Catalytic oxidations of alcohols - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 132

oxometal mechanism (see Figure 2). It has long been known that ruthenium
tetroxide, generated by reaction of ruthenium dioxide with periodate,
smoothly oxidizes a variety of alcohols to the corresponding carbonyl
compounds 35 .
Griffith and coworkers 36 reported the synthesis of the organic soluble
tetra-n-butylammoniumperruthenate (TBAP), in 1985. They
later found that tetra-n-propylammoniumperruthenate (TPAP),
is even easier to prepare, from and in
water 37,38 . TBAB and TPAP are air-stable, non-volatile and soluble in a wide
range of organic solvents. Griffith and Ley 39,40 subsequently showed that
TPAP is an excellent catalyst for the selective oxidation of a wide variety of
alcohols using N-methylmorpholine-N-oxide (NMO) as the stoichiometric
oxidant (Reaction 8).
More recently, the groups of Ley 41 and Marko 42 independently showed
that TPAP is able to catalyze the oxidation of alcohols using dioxygen as the
stoichiometric oxidant. In particular, polymer supported perruthenate (PSP),
prepared by anion exchange of with a basic anion exchange resin
(Amberlyst A-26), has emerged as a versatile and recyclable catalyst for the
aerobic oxidation (Reaction 9) of alcohols 41 , albeit with an activity ca. 4
times lower than homogeneous TPAP. Analogous to the above described
Ru/TEMPO system PSP displays a marked preference for primary versus
secondary alcohol functionalities 41 .
Examples illustrating the scope of PSP-catalyzed aerobic oxidation of
primary alcohols to the corresponding aldehydes are shown in Table 3.