Catalytic olefin epoxidations with KHSO 5: the first report on manganese hemiporphyrazines as catalysts in oxygenation reactions

Abstract

The oxidation of cyclooctene to cyclooctene epoxide by Oxone® (2KHSO 5·KHSO 4·K 2SO 4) as probe for evaluating the catalytic activity of a few manganese hemiporphyrazines has been studied. The oxidations have been carried out in an anhydrous two-phase system (solid Oxone®/solid catalyst/1,2-dichloroethane solution). In the absence of manganese hemiporphyrazine and/or of an aromatic nitrogen base only the slow stoichiometric epoxidation by KHSO 5 is observed. On the contrary, in the presence of pyridine and catalytic amount of manganese hemiporphyrazine (0.13–1% with respect to the organic substrate) either suspended in the reaction medium or adsorbed on a suitable polymer (silica gel or poly(vinylpyridine)) enhanced reaction rates are observed. The presence of an axial ligand in the coordination sphere of the catalyst appears to be essential for promoting the catalytic activity of the manganese complex. Moreover, the manganese hemiporphyrazine was subject to a colour change upon addition of the oxidant, thus suggesting the formation of a high valency oxo intermediate that oxidizes the olefin in a successive step. Under the experimental conditions adopted, epoxide yields up to 86% are obtained.