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Issue 9, 1997
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Stannanes as free-radical reducing agents: an ab initio studyof hydrogen atom transfer from some trialkyltin hydrides to alkylradicals

Abstract

Ab initio molecular orbital calculations using a (valence) double-ξ pseudopotential (DZP) basis set, with (MP2, QCISD) and without (SCF) the inclusion of electron correlation, predict that hydrogen atoms, methyl, ethyl, isopropyl and tert-butyl radicals abstract hydrogen atoms from stannane and trimethyltin hydride via transition states in which the attacking and leaving radicals adopt a colinear arrangement. Transition states in which (overall) Sn–C separations of 3.50 Å have been calculated; these distances appear to be independent of the nature of the attacking radical and alkyl substitution at tin. At the highest level of theory (QCISD/DZP//MP2/DZP), energy barriers (ωE1) of 18–34 kJ mol-1 are predicted for the forward reactions, while the reverse reactions (ωE2) are calculated to require 140–170 kJ mol-1. These values are marginally affected by the inclusion of zero-point vibrational energy correction. Importantly, QCISD and MP2 calculations predict correctly the relative order of radical reactivity toward reduction by stannanes: tert-butyl > isopropyl > ethyl. By comparison, SCF/DZP, AM1 and AM1(CI = 2) calculations perform somewhat more poorly in their prediction of relative radical reactivity.

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Article type: Paper
DOI: 10.1039/A701822C
Citation: J. Chem. Soc., Perkin Trans. 2, 1997,0, 1665-1670
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    Stannanes as free-radical reducing agents: an ab initio study of hydrogen atom transfer from some trialkyltin hydrides to alkyl radicals

    D. Dakternieks, D. J. Henry and C. H. Schiesser, J. Chem. Soc., Perkin Trans. 2, 1997, 0, 1665
    DOI: 10.1039/A701822C

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