Pyrazole bridges

The acetone complex [IrH2(Me2CO)(Hpz)(PPh3)2]BF4 reacts with potassium hydroxide to give 128 [94JOM(466)249 94JOM(467) 151]. The pyrazolate bridge... 

In spite of the significant differences in the catalysts and conditions applied, essentially the same kinetic model was proposed for the catalytic reactions with two pyrazolate-bridged dicopper(II) complexes, [Cu2(LEP)2]2+ and [Cu2(BLEP)(OH)]2+ in 1 1 methanol-water mixture (47). The product was confirmed to be 3,5-di-ter -butyl-l,2-benzoquinone (DTBQ). 

Acyloin 213 with thioamides, thiosemicarbazides, and methyl dithio-carbazate in trifluoroacetic acid give photochromic thiazole-, thiadiazine-, and pyrazole-bridged dihetarylethenes 254,255, and 256-258, respectively (Scheme 72) (OlIZVllS, 06ZOR882). 

When a pyrazole ring is used as a scaffold to two pendant carbene donor groups, dime-tallic complexes can be formed [75] (see Figure 3.22). Similar complexes were also synthesised for nickel, rhodium and iridium [76,77]. Appreciable metal-metal interactions could not be observed in any of these complexes, with the exception of argentophilic [77,78] or aurophilic [79] interactions. As with other functionalised carbenes, these pyrazole bridged ones have precedences, in this case amine [80,81], phosphino [82] and Cp [83] functionalised pyrazole ligands. 

It may obviously be tempting to modify the pyrazole bridge to apyridazine one [84], going from a five-membered to a six-membered heteroaromalic systan and lowering the electron donicity of the bridge unit in the process [69,70]. When Scheele et al. did just that [85,86] they found that the pyridazine ligand does not coordinate, at least not to mercury(II) [85]. 

Multimetallic cymantrenes such as (36) and (37) have recently been reported. An especially interesting multimetallic system is (38), in which two cymantrene units are linked by a pyrazolate bridge. Electrochemical measurements show that the two metal centers in (38) interact... 

Complexes 19-22 were reported to most likely have structures involving extended chains of copper ions linked by double pyrazolate bridges in analogy with the structures of species [Cu(4-Xpz)2] , where X = H, Me, and Cl (35, 36). However, it is possible that the presence of methyl substituents in the 3,5-positions of the heterocyclic ring, causing steric hindrance, prevents the formation of an infinite polymeric chain. 

Neutral pyrazolate-bridged dinuclear palladium(H) complexes of the general formula [Pd2X2(M-pz )2(PR,)] (Hpz = Hpz or Hdmpz X = Cl, Br, I PR3 = PBu3, PMe2Ph, or PMePh ) were prepared (67). These complexes were char-... 

Dinuclear pyrazolate bridged iridium(I) complexes were prepared by employing a synthetic route analogue to that used for the rhodium(I) derivatives,... 

Pyrazolate-Bridged Dinuclear Copper(II) Complexes Containing Binucleating Ligands... 

Fig. 27 Cationic portions of pyrazolate-bridged binuclear zinc hydroxide complexes.

Synthesis and characterization of unusual heterotrinuclear Co(III)Ni(II)Co(III) hy dr otr is (3,5-dimethylpyr azoly 1) borate complex with mixed 1,1 -azide and pyrazolate bridge... 

Flash vacuum pyrolysis reactions of 1 W-pyrazole, 3,5-dimethylpyrazole, and 3,5-diphenylpyrazole were carried out over ZCOY-7, NH4-Y, and Na-Y zeolites <01JOC2943>. A complete model for the prediction of H and C-NMR chemical shifts and torsional angles in phenyl-substituted pyrazoles has been published <01T4179>. Diphenylpyrazole was treated with triethylaluminum to afford a pyrazolate-bridged dialuminum complex <01CC353>. Spectroscopic studies have revealed 3-(2-pyridyl)-2-pyrazoline derivatives to be novel fluorescent probes forZn(II) ions <01TL9199>. 

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