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 ( i Pr 2 pzH) in toluene afforded the dinuclear magnesium pyrazolate [{Mg( i Pr 2 pz) 2 ( i Pr 2 pzH)} 2 ] ( 1 ). [{Ca( i Pr 2 pz) 2 ( i Pr 2 pzH) 2 } 2 ] ( 2 ) and [{Eu( i Pr 2 pz) 2 ( i Pr 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 i Pr 2 pzH, and Hg(C 6 F 5 ) 2 in toluene. This reaction with Sr metal led to the isolation of a unique byproduct, [Hg 3 ( i Pr 2 pz) 4 (C 6 F 5 ) 2 ] ( 4 ). High‐temperature direct metallation of barium with i Pr 2 pzH afforded [{Ba( i Pr 2 pz) 2 (py) 3 } 2 ] ( 5 ) upon treatment of the hydrocarbon‐insoluble homoleptic [{Ba( i Pr 2 pz) 2 } n ] with pyridine (py). X‐ray crystal structure analyses revealed dinuclear structures for compounds 1 – 3 and 5 with μ‐η n :η m bridging pyrazolato ligands, including the new μ‐η 1 :η 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 Hg 3 unit. It has μ‐η 1 :η 1 bridging pyrazolato ligands and terminal pentafluorophenyl groups.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)