Hydrophosphination Catalysis Using Low-Coordinate Iron Complexes

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Organophosphorus compounds are one of the most important species in chemistry, driving critical advances in areas such as medicine, metal extraction, nuclear fuel processing, lubricants, agrochemicals, materials and supramolecular chemistry. Their wide use as ligands to transition metals underpins many modern homogeneous catalytic processes, for example in metal-catalysed cross-coupling, alkene metathesis and C-H activation reactions. Classic synthetic routes to phosphines often display poor functional group tolerance, side product formation, and use a significant number of steps including stoichiometric amounts of additives, toxic metal reagents and protecting groups. These limitations lead to copious waste, representing a problem for atom economy. Hydrophosphination reactions involve the addition of a P-H moiety across an unsaturated bond, and offer the potential for 100% atom efficiency with the opportunity to generate significant complexity in the organophosphorus products using relatively simple starting materials. In particular, the hydrophosphination of C=X (X = O, N, S) bonds is a powerful way to introduce heteroatom functionality into products, but remains poorly explored due to the paucity of suitable catalytic complexes, competing side reactions and catalyst poisoning. Thus, the use of this reaction as a convenient strategy to heterofunctionalised phosphorus compounds has not been exploited. Driven by major global efforts towards chemical synthesis using earth-abundant and non-toxic metals, we propose to deliver a new approach for the syntheses of organophosphorus compounds using iron complexes as pre-catalysts for the hydrophosphination of heterocumulene compounds. Significantly, our complexes can catalyse novel diinsertion pathways for this reaction, which are very rare and usually difficult to control. These new reaction pathways have the power to unlock new reactions and synthetic methodologies. We will explore this hydrophosphination chemistry and use unexplored substrates to deliver new families of organophosphorus compounds and develop a rational approach to control reactivity and regioselectivity through the manipulation of the structure of the catalyst and the reaction conditions. This chemistry will be used to synthesise specific organophosphorus targets and the elucidation of the mechanisms for this catalysis will provide experimental and theoretical data to inform new reaction strategies that may be developed in new catalytic reactions. This research programme will thus deliver a wealth of fundamental knowledge in addition to a bank of new organophosphorus compounds, which will be made available to researchers in academia and industry.This research programme has the potential to have significant impact for a broad range of academic and industrial applications due to the extensive properties and potential uses of a range of very different organophosphorus species. We envisage that our approach to the catalysis of hydrophosphination will impact a range of hydroelementation reactions and may impact other methodologies such as homologation, polymerisation and selective oligomerisation reactions.