Synthesis, structural characterization, and properties of heavier alkaline earth complexes containing bis(pyrazolyl)borate or bis(3,5-diisopropylpyrazolyl) borate ligands

摘要

Treatment of a solid mixture of KBH_4 with six equivalents of 3,5-diisopropylpyrazole (iPr_2pzH) at 180 °C afforded KTp ~(iPr2)(iPr_2PzH)_3 in 53% yield. KBp~(iPr2) was synthesized in 56% yield by treatment of a 1:2 M ratio of KBH_4 and iPr_2PzH in refluxing dimethylacetamide. Treatment of MI_2 (M = Ca, Sr, Ba) with two equivalents of KBp or KBp~(iPr2) in tetrahydrofuran afforded MBp_2(THF)_2 (M = Ca, 64%, M = Sr, 81%), BaBp _2(THF)_4 (32%), and M(Bp~(iPr2)) _2(THF)_2 (M = Ca, 63%; M = Sr, 61%, M = Ba, 48%) as colorless crystalline solids upon workup. These complexes were characterized by spectral and analytical techniques and by X-ray crystal structure determinations of all complexes except KBp~(iPr2). KTp~(iPr2)(iPr_2PzH)_3 contains one κ~3- N,N,N-Tp~(iPr2)s ligand and three κ~1-iPr _2pzH ligands, with overall distorted octahedral geometry about the K ion. The iPr_2PzH nitrogen-hydrogen bonds are engaged in intramolecular hydrogen bonding to the 2-nitrogen atoms of the Tp iPr_2 ligand. The solid state structures of MBp _2(THF)_2, BaBp_2(THF)_4, and M(Bp ~(iPr2))_2(THF)_2 contain κ~3-N,N,H Bp and Bp~(iPr2) ligands, which form through metal-nitrogen bond formation to the 2-nitrogen atoms of the pyrazolyl fragments and metal-hydrogen bond formation to one boron-bound hydrogen atom per Bp ligand. SrBp_2(THF)_2has the shortest metal-hydrogen interactions among the series. A combination of preparative sublimations, solid state decomposition temperatures, and thermogravimetric analysis demonstrated that MBp_2(THF)_2, BaBp _2(THF)_4, and M(Bp~(iPr2)) _2(THF)_2 undergo solid state decomposition at moderate temperatures.