Molecular Structures of the Silicon Pyridine-2-(thi)olates Me₃Si(pyX), Me₂Si(pyX)₂ and Ph₂Si(pyX)₂ (py = 2-Pyridyl, X = O, S), and Their Intra- and Intermolecular Ligand Exchange in Solution

A series of pyridine-2-olates (pyO) and pyridine-2-thiolates (pyS) of silicon was studied in solid state and in solution. The crystal structures of Me₃Si(pyO) (<b>1a</b>), Me₃Si(pyS) (<b>1b</b>), Me₂Si(pyO)₂ (<b>2a</b>), Me₂Si(pyS)₂ (<b>2b</b>), Ph₂Si(pyO)₂ (<b>3a</b>) and Ph₂Si(pyS)₂ (<b>3b</b>) were determined by X-ray diffraction. For that purpose, crystals of the (at room temperature) liquid compounds <b>1a</b> and <b>1b</b> were grown in a capillary on the diffractometer. Compounds <b>1a</b>, <b>1b</b>, <b>2a</b>, <b>2b</b> and <b>3a</b> feature tetracoordinate silicon atoms in the solid state, whereas <b>3b</b> gave rise to a series of four crystal structures in which the Si atoms of this compound are hexacoordinate. Two isomers (<b>3b¹</b> with all-<i>cis</i> arrangement of the C₂N₂S₂ donor atoms in <i>P</i><inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mover accent="true"><mn>1</mn><mo>¯</mo></mover></semantics></math></inline-formula>, and <b>3b²</b> with <i>trans</i> S-Si-S axis in <i>P</i>2₁/<i>n</i>) formed individual crystal batches, which allowed for their individual ²⁹Si NMR spectroscopic study in the solid state (the determination of their chemical shift anisotropy tensors). Furthermore, the structures of a less stable modification of <b>3b²</b> (in <i>C</i>2/<i>c</i>) as well as a toluene solvate <b>3b²</b> (toluene) (in <i>P</i><inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mover accent="true"><mn>1</mn><mo>¯</mo></mover></semantics></math></inline-formula>) were determined. In CDCl₃, the equimolar solutions of the corresponding pairs of pyO and pyS compounds (<b>2a</b>/<b>2b</b> and <b>3a</b>/<b>3b</b>) showed substituent scrambling with the formation of the products Me₂Si(pyO)(pyS) (<b>2c</b>) and Ph₂Si(pyO)(pyS) (<b>3c</b>), respectively, as minor components in the respective substituent exchange equilibrium.