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

Abstract

Treatment of a solid mixture of KBH 4 with six equivalents of 3,5-diisopropylpyrazole ( iPr 2pzH) at 180 °C afforded KTp i Pr2( iPr 2PzH) 3 in 53% yield. KBp i Pr2 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 i Pr2 in tetrahydrofuran afforded MBp 2(THF) 2 (M = Ca, 64%, M = Sr, 81%), BaBp 2(THF) 4 (32%), and M(Bp i Pr2) 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 i Pr2. KTp i Pr2( iPr 2PzH) 3 contains one κ 3-N,N,N-Tp i Pr2 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 i Pr2 ligand. The solid state structures of MBp 2(THF) 2, BaBp 2(THF) 4, and M(Bp i Pr2) 2(THF) 2 contain κ 3-N,N,H Bp and Bp i Pr2 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 i Pr2) 2(THF) 2 undergo solid state decomposition at moderate temperatures.