Kinetics and Mechanisms of Oxygen Transfer in the Reaction of p-Cyano-N,N-Dimethylaniline N-Oxide with Metalloporphyrin Salts. 3. Catalysis by iron(III) Chloride

Article abstract of DOI:10.1021/ja00267a038

Decomposition of p-cyano-N,N-dimethylaniline N-oxide (NO) catalyzed by iron(III) chloride ((Cl8TPP)Fe^IIICl) yields as products p-cyano-N,N-dimethylaniline (DA), p-cyano-N-methylaniline (MA), and formaldehyde (CH2Cl2 solvent, 25 deg C, N2 atmosphere).Intermediate in the reaction are mono and bis NO complexes (Cl8TPP(Cl)Fe^IIINO and Cl8TPP(NO)Fe^IIINO, respectively).Oxygen transfer from the complexed NO species to the iron porphyrin is rate-limiting and provides the higher valent iron(IV) salts (IVO>^+. and IVO>^+.) and DA.The observed kinetics for reactions involving 10-100 turnovers of catalyst dictate that the catalyst is saturated in the formation of Cl8TPP(Cl)Fe^IIINO and that formation of Cl8TPP(NO)Fe^IIINO is unfavorable.The two iron(IV)-oxo porphyrin ?-cation radical species are converted back to the iron(III) porphyrin catalytic moieties by oxidation of DA -> MA + CH2O and oxidation of CH2O.Addition of 2,4,6-tri-tert-butylphenol (TBPH), 2,3-dimethyl-2-butene (TME), and cyclohexene results in the formation of TBP^. and the respective epoxides, thus inhibiting the oxidation of DA and CH2O.The kinetics of the overall reaction and formation of each product may be simulated by employing the reactions of Scheme II and eq l-r, and from the simulations, the rates and equilibria, leading to the formation of the two iron(IV)-oxo porphyrin ?-cation radical species may be determined as can minimal rate constants for the oxidations of DA, CH2O, and TBPH and the epoxidation of TME and cyclohexene.The results obtained herein with the electron-deficient porphyrin, (Cl8TPP)Fe(III)Cl, are discussed and compared to those obtained previously when employing (TPP)Fe^IIICl as the catalyst.