Azobenzenes to Azoxybenzenes

Molybdenum complexes catalyze the hydroperoxide oxidation of azo compounds to azoxy compounds, equation (146), in high yields [191]. Both [Mo02(dpm)2] (dpm = dipivaloylmethane) and [Mo(CO)6] have been used as catalysts and a range of substituents (Ri, R2) were employed. 

With [Mo(CO)e] as the catalyst the hydroperoxide oxidation of the mono-methoxy compound, XXVI, yields a mixture of nearly equal quantities of a- and /3-azoxy products. This change in selectivity suggests that variation in the oxidation state and ligand environment has resulted in different mechanisms for the Mo(0) and Mo(Vl) complexes. Johnson and Gould suggest transition states XXVIll and XXIX for reactions catalyzed by [Mo02(dpm)2] and [Mo(CO)6] respectively. 

---