Structure and Reactivity of Amphoteric Oxygen Species

• Published in: Bulletin of the Chemical Society of Japan Vol. 73; no. 3; pp. 535 - 552
• Main Authors: Ishiguro, Katsuya, Sawaki, Yasuhiko
• Format: Journal Article
• Language: English
• Published: Tokyo The Chemical Society of Japan 01.03.2000; Chemical Society of Japan
• ISSN: 0009-2673; 1348-0634
• DOI: 10.1246/bcsj.73.535

The structure and chemical properties of 1,3-dipolar peroxidic species (X+-O-O-) such as ozone (X = O), nitroso oxides or nitrenium peroxides (X = RN), carbonyl oxides or carbenium peroxides (X = R2C), and persulfoxides or sulfonium peroxides (X = R2S) have been attracting much attention from synthetic, biological, and theoretical standpoints. These active oxygen species can be classified into two types depending on whether the X+ is an enium (carbenium, nitrenium, silylenium etc.) ion or an onium (ammonium, oxonium, phosphonium, sulfonium etc.) ion, and their reactivities are quite different depending on the nature of X. The individual features as well as the overviews of structure and reactivities of these X-O-O species are reviewed. Ozone and nitroso oxides have an electrophilic character while carbonyl oxides usually act as a nucleophilic oxygen transfer agent, their reactivities being controlled by substituents. It is important to see whether or not XOO species can isomerize to the cyclic isomers. Although cyclic O3 is thermodynamically unstable, dioxiranes, the cyclic form of carbonyl oxides, have been isolated and fully characterized. It has been suggested that nitroso oxides isomerize to the cyclic form yielding the corresponding nitro compounds unimolecularly. In the case of persulfoxides (X = R2S), the dipolar structure (X+-O-O-) is important, their characteristic reaction being nucleophilic O-transfer to sulfoxides, while 3λ5-dioxaphosphirane (X = R3P) can exist only in the cyclic form, showing electrophilic reactivity. Effects of X's on structure and reactivity of these oxides were systematically examined by the density functional BLYP/6-31G* calculations. The inductive effect through σ-framework has been found to dominate the thermodynamic stabilities of carbonyl oxides, while the π-donating property of substituents governs the activation energy for the cyclization to dioxiranes.