Transition metal derivatives of polyhedral boranes and carboranes can form in different ways. Metallocarboranes often form "sandwich" structures where the metal is bonded between two closo-carborane ligands. These structures are more stable than metallocenes due to properties of the carborane ligands. Metal derivatives of polyhedral boranes can form direct bonds to boron atoms or ionic bonds to the cluster. One example is Cu2B10H10, which has a unique diagonal bonding structure unlike the typical "sandwich". These compounds have various applications including catalysis, organic synthesis, and medicine.

1. Transition Metal Derivatives of
Polyhedral Boranes and Carboranes
Han Song
Department of Chemistry
Penn State University
Chem 516 Presentation
11/30/2012

2. Structure
• Boranes and carboranes
• Metallocarboranes
• Metal derivatives of polyhedral boranes
• Summary

3. 1. Borane and Carboranes
1.1 Definitions:
Borane: is a chemical compound of boron and hydrogen.
Polyhedral boranes are large clusters with more than 6 Boron
atoms (usually 6-12).
Carborane: are compouds having as the basic structural unit of C
and B atoms arranged on the vertices of a triangulated polyhedron.
Closo, Nido, nido,
BnHn2- BnHn+4 C2B9H112-
Atkins, P. W.; Shriver, D. F., Inorganic chemistry. 4th ed.; W.H. Freeman: New York, 2006; p xxi, 822 p.
http://pubs.acs.org/cen/coverstory/87/8712cover2.html

4. 1.2 Properties:
closo-boranes (BnHn2-) and closo-carboranes(C2Bn-2Hn)
their structures resemble their hydrocarbon counterparts (aromatic
compounds), 3D aromaticity.
Stable!
nido-boranes and nido-carboranes (nest-like)
without the strict structural limitations, is relatively more reactive
Greenwood, N. N.; Earnshaw, A.; NetLibrary Inc., Chemistry of the elements. 2nd ed.; Butterworth-
Heinemann: Boston, Mass., 1997; p. 1344 p.

5. 2. Metallocarboranes:
• Origin
• Synthetic routes
• Some examples: transition metal derivatives
• The comparison between the metallocarboranes with
metallocenes and the possible reasons

6. 2.1 Oringin:
Hawthorne, M. F.; Young, D. C.; Wegner, P. A. (1965).
"Carbametallic Boron Hydride Derivatives. I. Apparent Analogs of
Ferrocene and Ferricinium Ion". Journal of the American Chemical
Society 87 (8): 1818–1819
C2B9H112- is isoelectric
with B11H11, which is an
analoge of C5H5-
The fact that C2B9H112- resembles cyclopentadienyl
anion gives a good explanation for the sandwich
structure of the Fe complex.

7. 2.2 Synthetic Routes (main pathways)
A. Coordination using nido-caborane anion as ligands (1965)
A. Polyhedral Expansion
Greenwood, N. N.; Earnshaw, A.; NetLibrary Inc., Chemistry of the elements.
2nd ed.; Butterworth-Heinemann: Boston, Mass., 1997; p. 1344 p.

8. 2.3 some good examples
1. Highly planar
2. Zn2B2 diamond-like structure
3. Weak Zn-Zn bond
Grimes, R. (2000). Metallacarboranes in the new millennium. Coordination Chemistry Reviews, 202, 773–811

9. 2.3 some good examples (continued)
C3B8H11 –
Fe (II)
Cp
Grimes, R. (2000). Metallacarboranes in the new millennium. Coordination Chemistry Reviews, 202, 773–811

10. 2.4 Comparison with Metallocenes
a. C2B9H11 2- anion b. C5H5-
It is generally accepted that the anion a usually works
much more efficient than anion b, therefore the bonding
in metallocarboranes are stronger than in metallocenes,
and thus more stable than metallocences.
Atkins, P. W.; Shriver, D. F., Inorganic chemistry. 4th ed.; W.H. Freeman: New York, 2006; p xxi, 822

11. 2.4 Comparison with Metallocenes (continued)
Possible reasons:
• In the nido-carborane structure, the bonds are tilted towards
one point, this bond angle favors the capping effect of the
“nest”.
• The electronegativity of the element Boron is smaller than that
of Carbon, thus it‟s more prone to share electron with the
aceptor.
• For di-anions, the charge of the nido-caborane anion is bigger
than that of the cp., so the charge interaction is also stronger.
Greenwood, N. N.; Earnshaw, A.; NetLibrary Inc., Chemistry of the elements. 2nd ed.;
Butterworth-Heinemann: Boston, Mass., 1997; p. 1344 p.

12. 3. Metallic Derivatives of Polyhedral Boranes:
In these compounds, the metal and the polyhedral boranes
can either be connected by direct bonding or ionic bonds.
A lot of them have similar sompund structures as the
carboranes, but here I will talk about the ones with different
structures.
• Synthetic Routes
• One example of the ionic bonded metal derivative

13. 3.1 Synthetic Routes
a. Borane plus Transition metal complex
b. Borane Anions plus transition metal complex
Chemical Society (Great Britain), Chemical Society reviews. Royal Society of Chemistry: London,,
p v. Volume 3, Issue 2, p.231

14. 3.2 One Example
Cu2B10H10
1. Cu(II) to center of the
diagonally opposite
edge.
2. diagonal, 5 atom
bonding environment.
Very different structure from the „sandwich‟ structure, indicating
different properties.

15. 4. Summary
• Most metal derivatives of carborane have the metal directly
bonded to the Boron atom, some polyhedral derivatives will do as
well (ionic bonds exist for metalloboranes).
• It is usually the nido-structures that bond with metals.
• Metallocarborane system is usually more stable than metallocene
system.
• Metal derivatives of polyhedral borane and carborane have wide
applications in catalysis chemistry, organic systhesis and medicine
etc..

16. Thank you!