Kinetics and Mechanism of Oxygen Transfer in the Reaction of p-Cyano-N,N-dimethylaniline N-Oxide with Metalloporphyrin Salts. 7. Oxygen Atom Transfer to and from (meso-Tetrakis(pentafluorophenyl)porphinato)iron(III) Chloride

Article abstract of DOI:10.1021/ja00245a041

The decomposition of p-cyano-N,N-dimethylaniline N-oxide (NO) in the presence of (meso-tetrakis(pentafluorophenyl)porphinato)iron(III) chloride ((F₂₀TPP)Fe^IIICl) provides p-cyano-N,N-dimethylaniline (DA) in 32 +/- 3percent, p-cyano-N-methylaniline (MA) in 50 +/- 5percent, 4-cyano-7-(dimethylamino)-2-benzofuranone-3-spiro-2'-cyano-5'-(dimethylamino)cyclopentadiene (BF) in 16 +/- 2percent, and formaldehyde in 30 +/- 3percent yield based upon (NO)_i.Material balance may be accounted for in all components.Appearance of products is first order in both NO and (F₂₀TPP)Fe^IIICl, and the second-order rate constant for the reaction has been determined to be (2.0 +/- 0.5) x 10² M^-1 s^-1.The observation that the formation of products DA, MA, and BF is associated with the same rate constant establishes the commitment step to be the bimolecular reaction of NO with (F₂₀TPP)Fe^IIICl.It is proposed that this reaction directly yields DA and the iron(IV)-oxo porphyrin ?-cation radical ((^{+._F20TPP)FeIV}O).That the formation of (^{+._F20TPP)FeIV}O + DA is rate controlling is substantiated by use of the reagents 2,4,6-tri-tert-butylphenol (TBPH), N,N-dimethylaniline (DMA), and N,N-dimethyltoluidine (DMT) as traps for the (^{+._F20TPP)FeIV}O species.The rates of oxidation of these trapping agents are independent of their concentration, and the rate constants calculated for the appearances of their oxidation products correspond to the turnover rate constant for the reaction of NO with (F₂₀TPP)Fe^IIICl in the absence of trapping agents.Formation of the products MA and BF must then be attributed to the rapid oxidation of DA by (^{+._F20TPP)FeIV}O.The formation of MA occurs by the oxidative demethylation of DA, and formation of BF is logically accounted for by the hydroxylation of DA to yield 2-hydroxy-4-cyano-N,N-dimethylaniline (DMP) which, on further stepwise oxidation, provides BF (much as in the stepwise 1 e^- oxidation of p-cresol to yield Pumerer's ketone).Increase in the concentrations of DMA and DMT results in exponential increase in the percentage yield of DA and decrease in the percentage yield of MA.In each case the asymptotic percentage yields of 68 +/- 7percent DA and 17 +/- 2percent MA are approached.The percentage yield of BF (17 +/- 2percent) is not changed by the presence of DMA or DMT at various concentrations or by their absence.These results show that a substantial portion of the immediate products DA and (^{+._F20TPP)FeIV}O reacts in a solvent-caged /(^{+._F20TPP)FeIV}O*DA/ pair prior to their diffusion apart.Once free from the caged pair, the (^{+._F20TPP)FeIV}O species oxidizes the traps DMA and DMT in preference to DA.The asymptotic yield of MA represents the percentage yield of MA obtained by oxidation of DA within the solvent caged pair.Since the percentage yield of BF is not influenced by the presence of DMA or DMT, all hydroxylation of DA must occur within the /(^{+._F20TPP)FeIV}O*DA/ species.By this reasoning, both the caged oxidative demethylation and hydroxylation of DA occur in ca. 17percent yields.Thus, within the ....