7‑Azaindol-1-yl(organo)silanes and Their PdCl2 Complexes: Pd-Capped Tetrahedral Silicon Coordination Spheres and Paddlewheels with a Pd–Si Axis

• Published in: Organometallics 2014-05, Vol.33 (10), p.2479-2488
• Main Authors: Wahlicht, Sven, Brendler, Erica, Heine, Thomas, Zhechkov, Lyuben, Wagler, Jörg
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om401220m

Supported by excess triethylamine, 7-azaindole (H L ) and dichlorodimethylsilane (Me2SiCl2), methyltrichlorosilane (MeSiCl3), and tetrachlorosilane (SiCl4) react, respectively, with formation of the 7-azaindol-1-yl-substituted silanes Me 2 Si L 2 , MeSi L 3 , and Si L 4 . 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 2 Si( μ-L ) 2 PdCl 2 , MeSi L ( μ-L ) 2 PdCl 2 , and Si L 2 ( μ-L ) 2 PdCl 2 . In addition to capping of the silicon coordination sphere by the pyridine N atoms of the dangling 7-azaindol-1-yl groups (in MeSi L ( μ-L ) 2 PdCl 2 and Si L 2 ( μ-L ) 2 PdCl 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 ) 4 PdCl should be energetically favored over its isomer Si L 2 ( μ-L ) 2 PdCl 2 ; however, isomerization into this paddlewheel compound requires higher temperatures (150 °C) or the addition of a Lewis acid (such as GaCl3).