Organometallic Catalysis

Organometallic catalysis lies at the heart of modern synthetic organic chemistry. Despite extensive methodology development in the field over the past few decades, some mechanistic aspects of it remain poorly understood. In the Lloyd-Jones Group, we aim to gain detailed mechanistic insight into a variety of transition-metal catalysed transformations via in situ structural determination and speciation, and comprehensive kinetic analysis. This work is often facilitated by isotopic labelling and computation.

Olefin Metathesis

Olefin metathesis is one of the most powerful methods for the formation of carbon-carbon bonds. Despite the development of robust ruthenium based catalysts over the past two decades applicability to industrial synthesis is surprisingly limited.1 This is in part due to a lack of in-depth understand of the three mechanistic events which occur: initiation, turnover and decomposition.2 Research within the Lloyd-Jones group successfully investigated the initiation stage for the third generation Grubbs catalyst G-III-Br by ethylvinyl ether,2 showing it to go via both dissociative and associative pathways, supporting the computational work of Trzaskowski and Grela.3 However, during this research it was established that the G-III-Br was undergoing decomposition due to an unknown source. Further work is currently being carried out to understand fully the source and mechanism of decomposition. Through understanding how and why it decomposes, such sources can be eliminated during metathesis allowing for greater industrial applicability.

Transmetalation in the Suzuki-Miyaura Reaction

Palladium(0)-catalysed cross-couplings are amongst the most utilised transformations in academia and industry.4 They employ a halide which, in the presence of a Pd0 catalyst, couples with a suitable transmetalating agent. The mechanisms of these reactions differ in the transmetalation step and depend on the nature of the transmetalating agent. Of utmost synthetic importance is the Suzuki-Miyaura reaction, where the transmetalating agent is an organoboron species. The reaction only occurs in the presence of a base, and the role of the base has been debated over decades. Recent kinetic studies by Hartwig, Amatore and Jutand, and Schmidt revealed that transmetalation in the Suzuki reaction occurs via the oxo-palladium pathway,5-8 in which the oxidative addition intermediate undergoes anion metathesis with the base, to then cross-couple with the neutral organoboron species. In collaboration with Dr Allan Watson (St Andrews) we are investigating the kinetics and mechanism of this critical anion metathesis event.

Dual-Catalyst Photoredox Catalysis

The last few years have seen an explosion in the development of synthetic methodology utilising photoredox catalysis, in particular Ni/photocatalyst dual-catalyst photoredox catalysis. However, despite the growing prevalence of this kind of reaction in both industrial and academic chemistry, the mechanisms of this type of transformation remain poorly understood. Work has recently started in the group seeking to probe the mechanism of dual-catalyst photoredox catalysis in detail by use of in situ illumination NMR spectroscopy.

References

  1. C. S. Higman, J. A. M. Lummis and D. E. Fogg, Angew. Chem. Int. Ed. 2016, 55, 3552–3565.
  2. V. Forcina, A. Garcia-Dominguez and G. C. Lloyd-Jones, Faraday Discuss. 2019, Advance Article.
  3. B. Trzaskowski and K. Grela, Organometallics 2013, 32, 3625–3630.
  4. X.‐F. Wu, P. Anbarasan, H. Neumann and M. Beller, Angew. Chem. Int. Ed. 2010, 49, 9047–9050.
  5. B. P. Carrow and J. F. Hartwig, J. Am. Chem. Soc. 2011, 133, 2116–2119.
  6. C. Amatore, G. Le Duc and A. Jutand, Chem. Eur. J. 2013, 19, 10082–10093.
  7. A. A. Kurokhtina, E. V. Larina, E. V. Yarosh and A. F. Schmidt, Kinet. Catal. 2016, 57, 373–379.
  8. A. F. Schmidt, A. A. Kurokhtina and E. V. Larina, Rus. J. Gen. Chem. 2011, 81, 1573.