Pyrazoles pyrazolato complexes

The metal-pyrazolate saga has been known since the pioneering work of Buchner in the nineteenth century. In the last few years, a definitive characterization of several binary complexes has been possible due to the advent of the recent method of ab initio structure determination from X-ray powder diffraction data. In this respect, it is likely that a number of new molecules and/or crystalline phases, which have so far escaped a complete characterization, will be structurally analyzed, thus confirming the variability of the coordination modes and stoichiometries attributable to simple pyrazolato complexes. 

In an attempt to gain more insight into the reactions of copper(I) pyrazolato complexes with dioxygen, we decided to use different pyrazoles, whose donor capabilities were modified by introducing substituents in the 3,5-positions. 

The pyrazolato copper(I) complex, [Cu(pz)] (Hpz = lH-pyrazole), and related copper(I) complexes having different substituents on the pyrazole ring are well known.1,2 For these pyrazolato derivatives, various synthetic routes have been reported. However, the methods are, in general, complex and do... 

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. 

Oro and co-workers have shown that the one-pot reductive carbonylation of RuCls n-HjO with zinc, in the presence of a pyrazole derivative, yields dinuclear, pyrazolato-bridged, carbonyl complexes. To our knowledge, this was the first report on a facile, one-step synthesis of substituted carbonyl clusters, starting from ruthenium chloride. The one-pot synthetic route described here gives [PPN][HRu3(CO)n] in a yield of 83%, with respect to RUCI3 n-H20 as the starting material. 

Similar dinuclear bridged pyrazolato Os-Ir and Os-Rh complexes of formula [(p-cymene)OsCl()u-pz)2lr(CO)2] were also reported, together with a theoretical study on an isomerization process observed in solution where the chloride moves from one metal center to the other [14]. A different approach was used by Oro [15], in collaboration with Trofimenko, in the reaction of [ML(pz)2(Hpz)] (L = CsMes, M = Ir (1) L = mesitylene or p-cymene, M = Ru) with [M C1 HB(3-i-Pr-4-Br-pz)3 ] (M = Co, Ni) to yield heterodinuclear complexes of formula [LM(/z-pz)2()u-Cl)M HB(3-i-Pr-4-Br-pz)3 ] containing a tridentate scorpionate ligand capping one metal, besides bridging the pyrazolates between the two metal centers (Fig. 21.6). 

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