Photochemistry of iodo iron(Ⅲ) complexes

摘要

Photoredox reactions occurring in irradiated methanolic solutions of trans-[Fe(5-R-salen)(CH_3OH)Ⅰ] or trans- [Fe(4-R-benacen)(CH_3OH)Ⅰ] have been investigated and their mechanism proposed. In the formulae, 5-R-salen~(2-) and 4-R-benacen~(2-) symbolize N,N′-ethylenebis(5-R-salicylidene-iminate) and N,N′-ethylenebis(4-R-benzoylacetoneiminate) open-chain N_2O_2-Schiff bases, respectively, with R = H, F, Cl, Br, I, CH_3, OCH_3, CF_3 and NO_2 groups. Methanolic solutions of these complexes are redox-stable in the dark, however, ultraviolet and/or visible irradiation induces photoreduction of Fe(Ⅲ) to Fe(Ⅱ). Depending cm the composition of the irradiated solutions, the formation of ~·CH_2OH radicals or solvated electrons was indicated by the EPR spin trapping technique. The final products of the photoredox reaction represent Fe~Ⅱ and formaldehyde with a molar ratio of c_(Fe_(Ⅱ)):c_(CH_2O)～2:1. The effectiveness of the photoredox processes is strongly wavelength-dependent, and is influenced by the peripheral substitutents R on the tetradentate ligands. In addition to the authors' results, a survey of the photochemistry of iodo complexes is given.