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). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 446–458, March, 2007.