A trimethyl-, triethyl-, or triisopropylsilyl group attached to the meta position of toluene retards the rate of permutational hydrogen/metal interconversion with butyllithium in the presence of potassium tert-butoxide by factors of 1.7, 3, and 7, respectively. Although remote from the reaction center, the substituents sterically impede the coordination of potassium to the arene electron sextet. pi-Arene/metal bonding may play a major role in modulating chemical and, by extension, biochemical reactivity.
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Masson et al. (2005) studied this question.
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