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

Treatment of a solid mixture of KBH4 with six equivalents of 3,5-diisopropylpyrazole (iPr2pzH) at 180 °C afforded KTpiPr2(iPr2PzH)3 in 53% yield. KBpiPr2 was synthesized in 56% yield by treatment of a 1:2 M ratio of KBH4 and iPr2PzH in refluxing dimethylacetamide. Treatment of MI2 (M = Ca, Sr, Ba) with two equivalents of KBp or KBpiPr2 in tetrahydrofuran afforded MBp2(THF)2 (M = Ca, 64%, M = Sr, 81%), BaBp2(THF)4 (32%), and M(BpiPr2)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 KBpiPr2. KTpiPr2(iPr2PzH)3 contains one κ3-N,N,N-TpiPr2 ligand and three κ1-iPr2pzH ligands, with overall distorted octahedral geometry about the K ion. The iPr2PzH nitrogen–hydrogen bonds are engaged in intramolecular hydrogen bonding to the 2-nitrogen atoms of the TpiPr2 ligand. The solid state structures of MBp2(THF)2, BaBp2(THF)4, and M(BpiPr2)2(THF)2 contain κ3-N,N,H Bp and BpiPr2 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. SrBp2(THF)2has the shortest metal–hydrogen interactions among the series. A combination of preparative sublimations, solid state decomposition temperatures, and thermogravimetric analysis demonstrated that MBp2(THF)2, BaBp2(THF)4, and M(BpiPr2)2(THF)2 undergo solid state decomposition at moderate temperatures.

The novel complexes KTpiPr2(iPr2PzH)3, MBp2(THF)2 (M = Ca, Sr), BaBp2(THF)4, and M(BpiPr2)2(THF)2 (M = Ca, Sr, Ba) have been prepared and structurally characterized, and their thermal stabilities were investigated.Figure optionsDownload as PowerPoint slideHighlights
► Preparation of MBp2(THF)n (n = 2 or 4) and M(BpiPr2)2(THF)2 (M = Ca, Sr, Ba).
► Unexpected formation of KTpiPr2(iPr2PzH)3.
► Synthesis of KBpiPr2 upon treatment of a 1:2 M ratio of KBH4 with iPr2PzH.
► The solid state structures of the new complexes were determined.
► MBp2(THF)n and M(BpiPr2)2(THF)2 decompose at moderate temperatures.