Reactivity of Substituted Benzenes toward Oxidative Addition Relates to NMR Chemical Shift of the Ipso-Carbon

The oxidative addition of benzene
derivatives to Pd0 catalysts is a key step in cross-coupling
reactions. In this work,
we show that the ipso-carbon chemical shift of substituted benzenes,
and in particular the δ22 component of the chemical
shift tensor, correlates with the free energy barrier for oxidative
addition. This correlation is traced back to the electron density
in the pz orbital of the ipso-carbon (perpendicular
of the ring-plane), with high electron densities favoring oxidative
addition. The correlation between chemical shift and free energy barrier
holds true for a variety of substituted benzenes, making chemical
shift a useful descriptor for predicting the reactivity of aromatic
substrates in oxidative addition.