Dioxygen Insertion into Metal-Carbon Bonds of Metalloporphyrins: Formation and Characterization of Alkylperoxy Metalloporphyrins

Abstract

Under photolytic and/or thermal-reaction conditions in organic solvents, dioxygen inserts into the metal-carbon bond of a series of metalloporphyrins, (P)M(R) and (P)M(R)(L), where P = octaethylporphyrin (OEP), tetraphenylporphyrin (TPP), or tetratolylporphyrin (TTP), M = Co(III), R = -CH₃, -CH₂CH₃, -CH₂C₆H₅, or CH₂C(CH₃)₃, and L = PR₃, pyridine, or 1-methylimidazole to form alkylperoxy metalloporphyrins, (P)M(OOR) and (P)M(OOR)(L). The alkylperoxy metalloporphyrns isolated have been characterized by ¹H NMR, FT-IR, UV-visible spectrophotometry, cyclic voltammetry, and elemental analysis. Activation parameters for dioxygen insertion into the Co-R bond have been determined from kinetic experiments. The insertion reaction proceeds via a Co(II) intermediate, which can be detected spectrophotometrically. The rate of formation of the (P)Co^III(OOR)(L) complexes is strongly dependent upon the Co-R bond dissociation energies of the parent (P)Co^III(R) complexes, which have been determined previously¹. The generality of this reaction for other metalloporphyrins and the utility of these complexes in understanding heterolytic and homolytic O-O bond cleavage reactions common in the biological manipulation of dioxygen by metalloporphyrins will be discussed.