Kinetics of Incorporation of Manganese (II), Cobalt (II), and Nickel (II) into Tetraphenylporphine in Dimethylformamide. Effect of the Acetate Anion

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The kinetics of incorporation of Mn (II), Co (II), and Ni (II) into meso-tetraphenylporphine (H_2TPP) in N, N-dimethylformamide (DMF) at 50°were dependent on the metal salts employed. The reaction was first order in total concentration of Mn (II) acetate, but half order in Co (II) and Ni (II) acetate. In DMF solutions of the metal acetate, an equilibrium exists between the dimer and monomer ; M_2 (OAc)_4⇌2M (OAc)_2. The halforder dependence can be explained as being due to predissociation of the dimer followed by reaction of a monomer with H_2TPP. The kinetic results show that Co (II) and Ni (II) acetate exist to a greater extent as the dimer, while Mn (II) acetate exists predominantly as the monomer. The reaction with perchlorate salts was first order in total concentration of Mn (II) and half order in that of Co (II) or Ni (II). The reaction with mixtures of perchlorate and acetate was most rapid at an [OAc]_T/[M(II)]_T ration of 1.0-1.5 at constant [M (II)]_T, where the subscript T indicates total concentrations. It can be concluded that the species M (OAc)^+ is more reactive than the fully solvated metal species or the monomeric metal acetate species, M (OAc)_2,and their reactivities follow the order Cu (II)>Zn (II)>Co (II)>Ni (II)〜Mn (II).
1979-12-25