Organometallic Chalcones Functioning as Radical Traps: Observations on the Solvated Electron Reduction and the C·H₂OH...

The pulse radiolysis method was used to investigate reactions between organometallic chalcones derived from ferrocene, cyrhetrene, and cymantrene substituted with a phenyl (R₁) or a 4'-benzo-15-crown-5 (B₁) moiety and the solvated electron e^-_sol and two radicals. The principal spectroscopic transformations resolved with the e^-_sol reactions reveal that the chalcone compounds react under a diffusion controlled condition. The chromophore in the reaction product is the radical anion chalcone, -C(═O)CH═CH-. The kinetics of the redox processes are consistent with the formation of the radical anion in a first step, followed by an E/Z isomerization reaction in the second step. The rate of the E/Z isomerization reaction is dependent on the chalcone substituent. Reactions with C·H₂OH and C·H₂Cl radicals are strongly affected by the nature of the organometallic fragment. The transient spectra for the reactions between C·H₂OH and C·H₂Cl radicals with the phenyl-substituted chalcone show weak, broad absorption bands at λ_ob < 400 nm. Only the ferrocenyl derivatives showed an intense absorption band with λ_max = 350 nm. The C-centered radicals react with organometallic chalcones with lifetimes less than or equal to a few microseconds, and the products are assigned as adducts of the C-centered radicals to the chalcone.