Pyrazole ligands

Trofimenko Coordination chemistry of pyrazole ligands 72CRV497... 

BrMn(CO)5] reacts with pyrazolate ion to yield the charged complex 38 (69JA5410). Here the metals are bridged by three pyrazolate ligands (71IC1372). 

ICA 97)19]. Compound 163 (R = Br) and perchloric acid yield 164, where the monodentate pyrazolate ligand is protonated. Potassium hydroxide regenerates 163 (R = Br). Dicationic complexes of the type 164 can alternatively be produced from [Rh2(r/ -Cp )2(/x-0H)3]Cl04 and perchloric acid in the presence of excess pyrazole, 4-bromopyrazole, 3-methylpyrazole, or 3,5-dimethylpyrazole. 

Interaction of // anj-[RhCl(CO)(/i,-dppm)]2 with pyrazolate ligands readily yields the so-called A-ftame complexes 175 (R = = H, X = Cl ... 

However, addition of bromine is accompanied by bromination of 3,5-dimethyl-pyrazolate and pyrazolate ligands at position 4, which is blocked in 4-methyl-pyrazolate. The product of electrochemical oxidation of 175 (R -- R = Me, R = Br) is 177 (R = R = Me, R = Br, X = CIO4). Chlorination proceeds similarly to bromination. 

Barranco, E.M., Gimeno, M.C., Laguna, A. and Villacampa, M.D. (2005) Gold and silver complexes with the ferrocenyl-pyrazolate ligand FcCH2pz. Inorganica Chimica Acta, 358 (14), 4177 182. 

Figure 7 Structure of an 18F-labeled pyrazole ligand for brain uptake (see Table...

Table 1 Brain Uptake Data for the 18F-labeled Pyrazole Ligand of Figure 7... 

Pyrazolate as a ligand can exhibit various coordination modes, inter alia, monodentate, exo-bidentate, and endo-bidentate. Several review articles have been published in the field.556-559 The use of pyrazole in the modeling of biological systems was also reviewed.560,561 The most common application of pyrazole ligands is to use its exo-bidentate coordination mode linking two metal centers that may be identical or different (compare Section 6.3.4.12.6). Polypyrazolylborates and related ligands are covered in the subsequent section. 

Unsymmetrical compartmental pyrazole ligands with different chelating side arms in the 3- and 5-positions have been developed for the controlled synthesis of unsymmetric dinickel(II)... 

Compartmental pyrazole ligands (14) can be used to form bimetallic complexes (15).157 This ligand enforces a separation distance between the metal ions. Stability constants were calculated showing a stability for both mononuclear and dinuclear compounds that was less than Cu11 but greater than Nin. 

Chelating pyrazole ligands are also known. The pseudo-octahedrally coordinated zinc complex ZnL2(pyridine)2 was formed where L = 5-(4-methoxyphenyl)pyrazole-3-carboxylate.850... 

During the time of the Olin reports, the first examples of oligomeric boron-bridged (l-pyrazolyl)borate systems appeared from the laboratory of Trofimenko at DuPont Chemicals 24 He reported the synthesis of poly(l-pyrazolyl)borates (6) (Fig. 5) from the reactions of alkali metal borohydrides with the pyrazole ligand. The (l-pyrazolyl)borate ligand was obtained from two pyrazole units when bridged by a BR2 unit on one side and by a metal or onium ion on the other. Even though reports... 

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