which the coordination mode of carbene ligands is similar with that in L2Ag2(PF6)2. Preliminary catalytic tests show that all these complexes exhibit highly effective catalytic activity in the three-component coupling reaction of alkyne, aldehyde and amine forming propargylamines.

Synthesis, structure, and magnetic properties of the halide-bridged dimeric complex [(bpmaL1)Fe(μ-Cl)Cl

Complexation of FeCl2·4H2O with N,N-Bis{(1-H pyrazole-1-yl)methyl}aniline [bpmaL1] gave air-stable dichloro-bridged binuclear iron(II) species (1a) having five-coordinated iron, which was characterised by X-ray crystallography and magnetic susceptibility. The geometry at each iron centre of 1a is a distorted trigonal bipyramid with two equivalent half-molecules providing overall Ci symmetry. One of the pyrazolyl nitrogen atoms (N1) and a chlorine atom (Cl2)# form one apex of the distorted trigonal bipyramid. The magnetic parameters indicated only a weak antiferromagnetic coupling, despite the presence of two chloro ions, and dominant zero-field-splitting parameters. The relatively long Fe⋯Fe distance of 3.8118(6)Å within the chloro-bridged dimer excludes direct interaction between the iron(II) ions. Thus, the antiferromagnetic coupling between the two iron(II) ions of 1a is attributed to superexchange through the chloride ions. Compared to the analogous cobalt complexes, the activity of α-olefin polymerization towards ethylene, norbornene, 1-octene and methyl methacrylate (MMA) was virtually zero, 1a is the first bis-pyrazole based dinuclear and five-coordinated iron(II) complex.

Synthesis, Characterization, and X-Ray Structures of 2-(3,5-Dimethylpyrazol-1-Yl)Phenyl-Based Organoselenium Compounds and Their Glutathione Peroxidase (Gpx) Like Activity

The synthesis of a series of 2-(3,5-dimethylpyrazol-1-yl)phenyl-based organoselenium compounds, (dmpzC6H4Se)2 (1), dmpzC6H4SeR (dmpz = 3,5-dimethylpyrazol-1-yl; R = (CH2)nY; Y = OH, NH2, and COOH), and dmpzC6H4SeX (X = Cl, Br, or I) is described. The compounds are characterized by IR, NMR (1H, 13C{1H}, 77Se{1H}), and mass spectral (MS) data. The molecular structures of (dmpzC6H4Se)2, dmpzC6H4SeCH2COOH, and dmpzC6H4SeCH2CH2OH have been established by X-ray crystallography. The two latter compounds are associated in the solid state through intermolecular hydrogen bonding between the OH proton and the pyrazolyl nitrogen atom of the adjacent molecule. Glutathione peroxidase (GPx) like catalytic activity of these compounds has been evaluated by using hydrogen peroxide (H2O2) as substrate and dithiothreitol (DTTred) as thiol cofactor in CD3OD, and the progress of the reaction was monitored by 1H NMR spectroscopy. All the compounds exhibited the GPx-like catalytic activity. Among these, the ones containing alkylamino groups showed the best activity. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Synthesis and reactivity of bis(3,5-dimethylpyrazol-1-yl)methanes functionalized by 2-halophenyl groups on the methine carbon

Three new bis(3,5-dimethylpyrazol-1-yl)methanes [(2-XC6H4)CH(3,5-Me2Pz)2, X = F, Cl and Br] functionalized by 2-halophenyl groups on the methine carbon atom have been synthesized. Upon heating (2-XC6H4)CH(3,5-Me2Pz)2 with Mo(CO)6 or W(CO)5THF in THF at reflux, complexes (2-XC6H4)CH(3,5-Me2Pz)2M(CO)4 (X = F or Cl, M = Mo or W) were obtained. While the similar reaction of (2-BrC6H4)CH(3,5-Me2Pz)2 led to the oxidative addition of the C–Br bond to the Mo or W center to give complexes (C6H4)CH(3,5-Me2Pz)2M(CO)3Br (M = Mo or W). In addition, 2-ImC6H4CH(3,5-Me2Pz)2 (Im = imidazol-1-yl) has been obtained by the reaction of (2-BrC6H4)CH(3,5-Me2Pz)2 with imidazole, which subsequently reacted with PhCH2Cl to form 1-{2-[bis(3,5-dimethylpyrazol-1-yl)methyl]phenyl}-3-benzylimidazium chloride. Treatment of this imidazole salt with Ag2O and succeedingly with W(CO)5THF or Ru3(CO)12 yielded N-heterocylic carbene complexes LW(CO)5 and LRu3(CO)8(μ-H)(μ-Cl) (L = 1-{2-[bis(3,5-dimethylpyrazol-1-yl)methyl]phenyl}-3-benzylimidazol-2-ylidene), respectively. In the former, L acts as a monodentate ligand by the carbene carbon to the tungsten atom, and two pyrazolyl nitrogen atoms do not take part in the coordination to the metal center. While in the latter, L serves as a bridging bidentate ligand by one pyrazolyl nitrogen and the carbene carbon atoms to a Ru–Ru bond, and a hydride along with a chloride ligand bridges this metal–metal bond.

Steric Effects on Uranyl Complexation: Synthetic, Structural, and Theoretical Studies of Carbamoyl Pyrazole Compounds of the Uranyl(VI) Ion

New bifunctional pyrazole based ligands of the type [C(3)HR(2)N(2)CONR'] (where R = H or CH(3); R' = CH(3), C(2)H(5), or (i)C(3)H(7)) were prepared and characterized. The coordination chemistry of these ligands with uranyl nitrate and uranyl bis(dibenzoyl methanate) was studied with infrared (IR), (1)H NMR, electrospray-mass spectrometry (ES-MS), elemental analysis, and single crystal X-ray diffraction methods. The structure of compound [UO(2)(NO(3))(2)(C(3)H(3)N(2)CON{C(2)H(5)}(2))] (2) shows that the uranium(VI) ion is surrounded by one nitrogen atom and seven oxygen atoms in a hexagonal bipyramidal geometry with the ligand acting as a bidentate chelating ligand and bonds through both the carbamoyl oxygen and pyrazolyl nitrogen atoms. In the structure of [UO(2)(NO(3))(2)(H(2)O)(2)(C(5)H(7)N(2)CON {C(2)H(5)}(2))(2)], (5) the pyrazole ligand acts as a second sphere ligand and hydrogen bonds to the water molecules through carbamoyl oxygen and pyrazolyl nitrogen atoms. The structure of [UO(2)(DBM)(2)C(3)H(3)N(2)CON{C(2)H(5)}(2)] (8) (where DBM = C(6)H(5)COCHCOC(6)H(5)) shows that the pyrazole ligand acts as a monodentate ligand and bonds through the carbamoyl oxygen to the uranyl group. The ES-MS spectra of 2 and 8 show that the ligand is similarly bonded to the metal ion in solution. Ab initio quantum chemical studies show that the steric effect plays the key role in complexation behavior.