Kinetic parameters for the reduction of copper(II) complexes in atom transfer radical addition (ATRA) in the presence of free-radical diazo initiator (AIBN) were determined using both experimental and kinetic modeling techniques. The rate constant of decomposition of AIBN (k(dc)) in various solvents was determined at 60 degrees C using UV vis spectroscopy. Rate constants of deactivation (k(d,AIBN)) of [Cu-II(TPMA)Cl][Cl] (TPMA=tris(2-pyridylmethyl)amine), [Cu-II(Me-6-TREN)Cl][Cl] (Me6TREN = tris[2-(N,N-dimethylamino)ethyliamine), [Cu-II(PMDETA)Cl-2] (PMDETA = N,N,N',N '',N ''-pentamethyldiethylenetriamine), and [Cu-II(bpy)(2)Cl][Cl] (bpy = 2,2'-bipyridine) complexes by radicals generated from the decomposition of AIBN were measured using the TEMPO-trapping method in a competitive clock reaction. Activation rate constants (k(a,AIBN)) were finally estimated from kinetic modeling utilizing the experimentally determined rate constants of decomposition of AIBN and deactivation. The effect of k(a,AIBN) k(d,AIBN) k(dc) and initial AIBN concentration on the overall copper(I) and copper(II) concentrations in the initiation step of the ATRA process was also evaluated through kinetic modeling.