Reaction pathways and energetics for the conversion of benzene to phenol by FeO+ in the gas phase are discussed using density functional theory calculations at the B3LYP/6-311+G** level of theory. Three reaction pathways are available for this reaction. The first one is a nonradical mechanism to form a hydroxo intermediate, HO-Fe+-C6H 5, via H atom abstraction with a four-centered transition state, which occurs at a coordinatively unsaturated metal center. The second one is a radical mechanism to form a phenyl radical and an FeOH fragment as an intermediate via H-atom abstraction with a linear C-H-O transition state. The third one is an oxygen-insertion mechanism to form an arenium intermediate via electrophilic aromatic addition. The energies of the transition states with respect to H-atom abstraction (relative to the dissociation limit) increase in the order of the first, third, and second mechanisms. A detailed analysis of the potential energy surfaces shows that the first mechanism is most likely to occur when the metal active site is coordinatively unsaturated. The second mechanism is energetically unlikely. The third pathway is branched into cyclohexadienone and benzene oxide, which are formed by a 1,2-hydrogen migration and a ring closure in the arenium intermediate, respectively. Cyclohexadienone can play a role as an intermediate when the metal active site is coordinatively saturated, whereas the formation of benzene oxide is unlikely to occur under ambient conditions because of its extremely high energy.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry