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

Article abstract of DOI:10.1021/ja00285a018

meso-(Tetrakis(2,6-dimethylphenyl)porphinato)iron(III) chloride ((Me8TPP)Fe(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 CH2O.All evidence supports these reactions to occur by equilibrium ligation of NO to iron(III) porphyrin followed by rate-detrmining oxygen transfer to yields as intermediate products DA and the iron(IV)-oxo porphyrin ?-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 (Me8TPP)Fe(III)OCH3 are comparable to those of the unsubstituted meso-(tetraphenylporphinato)iron(III) methoxide ((TPP)Fe(III)OCH3).The following results are, therfore, not surprising: (i) The second-order rate constant (k_ak_b/k_-a) for reaction of (Me8TPP)Fe(III)Cl with NO is but 3.3-fold smaller than in the case of the reaction of NO with (TPP)Fe(III)Cl; (ii) the percentage yields of products (DA, 53percent; MA, 24percent; A, 3percent; FA, 8percent; H, 7percent; MD, 5percent) are comparable to when (TPP)Fe(III)Cl is employed; and (iii) oxidation and epoxydation of added substrates are not rate-determining.Of considerable interest is the finding that epoxidation reactions using NO with (Me8TPP)Fe(III)Cl occur in much higher yield (80percent to 100percent) than when (TPP)Fe(III)Cl is used as the catalyst.