Organometallic Carbonyl Cluster Chemistry
Associate Professor Leong Weng Kee
Research in my group deals with the chemistry of organometallic compounds, and one of the main focus has been
that of organometallic carbonyl clusters. These are compounds that contain metal-metal bonds
acidic ligand CO. The presence of more than one metal centre in an organometallic cluster presents the opportunity
for much more patterns and sites for reactivity. For example, although the chemistry of homometallic carbonyl
clusters is already well-established, it can still throw up surprises. In a recent piece of work, we were able to
observe the conversion below:
R
R
Os
Os
N
C
CH3
O
O
O
R
O
O
- CH3CN
Os
Os
Os
H
Os
O
Os
Os
Os
H
H
Analysis of the conversion process as followed by 1H NMR spectroscopy yielded ΔH‡ = 110 ± 3 kJ mol-1 and ΔS‡ = 14
± 10 J mol-1 K-1 for this process, thus suggesting an ID mechanism.1
Another example is the isolation of the cluster Ru4(CO)8(μ-OOCAd)4(PPh3)2, (Ad=1-adamantyl), the structure of
which is shown below.
This is a linear, electron-deficient cluster, and calculations show that there is delocalisation of electrons along the
metal-metal chain.2 We have since been able to prepare a number of other analogues, including the osmium
congeners. A collaborative effort with Dr Sum Tze Chien in the PAP division is currently underway to assess the
potential of these compounds to act as molecular wires.
Much of our work in this area of research, however, focuses on mixed-metal systems; either with different
transition metals or transition metal with main group metallic elements. Examples of the former include an Ru-Os,
Ir-Os and Os-Pd combinations, while examples of the latter include Os-Sb and Os-Bi combinations. A recent
example is the reaction of an RuOs mixed metal cluster with azulene, which shows the unusual bonding mode that
can be adopted by the ligand, as well as the different reactivity of the metal centres.3
Ru
Os
H
Ru
Os
Os
Os
+ azulene
H
Os
H
Os
+
H
H
Os
Os
1
R. Ganguly and W.K. Leong. Organometallics 2011, 30, 3966-70.
S.P. Oh, B.Y. Chor, W.Y. Fan, Y. Li and W.K. Leong. Organometallics 2011, 30, 6774-7.
3 Y.L.K. Tan and W.K. Leong. J. Organomet. Chem. 2011, 696, 2373-9.
2
Os
Ru
Ru