Structural Trends in Alkaline Earth and Rare Earth Metal 3,5‐Diisopropylpyrazolates

Abstract

AbstractA series of 3,5‐diisopropylpyrazolates of magnesium, calcium, and strontium in addition to a divalent europium analog continues our investigation on the differences and similarities between the alkaline earth and divalent rare earth metal elements. The alkane elimination reaction between dibutylmagnesium and excess 3,5‐diisopropylpyrazole (iPr2pzH) in toluene afforded the dinuclear magnesium pyrazolate [{Mg(iPr2pz)2(iPr2pzH)}2] (1). [{Ca(iPr2pz)2(iPr2pzH)2}2] (2) and [{Eu(iPr2pz)2(iPr2pzH)2}2] (3) were obtained as the product of redox‐transmetallation/ligand‐exchange reactions between an excess of the corresponding metal, 2 equiv. of iPr2pzH, and Hg(C6F5)2 in toluene. This reaction with Sr metal led to the isolation of a unique byproduct, [Hg3(iPr2pz)4(C6F5)2] (4). High‐temperature direct metallation of barium with iPr2pzH afforded [{Ba(iPr2pz)2(py)3}2] (5) upon treatment of the hydrocarbon‐insoluble homoleptic [{Ba(iPr2pz)2}n] with pyridine (py). X‐ray crystal structure analyses revealed dinuclear structures for compounds 1–3 and 5 with μ‐ηn:ηm bridging pyrazolato ligands, including the new μ‐η1:η5 linkage, and further stabilization of 1–3 by intramolecular hydrogen bonding between the terminal pyrazole donor and terminal 1 or bridging pyrazolato ligands in 2 and 3. The trinuclear 4 displays the first example of a complex with an open, triangular Hg3 unit. It has μ‐η1:η1 bridging pyrazolato ligands and terminal pentafluorophenyl groups.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)