Measuring the kinetic isotope effect at natural isotopic abundances for discriminating between the homogeneous and heterogeneous catalytic mechanisms in the Heck and Suzuki reactions

The kinetic isotope effect (KIE) at the natural abundances of bromine and carbon isotopes in the substrates of the Heck and Suzuki reactions have been investigated to determine the true nature of catalyst in these reactions. Data processing has demonstrated that statistically significant differences between KIE values for the Suzuki reaction of nonactivated bromobenzene are observed upon the replacement of the soluble catalyst precursor with the insoluble one. This finding unambiguously indicates that the reaction takes place on heterogeneous palladium species. Similar experiments on the Heck reaction have demonstrated that the KIE values are insensitive to the nature of the catalyst precursor, which is consistent with the true homogeneous mechanism of catalysis.