Chemistry of Arylphosphines with Singlet Dioxygen
We are exploring the chemistry of arylphosphines with singlet oxygen. The main goal of this work was to directly observe the primary intermediates of this reaction, and to investigate the oxidizing power of these peroxidic species. Such peroxidic intermediates are even better oxidizing agents than singlet oxygen itself and therefore rapidly react with unreacted starting material. It is therefore not surprising that such species are very difficult to observe. To prevent (or at least slow down) reaction of intermediates with starting material, we have been studying arylphosphines possessing substituents in the ortho position of the aromatic rings. At very low temperature (- 80 °C), we have been able to directly observe and study several phosphadioxiranes. These compounds are indeed powerful oxidants: They epoxidize olefins, and intramolecular hydroxylation of an aromatic ring has also been observed by our group. For a recent review article in Chemical & Engineering News, click here. (Chemical & Engineering News 2003, 81(14), 28-31.) Several other unprecedented species obtained under protic conditions have also been characterized. The various reactions of a phosphadioxirane are shown below. Several other phosphines are currently under investigation.