Photoredox Reactions Occurring in Methanolic Solutions of Iron(III) Azido Complexes with N,N′-Ethylenebis (salicylaldiminato) Schiff Base Derivatives

Summary.

Photoredox reactions occurring in irradiated methanolic solutions of trans-[Fe(N ₂ O ₂ ) (CH₃OH)N₃], where N ₂ O ₂ ²⁻ are tetradentate open-chain N ₂ O ₂ -Schiff base N,N′-ethylenebis(R-salicylaldiminato) or N,N′-1-methylethylenebis(R-salicylaldiminato) ligands denoted as R-salen and R-sal(Me)en, respectively (R=H, 5-Cl, 5-Br, 4-OCH₃), have been investigated and their mechanism has been proposed. The complexes are redox stable in the dark. Ultraviolet and/or visible irradiation of methanolic solutions of the complexes induces photoreduction of Fe(III) to Fe(II). As an intermediate, •CH₂OH radicals were identified by EPR spin trapping technique. The final product of the photooxidation coupled with the photoreduction of Fe(III) is formaldehyde. The efficiency of the photoredox processes is strongly wavelength dependent and influenced by the peripheral groups R of the tetradentate ligands. Differences between the course of photochemical changes induced by 254 nm radiation and the other wavelengths of incident radiation is rationalized by involving azide anions photoreactivity in observed redox changes.