Pentacoordinate silicon complexes with dynamic motion resembling a pendulum on the S(N)2 reaction pathway

• Published in: Dalton transactions : an international journal of inorganic chemistry 2013-08, Vol.42 (30), p.10971-10981
• Main Authors: Sohail, M, Panisch, R, Bowden, A, Bassindale, A R, Taylor, P G, Korlyukov, A A, Arkhipov, D E, Male, L, Callear, S, Coles, S J, Hursthouse, M B, Harrington, R W, Clegg, W
• Format: Article
• Language: English
• ISSN: 1477-9234
• DOI: 10.1039/c3dt50613d

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.