title: Pentacoordinate silicon complexes with dynamic motion resembling a pendulum on the S(N)2 reaction pathway.
abstract: A series of glutarimide derivatives which has two carbonyl coordination sites for intramolecular pentacoordination at silicon with a X(1+n)SiC(3-n)O moiety have been synthesised and characterized. The substituent (leaving group) effects on the Si-O bond exchange between the two coordination sites (resembling a pendulum) have been studied by comparison of the differently substituted (X = F, Cl, OTf, Br and I) structures. The activation parameters for the Si-O bond exchange process were measured by NMR and separately computed and are consistent with the strength of Si-O bond coordination and the nature of the leaving group, X. The temperature-dependent (29)Si NMR spectroscopy is supported by X-ray crystallography and shows that the tetrahedral reactant is converted into pentacoordinate intermediates by intramolecular O-Si association followed by reversion to a tetrahedral geometry by Si-X dissociation. The two association/dissociation patterns offer a model for nucleophilic substitution at a silicon atom. A continuum of structures on the S(N)2 reaction profile from the glutarimide derivatives correlates reasonably well with the structural data obtained from derivatives of lactams, diketopiperazines and quinolones.
authors.affiliation: Department of Chemistry and Analytical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK. muhammad.sohail@qatar.tamu.edu
authors.forename: M
authors.initials: M
authors.lastname: Sohail
authors.forename: R
authors.initials: R
authors.lastname: Panisch
authors.forename: A
authors.initials: A
authors.lastname: Bowden
authors.forename: A R
authors.initials: AR
authors.lastname: Bassindale
authors.forename: P G
authors.initials: PG
authors.lastname: Taylor
authors.forename: A A
authors.initials: AA
authors.lastname: Korlyukov
authors.forename: D E
authors.initials: DE
authors.lastname: Arkhipov
authors.forename: L
authors.initials: L
authors.lastname: Male
authors.forename: S
authors.initials: S
authors.lastname: Callear
authors.forename: S J
authors.initials: SJ
authors.lastname: Coles
authors.forename: M B
authors.initials: MB
authors.lastname: Hursthouse
authors.forename: R W
authors.initials: RW
authors.lastname: Harrington
authors.forename: W
authors.initials: W
authors.lastname: Clegg