Catalytic oxidations of alcohols - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 137

The use of these ruthenium pyrochlore oxides as catalysts for the
aerobic oxidation of alcohols would seem to be worthy of further
investigation. Presumably the function of the bismuth (or lead) is to facilitate
the reoxidation of the ruthenium, by dioxygen, in these catalysts.
A ruthenium(III) salen complex anchored to a chloromethylated
styrenedivinylbenzene copolymer (see Figure 8) was reported 54 , 55 to be 75
times as active as the homogeneous analogue in the aerobic oxidation of
benzyl alcohol. However, recycling of the catalyst led to a 35% loss in
activity due to facile leaching of the ruthenium. Moreover, we note that it is
highly unlikely that the oxidation sensitive salen ligand survives the reaction
conditions.

The aerobic oxidation of alcohols proceeds smoothly at room
temperature in the presence of one equivalent of an aldehyde, e.g.
acetaldehyde, and a catalyst comprising a 1:1 mixture of and

in ethyl acetate (Reaction 13) 56 .

Representative examples are shown in Table 5. The results were
rationalized by assuming that the corresponding percarboxylic acid is formed
by cobalt-mediated free radical autoxidation of the aldehyde. Subsequent
reaction of ruthenium(m) with the peracid affords oxoruthenium(V)
carboxylate which is the active oxidant. Compared to the aerobic oxidations