The mercuration o f 5,10,15,20-tetrakis(4-methylphenyl)porphyrin com plexes M(TTP)** (2a—c; M = Ni, Pd, Pt) is described. Treatment of Ni(TTP) (2a) with mercuric acetate in refluxing benzene and subsequently with aqueous sodium chloride yields a mixture of species M(TTP-Hg„Cl„) (1 < n < 3) from which the monomercurial, Ni(TTP-HgCl) (3a) is isolated in 35% yield after silica chromatography. A more rapid reaction occurs with mercuric trifluoroacetate in chlorobenzene. With this system, Pd(TTP-HgCl) (3b) and Pt(TTP-HgCl) (3c) along with their bis-, tris-, and tetrakis-mercurated analogs are obtained. The reaction times indicate that replacem ent of N i” by Pdn and Pt11 progressively diminishes the rate of electrophilic attack at the porphyrin periphery, consistent with a decrease of the total density of negative charge on the porphyrin ligand in these complexes.