KINETICS OF ELECTROPHILIC SUBSTITUTION REACTIONS INVOLVING METAL IONS IN METALLOPORPHYRINS

The kinetics of electrophilic substitution reactions involving the replacement of one metal ion for another coordinated in tetraphenylporphin (TPP) complexes have been investigated in pyridine solutions. The reactions studied were Zn(II)-CdTPP, Zn(II)-PbTPP, Zn(II)-HgTPP, and Cu(II)-ZnTPP. These reactions were all first order in metalloporphyrin. The Hg(II) and Cd(II)TPP reactions were first order in Zn(II), while the PbTPP system was second order in Zn(II). With ZnTPP, the kinetics were first order in Cu(II) and inhibited by Zn(II). Hg(II) was found to catalyze the Zn(II)-PbTPP reaction. The replacement reactions can be faster or slower than the corresponding insertion of the metal ion into the free-base porphin, and no evidence for a free-base intermediate was observed. © 1969, American Chemical Society. All rights reserved.