Mechanistic Studies of Transition-Metal Mediated Catalysis

Research in the Nelson group focusses on understanding mechanisms and structure/activity relationships in chemical reactions mediated by transition metals. Most of our work is experimental in nature, but there are limits to what can be done by experiment; insight from high-quality calculations supports and tests our hypotheses from experimental work. Studies will be conducted to check proposed mechanisms by modelling intermediates and transition states on the reaction pathway using Gaussian09. Structure/activity relationships will be probed by understanding how the energies of these intermediates and transition states change as different substituents are added or removed to the structures.

Ongoing projects include:

• Studies of palladium- and nickel-catalysed cross-coupling reactions, specifically looking at the effect of the structure of the ligand on reactivity, and ‘privileged’ substrates that will react in preference to others. Experimental work has identified several classes of substrate that undergo reaction anomalously quickly, or in preference to other highly-reactive substrates. Computational studies allow us to unpack these reactions and identify why this selectivity is observed. By doing so, we can triage new reactions to understand the preferred site of reactivity, reducing experimental workload using simple computational calculations.
• Studies of ruthenium-catalysed C-H functionalisation using well-defined ruthenium carboxylate complexes, and the effect of different directing groups on selectivity. Experimental studies have ranked several directing groups in order of their reactivity, and now we seek to understand which fundamental step of the reaction determines this selectivity. This will help us design new catalysts and new reactions, and confidently apply these C-H functionalisation reactions in retrosynthesis.
• Studies of new ligand systems such as those based on selenium derivatives of N-heterocyclic carbenes. Our studies of their initial coordination chemistry to metals such as copper, silver, and gold – and those of others working in the field – have revealed a number of possible structures. The structure that is preferred in solution will have a considerable effect on the stability, reactivity, and potentially selectivity of these catalysts, so we are using computational studies to understand why specific ligand yield specific structures.

This work is important because it adds an important extra dimension to our research, and one that often leads to a more well-rounded, solid, and complete study. We seek not only to understand experimental observations from the laboratory, but to be able to calibrate our calculations so that we can confidently predict selectivity and reactivity in new scenarios. As such, the use of theoretical calculations can help us publish our (predominantly experimental) work in more impactful journals that cater to a broader audience.

For more information about the project contact Dr David Nelson (david.nelson [at] strath [dot] ac [dot] uk), Strathclyde Chancellor’s Fellow at the Department of Pure and Applied Chemistry at the University of Strathclyde.

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