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A kinetic and mechanistic study of nucleophilic substitution at a pentacoordinated silicon atom

Bassindale, Alan R.; Parker, David J.; Taylor, Peter G. and Turtle, Robert (2009). A kinetic and mechanistic study of nucleophilic substitution at a pentacoordinated silicon atom. Zeitschrift für Anorganische und Allgemeine Chemie, 635(9-10) pp. 1288–1294.

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A model system for the exploration of nucleophilic substitution at a pentacoordinate silicon centre is reported. The degenerate nucleophilic exchange of free N-methylimidazole (NMI) with coordinated NMI in a chiral pentacoordinate silicon compound, 4, has been studied by dynamic NMR spectroscopy. In 4 the axial ligands are N-methylimidazole and an intramolecularly-coordinated and chelating oxygen atom of an amido group. The equatorial ligands are N-CH2, Ph and Me. Two competing mechanisms for the nucleophilic substitution at silicon have been distinguished from the data. One mechanism takes place with retention of configuration at silicon and is zeroth order in added nucleophile. This is interpreted as involving rate limiting dissociation of the N-methylimidazole followed by rapid re-association of another NMI molecule. The other mechanism takes place with both inversion and retention of configuration at silicon but is also of zeroth order in added nucleophile. A mechanism for this reaction in which the O-Si coordination is lost in the rate-determining step is consistent with the data. In this particular example there is no evidence for a mechanism in which pentacoordinate silicon is attacked to give a hexacoordinate intermediate or transition state.

Item Type: Journal Article
Copyright Holders: 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
ISSN: 1521-3749
Keywords: silicon; nucleophilic substitution; reaction mechanisms; hypercoordination
Academic Unit/Department: Other Departments > Vice-Chancellor's Office
Other Departments
Science > Life, Health and Chemical Sciences
Interdisciplinary Research Centre: Biomedical Research Network (BRN)
Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
Item ID: 25701
Depositing User: Peter Taylor
Date Deposited: 28 Dec 2010 16:24
Last Modified: 15 Jan 2016 15:35
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