Structural characterization of tris(pyrazolyl)hydroborato and tris(2-pyridylthio)methyl lithium compounds: Lithium in uncommon trigonal pyramidal and trigonal monopyramidal coordination environments

Abstract

X-ray diffraction reveals that the molecular structures of the tris(pyrazolyl)hydroborato and tris(2-pyridylthio)methyl lithium compounds, [TpBut,R]Li (R=H, Me) and [κ4-Tptm]Li, respectively exhibit three-coordinate trigonal pyramidal and four-coordinate trigonal monopyramidal coordination geometries, both of which are uncommon for lithium. Accordingly, [TpBut]Li and [TpBut,Me]Li bind additional ligands to form four-coordinate adducts, such as [TpBut]Li(NCMe), [TpBut,Me]Li(NCMe), [TpBut]Li(pzButH), [TpBut,Me]Li(pzButH)·(pzButH), [TpBut,Me]Li(OH2), [TpBut,Me]Li(OH2)·(pzH) and [TpBut]Li(OH2)·(THF), each of which has been structurally characterized by X-ray diffraction in the solid state. In solution, however, dissociation of the ligand (L) from the adducts [TpBut,R]LiL is facile such that the adducts exist in equilibrium with [TpBut,R]Li and L, as demonstrated by NMR spectroscopic studies.