2-N-(Quinoline-8-yl)iminomethylphenolate – A (ONN)-tridentate ligand system in silicon complex chemistry

Condensation of salicylic aldehyde with 8-aminoquinoline afforded (ONN)-tridentate ligand 2-N-(quinoline-8-yl)iminomethylphenol (1), which was obtained as a crystalline solid for the first time and characterized by X-ray diffraction. Reaction between 1 and phenyltrichlorosilane in the presence of triethylamine results in the formation of the 1:1 chelate complex dichloro-[2-N-(quinoline-8-yl)imino-methylphenolato]-phenylsilane (2a) bearing a hexacoordinate silicon atom. The crystal structure of 2a∗CHCl3 reveals a rare coordination pattern: Although carrying two chlorine atoms, the hexacoordinate Si atom coordinates the tridentate ligand’s imine N atom in the trans position to the phenyl group. Silylation of 1 with hexamethyldisilazane and synthesis of dichloro-[2-N-(quinoline-8-yl)iminomethylphenolato]-methylsilane (2b) yielded few crystals of [2-N-(quinoline-8-yl)iminomethylphenolato]-salicylaldiminato-methylsiliconium chloride (2b′) as byproduct. 2b′ is the first structurally characterized main group element complex of salicylaldimine. This bidentate ligand exhibits an unusually strong N → Si coordination.