School of Chemistry, UNSW

The Ball Research Group

Directed by Dr. Graham E. Ball

Research Interests

Nuclear magnetic resonance spectroscopy is arguably the most powerful tool available to the chemist for determining molecular structure and motion within molecules. It is the key tool in our investigations. Research focuses on innovative use of NMR spectroscopy to solve interesting and important chemical problems, most often in the areas of inorganic and organometallic chemistry.

1. Structure and Exchange in short lived alkane complexes

As expected, simple saturated hydrocarbons, alkanes, are extremely poor ligands and complexes containing these molecules acting as discrete ligands are very short lived, with lifetimes less than 100 ms at room temperature. We have successfully directly observed alkane complexes using NMR for the first time using a combination of photochemistry to generate the reactive alkane complex and low temperatures to stabilise it for sufficient time to allow characterization.

reaction generating alkane complex

These molecules are of interest both from the standpoint of basic coordination chemistry and because alkane complexes are known intermediates in the C-H activation process, a potentially useful route to functionalising these relatively unreactive hydrocarbons found in petroleum.

Current research is aimed at answering questions such as how does the alkane bind to the metal centre? Can we observe complexes with ligands that bind even more weakly than alkanes using NMR?

(Below, left) Setting up a 500 MHz NMR spectrometer for an in situ photolysis experiment at low temperature. (Below right) Monitoring the formation and disappearance of an alkane complex under conditions of UV irradiation at -90 °C. Absorption of a UV photon results in the loss of a carbonyl ligand. Cyclopentane replaces the CO as a ligand to the metal.

NMR spectrometer setup time resolved NMR spectra showing formation and disappearance of alkane complex

The experimental work is being backed up with theoretical calculations in collaboration with Prof. I. Dance. Here, the calculated lowest energy structure for the alkane complex CpRe(CO)₂(cyclopentane) is shown.

Geftakis, S.; Ball, G.E. "Direct Observation of a Transition Metal Alkane Complex, CpRe(CO)₂(cyclopentane), Using NMR Spectroscopy", J. Am. Chem. Soc., 1998, 120, 9953.

2. Hydride and dihydrogen complexes

Transition metal hydride complexes are well known to be excellent catalysts for hydrogenation reactions. Dihydrogen complexes contain a hydrogen molecule that is essentially intact but acting as a ligand. We have an ongoing interest in these classes of compounds. We are interested in answering questions such as can we accurately determine the location of the hydrogen atoms in such molecules and interatomic distances? This can be difficult using crystallographic methods. Can we determine how "strongly" dihydrogen molecules interact with the metal in their complexes? We have been answering this later question by measuring spin-spin interactions between the metal and the protons in the dihydrogen moiety.

Hydride and dihydrogen complexes also often show interesting mechanisms of fluxionality, i.e., the hydrogen atoms interchange their positions within the complexes. NMR is ideally suited to revealing how these molecular reorientations take place.

Below: Investigating an exchange mechanism in a polyhydride complex.

2D NMR spectrum of Re-Ru complex structure and labeling of Re-Ru complex

3. NMR characterisation of substituted fullerenes

This project is in collaboration with Prof. Steve Pyne and Dr. Paul Keller, University of Wollongong.

Since its discovery in 1985, [60]-fullerene (C₆₀) and its homologues have shown promise for exciting new developments and applications in areas such as medicinal chemistry and materials science. The synthetic goals of this work, carried out at the University of Wollongong, involves developing methods for preparing optically active, multi-functionalized fullerene derivatives in a regioselective and diastereoselective manner and investigating their applications. At UNSW, we are using NMR spectroscopy as a robust and definitive technique for the assignment of regiochemistry in these compounds. Experiments such as the straightforward INADEQUATE sequence and more involved methods such as ADEQUATE and ¹³C-¹³C TOCSY are currently being employed.

Below: A trans-4 difunctionalized fullerene and an INADEQUATE NMR experiment used to identify the substitution pattern.

difunctionalised C60 fullerene INADEQUATE spectrum of difunctionalised C60 fullerene

Burley G.A.; Keller P.A.; Pyne S.G.; Ball G.E. "Unexpected regiochemistry of a tethered bismethano[60]fullerene", Chem. Comm., 2000, 1717.

4. Structure elucidation