Catalytic and stoichiometric oxidation of N,N-dimethylanilines mediated by nonheme oxoiron(IV) complex with tetrapyridyl ligand

Abstract

Abstract Nonheme iron(II) complex, [(N4Py*)FeII(CH3CN)](ClO4)2 (1) with pentadentate tetrapyridyl ligand (N4Py*\u202f=\u202fN,N-bis(2-pyridylmethyl)-1,2-di(2-pyridyl)ethylamine) has been shown to catalyze the oxidation of N,N-dimethylaniline (DMA) with H2O2, tert-butyl hydroperoxide (TBHP), peracetic acid (PAA), meta-chloroperoxybenzoic acid (mCPBA) and PhIO resulting N-methylaniline (MA) as the predominant product with N-methylformanilide (MFA) as a result of a free-radical chain process. The product composition (MA/MFA) is remarkably influenced by the electron density on the substrate, especially in the 1/mCPBA system, and by the co-oxidants used. No formation of MFA occurred when the oxidation of DMA was carried out in the presence of 1 with PhIO as co-oxidants under argon. Based on spectral investigation (UV–Vis) of reaction systems above, oxoiron(IV) intermediate, [FeIV(N4Py*)(O)]2+ (2) has been suggested to be the key active species of the N-dealkylation reaction in all catalytic systems. The shift in the λmax value of the oxoiron(IV) species in the presence of DMA from 705 to 750\u202fnm, and the new intense absorption in the range of 5–600\u202fnm indicates a complexation and charge-transfer (CT) type interactions between the oxidant and substrate. The stoichiometric oxidation of various N,N-dimethylaniline derivatives with 2 provided clear evidence (Hammett correlation with ρ\u202f=\u202f−1.99, and the large negative slope (−4.1) from the logkobs versus Eoox (DMAs) plot) for the rate-determining electron transfer (ET) followed by a proton transfer (PT) process.