1/1 adducts from oxiranes or thiiranes and cadmium, zinc, or magnesium α,β,γ,δ-mesotetra-phenylporphyrins were obtained in benzene and complexation constants determined. Results agree with the theory of 'hard and soft' acids and bases.Demetallation of the metaloporphyrins of Cd, Zn, and Mg is achieved with thiols. The cadmium porphyrin reacts with sulfur heterocycles which contain a β hydrogen to yield the free porphyrin and a thiolate of cadmium. If this heterocycle is methylthiirane, the organocadmium compound formed may initiale the subséquent in situ stereospecific polymerization of methylthiirane.