Pyrazolato ligands

Torralba, M.C., Ovejero, P., Mayoral, M.J., Cano, M Campo, J.A., Heras, J.V., Pinilla, E. and Torres, M.R. (2004) Silver and Gold Trinudear Complexes Based on 3-Substituted or 3,5-Disubstituted Pyrazolato Ligands. X-Ray Crystal Structure of cyclo-Tris p,-[3,5-bis(4-phenoxyphenyl)-lH-pyrazolato-KN ... 

Figure 6 Example of a structure with two bridging pyrazolato ligands, resulting in a dinuclear unit...

The reaction of magnesium bromide with potassium 3,5-di-tert-butylpyrazolate, K[Bu 2pz], in toluene affords Mg2(Bu 2pz)4 in THF the product is Mg2(Bu 2pz)4(THF)2." Both of these are dinuclear complexes with two bridging pyrazolato and two chelating ry -pyrazolato ligands. TMEDA binds to the unsolvated compound or displaces THF from the solvate to give Mg(Bu 2pz)2 (TMEDA), which is a mononuclear species with two ry -pyrazolates and chelating TMEDA. 

Reduction of the pyrazolate complex TiCl2(N2C3HBut2)2 by Na/Hg in THF or toluene gave TiCl(N2C3HBut2)2(THF)2 or (TiCl(N2C3HBut2)2)2 (82) respectively.937 Structural data reported for both products confirmed the bidentate binding of the pyrazolato ligands to Ti. 

Figure 18 The pyrazolato ligand acting as bidentate and as dinucleating in [Cr(/z-pyrazolato)2(t7 -pyrazolato)2] (a), and as a bridge in the chain compound [Co(/it-pyrazolat02]oo (b). ...

In contrast to this, in tantalum fiuoroximates, all the d orbitals of the central atom are equivalent, and the oximato group could be situated with equal probability in either the equatorial or the perpendicular plane. This produces a sharp decrease in the barrier for ligand rotation in tantalum fluorocomplexes. Correspondingly, the F NMR spectra show equivalent signals from equatorial fluorine atoms even at -30 °C [59]. Probably, the equivalence of d orbitals of the central atom also accounts for the low rotational barrier of pyrazolato ligands in the complex [Ta(ir -pz)2(Ti -pz)3 [84]. 

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