The g-values of ESR spectra of superoxide (O-2(.-)) complexes with various organotin compounds acting as Lewis acids were determined in acetonitrile at 143 K. The binding energies (DeltaE) in the complexes between organotins and O-2(.-) have been evaluated from deviation of the g(zz)-values from the free spin value. The DeltaE values are well correlated with the catalytic reactivity of organotins as well as a series of metal ions acting as Lewis acids to promote electron transfer from cobalt(II) tetraphenylporphyrin to O-2, which would not occur in the absence of Lewis acids under otherwise the same experimental conditions.