'EPSRC/NSF Workshop Collaborative Proposal' Catalytic oxidative C-H bond functionalisation with high oxidation state N-heterocyclic carbene complexes

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Burning petrol and other hydrocarbons from fossil fuels is enormously damaging to the environment, and wasteful of these diminishing resources that should be used to make drugs, vitamins, and other important chemicals that improve the quality of life. However, the carbon-hydrogen bonds in these hydrocarbons are not only strong, but similar in strength, so selectively exchanging some of the hydrogens for the reactive groups that make the molecules into useful chemicals is difficult. Car catalytic converters use palladium particles to help fully oxidise the unburnt hydrocarbons in the exhaust, and protect us from petrol and carbon monoxide poisoning. The catalyst make the oxidation easier (they lower the energy barrier to the reaction).We have found that if you can dissolve the palladium in a solution (by surrounding each metal cation with binders, or ligands, to keep it solvated) it can be more selective, and pick up one hydrocarbon at a time, and thus also pick up another added reactive group. The moment the hydrocarbon becomes stuck to the palladium centre, it becomes much easier to remove one of its hydrogens, so it can be replaced with a useful, reactive group. Thus the solvated palladium compounds catalyse the formation of more complex compounds from simple hydrocarbons. We have made very selective ligands that stick more strongly to the palladium cations that any others, and make them even more reactive, but take up just enough space to make sure this reactivity is always highly selective for certain hydrogen atoms. This will help to make much more elaborate drug molecules, more selectively. Most importantly, the ligands help to stabilise the palladium in the middle of the combination step, when it is very electron deficient, and thus prone to damage. This will also allow a wider range of groups to be added. In the extreme, and most academically exciting palladium reactions, we plan to make stable molecules that mimic the most fragile intermediates in these reactive group additions, so we can study them in detail, and so that theoreticians can base calculations on the models to predict the future of palladium catalysis.So in the future we will need less palladium, and be able to make a wider range of complex drugs and pharmaceuticals from the simplest of fossil fuels, and biomass-derived organic compounds.