Chemistry Reference
In-Depth Information
Fig. 31 Energy profiles for the reaction of CO with Au
2
O
+
. All energies are given in electron volts
(eV) relative to the energy of the reactant at 0 K. Shown are ER-type (
blue
) and LH-type (
red
)
mechanisms. For the ER-like mechanism, a barrier of 0.2 eV and an excess energy of 2.5 eV have
been calculated for the rate-determining step. For the LH-like mechanism, the calculated barrier
and excess energy are 2.08 and 4.58 eV, respectively. Figure reproduced from [
306
]
2+
2+
N
N
-Au
N
N
-CO
-H
2
O
O
O
Au
Au
Au
Au
O
N
N
N
N
2
1
Scheme 2 Loss of H
2
O from dinuclear gold(III) oxo cluster coordinated by 2,2
0
-bipyridyl ligands
[
306
]. Au
2
O
reacts with one molecule of CO to yield Au
2
. Theoretical calculations
reveal that the CO directly attacks the O atom of the cluster. Thus CO oxidation of CO
by Au
2
O
proceeds via an Eley-Rideal (ER)-type mechanism rather than attacks at
Au via a Langmuir
Hinshelwood (LH)-type mechanism. In contrast, Au
2
O
+
requires
adsorption of two molecules of CO for oxidation to proceed. The DFT calculations
highlight that both ER- and LH-type mechanisms can operate (Fig.
31
).
Tyo et al. have reported on the gas-phase fragmentation reactions of dinuclear
gold(III) oxo clusters possessing a rhombic Au
2
O
2
core and 2,2
0
-bipyridyl ligands
with substituents in the 6-position (bipyR) [
312
]. The clusters were synthesised as
hexafluorophosphate salts in solution and were transferred to the gas phase via
ESI-MS to yield the free dications [(bipyR)Au(
-O)
2
Au(bipyR)]
2+
. A noteworthy
aspect of this report is the use of condensed phase IR spectroscopy, gas-phase
IRMPD and DFT calculations to provide evidence that isomerisation of the
substituted complexes does not occur in the gas phase. CID of this series of
complexes revealed a significant effect of substitution. The parent, un-substituted
complex, 1, fragments via loss of H
2
O, presumably forming the organometallic ion
2, (Scheme
2
) via a rollover cyclometalation reaction [
313
]. This ion subsequently
undergoes loss of Au and CO (Scheme
2
).
ΚΌ
