Catalysts for selective aerobic oxidation under ambient conditions - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 253

disadvantage of acetonitrile is that when it is used as a solvent, an induction
period can occur during the catalytic reaction. For these reasons we looked
at the possibility of using other solvents. Figure 6 shows two of the four
solvents (trifluoroethanol and acetonitrile) in which catalysis of CEES
oxidation to CEESO occurs. Three of the four solvents, trifluoroethanol,
nitromethane and 1,2-dichloroethane, do not exhibit a measurable induction
period. The highest rate is observed in trifluoroethanol. It is also noteworthy
to mention that a complete conversion of CEES to CEESO can be achieved
in trifluoroethanol. When ethanol or acetone is used, the Au(III) is
immediately reduced to colloidal Au(0), which cannot be reoxidized by
In tert- butanol, Au(III) is reduced to Au(I) but reoxidation of Au(I) to
Au(III) is not observed. In pyridine, a mixing of and CEES
does not result in precipitation of AgCl indicating that the active catalyst is
never formed. In perfluoropolyether (PFPE) solvents at least one component
is insoluble, so these reactions are not entirely homogeneous. These systems
are classified as heterogeneous and are discussed below.

Binding of solvent molecules to Au(III), eq 7 in Scheme 1, as well as a
shift of the equilibrium between the cation 2 and neutral 1 (eq 8) should be
considered. For example, acetonitrile binding to both Au(III) and Au(I)
complexes is well precedented 35,69,70 , and the solvolytic equilibrium, eq 43,
has been studied in (95:5, v/v) by Canovese et al. 71