59575-75-6Relevant academic research and scientific papers
MLCT photodissociation of low-spin ferrous bis(dioximate) complexes. Comparison of ground- and excited-state reactivity
Stynes, Dennis V.,Chen, Xuening
, p. 3145 - 3151 (2008/10/08)
Photochemical axial ligand substitution reactions of low-spin FeN4XY complexes, N4 = bis(dimethylglyoximate) or bis(naphthoquinone dioximate) and X or Y = CO, PBu3, P(OBu)3, BzNC, or MeIm, are shown to proceed via a dissociative mechanism in toluene solution. Quantum yields generally decrease as the π-acceptor strength of the axial ligand decreases: CO ? BzNC ～ P(OBu)3 > PBu3 ≥ MeIm. Ratios of quantum yields for loss of X vs. Y from the same FeN4XY complex provide a measure of excited-state rate constant ratios. These ratios are similar to corresponding ground-state values. Apparent activation energies for Fe(DMGH)2(MeIm)X for X = CO, P(OBu)3, BzNC, and PBu3 of ～ 1, 4.3, 4.6, and 8.1 kcal/mol, respectively, are obtained from the temperature dependence of the quantum yields. The wavelength, temperature, and ligand dependence of quantum yields in a variety of FeN4XY systems, including hemes, are most consistent with a common low-lying ligand field photoactive state, involving dz2 population, with a lifetime in the picosecond range. Higher quantum yields for π acceptors are rationalized in terms of a substantial decrease in π bonding in the axially elongated excited-state complex. A strong case is made for a common photochemical mechanism for all FeN4 systems including hemes wherein the axial ligand bonding in the excited state resembles that of a cobalt(II) ground-state analogue.
