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At least 1,063 records · Page 59Linked to original sources
PubMed2005

First example of a 2:1 cocrystal of mixed Cu(I)/Cu(II) complexes and a novel ferromagnetic bis(mu-hydroxo)dicopper(II) complex with a bis(pyrazol-1-yl)methane bidentate ligand.

A unique 2:1 cocrystal of mixed Cu(I)/Cu(II) complexes [Cu(I)(H2CPz2)(MeCN)2](ClO4) (1) and [Cu(II)(H2CPz2)2(ClO4)2] (4), a novel ferromagnetic ClO(4-)-bridged bis(mu-hydroxo)dicopper(II) complex, [Cu2(H2CPz2)2(OH)2(ClO4)](ClO4)(CH3CN)(0.5) (5), and a bischelated copper(I) complex, [Cu(H2CPz2)2](ClO4) (2), prepared from a one-pot reaction of [Cu(MeCN)4](ClO4) and H2CPz2, are described. The structures of these complexes have been determined by X-ray crystallographic methods. The Cu(I)-N(acetonitrile) bond distances in complex 1 are nonequivalent (1.907(8) and 2.034(9) A), leading to the dissociation of one MeCN to form a Y-shaped complex, [Cu(I)(H2CPz2)(MeCN)](ClO4) (3), which is oxidized readily in air to form complex 5 with a butterfly Cu2O2 core.

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PubMed2006

Assembly of lipophilic tetranuclear (Cu4 and Zn4) molecular metallophosphonates from 2,4,6-triisopropylphenylphosponic acid and pyrazole ligands.

A sterically hindered aryl phosphonic acid ArP(O)(OH)2 (2) (Ar = 2,4,6-isopropylphenyl) was synthesized and structurally characterized. ArP(O)(OH)2 forms an interesting hydrogen-bonded corrugated sheet-type supramolecular structure in the solid-state. A three-component reaction involving ArP(O)(OH)2, 3,5-dimethylpyrazole(DMPZH), and Cu(CH3COO)2.H2O produces the tetranuclear Cu(II) compound [Cu4(mu3-OH)2{ArPO2(OH)}2(CH3CO2)2(DMPZH)4][CH3COO]2.CH2Cl2 (3). A similar three-component reaction involving ArP(O)(OH)2, 3,5-dimethylpyrazole, and Zn(CH3COO)2.2H2O yields the tetranuclear Zn(II) compound [Zn4{ArPO3}2{ArPO2(OH)}2{DMPZH}4(DMPZ)2].5MeOH (4). While 3 has been found to have an asymmetric cage structure where two dinuclear copper cores are bridged by bidentate [ArPO2(OH)]- ligands, 4 possesses an open-book tricyclic structure composed of three fused metallophosphonate rings. Magnetic studies on 3 revealed antiferromagnetic behavior.

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PubMed1997

Structural Diversity in the Reaction of Mono- and Disubstituted Pyrazoles with Titanium Tetrachloride. Importance of Hydrogen Bonding and Trends in cis/trans Geometry of Binary Adducts with Unidentate Ligands.

Treatment of titanium tetrachloride with 3,5-di-tert-butylpyrazole affords the complexes [3,5-(C(CH(3))(3))(2)C(3)H(3)N(2)](2)[TiCl(6)] and (3,5-(C(CH(3))(3))(2)C(3)HN(2))(2)TiCl(2) in 37 and 42% yields, respectively. An analogous reaction with 3,5-dimethylpyrazole, 3-methylpyrazole, 4-bromopyrazole, and 4-iodopyrazole leads to the formation of corresponding TiCl(4)L(2) binary adducts in 30-86% yields. Crystal structures of [3,5-(C(CH(3))(3))(2)C(3)H(3)N(2)](2)[TiCl(6)], (3,5-(C(CH(3))(3))(2)C(3)HN(2))(2)TiCl(2), TiCl(4)(3,5-(CH(3))(2)C(3)H(2)N(2))(2), and TiCl(4)(4-IC(3)H(3)N(2))(2) were determined. [3,5-(C(CH(3))(3))(2)C(3)H(3)N(2)](2)[TiCl(6)] crystallizes in the space group C2/c with a = 18.892(4) Å, b = 7.1200(10) Å, c = 24.461(6) Å, beta = 103.78(2) degrees, and Z = 4. (3,5-(C(CH(3))(3))(2)C(3)HN(2))(2)TiCl(2) crystallizes in the space group P2(1)/n with a = 12.283(10) Å, b = 17.891(8) Å, c = 12.580(6) Å, beta = 90.96(4) degrees, and Z = 4. TiCl(4)(3,5-(CH(3))(2)C(3)H(2)N(2))(2) crystallizes in the space group C2/c with a = 12.087(2) Å, b = 12.922(3) Å, c = 10.403(2) Å, beta = 92.08(2) degrees, and Z = 4. TiCl(4)(4-IC(3)H(3)N(2))(2) crystallizes in the space group C2/c with a = 9.252(2) Å, b = 8.660(2) Å, c = 19.652(4) Å, beta = 102.14(3) degrees, and Z = 4. An analysis of factors governing the cis/trans geometry of MCl(4)L(2) (M = Ti, Zr, Hf) complexes is offered.

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PubMed1999

Oxidative-Addition Reactions of Diiodine to Dinuclear Rhodium Pyrazolate Complexes.

The pyrazolato (Pz) rhodium(I) complexes [{Rh(&mgr;-Pz)(CO)(L)}(2)] (L = CNBu(t), P(OMe)(3), PMe(2)Ph, P(OPh)(3), P(p-tolyl)(3)) result from the reaction of [{Rh(&mgr;-Pz)(CO)(2)}(2)] with the appropriate L ligand in a trans:cis ratio ranging from 60:40 (L = CNBu(t)) to 95:5 (L = P(p-tolyl)(3)). The pure trans isomers add 1 molar equiv of diiodine to give the dirhodium(II) complexes [{Rh(&mgr;-Pz)(I)(CO)(L)}(2)] (L = CNBu(t) (6), P(OMe)(3) (7), PMe(2)Ph (8), P(OPh)(3) (9)). These complexes incorporate two iodide ligands trans to the rhodium-rhodium bond, as substantiated by the X-ray structure for 7, while the complex [(P{p-tolyl}(3))(CO)(I)Rh(&mgr;-Pz)(2)(&mgr;-CO)Rh(I)(P{p-tolyl}(3))] (10) contains a bridging ketonic CO ligand, due to the insertion of a terminal CO into the metal-metal bond. The metal-metal bond formation involves a 2e oxidation, since identical compounds (6-9) are obtained by oxidation with [Fe(Cp)(2)](PF(6)) followed by addition of potassium iodide. Further reactions of the dirhodium(II) complexes 6-9 with diiodine leading to the metal-metal rupture are electrophilic additions, as exemplified by the reactions with the positive iodine complex [I(Py)(2)](+). They start at the "endo site" (the metal-metal bond) if it is sterically accessible to the electrophile, to give directly the dirhodium(III) complexes [{Rh(&mgr;-Pz)(I)(CO)(L)}(2)(&mgr;-I)](+) (L = CNBu(t), CO). Otherwise, as for the complexes with P-donor ligands, abstraction of a iodide ligand trans to the metal-metal bond (the "exo site") occurs first, to give the dirhodium(II) cationic complexes [(PR(3))(CO)(I)Rh(&mgr;-Pz)(2)Rh(CO)(PR(3))](+) and triiodide. These react again with diiodine to give dirhodium(III) complexes [{Rh(&mgr;-Pz)(I)(CO)(PR(3))}(2)(&mgr;-I)](+) similar to those described above, but with triiodide or pentaiodide as counterion, as substantiated by the X-ray structure of [{Rh(&mgr;-Pz)(I)(CO)(PMe(2)Ph)}(2)(&mgr;-I)]I(5) (18). The diiridium(II) complexes [{Ir(&mgr;-Pz)(I)(CO)(PR(3))}(2)] (PR(3) = P(OPh)(3), PMe(2)Ph) also react with diiodine to give the cationic diiridium(III) complexes [{Ir(&mgr;-Pz)(I)(CO)(PR(3))}(2)(&mgr;-I)]I(3) through a reaction pathway involving the "exo site", while no reaction is observed for [{Ir(&mgr;-Pz)(I)(CO)(2)}(2)]. Finally, replacement of a carbonyl ligand in [{Rh(&mgr;-Pz)(I)(CO)(L)}(2)(&mgr;-I)](+) (L = CNBu(t), CO) by iodide gives the compounds [(CO)(L)(I)Rh(&mgr;-Pz)(2)(&mgr;-I)Rh(I)(2)(L)].

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PubMed2003

Synthesis, structure, bridge-terminal exchange kinetics, and molecular orbital calculations of pyrazolate-bridged digallium complexes containing bridging phenyl groups.

Gallium complexes containing bridging phenyl groups were prepared and characterized. Treatment of triphenylgallium with 3,5-dimethylpyrazole, 3,5-diphenylpyrazole, or 3,5-di-tert-butylpyrazole in a 2:1 stoichiometry afforded the phenyl-bridged complexes (C6H5)2Ga(mu-Me2pz)(mu-C6H5)Ga(C6H5)2 (62%), (C6H5)2Ga(mu-Ph2pz)(mu-C6H5)Ga(C6H5)2.C7H8 (62%), or (C6H5)2Ga(mu-tBu2pz)(mu-C6H5)Ga(C6H5)2 (40%), respectively, as colorless or off-white crystalline solids. These complexes were characterized by spectral and analytical methods, X-ray crystallography, bridge-terminal exchange kinetics, and molecular orbital calculations for simplified models. The molecular structure of (C6H5)2Ga(mu-Me2pz)(mu-C6H5)Ga(C6H5)2 consists of a dimethylpyrazolato ligand with a diphenylgallium group bonded to each nitrogen atom. A phenyl group acts as a bridge between the two gallium atoms. The kinetics of bridge-terminal phenyl exchange was determined by 13C NMR spectroscopy between -30 and +30 degrees C, and afforded the following range of activation parameters: DeltaH = 6.0-8.9 kcal/mol, DeltaS = -23.1 to -32.0 eu, and DeltaG(298) = 15.5-15.8 kcal/mol. The large, negative values of DeltaS imply ordered transition states relative to the ground state, and rotation along the N-GaPh3 vector without gallium-nitrogen bond cleavage. Molecular orbital calculations were conducted at the B3LYP/6-311G(d,p) level of theory on the simplified model H2Ga(mu-pz)(mu-C6H5)GaH2. The predicted out-of-plane phenyl group orientation arises from electronic interactions, in which hybridized orbitals on the phenyl group create delocalized molecular orbitals. However, the energy difference between a planar Ga2N2C ring and one with the bent carbon atom is only 1.77 kcal/mol, implying that the molecular orbitals provide little stabilization to the out-of-plane phenyl ligand. The combined results suggest that the close proximity of the gallium atoms is the principal determinant of the bridging phenyl interactions, and that complexes of the heavier group 13 elements with bridging hydrocarbon ligands are likely to be more accessible than the current state of the literature would suggest.

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PubMed2002

First nucleophilic aromatic substitution of annelated pyrazole.

3-Chloropyrazolo[3,4-c]quinoline 5, 3-chloropyrazolo[3,4-c]isoquinoline 6, 1,2-dihydro-1,2-dimethylpyrazolo[3,4-c]quinolin-3-one 8, and 1,2-dihydro-1,2-dimethylpyrazolo[3,4-c]isoquinolin-3-one 10 were obtained by acid-induced nucleophilic aromatic substitution (S(N)H) of H-3 in N-hydroxypyrazolo[3,4-c]quinoline 1b and in N-hydroxy pyrazolo[3,4-c]isoquinoline 3b. In the acid-induced chlorination, 3b was far more reactive than 1b, whereas the related N-hydroxypyrazolo[4,3-c]quinoline 2b and N-hydroxypyrazolo[4,3-c]isoquinoline 4b were completely unreactive toward S(N)H under identical conditions.

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PubMed1996

Regiocontrolled Syntheses of 3- or 5-Fluorinated Pyrazoles from 2,2-Difluorovinyl Ketones(1).

2,2-Difluorovinyl ketones 1 react with monosubstituted hydrazines to afford 5-fluoropyrazoles in a regioselective manner via replacement of the fluorine by the substituted nitrogen of the hydrazines and dehydration between the carbonyl group of 1 and the NH(2) end. The reactions are successfully effected for both aliphatic and aromatic hydrazines in aqueous ethanol under neutral conditions and in THF under basic conditions with butyllithium, respectively. A similar ring-forming reaction of 1 with hydrazine monohydrate is induced by the addition of trifluoroacetic acid to give N-unsubstituted 3-fluoropyrazoles, which in turn react with alkyl and aryl halides in the presence of sodium hydride, leading to a regiocontrolled synthesis of 3-fluoropyrazoles.

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