Cu(I) complexes containing trispyrazolylborate ligands efficiently catalyze the atom transfer radical addition (ATRA) of polyhalogenated alkanes to various olefins under mild conditions. The catalytic activity is enhanced when bulky and electron donating Tp(x) ligands are employed. Kinetic data have allowed the proposal of a mechanistic interpretation that includes a Cu(II) pentacoordinated species that regulates the catalytic cycle.