Electronic property and reactivity of (hydroperoxo)metal compounds

DFT calculations were done for the (hydroperoxo)metal complexes with eta (1 )-coordination mode, where metal ions are Fe(III), AI(III), Cu(II) and Zn(I I). Results shows that 1) the electron density at the two oxygen atoms of t he hydroperoxide ion is highly dependent on the angle O-O-H in M-OOH specie s and the difference in electron density between the two oxygen atoms reach es a maximum at the angle O-O-H = 180 degrees, 2) total electron density at the two oxygen atoms of the peroxide ion increases by approach of methane to the (hydroperoxo)metal species in the cases of Fe(III) and Cu(II); on th e other hand, significant decrease of the electron density on peroxide oxyg en atoms was observed for the cases of Al(III) and Zn(II) compounds. These findings suggest that the (hydroperoxo)metal species acts as an electrophil e in the former cases (M = Fe(III), Cu(II)) and as a nucleophile for the la tter two compounds (M = Zn(II), AI(III)). The electrophilicity observed for the Fe(LII) and Cu(II) complexes is attributed to the presence of unoccupi ed- or half-filled d-orbitals interacting with the hydroperoxide ion. 3) Tw o oxygen atoms of the (hydroperoxo)-compounds of Fe(III) and Cu(II) complex es exhibit quite different reactivity toward the substrate, such as methane . When methane approaches the oxygen atom which is coordinated to a metal i on, a strong decrease of electron density at the methane carbon atom occurs with concomitant increase of electron density at the peroxide oxygen atoms inducing its heterolytic O-O cleavage. When methane approaches the termina l oxygen atom, an oxidative coupling reaction occurs between peroxide ion a nd methane; at first a nucleophilic attack by the terminal electron-rich ox ygen atom occurs at the carbon atom to induce C-O bond formation, and a sub sequent oxidative electron transfer proceeds from substrate to the metal-pe roxide species yielding CH3-OOH, CH3OH. or other oxidized products. These r esults clearly demonstrate that the (hydroperoxo)-metal compound itself is a rather stable compound, and activation of the peroxide ion is induced by interaction with the substrate, and the products obtained by the oxygenatio n reaction are dependent on the chemical property of the substrate, redox p roperty of a metal ion, and stability of the compounds formed in the interm ediate process.