The kinetics and mechanisms of oxygen transfer in the reaction of p-cyano-N,N-dimethylaniline N-oxide with metalloporphyrin salts. 4. Catalysis by meso-[tetrakis(2,6-dimethylphenyl)porphinato]iron(III) chloride

Abstract

meso-(Tetrakis(2,6-dimethylphenyl)porphinato)iron(III) chloride (Me/sub 8/ TPP)Fe/sup III/Cl) is a catalyst for the conversion of p-cyano-N,N-dimethylaniline N-oxide (NO) to p-cyano-N,N-dimethylaniline (DA), p-cyano-N-methylaniline (MA), p-cyano-N-formyl-N-methylaniline (FA), p-cyanoaniline (A), N,N'-dimethyl-N,N'-bis(p-cyanophenyl)hydrazine (H), N,N'-bis(p-cyanophenyl)-N-methylmethylenediamine (MD), and CH/sub 2/O. All evidence supports these reactions to occur by equilibrium ligation of NO to iron(III) porphyrin followed by rate-determining oxygen transfer to yield as immediate products DA and the iron(IV)-oxo porphyrin ..pi..-cation radical. Stepwise oxidation of DA by the higher valent iron-oxo porphyrin species is responsible for the formation of the other products (i.e., DA ..-->.. ..-->.. FA, DA ..-->.. MA ..-->.. A, 2MA ..-->.. MD, and 2MA ..-->.. H). The oxidation potentials of (Me/sub 8/TPP)Fe/sup III/OCH/sub 3/ are comparable to those of the unsubstituted meso-(tetraphenyl-porphinato)iron(III) methoxide ((TPP)Fe/sup III/OCH/sub 3/). The following results are, therefore, not surprising: (i) the second-order rate constant (k/sub a/k/sub b//k/sub -a/) for reaction of Me/sub 8/TPP)Fe/sup III/Cl with NO is but 3.3-fold smaller than in the case of the reaction of NO with (TPP)Fe/sup III/Cl; (ii) the percentage yields of products (DA, 53%; MA, 24%; A, 3%; FA, 8%; H, 7%; MD, 5%) are comparable to when (TPP)Fe/sup III/Cl is employed; and (iii) oxidation and epoxidation of added substrates are not rate-determining.