Beschreibung:
<jats:title>Abstract</jats:title><jats:p>The photochemistry of iron azido complexes is quite challenging and poorly understood. For example, the photochemical decomposition of [Fe<jats:sup>III</jats:sup>N<jats:sub>3</jats:sub>(cyclam‐ac)]PF<jats:sub>6</jats:sub> ([<jats:bold>1</jats:bold>]PF<jats:sub>6</jats:sub>), where cyclam‐ac represents the 1,4,8,11‐tetraazacyclotetradecane‐1‐acetate ligand, has been shown to be wavelength‐dependent, leading either to the rare high‐valent iron(V) nitrido complex [Fe<jats:sup>V</jats:sup>N(cyclam‐ac)]PF<jats:sub>6</jats:sub> ([<jats:bold>3</jats:bold>]PF<jats:sub>6</jats:sub>) after cleavage of the azide N<jats:sub>α</jats:sub>N<jats:sub>β</jats:sub> bond, or to a photoreduced Fe<jats:sup>II</jats:sup> species after FeN<jats:sub>azide</jats:sub> bond homolysis. The mechanistic details of this intriguing reactivity have never been studied in detail. Here, the photochemistry of <jats:bold>1</jats:bold> in acetonitrile solution at room temperature has been investigated using step‐scan and rapid‐scan time‐resolved Fourier transform infrared (FTIR) spectroscopy following a 266 nm, 10 ns pulsed laser excitation. Using carbon monoxide as a quencher for the primary iron‐containing photochemical product, it is shown that 266 nm excitation of <jats:bold>1</jats:bold> results exclusively in the cleavage of the FeN<jats:sub>azide</jats:sub> bond, as was suspected from earlier steady‐state irradiation studies. In argon‐purged solutions of [<jats:bold>1</jats:bold>]PF<jats:sub>6</jats:sub>, the solvent‐stabilized complex cation [Fe<jats:sup>II</jats:sup>(CH<jats:sub>3</jats:sub>CN)(cyclam‐ac)]<jats:sup>+</jats:sup> (<jats:bold>2 red</jats:bold>) together with the azide radical (N<jats:sub>3</jats:sub><jats:sup>.</jats:sup>) is formed with a relative yield of 80 %, as evidenced by the appearance of their characteristic vibrational resonances. Strikingly, step‐scan experiments with a higher time resolution reveal the formation of azide anions (N<jats:sub>3</jats:sub><jats:sup>−</jats:sup>) during the first 500 ns after photolysis, with a yield of 20 %. These azide ions can subsequently react thermally with <jats:bold>2 red</jats:bold> to form [Fe<jats:sup>II</jats:sup>N<jats:sub>3</jats:sub>(cyclam‐ac)] (<jats:bold>1 red</jats:bold>) as a secondary product of the photochemical decomposition of <jats:bold>1</jats:bold>. Molecular oxygen was further used to quench <jats:bold>1 red</jats:bold> and <jats:bold>2 red</jats:bold> to form what seems to be the elusive complex [Fe(O<jats:sub>2</jats:sub>)(cyclam‐ac)]<jats:sup>+</jats:sup> (<jats:bold>6</jats:bold>).</jats:p>