New developments in the chemistry of peroxo-metal and chromium(VI)-oxidant systems

Abstract

The importance of syntheses and studies of reactivity of peroxo-metal compounds, which provide a heuristic approach in this field for an understanding of catalytic oxidation reactions, has been highlighted. Innovative approaches and their scope in the synthesis of new heteroligand peroxo-metal compounds are described. The metals are drawn from Ti, Zr, V, Cu and U; heteroligands include F^-, Cl^-, SO₄^2-, CO₃^2-, ethylenediamine, 2,2'-bipyridine, 1,10-phenanthroline and glycine. Various reactions of some of these compounds are summarized. The oxidations of organic substrates involving a new Cr(VI) reagent, pyridinium fluorochromate, C₅H₅NHCrO₃F (PFC), are described. PFC in dichloromethane oxidizes primary and secondary alcohols to the corresponding aldehydes and ketones, benzoin and a tricyclic allylic alcohol to benzil and a tricyclic enone, and anthracene and phenanthrene to anthraquinone and phenanthrene-9,10-quinone, respectively. Selective oxidation of secondary alcohols in the presence of primary ones, including that of 5-andostrene-3β, 17β-diol to the 17-keto steroid, by PFC is another significant feature of the oxidant. The oxidation of PPh₃ to OPPh₃ provides a clear-cut example of an oxygen transfer reaction involving the PFC system. Synthetic utility of the new reagent is accentuated.