Treatment of (meso-tetraphenylporphyrinato)tin(IV) sulfide, (TPP)Sn=S, with (meso-tetra-p-tolylporphyrinato )tin(II), (TTP)Sn11, in toluene results in the reversible exchange (K = 1.21 ± 0.03 at -10 °C) of a sulfur ligand to form (TPP)Sn11 and (TTP)Sn=S. The net result is a formal two-electron redox process between Snii and Sn1v. This occurs with a second-order rate constant at 30 °C of 0.40 ± 0.05 M-1 s-1 (AH* = 10.9 ± 0.9 kcaVmol, !l.S* = -24.1 ± 2.8 cal(mol·K)-1). Similarly, treatment of (meso-tetraphenylporphyrinato)tin(IV) selenide, (TPP)Sn=Se, with (meso-tetra-p-tolylporphyrinato)tin(II), (TTP)Snn, in toluene results in the reversible exchange (K = 1.45 ± 0.13 at -10 oq of a selenium ligand to form (TPP)Sn11 and (TTP)Sn=Se. This reaction occurs with a second-order rate constant at 30 oc of 87.3 ± 8.06 M-1 s-1 (Ali* 9.3 ± 0.5 kcaVmol, !l.S* = -18.8 ± 1.5 cal(mol·K)-1 ). Discussion of an inner sphere mechanism involving a ,u-sulfido or a ,u-selenido bridged intermediate is presented. The rate ratio of selenium to sulfur atom transfer is 218:1 at 30 °C. This rate behavior follows the "normal" trend as observed for the analogous halogen transfer reactions (1- > Br- > Cl- > F-).