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

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 )ϭN(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 )ϭN(CH 2 -C 6 H 5 )]-5-OCH 3 }SiX 2 (X ϭ Cl, F) reveal alltrans-configuration in solid state. The difluorosilicon complex

Hypercoordinate Silicon Complexes of (O,N,N′ vs. O,N,O′) Schiff Base Type N‐(2‐Carbamidophenyl)imines: Examples of Exclusively O‐Silylated Carbamides

“…This effect was also observed for other Si-Cl/Si-F pairs of N-donor-substituted hypercoordinated silicon complexes and is not limited to such compounds bearing trans-disposed N-Si-X bonds. [8] Surprisingly, the 29 Si NMR spectrum of the crude product solution of 4a exhibited a small signal at δ = -172.5 ppm, indicative of the presence of a hexacoordinate silicon compound. During our attempts to crystallize 4a from this solution, some crystals formed that, upon X-ray diffraction analysis, provided an answer as to which additional hypercoordinate silicon complex had formed in this reaction (Scheme 5, Figure 4).…”

“…The o-iminomethylphenolate O,N braces are situated in one plane with their N and O atoms trans to one another, an arrangement also found for other hexacoordinate silicon complexes of bidentate Schiff base ligands. [8,9] The position trans to the Si-bound phenyl group is occupied by a carb- amide carbonyl O atom, which renders this compound a further example of a hexacoordinate Si complex with a faccoordinated O,N,OЈ ligand. In sharp contrast to the previously presented hexacoordinate silicon complexes, this Si1-O3 bond is remarkably longer, which thus gives rise to its interpretation as a formal dative bond.…”

8-oxyquinolinate and 8-oxyquinaldinate in silicon complex chemistry — a new face of old ligands

“…The solvent was removed from the filtate under reduced pressure and the crude solid product was extracted with hexane (150 ml). From the hexane (3). A solution of sodium 8-oxyquinolinate [8] (1.15 g, 6.88 mmol) in THF (20 ml) was added to a cooled (-10°C) solution of compound 2 (2.45 g, 6.99 mmol) in THF (50 ml).…”

“…Yield: 1.60 g (2.78 mmol, 59 %). 1 H NMR (CDCl 3 ), δ, ppm (J, Hz): 2.32 (9H, s, CH 3 ); 6.95 (3H, d, 3 X-Ray structure analyses. X-Ray structure data were recorded on a Bruker-Nonius-X8-APEX2-CCD diffractometer with MoKα-radiation (λ = 0.71073 nm) and semi-empirical correction (SADABS).…”

“…Hypercoordinate silicon complexes with bidentate chelating ligands attract the interest of researchers for purposes such as studying stereochemical interconversions [1] and Si-E (e.g., E = Cl, Br, C) bond activation by hypercoordination [2,3] as well as measuring the "coordination power" of various ligands [4], or vice versa: the lack of coordination at Lewis-acidic Si atoms bearing electron withdrawing substituents [5]. Si complexes of 8-oxyquinolinate derived bidentate ligand systems were also used for studies on potential anti-cancer drugs [6,7].…”