Activation entropy as a dominant factor in the oxidative addition of some group IV hydrides to an iridium(I) complex

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Abstract
The kinetics of the reactions[Formula: see text]have been studied (M = Si, Ge, Sn). All three reactions proceed by predissociation of the iridium complex and concerted cis addition of Ph3MH to the square-planar intermediate. The relative rate of addition of Ph3MH increases in the order Si (1) < Ge (18) < Sn (70) and the difference in rate within experimental error is due entirely to change in ΔS0. It is concluded that, for this particular series of oxidative addition reactions, solvation effects related to a change in polarity on passage to the transition state are more important than bond energies, or acid–base properties, in determining relative reaction energetics. The relevance of entropy barriers to the problem of paraffin activation is discussed.

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