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

X-ray diffraction reveals that the molecular structures of the tris(pyrazolyl)hydroborato and tris(2-pyridylthio)methyl lithium compounds, [Tp(But,R)]Li (R = H, Me) and [kappa(4)-Tptm]Li, respectively exhibit three-coordinate trigonal pyramidal and four-coordinate trigonal monopyramidal coordination geometries, both of which are uncommon for lithium. Accordingly, [Tp(But)]Li and [Tp(But,Me)]Li bind additional ligands to form four-coordinate adducts, such as [Tp(But)]Li(NCMe), [Tp(But,Me)]Li(NCMe), [Tp(But)]Li(pz(But)H), [Tp(But,Me)]Li(pz(But)H)center dot(pz(But)H), [Tp(But,Me)]Li(OH2), [Tp(')(But)(Me)]Li(OH2)center dot(pzH) and [Tp(But)]Li(OH2)center dot(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 [Tp(But,R)]Li is facile such that the adducts exist in equilibrium with [Tp(')(But)(R)]Li and L, as demonstrated by NMR spectroscopic studies. (C) 2013 Elsevier Ltd. All rights reserved.