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The photochemistry of iron azido complexes is quite challenging and poorly understood. For example, the photochemical decomposition of [Fe(III)N(3)(cyclam-ac)]PF(6) ([1]PF(6)), 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(V)N(cyclam-ac)]PF(6) ([3]PF(6)) after cleavage of the azide N(α)-N(β) bond, or to a photoreduced Fe(II) species after Fe-N(azide) bond homolysis. The mechanistic details of this intriguing reactivity have never been studied in detail. Here, the photochemistry of 1 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 1 results exclusively in the cleavage of the Fe-N(azide) bond, as was suspected from earlier steady-state irradiation studies. In argon-purged solutions of [1]PF(6), the solvent-stabilized complex cation [Fe(II)(CH(3)CN)(cyclam-ac)](+) (2red) together with the azide radical (N(3)(.)) 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(3)(-)) during the first 500 ns after photolysis, with a yield of 20%. These azide ions can subsequently react thermally with 2red to form [Fe(II)N(3)(cyclam-ac)] (1red) as a secondary product of the photochemical decomposition of 1. Molecular oxygen was further used to quench 1red and 2red to form what seems to be the elusive complex [Fe(O(2))(cyclam-ac)](+) (6)., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The laser-flash photolysis of the high-spin azidoiron(III) complex [FeIII(Me3Cyclam-ac)(N3)]PF6 ([ 1]PF6) in liquid acetonitrile solution at room temperature was explored by time-resolved Fourier-transform infrared spectroscopy. Excitation of [ 1] at 480 and 266 nm induced a photoreduction of the metal center and generated [FeII(Me3Cyclam-ac)(NCCH3)]+ ([ 2]) and azidyl radicals. Both photoproducts were detected independently through scavenging experiments. The metal-containing fragment was quenched with carbon monoxide to generate an iron(II) carbonyl complex, whereas the nitrogen-containing fragment was quenched with iodide to form azide anions. In the presence of N3−, the photoreduction created the elusive hexanitrogen radical anion N6.− as a transient byproduct. [ABSTRACT FROM AUTHOR]

Flash photolysis combined with step-scan and rapid-scan Fourier-transform infrared spectroscopy was carried out to explore the photochemistry of a puckered, quasi-square pyramidal ferracyclobutadiene, [Fe{κ2-C3(NEt2)3}(CO)3]BF4 ([ 1]BF4), that features three additional carbonyl ligands in the metal coordination sphere. In liquid solution at room temperature, an excitation with λ=355 nm light resulted in the loss of one CO ligand, which is cleaved from a basal metal-coordination site. Within the time resolution of the experiment, a solvent molecule promptly refills the resultant vacancy at the coordinatively unsaturated metal center. In the weakly interacting liquid, dichloromethane, the counterion of the complex is subsequently able to substitute the solvent in the coordination sphere of the iron center, thereby forming as a stable product a neutral dicarbonyl tetrafluoroborato iron(0) species containing a four-membered ferracycle. [ABSTRACT FROM AUTHOR]

Give me five: Time‐resolved Fourier‐transform IR spectroscopy is used to time‐resolve the formation and the reaction dynamics of a fourfold symmetrical nitrido iron(V) complex (light blue C, red Fe, blue N) in liquid solution under physiological and technologically relevant conditions. [ABSTRACT FROM AUTHOR]

Review: 121 refs. [ABSTRACT FROM AUTHOR]

Recently, the complex cation [(cyclam-ac)FeIII(N3)]+ has been used in solid matrices under cryogenic conditions as a photochemical precursor for an octahedral iron nitride containing the metal at the remarkably high oxidation state +5. Here, we study the photochemical primary events of this complex cation in liquid solution at room temperature using femtosecond time-resolved mid-infrared (fs-MIR) spectroscopy as well as step-scan Fourier-transform infrared spectroscopy, both of which were carried out with variable-wavelength excitation. In stark contrast to the cryomatrix experiments, a photooxidized product cannot be detected in liquid solution when the complex is excited through its putative LMCT band in the visible region. Instead, only a redox-neutral dissociation of azide anions is seen under these conditions. However, clear evidence is found for the formation of the highly oxidized iron nitride product when the photolysis is carried out in liquid solution with UV light. Yet, the photooxidation must compete with photoreductive Fe–N bond cleavage leading to azide radicals and an iron(II) complex. Both, redox-neutral and photoreductive Fe–N bond breakage as well as photooxidative N–N bond breakage occur on a time scale well below a few hundred femtoseconds. The majority of fragments suffer from geminate recombination back to the parent complex on a time scale of 10 ps. Upper limits of the primary quantum yield for photooxidation are derived from the fs-MIR data, which increase with increasing energy of the photolysis photon. [ABSTRACT FROM AUTHOR]