Estimating the (CO)5Cr–(2-benzene) bond dissociation enthalpy: reaction of the (CO)5Cr(2-benzene) complex with a series of (CH3)nTHF (n = 0, 1, 2, and 4) ligands

The displacement of the benzene ligand from the photolytically generated (CO)5Cr(2-benzene) complex by THF and a series of methyl substituted (CH3)nTHF (n= 1, 2, and 4) ligands was studied using the technique of laser flash photolysis. The data suggest that two independent pathways (D and Id) contribute to the overall displacement of the benzene solvent from the Cr center. The contribution of the Id pathway increases as the steric bulk of the MenTHF ligand is reduced from Me4THF to MeTHF. The activation enthalpy of 11.4 ± 1.1 kcal mol–1 obtained when the entering ligand is Me4THF is considered to be a lower estimate of the (CO)5Cr–(2-benzene) bond dissociation enthalpy. A detailed energetic profile of the substitution reaction is presented.