Competitive Intramolecular Amination as a Clock for Iron-Catalyzed Nitrene Transfer

Reaction of the complex [(TpPh,Me)FeII(NCMe)3]BF4, where TpPh,Me = hydrotris(3-phenyl,5-methyl-1-pyrazolyl)borate, with the iodonium heteroylide PhI═NTs (1.5 equiv) is proposed to result in the insertion of N-tosylnitrene into one C–H bond at the ortho ring position of a 3-pyrazole phenyl substituent; subsequent deprotonation of the nascent aniline and one-electron oxidation of iron forms TsNH2 (0.5 equiv) as a coproduct. The covalent ligand modification and oxidation results in an intense purple-brown anilinato–iron(III) LMCT chromophore. This intramolecular reaction is utilized as a consistent clock to determine relative rates of competitive intermolecular nitrene transfer to added substrates, specifically to para-substituted styrenes and thioanisoles. Prior addition of substrate to the reaction of PhI═NTs with the iron(II) complex attenuates the CT absorbance of the equilibrium solution. Fitting of the concentration-dependent absorption data gives the ratio of intra- versus intermolecular nitrene trans...