The photochemical removal of p-xylene from [(η5 -C5H5)Fe(η6-p-xyl)]+ (p-xyl = p-xylene) has been studied as a function of solvent (propylene carbonate, CH3OH, CH3CN, CH2Cl2) and as a function of the anion present ([formula-omitted]) in CH2Cl2 solution. The quantum yield for p-xylene release varies from a high of 0.81 in water to a low of 0.084 in dichloromethane. The variation in quantum yield is indicative of solvent or anion assistance in the chemical step in which p-xylene is released from Fe. This interpretation of the quantum yield data establishes the relative nucleophilicity of the solvents and anions studied: H2O ≍ propylene carbonate ≈ CH3OH > CH3CN > [formula-omitted]- > [formula-omitted] > Br- ≈ [formula-omitted] ≫ [formula-omitted] > CH2Cl2 ≍ [formula-omitted] ≍ [formula-omitted]. The medium assistance observed in these arene replacement reactions contrasts the dissociative behavior observed for LF excited states in other organometallic transition-metal systems.