7-azaindol-1-yl(organo)silanes and their PdCl₂ complexes: Pd-capped tetrahedral silicon coordination spheres and paddlewheels with a Pd-Si axis

Supported by excess triethylamine, 7-azaindole (HL) and dichlorodimethylsilane (Me₂SiCl₂), methyltrichlorosilane (MeSiCl₃), and tetrachlorosilane (SiCl₄) react, respectively, with formation of the 7-azaindol-1-yl-substituted silanes Me ₂SiL₂, MeSiL₃, and SiL₄. In these compounds the silicon atom adopts [4+2], [4+3], and [4+4] coordination, respectively, with the pyridine N atoms of the 7-azaindol-1-yl groups capping the tetrahedral Si coordination sphere from distances of >3 Å. Two pyridine nitrogen atoms of these silanes replace the acetonitrile ligands of [PdCl₂(NCMe)₂], thus forming the complexes Me ₂Si(μ-L)₂PdCl₂, MeSiL(μ-L) ₂PdCl₂, and SiL₂(μ-L)₂PdCl ₂. In addition to capping of the silicon coordination sphere by the pyridine N atoms of the dangling 7-azaindol-1-yl groups (in MeSiL(μ-L) ₂PdCl₂ and SiL₂(μ-L)₂PdCl ₂), these three palladium complexes exhibit capping of one tetrahedral face of the Si coordination sphere by the palladium atom (with Si···Pd separations of 3.34, 3.43, and 3.31 Å, respectively). According to computational analyses, the paddlewheel complex ClSi(μ-L)₄PdCl should be energetically favored over its isomer SiL₂(μ-L)₂PdCl₂; however, isomerization into this paddlewheel compound requires higher temperatures (150 °C) or the addition of a Lewis acid (such as GaCl₃).