Structural trends in alkaline earth and rare earth metal 3,5-diisopropylpyrazolates

A 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 (iPr(2)PzH) in toluene afforded the dinuclear magnesium pyrazolate [{Mg(iPr(2)pz)(2)(iPr(2)PzH)}(2)] (1). [{Ca(iPr(2)pz)(2)(iPr(2)PzH)(2)}(2)] (2) and [{Eu(iPr(2)pz)(2)(iPr(2)PzH)(2)}(2)] (3) were obtained as the product of redox-transmetallation/ligand-exchange reactions between an excess of the corresponding metal, 2 equiv. of iPr(2)PzH, and Hg(C6F5)(2) in toluene. This reaction with Sr metal led to the isolation of a unique byproduct, [Hg-3(iPr(2)pz)(4)(C6F5)(2)] (4). High-temperature direct metallation of barium with iPr(2)PzH afforded [(Ba(iPr(2)pz)(2)(py)(3))(2)] (5) upon treatment of the hydrocarbon-insoluble homoleptic [{Ba(iPr(2)pz)(2)}(n)] with pyridine (py). X-ray crystal structure analyses revealed dinuclear structures for compounds 1-3 and 5 with mu-eta(n):eta(m) bridging pyrazolato ligands, including the new mu-eta(1):eta(5) 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 H93 unit. It has mu-eta(1):eta(1) bridging pyrazolato ligands and terminal pentafluorophenyl groups. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)