Catalysts for selective aerobic oxidation under ambient conditions - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 240

In our studies polar, aprotic solvents such as have primarily been
used (see also sections 15 and 16). Nevertheless, the Au(III)-thioether
coordination and the redox chemistry in the two systems are otherwise very
similar. The two reactions depicted in eq 9 have the rate constants for 1
and for 2. Since 1 is the most reactive complex, eq 9 is written in terms of
1 and its redox products, and The subsequent
steps, eqs 10 and 11, are fast and consequently kinetically inaccessible
processes.
Of the several possible mechanisms for the rate-determining redox step,
eq 9, but one is more consistent with all available data (see the next section
for details) and involves bimolecular attack of thioether on a coordinated
chloride ligand of Au(III). This mechanism has been proposed for some
stoichiometric thioether oxidations by Au(III). 45,46,48 None of the data on
our system contradicts this mechanism. It is also consistent with the increase
in rate when is replaced by under otherwise identical conditions (see
also section 12). Inner sphere ligand transfer redox processes, including
reduction of Au(III), are known to proceed faster for compared with
ligands. 46, 49 For example, is reduced by sulfite and
hydrogen sulfite ca. 10 times faster than
Interestingly, this kinetic preference is in the opposite direction from the
reaction enthalpy since the metal centers with the have higher

potentials and are stronger oxidants than their
Since is large and then
The equilibrium expressions from eqs 7-
8, Scheme 1, and reaction mass balance expressions afford eqs 12 and 13.

Eqs 13 -15 can be used to obtain the expressions for [1] and [2] , in eqs 16
and 17.