Dynamics of Photosubstitution Reactions of Fe(CO)5: An Ultrafast Infrared Study of High Spin Reactivity

The photosubstitution reactions of Fe(CO)5 with alcohols and triethylphosphine have been studied in room temperature solution using femtosecond UV pump IR probe techniques. The dynamics of Fe(CO)5 in alcohols show that the coordination of the hydroxyl group of the solvent with triplet Fe(CO) 4 is generally much faster than the coordination timescale observed with comparable singlet species. The physical reason for this is the fact that the metal C-H agostic bond is much weaker for triplets, thus allowing fast rearrangement to the hydroxyl group of the alcohol. In the case of triethylphosphine photosubstitution, the reaction is divided into parallel channels which include intersystem crossing and a spin conserving double carbonyl loss. The intermediates observed were studied using density functional theory (DFT) as well as ab initio quantum chemical calculations.