New Horizons in Organometallic Chemistry

By James R. Bour

Our first indications of the scientific future historically lie in the discoveries made in instrumentation and analytical methodology. Of the 112 Nobel prizes awarded in physics, at least 34 were awarded directly to advances in instrumentation and analytical methodology. Many more have been awarded for discoveries specifically enabled through these analytical advances. The story is much the same in the chemical sciences. From mass spectrometry to cryo-electron microscopy, it’s hard to imagine opening up an issue of major natural science journals without seeing discoveries critically dependent on such analytical developments. Organometallic chemistry is no different, in analytical advances we can find the first signs of our field’s future.

To fully understand the impact of analytical methodologies on progress in organometallic chemistry, we don’t have to look much further than one of the first artificial organometallic complexes ever reported ( [(2-C2H4)PtCl2]2 )(1). Not long after William Christopher Zeise published his eponymous organometallic dimer in 1827 did controversy over its identity arise. Justus von Liebig asserted that Zeise had not synthesized the ethylene adduct as reported, but had actually synthesized a closely related etherate(2). Liebig’s compositional analysis, which was confounded by inadvertent hydration of the complex, indicated that Zeise’s dimer carried with it added mass in the form of oxygen. Conclusive proof (by mid 19th century standards) of the original formulation did not arrive until 1861 when Griess reported that thermolysis of Ziese’s complex in the presence of bromine yielded ethylene dibromide and that treatment with ethylenediamine yielded ethylene(3). Meaningful insight into the nature of metal-olefin bonding in this molecule would not come for even longer.

In 1951 Chatt and Duncanson reported and analyzed the infrared spectrum showing which showed reduction in the C—C bond order(4). Stories such as these illustrate that, like many other areas of science, the seeds of innovation in organometallic chemistry lie dormant until analytical methodologies and instrumentation catch up to our imaginations. So what then, is today’s equivalent of Griess’ chemical tests? or Chatt and Duncanson’s infrared spectra? What areas of organometallic chemistry have historically lacked the necessary instrumentation to fully exploit their potential? Once again, the answer lies in retrospection. Over the past 40 years the majority of organometallic reactivity has been studied in solution phase systems. Organometallic chemistry at the interface of solid and solution phases (surfaces) has garnered significantly less attention. It is likely that this disparity is due, at least in part, to the tremendous advances in NMR and EPR spectroscopy. These analytical tools enable unparalleled insight into organometallic structure and reactivity but have been traditionally relegated to the characterization of molecular species. Correspondingly powerful methodologies for the analysis of surface organometallics are just now becoming available. In particular, recent developments in solid-state NMR, electron diffraction, and in-situ x-ray absorption spectroscopies are shining new light on the properties of surface organometallics. If history is any indication, the future of organometallic chemistry lies at the interface of solutions and solids and the future looks bright.

What can we expect from a shift toward surface chemistries? First, we can expect to gain insight into established systems. Surface organometallic chemistry is not new, but detailed insights into molecular speciation of such systems are still rare. In fact, the first organometallic-related Nobel prize was awarded to Sabatier for his studies of heterogeneous hydrogenation catalysts. Substantial questions of mechanism and surface speciation remain, even in systems as well- established Sabatier’s. Secondly, these insights into surface chemistries will aid in the development of patently new catalysts. Improved understanding of chemical reactivity at surfaces will drive the development of new catalysts and ultimately address some of humanities grandest challenges.

References

  1. Zeise, W. C. Pogg. Annalen der Physik 1827, 9, 632.
  2. Liebig, J. Annalen der Chemie, 1834, 9, 1.
  3. Griess, P.; Martius, C. A., Annalen der Chemie, 1861, 120, 324.
  4. Chatt, J., and Duncanson, L. A., J. Chem. Soc., 1953, 2939
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