Synthesis and Reactions of Platinum(III) Complexes with Protoporphine Ligands in Mixtures of Acetic and Sulfuric Acids

Unusual stable platinum complexes (Cl)PtIIIP were obtained by the reaction of K₂PtCl₆] with porphyrin H₂P (full methyl ethers of proto-, meso-, deutero-, and hematoporphyrin) in a 1:2 molar ratio in boiling pyridine. The forms of existence, kinetics and mechanism of dissociation of metal porphyrins in AcOH-(0.3-2.1) M H₂SO₄ mixtures were studied at 300-330 K. The reaction has first-order with respect to metal porphyrin, low E values (21-48 kJ/mol), and negative S values (-145- to -224 J mol^{- 1} K^{- 1}). The dependence of the formal first-order rate constants on H₂SO₄ concentration is linear at low values of this latter (up to 1.5 M). The mechanism of the electron density redistribution produced by functional substitution in positions of the macroring was studied to establish that the character of the dependence of the dissocia- tion rate on the macroring nature is determined by restricted -electron density transfer from the metal atom to a coordinated N atom.