Synthesis and molecular and crystal structures of mono-and bis-chelate hypercoordinate silicon compounds containing the C,O-chelating 2,2-dimethyl-4-oxo-2,3-dihydro-1,3-oxazin-3-ylmethyl ligand

New mono-and bis-chelate hypercoordinate silicon complexes containing the monoanionic C,O-chelating 2,2-dimethyl-2,3-dihydrobenzo-1,3-oxazin-3-ylmethyl (BonCH2) ligand were synthesized starting from 2,2-dimethyl-2,3-dihydrobenzo-1,3-oxazin-4-one (1) through its TMS derivative 2. The reactions of compound 2 with the chlorosilylmethylating agents ClCH2SiMe2Cl, ClCH2SiMeCl2, and (ClCH2)2SiCl2 followed by the transformations of the initially formed chlorosilanes BonCH2SiMe2Cl (3), BonCH2SiMeCl2 (6), and [(BonCH2)2Si(Cl)]+Cl− (8), respectively, into the target products afforded neutral monochelates, viz., monofluoride BonCH2SiMe2F (5) and difluoride BonCH2SiMeF2 (7), and the bis-chelate disiloxane cation-anion complexes {[(BonCH2)2Si]2O}2+·Cl−·ClHCl− (9) and {[(BonCH2)2Si]2O}2+·2TfO− (10). The reaction of ditriflate 10 with boron trifluoride etherate produced fluoride triflate (BonCH2)2Si(F)OTf (11). The X-ray diffraction study of compounds 5, 7, 9, 10, and 11, as well as of NH-heterocycle 1 and disiloxane (BonCH2SiMe2)2O (4) studied earlier, demonstrated that the Si atoms in complexes 5, 7, 9, and 10 are pentacoordinate through the formation of an intramolecular O→Si bond. The coordination of silicon in fluoride triflate 11 can be described as 5+1. In disiloxane 4, one of two Si atoms is pentacoordinate. Dinuclear cation-anion complexes 9 and 10 contain the diastereomeric bis-silylium ions {[(BonCH2)2Si]2O}2+, which differ in the configuration of the chiral bis-chelate fragments (BonCH2)2Si. In complex 9, these fragments have opposite configurations (ΛΔ); in ditriflate 10, the same configurations (ΛΛ).