A Combined Spectroscopic and Computational Study on the Mechanism of Iron-Catalyzed Aminofunctionalization of Olefins Using Hydroxylamine Derived N-O Reagent as the "Amino" Source and "Oxidant".

Herein, we study the mechanism of iron-catalyzed direct synthesis of unprotected aminoethers from olefins by a hydroxyl amine derived reagent using a wide range of analytical and spectroscopic techniques (Mössbauer, Electron Paramagnetic Resonance, Ultra-Violet Visible Spectroscopy, X-ray Absorption, Nuclear Resonance Vibrational Spectroscopy, and resonance Raman) along with high-level quantum chemical calculations. The hydroxyl amine derived triflic acid salt acts as the "oxidant" as well as "amino" group donor. It activates the high-spin Fe(II) ( = 2) catalyst [Fe(acac)(HO)] () to generate a high-spin ( = 5/2) intermediate (), which decays to a second intermediate () with = 2. The analysis of spectroscopic and computational data leads to the formulation of as [Fe(III)(acac)--acyloxy] (an alkyl-peroxo-Fe(III) analogue). Furthermore, is formed by N-O bond homolysis. However, it does generate a high-valent Fe(IV)(NH) species (a Fe(IV)(O) analogue), but instead a high-spin Fe(III) center which is strongly antiferromagnetically coupled ( = -524 cm) to an iminyl radical, [Fe(III)(acac)-NH·], giving = 2. Though Fe(NH) complexes as isoelectronic surrogates to Fe(O) functionalities are known, detection of a high-spin Fe(III)--acyloxy intermediate (), which undergoes N-O bond cleavage to generate the active iron-nitrogen intermediate (), is unprecedented. Relative to Fe(IV)(O) centers, features a weak elongated Fe-N bond which, together with the unpaired electron density along the Fe-N bond vector, helps to rationalize its propensity for -transfer reactions onto styrenyl olefins, resulting in the overall formation of aminoethers. This study thus demonstrates the potential of utilizing the iron-coordinated nitrogen-centered radicals as powerful reactive intermediates in catalysis.