Catalytic oxidations of alcohols - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 133

In a more recent variation on this theme a tetraalkylammonium
perruthenate tethered to the internal surface of mesoporous silica (MCM-41)
was shown 43 to catalyze the selective aerobic oxidation of primary and
secondary allylic and benzylic alcohols (Figure 6).
Surprisingly, both cyclohexanol and cyclohexenol were unreactive
although these substrates can easily be accommodated in the pores of MCM-
41. No mechanistic interpretation for this surprising observation was offered
by the authors.
Indeed, only sparse attention has been paid to the mechanism of
perruthenate-catalyzed alcohol oxidations. Although TPAP can act as a
three-electron oxidant the fact that it selectively oxidizes
cyclobutanol to cyclobutanone militates against free radical intermediates