Crystallization by Slow Halogen Exchange in Hypercoordinate Silicon Chelates and the first X‐ray Structure of a <i>trans</i>‐Featured Hexacoordinate Difluorosilicon‐bis‐Chelate

Abstract

Abstract Starting from silicon tetrahalides SiCl 4 and SiBr 4 , respectively, and the bidentate 2‐iminomethylphenol‐type ligand HO‐C 6 H 3 ‐2‐[C(C 6 H 5 )=N(CH 2 ‐C 6 H 5 )]‐5‐OCH 3 , three novel complexes with hypercoordinate silicon atom were synthesized. Their coordination spheres consist of two halogen atoms (F, Cl, Br) and two six membered ring systems created by chelating bidentate ligands of 2‐iminomethylphenolate type. Demonstrated by crystal structure analysis, the dichloro‐ and difluorosilicon complexes {O‐C 6 H 3 ‐2‐[C(C 6 H 5 )=N(CH 2 ‐C 6 H 5 )]‐5‐OCH 3 }SiX 2 (X = Cl, F) reveal all‐trans ‐configuration in solid state. The difluorosilicon complex {O‐C 6 H 3 ‐2‐[C(C 6 H 5 )=N(CH 2 ‐C 6 H 5 )]‐5‐OCH 3 }SiF 2 is the first X‐ray crystallographically proven example of a trans ‐featured difluorosilicon‐bis‐chelate. Its all‐trans ‐configuration, however, is not retained after dissolution. The formation of an octahedral complex with cis ‐arranged fluorine atoms is 1 H NMR spectroscopically proven by the coupling pattern of diastereotopic benzyl methylene protons of the chelating ligands.