The reactions between
trans-[Au(CN)
2
X
2
]
-
(X = Cl or Br) and Me
2
S have been studied by
conventional and high-pressure stopped-flow spectrophotometry in acidic
aqueous solution containing 10% (w/w) methanol. The overall
stoichiometry Au
III
∶Me
2
S is
1∶(1.0 ± 0.1) in agreement with the reaction:
trans-[Au(CN)
2
X
2
]
-
+ Me
2
S +
H
2
O → [Au(CN)
2
]
-
+ Me
2
SO + 2H
+
+ 2X
-
. Initial rapid substitution
processes result in the formation of a pre-equilibrium between transient
gold(III) complexes, which are reduced to
[Au(CN)
2
]
-
in a subsequent slower redox
process. Complexes trans-[Au(CN)
2
X(Me
2
S)]
with an asymmetric electron distribution along the X–Au–S
axis are reduced rapidly via an intermolecular process, in
which Me
2
S attacks a co-ordinated halide. The complex
trans-[Au(CN)
2
(Me
2
S)
2
]
, on the other hand, undergoes slow reduction to
gold(I) involving a water molecule. The rapid halide-mediated
oxidation of thioethers implies that reduction of metal ions in
biological systems by such moieties should be favoured in extracellular
environments, where the chloride concentrations are high.
The reactions between
trans-[Au(CN)
2
X
2
]
-
(X = Cl or Br) and Me
2
S have been studied by
conventional and high-pressure stopped-flow spectrophotometry in acidic
aqueous solution containing 10% (w/w) methanol. The overall
stoichiometry Au
III
∶Me
2
S is
1∶(1.0 ± 0.1) in agreement with the reaction:
trans-[Au(CN)
2
X
2
]
-
+ Me
2
S +
H
2
O → [Au(CN)
2
]
-
+ Me
2
SO + 2H
+
+ 2X
-
. Initial rapid substitution
processes result in the formation of a pre-equilibrium between transient
gold(III) complexes, which are reduced to
[Au(CN)
2
]
-
in a subsequent slower redox
process. Complexes trans-[Au(CN)
2
X(Me
2
S)]
with an asymmetric electron distribution along the X–Au–S
axis are reduced rapidly via an intermolecular process, in
which Me
2
S attacks a co-ordinated halide. The complex
trans-[Au(CN)
2
(Me
2
S)
2
]
, on the other hand, undergoes slow reduction to
gold(I) involving a water molecule. The rapid halide-mediated
oxidation of thioethers implies that reduction of metal ions in
biological systems by such moieties should be favoured in extracellular
environments, where the chloride concentrations are high.