Kinetic control of the transmetalation of labile metalloporphyrins in individual and mixed solvents

Abstract

Transmetalation reactions of cadmium complexes of tetraphenylporphine (CdTPP, I) and tetrabenzoporphine (CdTBP, II) in individual and mixed solvents have been investigated. For individual solvents, provided that the reaction proceeds via the same mechanism, its rate generally increases as the donor number increases in the order DMSO < DMF < PrOH-1 < MeCN (CdTPP-Zn(OAc)2-Solv system). On passing to the CdTPP-Cu(OAc)2-Solv system, the reaction rate order changes to DMSO < PrOH-1 < MeCN < DMF because the transmetalation mechanism changes from mixed to associative, as follows from the reaction order with respect to the salt being zero. The effect of the DMSO-DMF mixed solvent on the transmetalation reaction is limited to changing the reaction rate through alteration of the stability of the [CuX2(Solv1) n − m − 2(Solv2) m ] solvated salts. The trans effect of the ligands in the solvated salts does not increase the transmetalation rate.