Kinetics of the reactions of divalent copper, zinc, cobalt, and nickel with a deformed water soluble centrally monoprotic porphyrin

The kinetics of incorporation of Cu2+, Zn2+,Co2+, and Ni2+ into the free base H-2-BrP(4)(4+) and centrally monoprotic H-BrP(4)(3+) forms of the deformed and water soluble beta-octabromo-tetrakis(N-methyl-4-pyridyl)porphyrin were studied at 25degreesC, I=0.10 (NaNO3/HNO3). Below pH 7, the reactions were first-order in porphyrin and metal, and the rate constants increased with an increase in pH. The monocation H-3-BrP(4)(5+) did not incorporate metal ions, and H-BrP(4)(3+) reacted several hundred times faster than H-2-BrP(4)(4+). The incorporation rate constants for the pre-deformed H-2-BrP(4)(4+) were similar to10(3) times larger as compared to the more planar tetrakis(N-methyl-4-pyridyl)porphyrin. For both porphyrins, the reactivity order was Cu2+>Zn2+>Co2+> Ni2+. While Cu2+ reacted similar to10(4) times more rapidly than did Ni2+ the ratios of the metalation rate constants of H-BrP(4)(3+) to the water exchange rate constants of the metal ions varied by no more than a factor of 4 across the series. (C) 2002 Elsevier Science B.V. All rights reserved.