Catalysts for selective aerobic oxidation under ambient conditions - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 245

Oxidation of CEES to CEESO by alone occurs very slowly (if at
all), but the reaction is efficiently catalyzed by p -toluenesulfonic acid. In the
presence of this strong acid or our Au(III)-based catalyst, the reaction
proceeds upon mixing. Thus, if is formed as an intermediate in our
system (eq 11), it should immediately react with CEES. In this case one half
of the total CEESO formed in a catalytic reaction could derive from reaction
of with CEES. However, oxygen-18 labeling experiments show that
the CEESO produced in the early part of the reaction (up to 10 turnovers) is
and The somewhat lower in the CEESO than in
the used derives in part from water present in the initial This
Au catalyst precursor compound is hygroscopic and very hard to dry. The
percentage of in the CEESO also decreases with an increase of CEES
conversion. For example, the incorporation into CEESO product was
~60 atom % after 60 turnovers. The dependence of incorporation percentage
on the extent of CEES conversion is consistent with a consumption of
labeled water during catalytic turnovers. The water concentration remains
unchanged in the overall reaction: one water molecule is consumed in eq 9
but it is immediately regenerated in eq 11 resulting in a dilution of
pool with Thus, CEESO is produced in the reaction involving

exclusively but not or If alone were involved, the

ratio would not exceed 50%.

11. REOXIDATION OF Au(I) BY DIOXYGEN.
CATALYST PREPARATION FROM Au(I) COMPLEX

The isotope labeling and kinetic studies of CEES sulfoxidation by
reveals that reoxidation of Au(I) by in the presence of protons does
not proceed via eq 28, and is not formed as an intermediate. As
indicated above, this re-oxidation reaction is not a rate limiting process,
therefore its mechanism can not be assessed kinetically. This reaction is also
not precedented in the literature.
Au(I) forms linear, trigonal planar or tetrahedral complexes, with the
linear geometry being the most common. 43 The complexes and

are colorless (for lignad,
easily prepared by reduction of in ethanol and isolable with bulky
ligands 52 , and stable in acetonitrile. 33,34,42 The complex is of
considerable commercial importance, since it is used in the extraction of
gold from its ores and in gold electroplating applications. It is polymeric
with a linear Complexes of Au(I) with
thioethers of formula are usually prepared by reduction of
in the presence of appropriate dialkylsulfide, eq 29. 29,43,54